Slipping end mill in ER collet

Hi all,
Was messing around trying to mill a bit of cast iron flat today. I've got an ER40 chuck on 3MT and was using a 12mm 4 flute HSS end mill in
it. Started off fine, did a number of passes (about 6mm depth of cut, 3mm width of cut), then for unknown reasons the mill started shifting down in the collect by a fraction of a mm on each pass, so rather than a nice flat surface I ended up with a terraced effect :-( I repeated reset the end mill in the collet and tightened it up as much as I could but it would still start to slip after a few passes. Can't same I'm too thrilled by this. I ended up swapping to a Clarkson Autolock with a pretty knackered 1" endmill which did the job, if a little loudly! Anybody do tool grinding by post on the board? Music get a few cutters back in to useable condition.
Any thoughts on this? I'm wondering if it's because I was using a 1/2" collet in the ER chuck, 12mm should still be within the useable range of the collect. Was also wondering if it was heat related, thermal expansion of the chuck at a different rate the collet/end mill causing it to loosen, I wasn't using any coolant so some heat was being generated :-S Bit annoying having invested in the ER setup if it's not going to be reliable.
Cheers, Rob
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Unless the collet was really 13mm and badged as 1/2", in which case I suspect you would close to the limit of it's gripping power.
Peter
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I've had trouble with cutters working down in ER32 when taking heavy cuts, so I try to use the good old Autolock when I can in that situation. There are low friction 'milling nuts' available for ER32, supposed to enable you to get the collet tighter, they're not cheap & I've never tried one but might be worth looking into.
Cheers Tim
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wrote:

I rest my case, exactly what I was talknig about the other day. Stick with Clarksons !!! Bob

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Do you remember if they were weldon type cutters with a flat on them? Apparantly weldon shanks in an ER collet system suffer from a 30% reduction in clamping force on the end mill, according to Rego-Fix who invented the ER system. That was something I never knew until tonight, detail here: http://www.rego-fix.com/colletcare /
Peter
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On 10 Mar 2007 14:14:27 -0800, "Peter Neill"

I don't think so, I've got very few Weldon type cutters, but I wouldn't rule it out.
Cheers Tim
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Thanks Peter - that told me quite a few things I didn't know about ER collets. Must get a suitable torque wrench!
Actually I find the ER 25 set I use on my FB2 is quite reliable - I am more likely to suffer workpiece movement if I'm using to much overhang - but then I try to avoid hogging it.
David
--
David Littlewood

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Thanks for all the thoughts guys, just to answer some of the questions.
It's a genuine 1/2" collet - I got the chuck/collets on Ebay shipped from the US for about half the price I'd pay in the UK, and we all know how much they love imperial ;-) I can also confirm it's 1/2" because I had to buy a 13mm collet specifically to use a 13mm cutter once.
I do (now) fit the collets properly in to the release ring on the nut, I didn't at first as I had no idea you were supposed to but then I came across some instructions on ArcEuro IIRC a few months ago, suddenly it all made sense!
The cutters I have are all either straight shank or threaded.
Will check nut and chuck for hairlines - hopefully not!!
I should probably double check the collet slots are free of swarf, pretty sure they are but worth a look.
Which leaves tightening which could well be the issue. I normally bung the chuck in a vice (with rubber jaws) to hold it while I heave on with the C-spanner, could well be that's not enough. I haven't got a suitable spanner to fit the flats on the chuck, so maybe I should come up with a cunning bench fixture as well. Would be nice to be able to change cutters without removing the chuck from the mill. Do you think that would be possible if I made a suitably long enough spanner to hold against the chuck flats? Checking out the rego-fix site, how the heck would you use a torque wrench on the chuck nut?!!
Cheers, Rob
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Rob Hi,
Prompted by your comments I've just checked the spanners I used for tightening the ER32 collets on my little RF25. The spanner I used to hold the chuck is 14" long and I use the peg type (4 pegs) spanner on the nut (mine came with the set but ArcEuro do one similar). This is about 10" long and I have a piece of flattened tube (15" long) which slips over the handle, I initially made this for undoing the nut as I found that the most difficult bit but to be honest was guilty of using it to "snug" up the collet as well. I tighten the nut very firmly but can do it OK with the chuck in the spindle, releasing the nut can be more problematic. Although I don't use a copper faced hammer to tighten mine it was standard practise at work and I'm sure that is why they make the spanners so short, they expect them to be wacked. While I worked in Aerospace and torque spanners were everywhere I've never seen one used to tighten a collet? I have seen nuts crack and they go with a real bang; when the nut is tight the crack becomes really obvious so you won't miss it. Hard to see with the nut off though. I have avoided buying one of the single peg C spanners as I can't see how you will ever get it tight enough without damaging the location slot. Please don't take these comments as "best practise" it is just what works for me.
Best regards
Keith
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Thanks for the thoughts Keith. I just checked over the chuck, no signs of cracking - phew. I measured the A/F on the chuck, came to 44m, hmmm won't be buying a spanner for that at homebase ;-) Just snagged a 15" adjustable spanner on fleabay that goes up to 45mm for the time being. I see chronos sell an ER40 suitable 4 pin nut spanner for a not toooo excesive (for them) price, think I'll pick one of those up rather than continuing with the 1 pic C-Spanner that came with the set, I think you're right that they increase the risk of damage to the nut. I'll give it all another go on some scrap once I get that lot in, trying with a 12mm cutter and a 1/2" cutter in the 1/2" collet to see if I get anymore slippage..
Cheers, Rob
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jontom snipped-for-privacy@hotmail.com writes

