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The Best Guide to Selecting the Right Steel

Written by Corey Rasmussen in Basics Last Updated June 19, 2021

Although it was 20 years ago, I remember it like it was yesterday. I was on the phone with the local steel supplier ordering some bar stock. He asked if I wanted it “hot or cold”. I had no idea what he was talking about. Totally embarrassing!

I don’t want the same to happen to you. With a little bit of knowledge on the subject, you can avoid the embarrassing conversation that I had.

Steel is definitely the material of choice in our current world.  Plastics and composites are on the rise, but steel will remain prevalent because of its availability, cost, malleability, durability, weldability, and machinability. The biggest drawbacks are its high density and poor corrosion (rust) properties.

Steel comes in 4 main types: structural shapes, tubing, plate and bar. Properly selecting steel involves understanding the alloys used, how the material is processed including tempering and forming. Welded steel with carbon contents above 0.3% need special processing to prevent cracking.

To begin with, I highly recommend obtaining a stock list from your local steel supplier. This can be a valuable resource as you gather information regarding available sizes and shapes, weights and grades. It will help you save time in the design process and be an invaluable resource throughout your career.  Minimal familiarization will show that steel comes in:

  • Structural shapes
  • Tubes and pipe
  • Plate or sheet
  • Bar

Structural Shapes

Structural shaped steel comes from the mill in many different shapes and sizes. These are beams (S, W, and M), Channels (C and MC), I-Beams, and Angles.

I-Beams

The first type we will be discussing is the S-Beam or otherwise known as Standard American Beams. The S-Beam is also sometimes known as an I-Beam due to their shape which look like a capital I. In general, these are primarily used in the construction industry, but can also be found in truck frames, lifts, and many other similar applications. S-Beams can be measured by the height (H) and weight per foot (H X wt/ft). For example, S6X12.5 would represent a beam that is 6 inches tall and weighs 12.5 pounds per foot.

Another type is called the Wide Flange Beam or W-Beam. These beams have flanges that are nearly parallel to the top and bottom of the shape unlike the traditional S-Beam. W-Beams are commonly found in many structural applications such as bridges and buildings and have a greater variety of sizes. W-beams are measured by the height (H) and weight per foot (H X wt/ft). With all the variations you will need to determine the width and thickness from a steel stock list.

A third type of structural steel beam is known as the M-Beam or Junior Beam. These have a comparatively lighter weight than the other two beams we have discussed. Overall, M-Beams are very limited in use due to the lack of availability in sizes.

Channel

Another type of structural steel is found in both C Channels and Marine Channels (MC). These have a C-shaped cross section and are measured by the height and weight per foot. Marine Channels are mostly used in the cargo shipping and auto industry. Both C and MC channels are often seen as less costly solutions for short to medium-span structures.

Angle Beam or Angle Iron

Angle beams take an L shape, with two legs that meet at a 90-degree angle. Angle beams have the option of coming in equal or unequal leg sizes and are measured by the length of each side and thickness. Even when the length is unequal on both sides it will have the same thickness on each. Angle beams have a radius on the inner corners while the back of the angle always remains square and are commonly used in floor applications because of the limited structural depth.

Tubing and Pipe

Steel tubing is tough and durable. Sizes vary and can be found in round, square or rectangular form. Since tubing is very strong, it has a wide variety of structural and architectural applications including automotive, railing, and outdoor home furnishings. Round tubing controls the tolerance on both on the OD (Outside Diameter) and the ID (Inner Diameter). Round tubing is stock based on the OD and thickness of the tube. The ID can be found by subtracting twice the thickness from the OD.

Three top common materials:

  • 1018 cold drawn up to 65 KSI
  • 1026 Cold Drawn up to 72 KSI
  • 1026 DOM at 75 KSI (Very Tight Tolerance)

Round Tubing

Thus, DOM is made by taking a tube of larger diameter and force it through a series of dies in order to make it smaller. This process gives it a very tight tolerance wall thickness and increased strength. Square and rectangular tubing is specified by the two dimensions and the wall thickness (i.e. 2X2X1/4). It is primarily available in ASTM A500B (46 KSI) and A500C (50 KSI). The main thing to keep in mind is that there will always be a seam on the inside, and they will have rounded corners on both the inside and the outside.

Pipe

Piping is formed cylindrical tubes that come in a number of different of sizes. Steel piping is mainly used to meet the needs of water, oil, and gas industry needs. In terms of form, the OD (Outside Diameter) of the tube is controlled because a fitting is put over it. With piping the ID (Inside Diameter) is not important as the thickness is measured in schedules from thin to thick (10, 20, 40, 80 or extra heavy,120,160 or double-extra heavy).

