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Re: Re[2]: Scott gap



At 05:09 PM 4/12/00 -0600, you wrote:
>Original Poster: "Paul Mathus" <pmathus-at-learningco-dot-com> 
>
>     Thanks, Terry.
>     
>     I've checked out the nice pictures on your page already, and found a 
>     few posts in the archives. 
>     
>     The mechanical construction seems very simple.  I guess my main 
>     questions are:
>     
>     What material did you use for the baseplates?  G-10?  I'd rather use 
>     HDPE if you think it could take the temperatures.  G-10 seems to be 
>     rated to 275 degrees Fahrenheit.  If there's a material that's cheaper 
>     and easier to machine that can take the heat. . . On a side note, does 
>     anyone have any data on how hot their gap pipes generally get?

      <snip>

Here's some material offered by McMaster-Carr I've been thinking about
using for SRSG rotors. It might be good for this type of gap too, maybe. ;)

A 1/2" thick, 12" x 12" square is $12.54 

Electrical Grade Fiberglass (GP03)
• Color: Opaque red
• Temp. Range: 0° to 400° F
• Tensile Strength: Excellent
Enhanced electrical insulation properties and a flame-resistant additive
make this material ideal for electrical applications. It is a glass
fiber-reinforced polyester. Material meets UL-94V0 standards.
• Impact Strength: Excellent
• Excellent electrical insulator
• Use indoors
• Easy to machine

Notice that the temperature goes to 400° F, and it's listed as easy to
machine.

Other specifications:

Tensile Strength: 10,000 psi
Impact Strength: 8.2 ft.-lbs./in.
Dielectric Strength: 400 V/mil
Tracking Index: 500 volts
Durometer: Barcol 50
Coefficient of Thermal Expansion: 2.010 -5 in./in./°C
Weather Resistance: Material is not weather resistant. Resin will break
down over long periods of exposure to the outdoors.

Processing--

Machinability: Can be easily machined. Can be cut with a hacksaw, diamond
grit saw blade, and carbide tip saw blade. Holes are easily created using
conventional drill bits and milling bits. A dust mask and gloves should be
worn when working on this material.
Welding: Not recommended.
Scratch Resistance: Moderate.
Chemical Resistance: Use with mild detergents. Do not use with strong acids.

The original GP03 page is at http://www.mcmaster-dot-com/pdf/106/3088.pdf
The extra specifications are at http://www.mcmaster-dot-com/pdf/106/8549KAC1.pdf

Here's some G-10/FR4 Garolite specs:

A 1/2" thick, 12" x 12" square is $46.87

• Color: Opaque brownish-green (except where noted)
• Temp. Range: 0° to 284° F
• Tensile Strength: Excellent
An outstanding electrical insulator, this continuous-woven glass fabric
lami-nated with an epoxy resin absorbs virtually no water and offers good
dimen-sional stability. Meets UL-94V0 standard for flame resistance unless
noted.
• Impact Strength: Excellent
• Excellent electrical insulator
• Use indoors
• Difficult to machine

Notice that the temperature goes to 284° F, and it's listed as difficult to
machine.

Other specifications:

Meet the following standard: UL94V-0 for flammability and Mil l 24768/27.
Tensile Strength: 40,000 psi
Impact Strength: 7 ft.-lbs./in.
Dielectric Strength: 500 V/mil
Durometer: Rockwell M: 110
Coefficient of Thermal Expansion: 1.8210 -5 cm/cm/°C
Weather Resistance: Material is weather resistant.

Processing--

Machinability: Can be machined using carbide tools.
Welding: Cannot be welded, but can be glued.
Scratch Resistance: Material has good scratch resistance.
Chemical Resistance: Use with dilute acids and some organic solvents. Do
not use with acetone, alkalines, and strong acids.

The original G-10 page is at http://www.mcmaster-dot-com/pdf/106/3092.pdf
The extra specifications are at http://www.mcmaster-dot-com/pdf/106/8667KAC1.pdf

The only real difference I can see, as far as specs are concerned is that
G-10 has a tensile strength of 40,000 lbs/sq.in., while GP03 has a tensile
strength of 10,000 lbs/sq.in. Everything else seems very close. The
difference in tensile strength might matter as far as a rotor is concerned,
but I'll still probably try it. For a Scott gap, it should be fine.
Comments?

Dan 
ntesla-at-ntesla.csd.sc.edu