Square Tubing Doesn't Telescope

A

Allan

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I have a project that requires a 4" tube to telescope over a 3 1/2" tube. I cut a 3/4" slice of the large tube off and filed the weld seam away. But it is still a skootch ( technical term) too small to slide down the 3 1/2" tube. The side walls of the large tube are bent in a bit and interfere. Once the height is set there will be no more adjustments. But I still want a nice slip fit.

Any suggestions for how to make this work? I am thinking full bush league here and using an angle grinder with a sanding disc to grind away the small tube a wee bit, Then use a belt sander to finish the job and smooth out any high and low spots.

I had also considered using one of the broaching methods to broach out the inside of the large tube a bit. The small tube will be about 4 feet long and the large tube about 3 feet.

What have you used to accomplish this? If you have not done this what ideas do you have that are affordable and not overly time consuming? I have several months before the job needs completion- a rarity in my experience. Usually the parts are needed tomorrow.

Cheers.
 
Make a mandrel that just fits in the larger tube then force it through the tube.
That can be done with a threaded rod or a press...
 
Thanks, sdelivery. That might be the gold medal. Its pretty heavy wall but inclined planes on threads have a lot pf power. I guess the mandrel could be just mild steel with a bit of a taper and some lube on it.

C-bag, thanks for that but I had already removed the weld.
 
Can you dimple the length of the side of the inner tube to clear the weld?
 
Two ways to make a long hole wider: electrochemical attack (basically etching), or
with the appropriate licenses, and a few meters of det cord, shock wave impingement...
but that won't necessarily leave the hole square. The upside, is that it'd
take care of the 'bent in a bit' problem, and has the 'not overly time consuming' property.

A gentler approach might be to pack the tube with sand, heat it REAL hot, then hammer the
sand tight and cap it. Apply CO2 to fast-chill the metal.
The temperature coefficient of expansion for steel is ~11E-6, and limestone sand is ~8E-6, only
slightly less, but the steel will chill faster than the stuff packed inside.
 
Why don't you just buy telescoping tube? Way easier.
 
I had the same problem with 3-1/2" and 4" pipe. I turned a swage with a lead section that had a diameter to fit the i.d. of the 4" pipe and a rear section with a diameter to match the o.d. of the 3-1/2" pipe. I used a 20t. hydraulic jack to push the swage through the 4" pipe and got a nice sliding fit. The total length of the swage was around 4" with each section being 2" and a gentle taper for a transition.
 
Can the outer tube have a slot in it? If so, you can mill a long slot down the welded side of the larger tube. You can then slightly pry the slot open a bit more. Not sure what you are working on but that slot could also be used for a bolt or wing-nut etc. to clamp the inside tube from sliding once adjusted.
 
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