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cutter slippage using ER series collets

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John Rutzen27/09/2019 22:00:31
129 forum posts
1 photos

HI , I was doing some milling today using a 3/4 inch end mill in my ER25 collet chuck and the the cutter advanced itself into the work, spoiling the job. It's happened before and I wondered if anyone had the same trouble and had found a solution. It never happened with the Clarkson Autolock chucks because the screw thread on the cutter prevented it. Nowadays I'm stuck with the collet chuck and plain shank cutters.

Chris Evans 627/09/2019 22:13:38
1525 forum posts

When I was working on CNC mills we had a bench mounted holder to drop the iso40 tooling into and really tighten the chuck. The pull down you are getting also happens on other systems like R8.

David Davies 827/09/2019 22:25:34
64 forum posts
5 photos


do youu use a ball bearing type closing nut? These allow application of the high torque required to close these collets with ease. I use them on my ER 32 & 40 gear, I assume they are available for ER 25.



Emgee27/09/2019 22:47:26
1319 forum posts
211 photos

If a 3/4" shank has been turned/ground down to fit an ER25 16mm collet then perhaps the part being held in the collet is not parallel so allowing the slip experienced.

I have experienced tool creaping down when cutting 40mm on flutes x 2mm DOC on a 12mm 4 flute cutter, my remedy was to change the cheapo collet for a Schaublin/Emco made one.


John Reese27/09/2019 23:20:12
817 forum posts

I think most of us under-tension the collet nut. I believe the iseal tightening torque for the ER32 size is around 100 A young strong man in his prime might be able to achieve that torque with the wrenches provided. For those of us that are old and decrepit there is no way to tighten the collet sufficiently without putting a cheater pipe on the spanner.

Mike Poole27/09/2019 23:31:50
2248 forum posts
52 photos

Obviously you are using a reduced shank cutter which is probably going to push ER 25 a bit harder. The correct torque for tightening an ER chuck is surprisingly high and worth checking that you are meeting this requirement. To get to the bottom of this some checking is required that everything meets the specification for this setup. Unless you have spent big bucks on a Regofix setup or similar quality then I feel it is not unreasonable to suspect that some of the hardware is maybe off spec or maybe you are not meeting the tightening recommendations. Check everything.


Nick Hulme27/09/2019 23:47:06
715 forum posts
37 photos

Unlikely to slip if used correctly on a good quality tool shank, read up on what bits should be clean and oil-free when fitting the tool and use the correct torque.
Blaming the tools and all that :D

Bandersnatch28/09/2019 01:21:17
1333 forum posts
40 photos

Surprisingly - to me - there is actually a 3/4" ER25 collet available.

Seems to me at that size, such a collet might be getting a bit thin ... with reduced gripping ability.

Thor28/09/2019 06:05:01
1147 forum posts
32 photos

Hi John,

I have never had any cutter slip in my ER chucks, I do use ball bearing closing nuts. As John R says you need a high tightening torque, 77 ft/lbs for an ER 25 size collet according to this website.


not done it yet28/09/2019 06:10:19
3757 forum posts
15 photos

For standard er25 collets, the recommended tightening torque is given, on the net, as 85Nm. That is fairly typical of a small car wheel nut. I use a 500mm torque wrench to tighten my wheel nuts.

thaiguzzi28/09/2019 06:43:32
601 forum posts
131 photos

What is ER ?

All my cutters are threaded (still available) and never slip in my Clarkson type Vertex holder.

Just joshin....

JasonB28/09/2019 08:09:25
16870 forum posts
1815 photos
1 articles

What size cut were you taking? Your mill is not rated for that size of milling cutter so unless using it for light cuts the slip may have been better than overloading it.

I think those using screw shank cutters will find it harder to get them so may as well move with the times. Looking through one makers catalogue, of the 386 pages covering non indexable cutters not one screwed shank is shown, another suppliers catalogue has 55 pages of which 5 are screwed shank and you don't get many options only 2 or 4 flute no material specific cutters, coatings for better performance and no sign of carbide. Also as per a thread yesterday you are now having to pay more for screwed than plain or Weldon as they are not being made in vast numbers as almost all of industry has moved on.

