Pros and Cons of the ER collet system

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris Trice on 17/09/2016 19:53:37:

The only way to get perfect line contact along the length of a cutting tool from a holder that "crushes" is either a rubber type collet with separate metal blades or a metal collet whose bore exactly matches the cutter and/or the spindle it fits into with negligible "crush".

.

Chris,

A small ammendment, if I may:

… either a rubber type collet with separate metal blades [or the all metal Burnerd MultiSize] or …

MichaelG.

[Nick HulmeParticipant @nickhulme30114]

Posted by Raymond Anderson on 17/09/2016 19:10:28:

Listen folks,

Ah yes, the old "I'll no longer partake in this as it's beneath me" response used by all who reach the end of their knowledge and wit.

I particularly liked the reference to the use of Dykem, carbide tooling and good quality examples of the tool holding system being discussed as "Agricultural" and "Comic Cuts", obviously an experienced and skilled engineer's point of view…….

Raymond I think you've summed yourself up quite well there from your chair

– Nick

[Neil LickfoldParticipant @neillickfold44316]

This is what I made for holding various parts at work. I make support pieces to support the collet at the back end, either as a button or as a combined end stop and collet support. For some jobs I make a collet specific to that part with a step in it or what it needs. The outer shape of the ER40 blanks is a standard program in the lathe, so just need to edit the ID detail. These normally work over a small part size range, less than 0.1mm variation. I have also made some Delrin solid colets, and use them as distortion collets. The part neatly slides into the plastic with an end stop on the collet chuck body. So makes it into a dead length set up. Then the plastic distorts and holds the part nicely. With a steel step collet and stop I can hold and second op some quite thin parts down to about 1mm thick. Neil

[Raymond AndersonParticipant @raymondanderson34407]

Very nice Nick, Is that the collet holder in the center ? Is it held in a 4 jaw ind and dialed in, or is it held in soft jaws. Either way very nice set up. In the top left I think is an Aluminium blank, to get the 0.1 mm range how many times do you slit it ? I take it the parts with the Cap heads are the combined length stop and plug. I like it.

cheers.

[Michael HornerParticipant @michaelhorner54327]

Posted by Neil Lickfold on 18/09/2016 08:07:32:

This is what I made for holding various parts at work. I make support pieces to support the collet at the back end, either as a button or as a combined end stop and collet support. For some jobs I make a collet specific to that part with a step in it or what it needs. The outer shape of the ER40 blanks is a standard program in the lathe, so just need to edit the ID detail. These normally work over a small part size range, less than 0.1mm variation. I have also made some Delrin solid colets, and use them as distortion collets. The part neatly slides into the plastic with an end stop on the collet chuck body. So makes it into a dead length set up. Then the plastic distorts and holds the part nicely. With a steel step collet and stop I can hold and second op some quite thin parts down to about 1mm thick. Neil

Hi Neil

Thank you for showing us a practical example of a ER40 collett chuck.

If you took one of your blanks and shrunk fit a milling cutter into it. Would this alleviate the line contact that is mentioned in the above threads?

Cheers Michael

[Raymond AndersonParticipant @raymondanderson34407]

Just replicated Nick's test . Used a test bar 20mm that I had made from Strongbar uk have put the pics in the Album ER The test bar I had made was for fitting a Collet chuck to a backplate as accurate as I could get it. For the test bar I specified the following, Straightnessm Roundness, and Parallelism as 0.005 µ or better. Will also put the quote for the test bar in the same album [ In case any "doubting Thomas's dispute the test bar ] Will have to wait approx 60 mins before I can convert the pdf quote to jpeg.

The findings were exactly the same as Nick's. It appears there is "point contact " at 8 areas corresponding to the slots in the collet. The back end also shows the same only they are offset by the width of a slot. I certainly had no intention of grinding a flat on the pricey test bar, so held the free end in another ER 40 collet / collet block.

Tightened until I could barely twist it, then a bit more until it would not turn with a shifter on the collet block. There is an area between the front and back of the collet that receives no clamping.. I don't know how accurate the findings are because I dont know what torque I or Nick put on. Was it over or under the specified torque for that Ø ? I don't know ! Should the collet have been a "virgin " one ? again I couldn't say.

Cheers.