For example, a 3/4 inch schedule 10 pipe would have a very thin wall. I do not recommend using a schedule 10 pipe unless you are using it to transfer torque. With piping neither the ID or the OD match the dimension specified. For example, a one-inch pipe is really 1.3 inches in diameter and the ID of a schedule 40 pipe is generally about one inch.

Rectangular Tubing

Tubing is also available in square or rectangular cross sections. Interestingly, these shapes are made from round tubes that are forced through a mandrels to make them square. These shapes have poor tolerances on the size and radius in the corners.

Plate or Sheet

Plate steel is exactly what it sounds like; large flat sheets of steel. Thicknesses of plates are measured in fractional sizes and generally start at 3/16 of an inch and are available in 1/4, 5/116, 3/8,1/2, 5/8, 3/4, etc). Sizes thinner than 3/16 are usually measured in gauges.  With gauge sizes, the smaller the gauge, the thicker the plate.  

Generally, plates have a width of 4 to 6 feet or larger and lengths up to 40 feet although standard sizes are 10-12 feet. 

Cutting Plate

Plate is an excellent choice of raw material because parts can be cut to any shape using CNC programs.  Popular methods of cutting include water jet, fiber optic laser cutter or plasma cutters.

A waterjet cutter is a common industrial tool that can cut many different types of materials using a very high-pressure jet of water or a mixture of water and often an abrasive substance. Abrasive waterjet is typically used to cut harder materials, such as steel, ceramic, stone, wood and glass.

A fiber optic laser uses a beam of light to cut through various hard materials which include sheet metal, wood, diamond, glass, plastics and silicon. The light is guided and through the means of fiber optic cable. The amplified light is then straightened and focused by a lens onto the material to be cut.

A Plasma cutting machine cuts through material by means of an accelerated jet of hot plasma. These materials include steel, aluminum, brass and copper, along with other conductive metals as well. Plasma cutting is often used in fabrication shops, automotive repair and restoration, industrial construction, and salvage and scrapping operations.

Plate Alloys

Plate is categorized using ASTM code such as:

  • A36
  • A572 Grade 50 KSI
  • A656 Grade 80 KSI
  • T1 A514 (Type 1 and 2)

There are also other brand name steels such as those made by SSAB which has many types of high strength steel including the Domex and Strenx line which is a low-alloy, cold-formed steel intended for use in the automotive and engineering industries.

Forming Plate Steel

Another benefit of using plate steel is that it can be bent or formed. Forming is a process induces loads causing permanent deformation which is cold working the material. You should expect a reduction in ductility and increase in yield strength around the bend line.

When forming, choosing the right radius is important. If the radius selected is too small, the plate may crack. When forming thin (<1/4″ [6mm]) materials of low strength (<36ksi [248 MPa]) plate, you can use a radius equal to the material thickness. As your thickness and strength increases, you will want to consider a radius up to 4x the plate thickness.

Bar Stock Steel

Bar stock is another common shape.  This is steel that has been drawn to a specific shape.  Readily available shapes are round, square, rectangular, and hexagonal.  Round bar can be used for pin material and has some special availablities.  First, it can come Turned, Ground and Polished(TGP). This means that the diameter is very tightly toleranced, usually to +0.000/-0.001”.  Second, you can get certain sizes with plating already on it.  The most common plating is chrome.

Finish

Bar and Tubing have two unique things to consider, the finish (or condition) and the alloy.

The steel finish mainly comes down to whether the steel is hot or cold.  Hot-rolled steel if formed at the steel mill is extremely hot and then formed and molded to shape while it’s still hot.  Hot-rolled steel has very rounded corners, and generally applies to different types of bar stock. When cooled off hot-rolled steel will shrink slightly thus giving less control on the size and shape of the finished product when compared to cold rolled.

Cold-rolled steel is created when hot-rolled steel is processed further by running it through rollers and conforming it to a certain smaller shape. Cold-rolled steel has sharp edges and very tight-tolerance sides.  Because of the cold working, cool-rolled steel will have a higher yield strength than hot-rolled steel.

Here’s a quick overview of the differences between hot-rolled and cool-rolled steel:

  • Hot-rolled steel
  • Pretty soft for steel
  • High elongation
  • Low yield strength.
  • Rounded corners
  • Cool-rolled steel
  • Higher yield strength,
  • Lower ductility,
  • Tight tolerances
  • Sharp edges

Here’s another way to remember the difference:  If you were to drop hot-rolled steel on your foot, your foot would be crushed.  If you drop cool-rolled steel on your foot, your foot will most likely be cut off.

