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1/2" end mill pulling out of collet

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Jake2465

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#1
I was running a test program yesterday night and about 20 minutes into it I noticed that my Z heights started acting strange; the end mill was digging deeper than it was supposed to. At first I thought perhaps the encoder on the Z had some problem, but then I noticed that the end mill looked a lot longer than I remember it being. I pulled that tool holder out and checked the tightness of the collet nut. It was tight, but not ridiculously tight. So, I just cranked on the wrench a little more. Is there an actual foot poundage that should be used for ensuring the end mills don't slip out of the collet besides using the German "goot-n'tite" method?

I run with the DA180 collets and the NMTB30 tool holders.
 

RJSakowski

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#2
I was running a test program yesterday night and about 20 minutes into it I noticed that my Z heights started acting strange; the end mill was digging deeper than it was supposed to. At first I thought perhaps the encoder on the Z had some problem, but then I noticed that the end mill looked a lot longer than I remember it being. I pulled that tool holder out and checked the tightness of the collet nut. It was tight, but not ridiculously tight. So, I just cranked on the wrench a little more. Is there an actual foot poundage that should be used for ensuring the end mills don't slip out of the collet besides using the German "goot-n'tite" method?

I run with the DA180 collets and the NMTB30 tool holders.
I use the Tormach TTS system which uses a 3/4" R8 collet with ER20 tool holder. I have had pullout occur when side milling. Usually it is associated with heavy cuts. A high helix end mill is more prone to pullout. Conventional milling is more prone to pullout than climb milling. Pullout issues are usually solved by re-tightening the collet.

I don't torque my ER collets but it would be safe to say that I tighten the snot out of them. The final tightening usually involves arranging the wrenches in a pliers-like fashion and tightening one against the other. Based on the lever length , I would estimate something like 20 -25 lb.-ft. of torque

I don't have a power drawbar but I tighten the drawbar fairly tight with a 6" wrench, probably something like 30-40 lb.-ft. of torque.

Looking at the DA180 collets, they have a much faster taper than the ER collets which means a lower mechanical advantage. This in turn means more torque has to be used to get the same holding power. Another factor can be increased friction in the threads of the collet chuck. A light lube on the threads will increase the torque used to tighten the collet.
 

Bob Korves

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Kenny G

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#4
I have wondered about that myself . I had a roughing end mill do that but pretty much chalked it up to a dull cutter.I have also heard that climb milling will tend to do it. An end mill holder may be the best way to go. I guess I was wrong it must be conventional milling rather than climb.
 

Jake2465

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#5
Ugh, that's unfortunate for me. For now I will just have to work with what I've got as all of my tool holders are collet type. I will just have to crank on them really good until I can afford to go with something more suitable. I have not purchased any of those weldon style tool holders for two reasons: the length of the end mills cannot really be adjusted and the end mills need to have flats ground in the sides. So making the switch to that style of tool holder will probably drive the cost of the end mills up.
 

T Bredehoft

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#6
I'm slowly buildilng a set of Weldon holders for my PM25. I've got 1/8 and 3/8 so far, hope to get 1/4 soon and then duplicates. It's a lot easier to put a holder in the snout than a collet and tool.
 

JimDawson

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#7
Ugh, that's unfortunate for me. For now I will just have to work with what I've got as all of my tool holders are collet type. I will just have to crank on them really good until I can afford to go with something more suitable. I have not purchased any of those weldon style tool holders for two reasons: the length of the end mills cannot really be adjusted and the end mills need to have flats ground in the sides. So making the switch to that style of tool holder will probably drive the cost of the end mills up.
I've not had that problem, but I tend to be a bit heavy handed in tightening the DA collets, using a 12 inch crescent wrench and pull on it until it stops turning. :) Most endmills by default have Weldon shanks, only some of the smaller single end carbide don't, most of the smaller double end carbide do. For heavy cutting, I use tool holders.
 

Jake2465

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#8
I've not had that problem, but I tend to be a bit heavy handed in tightening the DA collets, using a 12 inch crescent wrench and pull on it until it stops turning. :) Most endmills by default have Weldon shanks, only some of the smaller single end carbide don't, most of the smaller double end carbide do. For heavy cutting, I use tool holders.
I am about to buy a 1.5" crows foot so I can put my click style torque wrench on there... Funny that it lasted for 20min before starting to pull out of the holder.
 

cjtoombs

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Tormach used to have a very good white paper available on this, but it has apparently been replaced with this article (the link to the paper in the article is broken). I have used the recomendations from the white paper and have not had any collet pull out since using them. Here is the link to the article.
https://www.tormach.com/blog/best-practices-for-preventing-collet-slip/
 

whitmore

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[QUOTE="JimDawson, post: 612356, member: 29628"... I tend to be a bit heavy handed in tightening the DA collets, using a 12 inch crescent wrench and pull on it until it stops turning. :) Most endmills by default have Weldon shanks, only some of the smaller single end carbide don't...[/QUOTE]

I had a similar problem with a single end carbide mill, which was in a router (and used on wood). A router chuck doesn't
have the right construction to use a heavy wrench, but it was possible to roughen the shank by dipping it in boiling hot
chlorine bleach. Once the mirror finish was dulled, the collet held it much better.

