Standard steel tube sizes vs bearing sizes

I want to make a tool post mounted gringing spindle for my lathe. I have a 6" long ER20 spindle with a 20mm shaft. The obvious bearing options are 7204 (47mm OD) or 7304 (52mm OD). My question is, why do all the standard seemless tubes (for the body) come in sizes that are largely incompatible with the bearing OD?

The standard sizes either have an ID so large it would only leave a 1mm internal shoulder to butt the bearing against (55x45mm tube), or the OD would only allow for a 1.5 or 2mm wall around the outside of the bearing (2" OD tube) Im trying to avoid using solid round bar (say 55mm OD for a 47mm OD bearing) and having to turn most of it into swarf.

When at work I used thick walled steel tubing. We just ordered from local steel suplier and only had to order the correct length for job plus a small amount to clean up.

David

You only need a clearance hole for the shaft so a 22mm hole would be easy enough to drill out from solid and the thicker wall will be better should you need to tap it for any fixings or machine flats for mounting.

If you can get hold of some schedule 160 pipe, nominal 63.5 od, that has a wall thickness of 9.52 so plenty of material to form a shoulder. Try local tube stockists or hydraulic engineering firms for an off cut.

HTH

Dave

Sorry mis-read table. Nom 50.8 bore schedule  160 tube has  60.3 od and a wall of 8.7. This gives a bore of approx 43. Would that suit?

Edited By David Davies 8 on 25/09/2020 08:22:51

Turns out I've assumed the extensive range of sizes offered by M-Machine aren't exhaustive and there is a 2-1/8" x 1/4" wall that would suit. Just need to see if there is some where local I can find that size now.