Another way that steel can be processed is by quenching and tempering (Q&T). The quenching and tempering process gives you a very tightly toleranced piece of steel, like cold rolled, but its strength will be increased over cold rolling. Its ductility and machinability will go down.  As a result, many will machine a bar in its cold rolled state and then have the quench and tempering process added.  Here’s how the process of quenching and tempering steel goes:

  1. A piece of hot-rolled steel is taken and turned into cool-rolled.
  2. The steel is then heated up so that it can be annealed.
  3. After that, the steel is quenched in either water or oil (depending on the type of steel and the process for that particular type). This tempers the steel.
  4. The steel may be heated after that in order to soften it up a bit.

Alloy

Bar stock and tubing are classified with a composite four-digit alloy identifier.  One of the most popular identifiers for bar and tube is C1018. C1018 is your generic and most widely-available steel. The C indicates that the bar is cold rolled. H would mean hot rolled

In this example, the first two numbers (10) are an alloy number.  The higher the number, the more complicated the alloy. 10 is plain, generic carbon steel, nothing fancy.  Common alloy numbers are 10, 11, 12, 41, 43, and 86.

The last two numbers (18) represent the carbon content of the steel.  As a number goes up, your ability to harden that material goes up.  For example, if you had a C1018 pin, you wouldn’t be able to get that very hard, even with processes such as induction hardening (heating up the outside of a material in an attempt to harden it).  However, if you were working with a steel with a higher carbon content, such as 30 or 35, you’d be able to harden it quite a bit.

Weldability

Weldability is another consideration when selecting a material. Here are a few guidelines concerning welding:

  • If the carbon content is 30 or less, it is readily weldable.  You’ll be able to weld the material with no problem, providing you use the right type of welding rod.
  • Once you get in the range of 31 through about 45, you’ll have to complete some special processes before welding your material.  At 31, it starts to become harder for the steel to resist cracking due to the high temperature gradients of the welding process. In light of this, you’ll want to do certain things:
  1. You’ll have to use a specialized rod. (There are handbooks available to help you decide which rod to use as well as consulting a Certified Weld Instructor)
  2. You’ll want to heat the material up before you begin welding it.
  3. Finally, you’ll want to do a controlled cool-down of the material. The controlled cool-down helps to prevent the material from cracking as it cools down.
  • Although the number is somewhat debatable, as a general rule, anything with a carbon content greater than 46 is not weldable.  It’s best to try different processes, such as bolting, to join materials.

Rarely, you will see the letters L or V between the two sets of numbers.  These represent Lead or Vanadium.  A leaded steel is very easy to machine, but can only be welded with a TIG process (if at all).  Vanadium steel is also a great choice for design, but it also had limited weldability mostly due to the carbon content of available alloys (i.e. 10V45)

Ductility

The final thing to be aware of when classifying steels is ductility or elongation.  Ductility is the “stretchiness” of a material.  Glass is not ductile, but most plastics are.  Many design standards have a minimum ductility requirement for a material to be considered ductile.  If the material has a ductility above the requirement, there is usually a reduction in design factor requirement.  ASTM standards generally will use 10% elongation for a material to be classified as ductile.  At is threshold, the design factor reduces from 5:1 for brittle materials to 2:1 for ductile materials.  As you can see, there is a benefit for selecting a ductile steel.

Ductility is measured straight from the stress strain curve.  As steel is loaded in tension, we will want to keep it in the elastic region (between the origin and the yield point).  As we load the steel past the yield point, the material deforms more without a significant increase in load. This is the plastic region. 

As the load increases the ultimate stress is reached and the material fails.  If the two pieces are put back together and the length is measured, we can plot the maximum stress and strain on the plot.  This final length is then compared with the initial length as a percent and that is the ductility.  Standard tests are done with a 2” long sample.  For example, we have a 2” sample and the final length after breaking is 2.4”.  The ductility is measured by (2.4”-2.0”) / 2.0”=0.2 or 20%.

Conclusion

We have discussed the basics of selecting steel.  Steel comes in structural shapes, tubing and pipe, plate or sheet and bar.  We’ve discussed the alloy, finish and ductility of the materials.  After reading this, you will have a better understanding about the basics of steel selection, so that you will impress your boss by selecting the right material for the job.

A Simple Guide to Applying Cylindrical (GarMax, Polygon) Bearings

Written by Corey Rasmussen in Mechanical Design Last Updated August 19, 2020

As a design engineer, when I have pivoting members, one of my favorite bearings to use are fiber reinforced bearings.  They are easy to apply and are very predictable.

Typical Cylindrical Bearing
Image courtesy of GGB

Fiber reinforced cylindrical bearings are round bearings with no moving parts.  The inside diameter is coated with a low friction surface that is usually either nylon or Teflon.  Carbon fiber is then wound on the outside to give ample strength.

