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rotate
02-21-2008, 01:24 PM
As I was trying to machine MT2 taper yesterday, it occurred to me that if the angle is off by just a small fraction of a degree, the two tapered parts would in theory touch at only one place (i.e. a ring).

This got me thinking that even with two very accurately machined tapered parts, the actual surface area of contact must be relatively small relative to the total surface area of the taper. Is this correct?

2ManyHobbies
02-21-2008, 02:39 PM
In theory, the entire surface of both sides touches. A little blue would tell you how close the taper you cut matches your spindle/tailstock/whatever. You'll probably only get a ring on one end if you cut your taper angle too shallow or too steep.

Obviously be very careful when test-fitting. Make sure everything is clean and smooth, and don't force anything.

If I did my math right, then ~4.4 seconds of arc should be about .001" difference in diameter. Are you cutting with tailstock offset, taper attachment, boring head in the tailstock, or the compound? The compound may be difficult to set to the exact angle you need, but any of the other options should be easy to set and verify with an indicator...

rotate
02-21-2008, 03:39 PM
I was using tailstock offset and had hell of time get it adjusted just right. I was using a dial indicator for the setup but found it very time consuming and frustrating.

I didn't use the boring head offset method because I currently don't have the means to mount the boring head to the tailstock, but I can see that method being a great deal easier.

oldtiffie
02-21-2008, 04:29 PM
I was using tailstock offset and had hell of time get it adjusted just right. I was using a dial indicator for the setup but found it very time consuming and frustrating.

I didn't use the boring head offset method because I currently don't have the means to mount the boring head to the tailstock, but I can see that method being a great deal easier.

Never mind the boring head.

That was a very clever way by John Stevenson to mount a cross slide in the vertical plane and to have a ball fitted into it.

So, is there an alternative?

There is at least one. There are probably others.

Put your tail stock to the rear of the lathe - or remove it.

Mount/fix an angle plate or similar to your lathe bed - and with the front face square to the head-stock spindle (or the front of the lathe bed).

Fit a small lathe top slide - or similar to the front (vertical) face of the angle plate.

Fit/place anything with a ball on the front face into the cross-slide and set it at spindle centre height.

You have now duplicated the set-up and principle of John Stevenson's set-up and are now ready to set/adjust for your taper-turning by using the cross-slide and to get going.

Duplicating John's set-up is not important - but duplicating the under-lying principle is.

John demonstrated a very clever use of using what was available.

GKman
02-21-2008, 04:37 PM
Learned the principle of this from the smart guys here. May have added a twist of my own but probably not. Just grateful to have to pass on.

1. Align the toolholder with the compound and lock for now. 123 block makes a good flat plane to push them into alignment.
http://img.photobucket.com/albums/v494/gkman/P2210051.jpg

2. Align the toolholder with a known sample taper held between centers by rotating the compound and lock. In this case the Jacobs taper on the left end of the Jacobs/Morris spindle. The compound is now set at the correct angle.
http://img.photobucket.com/albums/v494/gkman/P2210052.jpg

3. Replace the sample with your work piece, reset the toolholder as needed and turn (in this case bore) the taper with the compound.
http://img.photobucket.com/albums/v494/gkman/P2210053.jpg

4. Check your work. Sharpie mark pretty much shows smudges from end to end. It didnít the first time and I just made another pass at the same settings leaning on the toolpost a little at one end of the pass. As you have seen, it doesnít take much. Enjoy a beverage of your choice, homebrewed Starbucks for me.
http://img.photobucket.com/albums/v494/gkman/P2210054.jpg

J Tiers
02-21-2008, 07:31 PM
As I was trying to machine MT2 taper yesterday, it occurred to me that if the angle is off by just a small fraction of a degree, the two tapered parts would in theory touch at only one place (i.e. a ring).

This got me thinking that even with two very accurately machined tapered parts, the actual surface area of contact must be relatively small relative to the total surface area of the taper. Is this correct?

Not really......

Just had this a bit ago.... the infamous 2MT blanks from a recent thread..... They were more than the allowable 0.002" per foot "off" on the taper.

In the process, I noted that my Bison rotating center had an essentially perfect taper, blued up all around over full length. The bad blanks touched at a ring at fat end only.

I ground them "in", actually used the TP grinder, (royal pain). I finally got them to touch over most of the taper, but by no means as evenly as the Bison part. The TP grinder isn't provided with as good a set of bearings as Bison's grinder, and the wheel is narrower, and my T/S ram is a bit looseish.

Even so, they touched over nearly the full length, just not at every point.

There is a certain amount of "give" to everything, and very close tapers will conform under pressure. At least they will if so made as to have any 'give". A taper cut in in a large solid block might have less than a "tube" like the ram.