Truning an MT4 down to an MT3

According to Dave August :

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Not quite, I'm afraid. According to _Machinery's Handbook_:

MT3 0.60325 inch/foot MT4 0.62326 inch/foot

The only two of the Morse tapers which have precisely the same taper are the MT4-1/2 and the MT7 (0.62400 inch/foot on each).

Hmm ... maybe you were lucky. Do you have spotting blue? Blue up the arbor (as thin a layer as you can manage), fit it in the tailstock and gently twist it before pulling it out. That will give you an idea how close it is.

Since the MT4 has a slightly steeper taper, I suspect that you will find that most of the contact is at the large end -- which is at least better than most of the contact being at the small end. :-)

I would have expected that arbor to be hardened and ground on the OD of both the Morse and the Jacobs tapers -- you lucked out there, too.

Good Luck, DoN.

Hey Dave,

Ummmm.....you do know that MT3 to MT4 sockets (and other adapter sizes) are available. They are called "Extension Drill Sockets", and for instance from KBC Tools would be a KBC # 1-5161--045 .

page 406

Using them will lose you some "between centres" distance.

Brian Laws>I'm posting this because the question seems to come around here pretty often

A centre in the headstock is a _live_ centre. Honest!

The other trick is to mount a bit of stock in a collet and then turn a 60 degree taper on it. Only takes a few minutes more than taking a truing cut off a proper (soft) live centre, which you would do for precision work anyhow.

Regards Mark Rand RTFM

Don, as a matter of intrest, the 10 microinches per foot (an inch in 227+ miles) or

Don,

I spotted it with a Sharpie, and it looked good the me, I see contact down the full length of my surface.

Guess I was lucky.. I'll take it :-) But geez .020 difference per foot on the 3 inchs I turned is probably good enough... that works out to .005 over the length I turned...

Honestly when I did my measurement with the 3 basackwards to the 4 I got about .001 difference down the 3 inchs I measured, I chalked that up to my test rig...

And yeah I gave it a quick file test to make sure it wasn't hardened.. FYI al the MT's I have seem to be un-hardened..

Oh and funny I never though of digging out one of the three Machinerys Hand books I have and checking the taper specs.. DUH.. :-)

Dave

Brian,

Sure I know about those, I have several 2-3 and 3-2 an 2-1 from when I had a smaller lathe,

And as I said, my friend just thought I'd blow the 10 bucks and buy a MT3-Jacobs and replace it..

I said I just figured I had nothing to loose :-)

--.- Dave

Mark,

LOL.. Uh.. yeah... I'll guess it is... :-)

I thought about doing that, but figured getting a dog on the already tapered piece was gonna be a bitch...

I also thought about trying to get a good enough grip on the tang end in a collet (it is turned round), but it wasn't a nice size, IIRC it was like .970.. and I only have 1/16 collets... the .970 was just too small to "fudge" in a 1.00, and too big to "jam" in a 15/16.. now If I'd had a

21/32... I still probably wouldn't have done it.. :) Just didn't look like enough grip... which is probably wrong since I bet the surface area of contact was larger than what I had from the Jacobs jaws on the 1/2 CRS... I just didn't like how the contact would be on the collet, not enough surface on 2 of the sides... or worse only contacting 2 of the sides...

Did you miss that the second significant figure was different? That is 0.020010" difference per foot, or 0.001667" per inch, not merely

0.000010" per foot.

Yes -- I was surprised by the difference there and double checked the table from _Machinery's Handbook_. This was the table which gave the ASA tapers, which mix B&S, Morse, and Jarno, IIRC, and which is the only place that I've seen the MT 4-1/2 listed (which is what is present in my lathe's spindle).

Enjoy, DoN.

According to Mark Rand :

Though the terminology has drifted since the days when there were no ball bearing tailstock centers. :-)

Or -- chuck some stock in the 3-jaw chuck and turn the 60 degree taper, and that gives you a surface (the side of the chuck jaw) to drive the dog.

Since I've never found a 4-1/2 MT center for my lathe, I took the time to set up the taper attachment to match the spindle's taper, and turn a pair of adaptors -- one 4-1/2 MT to 3 MT (to match the proper tailstock), and one 4-1/2 MT to 2 MT (to match the earlier tailstock which I used when not using the bed turret until I got the proper tailstock. Both had the same bed fitting and the same center height, but the smaller one was made for an earlier Clausing with a smaller spindle thread. Mine came with a 2-1/4-8 spindle thread, and I later replaced it with an L-00 spindle, which is they one which has the 4-1/2 MT taper.

Enjoy, DoN.

you don't need forks to remove a Jacobs chuck from it's arbor. Simply open the jaws wide, drill a hole through the bottom of the chuck, 5/16 is about right, then place a 5/16 rod through the hole and 1. Hit it with a hammer, or 2. use an arbor press, or 3. use an air chisel with a long pointy chisel. out pops the arbor.

place arbor between centers and cut taper to suit.

Naa using the BP to make a "pickle fork" was MUCH more fun...

'cides I like to make tools and now I have one, don't forget I said I have several of the 14N's, eayser to make the tool than keep drilling holes in chucks.

--.- Dave

WOOPS!!!!!! ...lw...