The ultimate solution, would be to shrink a collet-shaped collar onto the shank; the collet chuck would hold that quite securely.
 

Jake2465

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#11
I am definately going to try and go for a set torque for the collets. I definately dont want this to be a recurring issue. I like the DA180's because they dont taper lock like the TG75's do. I have to use my shop press to remove the collets out of those... Thats too much hassle and I cannot use double ended tooling as the press will destroy one end every time.
 

Ianagos

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#12
If your tg75 are getting stuck then your collet nut is probably broken. Just pick up a set of er32 and you should be fine.
 

jbolt

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#13
I don't use DA collets but I know you can get non-pull out collets that are used with Weldon style cutters.
 

derf

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#14
I've never had any problems with the larger DA collets, but I did break some nuts on the small ones. Get some rigid tool holders and grind your own flats where they need to be. I found a decent selection of NMTB 30 holders at Grizzly, reasonably priced.
 

Janderso

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#15
I was having a problem with my end mills slipping out of the R8 collets. I replaced the draw bar, I bought it from H&W Machine or is it H&H, no H&W. It solved my problem.
 

mmcmdl

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#16
Way back when in my apprenticeship my buddy scrapped a very expensive pump shaft on a DeVleig jig bore when the end mill pulled out . He was machining a precision keyway . We had to re-make the entire shaft . All apprentices were shown what had happened . End mill holders were always used after that . Make sure your end mills are pulled down to the top of the flats also . If it moves , at least it moves up and not down into your part !
 

Janderso

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#17
I was having a problem with my end mills slipping out of the R8 collets. I replaced the draw bar, I bought it from H&W Machine or is it H&H, no H&W. It solved my problem.
Until last night.
I was using a 3/8 center cutting end mill, the tool moved up in the collett as I was bringing the quill down for another pass in a pocket. I then lost confidence in the DRO readings.
Even though the DRO reads movement, I started over with the set-up.
I guess i'll need to convert to flats on the end mills and modifying the R8 collets ?
 

Janderso

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#18
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Boswell

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#19
I use an R-8 spindle and a combination of End Mill holders with Set screws and Collets. No problem getting the Set-Screw holders.
 

Winegrower

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#20
I use an R-8 spindle and a combination of End Mill holders with Set screws and Collets. No problem getting the Set-Screw holders.
Yes, I also had troubles with my R8 collets, mainly the 3/4” endmills. So I bought a 3/4” tool holder, Problem fixed.
 

magicniner

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#21

BaronJ

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#22
Bob, will those holders work in a standard R8 spindle?
Hey, I know it's a dumb question but there it is.
You can buy or make Weldon style cutter holders that fit R8.

I would check that your collets are clean and there are no burrs inside them, also check that the cutter shank is clean and dry without any burrs.
It does take quite a bit of force to tighten them properly. A wipe with an oily finger on the taper helps.
 

macardoso

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#23
Ugh, that's unfortunate for me. For now I will just have to work with what I've got as all of my tool holders are collet type. I will just have to crank on them really good until I can afford to go with something more suitable. I have not purchased any of those weldon style tool holders for two reasons: the length of the end mills cannot really be adjusted and the end mills need to have flats ground in the sides. So making the switch to that style of tool holder will probably drive the cost of the end mills up.
I have used ER20 collet tool holders for tools up to 1/2" and 3 HP into the tool without slippage. Make sure your tools and collets are clean and dry, make sure you are using the exact right size for the shank (metric 12mm for a 1/2" tool isn't good), and make sure you install them in the ER nut properly.

Edit: I tighten mine with some big wrenches, probably 30 ft/lbs or more for a big tool. Tighter than you would think you'd need.
 

ddickey

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#24
I was having a problem with my end mills slipping out of the R8 collets. I replaced the draw bar, I bought it from H&W Machine or is it H&H, no H&W. It solved my problem.
Really? Why? Better threads?
 

rcaffin

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DA180 is OK for small cutters on high speed routers on timber. I would NOT use them on metal. The tapers are wrong.
R8 is tolerable for a while and if done up properly should hold. But they are expensive and come in limited sizes. Antique.
ER collets are far far more reliable and far easier to use. That is why they were invented and are now a bit of a standard. ER32 is quite strong. Do not try jamming an over-size cutter into a small collet: bad move.

Cheers
Roger
 
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