Re: [CAD_CAM_EDM_DRO] Ball/acme screw question

Brian,
Actually, I'm somewhat of an expert, and the reason for a multi-lead
screw is this. You want a nut that will advance 1" in 4 revolutions, but if
the shaft is fairly small in diameter, the depth of the thread, if you cut
it for a normal 4 threads/inch, would weaken the shaft considerably.
Instead, you cut it 4 threads/inch, but at the depth used for 8
threads/inch. You then have spaces between the threads in which to cut an
additional lead at the 8 threads/inch depth. You then end up with a screw
that appears to have 8 threads/inch, but the nut will advance 1" for 4
revolutions. The whole thing has to be done on a lathe, and sounds
complicated, but it really isn't. In the past, I've generated screws with as
many as 4 leads. They looked like the threads were very fine, but the nut
would fairly fly down the screw.
You just had a lesson in "Screwing 101".

Marv Frankel
Los Angeles

----- Original Message -----
From: "Brian" <ka1bbg@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, October 28, 2002 2:41 PM
Subject: Re: [CAD_CAM_EDM_DRO] Ball/acme screw question


> Hi, I am no expert but a few things to think about. Multiple lead acme
> screws means you have several threads instead of one so they tend to last
> longer and are stronger. Rolled acme thread has been going on for a long
> time and the acme rods i bought the other day are nicely finnished and a
> quick check says their ok on the length. a "v" thread begins to wear
quickly
> and once it gets sloppy it weakens as it wears out. an acme thread stays
> rugged even as its wearing to a point. As for efficient i cant answer but
> there are ground threads of all kinds out there some last for many years
> even if they are "v" or acme or even buttress thread. Each has a best use.
> Take a look at the size you want and then look at the different grades
> available. 1/2-10 acme b2 is the cheapest because of so much use, if you
> order a 15/16-16 thread custom made to your spec's then expect to pay
> premium big bucks. Sometimes the nut and the retaining method(back to back
> bearings or nuts) is the most important part. cul brian f.
> ----- Original Message -----
> From: "JJ" <jj5412@...>
> To: <cad_cam_edm_dro@yahoogroups.com>
> Sent: Monday, October 28, 2002 4:53 PM
> Subject: [CAD_CAM_EDM_DRO] Ball/acme screw question
>
>
> > (Hoping this is on topic)
> >
> > In my quest for constant upgrades to my CNC mill/router/pcb thing, I
> > have a couple of questions:
> >
> > Why would you choose a multistart screw over a single start screw?
> >
> > Are acme thread screws more efficient that generic threaded rod?
> >
> > ADVthanksANCE,
> > JJ
> >
> > Be Kind, Be Careful, Be Yourself
> >
> >
> >
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>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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>