[schilpr]

I'm still working on getting my mill CNC enabled, but am planning on building a cnc plasma table next.

I'm looking for some help.

Table will be anywhere between 2'x2' and 4'x4' (leaning towards the larger size)
Tolerance around 0.05" or 1mm (yes not very precise)
cut depth 1/8", 1/4" or 3/8" plate
water table
using my existing Miller spectrum 375 Extreme plasma

These are some of my questions

• I want to use threaded rod as my rack and pinion (stationairy rod, nut with gear driven by motor that's moving). What kind of issues will this give me?
• Can I run a table like this with only 1 motor on the X axis or do I need 2?
• Would like to make the Z axis stationary with a slide mechanism to allow it to go up but not down below a set level.. I don't think my plate will vary in thickness enough to worry about cutting head touching.
• Planning to make most of my construction out of aluminum, issues?
• Xylotex kit for controls
• EMC for software

Any thoughts, help or ideas would be welcome.

Rob

[jcc3inc]

Sir,

I will be happy to send you pictures of a small table I made as a test bed for my machine controller.

Having once been in the business of making cutting machines, I would NOT use threaded rod for either axis drive. Rack and pinion is economical and very practical.

I would choose steel tubing and steel products for economy and durability.

You can reach me at jccinc-at-owc-dot-net

Regards,
Jack C.

[Torchhead]

I'm still working on getting my mill CNC enabled, but am planning on building a cnc plasma table next.

I'm looking for some help.

Table will be anywhere between 2'x2' and 4'x4' (leaning towards the larger size)
Tolerance around 0.05" or 1mm (yes not very precise)
cut depth 1/8", 1/4" or 3/8" plate
water table
using my existing Miller spectrum 375 Extreme plasma

These are some of my questions
##################################################
I want to use threaded rod as my rack and pinion (stationairy rod, nut with gear driven by motor that's moving). What kind of issues will this give me?

1. Lots of friction. Low efficiency (torque transfer %).
2. Slow speeds unless you gear the motor to nut UP. See my comment on the xylotex about speeds.

Can I run a table like this with only 1 motor on the X axis or do I need 2?

IF you can live with the vibration and flex when the torch is cutting at the end opposite the driven side. It can get ugly at higher speeds. It's not unusual to see 1/8" of flex in a machine driving one side. Cutting smooth arcs and circles can be an exercise in frustration. The wider the gantry the worse it is. A mini-plasma table (2 X 2 ) has pretty limited use. The cost differential is not enough to use that as the deciding factor.

Would like to make the Z axis stationary with a slide mechanism to allow it to go up but not down below a set level.. I don't think my plate will vary in thickness enough to worry about cutting head touching.

Might as well set it up with a drag tip and a spring loaded head. It works poorly for doing any detailed cuts, but it's better than buying boxes full of Miller consumables.

You are dealing with gaps of 1/16 of an inch as it cuts. A change of .035 can make a lot of difference in the cut quality. 1/8 material WILL warp more than that. Then you have to deal with the piercing. If you do that at the same height you cut at, you better stock up on consumables. Blow back will clog the tip and then ruin the nozzle and usually the electrode. It's worse on thicker material. Imagine dropping a big rock in a bucket of snot. How close do you want your face to that?


Planning to make most of my construction out of aluminum, issues?
Nothing wrong with AL if it's got the cross sectional area to not bend easily or has good bracing.

Xylotex kit for controls

That is a 24V based kit. Steppers spin as fast as there is voltage to charge the coils. The max RPM you will see out of that combination will be about 250 to 300 RPM. Divide that by your TPI of the leadscrew (lets say 10) and you get about 30 IPM MAX. Proper feedrates for plasma are critical. 30 IPM is WAY too slow for any material that 375 can cut. You can step up the speed to the drive nut with toothed belts but then you will lower the available torque. The faster you spin a stepper the less torque it can produce (gearing paradox). Why do you need torque? For acceleration which gives you sharp turns. Low acceleration = rounded corners

Xylotex drives do not have opto isolated inputs so motor ground noise and plasma cutting noise all transfer back to the PC logic ground. Do this. Pull your PC running EMC over close top your plasma cutting table and clip the PC chassis over to the table frame. Fire the torch and do a few cuts. If the PC doesn't reboot/freeze or go into "stunned" mode then you have a chance of making the Xylotex unit run with plasma.

Look to the Gecko G540 motor driver. It's rigged up for 4 axis (or less) for when you discover you really do need the other two motors. Uses 48V and higher current drivers so you get more than double the performance out of the same motors, and has isolated inputs so logic ground can stay separate from motor or table ground.


EMC for software
Once again, a good choice if you are comfortable with a lot of DIY. It's gotten a lot better with the advent of EMC2. If you are a Linux kinda guy then go for it!


Any thoughts, help or ideas would be welcome.

Rob

I understand you are trying to do this on a shoestring. Nothing is a deal if it won't cut right when it's finished.

TOM caudle
www.CandCNC.com
Home of the World's Lowest Cost Digital THC
www.CandCNC.com/LCTHC.html

[schilpr]

I'm still working on getting my mill CNC enabled, but am planning on building a cnc plasma table next.

