Help Please: Top-Slide Angle Setting.

Well, my curiosity got the better of me out in the shed this morning, so I had to set up and check old GHT's mathematics on the relatively little influence of tool or DTI height on a taper.

So I set up an MT2 centre between centres as shown below and using a dial gauge mounted solidly to the topslide by clamp, set the topslide to achieve a 0-0 reading along the MT2 taper, plunger set at centre height.

Then set the plunger 10 thou above centre. Result: Still got a 0-0 reading (on my .001" graduated gauge).

Set the plunger 30 thou above centre. Result: about half a thou of needle movement from one end to the other. Maybe as much as 3/4 of a thou on some passes. But closer to a half, I reckon.

Plunger 1/8" above centre, as in pics below. Result: About 2 or 3 thou of variation, end to end.

Conclusion: Old GHT was right. Unless you are waaay off centre height by say 1/8", it will not make a noticeable difference. Set to centre height by eyeball should be good enough for us bodgers. Also I reckon he was right about the concavity along the way being only one millionth of an inch. Certainly no sign of it by my crude 1 thou measuring device.

One thing I did notice is that the thou or less of necessary clearance on the topslide gibs, amplified by the leverage distance out to the dial gauge point, can give a different reading on the return pass than on the initial pass by a thou or two. So make all measurements starting at the tailstock end and ending at the headstock end, and disregard readings on the return pass so all slack is taken up in the same direction as cutting forces.

I always finish off such tapers with some emery cloth and oil to get a nice smooth finish without tool marks and find it is easy to "adjust" the taper by a thou or a fraction thereof in the process if needed for the very final fit. Usual method is to put felt pen marks along the length of the taper then fit a 2-3MT sleeve over it and rotate it about half a turn and back. The pen marks rub off on the high spots. Works better than gooey bearing blue for this.

Edited By Hopper on 30/05/2023 11:11:33

A while ago, there was a thread about how miunting a tool away from centre height affected the parallelism, or taper.

The conclusion was that over short distances the variation was minimal.

Hopper has conformed this

Thanks

Howard

To get away from this problem I sometimes fit a right angle round bar to the end of dti shaft and then dti above centre height. the bar drops vertically so is always on centre height.

David George's post number 3 has everything needed. I had to use the same method even while having the infinitely superior taper turning attachment on the Smart & Brown model A. Morse tapers require second of arc precision and are all different for some reason.

Edited By old mart on 30/05/2023 16:58:40