JJ,
You do not use the O.D. of the screw in the I.D. of the bearing. The
ends of the screw are machined or ground to the next standard size down, to
a snug fit in the bearing I.D.. My R & D in this kind of thing, is usually
done in the McMaster-Carr web site. www.mcmaster.com . They have bearings of
every size and shape available.
Marv Frankel
Los Angeles
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----- Original Message -----
From: "JJ" <jj5412@...>
To: <CAD_CAM_EDM_DRO@...>
Sent: Tuesday, October 29, 2002 4:23 PM
Subject: RE: [CAD_CAM_EDM_DRO] Ball/acme screw question
Thanks for all the info everyone!
One last (for now) question: Are acme screws their true diameter? Ie. If
I buy a 1/2" screw, do I plan on using 1/2" ID bearings?
Okay, one more: Does anyone make small mounting flanges for acme nuts? I
just can't see a 2.600" flange for a 3/8" rod.
Thanks again,
JJ
Be Kind, Be Careful, Be Yourself
-----Original Message-----
From: Marv Frankel [mailto:dcdziner@...]
Sent: Monday, October 28, 2002 11:11 PM
To: CAD_CAM_EDM_DRO@...
Subject: 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@...>
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@...>
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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