Enlarging Involute Cutter IDs

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gwrdriver
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Enlarging Involute Cutter IDs

Post by gwrdriver » Tue Sep 20, 2022 11:14 am

I have acquired a couple of 22mm ID involute gear cutters which I need to use on a 1"diam horizontal arbor. I've checked into all the hardware options I can find which might solve the problem and give me a 22mm arbor for my mill (R8), but nothing will fill the bill. An R8 vertical stub arbor (the mill is H-V) won't quite do the job.
So my question is, if I was to go in that direction, what would you do to enlarge the IDs of the cutters IDs to 1"? I have an option in mind, and cost is always a factor, but I'm interested in hearing any suggestions and options you might have. (Unfortunately I don't have ID grinding capability.)
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RSG
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Re: Enlarging Involute Cutter IDs

Post by RSG » Tue Sep 20, 2022 2:23 pm

Doubt you'll be able to bore them since they will have been hardened. Easiest fix is to machine an arbor with a straight shank to accommodate your mill.
Vision is not seeing things as they are, but as they will be.

Harold_V
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Re: Enlarging Involute Cutter IDs

Post by Harold_V » Tue Sep 20, 2022 5:00 pm

Without grinding capability, your chance of success borders on zero. You can expect those cutters to be at least 62Rc. That degree of hardness does not lend itself to machining, especially if there's a keyway involved.

RSG's suggestion is right on the mark. It's not all that hard to make an arbor that will serve the purpose. Light cuts (in use) may even eliminate the need for a keyway, which will prove to be troublesome due to stresses in the material (it won't stay straight). It can even be a straight shank that fits your largest collet (7/8" collets are available). If you expect its use to be only once, even mild steel will serve the purpose. If you expect repeated use, choosing a little tougher material to prolong its useful life (chrome moly or Stressproof) might be a better choice. 4140 HT might be a good choice, as it's pre-hardened, yet machinable. Stressproof machines a little nicer. Both are acceptable.

As an option, it's not beyond reason to mount a small grinder in the toolpost of your lathe and grind them to size. I'd make that my last choice, though. The mess involved makes it a bad choice, exacerbated by not having coolant to prevent heating the cutter.
H
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Bill Shields
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Re: Enlarging Involute Cutter IDs

Post by Bill Shields » Tue Sep 20, 2022 6:02 pm

time to go metric anyway.... :mrgreen:
Too many things going on to bother listing them.

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gwrdriver
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Re: Enlarging Involute Cutter IDs

Post by gwrdriver » Wed Sep 21, 2022 10:09 am

Easiest fix is to machine an arbor with a straight shank to accommodate your mill.
And I agree, but one never knows what clever ideas are out there, if you ask.
Many thanks for the sensible opinions and suggestions. A substitute arbor is the most doable option, considering I no longer have a grind shop in the garage. Any attempt to do a makeshift internal grind, no matter how well protected, would I fear result in an awful mess.

An alternative would be to go to the next smaller DP (18), and those cutters fit my arbor, but this is for a model where appearance and proportion are more important than mechanical strength.and the 16Dp is the perfect tooth size for the job.
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choprboy
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Re: Enlarging Involute Cutter IDs

Post by choprboy » Wed Sep 21, 2022 10:10 pm

As I understand it from your original question, you don't want to use a standard R8 blank arbor or stub arbor and turn the blank/stub down to size because it is too short to use in the horizontal position and have support on both ends, correct?

If so, could you turn a long arbor rod with the correct outer support and cutter diameters and then either press it into a drilled/reamed hole in a R8 blank arbor or hold the inner end of the arbor in a R8 collet?

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gwrdriver
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Re: Enlarging Involute Cutter IDs

Post by gwrdriver » Thu Sep 22, 2022 9:35 am

Yes, that's very nearly how I would do it.
In order to minimize the length of the arbor, increase its stiffness, and simplify construction, I'll be looking at turning a plug for the overarm outboard carrier, reamed 2 or 3MT, for a live center.

However, because my right hand is currently in a cast, which has ended workshop activity (but not thinking) for a while, it may be that a stub arbor in the vertical axis would work dimensionally. The problem would be the minimum spindle speed which IMHO is too high.
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arborist
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Re: Enlarging Involute Cutter IDs

Post by arborist » Wed Sep 28, 2022 1:46 pm

Similar to above, a good starting point for an arbor of any size, imperial or metric, is an ER32 or ER40 collet chuck and a piece of ground bar (drill rod, silver steel, hydraulic ram chromed rod) of the appropriate diameter and length. You can make it any length you like and the end detail to anything suitable.

3D printed bushes can be used so you can reuse many of the arbor spacers off an existing, bigger one. The collet and nut give a good, flat surface for the spacer to bear on.

The biggest challenge is the securing nut but if you can make a standard RH thread one work, the flange nut off a mill clamping set can be a good starting point.

wally318
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Re: Enlarging Involute Cutter IDs

Post by wally318 » Thu Sep 29, 2022 2:58 pm

My suggestion Is buy a R8-JT4 drill chuck arbor.
It will be hardened to some extent.
You can buy one fairly inexpensive @ Toolots,
a lot less than the shipping cost of a 22mm stub
\arbor from europe.
Dial in very carefully. Turn down the taper to 22mm
or fit to cutter. Now you have a 22mm stub arbor.
Set up and thread the end for a 22mm or 3/4" thread.
Can be either LH or RH thread.\
Mill shaft for a short woodruff key in the area you will place
the cutter on the stub.
I would recommend carbide tooling for this though.
It will be RC 40-50 hardness.

wally318
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Re: Enlarging Involute Cutter IDs

Post by wally318 » Thu Sep 29, 2022 3:15 pm

Sorry. I re-read the OP and didn't see it was being used in the Horizontal mode.
So nix my first idea.
If you're committed to using the 22mm ID cutters
the I would suggest taking a 7/8" horizontal arbor
and turning down a short section at the outboard end
to 22mm or .866 on 8 or 9 thou.
You won't have to touch the thread, mine measures
.864" or the keyway. If need be you can just file
a few thou off the top of a short section of key.
And stage your table/dividing head to work under that outboard section.

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SteveM
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Re: Enlarging Involute Cutter IDs

Post by SteveM » Thu Sep 29, 2022 4:00 pm

Harold_V wrote:
Tue Sep 20, 2022 5:00 pm
... keyway, which will prove to be troublesome due to stresses in the material (it won't stay straight).
Would milling an identical keyway on the other side for symmetry solve that problem?

Steve

Harold_V
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Re: Enlarging Involute Cutter IDs

Post by Harold_V » Thu Sep 29, 2022 4:26 pm

SteveM wrote:
Thu Sep 29, 2022 4:00 pm
Harold_V wrote:
Tue Sep 20, 2022 5:00 pm
... keyway, which will prove to be troublesome due to stresses in the material (it won't stay straight).
Would milling an identical keyway on the other side for symmetry solve that problem?
It certainly offers an opportunity to balance the internal stresses.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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