re: make your own rail supports?

Jeff,

Well let's get that stick out of your spokes...

Be sure to check the pricing for yourself. One mans "too much is
anothers' "you're kidding, that's Sooo inexpensive".

I believe Greg Pettingill (Cote engineering) developed the Supertech
aluminum filled polyurethane parts and techniques.(Or helped Dennis
Bohlke develop them) He (Greg) has some references and suppliers on
his website. Try a search.

Also look into ciba-geigy's line of RTV polymers, which has been used
for machine parts. And Anocast, a division of Anorad, makes a product
that has been used by Light Machines corp. and others for
cnc "machine base" castings for many years. You might even try
a "filled" epoxy. Call Gougeon Brothers, makers of the WEST system
epoxy. They have been using epoxy in wierd and wonderful ways for
many years. System Three is another "boat builder" epoxy supplier.

FWIW*, I like the idea of "molded" parts, just not that particular
technique for that application. So here's another approach to molding
a full support for a round rail:

Drill your machine structure for the screws as if you 'already' had
fully supporting rails. Now, get some screws long enough to allow the
shafting to be at the height you desire. Coat them with release
agent. And by using some thinwall tubing as "spacers" or "standoffs"
we can mount the rail. Use thinwall because the thomson "open" style
ball bushing linear bearing (and its clones) wraps around the shaft
more than you first think...

Anyway, take your time and adjust the round rail(shaft) with shims
until it meets your precision criteria for flat and straight. Next
decide if you want it to be adjustable in the future. If so, get some
mold release that will work with the poly you plan to use. Coat the
bottom of the shaft and the area where the shaft meets the screws.

From here your path will depend on the size of your machine, and how
mauch work you want to do for "prettiness". Suffice to say that you
mix the filled poly and either pour it into a "created" mold, or
spread it like peanut butter with a knife, forming the rail bed.

The "mold" can be made with anything from masking tape to wood to
plastic to sheet metal; and the poly is poured through holes in the
machine structure made for this purpose (and which serve to "lock"
the support to the machine structure; more so if you countersink the
pour holes for a "dovetail" effect). The machine structure is turned
upside down to facilitate this "pour". Or pour through similar holes
in the "mold" sidewall, with the machine on its side, leaning against
a wall so the pour is "level".

Or just "paint it on" with a butter knife, like a medern abstract
painter (make the mixture a bit thicker so it doesn't run)

Or best, IMO, combine the two, as is done in welding, and "stitch and
glue" boat and aircraft construction. This means we use the thicker
stuff with a butter knife to "fix" or "tack" the alignment we took
pains to create. Let this set up. THEN, add the "pretty" full-
supporting goo...

Hope this helps.

Ballendo

*- For What It's Worth

--- In CAD_CAM_EDM_DRO@y..., "jeffgnu" <zbadone@b...> wrote:
> No I haven't priced the poly yet, I liked the idea when I seen it.
>
> Dam you :^)
>
> You had to go and throw a stick in my spokes, didn't you!
>
> Back to the drawing table/spreadsheet
>
>
> --- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:
> > Jeff,
> >
> > Have you priced/sourced the filled polyurethane yet? Petty pricey
> > stuff...
> >
> > > > predrilled rails. Thats why I'd start with closed