Crossfeed Rebuild: Straight or Acme Thread?

Uglydog · Feb 1, 2015

I'm rebuilding the Crossfeed on a 16x30 Boye and Emmes with a factory taper attachment.
She had Straight thread.
I've read about Ball Screws, and understand they are a bad option for this application.
As long as I get the pitch correct, is there a reason I should stay with Straight Thread instead of going with Acme?
My local metals supplier as Acme in stock.

Thank you,
Daryl
MN

Mcgyver · Feb 1, 2015

what's a straight thread? Square or 60V or something elose or maybe a spline??

moonlight machine · Feb 1, 2015

You want to check out Green Bay Mfg. Proper Acme lead screws and nuts. The thread to nut fit could not be better, as long as you are doing it you might as well make a good job of it.

Uglydog · Feb 1, 2015

Mcgyver said:
what's a straight thread? Square or 60V or something elose or maybe a spline??

Sorry, my error.
I've heard it called straight thread (likely inaccurate).
It's square thread.

Daryl
MN

Uglydog · Feb 1, 2015

thermite said:
'Conventional' vee thread forms are meant to hold things. In one place. For their duration of service. ELSE be replaced when need be. Flywheel bolts and such. May be used for but ONE assemby cycle, then new ones fitted with new or rebuilt flywheel. Cost has to be kept low accordingly.

Acme threads are meant to MOVE things. Often. All their long lives. Cost more to make, don't make good fasteners, but earn their keep where appropriate.

Crossfeed is to move now and then?

Use Acme. Everyone else did. Even cheap-arse cee-clamp makers

Bill

Explanations can't get much simpler than this.
Thank you.

Daryl
MN

Uglydog · Feb 1, 2015

moonlight machine said:
You want to check out Green Bay Mfg. Proper Acme lead screws and nuts. The thread to nut fit could not be better, as long as you are doing it you might as well make a good job of it.

I appreciate the prompt to check out Green Bay Mfg!

Daryl
MN

CBlair · Feb 1, 2015

As long as the pitch is the same I see no reason why you would not want to use the Acme thread. If the pitch is off your dial wont read correctly and your power feed would be off as well. Of course if there is some reason they chose a square thread over the acme then I cant imagine what that reason could be. Unless they were shooting for a finer pitch than is possible with the Acme form?

Charles

Uglydog · Feb 1, 2015

thermite said:
They would not have been easy to execute well, but lots of 'Old Iron' justifies going that extra mile just to prove that if THEY could do it then, we still can do it NOW. Preservation of will and skill as much as metal.

Bill

Bill,
As someone who values the old stuff. This sounds like a dare to cut some Square.
I might be up to accepting the challenge, never done it before. Hmmmm, how much scrap can I make?
A quick PM and google search gives some pointers. I know don't have any vintage texts on this topic.
Does anyone have any Tips and Tricks, or are you aware of any publications addressing the subject?

Daryl
MN

iwananew10K · Feb 1, 2015

The nut is the killer.

johnoder · Feb 1, 2015

Both the L&S and GK have square threads cross slide/compound/tailstock

PDW · Feb 1, 2015

thermite said:
Pictures, please, if you cut a square thread and well. It hasn't been all that common for a while now.
Bill

I don't get that - square thread has to be the easiest thread form to cut. Here's the steering gear for my boat - 2 TPI LH square thread. Just grind the tool a little undersize on the width, get to depth and move sideways a touch to clean up the flanks. Easy as can be.

I *hate* cutting ACME thread.

Mind you given a choice between buying small diameter ACME threaded rod with nice matching nut versus cutting square thread then making the nut, I'd buy the ACME in a heartbeat.

PDW

jhruska · Feb 1, 2015

I love cutting ACME threads

Here is some trivia about Square Threads.

from 'Advanced Machine Work' 7th ed. Robert H. Smith MIT
Industrial Education Book Company Boston, USA
1910, 1912, 1915, 1917, 1919, 1922

Uglydog · Feb 1, 2015

jhruska said:
I love cutting ACME threads

Here is some trivia about Square Threads.

View attachment 129105 View attachment 129106 View attachment 129107 View attachment 129108 View attachment 129109

from 'Advanced Machine Work' 7th ed. Robert H. Smith MIT
Industrial Education Book Company Boston, USA
1910, 1912, 1915, 1917, 1919, 1922

Found the free and legal pdf of this text.
https://ia802604.us.archive.org/16/items/textbookofadvanc00smituoft/textbookofadvanc00smituoft.pdf

Thank you,
Daryl
MN

Uglydog · Feb 1, 2015

PDW said:
Mind you given a choice between buying small diameter ACME threaded rod with nice matching nut versus cutting square thread then making the nut, I'd buy the ACME in a heartbeat. PDW

iwananew10K had similar sentiments.
Nuts!!

Daryl
MN

hobbyman · Feb 1, 2015

I recently cut a square double start thread for my Graziano. Over six hours cutting the bar about 21 inches of thread. This is the second cross slide screw I have done. Did my first about 40 years ago for a Raglan lathe. Unless one has lots of time it is much easier to purchase an Acme. This screw still has not been installed. I am putting it off and putting up with a worn out screw until I get enough nerve to cut the original shaft that has an integral helical cut gear on it.

jhruska · Feb 1, 2015

Why did the thread job take so long? Chatter problems?
Follow rest cures most chatter, after that it's tool geometry, tool height, or loose compound/cross-slide gibs.

new_guy · Feb 2, 2015

We cut acme all day in in 316 not hard when you get going

Richard King · Feb 2, 2015

Dog, drive across the River to Rogers and stop and talk to Ron Dewalt at Precision Machine Rebuilding, he probably has a short shaft of Acme he might sell you cheap. Rich

johnoder · Feb 2, 2015

Three start square I messed up. Customer got the good one and its nut - WW1 SE5 biplane stabilizer trim

Uglydog · Feb 2, 2015

Richard King said:
Dog, drive across the River to Rogers and stop and talk to Ron Dewalt at Precision Machine Rebuilding, he probably has a short shaft of Acme he might sell you cheap. Rich

I know where that is!
Perhaps tomorrow if I get off early enough.
Richard, If you get this way I may ask you to take a look at a compound on a different lathe, and the ways on this one.

Thank you,
Daryl
MN

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