R8 spindle collet drive pin--need advice

Orrin · Oct 12, 2009

The collet drive pin is missing from the R8 spindle of my "new" Sharp mill. It does not appear to be sheared off; it is just plain gone.

Are these pins pressed in? If so, I would appreciate your opinions about the way I'm thinking of replacing it--if it needs replacing.

First off, I don't want to go through the major surgery of removing the spindle. Instead, I'm thinking of making an insertion tool. I'd do this by drilling a blind hole crosswise and partially through and near the end of a long rod or piece of key stock. It would be sized to be a snug, but loose fit for the replacement pin.

With the aid of a mirror I'd use the rod to position and start the drive pin in its hole. Once started, I'd drive a soft wedge into the spindle, along the insertion tool, pressing the pin into place. I'm considering using Loctite to give it a firm grip.

I don't know whether the previous owner purposely removed the pin or spun it out. The 3/4" collet has been ruined by something spinning and galling in it. Maybe the two discrepancies are connected to a common event.

Are any of you operating your mill without a collet drive pin? I'm wondering if the one in this machine was perhaps purposely removed. It has a Kurt power drawbar and it would seem as if some serious buggering could happen if the drawbar sucked the collet in without the pin being aligned with the collet's keyway. If this ever happened, the drive pin would seem to be a nuisance, not an asset.

Regards,

Orrin

Dimitri · Oct 12, 2009

Do you even need the drive key?

The amount of mills I have come across without the drive key seems to be very high. Especially the newer import machines. Perhaps for the torque requirements of the R-8 collet its not really needed? Or atleast I have never had the collet and tool spin on me from over pressure, however I generally do not run a machine too hard.

Dimitri

The real Leigh · Oct 12, 2009

Not needed

This subject has been discussed here innumerable times. Check the archives in the Bridgeport section.

I've run Bridgeports for 45 years and I can't remember a single machine that had the pin in the spindle. On that machine the pin can be replaced without disassembling the spindle.

I'm not familiar with your particular machine.

- Leigh

Glacern · Oct 12, 2009

Hey Orrin,

Removing the pin and leaving it out is common practice with mills similar to your Sharp. The pin consists of two set screws, one to serve as the pin, and one to lock the other in place. In order to access the set screws, one would first remove the lower cap of the quill with a spanner wrench (reverse threaded).

The taper itself should provide sufficient resistance to slipping, making the pin more trouble than it's worth. So once it's out, it usually stays out.

-Sol
Glacern Machine Tools

Carl Darnell · Oct 12, 2009

Don't worry about it, you don't need it.

L Vanice · Oct 12, 2009

Rockwell did not even put a hole for a pin in their R8 spindle. I have had my mill 35 years and never needed the pin. Be sure your drawbar is not tight in your collet threads, though.

Larry

67Cuda · Oct 12, 2009

The only reason you need the pin is to prevent the collet from potentially spinning in the quill and gouging the mating surface. Just a matter of how lucky do you feel. I prefer the pin in. Follow Glacern advice on putting one in.

Tom

Keith Krome · Oct 12, 2009

When I received the Vectrax mill here at work (which I've been very pleased with), the drive pin would interfere with the collet insertion. Either the pin stuck out too much, or the cheap collets didn't have a deep enough groove.

I ended up sticking a boring bar in the vise and reducing the pin's height. Works great now with the collets (proper).

On the other hand, most other mills I've used have the key either missing or sheared off (I doubt someone went to the trouble to actually remove one). The mill works fine without it. If the collets are decent, it shouldn't matter their orientation.

As others have said, make sure your drawbar threads in freely.

cuslog · Oct 12, 2009

Not a professional here but it seems to me that the pin is (was) there for a reason ie; reducing the likelihood of the collet spinning in the taper. 99.9% of the time you don't need it but fot that 1 in a 1000 time when either the endmill spins and galls the collet or the collet spins and galls the taper, you really don't want it to be the collet spinning in the taper.

moonlight machine · Oct 12, 2009

That wimpy ass little pin isn't going to stop any collet from slipping. the only reason it is there is if the threads in the collet are full of chips or whatever and it wants to spin when you tighten the draw bar. Blow the threads out and give it a drop of oil once in a while and it will be fine. The pin has ben out of my Bridgeport since I bought it in 1978.

ZAGNUT · Oct 12, 2009

moonlight machine said:
the only reason it is there is if the threads in the collet are full of chips or whatever and it wants to spin when you tighten the draw bar.

never thought of it but that's the best reason for the pin being there that i've heard so far.

when using a machine with the pin in place i invariably put the collet in 180° off and find myself cussing at inanimate objects. tool changes with a hand held impact wrench are faster on my machine that on my friend's machine with a real power drawbar and the idiot pin in place. if i could find one i would love to slip him an unslotted collet or two and stand back and catch the comedy on video

dave

misterT · Oct 13, 2009

If you do replace the pin make sure to put a collet in the spindle first to make sure it clears the collet. I screw the pin in untill it meets the collet then back it off 1/2 turn. Most of the mills I have worked on have the pin, Ironically the one I have was not designed for a pin.

HelicopterJohn · Oct 13, 2009

Set Screw Locking Package

Bridgeport offers a replacement set screw package. The first one screws into the spindle and has a square end on it approximately .125 deep and the other end has a female socket for you standard allen wrench. The second screw is about .125 thick with a female socket for a standard allen wrench. The hex goes all the way through the thickness of this screw. This one basically locks the first one in place. They are hard to adjust as when you put pressure on the second one it tends to cock the first one slightly increase the drag on collet during the installation and removal process. You just have to play with the installation to get it right.