To properly apply a cylinderical bearing an engineer must address all of these:

  1. Selecting the size and wall thickness
  2. Calculating the bearing pressure
  3. Determine frictional forces
  4. Calculate surface velocity
  5. Estimate life cycle
  6. Identify and minimize misalignment
  7. Assembly Considerations
  8. Common Issues

Let’s dive deeper:

Fiber reinforced cylindrical bearings are a subset of cylindrical bearings, but as mentioned, they have no moving parts.   Typical cylindrical bearings have an inner and outer race, balls or rollers and seals.  Having no moving parts makes the design more robust.

Are they useful in engineering design and if so, how useful?

As I look back on the last 15-years of my design career, cylindrical bearings stand out as being one of the most reliable and commonly used items in nearly all of my projects.  They can be trusted to perform.

Technically, they are classified either as filament wound, self-lubricating bearings or simply by their brand names such as GarMax or Polygon. These bearings are unique because they have no moving parts.

The outside diameter is pressed into a bore and the pin is able to rotate on the inside diameter of the bearing.  The bearings are formed by first putting a wear material like PFTE (Teflon) on the surface and then a winding material like carbon fiber or fiberglass on top.  These bearings are a good choice for their:

  • High load capacity
  • Inexpensive pricing
  • High temperature capability
  • Minimal to no maintenance
  • Long life
  • Small form factor

The main reason to steer away from these is high surface velocity.

Like any other bearing, there are several important things to keep in mind in the design:

1. Selecting the Size and Wall Thickness

Cylindrical bearings are specified in 16th of an inch size and come in 1/8 and ¼” wall sizes (metric versions are also available).  For example, if we were specifying a GarMax bearing of GM1620-16 the form is the:

  • Product code -GM
  • Inside Diameter, ID – 16 (1 inch)
  • Outside Diameter, OD – 20 (1.25 inch and thus a 1/8 wall)
  • Width – 16 (1 inch)

This is great because if you want to change to another type or supplier, you just change the product code using the formula above.   It’s simple enough that you could extrapolate that to get other sizes.

Cylindrical Bearing Thickness

There are no hard guidelines here. I have found that if the bore size is fixed, lean toward a 1/8” wall bearing.  This allows you to use a larger pin with more strength. 

I learned this from a custom cylinder application were the loads were high and caused damage to the pin.  Because of part interchangeability, we were not inclined to change the rod eye size of the cylinder, but we found that if we changed the bearing from a ¼” wall to a 1/8” wall we could use a ¼” larger pin.

This brought our design factors back up to allowable limits. 

If the bore size is fixed, lean toward a 1/8” wall bearing. If the pin diameter is fixed I recommend a 1/4” wall bearing.

If the pin diameter is fixed and the bearings are pressed in a tube, I would recommend a 1/4” bearing. 

Tubing is readily available in 1/8” steps of wall thickness and in DOM tubing (the good stuff) up to 5/8” thick.  This allows me to machine my bore about 1/4” bigger than the ID on only a little bit deeper than the bearing depth on each side.

The thicker bearing prevents the need for cleaning up the tube’s stock ID between the bearings.  As a result, I can machine this bore up to 1/8” off center (eccentric) and still not have any interference with the pin.  This can be a big time saver in your machine shop.

2. Calculating the Bearing Pressure

Bearing Pressure (P) — Calculating the pressure for the bearing is important.  First, find the area by taking the inside diameter and multiply it by the width.  This number is a representative stress because the edges see no load and the center sees most of it.  Let’s make our area one square inch.

We calculate the pressure by taking a force (1000 pounds), and divide it by the area (1 square inch) so our answer is 1000 PSI. 

The bearing manufacturers have guidelines for the allowable pressures for many different applications.  Generally they range 5000 psi 10,000 psi and some can be higher.

How pressure is distributed in a bearing

3. Determine the Frictional Forces

Calculating the friction for the joint is also important.  We will need to determine the frictional properties of the design and determine how much torque it is going to take; under load, to rotate the pin.  And that’s critical if you’re going to size a cylinder or hydraulic motor that forces the motion.  The general formula for calculating torque is equal to

T is torque in in-lbs., F is the force in lbs., and D is the diameter of the pin in inches. The diameter is divided by 2 for this reason:  You are going to be rubbing on the bottom edge leaving a slight gap at the top.  As a result, the pin will press at the center of the bearing at half the diameter. 

The chart below is typical of cylindrical bearings.  You can see from the chart below that as you increase pressure on the bearing, your coefficient of friction actually goes down.