I'm looking for some help.

Table will be anywhere between 2'x2' and 4'x4' (leaning towards the larger size)
Tolerance around 0.05" or 1mm (yes not very precise)
cut depth 1/8", 1/4" or 3/8" plate
water table
using my existing Miller spectrum 375 Extreme plasma

These are some of my questions

• I want to use threaded rod as my rack and pinion (stationairy rod, nut with gear driven by motor that's moving). What kind of issues will this give me?
• Can I run a table like this with only 1 motor on the X axis or do I need 2?
• Would like to make the Z axis stationary with a slide mechanism to allow it to go up but not down below a set level.. I don't think my plate will vary in thickness enough to worry about cutting head touching.
• Planning to make most of my construction out of aluminum, issues?
• Xylotex kit for controls
• EMC for software

Any thoughts, help or ideas would be welcome.

Rob

I'm still working on getting my mill CNC enabled, but am planning on building a cnc plasma table next.

I'm looking for some help.

Table will be anywhere between 2'x2' and 4'x4' (leaning towards the larger size)
Tolerance around 0.05" or 1mm (yes not very precise)
cut depth 1/8", 1/4" or 3/8" plate
water table
using my existing Miller spectrum 375 Extreme plasma

These are some of my questions
##################################################
I want to use threaded rod as my rack and pinion (stationairy rod, nut with gear driven by motor that's moving). What kind of issues will this give me?

1. Lots of friction. Low efficiency (torque transfer %).
2. Slow speeds unless you gear the motor to nut UP. See my comment on the xylotex about speeds.

Can I run a table like this with only 1 motor on the X axis or do I need 2?

IF you can live with the vibration and flex when the torch is cutting at the end opposite the driven side. It can get ugly at higher speeds. It's not unusual to see 1/8" of flex in a machine driving one side. Cutting smooth arcs and circles can be an exercise in frustration. The wider the gantry the worse it is. A mini-plasma table (2 X 2 ) has pretty limited use. The cost differential is not enough to use that as the deciding factor.

Would like to make the Z axis stationary with a slide mechanism to allow it to go up but not down below a set level.. I don't think my plate will vary in thickness enough to worry about cutting head touching.

Might as well set it up with a drag tip and a spring loaded head. It works poorly for doing any detailed cuts, but it's better than buying boxes full of Miller consumables.

You are dealing with gaps of 1/16 of an inch as it cuts. A change of .035 can make a lot of difference in the cut quality. 1/8 material WILL warp more than that. Then you have to deal with the piercing. If you do that at the same height you cut at, you better stock up on consumables. Blow back will clog the tip and then ruin the nozzle and usually the electrode. It's worse on thicker material. Imagine dropping a big rock in a bucket of snot. How close do you want your face to that?


Planning to make most of my construction out of aluminum, issues?
Nothing wrong with AL if it's got the cross sectional area to not bend easily or has good bracing.

Xylotex kit for controls

That is a 24V based kit. Steppers spin as fast as there is voltage to charge the coils. The max RPM you will see out of that combination will be about 250 to 300 RPM. Divide that by your TPI of the leadscrew (lets say 10) and you get about 30 IPM MAX. Proper feedrates for plasma are critical. 30 IPM is WAY too slow for any material that 375 can cut. You can step up the speed to the drive nut with toothed belts but then you will lower the available torque. The faster you spin a stepper the less torque it can produce (gearing paradox). Why do you need torque? For acceleration which gives you sharp turns. Low acceleration = rounded corners

Xylotex drives do not have opto isolated inputs so motor ground noise and plasma cutting noise all transfer back to the PC logic ground. Do this. Pull your PC running EMC over close top your plasma cutting table and clip the PC chassis over to the table frame. Fire the torch and do a few cuts. If the PC doesn't reboot/freeze or go into "stunned" mode then you have a chance of making the Xylotex unit run with plasma.

Look to the Gecko G540 motor driver. It's rigged up for 4 axis (or less) for when you discover you really do need the other two motors. Uses 48V and higher current drivers so you get more than double the performance out of the same motors, and has isolated inputs so logic ground can stay separate from motor or table ground.


EMC for software
Once again, a good choice if you are comfortable with a lot of DIY. It's gotten a lot better with the advent of EMC2. If you are a Linux kinda guy then go for it!


Any thoughts, help or ideas would be welcome.

Rob

I understand you are trying to do this on a shoestring. Nothing is a deal if it won't cut right when it's finished.

TOM caudle
www.CandCNC.com
Home of the World's Lowest Cost Digital THC
www.CandCNC.com/LCTHC.html

Thanks for the input.

For me a large part of the fun is making the parts I have work to do the things I want, I'm not doing this to make a living (although I do make a living with my tools) a manual plasma cutter is good enough for what I do.. just seems like a nice thing to build a CNC out of it.

Most of the parts I make are build from 1/4" or 3/8" of 8" inch wide plate, brackets, mounts and things like that. So the 2x2 table is plenty big. Not looking to make big items, when I do larger stuff it's in 18 or 20 gauge that's easy to cut with the table or the sheers.