My Recently Finished CNC Plasma Table

[Jcar]

Hello All,

I’ve had my CNC plasma table up and running for a couple of months now, and am finally getting around to doing a post on it. I’ve been reading through the “Zone” for a year or so and have found a great deal of useful information. This project would not have been possible without cnczone.com. This post is my attempt to give back a little to the “Zone”.

The machines working envelope is 61” by 61”. This was limited by the availability of linear rails on ebay and space constraints in my shop. I had a very hard time finding anything over 80” at a reasonable price. I looked into new rails, but the $3500 price tag was beyond my budget. I ended up with two 78” NSK20’s for the Y axis, one 65” THK35 for the X axis and one 28” IKO15 for the Z axis. The Z axis rail was cut in half to give me two 14 inch lengths.

The design is an open gantry (i.e.. the cutting/water table is separate from the drive/linear motion system). I like the fact that heavy sheets of steel placed on the table cannot deflect the linear motion components of the machine. I also thought it may be handy to roll the table out with a pallet jack, and allow me to cut stuff like 12 inch I-beam that would not fit between the gantry and table. The gantry is constructed from 3” square steel tube with a wall thickness of .125” and is anchored to the floor with height adjustable anchors. These anchors made leveling the machine a breeze…….. well maybe not a breeze. The legs of the gantry were braced with 45 degree braces due to this nasty little thing called “Inertia”.

The X axis and both sides of the Y axis are driven via rack and pinion. Each of the three use the same type of drive (all parts are identical). Basically I designed 1 drive and made 3 of them. Each drive pivots, at one end, on a ½” diameter precision shoulder bolt and is pulled toward the rack with a spring on the other end. These drives consist of a 270 oz stepper motor coupled to a 14 tooth XL timing belt pulley which drives a 60 tooth XL timing belt pulley which is coupled to a 14 tooth pinion gear. How’s that for a run-on sentence…. I used 16 pitch 14 ½ degree racks and pinions. The 4.29:1 drive ratio, coupled with the 14 tooth pinion gear, achieves .641” of travel for 1 revolution of the stepper motor. This ratio seemed like a nice compromise of speed and accuracy. With a 10 micro-step G201 Gecko drive and a 200 step/rev motor, one micro-step equates to .00032 inches of travel (200 X 10 X .0003205 = .641”). I’ve tested the machine’s rapid speed at up to 850 ipm. I suspect the machine could run faster with Mach3’s new increase in kernel speeds, but 850 ipm rapids scare me enough as it is. I’ve limited rapid speeds to 450 ipm. The acceleration values in Mach3 are set to 45 inches/sec/sec. I’ve run acceleration values as high as 150 inches/sec/sec, however the sudden jarring of acceleration and deceleration seemed a bit excessive. I was afraid of shearing the roll pins that I had used to attach the pinion gears to their drive shafts.

The Z axis motor is connected to a 14 tooth XL timing belt pulley which drives a 28 tooth XL timing belt pulley which is coupled to a 4 start, 8 pitch, ½” diameter lead screw. I used a multi-start thread in order to increase the distance traveled per revolution and thus increase travel speed. With this thread I get 1/2” of travel per revolution of the screw. Unfortunately this was a little too much, with my original 1:1 pulley to pulley ratio, and the weight of the Z axis would back drive the screw and the Z axis would slowly drift downward into the cutting table when power wasn’t applied to the Z axis stepper motor. The new 2:1 pulley to pulley ratio stopped this. With this setup I get .250” of travel per stepper motor revolution. I haven’t tested the Z axis for maximum speed. However, I've set it to 150 ipm, which seems to be more than adequate for what I’m doing.

If you’re thinking about adding a water table to your setup, I have 3 words of advice…. “Just do it!!!” You won’t regret it. Prior to adding the water table to my system, I would open every window and door, in my shop, and turn on the fans. I would still end up with a layer of black dust that settled on every surface perpendicular to gravity. This dust would not just settle close to the machine, but on every square inch of my 20’ X 40’ shop. Nasty stuff!!! With the addition of the water table the dust problem has been reduced by at least 95%. I don’t have to open doors and windows anymore when I’m cutting. I have three 8” ports in the walls that can be hooked up to a ventilation system, and have yet to use them. Plus, I get to enjoy an air conditioned shop, as opposed to the 100 degree outdoor temperatures we’re currently having in Kentucky. The water table’s construction is similar to that shown in a PDF file from Thermal Dynamics that I found on the net, which uses compressed air to raise and lower the water level. Water in an inner tank is displaced by compressed air and flows out and up into the area below the sheet that is to be cut. The top of the support slats are ½” below the top lip of the table. The slats are 2 ½” tall and are set into slots in 3 “hangers” which are welded to the top of the inner tank. The distance from the bottom of the slats to the top of the inner tank is 1”. Therefore if I’ve adjusted the water height to just touch the underside of a sheet, I have 3 ½” of water below the sheet. Personally I think a water level of ¼” below the sheet works the best. The green/amber color of the water is due to an additive called “Plasma Quench”, which is available from Koal Industries. Plasma Quench keeps steel from rusting and keeps the water from going rancid. Since the steel doesn’t rust I don’t get brown murky water. The cut particles of metal just sink to the bottom for later removal. The water stays a transparent green/amber color with no smell. Based on my limited time using it (about a month), Plasma quench seems like a very useful product.

