Machinist Jack

[PJs]

This machinist jack was a quick gift for my brother. Not as pretty or versatile as others, like Pauls beautiful set but more about seeing if and how well I could turn 4140 on the peanut (mini). I've had a piece of 1" I got for another project which was kind of burning a hole in my pocket to give it a try, so off I went. I was also inspired by Brians ring gauge and the discussion of chatter and turning tools.

Years ago I had a Starrett "Little Giant" jack set and liked the versatility of it so I wanted to model the bases for it similarly for my brother. I haven't made the other parts for it but they can come later and the screw is a bit rudimentary, mainly because I didn't have any hex stock the right size to make one.

The first thing I had to do was cut off a piece of the bar so it would fit in the mini and would like to give a shout out for the Diablo Steel Demon blade I picked up a while back for the saws all!! Excellent finish results and felt like cutting aluminum!

Most of this I did on the fly and the pictures are mainly of the finished pieces but it's pretty self explanatory. I did mic it all at the end and put it in my sketch book to make a drawing from it and the future attachments.



Starting with a piece about 3.5" long, I used my bump roller to get it as true as I could then faced it off both ends and took a couple of clean up passes on the OD with a HSS bit. The top piece is tapered at 36º inclusive...not sure why, just was aesthetically pleasing. I used carbide TCMT inserts for hogging off most of it then switched to HSS for the final couple of passes. As you can see I got a bit of chatter in the middle section but think it was due to slop in the compound. All that was necessary was to use a 240 grit sponge and about 30 seconds with some crocus cloth to get what you see here.

Next was to drill (Q bit) and tap the hole for 3/8-24. Started with a center drill, went to a 1/4" and drilled as deep as I could, then to a 5/16" bit and finally the Q bit. Started the tap in the lathe maybe 6 threads. The mic'd the length of top and base plus enough for the counter bore and shoulder. Held it with a live center in the tail stock and proceeded to part it off by creating a groove where the shoulder would be on the bottom piece (shoulder diameter). Then moved the carrage over about a 1/16" (width of parting tool) and finished parting it off.

Once parted I reversed the top and faced it off to begin the counter bore. The mistake was using a carbide tipped boring tool. I should have taken the time to grind a HSS one because as I was getting into the last pass or two, it Hogged in on me. Ended up having to take it out a little further than I wanted to match the diameter of the bottom shoulder. It ended up with .015 radial clearance instead of .002-3 I wanted. Still works but not my best from being in a hurry. You can also see more chatter internally from the carbide.

Finished tapping the hole on the bench, then re-bored the bottom piece to a "W" bit for close tolerance through hole on the 3/8 screw. The screw was the only hex I had (3/8-24 x 1.5) so I faced the head and underside with an undercut at the top of the threads so I could be flush with the top with or without the nut. The nut was from 1/2" hex brass and made it .236 thick.

All Done I decided to blue it with some Birchwood Casey blue. A bit blotchy on the bottom piece but shouldn't rust. These are the finished shots.



Basically it can range from just over 1.6" up to about 3.8" safely.