Logan 400. Headstock. (Total Logan 400 Rebuild)

[wa5cab]

MJ,

Are the collets 3C or 3AT? I don't have any 3C extras but have quite a few extra used 3AT because I've several times bought misc batches on my way to getting a full 32 or so piece set. If they are 3AT and you want me to check whether or not I have any that you're missing, send me a PM with the list.

Robert D.

 

[Mister Ed]

Very nice. I'm glad my lathe is not all apart ... I would not get it back together this summer. Bought a, new to me, Jet 8x36 mill and have yet to actually put it to work.

 

[mjhenks]

Robert,

I believe what i have are 3C collets as i believe the unit came from a South Bend. The Adapter for the spindle though fits the Logan. At least it sure seems like it does. I did a comp on the adapter and the MT adapter i pulled out of the spindle a few months ago and they look very close as far as taper and diameter.

Once i get the apron back together i can do some testing.

What is the whole collet set anyways? Seems like 1/2" is the biggest you can likely fit in there. I have 6 unique sizes and lots of duplicates.

 

[wa5cab]

MJ,

3AT and 3C, if unmarked, are easy to ID. I have one or two collets that are odd lengths but two Hardinge drawings that I have copies of give the length of the 3AT as 2-5/16" and of the 3C as 2-11/16. That length figure is to the large end of the taper, so does not include the swell of the radius on the large end. Which is about 1/16" and 3/32" respectively. The threads are so close to the same (0.637-26 and 0.640-26) that most draw tubes will fit either one.

Another document from Logan gives the max capacity of both families as 1/2" round, 7/16" hex and 11/32 square. In round, both are or were available in 1/64" increments so a full set would be 1/64" to 1/2", or 32 pieces. However, collets under 1/16" are rare, maybe because the machines that the collets will fit are a bit large to be working on anything that small.

The collet closer adapters are most commonly made to fit a 3MT spindle taper, so any of them would fit any lathe with a 3MT taper in the spindle. 3MT spindle taper usually means about 25/32" bore so most draw tubes are 3/4" OD. Most handwheel operated draw tubes can be made to fit any of the lathes that the adapter will fit by adjusting the length of the beveled spacer/thrust bearing.

Robert D.

 

[mjhenks]

Robert,

Thank you for the additional information. My collets measure about 2-9/16 in length and are Hardinge and CMC brand. Honestly was told that they were 3C and am taking it on face value. They came from a South Bend. I have 6 unique sizes and about 10 duplicates.

My draw bar is about 6" too long. I cannot tell for sure but i believe it has been adapted from something. The hand wheel has been re-welded and an extension added to the back side with cross holes. Likely i will cut it short and re-thread it for the Logan.



Matthew

- - - Updated - - -

How much hand wheel slop does your apron have???

So i finally got the bushings made and installed in the apron. I am still not 100% happy with them but they will do for now. I think the bore into the cast iron should have been done better. For now though my lathe has an apron again. Yaaa!!!

So how much slop does your hand wheel have. See below.



By feeling behind the apron i can tell that most of this is gear to gear or gear to rack slop. How much is normal though? When threading the weigh of the handle going from end to end in the slop puts load into the system and changes the pitch. I am sure it will also affect finish on normal cuts as well. (Or i may just be looking for perfection.... Not sure which yet :thinking

When i started working on the apron bushings i had 10x as much slop so the bushings have corrected most of it. After these pictures were taken i shimmed down the rack by about .028" which helped a little more.

I also got some mounts for my AXA tool holders and made a mount for my draw bar parts. All mounted right next to the lathe. Just have to find a home for the actual draw bar.



Matthew

 

[mjhenks]

In doing more research i realize my collets are 1A collets which is why they are shorter than the 3C. 1A turns out to be the South Bend version of the 3C collet. The only difference is the length which is ~1/8" shorter. Hence why my collet measure shorter.

Wonder why they did that.:thinking:

 

[Mister Ed]

Looking good Matthew! I have some backlash in my hand wheel ... but can't sit here and say how much. I have never noticed any effect while the half nuts are engaged (I don't thread a bunch either).

 

[wa5cab]

Yep, you're right. Had I looked at the other collet dimension chart that I have, I would have spotted that last night. Sorry.

As to why they did it that way, probably the same reason that any other manufacturer makes parts that don't fit other brands. Trying to generate a captive customer base.

On modifying your drawbar assembly to fit, I think I would to it the other way. Making the proper threads inside the cut off drawbar is not going to be a trivial exercise if you have to single-point it and the proper tap is going to cost a fortune even if you can find one. If the thing is really about 6" too long, and if the existing threads are OK, I would cut off the other end and bore the handwheel to fit. Initially, as I doubt that there are any standard dimension charts floating around, I would drill and tap the handweel hub for several set screws. Once I got the length set to suit, might later go back and have it welded or brazed. A good rule of thumb is when the collet is properly closed on a nominal diameter workpiece, to have at least one half but not more than three fourths of the threads engaged.

Robert D.

In doing more research i realize my collets are 1A collets which is why they are shorter than the 3C. 1A turns out to be the South Bend version of the 3C collet. The only difference is the length which is ~1/8" shorter. Hence why my collet measure shorter.

Wonder why they did that.:thinking:

 

[mjhenks]

Looked over how i could shorten the draw bar today. No chance at passing it through the head stock and being able to single point it. No chance of getting a .641-26 tap.

Best idea i had was to clamp the back side of the handle, put the shaft in a steady rest and attack it that way. Sounds interesting....

After looking it over i realize that the shaft, front and rear have been added to the handle. This has already been modified. The rear short shaft is welded in place. No idea what it would be for. It has cross holes in it for some purpose. The front shaft was brazed in place. They bored out the seating diameter for the back of the spindle and brazed in a new shaft. That i can work with.



Time to get out the MAP gas and un-braze the shaft. Shorten it and braze it back on. I think at the same time i will evaluate removing the short shaft from the rear.

 

[wa5cab]

MJ (please sign all posts),

Not that 0.001" would matter much but the thread spec is 0.640"-26.

My guess is that the short tube sticking out the back side of the handwheel is for set screws to steady long thin stock. I would cut it off flush with the weld and then face the hub back to original. You should be able to chuck on the draw tube or on the machine side hub. Then, assuming that the draw tube is long enough, cut it off flush with the small diameter of the thrust bearing (thrust bearings should be a slip fit on the draw tube, not brazed to it). Next, cut off the thrust bearing and bore it to fit the tube. Cut off the short stub of draw tube. And bore the handwheel through to a slip fit on the draw tube. Finally, as you might want to use the closer on 3C and/or 3AT, I might use set screws in the wheel hub instead of brazing the tube again. Of course, you could also make three thrust bearings of different lengths or make one plus two ring spacers.

Robert D.