Die Polishing

[Wolftracker]

I have a Corbin de-rimming die that works OK but is scratching the RF jackets. It appears to need internal polishing and I was wondering if anyone here could tell me what they use for materials, lapping compounds and technique. I don't have much in the way of tools, other than a drill press and hand drills. Thanks!

[trevj]

Check out the Corbin Bro's sites and they have some of their die making info there.

Various grits of diamond lapping compounds are available for not too much money. Be aware that lapping the die will make it larger, though it may not make a significant difference in the size.

Laps can be made of pretty much any metal that is softer than the die. Charge the lap (embed the lapping compound into it), then spin it in the die, while keeping it in alignment and moving back and forth through the die. Repeat as required.

Internal lapping can be so simple, or so frustrating, depending on how it goes, eh. You do need to be able to measure the results somehow, too. If all you care about is smooth, lap it a bit, then clean it and try it again.

Cheers
Trev

[Char-Gar]

I have polished lots of dies and it is very simple and you have everything you need but a few supplies you can buy locally. I use a bore mop wraped with strips of shop paper towels. You want to use enough paper to give a good fit, plus the paper is a mild abrasive itself. I use Mother's Mag Polish which is available at any automotive parts store. Any metal polish including toothpaste can be used in a pinch, but they vary in how abrasive they are.

Drop the drill press speed down to the lowest and put the bore mop in the chuck. Wrap the paper and slather the Mother's on the paper. Turn on the press and run the mop down into the die and leave it there for 10 or 15 second. Up and down a couple of times won't hurt. Now clean the inside of the die with alchohol and you are done. You will be suprised how much polish this will do and it will not change any dimensions.

I polish most of my reloading sizing dies this way. I don't use carbide dies at all. This will remove any roughness in the die that leave scratches on the cases and reduced the amount of force needed to size the case significantly. I would be very reluctant to use any lapping compound as there is a high chance of changing the dimensions of the die.

[MIBULLETS]

I have a Corbin de-rimming die that works OK but is scratching the RF jackets. It appears to need internal polishing and I was wondering if anyone here could tell me what they use for materials, lapping compounds and technique. I don't have much in the way of tools, other than a drill press and hand drills. Thanks!

I had this happen to me too. What I found on mine was that there were some places that had very small amounts of brass sticking to the the tapered part that does the de-rimming. Almost like fouling in a barrel. It was very difficult to see though. I used some copper solvent on it to get the brass off, then just polished it with a cotton type cone and my rotory tool using some Flitz. Works like new now.

If yours is really scratched and it is the older style with the threaded top portion, you can just just order the ring from Corbin. I think he was asking $50 for it when I looked before I fixed mine.

[DukeInFlorida]

If you are impatient, and run DIRTY/GRITTY/DUSTY/SANDY brass through your de-rimming die, you will certainly scratch it. And, it will remain damaged, and continue to scratch the brass you derim.

As with any brass you send through any die: Clean it first!!!! Swaging lube won't save you from a piece of sand.

[Wolftracker]

Thanks for the information fellows. I'll start with the least aggressive and simplest method and work up from there. I do clean my rimfires but this was a used die. Heavily used, I suspect. One of these days, I'll get the tools to make my own.