Reaming options for a 52mm bearing on a custom moped headtube

General Discussion
1

Hi folks,

The custom moped I’m building needs a 52mm SKF bearing and I’m trying to figure out what my options are for reaming the bearing seats post welding? Ofcourse this is not a bicycle standard so bicycle tools are out. I’m re-using the front suspension from an existing scooter so am stuck with a 28mm steerer tube and the only tapered roller bearing I can get is this one:

So far i’ve tried:

  • Custom reamer. This is a dead end - no one seems to want to do this. If you know of shops please let me know!
  • Sleeve / adaptor cups and use a existing park tool reamer. This is what I’m working on now but its not so simple since I need a inside shoulder for the bearing / sleeves to rest on and then the HT becomes crazy thick.
  • Custom fixture and bore it on a Bridgeport somehow? This seems hard and painful and I want to avoid this at all costs

Is there something else I can try? All ideas welcome.

Pic for attention. Its the head tube in quesiton:

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2

Here is what I would do:

Use (or make, on a lathe) a 58-60mm OD, 55.5mm ID tube,

Ream inside to 55.95mm with this park tool reamer

Then make a custom bearing cup from aluminium for this SKF tapered roller bearing, basically replacing part no. 6 in this picture to provide the shoulder for the bearing

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3

Having done it with a boring head on a Bridgeport, I don’t see what the problem is. Certainly for fastest throughput in production you’d want a rigid setup, but if you’re only making one, you can afford to take light cuts, and the fixturing can be ad hoc, jury-rigged.

Try to have it near-net before welding since obviously it’s easier to do on a tube than on a frame. Leave as little extra metal as possible to let you clean up the weld distortion. A plug in the tube during welding can reduce the distortion, might not even need post-weld machining if the stars align.