Re: CNC Plasma Help

I'll have to get back to you with the exact specs on the rack and pinion drive components. (I'm not near the machine right
now.) Off the top of my head, I'd say the rack is 3/4 wide by 3/4 high and maybe 10 or 12 pitch. The rack is attached along the
X axis so the teeth are on the side of the rack. The pinion that engages the rack is between an inch and 1 1/4 in diameter. The
rack and pinion are positioned in this manner so the dirt will not collect in between the teeth of the rack. The rack on the Y
axis is attached with the teeth pointing down for the same reason. The pinions, encoders, gear reducers and servo motors are
attached to a plate that pivots on one point. A spring holds the pinion against the rack when the drive is engaged. A toggle is
used to overcome the spring pressure to disengage the drive.

Each axis rides on one inch Thompson linear ways. Instead of linear bearings that would quickly foul from all the grit that
plasma cutting generates, each axis rides on inch and a half sealed bearings grouped in pairs that are each set at 90 degrees to
each other. This arrangement also promotes self cleaning.

The size of the motors that you will need will depend on how heavy you build the gantry and how fast you need the cutting speed
to be. Overcoming inertia and top end speed are the biggest factors in determining the size of the motors. My machine has a lot
of mass. It's built out of quater inch wall, 4 inch square tubing. It will cut an area 72 x 126. I think the servos each usually
pull about 3 amps.

Jay Hayes
Weston, WV

Mark Ehle wrote:

> From: "Mark Ehle" <markehle@...>
>
> Jay -
>
> Can you give us an idea of the mechanics of the rack-and-pinion drive?
> Diameter / pitch / # of teeth / size of driving motors?
>
> I have acquired all of the necessary parts to put together an O/A table,
> about 4 feet by 5 feet. The only thing I lack is the drive system, and after
> reading your post I have pretty much decided to go with rack and pinion. I
> was thinking of using a section of timing belt or lead screw, but It would
> be slick to be able to disengage the motor from the rack to move the
> carriage quickly.
>
> I need to know how strong a stepper motor to use and what size rack to use.
> Also, where is the best deal on racks?
>
> Anybody out there got some ideas / answers?
>
> Thanks!
>
> Mark Ehle
> Battle Creek, MI
>