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lynnl
12-23-2013, 03:24 PM
I made a male MT 1 taper to fit in a wood lathe tailstock. When I inked it up to test the fit I find it seems to bulge slightly along the middle of its length.

I'm puzzled as to how that could happen. I used a taper attachment, and it would seem that if I had the angle wrong it ought to be rubbing at one end or the other, NOT in the middle.

If the tool were "pushing off" I'd think that would be most pronounced at the big end.

At the start I took great pains to insure the tool bit was at center height, to include a trial facing cut to make sure there was no pip above or below the tool tip. Even so, I can't see where being off on the center height would explain the bulge in the middle.

BTW, the bulge is not visible, nor detectable with a straight edge placed alongside the taper, only by inking and twisting inside the mt 1 bore.

Any thoughts?

(added) Of course the real issue is that it doesn't hold tightly.

Also, I have an MT 1 reamer which I lightly applied to the bore to insure it's clean.

Edwin Dirnbeck
12-23-2013, 04:01 PM
The first thing you vill do is try to find a known good taper and see if it fits . If it does ,then you must shpin the part that you made and lightly slowely stone or polish the high area until it fits.If a known good taper doesnt seat correctly ,you must take the quill out of your tailstock and chuck it up and spin it . You will then make a saw cut on the end of a 8 inch piece of 3/8 wood dowel and shtick a short piece of emery cloth in it and selectively polish the female bore until you get a good ring fit.Then you will clean and oil your machine. lynnl ,excuse my feeble attempt at humor,I was just reiminicing about an old German toolmaker who taught me many many years ago and using his vernacular.This should work . good luck and merry Christmas,Edwin

jlevie
12-23-2013, 04:05 PM
Consider the possibility that your part may be fine and the error is in the lathe spindle.

jep24601
12-23-2013, 04:13 PM
Consider the possibility that your part may be fine and the error is in the lathe spindle.
Yes - a lot of Morse arbors are relieved in the middle. This could result in your spindle not wearing evenly. Nothing to stop your arbor from being relieved in the middle too.

sch
12-23-2013, 05:08 PM
There was an article somewhere, had to be HSM or MEW, maybe 15 yrs ago about cutting tapers, and mention was made that if the tool was slightly above center, a barrel would be cut instead of a cone
and if below center..... ah dunno, memory fails as to whether still a barrel or an hourglass. At any rate anything other than dead center would result in something other than a straight line along the cut,
being off tangent. Amount of barrel would be in thousandths IIRC.

Jaakko Fagerlund
12-23-2013, 06:38 PM
I too suspect uneven wear in the female part due to relieved Morse tapers (which is quite an odd thing to do, considering that Morse tapers hold in place with friction and the relief doesn't actually help in that sense).

lynnl
12-23-2013, 07:41 PM
I'm sorry, I failed to mention that I have two other MT #1 male tapers, including the original that accompanied this tailstock (it's a Rockwell Beaver lathe), another is a mount/arbor for a Millers Falls 3/8 drill chuck that came with the lathe when I bought it (used). Both of those are nice fits in this bore. ...neither are relieved in the middle.

I tried laying the "troublesome" taper on an old cast iron surface plate I have, to see if I could detect any rocking (end to end); I could detect no rocking, it seemed to lay nice and flat. So any error is probably on the order of tenths, or maybe microns.

I have done a little polishing/sanding on that middle (bothersome) section; I guess I need to get a little more aggressive.

This brings to mind a question I've occasionally pondered before: Is/are there any particular area(s) of the taper that provide more of the gripping power? i.e. big end? ...little end? ...the two ends?
The presence of those relieved mid sections on some tapers suggest the ends are more important, though maybe that's just for accurate alignment.

sasquatch
12-23-2013, 07:44 PM
Maybe different , but you see M/T drills with turned down center sections. Often the size is stamped in that section. I have a bunch of M/T 1 bits like that.