Pros and Cons of the ER collet system

My understanding is that none rely on the key to prevent rotation under load, the purpose of the key being to allow the collet to be tightened down until the friction of the taper takes over and grips solidly.

Martin.

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< no further comment >

The only thing I can think of is where the collets are used towards the extreme end of their capacity - something like gripping a 7/16" (11.11mm) cutter in a 12 to 11mm collet. Under these circumstances and referring back to my post near the bottom of page three of this thread, you can see the small gaps that appear between holder, collet and cutter (second pic), and I wonder if this might be enough to allow the cutter to deflect under heavy load resulting in chatter etc.

Martin.

The only weakness I can see with the ER system is that an overly high Radial force on the end of whatever it is holding will generate a couple which tries to rotate the collet around a horizontal ( if the collet is in a vertical orientation) axis somewhere between the two tapers and at right angles to the radial force. As the tapers are not overly long and are of a fairly high angle "excess" force could cause some movement and allow the collet to shift off axis. ie no longer be coaxial to the spindle. This would be worse when used for work holding as the work can be many time longer than the typical end mill. This however should not be an issue as it would be usual to support the other end in a centre or a fixed steady. The effect should be less pronounced at the smaller sizes in each series. Certainly attempting to hold short pieces of work which do not fully engage both tapers and attempting to carry out heavy cuts is asking for trouble as the collet can distort and the workpiece can be wrenched out of true. As I say used sensibly I cannot see the system as anything but convenient and useful to our needs.

regards Martin

Yes Raymond, tongue firmly in cheek, I use ER on my mill and lathe for work and tool holding also use on JS hex and square blocks and have a small ER 11 fitted on my Arrand spindle. No complaints at all. I suspect that most of the home workshop community rarely approach the limits of the ER system and will be entirely satisfied. The industrial user will want to run near the limits of maximum machining rates to maximise productivity and will thus expose any limitations of the ER design.

Mike

If I am proved wrong then I will be the first to admit it. Michael P, I too use the collet blocks and find them great as I do with all me ER stuff. And Yes, of course the forces we are talking about are far in excess of what we would ever subject them to. It just that I say that there are better milling chucks than ER, and there IS a fall of in performance when dealing with Heavy Radial loads compared to Axial loads. A dedicated Milling chuck ala Albrecht, Schunk et al will always be stronger and better able to cope with these Heavy Radial loads. I am trying to find out the reason [s] for this. Of course it's purely academic to our needs but it does "bug me "

cheers.

O.K. ... let's try this:

Assuming that by 'Radial loads' we mean loads applied radial to the cutter ... These will produce [via leverage] a force which attempts to 'rock' the collet in its holder.

The ER collet is slit from both ends, and is therefore relatively 'soft'

[whereas it would, ideally, be near rigid].

It is therefore [a little] more likely to wriggle-out of the holder.

< Discuss > nicely please.

MichaelG.

Did you read my post 3 back Michael? That's what I addressed.

also

I would tend to use the word 'more unstable' relative to collets with less slits?. Maybe ER is 'relatively elastic'

All things deform to some extent and ER collets are essentially an annulus of tall blocks standing on one side which has ultimately to be less stable than a similar system with less slits. As I say they still do what they are supposed to do.

Martin

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Apologies, Martin ... No I didn't

I was just trying to get away from some of the ambiguous terminology that seems to have been confusing the issue.

Glad to see we are on the same page

... You have 'priority' of course.

MichaelG.

No wonder we poor beginners get confused by this hobby sometimes. It's a good job I didn't read this thread before ignorantly buying ER32 and finding they work fine for me.

My simple take is that the different collet designs, like all tools, are some sort of compromise. Which tool is 'best' depends on the job in hand, not on pure theory, heritage or opinion. A collet that does well in one circumstance will perform less well in others.

ER provides a wide clamping range and good grip provided the rod fits fully into the clamp. This is as you would expect because tt was designed to hold tools. ER is not good at holding short items that don't fit the clamp properly, but otherwise it has good 'general purpose' characteristics.