Image courtesy of GGB

This is a good thing because it means that as I load the bearing up more and more it actually gets easier to turn.  But be cautions. If the bearing is oversized, pressures will be low (below 5000 psi), I can actually have a bearing and that is very hard to turn or worse it makes a lot of noise because low pressure leads to unwanted vibration creating unwanted noise.

I was once party to a design that had a bearing that was so loud it sounded like an irate whale. And you could hear it from half-a-mile away.  We ran the calculations on it and found out that the pressures were around 1800 psi (very low).  We narrowed up the bearing to increase the pressure and the noise was gone!  So when you’re sizing bearings make sure that you look at the highest load and lowest load case.

4. Calculate Surface Velocity

This is the speed at which the pin surface sees movement.  This is usually measured in feet per minute (fpm).  So to convert from revolutions per minute (rpm), use the equation below. The 12 is a conversion from inches to feet so be sure to check your units.

Where V is the velocity in fpm, n is the rotation speed in rpm, and D is the diameter in inches.  These types of bearings generally have a cut off speeds between 10 fpm and 25 fpm.

PV – The next consideration is a PV factor.  It is simply the product of pressure and velocity.  It is essentially an empirical method of estimating the bearing life.  It balances the force and pressure to a limit.  For example if our limit is 36, we could have a pressure of 4 and a velocity of 9 or a velocity of 4 and a pressure of 9.  So we now have three limits on our bearing.

5. Estimating Life Cycle

Once we have the PV value, we then can calculate the estimated life cycle.  What is life cycle?  The life cycle is a function of multiple factors.  Most of them can be looked up in the manufacturer’s charts.

  • Cyclic life factor (Q) — This is provided by the manufacturer based on the bearing type
  • High load factor (aE)  — This is a derating factor if the pressure is on the high end of the spectrum
  • Temperature factor (aT) — Heat dissipation is important.  If the ambient temperature is elevated, a derating factor is needed.
  • Pin surface factor (aM) –The manufacturer will give you a table to look up this factor.  Generally a surface finish between 6 and 16 micro-inches is preferred.
  • Pin surface finish factor (aS) — Even a little roughness on the pin surface can act like sand paper and de-rate the bearing life.
  • Bearing size factor (aB) –This factor looks at the angular pressure area.  This factor decreases as the bearing diameter increases because the used area of the bearing gets smaller and smaller as diameter increases.

As mentioned, there are charts and tables where all this information can be found. To calculate the lifecycle (in cycles) you combine all those elements as shown below.

6. Identify and Minimize Misalignment

It’s a bearing’s worst nightmare when things don’t line up!  This can be remedied by proper machining, mechanical adjustments, or welding with the pin already in place.

Misalignment is measured in percent.  A 0.2% misalignment is defined as 0.002” per inch of bearing.  This level of misalignment is standard and no adjustments need to be made to the bearing pressure. A 0.6% misalignment is the highest I would ever consider allowing.

No matter what your P value is, your edge load stays constant.  For example, if I have a bearing with diameter 2”, width 2” and loaded to 10 ksi, I will have an edge loading of 34 ksi.  Quite a multiplier!

If you have a bearing that supports a cantilevered load, you are almost automatically at a 1% misalignment.  That is a lot! You are essentially expecting 0.010” of deflection in the joint. 

The edge loadings can easily double or triple the calculated P value. In the example above, a 1% misalignment would yield an edge loading of 45ksi.  Ouch!

I highly recommend changing a cantilevered design to include two bearings that are spaced apart so that the bearing takes two axial loads rather than a moment load. You will also reduce the friction that will resist motion in the joint.

7. Assembly Considerations

  • Bore sizes – Over the years I’ve had a hard time reconciling the fact that the bearing can come in with an outside diameter tolerance of 0.002 to 0.004, but I have to hold my bore to 1/3 or ¼ of that.  It’s not fair!  Honestly, I’m not sure how it works mathematically.  But it does!  I’ve used thousands of these over the years in dozens of different applications and when machined to the recommended bore sizes you will not have any problems with assembly or undue wear.  Opening up tolerances is usually a good cost savings so beware of attempts to change this.
  • Pin sizes – The same is true with the tolerances on pins.  We get a little help on this one, though.  If you have read my article on pins, you will see that I recommend the use of turned, ground and polished pre-chrome rod.  The manufacturers know that the TG&P rod comprises a large portion of the pin industry and as a result, the TG&P tolerance matches the manufacturer’s recommendation (Wow!)
  • Chamfers – When installing a bearing, I recommend adding chamfers to both the pin and the bore.  I recommend a 15°-30° x 1/16 (on the diameter) chamfer to ease alignment.
  • Bearing knockers – If you are assembling this bearing in high quantities, I recommend designing a bearing knocker.  The knocker is simply a steel component that matched the ID of the bearing.  It has at least one step to provide good contact on the edge of the bearing when pressure is applied.  The matched ID prevents the bearing from having any localized buckling.  A second step may be added if the bearing is to be recessed past the surface of the bore.  You may need this to get past your leading chamfer on the bore.