Gosh, chaps! Why not jump on it as well.
I must be doing something wrong, as my Emco ER25 holder only has a small tommy bar hole (well, 3 to be precise, but only to use 1 at a time). The tommy bar is 6mm x 100mm long, and used with a spanner holding the flats on the spindle it has proved perfectly adequate. Not even managed to bend the TB yet, though the bluing on the end is slightly worn.
Either I am expecting too little of my holder, or you are expecting too much, or you have a flawed design, or are doing something wrong. Now, I did say earlier that I avoid hogging cuts, my mill is not that big and I prefer to use a light drip of cutting oil rather than a flood as I'm a light user and the time I spent cleaning up would be more than the time spent machining. However, consider the other possibilities too. The tightening action is very powerful and it should not need that much force to give a good grip.
BTW, I also have a Clarkson milling cutter chuck, but since acquiring the ER25 set I rarely find the need to use it.
David
--
David Littlewood

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Assumning this is the same thing as a ER 16, ER 32, ect on this side of the pond. I would check both the cap and the body for a hair line crack.
Wes
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How do you tighten the collets? I've seen ER collets used in industry extensively, and very rarely seen anything work loose (in fact I've seen cutters come out of clarkson holders more). But the collets are always tightened in a bench mounted fixture, and the spanner usually given a "tap" with a copper mallet. I'm not sure it is possible to tighten them properly (for heavy use) in the machine.
ER collet sizes are usually in a 1mm range, so I presume you had a 12-13mm collet, which would work OK with 12mm or 1/2".
Regards Kevin
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Rob
I agree with Peter, most of the ER "imperial" collets I've seen are in fact re-badged metric that cover the size. Easy to tell, if it is a genuine 1/2" ER it will not accept anything larger. If you can get a 13mm drill in it then it is a remarked metric and with a 12mm cutter is right at the edge of its capability. I always use the smallest collet rather than the larger one, ie for a 12mm cutter I use the 11-12mm collet not the 12-13mm one.
Although this won't be applicable to your case a couple of issues that I have witnessed with ER systems might be of interest to others using them. A friend complained that his cutter was slipping all the time with these "bl**dy" ER things that I had recommended. When I went to look he was not engaging the closing nut into the extraction slot of the collet before fitting the cutter. The very thin extraction ring in the nut was trying to exert all the closing force and the front taper was not even in contact with the collet. My Vertex system won't even assemble in this manner but his ???? did as it had a much longer thread on the nut. Another "friend of a friend" had a problem after he had been cutting aluminium and although he had cleaned the collet it wouldn't grip a cutter to cut steel. He had made an excellent job of cleaning the outside and inside bore of the collet but had managed to leave a lot of aluminium in the collet slots and they couldn't close as they should. I keep bits of old credit cards to clean mine out before I put them back in the box. The last experience was a colleague who insisted on using them completly dry all the time as "oil would make them slip". After showing me a "clapped out" collet that slipped as soon as it was shown the job he was amazed that after a careful clean and a touch of oil on the outer surface of the collet and on the front taper and closing nut it worked much better. Not perfect this one as the collet had a fair number of burrs on the outer taper that needed stoning off (thrown into a box!) and these had marked the internal taper on the chuck as well, but simple lubrication in the right place gave a fair improvement in its holding power.
A more subtle issue I've had myself was when I bought a new closing nut as I had "monstered" the original nut slots by using the wrong spanner - "not me gov, must be the bloody night shift". Anyway I had my first slip with this new setup and faith was shaken as I don't push them too hard now that I have to pay for them myself. Turned out to be the nut extraction ring was contacting the edge of the collet extraction slot before the front taper contacted the collet. The result was much like my friend who was not assembling them correctly and a new nut from a different supplier returned things to normal. I haven't heard of this anywhere else so believe that I just got one that "slipped through".
I have to say that we used ER collets at work with very few problems despite some fairly heavy use. As I've already mentioned we always used the smallest collet that would take the cutter and only used the extremes of their holding range to hold drills etc, something they did very well. We never used Weldon type cutters.
Best regards
Keith
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I must admit that I do tend to push things to the limit just a tad at times but I haven't had any problems with ER32's Don't take any undue care with them but I do tighten in a jig that's bolted to the end of the bed and use a piece of tube on the spanner.
Not a big believer in Weldon tooling as if you have to weld it it's going too far.
. -- Regards,
John Stevenson Nottingham, England.
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Robbus wrote:

If the nominal size of a collet is 12 mm, its range is 11 .. 12mm. Do *never* go above the range. A 12mm collet can *not* hold a 12.7mm end mill. You need a 13mm collet for that.
Nick
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No worry, unless you are built like Mad Mountain Dean you won't get a 12.7 into a 12.0. The nut will prevent it opening above 12.1 max. -- Regards,
John Stevenson Nottingham, England.
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Yep, with a bit of huffing, puffing and cussing I did get a 13mm endmill in to the 1/2" collet, but there was no way I could do the nut up on the chuck, which was pretty annoying, about 15 annoying having to buy a 13mm collet just to use the one cutter.
Cheers, Rob
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