I am using Gecko 201’s to control each of the stepper motors. The Gecko’s are powered by a 42 volt power supply. The power supply was built according to the data sheets and information available from geckodrive. The parts to build the power supply were purchased from digikey. Once again, if you’re thinking about using Geckodrives, “Just do it!!!” They are a little pricey, however it’s definitely a case of “You get what you pay for”. You will be absolutely amazed at the amount of power Geckodrives can impart into a motor that’s barely larger than the palm of your hand (using sufficient power supply voltage, of course).

I am using cnc4pc’s C1G parallel port interface card . I’m using the latest lockdown release of Mach3 (Go Art!!!! Keep up the good work!!!) As for generating code, I think the simplicity and speed of Sheetcam is extremely hard to beat.

I’m using the THC300 torch height controller, available from Campbell Designs. As my local Hypertherm rep put it, “A torch height controller in NOT an optional item when it comes to a CNC plasma table. It’s a necessity”. After using my table with and without a THC, I wholeheartedly agree. It’s just something that you’ve gotta have. Figure it into your budget. Your cut edge quality, and consumable life will show for it.

If you’ve gotten this far, thanks, and I hope you’ve found some useful information.

Pictures of my machine can be found in the link to my gallery below.

Jcar,

http://www.cnczone.com/gallery/showg.../38704/cat/500

[zeoncomp]

Absolutely great "presentation" ... by far the best I've seen. Congrats - it looks great. At your convenience can you take some close shoots at the whole assembly servo - belt - pinion - rack ? That will be helpfull to continue with my project.

[Weldtutor]

Originally Posted by Jcar Hello All, I’ve had my CNC plasma table up and running for a couple of months now, and am finally getting around to doing a post on it. http://www.cnczone.com/gallery/showg.../38704/cat/500

Great description of your recently completed project. Thanks for sharing the information!

The photos show that you have done an excellent job of construction & will surely be an inspiration to others.

Fine job on the drive pivots to keep the pinions properly engaged in the racks.

[JEFFY]

Now that one hell of a nice table! You have got some very good ideas there, I'm going to have to barrow a few of them. Great idea on separate tank and gantry setup.

Your tank is huge, why so deep?

The additive that you added to the tank, was it in the form of an orange powder that turn it that color and what did it cost you? I think I know what it is and may have an alternative source.

Great job!

[massajamesb]

I give ya two thumbs up on that machine! Looks 100% in every aspect.
Although I have to say that I now have a craving for some green Jello.

[Scratch]

Looks great! and it's sooo nice and clean! and Is that an Xbox conroller or something...?

[bearracecars]

plasma quench is great. had it in my tank now for 9 months no smell no bugs
just add more water for evporation. i just haven't checked the ph balance. i did my tank with similiar design to the same one and it works great. my table is 67 x 129
bear

[svenakela]

It is an absolutely stunning machine, looks very professional!

[cut more]

Very Professional looking table!
I like the separate stock support table from the motion frame.
I tried searching for the pdf from thermaldynamics on the water table, but had no luck. Do you still have the link to that?
I really like your water table and being in the northeast, being able to not exhaust ~1000 cfm in the winter would be enjoyable!
Thank you for sharing your table.
Cutmore

[cnc metalcraft]

very clean table good job

[FL Knifemakr]

Well DONE Mr. C!!!! You really did one heck of a job on that.

[Jcar]

Thanks everyone, I appreciate the positive comments.

At your convenience can you take some close shoots at the whole assembly servo - belt - pinion - rack ?

Just above the pictures, in my initial post, you'll find a link to my gallery. There are several closeup shots of the drive system in there.

Your tank is huge, why so deep?

The tank is only half full of water, the rest is air inside the inner air tank. With this arangement I can release the air pressure and drop the water level below the bottom of my slat holders. In doing so, I can get parts out of the tank without having to dig around in a tank full of water.

The additive that you added to the tank, was it in the form of an orange powder that turn it that color and what did it cost you? I think I know what it is and may have an alternative source.

Plasma Quench comes in liquid form. I purchased a 5 gallon jug of concentrate for about $60. This is enough to treat 160 gallons of water. According to the MSDS sheets, Plasma Quench's active component is Sodium Nitrite. It's the same stuff that's used to preserve packaged meats. Yum!!!!

Is that an Xbox conroller or something...?

Yep......play a video game, cut some parts, play a video game, cut some parts.........sorry couldn't resist . Actually it's a Logitech USB game controller. I use it to jog and re-zero my axis' before running a part. It comes in very handy when I'm cutting on the side of the machine that's away from the keyboard.

I tried searching for the pdf from thermaldynamics on the water table, but had no luck. Do you still have the link to that?

It appears that the original link is dead. I do have a copy of the file, unfortunately it's larger than 500k and is too large to post. PM me an email address and I'll send you a copy.