RE: Plastics question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Hooper, Christopher AZ" <christopher.az.hooper@xxxxxxxxx>

Scott,
Wow, brain waves as was just going to give my 2 cents of Plexy. All my
coils are plexy, and spend many hours drilling, tapping and cutting
plexy. Spending a few extra $ for bits and blades is worth the cost. Cut
slow, drill slow, use H2O for a lube and the finish product will be
outstanding, Plexy sure makes nice coils indeed. The end process is to
take a torch (propane) and round the edges of the cuts, warning this
takes aptitude as to much heat and you have a burning mess.   Now
building control units out of plexy @
http://users.cableaz.com/~chooper/images/control1.jpg .


Rgs,
christopher robin

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, January 31, 2006 12:51 PM
To: tesla@xxxxxxxxxx
Subject: Re: Plastics question

Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

Actually, using ANY type of hydrocarbon as a cutting fluid for
acrylic or polycarbonate will almost guarantee crazing or cracking.
The most readily available "cutting fluid" for these materials is
just plain tap water, the "best" cutting fluids are synthetic soluble
oils specifically designed for machining solvent-sensitive plastics.

The tendency for acrylic to crack or craze is also highly dependent
on the material type (cast or extruded), and the stresses applied to
the material during machining (cutting tool speed, feed rate, heating
of cutting tool and workpiece, selection of correct tap drill
diameter, etc). In reality, tapping acrylic or polycarbonate should
be avoided if possible, and the parts through-bolted with a nut and
washer on the backside. If parts must be tapped, use long screws to
get lots of thread engagement and spread the load over many threads,
and control screw installation torque carefully.

The most common machining problem is simply drilling a hole. Using a
standard twist drill bit designed for metal is a recipe for disaster,
as the rake angle of the cutting edge will "grab" the plastic and
pull the bit into the material, leading to tearing-out the material,
chipping and cracking. Special drill bits are available for acrylic,
but it is easy to modify a standard drill bit for plastic work by
grinding the point to a 60 degree included angle (much "pointier"
than a standard 120 degree drill bit), and grinding the cutting edge
to a zero rake angle. This configuration will "scrape" material
rather than dig into it and will never "grab" the workpiece. If you
have never tried a drill bit of this type for plastic work, you will
be amazed at how easy it is to control the feedrate, and how clean
the resulting hole is.

Regards,
Scott Hanson


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, January 30, 2006 3:23 PM
Subject: Re: Plastics question


>Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
(snip)
>"When you tap the acrylic for the fasteners be sure to use kerosine
>if in a lathe.  Also gently (very gently) anneal the acyrlic after
>tapping in your oven to prevent the sharp tap edge points from
>expanding into cracks that will radiate to the edge of the acrylic
>and cause fastener failure.
>
>Dr. Resonance
(snip)