John Rutzen28/09/2019 08:46:39
129 forum posts
1 photos

HI, thanks for all the replies. I'm sure that it wasn't tightened enough. The spanner I have just isn't up to it. I've never heard of a ball bearing nut. I think the cutter was actually 20mm and the shank 16 mm so it was a good fit in the collet, sorry I just called it 3/4 because it was in a drawer labelled 3/4 cutters. I had sharpened it myself on my Quorn cutter grinder. I will have to make a longer and stronger spanner, the one supplied is useless.

Baz28/09/2019 08:48:33
284 forum posts

If the cutter moves in an ER system it is not done up tight enough, industry use ER all the time movement up or down is totally unacceptable, as mentioned elsewhere the cutter holders are dropped into a bench mounted holder so they can be tightened. Avoid holding cutters in R8 collets unless you have a power drawbar and even then keep your eye on it, I know that sometimes we have to use R8 to get sufficient clearance but go a bit slower and check a bit more often. I am fortunate in having a Clarkson chuck and a good selection of cutters and if clearances allow I prefer to use it, it may be old technology but it works!

David Standing 128/09/2019 09:12:18
1281 forum posts
46 photos

Also make sure there is NO swarf whatsoever in the slots of the collet, this can cause it to bind and not tighten as much as required, particularly if the shank/collet combination is that you are closing the slots up to the minimum (such as a 16mm shank in a 17-16mm collet).

Wherever possible I always use the smallest size ER collet possible, rather than 1mm bigger and trying to close it down to the minimum.

IanT28/09/2019 10:03:05
1383 forum posts
137 photos

I have a Clarkson milling chuck and always use that in preference to my ER chucks where possible. I'm fortunate to have a good selection of threaded cutters and I've not noticed any shortage of used ones at the shows I attend. However I do use ER collets for milling where I'm using 'new' (unthreaded) cutters and I've not had any problems - but then I generally don't take huge cuts. I also use ER quite extensively for work & fixture holding.

I have an ER32 ball-bearing closing nut and it certainly does help ease things and as I sometimes have problems gripping things too tightly, this is very useful.

But as David notes above, trying to close an ER right down to it's "minimum" size is not good idea. I now have sets of metric and imperial collets in both ER32 & ER16 - which have been acquired over time (so didn't seem too extravagant/expensive) - and it's now easier to select a collet nearest to the actual size required.

Obviously, a 1/4" collet is better at holding an old 1/4" unthreaded cutter (I still have some) than a 7mm collet but if I need to hold 6.2mm material, the 1/4" collet (6.35mm) is still better than the 7mm one.

I'm tending to also think of my imperial collets these days as 'odd-sized' metric ones and it's quite useful to have 3.175mm, 6.35mm, 9.525mm (etc) sized collets when I need them...



Edited By IanT on 28/09/2019 10:05:30

Vic28/09/2019 10:03:09
2374 forum posts
12 photos

What type of spanner are you using? I find this type more than long enough for bearing nuts:


Chris Evans 628/09/2019 10:14:37
1525 forum posts

All this makes me glad that I have Clarkson chucks for 1/4" to 1" shank and around 1500 threaded shank cutters to play with. I picked up loads of mainly new threaded shank cutters at a sale, industry now rarely uses HSS so available cheap at sales.

John Rutzen28/09/2019 13:21:25
129 forum posts
1 photos

I use a spanner I made because the supplied one was a mickey mouse affair. It's pretty robust but i do tighten it in the machine which is R8. The chuck is proper R8 shank one. I let go of most of my threaded shank cutters when i sold my old mill because it was too heavy to shift. Probably a mistake.

old mart28/09/2019 19:46:12
962 forum posts
104 photos

Using the original length spanner will usually give a lower tightness than recommended. I use er25 which only goes to 16mm, and I milled a spanner flat on the holder. The cutters are mounted before fitting the R8 into the spindle, and the spanners get leaned on on the top of a workbench, also used for undoing the collet. We all use this method, and have never had a slippage. One day I will make extensions for the spanners, I recon they need to be 12" long.

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