Straightened a chassis yesterday

[pooch]

Sagged chassis was looking around for something to chain it down to, a nearby railway track was not available.

Mate suggested a pipe bender.

After a look, it worked fine.

A 12 ton pipe bender fits under chassis and I chained it down at either end and blocked the chassis channel section to stop it twisting and crushing and simply pumped the bender.

Came out dead straight in 5 minutes.

[Logan]

Another way to do it is like a basic trailer with either angle iron side rails or pipe rails. Chain the frame down sideways on the trailer. And then you can jack up on it.

[BRENT in 10-uh-C]

Hopefully it will stay straight as now the frame has been stretched in two places. I realize folks use the bending method but the easier, -better way in my opinion is to use heat to shrink the original area that was stretched. This makes the entire frame rail equal strength throughout.

[ericr]

Originally Posted by BRENT in 10-uh-C

Hopefully it will stay straight as now the frame has been stretched in two places. I realize folks use the bending method but the easier, -better way in my opinion is to use heat to shrink the original area that was stretched. This makes the entire frame rail equal strength throughout.

I know you have explained these concepts repeatedly on the Barn and I am sure you are correct; but for present purposes can you briefly explain how these concepts are reconciled with the warnings we see in the
Bulletins that chassis parts should be straightened while cold, not heated,,,,

[TinCup]

Here is a link to a few pictures of a project where we straightened the frame on a 29.

1929 Frame Straightening

[BILL WILLIAMSON]

Sponsored Links (Register now to hide all advertisements)

If it took 80 ODD YEARS to sag, how long will it take to sag again, regardless if you did it HOT or COLD or with a SLEDGEHAMMER & a BLOCK of wood or a HOUSEMOVER'S JACK!
I left a note under Vermin's L/H scuffplate: "Gregg my son, be sure to jack up Vermin's saggy frame rails in 2093, Dad"

[pooch]

Originally Posted by ericr

I know you have explained these concepts repeatedly on the Barn and I am sure you are correct; but for present purposes can you briefly explain how these concepts are reconciled with the warnings we see in the
Bulletins that chassis parts should be straightened while cold, not heated,,,,

I would not use heat if I did not have to.

The frame was pressed cold back in 1928, the metal deforming process in pressing gives it some of strength also in the right angle bends along with its upper and lower chords.

It has taken 85 years of pounding to make it sag 1/4 inch, and most likely half of this was on dirt potholed roads in its early life.

To heat it unnecessarily in my opinion would weaken it at the point of heat, not restore it to a uniform original strength.

[BRENT in 10-uh-C]

Originally Posted by ericr

I know you have explained these concepts repeatedly on the Barn and I am sure you are correct; but for present purposes can you briefly explain how these concepts are reconciled with the warnings we see in the
Bulletins that chassis parts should be straightened while cold, not heated,,,,

First let me start by offering that someone suggesting it took the frame 80-odd years to sag is like seeing a flat tire on a Model-A wheel and suggesting it took 80-odd years for the tire to go flat! In real world some of us live in, we know that just isn't the case is it?



Now you refer to the Service Bulletins as warning against using heat on chassis parts. I fail to recall it specifically mentioning using heat on a frame rail but maybe if you have time, you can PM me the page number(s) where I can read it in the proper context.

To answer specifically about the frame rails, we need to start from the very beginning. The frame rail was stamped cold however it was formed in a specific way through known engineering techniques. The frame rail steel is much like a rubber band that has been allowed to normalize. You can stretch the rubber band however when you do, it will get thinner during the process. The thinner area is always weaker than a non-stretched area. This same mindset applies to the steel in a frame rail too. Unlike the rubber band, the metal does not have the ability to return to its' former state. Therefore when someone tries to bend the metal back to the original shape, the metal can only stretch in another area. Now we have created two structurally weaker areas. Now I will quickly agree that our Model-A's will likely never see the same adverse conditions they once did however isn't that a lame excuse to perform a substandard repair, ...especially when doing it correctly involves the same amount of labor with a superior end result?

The comment about using heat likely comes from "He said / She said" mindset where someone who was uneducated about the process made a comment that seemed believable, and now others have accepted it as fact. I have listened for years about some saying Ford parts have Vanadium in the steel and so it cannot be heated. When the truth is known, there is only trace amounts of Vanadium and the reason it was used was as a rust-prevention method, --not as a strength enhancer. The percentage of the Vanadium used is not of enough quantity to add any significant amount of extra strength.

Next, using heat on many parts can be compared to doing bodywork. Just because you purchased a gallon can of Bondo does not mean you must use the entire can on the body in one application. It is meant to be used in moderation and by only the amount that is truly needed. The same mindset applies about shrinking metal. There is not any need to heat the frame rail any hotter than it takes to make steam rise when water is placed on the hot surface. Just like using too much Bondo to fill a dent, turning the frame metal "red hot" is only abusing the metal and serves no useful purpose. Only an unskilled craftsman would do such a thing solely due to ignorance about the task he is trying to accomplish. One of the main reasons why we are involved in this type of forum is to gain knowledge on how to do something better and expand our abilities. For the folks who have tried the method of heat shrinking a bent frame (--or wheel, or sheetmetal), I have yet to hear anything but positive feedback from their results.

.

[MikeK]

OK, I've heard this heat shrink/ cold bend debate about frame straightening too many times. Let's apply a little engineering/ math:

If a 4' long straight edge across the motor mount shows a 1/4" (0.250000") sag, the difference in the top and bottom chord will be 0.00260". I dont know if it will be all stretch in the bottom chord or all compression in the top. Likely some mix of the two, as the same sectional area of the same material makes up both chords.

