Frame jig and heat shift

[rjwoods77]

Hey everyone,

Next year we are going to invest in some decent equipment to help control warpage. I am sick of this shit moving around when welding. We made a decent lower jig and when we unbolted it is shifted some. I have done a lot of space frames but this is the first one I am super anal about getting perfect. I am talking flex under 1/16 but the added effect of a bunch of little flexs adds up to a bigger flex. We have a flat surface(2" thick steel table) that we clap it down to. Release the clamps and boing!!!

So you teams out there that have the means, concern and bucks...

What have you found the most effective way of controlling warpage due to welding? What can you do afterwords short of puting the frame and the jig in a big oven to stress relieve it in the hopes of relieveing heat stress/warp? Are we the only ones having these problems?

Thanks for any response.

[GTmule]

getcha a big honkin train switch thawin propane torch, and get to cookin. (normalize it) That should help alot.

[Mike Cook]

Our jig was made like so: First, four pieces of .5 x 1 inch steel bars weleded together to make a box. This would located your x and y points. When you weld it, just tack each bar two or three times, be very quick. The key is not to heat it up to much. We also clamp the shit out of it. Still flex is common. We take these sqaure pieces and tack them to a 3 x 3 tower. When they were up there we checked for squareness. The overall lengths didn't change much but they sure wern't square anymore. So beat it with a hammer until it is sqaure. Done. I'd put up pictures, but that would spoil all the fun... I'm sure using thicker heavier jig tubing will reduce warping.

[Cement Legs]

Originally posted by GTmule:
getcha a big honkin train switch thawin propane torch, and get to cookin. (normalize it) That should help alot.

Im with GT. Use some type of heat source; propane, oxy-acet, etc, and relieve as much of the stress on the frame that you can before removing your clamps or taking it from your JIG.

Another less appealing option is to do your welds 1/4 turn at a time trying to balance the stresses but this takes a keen eye and lots of experience to get anywhere close to the above.

[rjwoods77]

What is a normal process of flame relieving the frame. Do I bolt it back down into the jig we have and just hit one node at a time? Any particular pattern of heating the nodes? Should I use a temp marker and if so what kind of heat am I looking at introducing?

[Lyn Labahn UW-Madison]

Rob,

Carrol Smith has a good outline of how hot steel is by color, and what temperature to stress relieve at in "Engineer to Win". You can also buy a marker like you said to ensure you are at the correct temperature. We use an Newport optical table for our jig. Having constructed two frames, I definately agree spring back is a pain in the ass. Since our jig is an optical table, and many of fixtures we make are CNCed aluminum, we can't put the whole frame in an oven. The way we ensure that the points, bellcrank pivots etc. are in exactly the right place, is to weld them on very last, and to use minimal heat with the TIG torch. It is not perfect by any means, but the results are pretty damn good!

[Cement Legs]

Originally posted by Rob Woods:
What is a normal process of flame relieving the frame. Do I bolt it back down into the jig we have and just hit one node at a time? Any particular pattern of heating the nodes? Should I use a temp marker and if so what kind of heat am I looking at introducing?

Hey Rob if you can get it back into your jig that may be worth trying depending on how much deflection you have. One option that someone just approached me with at school the other day is heat treatment by wrapping. I dont know exactly what the process is, but the jist of it is that some kind of thermal blankets are wrapped around the tubing of the frame and brought up to temperature. The person telling me about this was saying that you can use this process for a complete heat treatment. Anyway you would have to look into it because thats all that I know about that.

When I worked in the oil industry we did have a number of different 'crayons' that we would mark pipe with to verify its at high enough temperature to begin welding so that option is definitely available.

Oh and one last thing to keep in mind if you are going to try some type of stress relief with heat. Any enclosed volumes of air will rise in pressure dramatically when you start to heat things up, something you'll want to keep an eye on...

[BryanH]

When I was a kid I hung around a nearby backyard engineering shop. One thing I have never forgotten is Norm telling me how he welds wheel rims, tubes stress free by running 50% of the welds clockwise and the rest anti-clockwise. On 1" tube he would do 4 welds.
With Kart chassis the top half of all welds are done (1st run 3 to 12 o'clock, 2nd 9 to 12) in the jig then pulled out tipped upside down and finished same way and they stay flat.
Tig welded chrome moly must be correctly heat treated.

[Ben Beacock]

Originally posted by Rob Woods:
What is a normal process of flame relieving the frame. Do I bolt it back down into the jig we have and just hit one node at a time? Any particular pattern of heating the nodes? Should I use a temp marker and if so what kind of heat am I looking at introducing?

Be sure not to get it too hot(just barely into the 'red' I think), and make sure any sources of air movement are minimized so that the welds don't cool down too quickly.

[MikeWaggoner at UW]

Originally posted by Halfast:

Tig welded chrome moly must be correctly heat treated.

What about ER-70? It's not as good as 4130 rod, but you can can decent strengths with no heat treat.

[Moody]

here I am, thinking that ER-70 was better than 4130 rods, with or without heat treat(?)

dare we open this discussion again?

[karsten]

hi,
have a look at lionsracing.de .
in news from feb.2005 there is an
image of our jig. all tubes were
cut by laser straight from cad-data.

bye
karsten