What is acceptable tolerance for a frame??

Building my T on 32 rails, and i'm having to straighten Every part of my frame, because the rails and 37 X are f'ed up and i'm assuming i'm probably going a little overkill on trying to make everything right. What do you guys call a good job?

 

Not sure exactly what you are talking about, but if you talking about frame dimensions and tolerances of the dimensions, it would depend on where you are talking about. Got any more detail? Other than that I use plus or minus 1 Micron for every 1000 Feet stabilized at 72 degrees F at sea level and that's why I am still working on mine and not driving it.

 

I'm talking, how outta square is OK, twist, or just the body being off to the side, that sorta stuff

Its not that i'm trying to cut corners i just go a little crazy sometimes

 

Heres some help.. http://www.jalopyjournal.com/forum/showthread.php?t=166373&highlight=frame+tolerances

I would not be comfortable with anything over a 3/32" square and 1/16 parallel. IMHO.
Those are our tolerances for my day job and have gotten very used to them.

 

I read somewhere that Factory standards are like 1/8" or so. Thats new, so Imagine what kinda shape they are in after 100,000 miles of stresses from road driving. The surfaces we drive on aren't perfect either. So I'd keep it around 1/8".

 

Suspension points etc, I want them dead nuts. My 36 Truck Frame cross measurements front to back are within 1/16th I am happy with that, I would not be happy with a quarter inch. But again I am still not driving it.

 

I struggled with this same question quite a while and some guys who have built more rods than I ever will suggested trying to get closer than 1/8th was going to be near impossible.

I'm not sure I agree, but I find it difficult to read a tape measure down at 1/16th and be confident I'm reading it accurately. But 1/16th has become my target. 1/16th measured best I can probably means I'm within 1/8th most the time.

 

Exactly. So many components, your tapemeasure, square, rule, chalk, sharpie, welder, drill, and saw are only so accurate. I've been raised and mentored by professional old school carpenters. Thier margin of error is usually 1/16" to 1/8", I apply this to my metal and frame work.

My welding teacher was obsessed with getting everything as perfect as possible. So he'd spend weeks measuring and adjusting and such.

He either:

A.) Never Finished whatever he was building.
B.) Cobbled it together
C.) Or the rarest one, put it together like a normal human being.

 

When I boxed and installed a Dagel's X member in my 29 frame,it was dead square and wound up with about 1/16" twist.I thought that was real damn good.The twist I measured with a digital level,front crossmember was dead level,rear was off about a 1/16".

 

I hear people tell me all of the time that the are accurate to within 1/64", 1/32", 1/16" etc., yet none of them have any better tool to measure than a tape.

My chassis jig was built using laser measuring tools, and it is +/- 1/16".

My grandfather liked to say "If you can't make it perfect, make it adjustable".

Voltaire liked to say "The perfect is the enemy of the good".

 

I always heard within an eigth .These old cars were probably not that precise anyway .Just make sure its square when your done. These old fords you build basically you shake them for final adjustment .Make rear adjustible . In the trailing arms .

 

You want to try to get the frame as accurate as you can it is the foundation from where the rest of you project will be built off and judged against, shoot for dead nuts on and if it ends a 1/16" off then no harm. Frame rails are a time consuming to straighten original ones but if they were bought you probably paid good money for them take the time and get the right you won't regret it latter. Good luck.

 

I keep them within a 1/16 th. or find out what the problem is and correct.

 

I also like to keep as close as possible, but a 1/16th is the limit.

 

i can tell you that a framed car/truck (according to a.s.e. and icar you can be off 1/8" and a unibody 3mm) but personally if it were something i was building id want it dead on

 

I have to agree, 1/16 is common, I try to keep within that.
I chased an 1/8" on my frame seem like forever, but I did fix it, now it's dead on. Just take your time, measure 9 times and cut once.

And as a friend said, tack weld everything first, if it's where it needs to be, finish welding.

 

I shoot for dead nuts on anything I build (whether it's a car frame or a storage rack) but when it's all welded up I will accept 1/16 unless it is critical as in suspension mounts and then I will fix it or make it all adjustable. After all, there isn't a production car that doesn't have some level of adjustability built in. I have seen (read; measured) frames that drove straight and handled well that were 1/4" out of square, but it wouldn't happen on my car. I would accept 1/8" for a factory frame.

