What material (material for the lap tool itself) can the group
recommend to lap a ~1/4" hole in a piece of brass? I'd like to try and
reduce the amount of embeded abrasive that ends up in the piece itself,
and the only abrasive I have on hand is SiC and AlO.
All comments welcomed.
If you want the abrasive to imbed in the lap then it will have to be
softer than the brass, Possibly copper or alum might serve this
purpose. I havn't done it myself, all of my experience is with flat
castiron lapping plates. Did a lot of seals and such for turbine
engines that had to be flat to 3 heliun light bands, usually using
diamond compound for the final polish. gives a mice mirror finish :-)
ordinary Brasso Polish works perfectly with brass laps.
Brasso is a soft (breaks down quickly) abrasive.
Timesavers abrasives have a soft line as well if you need faster
Wipe/wash/wipe clean when done.
SiC is a bad thing to use on soft metals. Never goes away.
You'll have to probably go to lead for lapping, the lap material has to
be softer than the work piece. Both your abrasives will probably embed
in your workpiece, Brasso might work, tripoli, rouge or rottenstone
might be other choices. Test pieces would definitely be in order.
If you can't buy some Timesaver brand lapping compound and can only
use what you have on hand then a lead lap will work. But it must be a
soft lead compound. Pure lead would be best. You can pour it into a
hole drilled on the center line of two aluminum blocks. This hole
should be smaller than the lapped hole. When cool, roll the lead
cylinder on the abrasive, pushing down hard so that it embeds into the
lead. Next, wash the lead lap with solvent and a brush to remove any
loose abrasive. Drill another hole in the aluminum blocks that is the
same size as the hole to be lapped. Put the lead lap into it and use a
punch to "upset" or expand the lead into the hole. You are now ready
to lap the part. You can upset the lap in the brass too. Just be
careful not to jam the lap. Go slow and you should be OK. Use kerosene
or solvent as a cutting fluid.