Dovetail cutter???

[Olle]

Originally Posted by sheepherder

And a stock Luger front sight blade has the same angle???

Argh...I can't find $%^& around here!!!

Ah! I found it! What kind of RPM did you use for the dovetail cutter, after making the base cut???

I tried a sight blade in it, and even if I didn't tap it in all the way it seemed to fit very well. This is a carbide cutter, so I cranked it up all the way (2500 rpm) and ran it dry. The only precautions I took was to set the cutter as deep in the collet as I could to reduce vibrations, and I also brushed out the chips after each cut. It wasn't even remotely as scary as I thought it would be, no vibrations, no funny noises, no nothing. Just go for it!

[sheepherder]

Originally Posted by Olle

I tried a sight blade in it, and even if I didn't tap it in all the way it seemed to fit very well. This is a carbide cutter, so I cranked it up all the way (2500 rpm) and ran it dry. The only precautions I took was to set the cutter as deep in the collet as I could to reduce vibrations, and I also brushed out the chips after each cut. It wasn't even remotely as scary as I thought it would be, no vibrations, no funny noises, no nothing. Just go for it!

I did as you suggested; ran a 1/8" end mill down to sight base depth, then cut with Harvey dovetail cutter. Low cutting speed; extremely low [hand] feed.

I had no problems with the cut; my problem was with my depth measurement. I used two different calipers, one Starrett dial and one digital, and could not get the same measurement twice. The two also differed as much as 10 thousandths on a single depth measurement.

This applied to the sight blade itself as well as the cut.

I'll have to re-think how I want to do this in the future. I've tried a magnetic base dial indicator reading directly off the spindle and that is not precise enough either (too much play in the 'headstock').

This was matching a Luger sight blade with a 'new' dovetail; I've had no problems cutting dovetails and making my own sight blade for them & pressing the rough blade in and then finish machining it in place.

[Olle]

I didn't have any problems with the depth. I just indexed the end mill on top of the sight base, then I indexed the dovetail cutter on the bottom of the first cut. I hit it within 1/1000". Why are you using the spindle as a reference?

[sheepherder]

Originally Posted by Olle

Why are you using the spindle as a reference?

It's the part of the mill that moves up & down.

What do you use???

[Olle]

Originally Posted by sheepherder

It's the part of the mill that moves up & down.

What do you use???

Ah, I usually call that the "head", and the "spindle" is on the lathe. I thouht you were trying to make every cut with the centerline of the barrel as a direct reference. I assume that you have a dial and fine feed on the Z-axis, so why do the cuts end up wrong?

My procedure for this (as well as plunge cuts, grooves etc) is to move down until the end mill touches the work, zero the DRO and then start cutting. The fine feed on mine is like a Glock trigger, very gritty, uneven and can jump too far if you're not careful. The DRO helps a lot, as I can see the actual position without having to rely on the dial.

Working on these mini-machines can sure be aggravating, once you learn their shortcomings you have to come up with a lot of workarounds to get the accuracy you need. It would be nice to have those zero back lash ball screws, that should eliminate quite a bit of error.

[sheepherder]

Originally Posted by Olle

Ah, I usually call that the "head", and the "spindle" is on the lathe.

I should have said "quill".

Everything on this mill/lathe is crudely [Chinese] machined. One graduation of the 'quill' handwheel dial should be .040" according to the chart. But my dial indicator says .037".

But it's not the mill/quill I'm talking about. It's the dial calipers. The digital calipers is consistently .010" off in measurements under .100", compared to the mechanical calipers . Zeroing doesn't help. And I can't get consistent readings with the mechanical dial calipers. Starrett calipers.

Can't pin down the problem. The dial indicator method works pretty well for measuring the depth of cut, but trying to get a consistent measurement of say a front sight base is fairly unlikely.

[Olle]

Have you tried the Starrett with a standard, for example feeler gages? I have a Mitutoyo, and I try it with a known dimension now and then just to make sure that it's not out of whack. If it is, I'm sure that Starrett can recalibrate it for you.

I believe the small discrepancy in the dial setting could be due to the feed screw being metric. Seems like some older machines used metric feed screws, and for the US market they simply changed the dials to read the "closest standard equivalent". These are said to be a bit iffy sometimes, so if that's the case you may want to upgrade to true standard screws and dials.