Re: [CAD_CAM_EDM_DRO] lead screw or rack and pinion ?

Concerning welded tables:

My last machine was welded up out of A-36 square steel tubing.

One thing that is always of concern is distortion from welding stress.
And most of us can't do a stress relieve heat treat on a 4x8 table.
We can do vibratory stress relief, but the method has dubious results.

I had no post weld distortion over a couple thousandths by doing the
following:
-use a space frame design
- tack weld first, alternating to different points in a sequence that
minimises heat
-use low heat and minimum bead to do the job

I built the structure up on temporarily mortared in concrete blocks and
checked alignment with a surveyor's transit. It came out within
about a sixteenth or so... then the rail mounting surfaces were machined.

This is the one on the website.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.rabun.net/~leswatts/shop.html

----- Original Message -----
From: "turbulatordude" <davemucha@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, June 25, 2002 9:40 PM
Subject: [CAD_CAM_EDM_DRO] lead screw or rack and pinion ?


> Hi All,
>
> I am persuing the design of a 8ft x 4 ft router table, moving gantry
> style and am looking at the best way to move the table.
>
> seems the consensus so far is to power both sides to prevent racking
> of the moving gantry.
>
> the question is wheather it is better to use lead screws, driven by
> timing belts, lead screws driven by gears and solid shafting, or rack
> an pinion driven by timing belts or gears and solid shafting.
>
> of course alternate methods are welcomed. I'm in the design stages
> and it looks like I am going with Hi Win linear rails and bearings.
> (Mclem@ ??? on the list offers a good deal.
>
> I was thinking of using NEMA34 steppers to drive each axis, geared
> down as speed is not too important (yet) and it looks like the table
> is simple to build. I checked out welded tables and the twisting is
> too much to handle. seems like you have to learn a multitude to
> subjects to get a good result in this hobby. (Mariss makes driving
> the steppers just too easy)
>
> Dave