Re: linear bearing based on ground flat stock

Graham,

Sounds like an interesting project.

Consider swarf in the equation...

Roller Bearings riding on flats are just asking for "bumps in the
road". That's why you see so many alternatives which trade load
capability for a self-wiping or easily enclosed unit.

A roller bearing on round rails will be far easier to use
successfully, IMO. However it seems you might want the added
constraint to torque rotation that you'd lose using a single round
rail?

Bishop-wisecarver Dual-Vee bearings are well-proven. The competing
mfr. version Fred sells may be less expensive; but he may not have
the smaller size#1 wheels and rails that would seem to better suit
your project.

Consider using two round rails and 6 or 8 bearings. Techno-isel
shows how you might arrange two round rails in close proximity.

Oops. On re-read I see cheap AND light.

The Zoltar plain bearing idea works well--and uses a flat bar as
you've suggested--and if your materials are chosen carefully, it can
be used high speed. Very easy to mfr. as well. We use a version of
it in our smallest gantry routers.

Another thing to consider when using roller bearings is th eeffect
of small reversing moves over time. very hard on ball bearings,
which gain their long life by sharing the load over all the balls
and race area. Short repetitive moves can change this equation and
lead to unexpected? ly short life. Plane bearings have no such
limitations.

Hope this helps,

Ballendo

> In CCED, "Graham Stabler" <eexgs@...> wrote:
> I'm working away on a small triaglide in the background to my other
> projects to prove the principle of using Mach for the parallel
> kinematics for a 3-axis machine. I now have lots of super little
> bearing assemblies for the arm joints taken from hard drives and I
> also have three belt drive units from Epson printers, I know these
> work well and are very fast indeed.
>
> What I need now are three linear rails and carriages, they need to

be

> suitable for high speed, be cheap and light. I'm wondering about
> using some ground flat bar stock as a linear rail and make a

carriage

> that uses normal radial bearings running on this. I'd drill the

bar

> stock at regular intervals and support it along its length.
>
> I've seen something like this on a few machines including the
> torchmate plasma cutters. I'm interested in knowing exactly how

many

> bearings I should use, I could for example have a side bearing and

top

> and bottom bearing at each corner of the carriage but that would

seem

> to be overkill and I wonder about overcontraint. I can get the
> bearings very cheaply so I don't mind having 12 per carriages if I
> have to.
>
> Graham
>