Metric threads on the Atlas/Craftsman 6" and Mk2

[markba633csi]

I wanted to mount my Unimat collet chuck on my Mk2 lathe; the spindle has a MT2 taper. I have a MT2 x 1/2" collet and drawbar so I needed to make a 1/2" shank to 12mm x 1 male thread arbor to mount the chuck.
I found a metric chart for the Atlas 10F which uses the same change gears as the little lathes but I found several problems including the fact that I only have two of the required double keyway bushings, and it looked like the banjo wouldn't accommodate all the gears called for anyhow. Hmm, how do I do this?
Suddenly, I got it. Eliminate the 64T idler gear at position A and flip the remaining gears around, driving from the 32 tooth spindle gear instead of the 16. This drives the gear train at 2X speed which is exactly what is needed since the leadscrew is 16tpi instead of 8 on the 10F. Slick as bat guano on a shingle
Looks like this trick would work for several of the other pitches as well. I wouldn't try for 4.0 or higher- a 20 tooth gear on the leadscrew makes me nervous.
-Mark

 

[Bi11Hudson]

I have(had) a similar problem on a 12X36 Craftsman(101.27440). Different machine, different gears, same scenario. The machine has a full "Norton" change gear box. I also have the gears for a machine without QC capability. It can cut very close for most metric threading, about 5 decimal places. I also made a plastic 127/120 tooth set for true (to about 7 or 8 decimals) conversion. it's cheap plastic, not delrin. but will work when I need it.

There are(were?) 2 different banjos for the 12Xxx. I forget the machine number that didn't have the QC box, but it did have a more "complex" banjo. I acquired one and mounted ahead of the QC box. That and a few bushings and gear studs from Ebay and I was set to go.

The 127 tooth gear is the only way to get true metric conversion. 127 being a prime number, it's a little hard to come by. I made one by using a Modulus1 (25.4 DP) version from an Asian machine as a pattern. Most times, I run the "almost" conversion using smaller gears.

For the chuck(s), I have a MT-3 on the headstock. I took a Jacobs taper adaptor and cut it down to M12X1 metric for the UniMat chucks. Mine was a DB-200, the American sold machine of an SL-1000. I think. . . The small chucks aren't all that tight in the headstock, there's no stay bolt(EDIT) drawbar. But the small stuff I work that way I don't worry about. I haven't figured out how to drill (and tap) the small end of a MT 3 adaptor, short of boring all the way through.

.

 

[Ulma Doctor]

i like your thinkin' Mark

 

[wa5cab]

All Atlas MOLO's after 1957 include the Atlas or Craftsman 6" in the threading section. I have extracted just the 6" metric information and put it into Downloads. It uses two gears that are native to the 6", 52T and 44T. They have the same tooth count as called for in the conversion to all metric thread cutting on the 10" and both 12" when equipped with a QCGB. Some of you may remember that at the expense of not cutting 4 TPI, it allows you to switch between Metric and Inch by simply moving the sliding gear. The gear combo used is 52T and 44T which yield results almost as good as the 127/120 pair and are much easier to find and generally much cheaper. They also fit the 6" much better.

 

[markba633csi]

Arbor finished! Haven't measured the runout yet but it looks pretty decent
First single point metric thread I've cut-
-M

 

[wa5cab]

That looks quite good. My only suggestion if someone else needed to do about the same thing would be to first look around (including in the For Sale Forum on this site) for someone selling 2MT arbors such that the non-MT end was large enough to turn into whatever you needed it to be. Would save having to buy a 2MT x 1/2" collet if you didn't already have one.

 

[matthewsx]

Hi Mark,

Did you check runout yet?

John

 

[markba633csi]

John: Not yet, but I will soon as I finish some badly needed bench cleaning
I'll mount a dti on the compound and check the chuck taper itself
Robert: Yes a pre-made MT arbor blank would be handy; it would need threads on the small end for a drawbar

 

[wa5cab]

Well, if it didn't already have the 3/8"-16 threads, they would certainly have to be added (Never Ever attempt to use a Morse Taper cutter holder that is not drilled and tapped for a drawbar. Sooner or later it Will (not Might) come loose. But any decent (by definition) MT arbor intended for use in the headstock will already be drilled and tapped. If one isn't, don't buy it.

 

[Manual Mac]

When I adapted the 3 & 4 jaw 2-1/4” chucks from my early DB-200 to my SB9C & my 6” rotary table, I needed a MT-3 taper for the SB & a MT-2 blanks for the rotary table & I wanted to use my 3/8-16 drawbar on my SB & short bolt/draw bar for the RT.
I think I used MT dead centers, (may have used MT chuck arbors, I can’t remember, been too many years) which I put in the SB spindle & turned down the business end to the max thread size of the M12X1.
Anyway, I then put the chuck back on the lathe & chucked up the now short straight end and drilled & threaded the small ends for 3/8-16, for the drawbar.
I was then able to put the arbors in the spindle pulled tight with the drawbar & thread the MT adapters M12X1
As I could not thread metric, I matched best I could, 26TPI is an almost exact fit for M12X1.
I use these small chucks for many small jobs, there is no runout & I had no trouble turning & threading the arbors.
This worked for me, YMMV