Applying either straightening method, cold or heat, will cause one chord to compress (shorten) as the other stretches. Cold press will cause the chord acted upon (pushed with the jack) to re-compress while the opposite chord stretches. Heat shrink will cause the chord acted upon to shrink while the opposite chord will stretch. Whether the stretch/compress between the two chords will be 50/50 or 90/10 I don't know, but both chords will be affected by either method.

OK, let's assume the worst: 1) The sag caused only one chord to stretch or compress 0.0026". 2) The method or technique you choose and apply to straighten the frame acts only on the wrong chord. 3) Only one of your two frame rails was bent.
RESULT OF STRAIGHTENING: A frame that has one side 0.0052" longer.

If anybody thinks Henry's frames were accurate within 5 thousanths, think again! There's more slop than that in every bolt hole.

[Mike V. Florida]

I like to think of it this way, you know these bendy straws, the ones that you bend and the stay bent? One bent if you straighten the straw without collapsing some of the rings the straw will get longer.

As for the frame, how much longer, and will it made any real difference is the question.

If one is truly trying to restore the car as is left the factory I would think shrinking would be the answer. The question to you the restorer would be; how much is the bend, do I have the skills to heat shrink the bend, will if effect the rest of the build?

[BRENT in 10-uh-C]

Thanks Mike. I am not sure if all figures are applicable, ...and I really do not have the time to study them for validity at the moment but they add a dimension that I do want to explore when more time is available. I will say that it has been my experience that metal will stretch much easier than compress given the same amount of pressure in either direction. Maybe this is appearance alone but I find metal will usually re-arrange its' shape instead of compressing.

One thought/question about what Mike is suggesting is regarding the compressing of the upper chord. To bend something, doesn't a fulcrum need to be added to the equation? If so, wouldn't the top rail be the fulcrum? If so, it would become the strongest point so, I doubt much compression would be seen as a permanent set.

I have included some pictures of a Roadster pick-up frame below that had endured a hard life up until the time for restoration. I know this as fact because the owner's grandfather used it in his brick masonry business for many years hauling brick and mortar to the jobsite. This frame was sagging in several areas all exceeding .250" below a horizontal plane. The heat marks pretty much show the areas where heat & water were applied and to what part of the metal was moved (shrunk) to bring it into proper alignment.

[George Miller]

Originally Posted by pooch

Sagged chassis was looking around for something to chain it down to, a nearby railway track was not available.

Mate suggested a pipe bender.

After a look, it worked fine.

A 12 ton pipe bender fits under chassis and I chained it down at either end and blocked the chassis channel section to stop it twisting and crushing and simply pumped the bender.

Came out dead straight in 5 minutes.

I'm glad you took the time to get it right. We see so many bent frames on so called restored cars. I can not tell you how many times I have told some one that they needed to straiten there frame first. But they do not bother.
Then do not understand why the hood and body do not fit right.

[Smitty]

A neighbor and I straightened the frame in my coupe a couple of years ago. On Brents advice we used heat to straighten the frame using only enough to bring steam off the heated part of the frame rails. My neighbor is a race car fabricator and has a big steel table which he uses to build chassis, it is perfectly flat. He also told me that heating is the method he uses to straingten rear axle housings when the have been damaged in a wreck.
Been about 5 years and the frame is still holding alignment.
Steve

[stouchton]

Heating low carbon steel is just bad news.

Yield strength can be reduced by almost 50% - hence the need to cold form in the first place.

In addition, it is common place for truck manufacturers (such as Ford) to specify that no heat be applied while straightening a frame (this is for a modern truck....).

[BRENT in 10-uh-C]

Originally Posted by stouchton

Heating low carbon steel is just bad news.

Yield strength can be reduced by almost 50% - hence the need to cold form in the first place.

In addition, it is common place for truck manufacturers (such as Ford) to specify that no heat be applied while straightening a frame (this is for a modern truck....).

Are you certain about this? While I am not any metallurgist, mild-steel is just opposite of the characteristics you are suggesting. Modern truck frames are a high-tensile strength. Excessive heat is bad news for them and on a high-tensiled frame, I do agree with you that heat could likely reduce that by 50%.

On the other hand, mild-steel is very acceptable to heat and welding, and is often shaped or even forged with heat. Therefore I feel very comfortable in saying that heating to the proper level to create a shrink will not perform any adverse weakening effects to a frame.

[stouchton]

Brent - a structural engineer begs to differ with you.....

However, it is probably meaningless since the frame design in the Model A is probably overkill in the first place.

You also need to watch words like "yield strength" and "tensile strength". You can change the properties of steel (which these words allude too) but you cannot increase the overall strength of steel by heating it.

[BRENT in 10-uh-C]

Originally Posted by stouchton

brent - a structural engineer begs to differ with you.....

However, it is probably meaningless since the frame design in the model a is probably overkill in the first place.

You also need to watch words like "yield strength" and "tensile strength". You can change the properties of steel (which these words allude too) but you cannot increase the overall strength of steel by heating it.

........? ? ?

.

[Tom Wesenberg]

The AA might be overkill for most purposes, but the Model A frame is barely OK for not so fat people.

[pooch]

Overkill?

The frame twists at the steering box mount when you turn the steering wheel.

[stouchton]

Sorry guys - was just trying to find a friendly way not to start an argument