[shoot]

Hello all as a welder ive been wanting a cnc plasma for years, and finally thanks to lock downs ive had the time to start my design.
theres nothing new about the design, gotta keep the build cost down but build it in a way i could extend it if i chose thanks for looking.
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https://www.youtube.com/watch?v=mT-iGJO7smY&t=295s

[peteeng]

Hi Shoot - A few things to look at:
1) Direct drive to a rack and pinion will give you very high speeds and poor control for slow speeds, can be a notchy movement. You need to figure out the required speed range for the plasma then gear the motor to suit. Steppers run well between 0-500rpm then have small torque to 1000rpm. Direct drives run well 0-300rpm. If you figure out your gear ratio and then your machine speed at 300rpm I think you will be surprise how fast it is!! Most R&P are geared down 1:3 or 1:4...

2) Using bearings, nuts, bolts and commercial steel seems a low cost way to go but steel is not straight and bearings actually aren't cheap. They need eccentrics to adjust and all those bits add up to a cost that a round rail and car will be. So consider a commercial linear bearing system. Much better solution.

3) Because the steel is not straight the motor is usually mounted on a lever and spring so to keep the engagement constant. R&P's do jump out of engagement if they get light on engagement, lots of torque available!

4) Don't build or buy anything until you have finalised the CAD, identified suppliers and all costs to eliminate cost shock!!

Enjoy Peter

[shoot]

thanks for the post peteeng,given me a fair bit to chew on there

[rodw]

Here is a plasma primer that covers a lot of ground that will save a lot of mistakes.
Plasma Cutting Primer for LinuxCNC Users (full disclosure, I wrote it)
Pay attention to the short mention of ideal movement distance per rev. I got away with 30mm/rev but only just.

I'm not convinced a spring loaded pinion drive is a good idea. If you can build to accurate dimensions, its not necessary and can cause excessive wear.
Here is another thread where I asked bout spring loaded pinion drives and there were a couple of very experienced commercial plasma builders both said do not do it. So I didn't!
https://forum.linuxcnc.org/30-cnc-ma...d-pinion-drive
I have never regretted that decision. You will note that they saved me from making a mistake with direct drive pinions too!
I think that once you get into it, you will find the additional cost of a precision build is not that much more than a ghetto build (which was my initial plan)
Also make your table as solid as possible. I used 4" x 4" steel square section. Also pay attention to the rigidity of the gantry ends and the forces from inertia that will be applied to them.
Keep your gantry as light as possible.
You can build a high performance, accurate stepper driven machine with careful matching of motors, drivers and forces.
Mine accelerates at 0.5 g and rapid traverses at 36 m/min (1420 in/min) I did dial back the X axis from 0.8g which is up there with Tesla ludicrous mode!