[John Stevenson 1Participant @johnstevenson1]

Seeing as we are back onto MILLING cutters can anyone explain to me how you cannot get all round contact form say a 10mm cutter being inserted into a 10mm collet ?

 

Now WORKHOLDING and because of the differences in size, it's not always 10mm work that goes into a 10 – 9mm collet you will get line contact. Usually 8 lines for a standard ER collet.

 

But taken that the majority of people USING lathes as opposed to Googling them or polishing they do so with a three jaw chuck which on a good day has three contact lines what exactly are we discussing here ?

 

What i found frankly obnoxious in this post when I made a statement about commercial tool holding and work holding at a local aerospace company is that I was called a liar. Incidentally certain posters on this forum have had trips round there so it's not just my word on this.

 

All that has been offered in return is Googled information. No hard and fast proof and references to collets systems that do exist but are out of the reach of most of the tight arses posting. Even if one was to spring for these expensive holding systems most would be hamstrung by the skimpy deep groove radial bearing fitted to their skimpy hobby machines.

 

I'm afraid though that this is more forum related than post related.

I go on a variety of forums and this one is the worst one of the lot for negative statements, Googling and Google links abound, far, far more than practical posts..

 

Home Shop Machinist, Mad Modder, HMEM, Model Engine maker etc, most have more posts per day than this forum of a practical nature with a very low negative count posts.

Whereas on this forum it seems to be driven by certain people with a negative agenda. The vast majority who NEVER post any work they do and if many cases I question is they even get out into a workshop.

Just looked on another couple of other forums about the MEX show, virtually all positive comments, a few point out what could be improved but in a conversation and not a negative vein but on this forum you get the impression they wasted their time and everybody else's

 

So think before you post and it you can't be constructive or practical then don't bother.

Edited By John Stevenson on 18/09/2016 10:26:10

[Chris TriceParticipant @christrice43267]

"Seeing as we are back onto MILLING cutters can anyone explain to me how you cannot get all round contact form say a 10mm cutter being inserted into a 10mm collet ?"

You can.

"I go on a variety of forums and this one is the worst one of the lot for negative statements, Googling and Google links abound, far, far more than practical posts".

I agree. I left this forum for 18 months because of all the negative posts about Myfords and Myford owners from one of the moderators.

[Raymond AndersonParticipant @raymondanderson34407]

John, We don't know why it's not possible to get full contact round a toolshank with ER's Thats what some are trying to figure out. It should be possible on a parallel closing ER collet but isn't. And I think there is a big difference in the 3 or 4 LINES of contact [lines, if the chuck jaws are good ] and the 8/ 16 POINTS of contact with an ER The chuck will apply a lot more pressure that an ER surely. There are a few on this thread that don't think it's a waste of time, me included. There are a lot of threads on here that I think would be a waste of my time, so I ignore them, simple really.

None of us members have the right to say what topics are discussed, you included. I happen to think the motorbike posts on here are of no interest to me but I wouldn't say it's got to be constructive or practical or else don't post., Crap ! And If you are alluding to me saying "No Way " or No Chance [ im not sure which ] in the workholding part of this thread , I never used the word "liar " And never would.

So please get aff the soap box.

cheers.

[AjohnwParticipant @ajohnw51620]

This thread seems to have degenerated into theory and some manufacturers claims – always a dubious thing to just take on face value but some people will be very happy to accept the them especially if they have bought the item or wish to.

There are some facts about collapseable collet systems. Unless sizes are exact and exactly round there will always be point contact. Point contact is point contact clearances don't change that. Exactness is something that generally doesn't exist at some measurement level so even at silly levels point contact is still point contact.

Some one seems to think that machines suddenly became capable of achieving high metal removal rates. The fundamental limit on metal removal rates given that the power is available is the cutter itself. The next one is cutting speed. HSS allowed higher metal removal rates than earlier tool steels. Modern cutter materials allow even higher ones. The net effect is more chips per second off the cutter. More power is needed on the machines to take advantage of this as the cutting speed is higher. Torque needed at the cutter edge same or in practice very probably higher. I used carbide face mills in the late 60's. They had been around for a lot longer than that. So what's new. A bigger selection of cutter profiles and coatings.

