Rebushing an out of round barrel bushing

[Jon]

Funnily enough, I made a lesson on this subject for my third year students. As @nickelsilverhas already pointed out, that there is no magical fix just using a reamer in a jewelling tool, especially if you have to use several to open up the hole to the correct diameter for the bush. The hole will wander on a badly ovaled hole, no matter how good you think you are! Btw, what a lovely set-up you've made for your faceplate @nickelsilver.

It's a pity you can't post videos on here, as a couple of slides have them. The slide with the crosshair on the centering microscope picks up the outside of the hole as it is turned whilst centering the work with light taps on the side of the bridge or mainplate. That's the hardest part of the job, really. Once the hole is centred, or what is left of it, the hole is bored open just a tad smaller than the reamer which is 0.01 smaller than the bush you make. You can bore it to 0.01 undersize by measuring the hole with a plug gauge then fit the bush that is 0.01 mm bigger than the bored/reamed hole.

I do like this kind of work, as it's so satisfying when it all comes together

Edited March 20 by Jon

[SwissSeiko]

On 3/19/2025 at 12:35 PM, GuyMontag said:

another, less accurate option would be to try and center it based on the radius of the recess, then install a new bushing, then you can bore that out more accurately by setting the cutter height to the center of the part, and scoring two lines 90 degrees apart in rotation, and the center point it the drilling point.

[Neverenoughwatches]

46 minutes ago, SwissSeiko said:

another, less accurate option would be to try and center it based on the radius of the recess, then install a new bushing, then you can bore that out more accurately by setting the cutter height to the center of the part, and scoring two lines 90 degrees apart in rotation, and the center point it the drilling point.

not sure I'm entirely understanding the plan.  Basically filling the hole as best you can to center with a bush or brass plug then decide on the new bearing position ?

The new position based on dividing circles ?

[SwissSeiko]

2 hours ago, Neverenoughwatches said:

not sure I'm entirely understanding the plan.  Basically filling the hole as best you can to center with a bush or brass plug then decide on the new bearing position ?

The new position based on dividing circles ?

Basically yes. Center it as best as you can, bore out the hole until its concentric, then plug with brass. Then, you should mount the bridge on to the mainplate, and mount the whole mainplate with the bridge facing the headstock. Then center the arbor hole on the mainplate in the headstock, and drill a small hole through the mainplate and into the new bushing. Then reverse the mainplate in the headstock  again, and bore the hole to size. Then its in perfect alignment.