Pre-Stressed Steel Fabrication

The concepts of pre-stressed steel fabrication have been around for ages, but they are not often applied for simple welded structures like trailer frames or crane stands. Jig for Welding PerpendicularityI’m not talking about huge pre-stresses structures like bridges.  And, I’m not referring to full pre-stressed beams that normally dominate this kind of conversation.  This is more about the practical implementation of some of the basic principles to get results we want in our DIY projects.

Feeling the Heat

For purposes of this Mechanic’s Tip, we’ll limit the discussion to areas of heat distress from welding — causing weld warp.  (Or, sometimes we call it “Weld Pull” or “Draw” or welding distortion.)  See this post about avoiding beam weakening, and this post for the engineering.

We all know that the heat of welding causes materials to “move” or warp, and if you’ve been welding a while you’ve learned how to compensate.  Sure, there are lots of small steps that can help, so these ideas do not overshadow those.  Things like lot’s of tacking and moving around the framing are always important.  (Setup is also a key — like this example with tips for a trailer frame.)  However, these pre-stressed steel fabrication techniques can certainly help in some circumstances.  Think of it as another tool in your box.

What is “Weld Warp”

How many times do you weld 2 pieces together and afterword realize one is no longer straight.  The classic case is the “T” connection.  After the weld, the crossing piece is no longer straight.  This is particularly noticeable when the crossing piece is thin material, but it’s also a problem when welding heavier stuff like angle or channel.

The amount of weld warp (distortion) has a lot to do with where the welds are placed, and what the beam sections are.  Obviously beefier beams and/or smaller weld areas affect this less.

Pre-Stressed Steel FabricationThe first time I welded a tube to the center of a piece of channel, I was horribly disappointed that the channel (the crossing piece) was not straight. I really couldn’t see the warp, but it was obvious when I stood it up. The channel worked better as a rocking chair than as a sturdy stand.  Heat distress had caused the channel to warp slightly.  So, here’s how I solved the problem for future builds.

Solutions with Pre-Stressed Steel Fabrication

The idea is to pre-stress the member in a direction opposite how it will bend under welding heat.  To do this, First, take a guess as to how much the part will warp.  It’s usually not much.  For me the measurement was easy because the early sample was right there.  In this case, it rose about 3/32″ from the center (point of welding) to each free end.

Second, set up the welding so the beam is “bending” that amount in the opposite direction.  See the photo for details of how I do it for this gantry crane leg situation.  The 2 bottom beams are the same.  The 2 chunks between them in the middle are each 3/8″ thick.  The angle parts at the ends are 3/32″.  By clamping the beams together on each end, it makes a 3/32″ pre-bend for each side.

Third, weld it in place as you normally would to minimize warp — still with the jig.  As in the photo, tack the main beam at each corner, then after the pre-stress, tack the angle braces in place.

(Using lots of clamps – or weights – to hold things in place is always a good idea.

Welding while in stress will do 2 things:  First, the heat will relieve the stress at the point of weld allowing it to “relax” some.  Second, it will pull anyway as it cools, but it will pull from a position of stress relief — making it come back to nearly flat (if you’ve done the pre-stressing correctly).  This is the technique of pre-stressed steel fabrication.

Aluminum

A word of caution when welding aluminum (or for that matter when welding other materials).  The metals act different when heated, so play and test it before trying to copy the Pre-Stressed Steel Fabrication methods.  Also, read this article too about Aluminum Trailers.

The Best Way To Learn

Welding Steel FabricationAs usual, the easiest (and best) way to learn is to try it.  In the photos you can see the way I jig things.  The bar clamps secure perpendicularity.  The shims (wood) under the beams assure vertical position.  The (parallel) beam at the bottom clamps to the real bottom beam with proper spacers between so it bends and pre-stresses properly.  The pre-stressed steel fabrication never turns out perfectly flat, but in this case, it’s more important that the tips of the channel are the points of contact, so just a little over-bend works well.  Since this is a crane stand, weight from the load flattens it right out making it very stable.

In the final photo, the stands are side-by-side to check perpendicularity and the pre-stressing effect.  After this photo, each leg was set again with the clamps to finish welding.  I like to verify that things are correct before completing the welds.  It’s more work, of course, but any mistakes or oddities are much easier to correct — but that’s just me.

Experimenting like this is especially good if you’re just starting out with welding.  When you choose a new welder and begin to experiment, you learn a ton.

Good luck with these pre-stressed steel fabrication techniques.  Apply them as needed.  This also works very well with certain areas of a trailer frame.

