Re: Plasma cnc

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tyson S."
<timbercutter@y...> wrote:

> Yeah, the Hypertherm Powermax 1250 is top of the line
> for CNC plasma operations. It allready has the remote
> torch on/off terminal installed for the G-Code to run
> the torch. But at $3500 I say ouch. I am also drawing
> up plans for a combo plasma/router cnc machine and am
> looking at drive options. The ball screws for an
> 5'X10' table run in the thousands of dollars. I was
> wondering if anyone here has ever seen,used,heard of
> chain and sprockets instead of screws? My parents have
> a picture framing shop and they use a CNC mat cutter.
> I was looking at the gantry rails to see what kind of
> drive system was there and it's all small chain and
> sprockets. a littls smaller than a bicycle chain would

Dear Sir:
Thre most prqactical approach to longer travel for either a plasma or
router machine is rack and pinion. C & G Systems is a company I
started a number of years ago. We made plasma and oxyfuel cutting
machines and ALL of them were rack and pinion drives. You can buy
gear rack, 1/2 x 1/2 with 20 degree pressure angle and the drive
pinions to match. Combining rack end-to-end allows any length.
Rack and pinion has minimum backlash as you commonly preload the
pinion into the rack with a spring arrangement. All plasma machines
which I know of do this.

It is common to have dual side drive for larger machines (wider than
6 feet),but you should seriously consider single side drive with the
master rail having the guide wheels widely spaced and preloaded for
rigidity to do single side drive. Do a little calculating and
testing to see what deflections you get with a given load (in the
case of a router). With plasma you have no resistance to overcome
except for the F = M x A component. If you use steppers, it is
easier to achieve synchronization with dual side drives, but for
servos, we used a synchronizer setup consisting of resolvers with a
1000~ carrier and demodulator to provide a sync signal to the slave
side. Of course that is more involved!

While most of the people on this site use ballscrews for drive means,
I think they are overlooking a very viable alternative in rack and
pinion usage.

Jack C. Cain