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View Full Version : Tips on an ER-32 collet stop?



DICKEYBIRD
10-20-2011, 05:32 PM
Gotta use my lathe to cut a precise groove in a bunch of shafts and need to consistently grip the work. A great place for a collet stop but am not familiar with how it's done with ER collets.

I was thinking of making an expanding mandrel/plug with a long threaded rod in the center to go in t'other end of the spindle. Install the plug, adjust the rod and lock it with a jam nut. Install workpiece butted against the stop rod and tighten the bearing style collet nut (got one on the way from Maritool) with a torque wrench to ensure consistent clamping force.

Sound like a workable plan that'll hold the workpiece consistently within a thou or so? If not, got any better ideas? And no, 5C ain't an option at this time.:o

2ManyHobbies
10-20-2011, 06:02 PM
Wouldn't it be faster and more precise to just indicate from the end of the work?

Chuck it, indicate off the end, turn the leadscrew to zero, on your indicator plunge a form (or cutoff) tool to the cross-slide stop (or cross-slide indicator zero).

I'm not 5C tooled either so I see your extra time torquing and loosening collets, but I've always understood a collet-stop was for something like a really thin work piece that needed facing or length modification and might not use the full depth of the collet.

mike4
10-21-2011, 01:03 AM
Several of my ER32 collet chucks have an adjustable plug at the base of the collet , if yours are similar why not try to make a stepped replacement which can be adjusted to suit your application.
Michael

TGTool
10-21-2011, 11:17 AM
Dickeybird,

I've used the expanding collet in the spindle successfully to hold a stop rod up close to or in the collet for repetitive work. It's a perfectly good plan. Even though the collet (and presumably the workpiece) is moving into the adapter as it's tightened it should be held in good position by the stop.

DICKEYBIRD
10-21-2011, 11:53 AM
Thanks for the input TG; it's looking like that's the method I'll use. It'll take some time but worth it in the long run. There's a chance I'll be doing up to 700 of these things over the next few months.:eek:

Mike my lathe spindle is a homemade ER32 and has been bored out to 20 mm and doesn't have any threads for a plug. That'd be too easy.

2Many the shaft is about 14" long and its features wouldn't work well with trying to do repetitive dial-in setups. I'm needing something solid & repeatable without a lot of finagling.

2ManyHobbies
10-21-2011, 01:14 PM
There's a chance I'll be doing up to 700 of these things over the next few months.:eek:

2Many the shaft is about 14" long and its features wouldn't work well with trying to do repetitive dial-in setups. I'm needing something solid & repeatable without a lot of finagling.Ah geeze. @700, I'd be ditching my ER setup for a 5C even if I only got 3 of the one size collet I needed.

Go with your original plan. I'm not sure what force would be generated against your mandrel plug when the collet tightens down though. You'd figure that out quickly enough if you clamp and unclamp a test rod a few dozen times.

Heck, with 700, I might try U-shaped scrap on a faceplate with a locking lever. Just bore the scrap to the required dimension each time you work a batch. There wouldn't be any force on your stop at all.

Paul Alciatore
10-21-2011, 03:45 PM
I made a collet stop for my SB that does not depend on being attached to the collet itself. These are not ER collets, but the idea may be adoptable to your machine if you have a central hole through the back of your collet holder to allow longer stock to be used.

http://www.practicalmachinist.com/vb/south-bend-lathes/what-have-you-made-your-south-bend-147978/index7.html#post1190516

The threaded rod is reduced on the front end to fit all but the smallest collets: I believe I made it a bit under 1/8" diameter.

I think it is more accurate because it is fastened to the lathe spindle and not the collet. By attaching it to the rear of the spindle, it has a fixed point of reference instead of the collet which moves along the spindle axis when it is tightened and will be at slightly different places after being tightened if the OD of the parts or stock is different. This is a serious concern because, due to the angle of the tapers on the collets, a one thousandth difference in the diameter of the part will become 3 to 10 thousandths of lateral error in the location of a collet mounted stop. The taper actually amplifies the error.

You would need to make a nut plate for the rear end of your spindle and come up with a way of attaching it. Perhaps an expanding plug in the bore or a clamping style attachment on the OD.

In addition to better repeatability, it is also easy to adjust because the adjustment is made on the outside of the machine instead of deep inside the collet.

DICKEYBIRD
10-21-2011, 06:49 PM
Perhaps an expanding plug in the bore....Exactly my plan. A pipe bushing turned to fit the spindle ID, 4 slits cut into it with a pipe plug screwed in to lock it. The plug will be drilled & tapped for a length of allthread with the end turned down as your link showed. I think I'll center drill the end & silver-solder on a bearing ball to prevent wear and help with repeatability.

My Maritool order arrived this morning: an ER32 nut fitted with a bearing to reduce the friction plus a few collets. I got a 3/4" for this project to replace my well-worn one, a 25/32" and a 7/8." I didn't know such a thing existed. It's all VERY pretty and high quality. I'll be saving my pennies and replacing my cheap set a few at a time as funds are available.

PixMan
10-21-2011, 07:51 PM
Collet stops on ER collets generally don't work so well, and I do not recommend using them.

The problem lies in the fight between clamping force and the force of pulling the tool or workpiece that's in the collet back up against the stop.

In my direct experience, the collet may feel quite snug but the clamped object isn't held tight. If the ER collet cannot slide back in the taper as it's tightened, most of the clamping is against the stop. I have had milling cutters and drills spin or otherwise come loose in ER collets if I tightened up against the stop.

That said, many collet chucks come with a stop screw. The way to use those is to use them only for preventing something like a drill from pushing back into the collet.

I think this is why ER collets are traditionally used as tooling collets and NOT as work-holding spindle collets on lathes. I don't know of any good sturdy lathes that came out of the factory with ER collet setups. With a 5C collet, the stop moves back and forth with the collet movement, so clamping force is always fully exerted upon the work piece.

DICKEYBIRD
10-22-2011, 09:48 AM
Collet stops on ER collets generally don't work so well, and I do not recommend using them.

The problem lies in the fight between clamping force and the force of pulling the tool or workpiece that's in the collet back up against the stop.

In my direct experience, the collet may feel quite snug but the clamped object isn't held tight. If the ER collet cannot slide back in the taper as it's tightened, most of the clamping is against the stop. I have had milling cutters and drills spin or otherwise come loose in ER collets if I tightened up against the stop.

That said, many collet chucks come with a stop screw. The way to use those is to use them only for preventing something like a drill from pushing back into the collet.

I think this is why ER collets are traditionally used as tooling collets and NOT as work-holding spindle collets on lathes. I don't know of any good sturdy lathes that came out of the factory with ER collet setups. With a 5C collet, the stop moves back and forth with the collet movement, so clamping force is always fully exerted upon the work piece.No arguments from me P/M. ER32 is the only option in my case though as the little CNC lathe's spindle is homemade from an ER32 straight shank collet chuck and doesn't have provisions for a threaded button/stop.

Fortunately, the job requires the removal of a VERY tiny amount of free machining SS with a corresponding very precise location. The amount of grip required to hold the work is tiny. Repeatability is the issue and I'm hoping that if I mount up the work and torque the collet nut the same each time using a solid stop system, I'll get good results.

I'll report back later on how it works out but right now I gotta design & build a little tailstock and a more rigid webcam mount in between work and family committments. I need to train myself how to get by on Thomas Edison style catnaps.:D