[TheForge] Nuts

Fri Dec 12 11:19:01 2003

Ralph makes a really good point -- and may bring us to understand the
jamming problem Dan Tull talked about.  There are two classes of ACME
treads -- General Purpose and Centralizing.  Each class having a series of
tolerance divisions that set the fit of nut to thread.  For General Purpose
common use includes 2G, 3G and 4G -- with 2G being the preferred choice (it
has the most clearance) while 3G and 4G have less backlash in each case.

Likewise the Centralizing class has a series of tolerance that are in common
use 2C, 3C and 4C.  What is centralizing?  In the centralizing form the flat
crest of the tread is design such that it will hit the flat root of the
thread before both tapered sides of the thread will mate and prevent wedging
of the taper sides of the thread -- which could result in jamming.  In other
words the major diameter of the tread insure that only one taper face of the
tread can be in contact.  All of the power treads I work with in jacks,
mills etc where of the centralizing type.

You can find detailed information on this in Machinery's Handbook, just look
under ACME threads.

I have no idea if Dave Brown's ACME thread are General Purpose or
Centralizing -- might make a difference in how they would work in a vise,
clamps etc.

Dave Smucker

----- Original Message ----- 
From: "Ralph Sproul" <[email protected]>
To: <[email protected]>
Sent: Friday, December 12, 2003 7:13 AM
Subject: Re: [TheForge] Nuts

>         Any machinist in the crowd?  When thread taps are made they are
> offered in range from H1 - H7...........H1 being a very tight fit, and H7
> being the most loose.   When you buy taps and dies for general maintanance
> they are usually sold as H4's.
>         Are Acme threads for machine tools cut to tighter tolerances than
> those for a vice that would allow it not to bind?  Maybe some info on that
> could offer better results in your trial and error projects for clamping
> accessories.
>
> Ralph Sproul - Bear Hill Blacksmith
> Webster, NH
>
>
>
> ----- Original Message -----
> From: "Dave Brown" <[email protected]>
> To: <[email protected]>
> Sent: Thursday, December 11, 2003 10:47 AM
> Subject: Re: [TheForge] Nuts
>
>
> > At 09:02 12/11/03, you wrote:
> > >Somewhere I heard that Acme threads seize up to make breaking loose a
> vise
> > >difficult.
> > >i.e.  vise was not a good application. Anyone have experience w/  that?
> > >
> > >dan tull
> >
> > Dan,
> >
> > Looking at the bench vices in my shop (quite a few of them), they all
seem
> > to have ACME threaded shafts.
> >
> > Dave Brown
> > Heritage Smithing
> > Green Bay, WI
> >
> >
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