RE: Plastics question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sparktron01@xxxxxxxxxxx 

Chris

Outstanding workmanship on your controllers!  Looking forward to more
details of your large DRSSTC machine...

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA

 -------------- Original message ----------------------
From: "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)
>
>