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Using Pepe large disc cutters


#1

I acquired two of the larger disc cutters from Pepe and they come
with a warning about using them only with a press. First: is this
really true or is it a case of CYA? I tried to use a large/heavy C
clamp as a manual press to cut a disc and it bent the C clamp. So
second: Does any one know where I can find out what pressure is
necessary to cut 14 gauge silver? The Bonny Doon is too expensive
for me and there are presses (at Harbor Freight for instance) that
look like they would do the job but the critical info is the pressure
needed to make the cut. And third: does anyone have experience with
presses other than Bonny Doon?

Thanks in advance for any input. MaryAnn


#2
Does any one know where I can find out what pressure is necessary
to cut 14 gauge silver? 

It is difficult to give precise number, since there are many
variables, but to illustrate the calculations to arrive at some
indication of the force required we can proceed as follows:

Shear strength of silver (it is alloy and annealing state dependent)
we can assume for argument sake to be 11000 psi. This is the force
required to give start to shearing fracture. More pressure would be
required to extend the fracture through the thickness of the metal.

If you are using a punch of 1 inch diameter, the area of contact
with metal would be 3.14158 * (1/2)^2 = 0.79 square inches. Multiply
by shear strength and initial pressure would be 8639 pounds. For all
practical purpose a 1000 pounds would do it.

However 2 inch punch would require 34,558 pounds of initial pressure
and in a real world 40,000 would be closer to the truth. 14 gauge
would definitely require more force. Also condition of the punch
face, misalignment, and many other factors could increase these
requirements.

Leonid Surpin
www.studioarete.com


#3

For less than %100 one can get a 1/2 arbor press. I learned from a
hydraulics mechanic to strike the ram with a sledge which produces a
momentary couple of tons.

Bruce D. Holmgrain
JA Certified Master Benchjeweler
goldwerx.us


#4

I believe that this all becomes moot if the punch is a couple of
degrees off of perpendicular. All of the punches that I have
purchased are a little off from 90 degrees.

I failed to point this out during the punch sharpening discussion.
Check it out. If the first strike fails to punch through, turn the
punch a little and strike again. Do as necessary.

Bruce D. Holmgrain
JA Certified Master Benchjeweler
goldwerx.us