View Full Version : my first 'precision' project

09-03-2004, 08:18 PM
A friend picked up a valve seat insert installing kit which was missing the mandrel that the cutter rides on. In my igonorance i said 'no problem, ill make one real quickly..."

The cutter mandrel is 7" long. 3' at .627 then 3" at .342 then 1" at .313.
I made it out of O1 on my SB 13" lathe

I was able to keep tolerances +/- .00025 (according to my mircometer skills)

I heat treated by heating with a torch to deep cherry red then oil quenched. NExt i polished it with a scotchbrite and heated it to straw color with the torch again. After it started cooling it turned more brownish/purple, I guess i overheated it a little...

WHAT I LEARNED (after 4 prototypes and 2 finished products, one of which is undersize)

1) there is no substitute for a decent micrometer, vernier calipers dont cut it
2) O1 it a lot tougher to work with than mild steel or aluminum
3) precision work is a LOT more time and thought consuming
4) free cuts are really helpful on long/thin work
5) machining the larger diameter first increased its precision due to less flex in the piece
6) carbide cutters are a lot better for roughing. Probably finishing too, if i had a grinder to profile them
7) its a good thing the labor was free!

Did I do OK?

09-03-2004, 08:31 PM
Sounds like a job where a toolpost grinder would have been nice to have. If you keep your ear to the ground, you can probably find one for under $100. If you are as lucky as I was, someone will give you one because they think it's trashed, then $30 worth of bearings and brushes will make it work about like new. The nice thing about the TP grinder is it will machine hardened steel - so if your part warps during the heat treatment, you true it up while grinding to final size.

For your first go with high precision on an old SB, 1 out of three is not bad! I've done worse and I'm sure others have too. Look into the use of progressive grades of lapping compound next time. You can get almost a mirror finish and it goes pretty quick once you work out a process.

Fun stuff, ain't it?

[This message has been edited by vinito (edited 09-03-2004).]

Michael Az
09-03-2004, 08:45 PM
Good job and keep it up.

Paul Gauthier
09-04-2004, 12:59 PM
Only three tries??? you done good. Keep it up.

Paul G.