8. Common Issues with Fiber Reinforced Cylinderical Bearings

As will all things, there are several things that are bound to happen when applying fiber reinforced bearings.  Here are the most common.

  1. No lead in chamfer – Add a lead in chamfer of at least 1/16” deep.  I recommend a 15° angle so that the bearing has a smooth guide.  You must also insert the bearing at least as far as the chamfer to make sure the bearing is properly supported.
  2. Not cleaning out the bore – Frequently, paint overspray or other debris can mess with bore.  It doesn’t take much to make a negative impact to the design.  Use a flapper wheel tool to remove the paint, but don’t go crazy.  You machined that hole for a reason!
  3. Improper bearing installation – As mentioned, a slight press fit is recommended between the bore and the outside diameter of the bearing so it is going to take some force to install.  The most common method is using a hammer.  This one makes me cringe a bit.  There are so many things that can go wrong here.
    1. Even pressure distribution – There is no real way to make sure that a hammer blow is going to contact the edge evenly.  This can partially be avoided by having the hammer strike a flat piece of wood larger than the bearing. 
    2. Buckling – This is a thin walled tube we are dealing with and it will buckle.  Unlike steel, these bearings are anisotropic so when the compression loads are too high, the fibers will separate.  At this point, the bearing must be replaced.  As with all buckling, the best solution is to add more support over the length.  I recommend having a bearing knocker (blue part below) that will add support all along the inside of the bearing.  This nearly eliminates all buckling issues
  4. There is an unknown amount of force that the hammer can produce.  For large bearings, this can be properly sized, but for small bearings, you are likely to damage the bearing.  I have one recommendation for this; use a bearing press.  If you can’t get the piece to a bearing press, you can make one with a hollow cylinder (enerpac.com) and some all thread.  Simply insert the all thread through the bore, bearing, knocker, cylinder and a few (thick) plates with holes in them.  Add some nuts on the all thread until snug.  Then use the cylinder to push the bearing into the bore.

Final Thoughts

Calculating cylindrical bearings can be a little tricky.  To speed up the learning process, I have an example problem worked out for you.

I’ve also developed an online calculator for a quick check to see if your calculations are correct. It calculates pressure, velocity, torque and estimated life (including the factors).  You will need to be able to verify and interpret the results for the brand of bearing you’re using but it will save you time by calculating most of the information.

In conclusion, cylindrical bearings are wonderful. They allow high loadings in tight spaces.  They are largely chemical resistant, do not require lubrication and do not break the bank.  When designing, seek these bearing products out!  Remember, almost everything I design uses at least one of these bearings.

Enjoy designing!

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6 Easy Ways to Improve your Mechanical Design Skills

Written by Corey Rasmussen in Self Improvement Last Updated January 27, 2020

In this day and age, everybody wants the edge. Young engineers coming out of school want to have the skills necessary to be a great designer.  However, engineers coming out of school lack not only experience, but technical ability as well.  That’s okay.

Here are some ideas to help you get that edge quickly

  1. Know that the obvious solution is not always the best
  2. Brainstorm often
  3. Ask yourself what the next step I can do
  4. Leverage the strengths of others
  5. Fail more
  6. Be prepared for critique

College is where engineering fundamentals are taught and a love for learning is fostered; not where technical skills are developed and honed.  Early on in your career, you may not have a clue about what specific area of engineering you’d like to enter into.  Once you find an area that interests you, you can trust that these technical skills will be developed in your workplace.  Surprisingly, though, in my experience, many engineers don’t rely on their technical skills to give them that edge, but rather on the scientific mindset they have developed.  That’s our greatest asset!  So with that in mind, here are some easy tips for becoming a better designer from the start.

1. The obvious solution is not always the best

 

When a problem arises, there will often be a clear path forward for solving it.  Don’t stop there. Every problem in design has multiple solutions…search them out!  I wouldn’t stop thinking of solutions until I had at least four or five.  Keep going even if they are ridiculous or cost prohibitive.  In the changing times we live in, what is cost prohibitive today may not be in five years.  For example, led light bulb were $25 to $40 when first introduced, but now affordable at around $1.25. 

Every problem has multiple criteria that are often in competition with each other.  A classic example is cost and quality.  Generally speaking you have to sacrifice one for the other.  

