Machinist Jacks

I finally attempted threading away from the chuck tonight and I won’t be going back! I was able to thread at 365rpm (I may try higher next time) and no worrying about crashing in to the part. I think the threads turned out well as well

d3bbc075680497b2a6f9d89f3348c179.jpg

0abd9a1c29314db4e91dac02d45fef90.jpg


Thanks for the tip


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Ben17484 said:
I finally attempted threading away from the chuck tonight and I won’t be going back! I was able to thread at 365rpm (I may try higher next time) and no worrying about crashing in to the part. I think the threads turned out well as well

d3bbc075680497b2a6f9d89f3348c179.jpg

0abd9a1c29314db4e91dac02d45fef90.jpg


Thanks for the tip


Sent from my iPhone using Tapatalk
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Awesome and great work! Glad to hear that worked for you.
 
Correct me if I'm wrong, but since I have a thread on chuck mount, threading away from the chuck is not recommended. Wish this was a real option for me.
 
dkemppai said:
Correct me if I'm wrong, but since I have a thread on chuck mount, threading away from the chuck is not recommended. Wish this was a real option for me.
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Yes, that could definitely be a problem. I have read of some guys doing it, but their chucks had locking clips. Even then, I wouldn't take the chance.
 
Sorry for bombarding your thread with questions, but am I right in thinking that being able to have a higher rpm whilst threading enables a larger depth of cut? Or does it not work that way?


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Ben17484 said:
Sorry for bombarding your thread with questions, but am I right in thinking that being able to have a higher rpm whilst threading enables a larger depth of cut? Or does it not work that way?


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On a small lathe or small diameter workpiece it may well work the opposite way.
The ideal is to be able to match the cutting characteristics of the cutter with the workpiece and stay within the capacity of the lathe.
By cutting characteristics I mean speeds and feeds. By capacity of the lathe I mean stiffness and power.
The fundamental advantage of threading away from the chuck is not having to worry about crashing the tool into a shoulder or chuck. If you're threading toward a shoulder, the tendency is turn the RPM down, so the carriage is slow enough for the operator to prevent a crash. If threading away from the shoulder, you can probably turn the RPM up to speed up the process and optimize the other factors.
 
Ben17484 said:
Sorry for bombarding your thread with questions, but am I right in thinking that being able to have a higher rpm whilst threading enables a larger depth of cut? Or does it not work that way?


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No worries Ben,
I wouldn't say that necessarily. As 'extropic' explained, speed and feeds and stiffness and power all come into play. You have to find that sweet spot for your machine, and that depends on several factors. One benefit to threading away from the chuck (besides NOT crashing your lathe), is just the fact that now you can pay much more attention to the little details. It allows you to relax some and really watch, feel and listen to how your machine is running and reacting, and this is extremely important in finding that "sweet spot" that will produce the nice threads you're after. Time and patience my friend.
 
firemaker76 said:
So another tool crossed off the 'To Do' list. Made a pair of machinist jacks, and wanted to post a few pics.
I started by turning down some 1.250" diameter Heat Treated 4140 and made the screw/head pieces first. That way I could measure my thread pitch and make sure it was within proper 2A specs. Then I drilled the top of the heads to accept some .375" diameter bushings with a .0005" press fit.
After that, I turned the jack bodies down to 1.200". With the screw threads already done and within specs, I was able to bore and thread the bodies 3/4-20 and get a very smooth and precise fit with zero slop. Then I turned some grooves along the outside of the bodies for aesthetics and better grip. These were parted off and faced to an OAL of 1.750".
The extensions are made 1.000" long with an upper shoulder for the body to sit on and a lower inner shoulder in case another extension needs to be added. The shoulders mated up very well.
Finally I made some caps and drilled and reamed the bottoms to .375". This allowed them to engage the head bushings and spin freely. I also put several varying-sized diameter grooves around the top and milled a .075" deep V-groove through the center of the cap. This allows smaller diameter stock to engage the groove and sit dead center when supported by the jack. I did not realize how handy and necessary these little jacks were, but I use them all the time now.
One more quick note...I also attached a magnified pic of some chips from the 4140. I spent more time trying to remove these little monsters from my shop broom than I did actually building the jacks. Now I know why LOL. Take a look at the teeth on those chips!

Thanks for reading guys and Happy Machining!! Be safe.
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Thanks! Great write up!! Thanks for sharing.
 
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