RE: [CAD_CAM_EDM_DRO] are 3/4 shafts good for axis ?

Thompson bearings were used with great success on industrial cnc machines
for years and they run on round bars. Of course, the bearings and bars are
matched and the bearings are pre-loaded. We also supported the bars over
their full length for stability. I can't see using any type of just plain
round rod with bearings that are not matched to the rod for any type of cnc
machine, they simply would not be accurate enough. We began using THK
linear bearings back in the early 90's and those proved to be the best. An
Asian company named Star also makes similar bearings to the THK version. I
think you can purchase the THK or equivalent from McMaster-Carr.

I agree with Roland, just using round bar or even hollow rod (which would be
less likely to bend) with average type bearings is not a good idea.

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Roland Jollivet
Sent: Friday, April 20, 2012 7:25 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] are 3/4 shafts good for axis ?

I'm always amazed at the use of round bar and guides on smaller CNC
machines. Unless the bearings are pre-loaded by spec., I think they are
pretty useless. Looking at the gantry style, the whole gantry will rock to
and fro. They are generally not designed for machining machines, more for
shifting milk cartons etc.

If you examine the SKF, NSK or other good brand on the default clearance,
you'll see it's excessive. They are designed to take misalignent.

For the Z axis, anything round is a poor choice, unless you can adjust the
pre-load.

Regards
Roland

On 19 April 2012 20:09, Brian Worth <electromodeler@...> wrote:

> **
>
>
> Hi Dave,
> I used 20mm drill rod for mine, 400mm long, supported with one support in
> the middle, and "open" cheap chinese re-circulating ball type linear
> bearings. These bearings were so sloppy and such junk, I gutted them,
> replacing the bearings with home made Delrin "c" bushes in the existing
> carriages. It puts more load on the steppers, but it is strong as the
> proverbial brick sh**house. I machine wood and alu with no problems.
> Support in the middle is crucial in my opinion for anything over say 200mm
> (8").
> Regards, Brian
> --- On Thu, 19/4/12, turbulatordude <dave_mucha@...> wrote:
>
> From: turbulatordude <dave_mucha@...>
> Subject: [CAD_CAM_EDM_DRO] are 3/4 shafts good for axis ?
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Date: Thursday, 19 April, 2012, 16:45
>
>
>
>
> Hi all,
>
> I am designing a wood router with a 18 inch wide X axis.
>
> it looks like 3/4 inch shafts will fit the design really well, floating,
> connected to the ends, not fully supported along the length.
>
> I plan on using a trim router and will do cutting in wood.
>
> Anyone have experience with 3/4 inch shafting ? I am on the fence between
> 1 inch and 3/4 inch.
>
> If I was planning on doing anything stronger, I would use linear shafting
> that would be fully supported along the length, but that would cost more
> than the rest of this machine !
>
> Suggestions and feedback welcome.
>
> Dave
>
> [Non-text portions of this message have been removed]
>
>
>


[Non-text portions of this message have been removed]



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