MT2 collet slipping

[mgjParticipant @mgj]

The problem almost certainly won’t the MT slipping, it will be the tool in the collet. – lets not revisit the reasons why. I don’t want to get drawn, but it is a very common problem.

 

The real answer is a proper milling chuck, or an ER collet chuck and collets, but you can get nicely made 2MT single diameter toolholders with a grubscrew that work very well. They are quite cheap – in fact a set of 4 to cover the normal diameters is probably less than a milling chuck.

 

The other quick fix is to buy a 2MT soft centre (or make as suggested above), drill and tap for a drawbar, put it in the nose of the Myford, and then drill and ream to size for the cutters. Again – hold with a grubscrew. The little FC3 cutters are very very good for that.

 

Or, for a small donation to YDMES new track fund, you can have my Autolock and its 4 imperial collets, because I don’t use it. Then you can make a holder to fit the FC3 cutters which are much cheaper than the Clarkson threaded type in the smaller sizes, and that puts them straight into the Autolock, as if they were 1/2″ endmills. You can get Clarkson metric collets quite easily.

 

[Roderick JenkinsParticipant @roderickjenkins93242]

I once had a problem with a slipping 2MT end mill holder that drove me bonkers until I eventually sorted it out. It turned out that the draw bar was overlong and bottoming on the thread in the 2MT holder rather than tightening against the end of the spindle. The difference was so subtle that there was no obvious gap. Slipping a couple of washers on the draw bar solved the problem.

 

My Sharp Mill has a spindle with a 2MT and a Myford nose thread, the idea being to use the Myford 2MT collets. I’ve never found this to be terribly satisfactory for holding endmills and I had a 1/2″ mill come out in use, destroying the collet in the process. Getting a replacement was very expensive. Like MGJ I much prefer the Arrand type endmill holders with a reamed bore and a set screw . They work very well although they take up more headroom than the Myford arrangement . In my professional capacity I use a small Denford CNC mill and this has ER16 collets that are very secure for holding cutters.

 

I like using the Myford collets in the lathe and tend to buy PGMS these days.

 

If I were starting again I’d go for a set of ER25 collets with suitable chucks for use in the lathe or the mill. Then you have a choice of using imperial or metric cutters.

[mgjParticipant @mgj]

RJ we rather agree.

 

In particular the setscrew set up works very well on the smaller sizes of cutter. What the effective limit is for that arrangement, I don’tknow, since my larger (indexable) endmills have been set and crosspinned into R8 arbors.

 

My mill does still have its drive dog BTW. Others may feel its not necessary (though that begs the question as to where all the missing drive dogs or setscrews went), but when you do your university bit and they go through mechanisms and tapers, they often use machine tool tapers for experiment because they are so portable. Having done the maths for them, one knows fine well what they do and won’t do, which rather dispels the old wives tales.

 

I think too you are very wise to keep away from ordinary collets, again despite what some may or may not believe a manufacturer might do. Thank ou also for illustrating EXACTLY why I made the brave man comment earlier. Its a bit like a woman buying a pair of evening shoes and expecting them to do duty climbing Snowdon. Collets are excellent for fine light work, like reaming , edgefinding, some drilling, centre drilling and the like. They are not very good for holding milling cutters under milling loads. Again I don’t expect to be beleived, so I’d simply refer the doubters to TC’s book Milling Operations in the Lathe, where a number of the deficiencies of the plain 2MT collet are outlined.(Not that its the only publication by respected engineers to do so)

 

I also agree entirely about the ER collets. I wish I’d gone that route originallly, because you get collets which will hold cutters, its a drill chuck, and I imagine would also do duty for slitting saw arbors and the like . And they can go in the lathe too. So its probably the most flexible accurate and cost effective option.

 

 

 

 

 

Edited By mgj on 11/02/2011 18:22:52

[Gone AwayParticipant @goneaway]

I’ve been using regular end-mill holders in my mill but I’ve recently been trying an ER-25 collet chuck to save having to swap end-mill holders.

