[Vern Smith]

My Haas with the pneumatic draw bar has several warnings posted on it concerning the use of hard stops. My question is what exactly is a hard stop? I would think this would be something the limits the distance the draw bar can pull the collet into the spindle. The stop I have pictured below I have been using for years on manual machines to set the distance the stock piece projects into the collet before closing it. It does not limit the distance the collet can pull itself into the spindle taper.

Hopefully, the pictured stop can be used with the pneumatic draw bar without damaging the mechanism. Anyhow, my stop screws into the back of the collet itself, becoming effectively a part of the collet.

Vern

[Donkey Hotey]

I'm waiting for an answer on this one too. The SL-20 we just bought at work has all kinds of dire warnings on the side of the machine, describing world annihilation if you dare put some fixed length stop in there.

I haven't seen them but, I imagine that there is a class of hard stops that attach to the end of the drawtube. I suppose if the collet were pulled into one of those, it could potentially cause damage. Of course, I also have to wonder why the machine wouldn't just achieve its hydraulic clamping pressure and assume that it had clamped up.

My guess is that the collet stop you're using is harmless. I'm with you; I can't see any way that it could damage anything.

Then again, it's not a fixed-length stop (its Z position changes with the collet). So unless you have one of those super expensive dead length 'push' collet closers, all you're doing is getting a so-so depth stop.

Designed for power chucks, not collets but, I found this the other day. Kind of interesting. It attaches to the swarf cover on a power chuck and gives you a positive depth stop.
http://accustop.net/

[Vern Smith]

Now I don't feel completely out of the loop.

If this type of stop is not acceptable to the Haas closer then one has to wonder about the value of whole automated setup for collets if you are not using a bar feeder or puller. You can put a step in soft jaws with a chuck but the 5C is different.

Your web site info is a nice piece of equipment if you are running production with lengths too long to depth set in soft jaws.

Maybe everyone went home for the Holidays?

Vern

[tobyaxis]

The "Hard Stop"!!!!! I was wondering the same thing a few months ago when working with an SL20. I never heard of one before either.

Greg, I think you have something there. Hope the HAAS Apps guys chime in tell us what the hell this is.

I too do not think a 5C Stop is going to hurt anything. Being that I was working with 42" 40mm Shafts I was using a Bar Stop in on of the ID Holder Blocks. It made it possible to hold +-.005 on the OAL.

[Vern Smith]

For informational purposes this was posted on a forum that will go unnamed to my question.

" Do not attach dead length stops to this rotating union, The union will be destroyed"

Now what that refers to is the end of your drawtube, which is the portion that protrudes from the back of the lathe. If you notice, that portion does not move in and out with the drawtube, it remains in the same place. Inside however the drawtube does move, and if you were to attach anything into the non moving part, it would restrict the motion of the drawtube and actuator.

Now to answer your question, the collet closer can accept any stops that is mounted onto the collet itself, so the one you've posted is just dandy.

It certainly sound reasonable the the fellow who supplied it I consider a very reliable and knowledgeable source.

Vern

[Geof]

I just came across this thread and this puzzles me:

Now what that refers to is the end of your drawtube, which is the portion that protrudes from the back of the lathe. If you notice, that portion does not move in and out with the drawtube

This seems contradictory:

If it is the drawtube it has to move; if it doesn't move it cannot be the drawtube.

The hydraulic, or pneumatic cylinder assembly does not move, the drawtube does move. If a stop is attached to the drawtube, which I think is what the prohibition refers to, the stop will move so it is not much use as a stop.

It is possible to rig up a stop on a drawtube system:

Fabricate a bracket on which a bearing can be mounted co-axial with the spindle. Fasten the rod for the stop in this bearing and it will rotate with the spindle but will not move axially.

[Vern Smith]

Geof,

Your logic is hard to dispute and I had time today to take away enough shielding to see what is going on, kind of. The pneumatic actuator sits on the end of the spindle on bearings, one of which must handle thrust. It does not turn because it has all the air supply and bleed tubing attached to it. It has a simple safety system where by it is restrained from turning only by a rather thin sheet slot with a bolt protruding from the actuator through the slot. I assume if for some reason the actuator decides to synchronize itself with the turning spindle this provides "break away" protection. The plastic air lines probably get into the act as well.

With the spindle turning nothing visible on the actuator is moving, not even the center tube that matches the ID of the draw tube. If you somehow attached a "hard stop" to the draw tube it would naturally spin with the spindle and move axially whatever amount the draw tube moves in a open/close sequence. It you somehow attached this to the actuator you would have an object designed to spin and move axially attached to an object that is designed to do neither.

Your idea would surely work assuming you could find enough superstructure that far ( about 12") from the end of the spinning spindle to mount your pillow block and carrier bearings. With the draw tube being fed 40 lbs of air pressure the cage would need to be pretty stout. If I run into a situation where I need a stop deeper in the spindle than my simple collet stop I'll have to think about it some more.

Vern

[Geof]

It just dawned on me.....you are talking about the Royal collet closer????

If that is the case they are quite different to conventional hydraulic or pneumatic chucks because the cylinder does not rotate and all the closing forces are transmitted via thrust bearings.

Not that it makes a lot of difference because the outboard support I suggest does not interact with the drawtube and does not have to support much force because it is only you pushing things up against a stop mounted on it while you close the chuck.

[Vern Smith]

I should have been more explicit, as far as I know the unit is made by Royal and shipped with the Haas machines. It also powers the Samchully chuck also supplied with the machine.

Assuming the stop is actually a rod secured by our outboard support and protruding through the draw tube and acting as a back stop for whatever we put into the collet before it closes, will it not have to resist the forces of the collet retracting thereby forcing the "stopped" piece of bar to stand still while the collet scrapes against it as it retracts into it's clamped or fully retracted position?

I have long forgotten all those neat force vectors someone tried to teach me years ago but it seems to me maybe half of the pneumatic forces would be resisted by our "support structure". I'll let it to guys like you to determine the forces our hypothetical 40 lbs of air pressure would translate into when it reached the "support structure". The best option might be to spring for one of the big bucks collet closers that act as collet stops as well.

Vern

[Geof]

....Assuming the stop is actually a rod secured by our outboard support and protruding through the draw tube and acting as a back stop for whatever we put into the collet before it closes, will it not have to resist the forces of the collet retracting thereby forcing the "stopped" piece of bar to stand still while the collet scrapes against it as it retracts into it's clamped or fully retracted position?.....
Vern

You are correct; actually the stop is going to stop the collet closing fully. I am guilty of blinkered thinking and had in mind conventional three jaw chucks which do not pull back as they close.

How to solve the problem with the pullback type collets?

How much accuracy do you need, or how much repeatability? You could have a spring at the end of the stop so the collet would fully close compressing the spring slightly. If your parts where all the same diameter the amount of spring compression would be fairly consistent so you would get repeatability to within a few thou.

[SBC Cycle]

Designed for power chucks, not collets but, I found this the other day. Kind of interesting. It attaches to the swarf cover on a power chuck and gives you a positive depth stop.
http://accustop.net/

Don, the chuck that came on my SL-20 is a Kitagawa and they also sell a similar setup for the chuck. I've been meaning to get one and I ass-u-me it is a "safe" stop considering they manufacture the chuck that it bolts to. Now I'll have to compare the two. Thanks for the link.