Comments

1 Comment
Inline Feedbacks
View All Comments

We Found These For You . . .

Article
Aluminum Weld Adjustments
I’ve heard different opinions, so let’s look again at the Engineering and clear up some facts.  Maybe we can also debunk a few misconceptions.

Read The Article

Product
4' x 8' - 3500# Torsion Axle Trailer

Fully Engineered Blueprints are just the start with these Torsion Axle Utility Trailer Plans.  With the deck a little larger than tradition, you can put true 4' x 8' cargo inside!  Up to 3500 lbs.

Article
Replace Trailer Tires
Don’t mess around with your safety or unexpected trip interruptions.  The Best Reason to replace old or worn trailer tires is personal sanity, because who wants to deal with it on the side of the road?

Read The Article

Article
Trailer Axles - Springs - Wheels - and Tires
I’ll just drop by the parts store and grab an axle . . . . Well, trailer axles are not quite that simple, but knowing a few important details, we can certainly get the right one.  Here’s a quick guide…

Read The Article

Article
How To Make A Trailer Longer
Sometimes I wish my trailer was longer.  Is there an easy way to make a trailer longer?  Is that even possible?  And, what are the limits

Read The Article

Article
Welding Trailer Spring Brackets
There is some disagreement in trailer building about how to weld-on trailer spring brackets (also known as spring hangers).   Some of you have sent questions about which techniques are best, especially

Read The Article

Product
4x6 Utility Trailer Plans - View 1

Smaller size Trailer Plans for the DIY Builder.  This 4x6 Utility Trailer has a 2000# axle capacity and lots of options for customizing.  While it may be smallish, it’s tough and capable just the same.

Product
32' Tiny House Trailer Plans For DIY

With options for length, these blueprints address the unique needs of a Tiny House Trailer.  Low 8.5’ x 30’ or 32’ top deck height.  Up to 18,000 lbs total capacity.  Fully Engineered.

Article
Makeshift DIY Truck and Trailer
The coolest thing I saw last week was this guy with a very creative DIY approach to a pack trailer — and, of course, his tow vehicle!

Read The Article

Article
Example aluminum trailers
This question comes up often — because there are not many good plans for aluminum trailers out there.  We have great trailer plans, but none for aluminum.  Why?  As one of our Frequently Asked Questions, this one deserves a good…

Read The Article

Article
Review of the Folding Trailer Tongue
On a recent trailer, I experimented with a new folding tongue design.  Now it’s time to review — What do I like?  What would I do different if building another?

Read The Article

Article
What Are Your Essential Tools
We’ve been asked many times about “What are the most essential tools for your shop?” Well, that’s a hard question, because frustration and wailing are the result when the right tools are not available.

Read The Article

Article
Trailer Hitch Safety Chains
Do they accomplish the intended purpose?  Or are trailer safety chains just a legal pain in the rear?  Maybe the better question to ask, since we’re required to use them:  “How do we make chains effective?“

Read The Article

Product
20' Deck-Over Trailer

This is our longest 7000 lbs tandem axle deck-over trailer.  These plans are fully engineered and include so many options, because you expect more from plans at Mechanical Elements.

Article
Learn To Calculate the Axle Position
Trailer axle position?  This is a good question.  Unfortunately, there is some popular, but misleading information around.  So, how do you know proper trailer axle position?  Here’s the whole answer,

Read The Article

Article
What Do You Want for 2020
A new day, A new Year, and a new Decade!  We don’t get to say that very often, so it’s kind of cool.  Anyway, as we look to the near future for Mechanical Elements, we want to know what you…

Read The Article

Article
Using A Workshop Hydraulic Press
A shop press is a fantastic tool, and when you need it, there’s not much that can really substitute.  On the other hand, we need to keep things in order because when things go bad, they can easily go really…

Read The Article

Article
How Much Can I Tow?
There are 3 main factors with how much you can tow.  While it all seems simple, digging in makes it a little less clear.  Yes, it’s easy to look at the simple rating numbers, 

Read The Article

Article
Aligning Misaligned Holes
Sometimes, despite your best efforts, holes you drill for a project don’t quite align with those in the mating parts.  It’s maddening, and sometimes you feel dumb because it’s messed up, but there are ways to fix

Read The Article

Product
6' 10" width, 12' Length Trailer Plans

Blueprints for a Strong and Stable 6x12 utility trailer.  This single axle, 3500# capacity trailer with many options is ideal for a million uses.  We provide great DIY Plans for builders who want the best.