Machinist Jacks

Apologize for posting to an older thread, but could you enlighten a newbie as to the purpose/thinking behind the coencentric grooves in the cap? The V-Groove I get, but are the circles there for a pragmatic purpose, or because they look great. (And they do!)

Thanks,
Newbie in Snohomish, WA
 
Red96 said:
Apologize for posting to an older thread, but could you enlighten a newbie as to the purpose/thinking behind the coencentric grooves in the cap? The V-Groove I get, but are the circles there for a pragmatic purpose, or because they look great. (And they do!)

Thanks,
Newbie in Snohomish, WA
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No problem, thank you for taking time to look at the post. So the concentric grooves in the cap are really there for looks more than anything else. I did turn the grooves at .600", .800" and 1.000" diameters, but they serve no real pragmatic purpose. Thanks again for looking and commenting!
 
firemaker76 said:
Thanks very much! The hardened 4140 has a beautiful finish. I really enjoy working with it.
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Kinda late to the game.

So, I was wondering how the surface finish turned out so nice. So it's HT 4140 then? Do you need any special tooling geometry for this?
 
dkemppai said:
Kinda late to the game.

So, I was wondering how the surface finish turned out so nice. So it's HT 4140 then? Do you need any special tooling geometry for this?
Click to expand...
Yes sir, this is heat-treated 4140. I didn't use anything special, just standard CCMT carbide inserts. I did however keep a healthy feed and DOC. I found out very quickly that trying to take very light passes or sneak up on the OD did NOT work and resulted in terrible surface finish. Instead, I opted to calibrate my DRO as I was cutting. Basically, I took a .030 pass, stopped the lathe (without moving the cross-slide), checked the OD with a micrometer and punched that value in to the DRO. I repeated this a couple times until my micrometer and DRO matched up. This method proved to be very accurate and got me within .0005" almost every time. The trick is to make sure you keep (at least) the last two passes at the same DOC after your DRO is calibrated. I'm sure some of the veteran machinists on the forum here can explain this better than me, but hopefully this helps out. Thanks for looking and commenting! Happy New Year!
 
I prefer TPG inserts for nearly all work, including stainless and 4140HT; with its sharp edges, very light cuts can be taken without work hardening, sure, they have less edges than other types of inserts, but they can be sharpened by hand on to radius with a diamond wheel.
 
I will hardly address single participants in a forum, we all sit at a really big table.
Some commenters feel 'late' input is a lower tier of involvement. Not so. Check the home page, there are how many posts - not merely original threads? Discount likelihood your interests expand, to the point interest and searches take you into different territory. Barring some calamity, this information isn't volatile, 'newbies' are born everyday, methods expand because someone experiments, even when some of those fail.

Point is, machinist jacks are invaluable. Depending on workpiece size, many unaware just how large those get, capacity in 1000's of pounds.

- Personally, use of jacks is more of an inspection necessity, on a surface plate; leveling a casting or compound angular features to pull measurements. Sorry to point out, that means 3 jacks are a set.
- 2 suffice but require a 3rd element (even if not adjustable) somewhat higher than minimum the adjustable pair can do. Note; few commercial sets offer that option, seeing only potential as setup components.
- Adaptable (different heads, feet & bodies) jacks should be the standard. That makes logical argument for a case containing all the bits, easily transported to work area. Have a minimalist trait? Use an empty soup can.
- Any that cannot be set lower than your vise bed are worth avoiding. Of variety being castings, they will lose thread depth (and load bearing capacity) if you consider shortening them. Cutting foot bottoms out the screw.
- Very few (commercial) have good proportions of decent thread diameter, and fine thread pitch. Shop made versions never seem to follow that mistaken intuition. Try leveling a 20" long workpiece .002 with 16 TPI - 1 revolution @ 0.0625th inch - 0.002 is a serious feat of dexterity (0.0003472 increments of a turn).
- Well done, close fitting threads deserve complement. But without holes for tommy bar or wrench flats, very hard to turn under moderate loading.
- The concentric ring pattern is more practical than cosmetic. Unlike gauge blocks, rarely a workpiece and jack are equally clean, those are recesses for dirt, and irregularities on castings. The user, while scooting jack, around detects stability.
- Sometimes that enlarged surface shifts part laterally as it turns; if pointed, averts that. Alternately, make cap independent of screw.
 
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