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1950's collet question

bll230

Hot Rolled
Joined
Jun 14, 2007
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Las Vegas
I got a manual for a Hamilton hobber, because who doesn't like reading old hobber manuals? It includes a print of the work spindle so the necessary collet holders can be made by the user. Here it is, the collet angle is 9 degrees 32 minutes. That works out to 2.0153 inches per foot total or 1.0076 inch per foot that is the physical setting of a taper attachment.

Can anyone provide a rational for such an odd angle? I am at a loss.

IMG_0934.jpg
 
It is like a morse taper. They shot for a nice number and missed a little bit. rather then toss thousands of existing machines and collets they just accepted the existing standards after measurement equipment became good enough to measure it was not perfect.
They tried for 1 inch per foot and got 1.00 per foot or better. The modern micrometer came out around 1867.
Bil lD.
 
They used a 12" arbor between standard, 60 degree centers. They offset the tailstock center by exactly ONE inch. The arbor had the standard 60 degree holes to fit those 60 degree centers.

BUT the one inch offset did not allow the centers to seat properly in the holes and the effective distance was NOT 12 inches. It was less. So the taper is greater than 1" in 12".

I have always wondered about the use of offset centers for turning a taper. It can't work right. It just can't.

Alternate theory: they used a taper attachment with a stamped scale for the taper. The markings are probably 0.005" or more wide. And they were probably an equal amount off their proper locations. So an error between 0.005" and 0.010" is what you would expect.

Either way, they probably made a million of them on the same machine with the same set-up so they were all the same. And they made the reamers for the tapered holes on that machine too. By then, it was too late to change it. So then they had to copy the error in that original set up.

When I read some of the short cuts that many machinists on THIS board think are good enough, I cringe. These things still go on today.

PS: They had micrometers in 1950. Good ones too. I have one from that time frame and it checks out to +/- 0.0002" or better over it's full range. My worst complaint about it is the anvils are not completely flat: I can see a 0.0001" difference from one side to the other. It is not my best mike, but I do use it.
 
If I recall correctly, Brown and Sharpe taper is the only Self holding taper that in any way uses round numbers and it's no longer in use.

Blame it on the engineers and move on.
 
What makes you think the collet. was standardized in 1950 and not 1850? I found no reference to a Hamilton collet standard dimensions.
Bill D.

My Drill press was made around 1952 but the mt3 quill taper was standardized around 1864. Drills and arbors made today still follow the slightly off taper from 1864. 0.60235" per foot is what it is supposed to be, 5/8' per foot or 0.625. If you are in china and make it 0.625 like it should be all you will make is garbage since it will not engage existing tooling.
 
Thanks for checking, On my calculator the tan(9degrees 32'=9.533 degrees)*12 = 2.0153.

For arctan(2*1.000638/12) I get 9.4653 = 9 degrees 27.9'

Can you check again?

Even before I saw Australia I knew you from the UK. When I went to 5th grade in Oxford they called it "Maths." The other kids thought I was funny because I said "Math."
 
QT: [Can anyone provide a rational for such an odd angle? I am at a loss.]
It is hard to rationalize machine tapers when one looks at Morse and Brown and Sharpe with many only a few thousandth or tenths difference in TPI or TPF, when many or most could have been the same taper like Jarno did. Even Jacobe has some only a few thousandths difference.

Dimensions of Standard Tapers - VintageMachinery.org Knowledge Base (Wiki)
 
Even before I saw Australia I knew you from the UK. When I went to 5th grade in Oxford they called it "Maths." The other kids thought I was funny because I said "Math."

They've had a rapacious Feudal system and lying pols longer is all.

Wait 'til we elect a Sandalista as Prez, and we'll have a dozen flavours of "maths", plural, to empty one pocket or pay envelope into another "hole" as well. "Free" anything means free of ass and related ass-ettes, no more "money worries" 'coz you won't HAVE any. Money, nor ass, either one. Just worries. Humankind is meant to keep doing this shit until they get it all, right?

:(

Tapers: Oscar "jarno" Beale was B&S head guru when he invented jarno. Note from MT, B&S, Jacobs that it only NEEDS a very slight change in angle to get easy-release MT - good for drills - walk-out resistant B&S - good for mills - or damned-near WELDED-on Jacobs tapers.

Also note they all have CHANGES within their size ranges off the back of pragmatic experience and minor optimizations.

Beale tried to eliminate those with a mathematically regular plan. ANY size of jarno - even in-between or imaginary ones - has the same angle and has its size specs embedded right in its nomenclature.

As with the Metric system vs "US" fasteners, it looked right sweet as a "standard" ...on paper. But...didn't work as well in practice as all those irregular ones, each OPTIMIZED to do the job best in their size.

Run into any GENUINE oddball taper? Don't bitch. Just prepare to duplicate it, and be glad that isn't all that difficult to do that.

Probability is VERY high it was the result of testing to get best results for the mating alloys, hardness, wall thicknesses, balance of working stresses, hold & release, etc. - to serve its given application as well as it could BE served.

I did say "optimize"?
 
I have always wondered about the use of offset centers for turning a taper. It can't work right. It just can't.
It works better if your TS end can be "aimed" along the axis, not held parallel to it. Which isn't actually hard, especially if the job is to do "many", not just the odd one-off.

And why d'you think "bell" mouth curved side center drills and ball-end centres or cup centres with "the old bearing-ball trick" came to exist?

Not "perfect". Yah still have to compensate. Just less IMperfect as wear during the cut accrues.
 
Red, Lex, thanks for pursuing this and straightening me out. I was conflating the included taper, which is the taper attachment tickmark setting, with the triangle math of one side, which is the dial indicator setting of the taper.

You are absolutely right, I had the wrong result. Now taking your result and extending it, if I work backwards at 1 inch per foot, then the arctan of 1/12 gives 9.5273 degrees included angle which is then 9 degrees 31.637 minutes, or rounded to 9 degrees 32 minutes. Now we are back to EPA's comment, they used a inch offset in some fashion to get their taper.

I doubt I'll ever have need to make that taper, but I am thinking about a B&S 9 part I need to make, and this thread will help me stay straight on any taper attachment setting.

John
 
Any time you can't figure out the answer to a problem, you have left out the dollar sign. That being said, many oddball designs such as tapers are different so as to avoid copyright or patent litigation.

JH
 








 
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