A good workholding solution for difficult parts
 

A few years ago I had several re-constructive surgeries on my arms.
After each surgery they made a custom brace out of plastic that is
heated in water and formed around the offending limb. After the
swelling went down all I had to do was hold the brace above a steaming
tea kettle to soften the plastic enough to re-form the brace to a snug
fit. I saved all the braces. Then, last week, I had a job that
required re-threading a brass screw with a fancy round head. The head
was .750 dia and had a sharp edge where the rounded top met the
bottom. It also had an "antique" finish on it. I bored out a slug of
aluminum in the lathe and then heated it until pieces of one of the
braces would melt. After pushing in enough plastic to fill the hole I
held the threads in a drill chuck in the tailstock and pushed the head
of the screw into the plastic. After it had cooled the screw was held
tight enough to center drill. After centerdrilling a live center was
used to hold the screw in the plastic and the threads re-cut. It
worked very well. Rio Grande carries plastic with a similar
description. And you can get it clay filled for extra strength. So if
a hard to fixture part comes along this solution may be better than
Cerrobend.
ERS

Eric R Snow wrote:
A few years ago I had several re-constructive surgeries on my arms.

and more about a low-temp formable plastic used for fixturing

Eric,
That sounds great. I have used a cheap-o version sold in craft stores
for kid-type jewelry, IIRC. It comes in strips maybe 1"x6"x1/8" for a
few bucks. Rather weak and brittle but strong enough to hold an oddball
shape and bore out a hole. Definitely disposable.

Your stuff sounds better.
--
Fred R
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Eric R Snow wrote:

So if a hard to fixture part comes along this solution may be better than
Cerrobend.

What melting temperature does Cerrobend have?

I had very good experience with a Wood's metal wannabe. Wood's metal
melts at about 175°F, but contains cadmium. The alloy I have melts at
200°F but is non toxic. You can simply whipe it off from the metal you
clamped.

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de

On Sat, 17 Sep 2005 00:24:13 +0200, (Nick Müller)
wrote:

Eric R Snow wrote:

So if a hard to fixture part comes along this solution may be better than
Cerrobend.

What melting temperature does Cerrobend have?

I had very good experience with a Wood's metal wannabe. Wood's metal
melts at about 175°F, but contains cadmium. The alloy I have melts at
200°F but is non toxic. You can simply whipe it off from the metal you
clamped.

Nick
See the info at this link:
http://www.hitechalloys.com/hitechalloys_002.htm
Cheers,
Eric

On Fri, 16 Sep 2005 21:52:37 GMT, Fred R "spam
wrote:

Eric R Snow wrote:
A few years ago I had several re-constructive surgeries on my arms.

and more about a low-temp formable plastic used for fixturing

Eric,
That sounds great. I have used a cheap-o version sold in craft stores
for kid-type jewelry, IIRC. It comes in strips maybe 1"x6"x1/8" for a
few bucks. Rather weak and brittle but strong enough to hold an oddball
shape and bore out a hole. Definitely disposable.

Your stuff sounds better.
I wonder how different it can be? The stuff I have is not real
brittle. In fact, it bends pretty far before it breaks. But it will
break. I'm gonna head down to the local crafts store and see if they
have any and how well it compares to mine. Might be the same stuff.
ERS

Eric R Snow wrote:

See the info at this link:
http://www.hitechalloys.com/hitechalloys_002.htm

Thanks!
Reading the text, i would say, that Cerrobend contains cadmium (because
most/all the other metals have the hint that they are cadmium free). Not
something I would use without precautions.

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de

Eric R Snow wrote:

I wonder how different it can be? The stuff I have is not real
brittle. In fact, it bends pretty far before it breaks. But it will
break. I'm gonna head down to the local crafts store and see if they
have any and how well it compares to mine. Might be the same stuff.
ERS

Wonder if it might be an issue of purity and/or additives. There seems
to be more than a bit of Voodoo in formulating plastics, even before you
get to the manufacturing consistency problems.
--
Fred R
________________
Drop TROU to email.