Some solutions are great but its overall implementation might be a problem.  For example, decreasing a critical bolt torque value when there is a large field population of units can cause a problem.  You would need to have a firm cutoff date for the old torque, change all manuals, retrain internal and external maintenance personnel and probably add a notice decal to the area where the fastener is stating the new torque.  As you can see, not an easy task.

So, get multiple solutions and evaluate them later.  Ideas build on each other.

A good designer will have solutions that answer all of these questions:

  • What is the least expensive solution?
  • What is the most expensive solution? Is there opportunity to use new technology or automation?  As technology changes, this might be affordable in a few years.
  • How long does it take to implement? Rushing a solution often causes more problems than it fixes especially when the product is to be serviced for many years after the sale.  If you have too much time to implement, you can start to procrastinate or over think /over-test a design while missing out on sales opportunities.
  • Can safety or quality be improved?
  • Can waste be eliminated from the product or the process to produce it?
  • What is the ideal solution? Often you can back your way into this.

Having answers for these questions can get you thinking out-of-the-box to come up with innovative solutions for easy problems.

2. Brainstorm often

Let’s face it; we don’t have all the answers!  Good ideas come from others imputing ideas into your work and vice versa.  If you are like me, you might want to shoot down an idea that seems unworkable.  Don’t do that!  Resist the temptation to say anything negative about another idea.  At the start of a brainstorming session, if every “bad” idea is taken off the table immediately, people stop contributing.  And that’s the worst thing that could happen.  So, please don’t do that or if you see someone else doing that, stop them.  Yes, those ideas may be bad, but I have seen many times over the years, that those bad ideas can be shaped and formed into good ideas eventually.  When multiple people share their input, they can each bring a new viewpoint and build on the idea.  That’s teamwork!

I recommend a group of 4 to 8 people with at least 2 people from other departments.  This gives balance and promotes different perspectives.

3. What’s the next thing I can do?

This question governs my design process.  My mind doesn’t seem to follow any known logical paths when I am designing.  I am constantly shifting back and forth between modeling and calculations and then I’m working on an entirely different section of the design and then circle back again.  It may seem unstructured and frankly, bizarre, but the truth is very simple; I get stuck.  And often.  You will, too.  When I get stuck, I simply ask myself, what is the next thing I CAN do? 

For example, today I was modeling a bolted design and needed to know what bolt size and plate thickness to use.  I started working the calculations and determined that I needed more information from the model.  So I modeled.  My modeling got to a point where I needed more information from a part that was all the way on the other side of the design.  Before I knew it, I had my model in order and could finally come back to sizing my bolted joint. I discovered the next thing I could do.

In the midst of a design project there are times when you are really stuck.  You’ve hit a brick wall.  Perhaps you have trouble determining what your next tangible action could be.  In these cases I recommend windshield time.  This is the time you spend on your drive to and from work looking through your windshield.  Your brain is somewhat on autopilot (but keep your eyes on the road) and your mind is reaching into its subconscious.  (Ever pass a traffic light and struggle to remember if it was green or not?) That’s when new ideas often come.  I highly suggest that you immediately, but safely, write down or record these new ideas.  You don’t want to risk losing this groundbreaking new idea!  You may need to pull over first.  If you have an idea when you are asleep, get up and write it down.  Don’t fool yourself into thinking you’ll remember it in the morning, because you won’t.  Yes, it’s inconvenient, but definitely worth it.

4. Leverage the strengths of others

In case you didn’t know, you don’t know everything.  Woo hoo!  I can’t imagine the burden of knowing everything.  I remember when I was a teenager and I knew everything, but I digress.  Yes, you don’t know everything, but you can use that humbling truth to your advantage.  Find someone you trust to be your mentor and glean from their knowledge and experience. Now that I have been mentoring for a while, I thoroughly enjoy when young engineers ask me for guidance.  I relish the opportunity to be able to impart what I know to the next generation. Don’t be fearful to ask for help, because mentors are mentors because they want to help you succeed.   Be willing to ask for help and you will see your own knowledge and experience grow.  A little warning here, your mentor is going to push you and it will not be pleasant.  Know that they are grooming you so that someday you will be a mentor.

Another great advantage is leveraging the power of a team.  In a previous role, I worked with a woman whose skills were completely opposite from mine.  She enjoyed paperwork and getting things organized.  I enjoyed the technical aspects of design and am less…er….organized.  This relationship was very productive, and as a team, we launched one of the most profitable projects in the company’s history.  Knowing the strengths and weaknesses within your design team and leveraging them can really propel a project forward.

