Craftsman External Power Feed Mod

M

Michael B

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I’m a newbe hobbyist to this site & I’m sure I will get answers to a question I
have. I own a Craftsman 12”X 36” Quick change lathe. I saw a video on youtube
named MACHINE SHOP TIPS #83 by Tubalcain that has the same lathe I have, &
I liked his idea very much of power feeding lead screw from tail stock end.
I had a question but since I couldn’t contact him, here I am. To mount his
pulley he made a coupler, which I think was screwed onto lead screw after
removing the lock nut. I also have the same square side ball bearing lead screw
support like his. With the nut removed there is only 1/2” of lead screw exposed.
The nut is to remove any lead screw, end play movement or maybe preload the
bearings, lightly. After all this, my question is while watching his video, what
keeps this coupler from over tightening or backing off lead screw. I saw no set
screw in coupler on lead screw end, I did see a support for pulley end. I plan
to use gears, & think that small 1/2” will not need that support, once I know how
he made the lead screw coupler, still adjustable without a set screw. I guess he
could have drilled thru the pulley shaft end, & added a hex screw. What ideas do
you have, & do you think I should add an end support for a gear hanging on
1/2” of lead screw around 2” passed end of lead? Also I'm a very slow typist
(one finger) so my replies maybe slow.

Thanks for your time
Michael B
 
Michael,

I think that he has a 3996 or 101.28990 (I have the former). I've never bothered to watch that video but my guess if I wanted to do this (I don't) is that he drilled the coupling shaft through and tapped it through. Then after adjusting the lead screw thrust bearing preload properly, ran a socket head set screw into the hole to lock the coupler against the end of the lead screw. If instead you put two set screws into the side of the coupler, be sure that you put a lead shot or a brass plug into the screw holes before you put the screws in the holes. Like the ones in the screw holes on the threaded collar holding the spindle gear on.

Yes, you will need a bearing to the right of the gear or pulley on the coupler. Else you will eventually bend the threaded end of the lead screw. Which will be an expensive mistake to make.

But why do you think that this is necessary or even desirable?

Robert D.
 
The Tubalcain video says that the built in feed speeds are undesirably fast
 
wa5cab said:
Michael,

I think that he has a 3996 or 101.28990 (I have the former). I've never bothered to watch that video but my guess if I wanted to do this (I don't) is that he drilled the coupling shaft through and tapped it through. Then after adjusting the lead screw thrust bearing preload properly, ran a socket head set screw into the hole to lock the coupler against the end of the lead screw. If instead you put two set screws into the side of the coupler, be sure that you put a lead shot or a brass plug into the screw holes before you put the screws in the holes. Like the ones in the screw holes on the threaded collar holding the spindle gear on.

Yes, you will need a bearing to the right of the gear or pulley on the coupler. Else you will eventually bend the threaded end of the lead screw. Which will be an expensive mistake to make.

But why do you think that this is necessary or even desirable?

Robert D.
Click to expand...


Robert D. thanks for the reply & sorry I forgot to log out before. I thought the same, a screw in the end of his coupler, but with a smaller allen screw from pulley end, because I believe his pulley bore was only 1/2". I think the two set screws would be the best. I was hoping I wouldn't need an end support, but after thinking what you said, I do agree. You ask why I wanted this motor drive. The slowest feed speed on this lathe is .004 ipr & with a variable DC motor I can get down to .001 ipr or less & get the finer finish I'm looking for, & not have to listen to gear noise. I think mine is also a 101.28990, would you know it's age?

Thanks Michael
 
You can also add additional gears to your banjo and make the lead screw turn slower also. If you add an additional 16/32 gear it would slow it down in half and you could still use you qcgb for threading, just divide the setting by 2.
 
Rob,

I was going to say the same thing. Although the only time I ever felt that the feeds were too fast was for milling and parting off. A much more useful trick would be to figure out a practical way to run the cross feed at the same speed as the longitudinal feed.

Michael,

I hope that you do realize that you cannot make usable threads with s separate motor driving the lead screw. As far as gear noise goes, it never bothered me. And for finer finish, there is another way to do that that is a lot cheaper and easier. Use a cutter with a relatively large radius on the tip for finishing cuts instead of a sharp nosed cutter.

On the machine age, post the serial number in the sticky serial number thread up at the top of this forum and I can probably tell you within a couple of years. The 3996 and 101.28990 were made from late 1967 until early 1981. My 3996 was made in 1980.

Robert D.
 
I can't offer you much help but i'm very interested in your project. I've been looking to do something very similar but haven't had time since summer. The reason why i'm interested is trying to achieve a feed rate of .0005 IPR for deep hole/gun drilling (not related to firearms).
 
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