INT/ISO30 collets

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wally318
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Location: Kelowna, British Columbia

INT/ISO30 collets

Post by wally318 » Sun Dec 31, 2017 2:56 pm

In my rebuilding my Rockwell vert./Horz. mill and deciding on
tooling needed, I have often wondered whether there was such
an animal as 30 taper collet. Like in the pic.
I'm thinking they would come in very handy for using with
reduced shank drills in the Horizontal mode. Rather than giving up room
by putting a collet chuck in between.
Anyone ever see any of these or know where to get them?
The only ones I could find online are Asian made, but in metric and
not imperial sizes.
Attachments
collets.jpg

wally318
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Joined: Sun Jun 05, 2011 1:06 am
Location: Kelowna, British Columbia

Re: INT/ISO30 collets

Post by wally318 » Sun Feb 18, 2018 4:02 pm

Well. no-one is going to add to this post.
So I'll add some myself.
After some time passed I decided to take the plunge
and buy some of the Asian made ones.
I've included a pic below. After discussing it with some
work mates I decided rather than boring/grinding to
imperial sizes. I would order them oversized and make
sleeves to adapt to 1/4" 3/8" 1/2 " etc.
They look decently well made, require a 12mm drawbar.
Although not very hard.
Attachments
P1040024.JPG

earlgo
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Re: INT/ISO30 collets

Post by earlgo » Mon Feb 19, 2018 10:15 am

Does your Rockwell mill have a #30NMTB socket? I am assuming it does because of the #30 taper collets. Your solution may be ok for light cuts, but there is no way you have shown that secures the cutters from rotating under large cutting forces. If you have a #30NMTB socket the I'd suggest using end mill holders with set screws. SHAR and others make relatively inexpensive ones.

A friend once worked for a well known end mill manufacturing company and his job in the test lab was to push end mills to their breaking point. He said he always used an end mill holder with screws, and tightened the screws up as tight as he could get them. Of course he was supplied with precision tool holders so they would not affect the outcomes.
This is just a point of information and my opinion.

--earlgo
Deja Poo - The feeling you have seen all this crap before.

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wlw-19958
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Re: INT/ISO30 collets

Post by wlw-19958 » Mon Feb 19, 2018 11:13 am

Hi There,

I have a Rockwell horizontal mill and the
spindle is indeed No: 30NMTB.

Good Luck!
-Blue Chips-
Webb

wally318
Posts: 87
Joined: Sun Jun 05, 2011 1:06 am
Location: Kelowna, British Columbia

Re: INT/ISO30 collets

Post by wally318 » Tue Feb 20, 2018 2:36 am

Your point is well taken and understood.
Something I already considered before the purchase.
They are not meant to replace a collet chuck, just for unusual situations
that may arise.
I have read that some Rockwell verticals do not have the pin inside the
R8 spindle. I did not read of any ill effects, although I could see that happening
if you pushed and endmill or cutter too hard.

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wlw-19958
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Re: INT/ISO30 collets

Post by wlw-19958 » Tue Feb 20, 2018 11:02 am

Hi There,

I don't think the Rockwell vertical mills came
with a anti-rotation pin in the spindles. I have
added it to one at the shop I worked in long ago.

Good Luck!
-Blue Chips-
Webb

earlgo
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Re: INT/ISO30 collets

Post by earlgo » Tue Feb 20, 2018 2:15 pm

My buddy's Rockwell vertical mill has an R-8 spindle and the key is worn so badly that one needs to be really careful to get the collet aligned properly. If it is just close it dings the edge of the keyway and, of course, doesn't run true.
--earlgo
Deja Poo - The feeling you have seen all this crap before.

pete
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Re: INT/ISO30 collets

Post by pete » Mon Feb 26, 2018 4:03 am

It's my understanding the pin in the R8 taper was never intended as an anti rotation pin under cutting conditions Earl. It's there simply to prevent the tool from rotating until the taper starts to seat and then frictional forces keep it from further rotating as the drawbar gets fully tightened. A whole lot of highly experienced people over on the Practical Machinist forums all advocate removing that pin before not if a tool rotates while cutting and shears that pin off. When that happens it can sometimes do a real job of tearing up the spindle and wedging between the spindle internals and the tool making it very tough to even get the tooling out. I had a conversation with Forrest Addy about it via PMs awhile ago and he strongly advises removing it for the above reasons. R8 collets can still be tightened normaly with the drawbar with no problems after removing the pin. If you look at the cross section of that set screw / pin it would take very little force to shear it off. It's never going to resist even a mild crash so it was never designed for that purpose. Personaly I think it's still added to every mill with an R8 more because of tradition and some would complain it's needed because all the R8 shanks have that pin groove in them. I would love to hear Bridgeports logic about why it's still used even when it can cause some major headaches.

