ER collet not collapsing equally

PegroProX440 · Jan 30, 2020

This happens to a lot of my ER (20) collets and I'm not sure quite why. As the collet is tightened the spacing that allows it to collapse is not uniform, almost like it is twisting. I have not noticed any lack in tool life (not production, mostly one offs). All of my holders are either Pioneer or Mari and the collets are mostly from Mari with a few Parlec in the mix. I don't remember this happening at my last shop so I'm wondering whats the culprit.

Scruffy887 · Jan 30, 2020

They look a bit worn to me, rounded edges.

gregormarwick · Jan 30, 2020

Collet is twisting for sure, it happens when you are working in the collapse range and overtighten. The closer to the bottom of the collapse range to more they tend to twist. I have a rule in the shop to not exceed half the stated collapse range of the collet for this reason, and also because the smaller ones sometimes get stuck and shear off the edge of the ejection collar in the nut when collapsed too far.

Mike1974 · Jan 30, 2020

How does the collet look in the free state? Are the gaps even? If so, then yes it is twisting for some reason, if they are not even in the free state the collet is bad. Have you checked runout of your tool when the collet is twisted like that?

PegroProX440 · Jan 30, 2020

The collets look fine in their natural state. Fairly new collets as well, the holders were here before me. Ive been here a year.

fmari --MariTool- · Jan 30, 2020

gregormarwick said:
Collet is twisting for sure, it happens when you are working in the collapse range and overtighten. The closer to the bottom of the collapse range to more they tend to twist. I have a rule in the shop to not exceed half the stated collapse range of the collet for this reason, and also because the smaller ones sometimes get stuck and shear off the edge of the ejection collar in the nut when collapsed too far.

Good rules to follow. This is why we stock ER collets in 64th increments even though they can collapse much more.

Pergoprox440

wipe down the tool holder collet taper, make sure it is not oily. With a heavy oil or lithium grease apply a dab to the collet nut thread and the collet front 30 deg taper. See if that helps. What size collet are you using and what shank are you grabbing?

Mtndew · Jan 30, 2020

fmari --MariTool- said:
What size collet are you using and what shank are you grabbing?

That's the important quesiton.

Hardplates · Jan 30, 2020

Looks like a 17/64" collet grabbing a tap

PegroProX440 · Jan 30, 2020

17/64 on a .253 shank m6 tap

fmari --MariTool- · Jan 30, 2020

Almost borderline to where I would recommend a 1/4 collet. .001-.002 expansion is not a big deal.

PegroProX440 · Jan 30, 2020

The grease did not work. I tried the same tap, same collet in a fairly new Mari holder and i still got the same variable collapse. I checked the TIR of the tool and I was getting .0005 as close as to the nut as I could get. Its a tap so I cannot check it out on the end. It taps no problem and rarely do I break them. Would that offset catch in the nut that pulls the collet out (not sure on the real name) effect the compression. What if there was not enough clearance built into it and it pushes it to one side?

PegroProX440 · Jan 30, 2020

And thanks for your input Frank. Im not trying to bring any negative attention to your brand because I think its pretty great in most aspects. It may be factors that have nothing to do with the holders.

Rickyb · Jan 30, 2020

Mike1974 said:
How does the collet look in the free state? Are the gaps even? If so, then yes it is twisting for some reason, if they are not even in the free state the collet is bad. Have you checked runout of your tool when the collet is twisted like that?

A bit out of my realm here, but would a bearing collet nut help? It should reduce the twist force significantly. I use it exclusively on my er40s but don't know if it's available in the 20 size.

EPAIII · Jan 31, 2020

I would check for burrs and nicks and dirt in the collet holders and nuts.

Dumpster_diving · Jan 31, 2020

Is it possible there's something about the tap that is not concentric? Like maybe the square at the back end has a burr from being used with a crescent wrench and the burr is projecting out and contacting only a portion of the collet?

Try the same collet/collet-holder with a fresh endmill and see if you're getting that same weird result.

CarbideBob · Jan 31, 2020

Is the tool at collet face or the tip off center or do you just not like the look of the spaces?
Bob

PegroProX440 · Jan 31, 2020

Here it is collapsed on a 1/4 endmill and in its free state.

PegroProX440 · Jan 31, 2020

I just dont like the look

DavidScott · Jan 31, 2020

I vote it's a defective collet, the slots are too long so they don't give the support needed to connect the segments. Mine don't extend onto the face like the one you show, they end in the 30 degree angled section. Granted my smallest ER 20 is 5/16".

Are the segments connected to each other on the rear? It looks like some may be broken allowing them to move.

ER collet not collapsing equally

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