MT4 drawbar thread dimensions?

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ErichKeane

Making scrap at ludicrous speed.
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Hi all-
I bought a couple of new things for my new lathe tailstock (some chucks and a live center). All are size MT4. However, 1 of the chucks and the live center call themselves "CNC" ends, not "Tang" ends, so pulling the tailstock all the way back doesn't eject them (and doesn't have a spot for a wedge).

I, figuring this was a standard thread, bought a pair of M16x2.0 tang ends off amazon, which everyone advertises as the MT4 ends. However, it fit in neither of these! One had screw in the end that seems to measure on my threadpitch gauges as 1.25 thread pitch (didn't get diameter). The same screw does NOT seem to thread into the end of the other.

Does anyone know if there is a 2nd or 3rd standard for these??
 
Morse Taper collets & arbors that are intended to be used in a mill with a draw bar come both ways, imperial & metric. I'm not sure about the metric sizes but for imperial sizes commonly used in the US, MT4 uses 1/2-13" & MT2 & MT3 use 3/8-16"

I just did a quick search online & it looks like MT4 can be found with more than 1 metric size as well as whitworth for drawbars.

I'm not sure about your chuck but live centers aren't used in a mill with a drawbar. So for that MT4 live center I don't think you'll find a standard as it can vary by manufacturer & is not made for a draw bar thread. Most live centers don't come with a tang. They have a screw or cap or solid end. The cap normally found on non light duty model is usually a cap used to cap off access to the internals. The ones with a screw can be used to adjust the length of the arbor for ejection but is not actually a tang.

You're probably better off measuring the threads & make your own "tang", for the live center at least anyway.
 
ErichKeane said:
One had screw in the end that seems to measure on my threadpitch gauges as 1.25 thread pitch (didn't get diameter).
Click to expand...

The diameter would help. 1.25 is a really fine thread for an MT4 size. There are some not very common metric extra-fine and extra-extra-fine threads, but 14 mm is the only one with 1.25 pitch. I just can't imagine someone making a draw bar thread that uncommon. Measure the pitch and diameter in both pieces since the screw doesn't fit both.
 
darkzero said:
You're probably better off measuring the threads & make your own "tang", for the live center at least anyway.
Click to expand...

That was my original plan until I saw the pitch was metric :)

The screw cap in the end of the one is only 2 threads which makes it particularly difficult to measure. I feared these would be oddball enough to not be able to get a die or bolt at the hardware store(turn down head of cap screw, locktite a hunk of steel on the end, mill it into a tang).

The m16*2.0 was about the right diameter, but locked up about a quarter turn in.
 
Turns out 1 is 5/8-11, i had a bolt left over from another project that fit! I'll be able to attach a tang to that one. The other might be M16x1.5 instead of M16x2 (not 1.25 like I'd initially thought), so hopefully I can just get a bolt of those dimensions at the Ace Hardware near me.
 
Confirmed that they are M16x1.5 and 5/8-11. I bought a bolt that fits in each at the local ACE. My plan at the moment is to turn a reduced diameter on each bolt, then loctite on a bigger piece of steel. Then, use the mill to cut the sides of the tang. So, I've got a plan at least :)
 
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