Hi, I have built a cargo bike frame from steel tube tig weld and I have issues to insert the seat post in the seat tube. It should be the right diameter, but because it’s a tube with a weld mark all along and because the welding of the top tube, the seat post cannot fit in.
I tried to grind it with the available tools but because the welding marks seems to be harder than the tube, it didn’t do much.
I tried to look around and I think I would need a seat tube reamer similar to this : https://www.vittitrading.com/CYCLUS-TOOLS/CYCLUS-TOOLS-seat-tube-reamer-set-tool-holder-extension-5-reamer-of-your-choice///
But I am not sure it would actually solve my issue in this case. As I understand, I should have :
1) not get tube with welding mark
2) tig weld using heat spreader to minimize the marks
Can anyone with experience in tig welding frame can confirm? Thanks in advance!
by sk8erpro
4 Comments
r/framebuilding might be the place to ask
Use a narrower seat post and use a [shim](https://www.planetx.co.uk/products/jobsworth-alloy-seatpost-shim) like this you should be able to put the open side around the weld.
All frames should be reamed after welding, welding causes distortion.
Most quality frames are made with seamless drawn tubing, as opposed to ERW(rolled and welded) tubing like you have. Regardless, all seat tubes should be reamed after welding due to heat deformation.
You need to have your tube reamed to a proper diameter to accept a seat post or shim, but first you will need to grind or file down that weld. A reamer is only intended to remove a small amount of material to achieve uniform roundness, and big burrs/welds like that will stall or break a reamer. Half round file in the rough diameter of your tube will work, but still be tedious.