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View Full Version : diff. threads + silly idea?



Tony
07-26-2004, 02:53 PM
the discussion on differential threads got me wondering... seems it would be relatively straightforward to add a 'fine adjust' to a tool post by adding a diff. thread via a dovetail mount between the toolpost and toolholder.

typically, when i need to take fine cuts, i swing the compound and get out the calculator.. my compound is held in place by 3 PITA socket head cap screws that are usually full of junk.

it'd be mighty convenient to have a fine adjust right at the tool.

potential problems, anyone?

-tony

motorworks
07-26-2004, 04:08 PM
knucklehead
If your compound reading is radius,that is if you move in 0.001" it takes off 0.002" on the diameter of your work,then
for "fine" cuts set your compound at 14.5^ and for each 0.001" that you move your compound, it will take off 0.0005" off of your work.
Or
Set up a dial indicator on your tool post for finishing cuts.
e

gizmo2
07-26-2004, 11:19 PM
Three cap screws that get full of junk, so what's going to keep the junk out of your new set-up? If it's rigid enough to work, my guess is it'll have some close tolerance parts, that will lock up pretty fast with just a little gunk. No reason not to pursue it, just something to keep in mind, maybe.

Forrest Addy
07-27-2004, 12:43 AM
If I have to dial off accurate increments on a slide I use a 1" travel indicator on a biscuit magnet. Smaller lathes will require a bracket or something to make it work but that's easy to whip up from odds and ends.

So long as the indicator plunger accurately aligns with the axis motion your adjustments will be precise.

BTW, just because you dial in exactly 0.0081", it doesn't mean the tool will take exactly 0.0162 off the diameter. Life is a crap shoot in the small stock reductions.

[This message has been edited by Forrest Addy (edited 07-27-2004).]

JCHannum
07-27-2004, 07:18 AM
Setting the compound at 5.75 degrees will result in the compound advancing 0.0001" for each 0.001" movement.
Setting it at a small angle, and working the trig will get you the same results. See The Machinist's Bedside Reader #1 for details.
You will still need to do test cuts because, as Forrest notes, actual metal removal depends on several other variables.

dsergison
07-27-2004, 10:28 AM
the crap shoot http://bbs.homeshopmachinist.net//smile.gif

I try really hard to plan my incremental adjustments such that they are relatively even when I try to walk up on a value.

like with about three passes to go if I measure precisely and say I need to remove .0345" I do it with a pass at .012, .011, remeasure to verify I'm on the right track, and a if i am a final cut a .0115

still miss quite often, darn craps.

/just in case it's news to anybody maybe?