I have a couple of Bridgeports and one of them had an issue with the locking set screws. As it turns out the internal threads were stripped in the spindle. I drilled and tapped the hole to the next size. I then got a longer socket screw (with a deeper hex) and made a little jig to hold it and then ground a square end on it utilizing my surface grinder.

I then cleaned both the internal threads in the spindle and the modified set screw and applied blue loctite. I fit a collet in the spindle to check for the proper clearance for easy installation and removal. I left the mill sit for 24 hours piror to use. It has worked satisfactorily ever since.

Just some thoughts that may be of help.

John

Orrin · Oct 14, 2009

Thank you, all, for your advice. I now know that pin or no pin, it's nothing to worry about.

When I discovered it was missing it didn't seem worth losing any sleep over it; but, while checking out the Kurt power drawbar the instruction manual warned that the pin must be in place. It was at that point where it seemed prudent to discuss the matter, here.

HelicopterJohn, I'm particularly grateful for your description of the pin and locking screw. Now, I understand.

Best regards,

Orrin

stannp368 · Oct 14, 2009

R-8 spindle collet drive pin

Manufacturers go to the trouble to provide keyways in the collets for a reason. You don't want your end mill jamming & ruining the lower quill. Also, when you tighten the collet w/ the drawbar, you want the thd to screw in w/o frustration. Get that drive pin in where it belongs & at the correct length to avoid frustration in the future. You don't want downtime when on an important job then wish you had the drive pin. Even the large Bridgeport boring heads have them

gatz · Oct 14, 2009

would like to add a comment about installing the key/pin and locking set screw

after screwing in the key/pin to the correct depth--which takes a little trial & error to get it right; to install the locking set screw, use something like a small boring head or mounted drill chuck and hand turn it in either direction to put sideways pressure on the flat of the key/pin while having the brake on and locked, making sure your Allen wrench has not engaged into the key/pin; only the hollow locking setscrew. That way, it's as in-line as possible with the slot and not as likely to cause problems later.

Don't over-tighten....you could put a drop of low-strength thread-locker on it.

When the lower nose ring is re-intalled, don't over-tighten its setscrew as this will distort the quill shell and make it bind up when it is raised. (I think this topic was in another thread)

lane · Oct 14, 2009

Bridgeport pins are 1/4 32 thread. Some foreign machines use a step headed pin with a set screw behind it to lock in place . And I have seen some where the step on the pin was to long and has to be machined off so the collet will go in .

moonlight machine · Oct 14, 2009

Orrin said:
Thank you, all, for your advice. I now know that pin or no pin, it's nothing to worry about.

When I discovered it was missing it didn't seem worth losing any sleep over it; but, while checking out the Kurt power drawbar the instruction manual warned that the pin must be in place. It was at that point where it seemed prudent to discuss the matter, here.

HelicopterJohn, I'm particularly grateful for your description of the pin and locking screw. Now, I understand.

Best regards,

Orrin

At the last race team I worked at they had a Webb mill. (Like a Bridgeport on steroids) It has a Kurt power draw bar and for the 15 years I worked there it never had a pin, no problem at all. When I put a Kurt draw bar on my Bridgeport I will not be putting in a pin.

Newman109 · Oct 14, 2009

lane said:
Bridgeport pins are 1/4 32 thread. Some foreign machines use a step headed pin with a set screw behind it to lock in place . And I have seen some where the step on the pin was to long and has to be machined off so the collet will go in .

That's right. My Webb pin was worn a bit when I got the mill because it had been used with a "Snap Change" collet changer. I replaced it with a new 6mm "dogbone" setscrew. I had to shorten the nose of the new screw a couple of mm to make it fit. I also had to shorten the 6mm backup screw.

Using an end mill holder as a gauge, I screwed it in just enough to clear and used a drop of blue Loctite on each screw.

As mentioned above it's wise to use very little tension on the small screw that secures the nose cap on a Bridgeport or clone. It could distort the spindle.

By the way, I belong to the Pro R8 pin group.

Joe T. · Oct 14, 2009

Orrin said:
The collet drive pin is missing from the R8 spindle of my "new" Sharp mill. It does not appear to be sheared off; it is just plain gone.

Are these pins pressed in? If so, I would appreciate your opinions about the way I'm thinking of replacing it--if it needs replacing.

First off, I don't want to go through the major surgery of removing the spindle. Instead, I'm thinking of making an insertion tool. I'd do this by drilling a blind hole crosswise and partially through and near the end of a long rod or piece of key stock. It would be sized to be a snug, but loose fit for the replacement pin.

With the aid of a mirror I'd use the rod to position and start the drive pin in its hole. Once started, I'd drive a soft wedge into the spindle, along the insertion tool, pressing the pin into place. I'm considering using Loctite to give it a firm grip.

I don't know whether the previous owner purposely removed the pin or spun it out. The 3/4" collet has been ruined by something spinning and galling in it. Maybe the two discrepancies are connected to a common event.

Are any of you operating your mill without a collet drive pin? I'm wondering if the one in this machine was perhaps purposely removed. It has a Kurt power drawbar and it would seem as if some serious buggering could happen if the drawbar sucked the collet in without the pin being aligned with the collet's keyway. If this ever happened, the drive pin would seem to be a nuisance, not an asset.

Regards,

Orrin

I sheared the pin off on my CNC mill. Based on what I have read here it is no big deal. I have not had any problems since......

R8 spindle collet drive pin--need advice

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