Acme Threads

mystry_tour · Post by **mystry_tour** » Sun Jul 30, 2006 6:43 am

Hey guys can anyone do inturnal acme threads. I am in need of a small block about 4" sq with acme threads in it I think I mesured it to be 5 TPI

nektai · Post by **nektai** » Sun Jul 30, 2006 7:38 am

Mystry,

No experience here with acme threads or even internal threads for that matter. I believe that Mr Douglas has done both and I bet he can provide good information on the procedure. What is the part for?

mystry_tour · Post by **mystry_tour** » Sun Jul 30, 2006 8:47 am

its a small block that sits inside a chanel.....an acme screw runs through it and shen turned it slides a cast piece that loosens and tightens a wheel for a stroke sander....it is a half block with a threded hole in the top for the casting to mount to. If i could get the block made I could mill the half block and drill and tap the hole myself. I am just not familar with acme threads

crzypete · Post by **crzypete** » Sun Jul 30, 2006 10:21 am

It is important first identify if you are dealing with acme or square threads. Acme has an angle, to the sides with a flat top, square are simple boxes. Sometimes it is easier to replace both the screw and nut rather than matching a real oddball thread.

Generally female acme is best cut with a tap- a two step tap to be exact, so having the exact measurement of what you need is helpful- diameter and TPI. Also of note when you talk acme is whether it is left hand or right hand thread- it's common both ways.

A good solution might be to mount a bought nut or plate to the block- much cheaper to have someone else tap an acme in an industrial environment. Plus this makes a fun welding project.

Pete

mystry_tour · Post by **mystry_tour** » Sun Jul 30, 2006 9:19 pm

Hey Pete. Wish I had red this befor leaving the shop. Now do I mesure the major dia of the acme rod that gos into the block or the minor. The TPI are 5 but I didn't think to ck if it is left or right hand threads but I will be over there Tues morning so I can check. Strighten me up on this. Right hand threads the bolt tightens and for left hand turning the bolt left or counter clockwise the bolt tightens.....and what is a 2 step tap.....never heard of it.

crzypete · Post by **crzypete** » Mon Jul 31, 2006 8:45 am

WIth threads you measure the major diameter of the male thread, ie, with a 1/4-20 bolt it will just fit through a 1/4" hole and has 20 thread per inch.

A standard bolt/ screw is right handed, left handed is the opposite, it sounds like you have the correct nomenclature. Left hand comes in to play with a number of leadscrew operations to make the movement feel correct.

A tandem tap is this:

http://www.mcmaster.com/param/images/ta ... 350x50.gif

It cuts a standard angled thread, then enlarges it to the chunkier acme thread.

Pete

mystry_tour · Post by **mystry_tour** » Tue Aug 08, 2006 10:37 pm

HEY Pete....I got to get another look at the threads on the part this weekend. They aren't acme after all they are square threads. Shouldn't I be able to cut those with a parting tool of the same with of the thread grove???
I think I mesured it at 4 tpi.

crzypete · Post by **crzypete** » Wed Aug 09, 2006 8:19 am

Unfortunately it is not so easy. A parting tool can only cut straight in- no relief to turn threads with. A great reference on this subject is South bend's "How to run a lathe" If you don't own the book yet, it is a must have for every home shop lathe user.

Here's the pertinent page. Notice the small little drawing of the angled tool- that is what you will need to grind- oh what fun!:roll:

mystry_tour · Post by **mystry_tour** » Wed Aug 09, 2006 11:17 am

Thanks pete. I do have a copy of the SB How To book by chance

didn't even think to look there. Guess i need to start reading up on that. Might even start practising a bit when the power gets turned on.....lol more shop time.
Oh check out the Oliver site