Jaysin

 

I like mine to be within 1/8". I'm sure a car would handle and look just fine with much more variation than that, but 1/8" feels right to me.

 

Anyone who tells you their work is consistantly within 1/16 is either lying or doesn't know how to read a tape.

Frank

 

I read a tape for a living and have for 36 years, I know what a 1/16 is.

 

Doesn't mean that I don't miss my mark sometimes though.

I think a good rule of thumb is a more realist 1/8", like I said earlier, just take your time.

 

I agree, I may be wrong but it seems It would be most important to have the front and rear axles square to each other.

 

That is my point, some place you have to be dead nuts, some thing you can let slide. I'm not saying everything on my coupe is dead on, but some things are built in to the car that you can't plumb or level, that's just the way it was made.

 

But what does dead on mean? That was the problem I kept running into as I was trying to square a frame, how precise can I make a wheelbase measurement and the diagonals across the frame?

I toyed with mounting a dial caliper on a long frame to be able to triangulate my frame to the 1000th of an inch. In that example the precision of my mounting and the error of the caliper would combine and give me variability.

Getting it perfect is great, but those who are saying that aren't telling us what tools they are using to achieve it and its difficult to believe those tools are perfect no matter what they are or where they were made.

If I can rephrase the original question, it was what is a reasonable tolerance to shoot for in building a hot rod. The answer is probably different if you are building a rat rod as opposed to something to run on the salt. Most of our projects are somewhere in between.

I don't have enough experience personally to claim to know what those tolerances should be, but there does seem to be a consensus here that 1/16th is close enough. Okay maybe its not a consensus but more of an average...

Can those of you who are talking tighter tolerances tell us what tools you're using for your measurements? Its not too late to re-measure mine and perhaps make it better.

 

Hitting it perfect, dead on, gives you a good satisfied feeling. Yet being an 1/8th of an inch off is good to go. Just don't tell anyone, and no-one will ever know.

 

I think you could get it much closer on a frame jig. Assuming your jig is square. I on the other hand I built my frame on a fairly level shop floor. Most of it is withen 3/16 but some of it is a 1/4. Pickup handles great every one that drives it compliment on have well is handles. So I think in my world that is acceptable. And no odd tire wear.

 

A guy has to remember that back in the days of the riveted frames they were often a bit out of square and more so after being run for a while especially in trucks.

Tie into that, most likely if the frame got modified in the 70's or earlier the chance that it was done on a frame jig or table was somewhere between slim and none. Often up through the mid seventies frames got modified while under the vehicle and there were big debates ( for sure in Central Texas) about the merits of keeping the body on the frame during a build or removing it. If a guy did have the frame out of the rig most likely it was set up on a pair of sawhorses at best to be reworked.

I cut up the frame that was under my 48 that had the Camaro subframe because when the work was done on the rear of the frame to use coil springs a twist got welded into the frame. Most likely due to too much continuous welding on the same piece before moving onto the other side but there wasn't much out on welding a bit here and there to prevent warping the piece in those days. I probably could have taken it to a frame shop and had then jack it around on the frame machine to get it squared up but I didn't think about that at the time.

If it is something you can fix by putting it on a frame table or by doing the rework yourself head on otherwise if it is within original factory tolerances put it together and enjoy it. Someone is bound to have an old body and frame repair book that gives the + and - on what the frame can be and be within factory tolerance.

 

Just remember when you use a tape measure the closet you'll get is within .035. The eye cannot measure anymore accurate than that. Just be careful when you use the tape measure. When I do frame fabrication the only thing I use the tape for is to cut material. I layout my brackets out with Veneir calipers. I use calibers all the way up to 60". Unfortunately when you measure a frame diagnoly or longitudaly you have no choice but to use a tape measure. An another rule of thumb is once you establish the frame is suitably square. Establish a centerline and build your suspension off of that.

 

If you drive in Tucson the first pot hole makes the whole thing moot anyway!

 

1/16.......and 1/16.........