|Bill Dawes||20/01/2014 19:27:49|
|384 forum posts|
Hi all, having received financial sanction from my 'accountant; I am looking (at long last) at a new milling machine.
I am getting a bit confused over tapers and collets terminology. First of all the machine options are MT3 or R8, both either metric or imperial.
What I am finding confusing is all the tooling options available, MT, R8, 5C, ER which are then ER11, 20, 25, 32 etc.
What goes with what?
19538 forum posts
MT or R8 are the female tapers that the mills spindle can have so any tooling to be used will need to have a corresponding MT or R8 male taper such as a drill chuck or flycutter.
When it comes to holding cutters you then have a few more options, These could start with a range of MT or R8 collets with the advantage of a short projection but they are size specific so one collet fits one size only.
To get a bit of a better range you can buy an ER collet holder with a suitable MT or R8 shank to go in the machine and a range of collets to go in the other, as these collets each cover a small range thay can be used for things like drills or holding imperial cutters in a metric range of ER collets. The various ER numbers increase as the max capacity of that range increases so would depend on teh size of mill.
5C tooling is not used in the mill spindle but mostly on the lathe though the 5C collets can be used to hold work on the mill table
|Mike Poole||20/01/2014 21:46:29|
2845 forum posts
Although it is in common use on hobby milling machines the morse taper was designed as a self holding taper for drilling. To use the MT for milling a drawbar will be required, but this is true for most vertical mill toolholders. The problems arise if the drawbar is tightened enthusiastically and then the MT can need a good whack to release which will not do the bearings in the head any favours. The R8 still requires a drawbar but releases easily and was designed by Bridgeport for milling. The ER collet chucks are widely available and are ideal for end mills, slotdrills and parallel shank drills and any parallel shank tooling or setting aids. If the nose to table distance is not generous R8 direct collets can win a bit of extra height. My personal choice on a Warco VMC was R8 and an ER chuck, I also have an R8 shank flycutter and an R8 shank boring head. This is not usable on my Myford lathe which is MT2 but I accepted that when I made my decision to go R8. The ER collets I use on both machines which is useful but I had to make or buy an ER chuck for the lathe.
Edited By Michael Poole on 20/01/2014 21:48:08
|Gone Away||20/01/2014 22:22:15|
|829 forum posts|
I have a very similar setup but my mill started life as MT2. I got fed-up with that and converted to R8 which I'm much happier with. My left-over MT2 tooling I use on my ML7 one of which is an MT2 collet chuck which can be very handy in the tailstock .... I have collet chucks for the spindle that screw directly on to the nose.
[ I recently needed to remove a ballnut from a ballscrew. I made a keeper for the ball nut and held that in the tailstock collet. The ballscrew I held in the spindle collet. Moved the tailstock up to put them in contact and locked it. Unscrewed the ballnut onto the keeper. Easy and no chance of dropping balls. ]
314 forum posts
As a beginner I did quite a bit of research when I decided to buy a mill a year ago. It seemed obvious to me from reading lots of threads on here that for my use the R8 was the sensible choice. I bought a Sieg SX3, but if you are looking at smaller mills then R8 might not be an option. A lot of people suggest that they chose MT so that tooling can be transferred between lathe and mill but this didn't apply to me. In fact, I've got ER25 collets for the lathe and ER32 collets for the mill. I also got four R8 collets included with the mill but I've not needed to use them yet. Plenty of room above the table for what I'm doing at the moment.
|Tony Ray||20/01/2014 22:54:28|
|138 forum posts|
I have an SX3 with R8 spindle and an ER32 collet chuck. Whilst the ER 32 is useful now & again I find the R8 collets better for holding milling cutters requiring much less effort to close tightly around the tool. ER collets are known to require a fair bit of effort to close.
|58 forum posts|
I use an ER 40 collet holder on my Mill with a MT 4 taper and an ER 40 collet holder on my Lathe with a backplate.
My ER 40 Collet set is 3mm-30mm.
|Douglas Johnston||21/01/2014 09:55:20|
716 forum posts
I also got the choice of Morse taper or R8 when I bought my Myford VMB mill some years ago and felt I made the right choice with R8. R8 collets are cheap and readily available and release very easily. They give excellent grip with greater rigidity due to minimal overhang from spindle bearings. I woud strongly advise R8 over MT3.
|1747 forum posts|
My two mills have MT2 & MT3 tapers which I am careful not to over tighten and I think if I was buying a 'new' machine I would prefer R8 for this reason.
However, on the MT2 taper mill, I normally use a MT2 Clarkson Autolock - because some years ago I managed to ruin a large (and expensive) work piece, when the cutter was "pulled" from the collet chuck (probably because I was over enthusiastic with the depth of cut). I do have a MT2 ER32 collet chuck but prefer the Clarkson for this reason - although I've not had a cutter move in the ER when using non-Clarkson cutters.
On the MT3 taper I use direct holding collet holders made from MT3 blank arbors, which have two large grubscrews to retain the cutters (which have matching notches ground in them. I've not had a cutter move using these either but I am careful with them.
Before I had most of this kit, I used MT2 collets (the direct holding type) and these do have one very good advantage in my view, in that they effectively reduce the "overhang" between the lathe/mill 'nose' and the cutting end of the mill (when compared to other collet holding systems) - so are very useful where chatter is found to be a problem as they make the set-up a bit more rigid..
Edited By IanT on 21/01/2014 10:15:19
|Gone Away||21/01/2014 15:33:36|
|829 forum posts|
Known by whom? Not by me and I have several sets for both lathe and and mill. If you are anywhere close to the nominal size for the collet the effort is minimal - in fact the usual admonition for ER collets is "don't overtighten, just nip it up" because it's so easy to do that (overtighten). On the lathe, if I'm facing a bunch of small parts and swapping them frequently I simply hand-tighten without using the tools.
