Square tubing tolerances and adjusting them to match

I managed to remove the better part of the weld bead inside a piece of 2 1/2" square tubing with a slightly modified chisel bit on an air hammer.
Worked pretty decent. Hard to get the right angle on the chisel that won't dig in too deep or head up and out, but with practice I'll get better. Then my shoulder was hurting too much I had to bail for the day. Got lots of happy pills, though! The problem I just discovered is that despite how it all appears it should fit, it still doesn't. The two inch tubing isn't quite as square and as close to two inch as I would have expected. It's well within the tolerances (+/- 0.20") I found on the web, but tolerances are running into each other. The interference is from nothing one way to about six thou the other way. The radii are not (what's the term....) squared in the sense that each side of the bend matches the other. Like the radius going into the bend is good and coming out of the bend swings wide, like it didn't want to bend all the way on the trailing side of the bend. The shape, when viewed closely, is slightly like a diamond instead of a square. I didn't really start to see it all until I put a sanding disc to it. I'll have to get more sandpaper, most likely.
So in order to continue with my idea of slip joints using this tubing I'm going to have to sand down the two inch tubing where I expect them to slip together, or figure out a way to enlarge (or inside of) the 2 1/2" stuff. Any ideas? I wasn't expecting this at all and will change some of my plans a good bit.
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You are seeing a pretty standard set of tolerances for square tubing. In order to make this work on a consistent basis, you need to have a large gap (2" tube in 2-1/2"x.187 wall) or buy the special telescoping tube (Telespar??) that is produced to work properly in your application.
When you buy tube in mill quantities (20,000 pounds and up) you can usually specify better control of the squareness, weld flash, and corner radius. When you buy from the distributor, you get what you get.
Your first post mentioned that these were short pieces. How about a hardened steel block with the proper edges and corners, use the press to just push it though? That will fix the corners, iron down the flash, etc.
carl mciver wrote:

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| You are seeing a pretty standard set of tolerances for square tubing. In | order to make this work on a consistent basis, you need to have a large | gap (2" tube in 2-1/2"x.187 wall) or buy the special telescoping tube | (Telespar??) that is produced to work properly in your application. | | When you buy tube in mill quantities (20,000 pounds and up) you can | usually specify better control of the squareness, weld flash, and corner | radius. When you buy from the distributor, you get what you get. | | Your first post mentioned that these were short pieces. How about a | hardened steel block with the proper edges and corners, use the press to | just push it though? That will fix the corners, iron down the flash, etc.
I figured as much, so the idea of a "shaping broach" is starting to look attractive. I think I can make it from the two inch tubing and weld some fillers in a few places to make it stiff, with maybe some carefully placed welds on the outside. Put it on some 1 1/2" tubing and weld it in place. Using the right size piece as a driver and wail away. In order to make this work, I have to go do this funky thing here. In order to do that, I need to repair that tool and adjust it. To use that tool, I need to go get some of this nasty stuff. In order to get some of that stuff, I need to have some widgets. To get widgets I have to filangle a bit on the borders of the doodlewhopper. Fresh out of filanglers, though, and the store that had some just sold out to Lowe's and doesn't carry that anymore. I can make do with some gadget wanders, but the edges are all rusty and need to get replaced. Lessee what ebay has. Oh, crap, I forgot my user ID and password! After I get my user ID and password I will need my credit card for Paypal, but I left it in my favorite pair of pants, which is at the home of the girlfriend I just broke up with. In order to get the pants, I need to make up with her. In order to make up with her, I need some roses, and the nearest store that's open on a Saturday night is six miles away and I've got a slow leak in the truck tire. In order to take the truck I have to air up the tire. This could take awhile, because the compressor's all out of air. Now you can see why I gotta air up the tire on the truck before I can build the shaping broach! :)
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Time to kick back, pull up a chair, grab some rays, say nice things to the female set on Mother's Day, and the project will look easier on Monday. :)
carl mciver wrote:

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Sometimes the solution on a four inch piece is to weld up a piece out of four pieces of flat bar. I have made up sleeve units by clamping four pieces of flat bar on the outside or the smaller tubing and sandwiching strips of carboard between. Tack weld the pieces together then drive it off. Even the strips of cardboard can be a problem until you drive the sleeve off and remove the strips. Randy

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My low tech approach would be to put one of the less than 90 degree corners against the concrete floor and hit the other with a dead blow mallet. Maybe after your shoulder is better.
Dan
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