 

It works quite well but I do find I need to have 3 hands …. one to hold a wrench at the top of the quill to stop rotation; one to tighten the collet chuck; one to stop the end mill from dropping out until the collet gets compressed sufficiently.

 

(I am though using metric collets with inch cutters so I have some slack to take up).

[KWILParticipant @kwil]

Sid, You should be able to hold the body still enough by hand to get the initial bite which holds the cutter or even hold the cutter with one hand and swing the nut by hand, not the wrench, to get it all started. That is what I do when I use the ER..

[Gone AwayParticipant @goneaway]

No, I tried that, KWIL. The quill rotates long before the collet is tight enough. Even if I hold the quill between my thumb and forefinger and use my pinkie to support the cutter then tighten the chuck with the other hand (manually or with the wrench), the quill still slips in my hand before I can get any “bite” on the cutter.

 

I don’t doubt that I wouldn’t have the problem if the collet were size-on-size to the cutter and I’ll pick up some inch collets the next time I see some that are affordable (for me, considering that my metric ones do most everything I want).

[mgjParticipant @mgj]

Yes you do get that – there are some specific sizes where the inch equivalent is at the bottom of the range for that collet. Can involve quite a bit of winding then.

 

I was wondering – can you get the mill into slowest speed and use that as a lock?

 

A slightly longer term option would be to make a carrier for a cutter, and make that a close fit to a suitable size of collet. On my mill I have (in theory) standardised on the 1/2″ (Posilock) collet, so I have knocked up carriers for al the small FC cutters/edge finders etc I use. Means you very rarely have to change collets. (And in the ER application you’d get minmal take up problems) Just pick a collet that will cover the range of most uses.

 

Doesn’t work for everything – my .125 thich slitting saw for making forked rod ends is on a 5/8 shank arbor. Horses for courses but that gets over a lot of problems.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

 

Morse taper collets only work properly when they have the correct amount of flexibility to allow the active gripping part to close down almost parallel . The actual problem usually is that the thinned section between the gripping section and the drawbar engagement section is left too thick and/or the slits are any of too short/too few in number or not cut right through into the bore .

 

A 2MT collet which is going to be sucessful in holding a cutter will (when out of the spindle) close down sufficiently by hand pressure to grip a correct size bar so tightly that the bar cannot be turned by hand .

 

Use of plain tapered and tapered plus parallel collets for holding cutters is common practice in high class milling machines – apart from the well known R8 ones the W12 – W20 – W25 series collets are found in Schaublin and other super quality milling machines .

 

Tubal Cain’s explanation of the action of collets is only partly true – a correctly designed taper collet holding correct size bar closes down almost parallel . The severe gripping at one end which he describes only occurs to any great extent in conditions of gross misuse .

 

 

[Gone AwayParticipant @goneaway]

Posted by mgj on 12/02/2011 09:59:39:

Yes you do get that – there are some specific sizes where the inch equivalent is at the bottom of the range for that collet. Can involve quite a bit of winding then.

It’s not the winding per-se but the torque involved which is the problem – easily sufficient to turn the quill which then has to be restrained by one of my free (three?) hands. It’s not a great big deal really – I can wind the head down far enough to put a block of wood under the cutter to stop it dropping out, leaving (all) my hands free.

 

Bit of a nuisance is all but arguably better than changing regular milling holders.

Edited By Sid Herbage on 12/02/2011 17:21:37

[David HaynesParticipant @davidhaynes53962]

Hi All,
Just thought I’d let you know the collet situation, after over 3 weeks since first going down the collet route. I contacted the supplier, RDG Tools, (who also supplied the cutter). They are a good firm and they’ve been happy to take the MT2 set back and exchange it for an ER32 collet chuck that screws on the ML7 mandrel. I also managed to pick up a few used good condition ER32 collets. Instantly I have found a massive improvement; no more having to take off the change wheel cover or use a draw bar and complete grip of the cutting tool with only hand tightening the chuck. And the other surprise is how the cutter obligingly auto ejects when I undo it all!

