Re: Q re. unhardened shafting & linear bearings

Hi pete,

The problem with shaft rails is that they are less stable as linear
rails. A ball on a round shaft has in theory a very small surface for
contact (point contact), where a ball on a rail has line contact or
more points. One of THK rails of 15 mm(with) is just as stable as
round shaft with a diameter of 80 mm. I use Hiwin rails they are not
so expensieve, check Bob Campbell side for prices.
Good luck

Hugo


--- In CAD_CAM_EDM_DRO@y..., "bargain_fiend" <pete_simmons@b...>
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) 4140 20mm precision ground

shafting

> and linear bearings and support extrusion to suit. All enquiries

to

> supposedly knowledgeable persons (retailers of this stuff

basically)

> so far have resulted in what seemed to be uncertain answers.
> Responses were
> i) "Unhardened shafting is unsuitable since the hardened balls

will

> score the shafting" (No request for load, velocity, acceleration,
> whatever made) or
> ii) "I have never heard of this being done and have no pertinent
> information available" = Don't know I guess.
>
> So, has anyone here been as financially challenged as I am and

toyed

> with this situation. Or has sufficient theoretical knowledge to

give

> an informed answer.
>
> If this isn't dismmissed out-of-hand and I actually try this setup
> out will obviously post results here.
>
> Alternatively, has anyone ever tried using bronze/teflon/graphite
> impregnated/?? bushings as linear bearings? Have amps/motors with
> extra 'grunt' if required.
>
> TIA
>
> Pete S.