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.
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.
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?
Any one have a reason as to why this feed and calibration? rgentryatozdotnet
Bob Gentry wrote in news:88ocmap4pjc1sbp1g9h4l1kh8ea9cj0oqv@
4ax.com:
It's a natural consequence of a 16TPI lead.
16 threads per inch = 1/16 inch per thread
1/16" = 0.0625" so my guess is that you actually have an advance of 62 and a half thou per revolution instead of exactly 62.
Does not appear to be. The thread _is_ 16TPI and fits a standard 'v' gage nice and tight except for the points which seem to be just slightly flatter than standard.
As a side note. . The threads appeared to be buttress style. . . . untill I hit them with a toothbrush and cleaned off the oil.
You are correct. Put a 1" dial indicator on it and measured two turns at just a wee bit under 125thou. Guessing on a gage that reads .001 about .1248. Bob rgentryatozdotnet
Then the screw and dial may be a repair, used to avoid buying an Acme tap. I did that on my worn surface grinder with 3/4-10 threaded rod. It isn't difficult to engrave a custom dial with a rotary index, using a spreadsheet to calculate the turns. Were the numbers hand-stamped?
As you've heard it is a 16tpi screw. It is original.
Why didn't use a nice round number? Because they didn't need to. The round numbers are nice on a dial where you expect to pass zero multiple times. This is not how you use the toolslide on a shaper. Ordinarily you rough cut to a scribed line, mike the piece and crank the toolslide the 6 or 8 clicks you need for the finish cut.
The number of times you will go past zero is fairly low (keyways, channels etc) and you usually pass zero only once or twice.
They could have used a 1/4-20 thread like the Atlas, but 3/8-16 was more robust and still readily replaceable in the field.
They could have made their own thread, but that would have been anal retentive.
Sure -- convenient leadscrew pitches make for nice increments on the collars.
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. :-)
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. :-)
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. :-)
Nope -- the V-thread was the standard on the 7" shapers -- AMMCO, and my Rockwell/Delta which was a descendant of it. 3/8-16 screw, and the index marks and numbers appear to be rolled into the dial, not hand stamped.
Greetings DoN, If a person wanted to replace the 3/8-16 vee thread with an Acme thread form a tap is not required. The stub Acme thread form would work fine in this application and the minor diameter of a 3/8-10 stub Acme thread is .315. If a person had the skill to grind a 60 degree thread single point tool and use this tool to make a 3/8-16 nut then this same person would have the skill to grind a stub Acme single point tool and could single point a 3/8-10 stub Acme thread. The tougher part would be single point threading a long lead screw because it would need support while threading. A follow rest works well for this, I know because I have done this type of threading many times. The tough part is adjusting the follow rest as it wears. Lubing steady and follow rests can be problematical. I solved this problem by putting an oiler on my steady and follow rests. I use the old type with a glass reservoir and a sight so the oil flow can be observed. I direct the oil flow with a piece of piano wire that I stuff up inside a small diameter tube that the oil flows from. I pull the wire out so that it just barely clears the work. The drops of oil follow the wire and land directly where I want it to land. Eric
One reason to avoid threads too coarse for a given diameter is that the nut may spin on the leadscrew under pressure, making it difficult to machine parts with any accuracy.
The issue is the coefficient of friction of nut on screw while well oiled, and the angle the screw thread makes with the screw axis. If this angle is too large for the coefficient of friction, the nut will spin relative to the screw, rather than remaining where put.
The problem being that the existing thread in the dovetailed base of the compound is already 16 TPI, and changing to 10 TPI would mean irregular areas where the two threads remove metal from different places, thus weakening the thread overall, and making it wear out faster.
Without pulling the compound apart, I can't state the length of the leadscrew with any certainty, but I doubt that the working part is any longer than 3".
The bearing nut and the crank with dial both thread onto the shaft, so you would also need to replace those parts so you could thread them properly.
At 3" length, and 3/16" diameter you might be able support it with a half point dead center, if you took gentle cuts.
I've done it too. Including the time I made a test cross-feed leadscrew for my Clausing, and when I went to test it with an old nut, I discovered that I forgot to make it left-hand thread as needed. :-) At least this uses right-hand thread on the compound.
That sounds like a nice system. Thats for the description.
Greetings Don, You're welcome. When I put the oilers on the steadys I just drill and tap the steady for the pipe thread size of the oiler. For the steady on my 14 inch lathe I drilled a 1/4 pipe hole into the part of the steady that holds the vertical rest. So the oiler screws into a 90 degree elbow that screws into the steady. I then drilled a 1/8 hole that intersects the 1/4 pipe hole and pressed a 1/8 O.D. stainless tube into the hole and the wire then goes into the tube. This lets me guide the oil drops to exactly where I want them. Eric
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