R8 Collet dimensions

[Susquatch]

In preparation to start working on some vise clamps, I grabbed an old half inch R8 collet and a half inch end mill. The collet is part of an assortment of used Collets that came with my mill. I put the end mill into the collet and immediately noticed that there is a small internal shoulder. The bit slips in easily for about 5/8 of an inch. With a little bit more force it can be inserted till it hits the drawbar threads.

I'm assuming the shoulder should not be there.

But I'll be darned if I can figure out how it got there.

I'd also like to try and fix it. But it isn't a soft collet so I'm guessing it will probably have to be ground. It's either that or pitch it.

Any thoughts?

 

[RobinHood]

Carbide tooling spinning inside the collet? They needed to reach a ways into a part and inserted only a small portion of the shank, thus did not get enough of a grip on the tool?

 

[Susquatch]

Carbide tooling spinning inside the collet? They needed to reach a ways into a part and inserted only a small portion of the shank, thus did not get enough of a grip on the tool?

I really do like how you think!

That works for me! It isn't a big step. I don't think it would take long to do that, especially if the tool was threaded..... I have a few of those weirdos.

Thank you.

Do you think repair is an option?

 

[DPittman]

Ya know I think I have some r8 collets that also have that but am 99.9% sure it wasn't from tooling slipping in the collet.

I will try to remember to examine them tomorrow in the shop and report back here. If you hear nothing from me I either forgot again or dropped dead (50% chance of either of those thing happening)

 

[RobinHood]

The threaded end mills were originally designed for the Clarkson Autolock System.

Here are instructions on how to use the system:
http://www.denfordata.com/bb/viewtopic.php?t=1057

I have the R8 chucks to use those threaded shank end mills in. It’s a bit of an outdated system, but works really well.

I would try and stone the ridge off.

If you have multiple collets with the same problem, it could be that they came from factory like that - probably not the best quality to begin with. They are most likely not the Lyndex - Nikken brand.

 

[PeterT]

Curious, I've never seen a spec for how much shank depth anR8 collet is supposed to have for a given diameter. The Hardinge sketch makes it look like a wider chamber than the ID so tool could be pushed up until contact to drawbar threads but maybe that specific to their line? I tried searching some tooling catalogs but didn't see a dimension. I can measure mine just guessing maybe 2" insert length in 1/2" collet bore? Is there a chance your drawbar is long, threading through & EM contacting? I think most of my R8 tooling has blind threads but its been a while since I looked at a collet up close.

 

[Susquatch]

This Particular collet is a Hardinge. It is old but is in good shape other than the internal ridge. It has a chamber that begins right after the external cone. About 1.25" deep. Your drawings match what this collet originally looked like. The ridge on this collet starts about 5/8 of an inch in.

A half inch end mill slips in with pretty much perfect fit and friction until it hits the ridge. With a medium amount of additional force, it will slip past the ridge and then slips easily again.

Amazing how dirty the collet is inside. Never saw that with my naked eye! But I can use the excuse that they came with the Hartford Mill and I just gave not cleaned them yet......

No way it was touching the Drawbar - I was holding it in my hand. I almost always test fit Collets by hand before I install them.

My lathe 5C Collets do not have the ridge.

I've looked at the other Collets that came with the mill. The 11/16 and 5/16 Collets have a similar ridge about half way in but both with a significantly smaller difference. None of the other sizes have the ridge.

I really like @RobinHood's version of what probably happened. Not sure how to use a stone to fix it though.....

 

[DPittman]

Ya know I think I have some r8 collets that also have that but am 99.9% sure it wasn't from tooling slipping in the collet.

I will try to remember to examine them tomorrow in the shop and report back here. If you hear nothing from me I either forgot again or dropped dead (50% chance of either of those thing happening)

My mistake, I examined my collets and did not find that at all. I may have been thinking about my ER collets.

 

[Susquatch]

My mistake, I examined my collets and did not find that at all. I may have been thinking about my ER collets.

No problem!

I cleaned the 1/2" collet. The circular marks caused by spinning are unmistakable throughout the entire bore. But it turns out that ridge is actually more llike the backside of a rounded out groove. Only one explanation for that! You nailed it @RobinHood!

 

[PeterT]

I wonder if it was re-worked in the past. I cant think of a logical reason to have a shallow depth & step but who knows. Hardinge are premium brand but all bets off if its chowdered up. The bottom line is depends on what you intend to hold. Gripping force is a function of area, so if you are gripping a 1/2" EM or straight shank boring head or some higher load tool, the limited depth is working against you and gripping only on the 'hilltops' of circular marks is working against you. I'd be inclined to buy a new collet, they aren't horribly priced. OTOH if its to hold a low load tool (& assuming the mod job is straight), maybe that's good enough. Your call really. Generally speaking collets should be spanky smooth & as precise as the wallet allows. They are always hardened so modifying would, I assume, be a grind job.

 

[Susquatch]

I wonder if it was re-worked in the past. I cant think of a logical reason to have a shallow depth & step but who knows. Hardinge are premium brand but all bets off if its chowdered up. The bottom line is depends on what you intend to hold. Gripping force is a function of area, so if you are gripping a 1/2" EM or straight shank boring head or some higher load tool, the limited depth is working against you and gripping only on the 'hilltops' of circular marks is working against you. I'd be inclined to buy a new collet, they aren't horribly priced. OTOH if its to hold a low load tool (& assuming the mod job is straight), maybe that's good enough. Your call really. Generally speaking collets should be spanky smooth & as precise as the wallet allows. They are always hardened so modifying would, I assume, be a grind job.

Now that I know that most of the ridge is actually a rounded out groove, I don't have much stomach for trying to repair it anymore. I'll buy a new one and then use the old one as a spare or an expendable after I take the rough edges out of it.

 

[Susquatch]

One more related question guys...

I've been thinking about that groove and how it got there....

I assume that both collet, cutting tool and spindle bore should be degreased and clean before use, but what is the recommended drawbar torque? I doubt it relates to the strength of the thread on the Drawbar. But I bet it does relate to the clamping force on the collet jaws.

I did a quick search on-line just now. I've seen everything from a quick shove on a 10" wrench to your eyes need to pop out of their sockets and a few attempts at relating air powered drawbar tools to torque. But nothing that I would call solid advice.

Anybody here have info like that?