All of great interest to say Bridgeport etc owners or is it ? The gain at this level I hear is mostly finish. That comes from some one who now doesn't use anything else. I'll believe it when I try it. Variable speed Sieg's etc ???? Get real folks.

There has been one dramatic change. For pretty obvious reasons metal removal became rather unpopular. It wastes all of those chips. Then along came cnc and in some cases it was found to be economical to use metal removal techniques to save on tooling costs. In other areas the market would stand the increased cost of the finished article. It's much the same with flexible manufacture. It can't really compete with special purpose machinery but saves the cost of producing the machines to do specific jobs. The other change in this area is a big increase in machine rigidity. It's needed to obtain the finish that many items have to have.

John

–

[Neil LickfoldParticipant @neillickfold44316]

The collet blank is just from P20 tool steel. I put in 4 slits from the front to about 4mm from the back. Most times the parts are better than 0.02mm diameter and the 4 way slit is good enough. If more range is needed, I add 4 slits from the back and finish at the retract groove. The blackened collet chuck body, sits into 50mm bored softjaws that are torqued to 90NM on the M12 capscrews to keep it all the same. The hydraulic chuck pressure is set to #10 of 24. It was bored and threaded in the softjaws when it was made. It has dedicated softjaws and is always set in the same radial position. A really important and often over looked aspect of the chuck body is the concentricity of the outer thread for the nut and the 8 deg bored taper. If these are out, it will not work as well as when it is actually concentric. I make the thread to be quite a neat fit to the nut that is going to be used and only use the one bearing nut in this case, as it is used to hold parts and not cutters.

The plate sitting on the nut is the standard stop and can be used with the tube as an extension needing greater than 25mm diameter but less than 30mm. The cap-tube is the standard extension that takes 25mm diameter stop blanks and can be used with the other tube as an extra 75mm extension to the cap-tube.

I have made for carbide cutters with my CNC router which uses the ER16 collets, I made some shrink holders. They work really well. But I have access to the use of an induction heating unit which makes it easier to heat and get the cutters into the holder. Also I needed to modify the diameter of the collet at the front of the groove, otherwise you can't the nut onto the collet. There is a limit as to how long of an extension nose you can make and it's diameter in order to get it all together. I also made some other tools, like a 4 mm ball end with the ER16 shank to use as a setting piece to touch off with and finding the work piece position.

Neil

[Raymond AndersonParticipant @raymondanderson34407]

Certainly a well thought out piece of kit. very impressed. Neil , How are the blanks held for slitting ? obviously the ones that you slit from both ends have to be machined first then slit . The ones that are only slit at the front are they slit whilst still in the raw state, ie a bar before they are machined. The shrink fit holders you made will certainly provide a massive grip,. especially for use in a router. Excellent. work.

Ps, What is the make of lathe you use and does it have live tooling.

cheers.

[Raymond AndersonParticipant @raymondanderson34407]

Chris, You say you left this forum 18 months ago because of NEGATIVE posts about myfords and myford owners from one of the moderators, hmmm,,, Now I wonder who that could have been ?. I have a very good idea so we will just call him Mr Hypocrisy for now. or Mr Bumptious.[ either or ] any one of the 2 would be spot on.

Ps Any resemblance to any person living or dead, is purely incidental.

Edited By Raymond Anderson on 18/09/2016 18:36:14

[John Stevenson 1Participant @johnstevenson1]

Oh I'm pleased that has come up on this thread.
I'm 99.9% sure that's me.

But for the record I stated that Myfords are over rated and are living on a name. A point of view I still hold. A Boxford for example is a far better lathe and can be bought for half the price.

Why am I glad it's been brought up on this thread ?

Well there is no difference me saying what I do about Myford's and someone else saying there are better systems than ER's.

If there is a difference then it's  what I have said is better is actually cheaper, whereas what is being bandied about, on the ER's, for better is actually unaffordable to most of us here.

 

Edited By John Stevenson on 18/09/2016 20:20:49

[Mark CParticipant @markc]

I just created a fairly accurate model of one of my Er32 MT3 milling chucks and ran FEA on it. If I had not decided to change some of the loads I would have been able to post a photo of the load distribution but it will have to wait for the study to run which will take at least 45 mins. It does predict a clamping distribution that matches the picture of the collet with blue on (which is good as it is an expensive piece of software).

