Re: [CAD_CAM_EDM_DRO] Q re. unhardened shafting & linear bearings

bargain_fiend wrote:

>Hi all
>
>Recently had a small windfall and so can finally contemplate turning
>ideas into hardware. Have been lurking here for a while and haven't
>seen the info I seek discussed before, so here goes...
>
>Am contemplating a machine that moves a load of about 4 kgs. (~10
>lb.) at max velocity of ~4.5 m/min (though may go higher if
>possible). Total length of travel is 3m (10'). Have some
>*unhardened* (actually about 33C)
>

This is a hardness of 33 on the Rockwell "C" scale? That's not very hard.
I suspect that you WILL see wear on the shafts pretty quickly. If you
get the
linear bearings, you can just put one on the shaft and run it back and forth
a dozen times and see if you see any mark. If you DO see marks after just
a dozen traverses, don't use this shaft. The "real" stuff won't show a mark
after thousands of traverses. But, that shaft must be close to 50 C.

> 4140 20mm precision ground shafting
>and linear bearings and support extrusion to suit.
>

The raw shafting, in the hardened and ground finish, is actually quite
cheap.
The mounting rail, and the shafting that is drilled and tapped for the rail,
is very expensive. You might look into buying the bare, hardened rail and
doing the drilling and tapping yourself.

>Alternatively, has anyone ever tried using bronze/teflon/graphite
>impregnated/?? bushings as linear bearings? Have amps/motors with
>extra 'grunt' if required.
>
>

If this is for a clean operation, that might work. If it is to be used
with a
process that makes chips or dust, it probably will not work so well, as the
bearings may suffer accelerated wear. But, they might work better on the
soft rail.

Jon