Half inch does not equal 12mm
|jonathan olley||30/04/2019 21:30:44|
|21 forum posts|
Hi, i have come across an issue i wondered if any of the good folk out there would help me with. I'm a novice, so words with few syllables i can just about cope with... I am attempting to machine a cast Iron casting on the cross-slide of my ML7R using an original Myford 2mt 1/2"collet to hold a 12mm end mill. I realise that 12mm is 0.472 of an inch but had read somewhere that the collets closed approximately 0.5 of a mm so i thought it would work and hold the End mill in place. As it is, the fit is somewhere between a ‘sliding’ and a ‘location’ fit and therefore not suitable for fear the tool would work its way out. I guess I’ve answered my own question as to why this set-up has failed but wondered if anyone had any good ideas for a way to proceed? Since I am only taking very light cuts to reach a depth of no more than 0.059in, (1.5mm), is it ok to hold the end mill in the three or four jaw chuck and proceed with caution? Alternatively, if I bought a 1/2in cutter as I probably should have done in the first place, would the collet system work as it is supposed to? Thank you for any advice you can give.
|Michael Gilligan||30/04/2019 21:41:29|
14289 forum posts
" ... but had read somewhere that the collets closed approximately 0.5 of a mm so i thought it would work and hold the End mill in place."
jonathan ... please don't believe everything [you think that] you have read somewhere: That ^^^ only applies to collets like the ER series, that are slit from each end.
The Myford Morse Taper collets are intended for exact sizes.
YES ... the 1/2" shank cutter should be fine
Edited By Michael Gilligan on 30/04/2019 21:42:56
|Tony Pratt 1||30/04/2019 21:43:04|
|935 forum posts|
The 'Myford' type of collet will only hold the nominal size, i.e. a 1/2" collet will only hold a 1/2" shank or yes you can use a 3 or 4 jaw chuck to hold the cutter.
|John Haine||30/04/2019 21:47:48|
|2700 forum posts|
Original Myford collets are like hen's teeth and expensive. However you can buy ordinary MT2 finger collets quite cheaply to get the exact size. They can be held in by a drawbar (use threaded rod) or even using the Myford collet closer, though you don't get the self extracting feature with that.
|David George 1||30/04/2019 21:57:24|
977 forum posts
Hi Jonathan you would not be the first person to hold a cutter in a three jaw chuck but it depends what you are cutting. If it is tough steel you may have problems but if it was aluminium or brass you may get away with i but you should get a cutter to fit the collet or a collet to fit the cutter. If you were to ring Tracy tools you coukd get a reasonable prices cutter probably next day delivery is it worth risking a cutter moving to ruin the job an d nay be ruining the cutter as well.
|Phil P||30/04/2019 22:09:29|
|531 forum posts|
I am looking for a 3/64" Myford collet if anyone has a spare, once I obtain that elusive one I have a full set.
I will probably never use it, but it annoys the hell out of me that I dont have one !!
|1138 forum posts|
If you can't find one you could try and make one?
Edited By Thor on 01/05/2019 05:51:18
16587 forum posts
When I started out I held milling cutters in my 3-jaw working on iron & steel so it can be done but a 1/2" cutter in your existing collet would be better.
|Neil Lickfold||01/05/2019 08:18:31|
|575 forum posts|
You can make adapter bush, and hold other cutter sizes using a close fitting split bush. The bush needs to be in your case 12.70mm diameter or slightly larger at 12.75mm OD , with an ID of 12.00 max and a min of 11.96mm. The bush will need to be split.
|roy entwistle||01/05/2019 08:39:32|
|1066 forum posts|
Neil All due respects but do you realise how thin the walls of that would be ?
|Swarf, Mostly!||01/05/2019 08:56:20|
|499 forum posts|
Sounds like a wrapping of shim-stock to me!
|John Haine||01/05/2019 09:20:08|
|2700 forum posts|
I don't know if that size is available as a standard MT2 collet, but looking at these it does look to me as if it should be possible to cut a groove for the Myford retaining/removing nut at least on the smaller size collets which have more meat. Would probably need grinding rather than grooving tool. Might be a project for someone with a toolpost grinder?
|Martin Kyte||01/05/2019 09:29:55|
|1515 forum posts|
Make a split collet by all means but for the 3 jaw. You get to choose your own wall thinkness then.
Alternatively buy an ER collet set for the Myford nose, use a 1/2' inch shank end mill or if you are making flat surfaces on your casting use a fly cutter.
|jonathan olley||01/05/2019 10:58:48|
|21 forum posts|
To all of you that replied; Thank you so much for your time and consideration. I shall probably buy a 1/2" cutter as after a brief online search, there are quality HSS cutters new from £15.
Again, all your advice much appreciated. j.o.
|Neil Lickfold||01/05/2019 11:32:09|
|575 forum posts|
There is a trick to making thin wall parts for sure. It is best if you have a tube of metal to go inside the bored hole for support back into the main piece of material. Then you can turn down the OD to suite. If it is a long bush say 50mm long, then a long bar with a centre support will be needed. Make sure it goes into the solid part by about 5mm or more if using a centre, and about 1 /2 diameter long if not centre supported. Then the OD can be measured as it is internally supported. Dont use the same grade of metal for the sleeve support, ie free cutting steel sleeve with a free cutting support. It can pick up. I use castor oil between the inner and support sleeve. With this method you can make parts that have a wall section of around 0.1mm, is the thinnest wall I have made. But with a 12mm sleeve and 12.7mm od, with sharp tools, the outer can be turned in 1 final pass of 14mm down to 12.7 . The heavy wall will self support the part for about 2 diameters long. After that it will want to fail. If the tools are not sharp enough, it will deform and make the inside smaller.
1286 forum posts
+1 for the the simple, straightforward and obvious solution. The rest is over-think.
Edited By Bandersnatch on 01/05/2019 18:30:34
3794 forum posts
Bit of shim wrapped around the cutter as suggested should work ok. As will holding cutter in three jaw chuck if it is in good condition. I do all my milling the latter way. No problems.
|Andrew Moyes 1||02/05/2019 08:29:56|
|108 forum posts|
My old Myford catalogues say 'Collets are available in 64th increments in sizes 1/16" to 1/2" and from 2 to 13 mm in 1/2mm increments." So I don't think a collet as small as 3/64ths was made and would explain why you can't find one. I hope this helps!
|Howard Lewis||02/05/2019 13:17:51|
|2460 forum posts|
The only collets that I am aware of that will accept Imperial and metric of almost the same dimensions, are ER collets. Most of which can accomodate a difference of 1mm (0.0393" ) They are marked with the size range, such as "12 - 13"
If the collet carries only one size marking, it will be damaged if forced to accept anything smaller or larger!
As already advised, use a larger collet and a split sleeve, or make up a bush, and split it for use in the 3 jaw chuck, (But make sure that you always put it into the chuck in the same place. Usually, mark for No.1 jaw and always fit it here, to maintain concentricity. )
|Phil P||06/05/2019 11:29:31|
|531 forum posts|
You may well be right about that, I recently bought a 3/64" collet from "Myford" on ebay, only to be refunded and told it was out of stock. Maybe they never had one in the first place !!
I would be interested to hear from anyone else who actually has one just to confirm either way if they were ever available.
Edited By Phil P on 06/05/2019 11:30:22
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