I've got a 1987 Hafco clone mill that spent the first 21 years of its life in a jobbing machine shop being used almost daily. Its got a few scars as would be expected. Its got an R8 taper.

Even though I have had it since around 2007, I really haven't used it much until the last year or so (and even then not much)

Anyway one day last week I noticed there was visible run out in a cutter I had in my ER40 chuck. At first I thought it would be the cheapish collets I bought last year but decided to run a few checks anyway.

So the next day I set up an indicator and measured almost .003" run out on the periphery of the chuck.
I check a couple of my other arbors and the the run out varied between .002" and .003"
Periphery of the spindle nose was about .0005" so could live with that.

I decided to have a look at the internal taper. Not a pretty sight. Had quite a few bruises etc in it. No scores from an arbor slipping though. Just bruises from arbors not being cleaned properly before fitting I'd guess.

So then I had to figure out how to fix it. Started reading up on grinding it and whilst I have a tool post grinder I didn't want to commit to using that yet.

So eventually I decided to possibly sacrifice an arbor and try lapping the taper first. Dug out my cans of lapping compound (first time in at least 20 years) and got stuck in. Just put the machine in back gear and wound the VFD right back.
Bit of compound on the taper and some Inox on the top end (for lube) and just held the arbor in place with my hand. Did that for about 10 minutes all up (with frequent withdrawal, cleaning and re compounding). It came up pretty well I'm happy to say. Took all the high spots off. Its still got some bruises but can live with that.
On closer inspection of the taper on my ER40 chuck I could see a few marks on it as well so I gave it go in the spindle as well.
Woo hoo. Dialed up and now have less than .001" on the periphery of the chuck and slightly less in three places inside the chuck. All the other arbors are similar.

The lapping compounds I have are Pep brand, Course, Medium, and Fine.
These ones are pretty much the same grade as sold for engine valve lapping. I also have a can of oil mixed very fine which is about twice as fine as Pep fine.
I didn't use the course or medium (funnily enough) but did two goes with the fine, then went over to the very fine for the rest.
I didn't really expect to get as good a result as I did so pretty happy about that.

Sorry no pics.

Peter


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