In comparison, R8 has a lower clamping force, but that force is applied most strongly at the front. This is useful, making R8 better than ER for gripping short work. If the work happens to be long enough to fit a ER collet fully, then ER is back in the game.

Collets have design goals other than grip, for example R8 was designed for rapid tool changing. Whether a characteristic like tool change speed is important or not depends on the job. The wide range of possible optimisations is why there are so many different types of collet available.

My advice to a beginner setting up an average home workshop is that you won't go far wrong with ER collets. Once you've had some 'hands-on' and know better what you're about, it becomes much easier to make an informed choice.

I'm surprised that a discussion about collets should become controversial. Fortunately there's no danger of the argument escalating into a rencontre though. The gentlemen could never agree on the best sort of duelling pistol.

I'm all for robust debate and there are some real gems in this thread. I just wonder if the forum needs a tea-room style section for free speech. Like the service in the Monty Python "I've come for an argument" sketch. ('No you haven't...)

If I'm talking rubbish again please say so. I'm here to learn as well as be entertained.

Cheers,

Dave

Absolutely Dave.

It is however usefull to consider failure modes when pushed way beyond normal use as it gives albeit a cerebral understanding of the dynamics of the system and how it works. I would hate to discourage anyone from musing on stuff. We all like to think what happens if. . . .However I think it was probably the implication that ER collets are somehow less than adequate, which they are not, excited some comment. As I said not anything anyone should worry about under normal working conditions. I'm certainly not going to anyhow.

regards Martin

Just had a reply back from Fahrion who attached a pdf It makes interesting reading [at least for me ] It mentions various factors on their ER chucks that have an effect of increasing rigidity over standard ER chucks. Like I said I found it interesting. I will try putting it into me dropbox and if anyone could guide me to create a link to it that would be great. I have still to hear back from the other manufacturers.

cheers.

No rubbish Dave. ER is a sensible compromise for many people that just has a limitation compared with some other types.

Milling sizes are interesting in some respects. If I remember correctly R8 came about for Bridgeports. Max capacity 20mm same as ER32. Leaves me wondering if anyone needs to go bigger than that really and face mills start to look more attractive.

I suspect that ER dimensions are largely based on grip lengths for their max size so it is possible to arrange for that to be less of a problem by using more than one size. No one does sets going from say max ER16 to max ER32 though or to the same on ER25. Pity really as the collets saved this way may well pay for another chuck. Maybe a retailer will sell them like this as they would sell more chucks.

Here's me at the point of buying an complete set of ER40's. If it wasn't for a supply problem I would have. Not at all happy about what would be sticking out of the end of the miller if I used them on that. Since then I have thought more about what tooling I need to use and say the merits of a max cutter in ER25 as against ER32. I concluded that if I wanted to go bigger on end mills 25mm would be a good size but I don't want a complete collet set to just hold that so need to hold it some other way. Past that size face mills make more sense.

Having ER25 in my case going to ER32 for an extra 4mm isn't really worth it.

John

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Forget the link., I have just tried to store the pdf and have found out that Dropbox ended support for XP on the 29th Aug. So I cant add new files, and cant access me ones already in there unless I upgrade windows They can poke that right up .

cheers.

Try this one. No sign up or anything else and they hold items for some months. Just make sure you copy the link to the file.

**LINK**

John

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Thank you John. I will give it a go shortly.

Cheers.

Just tried, and got a message saying "failed due to network error " and in brackets [1.3mb] maybe it is to big ?

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All good stuff, Dave ... Except for the bit about needing a tea-room room style section

We've got one ... a whole 'topic'

Perhaps you should start a thread on it, called "I've come for an argument"

MichaelG.

No I thought it was to good to last. I've uploaded 25mb plus files to it in the past. Worth remembering in case they sort it out again,

The only other alternative I'm aware of is google drive. I do have a google email account but never use it.

John

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The Fahrion .pdf that Raymond mentions can be downloaded from my dropbox here