Right. As the glue is still curing on the sump, I figured I'd work on something else tonight. And what better than this damn spindle sleeve, which is what drove me nuts a couple of months ago... It was all still sitting there in the lathe, so I figured what the heck, let's crack on.
As per my last couple of posts, I've been making a "female" version of the spindle taper; the idea is, I can trial-fit the original spindle sleeve until it fits; then when I cut the steel piece, I can use the aluminium version to check the fit of that. However, having had a few months off, and having had no luck getting the taper to fit right, I decided to go back to step 1. That's where today's little adventure starts...
The first job was to re-measure that taper. I had a bit of a brainwave
(at least,
-I- think it's a brainwave). Wheras before I'd used calipers & measured in 2 places, this time I used the mill. Should be much more accurate. Here's the setup:
The original taper is clamped lightly to the mill bed. The dial indicator is setup to deflect as it bumps into the side of the taper. I used the "Y" axis to get it bang on the centre line (i.e. the point where deflection was at its maximum - see 2nd pic above). Having established this, I then backed away, and came back in, zeroing the dial. Once the dial read zero, reset the X-axis DRO to zero, and back away in the X axis.
Now raise the table by 1" (effectively lowering the DTI by 1"); and finally move the X axis back in to the taper. When zero is indicated, the taper-per-inch can be read directly off the DRO. It was 0.025":
Just for good measure, I repeated at 2" and 2.4" (that being almost the entire taper length), getting readings of 0.0495" and 0.0585" respectively.
Next, a bit of
triggery-pokery (you know, I've not used this much maths since I was in school....), gave me an angle of approximately 1.4
oJust before I go any further, I'd like to point out something that you, dear reader, as well as I both missed: Back in my very first post, I measured the taper-per-foot at 0.605". In fact, as you've probably guessed by the description above, I actually measured the taper-per-inch (reading 50.4thou - not bad for hand-held calipers).
What I failed to do was divide the result by two!
The actual Taper is 0.300"/ft - my machinery's handbook is not handy right now, so I don't know if that's a standard taper or not.
Anyway, back at t'lathe, I reset the cross-slide to 1.4
o as near as I could eyeball it, and re-cut the taper at the new angle. Then, the moment of truth: I blued up the original spindle adapter, and gently whacked it into the aluminium piece:
And there it is! It fits! It doesn't wobble about like a wobbly thing! It was actually quite an effort to get it back out again, it stuck that well, and here's where the blue has gone:
Now..... I realise the surface finish in there is a little sub-optimal (let's face it, it's sh*t) - that's because the boring bar chattered like mad. I'm not desperately worried, because the 3 lines of blue show it's basically the correct angle. All I'm interested in is that it grips top & bottom of the taper; I don't care about the middle (well, not much anyway). I've not taken it off the lathe yet, though; can anyone give me any hints on how to reduce chatter in the boring bar? If so, I will have a couple more goes at getting a better finish.
I was cutting at 430rpm, using an HSS tool, which seems quite chunky; but it vibrated like mad. It sang even more at 630rpm (the maximum my lathe will do), and about the same at 290. I didn't fancy going lower because I'm sure slower != better in this case. DOC varied, that last cut is about 0.005". But it chattered like mad at any DOC from 0.030" (the deepest I dared take) down to 0.001".
I'll probably be back on the sump tomorrow, but I'm MUCH happier now I know what I did wrong before. And especially now that the taper fits properly.
