On 2015-05-27, Bob Gentry wrote:
The AAMCO 7" shaper has a 'feature' I don't understand. Maybe one (or
more) of you guys has an answer.
All the machine tool feed collars I have used (not really all that
many) have been graduated in some even numbered manner. Fifty marks,
sixty marks, two hundred, etc.
Sure -- convenient leadscrew pitches make for nice increments
on the collars.
The graduated collar on the tool slide of this unit is different.
There is the usual '0' then the fifth mark is '5', then '10', etc.
This goes to the '60' mark.
Then there is one tick mark (two spaces) and then the orig. '0'
This actually _does_ result in a measured 62thou. advance per rev.
The same as my Rockwell/Delta 7" shaper (a descendant of the
AAMCO).
What this means is that they cheaped out and used some 16 TPI
shaft (not even an Acme thread, but a more common V-thread) as the feed
screw here. I've been tempted to try making something more reasonable.
But a 10 TPI would be way too coarse for that small a diameter. (Wrong,
after looking and measuring it, it is 3/8" diameter, not the smaller
diameter that I though that I remembered). 20 TPI could get you 0.050"
per revolution, but if you make it Acme, it results in problems finding
a tap to cut that. You would have to make some more Acme threaded stock
using drill rod, cut flutes, and harden it properly to have a chance at
tapping the nut. So -- I haven't yet been motivated to do this. :-)
Nothing major, but I sure do have to keep it in mind when feeding more
than one turn.
Anyone ever seen something like this elsewhere?
Yep. Emco F2 desktop milling machine, with metric leadscrews,
but inch graduations on the dials. 0.126" per revolution works out to
3.2004 mm/revolution, so it must have really been 3.2 mm/rev.
Even worse was a Jet 13x40" lathe at work which had a cross-feed
dial of something similar. I forget the details, and can't look it up
now, as I am retired, and the machine has no doubt been surplused long
since. We had to fight to keep the shop while I was there. (Actually an
Army R&D lab, and a lot of the work had to be done in the separate
machine shop elsewhere in the compound. :-)
Any one have a reason as to why this feed and calibration?
Sure -- cheap to make. Standard pitch screw -- just use
3/8-16 allthread, make a threaded collar to go on one side of the
bearing plate, and the crank with the dial on the other side.
O.K. MSC offers 3/8-10 threaded rod and matching nuts. 36"
long, and $52.36 with the nut. You would want to make a new dial,
larger in diameter to make 100 divisions readable. Their #01205863, and
other versions.
Looking at it, the base of the compound would have to be re-made
and tapped Acme 3/8-10, as there is not enough meat to drill it out and
press fit the nut into it, even after turning off the flange. This
means one of the double taps -- front end cuts V threads as a guide, and
the back end finishes to the proper Acme thread form.
O.K. MSC does *not* carry the 3/8-10 tap, so you would have to
make it after all.
Hmm ... they *do* have 1/2-10 Acme taps, so maybe you could go
that way. Since you would have to make the base of the compound anyway,
make it thicker, so you could tap it 1/2-10, and make a new bearing
plate for the mount of the screw to the crank and dial to offset the
center line to match. But the taps are up near $100.00, too. :-)
#04794103
At least the design is for a right-hand thread, the left-hand
taps are even more expensive. :-)
And -- the 1/2-10 rod is less expensive, at least. :-)
Enjoy,
DoN.
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