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BadDog
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Re: INT/ISO30 collets

Post by BadDog » Mon Feb 26, 2018 7:09 pm

My "pin" (screw) has been out for some years now. I removed it based on that same advice from Forest and others. Works just fine, and no worries. Also makes it easier if you need to make your own R8 arbor for something, though I've not had that need.
Russ
Master Floor Sweeper

earlgo
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Re: INT/ISO30 collets

Post by earlgo » Wed Feb 28, 2018 2:47 pm

Since there has been a small discussion about how effective the key is in a R-8 socket, it might be interesting to do some numbers.
The R-8 collet keyway is 5/32” wide, at worst case, if we assume the key is a pin .156in in diameter then the cross-section area is (3.14/4) * (.156^2) or 0.0191 in^2.
If the pin is made from mild steel, say 1018 annealed, then the yield strength is 53700 psi. The shear strength is typically .6 times the yield or in this case 32000 psi.
Stress on a part is equal to the load divided by the area or S=P/A. Conversely P = S*A Therefore if the stress is 32000 and the CSArea is .019 then the allowable shear load is 32000*.019 or 608#
The keyway in an R-8 collet is cut in the shank which is 0.949 inches in diameter and the radius at this section is 0.474.
Torque is calculated as Load * Lever arm. The Load for the pin to fail is 608# and the Lever arm is 0.474 in so the Torque T= 608# * .474in or 288 in-lb or 24 ft-lb.
If the pin is a hardened dowel pin then the shear strength is 130000 psi and since stress is proportional to strain we can merely ratio the above calculation to find the torque to shear the dowel pin.
130000/32000 = 4.06 so the torque on the R-8 keyway necessary to shear the dowel pin would be 4.06 * 24 or approximately 100 ft-lb.
Either the 24 ft-lb or 100 ft-lb is in addition to whatever torque is required to spin the R-8 collet in the socket. I do not know how to calculate this value as it depends on fit, finish, drawbar force, lubrication, etc.
Just some fun numbers to think about.
--earlgo
Deja Poo - The feeling you have seen all this crap before.

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BadDog
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Re: INT/ISO30 collets

Post by BadDog » Wed Feb 28, 2018 7:43 pm

I'm not sure it's a shear issue. In fact, I doubt one has ever truly sheared just from seat of the pants expectations of a such a screw in shear as you described. But I wouldn't be surprised to see a set screw (not a hardened pin) show associated damage.

As I think I understand it, the issue is that when the collet is not sufficiently secure such that the taper won't hold, the collet becomes scrifical as the dog pointed (not correct term) set screw digs in to varying degrees. And the screw tip is far from a great fit in the keyway either. So perhaps with a larger bore collet holding something with a lot of reaction torque, maybe a fly cutter or large face mill, and the shaft of the tool has a better grip on the collet bore than the collet has in the spindle taper. I know that this happens because I've got some collets (5C) with keyways clearly damaged in this way. Although they clearly got them out afterward, those with experience describe many events where the damaged collet was near impossible to get out. So I remain happy without the screw in place.

Reminds me of the conversation about tangs on taper drills being used to hold against rotation...
Russ
Master Floor Sweeper

earlgo
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Re: INT/ISO30 collets

Post by earlgo » Thu Mar 01, 2018 9:58 am

pete wrote:
Mon Feb 26, 2018 4:03 am
It's my understanding the pin in the R8 taper was never intended as an anti rotation pin under cutting conditions Earl. It's there simply to prevent the tool from rotating until the taper starts to seat and then frictional forces keep it from further rotating as the drawbar gets fully tightened.
Pete: I like this explanation the best of all. Thanks.
--earlgo
Deja Poo - The feeling you have seen all this crap before.

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