Quick question about MT sizes..

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haggard616
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Quick question about MT sizes..

Post by haggard616 »

I'm going to eventually buy one of the cheap HF or Grizzly mini mills. They use an R8 collet. So... I want to make a draw bar for my 8" South Bend, and I want to be able to use the same R8 collet set. I'm going to weld a bolt on the end of the draw bar that's 7/16 or 9/16 by 20tpi, don't remember off hand. Anyway, the bolt will thread into the R8 collet holder, which is a MT#3 if I'm not mistaken. The spindle through hole on my South Bend is 3/4". So I want to make sure a MT#3 will fit my spindle before I commit to this idea. It's hard to find the correct wording to use when searching online for the diameter of a tapered object as it's sort of a conundrum. I guess I'd like to know the small diameter on the end of a MT#3, but u don't know if the diameter on the end is constant or not? If I know the small diameter, I can then figure out how much purchase I would get on the collet holder in my spindle hole. Thanks in advance!
haggard616
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Re: Quick question about MT sizes..

Post by haggard616 »

Excuse me, by "collet holder" I meant Collet Chuck.
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Harold_V
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Re: Quick question about MT sizes..

Post by Harold_V »

Personally, I'd question the value of being able to use R8 collets in the spindle of a lathe. To my knowledge, there's a narrow selection of sizes at your disposal, and you're limited as to lengths that can be inserted (because such collets require a draw bar instead of a draw tube). If you are not aware, such collets are quite limited in the size they'll grip properly, with a recommendation to not exceed ± .001" from nominal. While you'd find the setup useful for a limited number of applications, it would be a false saving in the long haul. However, if your objective is to use the lathe as a mill, gripping common shank sizes of cutting tools (end mills, for example), it would make sense. I would encourage you to investigate other collet systems, so you have the degree of flexibility that collets should provide.

Harold
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Inspector
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Re: Quick question about MT sizes..

Post by Inspector »

By no means am I an expert but I am pretty sure there are no MT3 chucks that use R8 collets.

There are ones that will hold an ER32 series collet. When you get the mill you could get a R8 chuck to use the ER32 collets in it too.

http://www.shars.com/products/view/307/ ... let_System

You can get MT3 collets that will work in the lathe with a drawbar but the sizes they come in are limited. Probably the most economical way to use collets in your machine.

http://www.shars.com/product_categories ... er_Collets

There were collet setups to use 3C collets in the South Bend 9" lathes that may fit your 8". Poke around ebay.

Pete
Glenn Brooks
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Re: Quick question about MT sizes..

Post by Glenn Brooks »

You can check all the standard taper sizes in the reference section at littlemachineshop .com.

All morse tapers have a standard minimum and maximum size and are listed in a table. Also you can google mores tapers and find the dimensions...

R8 collets were developed by Bridgeport specifically for mill quills and are mostly universal on mills, but not used at all on lathe head and tail stocks. You might check your lathe and verify what taper is used...
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SteveM
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Re: Quick question about MT sizes..

Post by SteveM »

The Pros of MT3 collets are that they are cheap, easy to make a drawbar for and can go up to 3/4".
The con is that you can't pass long stock thru the spindle.

The ER adapter shown has the same pros and cons, with the additional pro that you don't need nearly as many collets, as the grip range is larger.

If you are planning to mill in the lathe, get MT3 end mill holders, as end mills can walk out of a collet (don't ask how I know).

Someone has an ER collet chuck mounted to a plate onto which you mount a backplate and then it threads onto your spindle like a 3-jaw. That system allows you to pass stock thru the spindle (and up to 3/4" stock - 3C collets only go up to 1/2" generally, although you can find 9/16").

You can get a MT to 3C adapter, 3C collets and a collet tube on ebay and make your own drawbar. All you will need is a handwheel which you can pick up on ebay or any flea market.

Steve
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rudd
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Re: Quick question about MT sizes..

Post by rudd »

"Someone has an ER collet chuck mounted to a plate onto which you mount a backplate and then it threads onto your spindle like a 3-jaw."
I bought one for ER 40 from Jeff a tools4cheap, he doesn't show any right now, might pay to ask him - he is VERY good to work with.
I just noted that littemachineshop is carrying some.... http://littlemachineshop.com/products/p ... uctID=2532

I have an ER40 collet chuck on my vertical mill, and the ER40 chuck-on-a-plate set up on the 13" SB - which lets me pass 1" stock through the headstock. I've been very happy with this set-up, other than I need to buck up and buy a bunch of the "in-between" size collets for holding work in the lathe. Right now I've got it by the 1/8ths and a couple of 16ths.

on edit - you might note you might need an adaptor to use MT in the headstock of the SB. Not sure if this applies to the older SB's like your 8". SB (1940 on) uses the same taper per inch, but very short, a regular MT sticks out too much. You would then get the next smaller MT size - i.e., my headstock is MT4 in taper, but requires an adaptor, so if I used MT collets, they would be MT3. Theres a guy in Illinois that makes and sells the adaptors, but it is something top consider.

before I found the "ER40 on a plate" I'd considered getting one of the straight shank ER holders, bolting a fairly thick hunk-o-steel onto a back plate and boring it for a heavy press fit on the large diameter of the ER chuck, cutting the "tail" off the chuck, and pressing it in. Might have worked.
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