Er32 Vs Dedicated Endmil Holders

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petertha

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I've got some nice dedicated R8 endmill holders in typical N-Am hole sizes, 0.375, 0.500. I rarely use the 0.250" or larger ones so kind of regretting buying a set way back when without knowing better. These have the lateral set screw to retain EM's against the anti-rotation notch ground in the shank. (Is that called Weldon shank?). I need to get some smallish metric EM's & typically their shanks are nominally same diameter as cutter vs. so-called 'standardized' NAm shank.

This got me thinking. My N-Am holders were not exactly cheap. I could probably justify buying say an ER32 holder for my R8 mill & collets and be set up for pretty much any EM, imperial or metric in this range. Is there a fundamental disadvantage to using ER collet for this purpose? For example there must have been a reason for integrating the set screw in this style. So is ER collet more prone to slipping in the collet? Coincidentally I bought a 0.5" carbide EM on ebay that had no ground flat so ended up grinding one in order to use. They said CNC so presumably some of those machines use spring collets? For reference I would say probably 0.5" would be the biggest size I'd consider running in ER.

What are good ER brands runout/quality wise?
I'm guessing tool change would be about the same effort - unscrew the ER cap vs. loosen the set screw?
 
The ER collet chucks and the Weldon style end mill holders both use up machine head room vs. a collet in the spindle. The Weldon holders are very strong at holding the end mills, the ER collets less so, but you really have to gronk down on them to hold things tight, or they can slip. Check the specs. for ER collet torque. End mills can slip and suck into the work if held in a R8 collet, but many or most of us do that anyway. I try to only use end mills in R8 collets on reasonably light work, and always tighten them down quite snug. I have a full set of Weldon end mill holders up to 1-1/4", not likely to use that size any time soon on my Millrite mill.

I am by no means an ER collet expert, and have actually never used one, but I think from my reading that buying a set by metric sizes makes the most sense, because that is what they were designed for, to fill all the sizes within their range using the minimum number of collets and without much overlap. The Imperial sized ER collets are more haphazardly sized and I think many of them are just relabeled metric collets. ER gurus, do I have that correct?
 
I have seen quite a few machinists make their own ER collet chucks to fit their various machines directly, buying just the nut and the collets. You definitely would need to be able to produce precision work to do that successfully, but it does help to save money and to eliminate stacked tolerances.
 
In theory Bob is correct that a metric set of ER collets are suppose to have enough clamping range to fit both metric and imperial. In practice, it seems to depend on the quality of the set and I have had some issues where they where suppose to cover a smaller range and didn't clamp down well. You are correct that the imperial sets almost never come as a complete set, vs. metric which usually comes in 1 mm increments. I went with a 1/32" inch set and had to back fill a few holes that they left out, this gives you a 0.0031 clamping differential between collets as opposed to .0394 for a 1 mm set. Since my indicators use both 10 mm and 12 mm shafts, I have metric collets for these specific diameters. These work much better than clamping down a 1/2" collet to 12mm.

On holding power, I have never had an end mill suck out of an ER holder, it clamps along the whole shaft of the end mill. I have had some apparent twist of the collet in the holder using a 3/4" end mill in an ER-32 collet system. This was in the early days when I was not aware of cleaning off the oil on the collets/holder, and I also use a bearing nut now which allows you to torque the collet in with less force. Beware, that the ER bearing nut does not work well when you compress a collet to its theoretical limit, I had the bearing go when a clamped my 1/2" ER collet down to 12mm. The ER collets seem to be more precise then my R-8 collets, but we are talking a few 1/10,000". You loose a little stack height using an ER system, I have never found it a problem, and can always use an R-8 collet if I have something very tall on the table. When it comes down to it, if you are only using the collets for end mills, you would be fine with an abbreviated set, most end mill shanks come in fixed dimensions, usually by 1/8". Since I also use the ER system on the lathe, I have invested in a 1/32" set of ER-40 because of the size range. I primarily use an ER-32 size on the mill, except for 7/8" and 1" shank end mills, and other large diameter shank tooling.
 
I've been using an ER32 set on my mill since I got it. I had a 1/2" EM slip out into the work recently. Even cranking down on the torque wouldn't get it not to slip. I ended up using a reg R8 collet for that job. Usually it hasn't been an issue.
 
I use an ER-32 chuck on the mill and an ER-40 chuck on the lathe. I've found the ER system to be an excellent tool holding system and have never had one slip. If you use collets of good quality, they are more accurate and secure than the R8 collets because they grab along the entire length of the collet instead of just the front 1/2" or so like an R8 does. If you need the best accuracy, a good nut made from hardened/tempered steel is recommended; I have an ETM and a Rego-Fix hardened nut for both chucks and they are vastly better than the cheap Chinese nuts out there, including the bearing-type nuts that I also have.

I also found that the quality of the collet makes a big difference. When I tested my ER-40 chuck on the lathe I got about 0.0007" of run out with cheap Chinese collets. My ETM collets got the run out down to 0.0002" so if accuracy and gripping power are of prime importance then having good quality collets and the right nut is important. You do need to torque the nuts down properly on an ER chuck. This is to prevent slipping but also because the accuracy ratings are measured at the proper torque.

I have an Imperial set of both ER-32 and ER-40 collets in 1/32" increments and, like all collets, they hold best at their stated size. While they will squeeze down to accommodate odd sizes they are not as accurate when doing so. This is fine for work holding in the lathe but for milling cutters you are better off getting the right size collet for that tool shank. I have metric ER collets for metric sized tooling and it does make a difference in grabbing power when the collet fits the tool.

If I were to buy an ER chuck again for use in a hobby-class mill, I would buy a Glacern ER-25/R8 chuck and a set of collets in 1/8" increments from Techniks, Lyndex, ETM or Crawford. This would hold most Imperial tooling that smaller mills can handle. I would buy metric collets as needed from the same makers to hold whatever metric tooling I have.
 
I have the Glacern ER32-R8 chuck and their 1/32" collet set. I have several Glacern products and I think they are very well made.
 
I have a set of 1/16 R8 collets for my mill, and a couple of Weldon R8 holders, 3/16 and 3/8. I'd use, if I had more of same plus 1/4, its handy to have end mills set up in the Weldon holders of various sizes. If changing from a drill chuck to an end mill, the Weldons require less head movement.
Both have their use.
 
I bought a Glacern keyless drill chuck for my lathe a while back when it came on sale. I agree, very nice quality & I was happy. I'm 99% sure they source from a 'good' Taiwan supplier because it looks conspicuously identical to another label I've seen sans label. Unfortunately with $U$C FX, their crazy shipping costs & obligatory dinger fees (outside their control), its coming out quite a bit more expensive landed. I can get a Lyndex/Japan locally for a competitive price. If its anything like the Lyndex mill arbor I have, very nice quality. Run-out was inside of what I could measure.

Speaking of, any feedback on Lyndex ER collets? They are coming out less than Techniks but I need to reference specs. I'm not quite as game to try Chinese bargain brand, sometimes you get lucky, sometimes not. Guess it depends on what the end use is but I read a story about a guy who figured he marred up his good toolholder with inferior out of spec collets that weren't fitting properly by the time he figured out what was going on.
 
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