Re: [CAD_CAM_EDM_DRO] extrusions and "potting"

If your just cobbling something together, and only using a drill press, you
probably don't need extrusions or castings Just make the parts from
aluminum bar stock. Cut it to size with a hack saw and drill your holes.
If you need flanges those can be made by sawing away areas you don't need.

For a filler between the bearings and the housings I'd use Bisonite. this
is a steel filled epoxy sold for action bedding. It is made about 12 blocks
from me. I was just over there a few minutes ago. It will flow well enough
to surround the bearings. I suppose you could squirt the stuff in with a
disposable plastic syringe. Another method would be to drill a fill hole in
the top of the housing so you can pour in the material. There are numerous
castable polyurethane's that will work as well. These can be filled with
glass beads or metal powders.

The job might not be aesthetically pleasing, but if done carefully it should
work and it should last. If you're careful with the epoxy and the release
agents, you should be able to replace the bearings easily if they wear out.

Most of the castable epoxies or urethanes will stick very well to
aluminum...and damn near everything else you don't want it to stick
to....provided it's clean before adding the castable

Just make ABSOLUTELY SURE none of the epoxy can get into the bearings.
Epoxy seems to have an affinity for getting where you don't want it...at
least it does when I use it. :-)

If you use Bisonite or other bedding compound, a release agent will be
furnished with it. You can buy release agents from most outlets that sells
epoxy. I've used ordinary Johnson paste wax when I didn't have any
"regular" release agent on hand.

Come to think of it....I think I'll use some Bisonite as spacers between my
bearing blocks and the steel tubing framework on my inletting machine. That
will be a lot quicker than grinding spacers to fit!

You might want to keep in mind that cast epoxies are generally a lot more
brittle than cast urthanes. Urthanes seem to machine a lot better than the
epoxies without cracking as much at the edges or at ends of a cut.

Smoke

> Hi All:
> That was what I had in mind when I got into this thread.
> If I recall correctly, the intent was to be able to cobble together a
> workable motion control system without access to a machine shop, hence the
> notion was raised that extrusions would be desirable if only the hole

sizes

> were.... etc, etc.
> Smoke, I understand completely, your point that a superior part can be
> produced more cheaply by casting and machining, but I am still considering
> the case where there ain't nuthin' more than a rusty drill press and a
> hacksaw to work with.
> Within those constraints, do you think that stock bedding compound in an
> oversize hole in an extrusion, say squirted in through an access hole

while

> the bearings are pre-assembled on a shaft will have the necessary
> mechanical properties to do the job?
> What's this stuff even like to work with. Can it be injected through a
> syringe?
> Will it stick to aluminum?
> What kind of mold release do you need so it doesn't stick to the shaft

too.

> I'm thinking, as Randy suggests, that a useable system could be put

together

> with almost NO tools if the material is handleable in the way I suggest,

and

> if it has the mechanical properties to do the job.
> You could build some pretty decent stuff using this "potting" technique

with

> weldments and extrusions, and no need for precision machining, but only if
> the stuff doesn't crumble and fall out over time.
> Cheers
>
> Marcus