Working on design for homebrew plasma...

[panozeng]

Well, after a year of lurking on here I am finally getting ready to start on a homebrew plasma table. For my first attempt at building one I am going to go with a 60" x 60" travel. I know it's nice to have a bigger table, but I have limited floorspace in my shop, and I can always support the rest of a sheet on stands beside the table. Almost all of my plasma needs are small plates and brackets anyway. Initially I am not going to have a Z axis; instead I'm going to make the cone shaped deflector around the torch head that will automatically lift it if something gets in the way. Down the road I will add the Z axis and a Campbell THC set up.

Drive:
After much deliberation between timing belts and rack and pinion I finally chose to go r&p; specially after finding a pair of 6' long rack gears in 14 1/2 pressure angle, 20 pitch brand new at a local used metal center for a great price. I like the idea of the smoothness of belts, but not the idea of a belt that long flopping around. I am still debating on whether driving the gantry from just one side will suffice - probably try it first and might end up adding a second rack gear with either a jack shaft or second stepper.

Rails:
I have 4 1" Thomson double width super pillow blocks I will probably use. I don't have long enough rails to go with it, so I will have to buy those. I thought about proving the machine out with cheap ground round mild steel bar first, but figure the bearings would wear into that pretty fast. Should probably just buy the real thing up front. I still keep thinking about the cantilevered arm design, and haven't ruled that out yet. About a year ago there was a company advertising such a machine on Ebay regularly - can't seem to find them or the machine now. Anyone remember how that was? I really like the concept, specially for using a single rack gear on the X axis, but wonder how much flexing would bit me. I haven't been able to find specs for the Thomsons on how much torque they are designed for.

Gantry:
I think I will be using a single 3" x 6" x .25 wall 6061 - T6 extruded aluminum tube for the gantry beam that I have access to. The tube would be laid down so that the 3" dimension would be the height, and the Thomson rails would be mounted on top. The rack gear would go on one side, and the torch holder on the opposite side to help keep the rack clean.

Motors and drives:
After spending a little time thinking about servos and gecko 320's I've decided to go back to the original plan of Xylotex and steppers. I will probably go ahead and get the 3 axis controller. I am debating between 259 ozin and 425ozin steppers right now. From most other experience on here it sounds like a 3 to 1 belt reduction is the way to go. I have a very healthy 90 amp plasma unit, so I'd like to see some pretty good cutting speeds (the manual recommends cutting 1/8" steel at 120ipm, 1/8" at 190ipm). I would definitely like to hear some comments on the stepper motor sizing... Any thoughts or suggestions?

Thank you,
Jason
www.tubularfab.com

[Redline]

I would get the Xylotex 4 axis and slave the x-axis with the a-axis.I have a 36 x 48 that is driven from one side.It does work,but it would be more rigid and faster having two motors on the X-axis.I say faster because the motors would share the work of moving the gantry around.This is just my opinion, I do this as a hobby no money made here.I am just lucky to stay afloat.


The other thing is the z-axis.You will find out right away that you will need a THC if you want consistant results in thinner materials.

You can get more speed out of the smaller motors, but I have 425's on mine and it will move at 200ipm with 2tpi screws.

[massajamesb]

As light as your gantry is, you could probably single drive it, and just run a shaft across to drive both sides of X. I would say that either the 269 or 425 should work for doing it that way, I have that 425 dual driving my X axis (via a jackshaft), and it works flawlessly. I think the larger one would work better, but the smaller one should work well too. That will be dependant on how easily your machine moves via the bearings. The option of a 4 axis board and dual driving X is also a good idea. You will definately not have to worry about sufficient torque and speed then

R&P will give you some incredible speed advantages, depending on the size of your final drive gear and your gear reduction. Even 1" of travel for every motor revolution should put you above 200 IPM very easily.

Good luck, and keep us informed on how it goes!