Mark

[Mark CParticipant @markc]

Ok, here is the predicted stress distribution for a 20mm collet (er32). You can see the stress is concentrated in 3 "rings". I have added a plot of the displacement (at exaggerated scale) which is also interesting

Mark

[Michael GilliganParticipant @michaelgilligan61133]

Very impressive work, and an interesting result, Mark

… The Location of the main pressure ring, just behind the groove, in particular.

… Is this effectively the 'pivot' when the cutter is loaded laterally, I wonder ?

I am a little worried though, by the displacement of the segements at 9 o'clock.

MichaelG.

[Neil LickfoldParticipant @neillickfold44316]

Raymond, I put a piece inside the collet that is about 0.01mm smaller than the bored collet. I just cut them slowly with a slitting saw on the cuter grinder, so not milled. Then debur them. I also make adapters from the ER40 to ER11 for holding 1mm drills etc. I also use them in the collet chuck when holding small parts, less than 6mm diameter. I wish that I had live tooling but it just has a 12 station VDI 50 turret, 6 outer and 6 inner.

Neil

[Raymond AndersonParticipant @raymondanderson34407]

Mark thanks for the FEA tests, very interesting, I also noticed the apparent displacement of a segment at 9o’clock was this as a result of the load test? Could you tell me what load was applied I am very interested in this topic Nice work.
Neil, many thanks for showing the set up certainly is very nice gear you have turned out, and very useful. I especially like the collet blanks and end stops Excellent.
Cheers.

[Mark CParticipant @markc]

The irregular displacement is a result of the displacement scale – the analysis was set to "automatic scale" . If I set it at scale 1 you would not see very much.

The maths going on in the background is quite complex (and a bit beyond me to be honest), the collet is subdivided into "elements" and this forms a "mesh" The shape of the mesh can be quite complex and often looks to be arbitrary. For this analysis I had it set to refine the mesh automatically so it refines it close to intricate features and leaves it coarse in plain areas with little in the way of features (slots small rads etc).

The load was set at 5 KN tension on the outside diameter of the chuck body and inside face of the closing nut to approximate the screw force from tightening the nut up. I chose alloy steels for the chuck and collet assy and carbide for the cutter shank. The whole assembly was provided with an "ideal" fixed anchor on the face of the MT3 shank (it is a requirement that something is fixed in simulation space).

I will attach an image of the whole thing in a moment and will try and load the word document report generated by SolidWorks.

Mark

[Mark CParticipant @markc]

Assy as promised….

[Mark CParticipant @markc]

i tried saving the report as a pdf but there does not seem to be any way to up-load it, sorry.

Mark

[MuzzerParticipant @muzzer]

Mark – one critical challenge with setting up an FE analysis is setting up the loads and constraints. In this case if I understand correctly you have applied loads to the "outside diameter of the chuck body and inside face of the closing nut to approximate the screw force from tightening the nut up". The difficulty is that as the load is applied, the force is transmitted through whatever surfaces happen to touch the 2 conical bores. I'm not sure where the forces were applied on the main taper but the distortion although exaggerated here would affect where the forces were applied and also the distortion resulting. Same is true for the movement of the collet segments against the bar, as clearly they would be constrained by the (line?!!) contacts with the bar surface.

The FEA you get with mid-range CAD is remarkably powerful given that it comes free with the installation (SW, Inventor, F360 etc) but you probably need some serious armchair tool such as Ansys to allow for the factors here.

Murray

[Mark CParticipant @markc]

Murray, this is not the free version of the analysis you get bundled with basic SW, I pay for this add-on (and it is a painfull experiance).

The analysis was done as an assembly not discrete parts although it was done at "ideal" sizes – all diameters started out co-radial etc.

Mark

[MuzzerParticipant @muzzer]

I've used the thermal FEA add-on for SW and I could understand the pain if I had to cough up for it. Mind you, Ansys would take the pain to another level.

I imagine it would need to know the modulus of the materials as well as the coefficient of friction between the 3 parts to model what happens. I expect you could set the nut and body to have very high moduli (ie very rigid) and the collet to have a realistic value for simplicity(?) given that it is essentially a spring. For a ground and hardened body and collet the coefficient of friction will be fairly low (0.2?).

Rather you than me though!

[Author]

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