Re: [CAD_CAM_EDM_DRO] Re: Alum. Extrusion Manufacturers

Thanks Randy,

Some of the Literature from various companys list some pretty decent specs. If
you think for a moment that whatever you'd actually attach to this linear
bearing (made from off the shelf extrusion) would be attached via the T-Slots,
then this thing really is adjustable as far as location accuracy. So, some
variables can be overlooked especially when using the extrusions in such short
lengths.

Some of what I have laying around here measures up very close to what the dxf
files were drawn at. Close enough that if they were the right openings, a
bearing could be pressed into it. If by chance things were "loose", I'd just
slide the items together with a bonding agent and set all of them on some
machined tooling plate. Once dry, it'd be close enough.

My goal for this, is really for the fellows who feel that "Threaded Rod" is a
good place to start for positioning requirements. So, a few thou here and there
is OK. It's not for the worlds greatest machine..... Just a good place to start
for a hobbiest or someone who has the itch to build something quick.

Seeing as how all Linear components are big bucks new, I'm sure any extrusion
company who runs with an idea like this will up the price on it. Too bad stuff
didn't fit by "accident"...... It'd been a cheaper solution.

Thanks Again,

Chris L

Randy Gordon-Gilmore wrote:

> At 02:39 PM 2/13/2002 -0600, CL wrote:
>
> >Make all of your extrusion lineup with center openings capable of press
> fitting
> >Linear bearings. They get pretty standard in size. You just cut off a
> length or
>
> You need to watch out for the extrusion tolerances. Commercial extrusion
> tolerance on, say a .625 diameter hole (a closed hole is the worst case for
> extruding, because the metal has to flow around the supports for the part
> of the die causing the hole and fuse back together) in the common 6063
> alloy is +/-.016". An extrusion is like putty when it comes out the
> extruding die. There is an inverse relationship between how quickly they
> squirt it out and how accurate it is--slower being more accurate but taking
> more machine time than "commercial" extrusion. And the parallelism between
> the hole and an adjoining surface will have its own tolerance.
>
> To hold +.001-.000 tolerance (straight and round) in the bore on an
> extrusion I just had done (specifically to mount an INA linear ball
> bearing) and keep it within .002" tolerance of an adjacent mounting surface
> took a special holding fixture and a roller-burnishing after boring.
>
> Best regards,
>
> Randy
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