At 01:56 PM 4/7/2004 -0500, you wrote:
>Google wasn't very helpful; all I got were advertisements
>and how-to's that say "Be certain to use the right cutting
>speed."
>
>We have a book with several more common metals (alum.,
>iron, several types of steel), but I also need to know about
>brass, plexiglas and delryn, among others.  The big Q about
>plexi is "What cutting fluid do I use to keep it from releasing
>its toxic smoke?".
>
>I'm really just looking for a nice table I can print out or
>download; I'd hate to buy a copy of "Machinery's Handbook"
>just for this one thing. :-p
>
>Mike H.

Both speed (SFM = surface feet per minute in non-metric land)
and feed (typically spec'd in thou per tooth) are important. Also
important are tooth rake angles and chip clearance angles for
some tools. Brass is grabby, especially with large negative rake
angle, BTW, but otherwise seems like  gummy yellow plastic in some ways. ;-)

Machinery's 26th edition offers rough guidelines for turning of
200-500 SFM for HSS and 500-800 SFM for carbide tools with
water soluble coolant (where compatible with the plastic).
Milling speeds are similar for thermoplastics (lower for thermosets).

They note that too slow a feed rate will result in surface cracks, and
too fast will result in a rough finish.

The rates are just starting points, a machinist will adjust them manually,
through experience, according to the part and machine rigidity and other
factors to get the best results.

BTW, the generic terms for Plexiglas (T.M. Rohm and Haas) and Delrin
(T.M. E.I. du Pont de Nemours) are acrylic and acetal respectively.

There are zillions of additives (for fire retardancy, dimensional
stability, UV stability etc.) that can and are added to the base
resins. If there is glass filler, then carbide tools are almost
essential.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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