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View Full Version : Help with Starrett Last Word.



Catshooter
11-29-2012, 08:40 PM
The task: a piece of cast iron with an existing .453 hole about .625 deep that I want to drill a .250 hole a further .700 or so. So I need to center the hole over the axis of my Sherline mill.

The trouble: Using the Last Word in a collet, sometimes I get dead center. Sometimes I off one axis by anywhere from .020 to .040. Both times (when it works, when it doesn't) I swing the LW through 360 degrees and get maybe .001 difference before drilling. Then after I drill, I'm either on or way off. I can see no error in how I'm doing it, but the results tell a different tale.

I'll be danged if I can tell how I'm screwing up. No one has ever shown me how to use a Last Word. Is there some technique or trick that I'm missing?

Thanks.


Cat

Bob Fisher
11-29-2012, 08:56 PM
How accurate do you need to be? I'd consider a shouldered sleeve with a .250 drill bushing in it . Depends on the variation in the existing holes. May or may not work for your application. Bob.

Mike Hunter
11-29-2012, 09:32 PM
may not be the last word, might be the drill. Try with a shorter drill bit like a screw machine drill or even better a center cutting end mill.

J Tiers
11-29-2012, 09:46 PM
Last Word indicators are notorious for being "sticky", and not indicating truly. Even brand new ones have been sticky when I have used them.

But of course a drill may flex and move "off" as well.

I'd BOTH ditch the Last Word, AND use a stub drill, or better, a nice rigid carbide spotting drill. Problem is that they may not reach to the bottom and leave enough for the collet etc to hold.

I don't like the end mill idea unless the mill is absolutely dead tight, without any 'give" in the quill (if it has one). End mills with their largeish diameter are bad at "hooking" and trying to kick the quill off-center.

A drill pretty much IS a center-cutting end mill, only with a pointy end instead of a slightly concave one..... and it does not cut on the side flutes the way an end mill does.

Catshooter
11-30-2012, 12:10 AM
Excellent thoughts gentlemen. Thanks. That opens doors for me.


Cat

Toolguy
11-30-2012, 12:31 AM
A ball end mill will spot a hole a lot better than a square end one. It also works good to start a hole on an angled or rounded surface. The Last Word indicators are pretty fidgety to use. The newer ones like Brown & Sharpe Best Test, Interapid, Fowler Xtest, etc. are much nicer to work with.