If you are working at the low end of the collet's range you do have to put a number of turns to take up the slack on the nut, some of which may require the wrench. But by no means would I describe it as a fair bit of effort. And for milling cutters, with a limited range of sizes, it's easy to buy individual collets of the exact sizes needed if you don't have them in the set.
|Andrew Johnston||21/01/2014 16:12:30|
5828 forum posts
By the manufacturers. The ER collet system was designed for tool holding, where the shanks are generally hardened, not for work holding. For ER32 here are the recommended torque figures from the Rego-fix website:
|Gone Away||21/01/2014 16:40:00|
|829 forum posts|
136 Nm ..... say 100 lbf.ft in old British Units on an 8mm collet. I'll take your word, Andrew, that that's "known" to the manufacturers:I don't know how relevant they are to the hobbyist. It sure isn't what I use (tool or work holding). Anything like. (I don't even think I - personally - could apply that much torque with the standard wrench). And I know from experience that the cut-out on my mill will pop before the cutter slips. On the lathe, the belts will slip first.
Like I said, "known by whom .... not by me".
|1747 forum posts|
My milling disaster was before ER collets were in more common use - so I was using some other form of collet holder (too long ago but not an Autolock type) and the mill was equipped with a Bridgeport head. I'm very sure I'd tightened it as far as humanly possible (because it was a bad habit I had back then) but even so, the cutter didn't just cut slightly over depth, it dug a very large gouge out of the work piece as the cutter 'walked' itself out of the collet and I was very lucky (in retrospect) to have not damaged the machine or break the 1/2" end mill.
So I wouldn't bet really big money that an ER collet chuck will never slip and not all "hobbyists" are using low powered machines. I try to be gentler with my tools these days and part of that involves taking smaller cuts!
|Howard Lewis||21/01/2014 18:14:25|
|4125 forum posts|
Being a "faster" taper, R8 releases more easily than Morse. (The International tapers for Industrial Milling machines are even "faster", but the drive to the cutter is via dogs on the holder, not the taper).
2 MT is a bit small, unless you have a small Mill.
So here are my experiences, if they are any help.
My Mill/Drill is 3MT, which matches the Tailstock on my Lathe, so allowing tool holders/drill chucks to be interchanged, if so wished.
To avoid belabouring the bearings in the Mill head, I turned down some of the lower part of the spindle pulley retaining nut, and made an "extractor" which, when needed, is fitted by two 1/4 BSF setscrews, to a plate surrounding the lower part of the nut, with a 1/4 BSF forcing screw to act on the slightly slackened drawbar.
If the forcing screw does not "break" the taper, a light tap with a mallet then does.
For tooling with a tang, the usual taper drift is used to release it.
Having bought a 2MT ER25 collet holder for my previous Myford ML7, this is now used with a 2 -3 hollow adaptor in the Mill/Drill.
If needed for the 2MT Rotary Table, a home made separator with a 1/2 UNF forcing screw removes the adaptor.
In the lathe, ER 25 and ER32 collet chucks are on home made backplates, which allow work to pass through the chuck, and into the mandrel bore.
With regard to tightening torques, I could not apply 100 lb ft to any of the ER collet nuts with my chuck spanners, but have not had plain shank end mills, up to 20mm dia. (16mm shank) work their way out.
But it is surprising just how tight the nut has to be to hold a tap firmly, in my home made ER25 Tailstock sliding Tap Holder on the lathe.
(Yes, I did lap the bore with emery tape around a collet, to get a good fit!)
But a useful safety device which probably avoids broken Taps!
The choice is yours!
|Bill Dawes||21/01/2014 18:49:47|
|384 forum posts|
Thanks guys, excellent replies, the mist is clearing.
Tony & Gary, the Sieg Super X3 is the one I am looking at, hoping for a trip up to ARC In Leicester in the next week or so. How have you got on with yours?
|Stub Mandrel||21/01/2014 19:06:50|
4311 forum posts
The tightening torque seems to be very dependent on the type of nut. I use a C-spanner with slotted nuts and a tommy bar in the chuck.
To hold cutters with shanks of around 10-13mm and plain nuts I found I had to apply plenty of force.
Since changing to ball bearing nuts I find ER25 easy to get nice and secure with much less force. The release force is never more than wrapping my hand around both tommy bar and spanner and squeezing hard.
314 forum posts
As this is the only milling machine I've ever used, I'm not sure my observations count for much but here goes. I bought the long table version which Arc have since stopped supplying (not sure why) but the rest of the machine is the same as the SX3. I find the extra space on the table useful as I can leave the vice bolted to one half of the table and have the other half free for clamping work direct. So far, I can't find anything to complain about and I think this mill should be capable of doing any work I'm likely to ask of it. When I first got interested in model engineering I bought a mini-lathe and am now wishing I'd gone for something bigger (upgrade looms). The only minor thing I've done to the mill is to add four M12 washers to the X-axis feed handle to keep the dog clutch permanently engaged (see below). I think a DRO system might be on the horizon. A borrowed engine crane was handy for lifting it onto the bench.
|Bill Dawes||22/01/2014 17:53:00|
|384 forum posts|
Thanks for that Gary, just out of interest do you know why the dog clutch? I assume it does not have a power feed to the table, or does it?
314 forum posts
One can be fitted to the other end of the table, but at £300 I don't think I'll be fitting one in a hurry. It kept disengaging while traversing quickly.
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