5. Fail more  

Ouch!  This is a tough one.  Many of us were raised with the notion that failure is bad.  Yes, it is bad when bearing the brunt of it, but don’t let that get in the way of learning from it. Here are two important examples of constructive failures:

The Exxon Valdez oil spill of 1989 was to-date one of the largest oil spills ever, at 10.8 million gallons.  It had a profoundly negative effect on the environment.  However, it brought about huge and lasting improvements related to the transportation of oil.  When the news of the spill broke, most newspapers reported that the captain was intoxicated and single-handedly caused this disaster.

Although he was drinking, he was not on duty at the time of the accident.  I’ve personally seen the causal map for this incident.  After ongoing investigation, it was discovered that, in fact, there were roughly twenty root causes for the accident.  Here are a few causes of the accident coupled with improvements made:

  • The ship was leaving the port at night with bad visibility – now large ships only leave during the day.
  • Computers (very new technology at the time) were newly implemented and replaced the human job of navigation.
  • The pilot of the ship was piloting alone because the navigator was replaced by a computer.
  • There were large areas of the harbor that were not visible by radar and the ship was not seen – More radar coverage was added and other harbors were analyzed for similar issues.
  • The ship was a single hull so that if the hull was punctured, oil would leak out even if the damage was minimal.  Today, most tanker ships have two hulls so that the outer hull can suffer damage while keeping the oil safe.
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The other example of a constructive failure is the Tacoma Narrows Bridge in Washington.  Known as “Galloping Girdie,” this suspension bridge would twist violently in the wind until it collapsed on November 7, 1940 after being open for only four months.  A suspension bridge spanning such a great distance at that time was new and fairly untested.  Apparently, solid beams supporting the roadway, which did not allow the wind to pass peaceably, was the design’s fatal flaw.  In fact, on windy days, the wind would get “hooked” inside under the roadway and violently lift one side of the bridge at a time.  After the collapse, wind tunnel testing showed that a solid web beam was not acceptable in suspension bridge design.  As a result, suspension bridges today are only made with open lattice frames.

Please don’t get the impression that I am asking you to purposely try to fail in this manner.  These were examples of huge failures.  Small failures are good.  You will learn more from a single failure that you will from a thousand successes.  When you fail, welcome it, dig in and learn something.

A final thought is to know when your design idea is a failure.  You may have been working on it for a few weeks now and you see that it has one or more fundamental flaws.  Brainstorm and ask for help on it, but be ready to abandon this design.

6. Be prepared for critique – say thank you when you get input/feedback

Let me say this up front–this is a hard one.  You may be tempted to say something like…”But I’ve worked for weeks on this idea and now someone is going to say bad things about my baby?  Not acceptable!”  Designing something is very personal because any design is a reflection of us.  Over the years, I have been able to identify who designed something based on characteristics I’ve seen in other designs of theirs. 

Design reviews can be the worst time for an engineer.  And it can be extremely humbling.  I once had a design review where a question from left field on slide 3, totally derailed the rest of the presentation (about 15 slides).  My design wouldn’t meet a critical, but unknown requirement, so I acknowledged the short coming and admitted that this design would be changing dramatically.  I remained calm and didn’t argue.  I spent the remainder of the time quickly pointing out on each of the remaining slides all the things that would now need to be redesigned.  It was humbling and yet memorable experience. 

Whether your design is reviewed by five of your peers or by two dozen upper level management personnel, it is a daunting situation.  So you need to be prepared for the coming critique.  View it as constructive criticism that could potentially build on your idea rather than seeing it as a personal attack.  There is no way to get around it; people will be asking you to defend every aspect of the design.  Just relax and take a deep breath. You know your design better than anyone else.  Here are some other tips to help with critique.

  • People’s words can hurt – Sometimes they don’t even know they upset you.  Don’t get upset and give them the benefit of doubt.
  • Be prepared, know your design inside and out – If there is an area of the design that isn’t finished or you don’t know how to proceed, let others know up front.  Don’t try to defend something you aren’t that attached to.  I will often lead a segment of the review with, “I really don’t like this idea, but it is the best thing that I have come up with.”  You’ve now turned the tables and taken a weak area of the design and allowed others to be involved in the process.  They will remember that.
  • Know when to defend your decision and when not to – Seems simple, but it isn’t.  Don’t get caught up in the emotion of the situation.
  • Say thank you – This one’s important.  Saying thank you after every question/remark shows that you value the input of others in your design.  It’s not easy at first, but quickly becomes habit.  It’s a sign of a mature and seasoned engineer.
  • Take notes – Show that you are serious about the input by writing it down.  If it is a large group or a short amount of time, get someone else to take notes.  Be sure to follow up with any unanswered questions in a timely manner.

As I applied these six principles in my engineering career, I saw that the quality of my work and my creativity improved dramatically.  I was also able to take on more responsibility and become a resource to my team.  I challenge you to implement these in your life so that you can enjoy the same growth that I did.

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