Thanks,
Dave

[KWILParticipant @kwil]

Dave,

 

If hand tightening will do, why do they supply matching spanners for the ER nut? It might be OK for light turning but any milling cutter use could easily pull the cutter into the job when taking a half decent cut.

[Anonymous]

I think most people would be surprised at the recommended torque levels for ER collets holding milling cutters. See the following link:

 

http://www.techniksusa.com/metal/torque_chart.htm

 

That’s why spanner flats are provided!

 

Regards,

 

Andrew

[David HaynesParticipant @davidhaynes53962]

Thanks for that. Not fair of me to tease though; I omitted to put the usual caveat after “complete grip of the cutting tool with only hand tightening the chuck. However, the nut should be then tightened as appropriate with the correct spanner”

Dave

[mgjParticipant @mgj]

Unless one only uses straight flute cutters

 

KWIL has a very good piont.

 

With a drill one is downfeeding so you are applying a pressure downwards, and the job is exerting an equal and opposite force upwards, and that is pushing a drill back into the chuck or taper.

 

With a milling cutter (often) you havent got that reaction – you are holding the cutter while milling a slot, and therefore there is a net outwards force. In a Clarkson type collet the cutter is held by being screwed in against a centre point, and it tightens with use. You don’t have that in a ER set up. The cutter can move forwards because of the helical flutes and vibration – because its not physicaly locked against the end/axial forces generated.

 

So I think one would agree, a nice firm squueze with a spanner would be very wise, (well essential really) without resorting to gorilla tactics.

 

 

 

 

 

 

[mgjParticipant @mgj]

Apologies – posts crossed.

[KWILParticipant @kwil]

With a drill down feeding….just like when you apply a non backed off drill into brass/copper/bronze

[VersabossParticipant @versaboss]

Posted by Andrew Johnston on 19/02/2011 11:50:38:

I

http://www.techniksusa.com/metal/torque_chart.htm

 

Can you trust them when they don’t even know the correct units for torque?   …

and for those who eventually don’t get it: ft/lbs it ain’t!

Greetings, Hansrudolf

[mgjParticipant @mgj]

Exactly KWIL – exactly. If you feed fast enough you maintain the load.

 

I used to back of my drills – even posted a pic on these forums of how to do it, but backing off and then resharpening became a PITA, and I thought about  the problem a bit from first principles.

 

So now I don’t. The danger bit is when you stick the drill into the centre hole and it can jump – and it should do if i’m right because the load is taken off. So now I just do a dimple, and feed such that I’m feeding faster than the drill cuts and the pressure is maintained. Don’t use a pilot either – just a really sharp 4 facet bit that cuts to size. No more grabbing.

 

(Same with parting off – if that reaction is maintained it won’t grab.Start applying a forwards force with high rake, or let the pressure off – feeble feed and it’ll jam up).

 

All this grabbing and binding is a forward force pulling the tool forwards into the space created by a tad of backlash in front of the feed nut. If you apply pressure it can’t grab because the feed nut is being forced back . If in so doing the system is going a bit quick, cut the revs – oh and feed alot of coolant to stop thermal expansion causing a grab – but thats a different phenomenon.

 

All backing off is, is just a smart name for a blunting the drill, which reduces the rate at which it cuts. Same detail – as we all know, feed faster and you reduce the effective rake – same principle, more convenient. Steel, gunmetal, bronze who cares – same bit different speed and feed rate.

Simples.

 

Give it a go and you will see what I mean.

