ok now we start the designing stage

[chathorne]

Hello all,

I’m thinking of building a CNC plasma table.

I've been lurking around here for a few days now. and you folks have gotten me inspired.
we run a company that manufactures Chromium Carbide Overlay Plate, the only way to cut this stuff is with a plasma, air arc gouging, or abrasive cutting (waterjet or cutoff saw), with the material being abrasive resistant the latter option is not the best. we do allot of fabrication and we've built all of our own automatic welding machines, but they are very simple.

what I’m worried about is the computer controls and interface. I've seen Mike Laws prints and I’ve seen Tom's kits from candcnc (I think that’s right)

so here's the million dollar question

if I build the table (similar to Mike's) and buy the kit, is it really plug and play??

or is there more I should know before I embark on this adventure??

thanks in advance for any words of wisdom

Carl

[Weldtutor]

Originally Posted by chathorne Hello all, I’m thinking of building a CNC plasma table. is there more I should know before I embark on this adventure??

Hi Carl
Welcome to CNCzone

Less than two years ago I couldn't even spell CNC.

I found this site, & with the help of many members I was able to build a plasma table & figure out how to operate it.

Mlaws plans were very inspirining & he also built my controls.

Tom has said there is no such thing as true "plug & play" but his customer support is fantastic & he will see you through the rough spots that seem to happen to most builders.

You will of course need a CAD program for patterns, CAM to make your Gcode & a control program (Mach or other)

Anyone who can put together automatic welding systems can likely figure out the above.

Lots of help is available on the forums here.

(Sure do like Arcair, with earplugs)
WT

[chathorne]

alright,

I'm looking at building a table that is 10'6" x 12'6"

will be cutting steel plate up to 1-1/2" thick
up to 9'0" x 11'0"


I'm working on drawings now and will post them soon

on a table this big would you guys still use ball screws? (they seem to be the preferred method of movement)

would you build the gantry out of steel or aluminum (to reduce weight)

last question (for now) would you make the table to hold water or open bottom?

[massajamesb]

ball screws would probably not be your best option, IMHO, look into spur gear and gear rack. They will hold up in that environment better.

Steel would be the ONLY way to go, even if you weren't wanting to cut 1.5" thick steel. Aluminum works for some things, but if you are going to build it that big, make it super strong.

Water table, hands down. Either so the material is partially submerged, or so the water level is within a couple inches of the plate.

With plate that thick, you should either look into oxyfuel cutting, or Hydefinition plasma, just me thoughts.


EDIT: I just looked at the material you would be cutting. Oxyfuel is probably not an option.

[chathorne]

tell me the difference between high def, & regular plasma
I know the biggest differance is the accuracy, but is it the machine or the plasma that makes the differance

is it just the type of plasma you use?

say you could build a cnc table and use either one?? upgrade when financially able.

The stuff we cut is Chrome Carbide Overlay Plate used in mostly mining and abrasive applications, anyway the accuracy part 1/16" 0.0625 is acceptable, of course better is better.

can't be oxy cut and i think that waterjet would be too costly due to the material being abrasive resistant (rockwell hardness 60-62 c scale)

[massajamesb]

Originally Posted by chathorne tell me the difference between high def, & regular plasma)

I am not the foremost authority on Hydef plasma, but it basically has much more control over the arc than standard plasma, giving a smoother cut and less bevel than standard plasma. Here is a pretty good link from some people who, IMHO, set the standard.http://www.hypertherm.com/technology/high_def.htm

Originally Posted by chathorne I know the biggest differance is the accuracy, but is it the machine or the plasma that makes the differance)

I feel that it is a little of both. Plasma is not an inherently accurate process, but it does fall within the guidelines you mention. With that said, there is really no reason to build a machine capable of cutting parts for NASA. At the same time, it never hurts to have an accurate and well built machine. You will have to try pretty hard to build a machine that is less accurate than the plasma process, though.
The amount of bevel seen on a piece of 1" thick steel cut with a 60-80 amp plasma, even though it might be a smooth kerf, will be beveled to a serious degree (no pun intended). The farther the arc has to travel to cut, the worse the bevel will be. Hydef plasma does not completely fix this, but it sure makes a difference.

Originally Posted by chathorne is it just the type of plasma you use?)

Brand specifications vary. I use a Thermal Dynamics plasma, but have used a variety of other brands. Though I like the results I get with my little tinker toy 40 amp TD plasma, I would give my left arm for one of my old Hypertherms Individual results may vary. I have heard (and seen) good and bad about every brand out there.

Originally Posted by chathorne say you could build a cnc table and use either one?? upgrade when financially able.)

yes, completely feasible. Build a simple cnc plasma table for now, and leave yourself room to upgrade. I imagine you will have a better grip on the issues at hand, especially when you have an example to go by in person.

Originally Posted by chathorne The stuff we cut is Chrome Carbide Overlay Plate used in mostly mining and abrasive applications, anyway the accuracy part 1/16" 0.0625 is acceptable, of course better is better.)

accuracies of conventional plasma are generally about .04-.08, depending on amperage, material thickness, cut speed, tips used, etc.

Originally Posted by chathorne can't be oxy cut and i think that waterjet would be too costly due to the material being abrasive resistant (rockwell hardness 60-62 c scale)

I bet you are right. Waterjet is a nice option, but an expensive one. I imagine you could have a nice Hydef plasma system for less than half of a basic waterjet capable of cutting that thick material.