OldTools Archive

Recent Bios FAQ

150883 paul womack <pwomack@p...> 2005‑10‑06 Re: Face vise
paul womack wrote:
> Blake Ashley wrote:
> 
>> Maybe an engineer can tell us how much force
>> is developed by a half-inch screw being turned by say 50 pounds at the
>> end of a 12 inch lever? 
> 
> 
> Lessee. A full turn of the lever moves
> the end through 2 pi R inches,
> i.e. 75 inches
> The screw moves through 1/2" per revolution.
> So the mechanical advantage is 75:1/2 or 150:1
> A 50 Lb force thus becomes 7500 Lbs!
> Even 10Lb becomes 1500 Lbs
> 
>    BugBear (who hopes he got that right)

Nope. He didn't...

People have pointed out that I read 1/2" as pitch,
when it was most likely OD.

Further research reveals that Record sell
a 1-ton (2240 Lbs); this is a small
100mm jawed engineer's vice.

Lee Valley shoulder and face vise screws
are OD 1 1/8" inch, pitch unspecified.

Some pixel counting on
http://www.leevalley.com/wood/page.aspx?c=2&p=41664&cat=1,41659
make it look like 7 TPI.

Which makes for a lot of force...
ratio is 75: (1/7) = 525:1
10 Lbs -> 5250 Lbs (~= 2 Tons)

Does anyone know the pitch of large (e.g. 2")
wooden screws?

    BugBear (second go)
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