 

 

 

 

,

 

 

 

 

Edited By mgj on 19/02/2011 15:24:54

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by Versaboss on 19/02/2011 13:44:32:

Posted by Andrew Johnston on 19/02/2011 11:50:38:

I

http://www.techniksusa.com/metal/torque_chart.htm

 

Can you trust them when they don’t even know the correct units for torque? …

and for those who eventually don’t get it: ft/lbs it ain’t!

Greetings, Hansrudolf

 

Hi, found the leaflet for my Teng Tools 70-350 Nm torque wrench yesterday, guess you can’t trust them either.

 

Regards Nick.

Edited By Nicholas Farr on 06/03/2011 08:14:49

[joegibParticipant @joegib]

Does anyone know the “correct” units for torque? (Rhetorical question)

 

I recently got interested in stepper motors in connection with a project I’m undertaking. Going through the manufacturers/retailers spec sheets defining various torque values for their products proved to be a maddening exercise. It seemed as though each one was employing different units for specifying torque!

 

In the end I resorted to an on-line torque converter to carry out comparisons — this one here:

 

Torque Converter

 

Somehow it didn’t surprise me that the software provided no less than 17 different units for specifying torque!

 

I hasten to say I’m not trying to start a torque war. Torque, torque not war, war.

Joe

Edited By joegib on 06/03/2011 11:24:00

[Nicholas FarrParticipant @nicholasfarr14254]

Hi joe, all them in your link look pretty valid to me. Obiviously when dealing with very small screws ect. Nm or lb/ft, lbf/ft, ft,/lbs or however you wish to term it, is a bit heavy handed, so you would use grams or ounces. Just use whichever is suited to the application, however Nm or KgM are often prefered.

 

Regards Nick.

 

 

[Keith LongParticipant @keithlong89920]

Hi

What Hansrudolf is referring to is that the units should by distance ( feet) MULTIPLIED by force (pounds force) not what is shown as ft/lbs. That actually means distance DIVIDED by force, which whatever it is, it certainly isn’t torque!

As Nick says the figure that Joe has found are all valid and which you use depends on whether you’re working in the mks, cgs or imperial system. The use of cm instead of m or inches instead if feet , ounces rather than pounds and grams rather than kilograms or newtons allows you to specify torque in sensible numbers without having to use powers of ten in the figure which usually leads to confusion – and stripped threads!!!

Keith

Edited By Keith Long on 06/03/2011 15:28:01

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Keith, I understood the reference, but I have also seen it written as ft.lb as shown on the leaflet in the photo I’ve posted, in many maintenace specs that i’ve come accross.

 

The usual way to write it is lbf.ft. Which is as you say is pounds force X feet. However while the forward slash is often considered as a devision it is a matter of interiptation as I’ve also seen it written as lb/ft, which also suggests it is pounds devided by feet. It is widely known that it is pounds X feet or feet X pounds. Funny but everyone seems to print Nm correctly, but metric is regarded easyer to understand.

 

Regards Nick.

Edited By Nicholas Farr on 06/03/2011 17:00:11

[Gone AwayParticipant @goneaway]

Posted by Nicholas Farr on 06/03/2011 16:54:12:

Hi Keith, I understood the reference, but I have also seen it written as ft.lb as shown on the leaflet in the photo I’ve posted, in many maintenace specs that i’ve come accross.

 

When (long ago) I received my education, using ft.lb for torque or lb.ft for work were considered schoolboy howlers. The convention was always the reverse even though the dimensions are the same.

 

Wouldn’t surprise me if there has been some relaxation since those far off days though.

[mgjParticipant @mgj]

Agreed.

Ft lbs (f) is pretty common.

 

By my maths it doesn’t matter if you multiply X x Y, or Y x X, the answer is the same!

 

Metric is a lot more consistent -much easier to do the load  calculations in metric. I still munch metal in imperial though.

 

Howlers – well so many different people are writing specs – what matters is getting it wrong, not how its wrtten! One jsust has to be a bit flexibe and adapt a bit?

Edited By mgj on 06/03/2011 17:32:45

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