Lapping Bushings

[Richard Jones]

What is your method for lapping steel die bushings, i.e., Wilson, to claimed size? I've done a few but am curious to know how others accomplish it. Of course, it would be better if a .225 marked bushing was actually .225, but that may be fuel for another fire.

What are you using for a lap?
Do you use a different size lap than the target measurement?
320 or 400 compound followed by Simichrome?

Thanks.

Rich

 

[spclark]

Sorry for the grumpy post... hadn't yet had my coffee when I read your question.

 

[Richard Jones]

All fair points, but I'd still like to know.

Thanks

 

[spclark]

As with anything mechanical we should start with a discussion of tolerances. Add in production considerations, economics become a factor.

Some brands are closer to being marked as true, Redding's for example generally conceded not to be. I don't have any Wilson's but those I bought from John Whidden (CRT?) measured as true-to-marked as I'm capable of measuring. Had some made by Neal Jones too long ago but I never measured them. Some with a Tubb die seemed to be 'close enough' but again that was ten years back & I don't have them anymore.

Move beyond that to taking on altering dimensions of production bushings, we need to address how to keep things parallel over such a short part length. Were I in a position to require more precision from a purchased part I'd start with asking the producer if they could please take extra care when manufacturing the item I'd be getting so it would meet my needs from the beginning.

"You get what you pay for" holds true here; closer tolerances likely will cost extra. Doing it yourself brings satisfaction, once you figure out how.

 

[Richard Jones]

Ditto on the Whidden/CRT. The .226 bushing I have from him is as close to stated as I can measure it. But, can't get any smaller than that from him.

I really don't understand how someone like Wilson can sell a .225 bushing that measures .2235..........

This http://www.swissettool.com/lapping-an-undersized-escomatic-guide-bushing/ makes sense to me, especially the part about tapering and working from the 'back' of the bushing.

A .224 bullet might make a good lap for this particular bushing, a '225'.

Thanks.

 

[spclark]

Rather than a copper-clad bullet as a lap, perhaps a pin gauge of appropriate size would be a better choice?

Along with a very fine grade of alumina or diamond abrasive compound?

How do reamer makers tool reamer pilots to 0.0001" with any precision?

 

[Toolbreaker]

Rather than a copper-clad bullet as a lap, perhaps a pin gauge of appropriate size would be a better choice?

Along with a very fine grade of alumina or diamond abrasive compound?

How do reamer makers tool reamer pilots to 0.0001" with any precision?

OP, Google "adjustable barrel lap". These aren't the best through-laps in the world to use (actually, they're kind of a pain to use), but they will get the job done with some patience and careful measuring, without breaking the bank.

I don't believe a pin gage would make a very good lap. A lap needs to be a softer material so that the abrasive can embed in it to cut. If the lap is the same hardness or harder than the material to be cut, then the abrasive will roll between the lap and parent material, eventually breaking down and embedding withing the softer of the two.

 

[GrocMax]

I have access to a Sunnen pin hone and both std and diamond stones. Works fine.

Need to smooth out the transitions after honing, otherwise the case necks get scratched up.

 

[Alex Wheeler]

I would not want to lap more than .0005" If its more than than bore it first. I have made laps from brass rod by slitting the end and threading a screw in to the end. The more you turn it in the more it spreads the rod.

 

[jfseaman]

I would not want to lap more than .0005" If its more than than bore it first. I have made laps from brass rod by slitting the end and threading a screw in to the end. The more you turn it in the more it spreads the rod.

How are you boring the bushings or necks of the dies?