Just getting started

[tjones14]

I have been tossing around the idea of putting together a CNC router or plasma cutter for a while. I am leaning more toward the plasma side but the gantry and table has me a bit stimied. I need at least 4x4 and I have to keep the completed build below $3,000. Needless to say I've been doing alot of web searching for parts, etc.

Currently I do not have access to much more than simple hand tools (except for a welder at my Dad's place, lol) so I'm not able to do any serious fabrication which means a DiY gantry kit of some kind is where I'm going to have to go. As far as the table itself is concerned, between my Dad's help and his welder, I shouldn't have any problem building it with parts I can pick up at a local hardware store. SO... here is what I'm thinking and I would love to know if I'm out of my mind on this....

I'm looking at starting with "Joe's Hybrid 4x4 CNC router kit". http://www.joescnc.com/themachines-hybrid.php and like I said earlier putting a nice sturdy table under it, and using candcnc.com Bladerunner 4 combo for the controller / drive motors. I know the kit is originally intended as a router build, however, since a plasma cutter won't have any tool load, I figure it should be more than sturdy enough for the build I am looking at.

I don't plan on cutting anything thicker than maybe 1/4" to 3/8" with this machine, predominately aluminum, but some steel, so I was also looking at a Hobart plasma cutter that I can pick up at Northern Tool just down the street from me. http://www.northerntool.com/webapp/w...6604_200336604

Just to throw this out there.. I understand that in many cases you get what you pay for, and having worked in the machine industry (mills and lathes) I know first hand the problems with having the "almost right tool for the job" instead of the "right tool for the job" because the first one cost a little less. I know that I could spend $15,000 on a small CNC Plasma system and do everything I am thinking and more. However, I'm not looking for a heavy duty, run all day, 5000 parts a week, machine. This is to tinker with and help out a friend with some one off (or 10 off) parts for a small business that he runs. Should things build then I'll use this to build a larger and more heavy duty machine. What I need to know is if this will allow me to cut those one off (or 10 off) parts with good tolerance control in less than 3/8" material, and if not what am I missing?

Thank you for any help / information that you can throw my way.

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[jimcolt]

The Hobart plasma system that you are looking at is a 12 Amp plasma system.....it is designed for hand cutting on gauge material....it will barely sever 1/4" material with an edge start......and may be able to pierce 3/16" thick material. You may be looking at it because it is self contained...has a built in compressor. It is doubtful it could cut 3/8".....and if it could, it would have to be an edge start and the cut speed would likely be in the 2 to 4 inch per minute range...very quickly getting the plasma beyond its duty cycle rating.

To cut the thickness ranges you suggest....you really need 40 to 45 Amps minimum...and some manufacturers 40 Amp systems will have trouble piercing 3/8". Due to your budget constraints...you should look for a used 40 Amp plasma...Craigslist is a good source. One of the best is a Hypertherm Powermax600...there are many out on the market...and it could suit your needs adequately.

Good luck on the table build....Tom at candcnc can probably offer some great suggestions.

Jim Colt

[tjones14]

yeah, you're right about the Hobart.

unfortunately after doing some more research it looks like I'm going to need a TCH controller and a few other things which is going to quickly take me outside of the budget that I'm restricted by.

Considering that I was going to fabricate a water table, I'm thinking that I might go back to a router build and figure out a way to apply coolant to the bits / endmills without destroying the router in the process.

Thanks for the info, I definately appreciate it.

[millman52]

yeah, you're right about the Hobart.

unfortunately after doing some more research it looks like I'm going to need a TCH controller and a few other things which is going to quickly take me outside of the budget that I'm restricted by.

Considering that I was going to fabricate a water table, I'm thinking that I might go back to a router build and figure out a way to apply coolant to the bits / endmills without destroying the router in the process.

Thanks for the info, I definately appreciate it.

I really don't think you will be able to cut any steel with endmills & a router. Aluminum you can probably get away with with a rigid machine.

[Torchhead]

If your $3000 budget includes the Plasma Cutter, you will have to build the mechanics and electronics on a shoestring. If you can find a used Hypertherm 600 or 900 at a good price, then you still need the motors, cables, drivers, interface, power supply (for the motors), control software and a few other odds and ends. A THC for use with MACH will be a minimum of another $400.00. Then you need the linear drive components. The fact you want a multi-use table starts to impact the cost because you need more rigidity and torque (heavier gantry) than for just plasma cutting. You have to properly size the final drive ratios to compromise so you can get the speeds you need for plasma (up to 300 IPM) and still have the torque you need for rotary cutting. These are two vastly different cutting processes that have to be accommodated with the same drive train!

There are a lot of components you can get at the hardware store but others will prove to be elusive. You can get all-thread for leadscrews but the extra fine pitch will have struggling to get more than about 45 IPM tops from a stepper system. They also are VERY inefficient on transferring energy (lots of friction). You won't find rack & pinion, gears, toothed belt pulleys, belts or v-groove bearings at the the hardware store.

You can buy the raw cards from us and save a few bucks if you have some experience building a CNC at that level. If you scrounge/borrow/steal the power supply and use something like the G540 Gecko motor driver you can bring the cost of the electronics in (including the DTHC) for around 1000.00 with good matched motors.

It's pretty easy to build a nice 4 X 4 or 4 X 8 plasma only table for about $5000 to $6000. Doing it for 1/2 of that AND making it dual purpose should be a series worthy of DIY TV!

You can use a mister system on rotary cutting for aluminum. You need a router with variable speed even for that. Forget cutting steel. You will never be able to get down to the correct RPM or torque to run an end mill in steel; even if you could, the cutting forces are such that vibration would ruin any accuracy.

TOM Caudle
www.CandCNC.com
TOtally Modular CNC Electronics.

[tjones14]

I wasn't really looking for multi purpose, I just found an easy (for me) gantry system (the Joe's stuff) and was going to build a Plasma with it. However, like you said, a plasma in the budget that I've got just isn't going to make it. That being the case, I mentioned switching to the router build. I think that's were the confusion set in.

[Torchhead]

Okay. A plasma only can be done for less cost and optimized for that type of cutting. Concentrate on keeping the gantry light. Have a look at the bare bones tables at http://www.PrecisionPlasmaLLC.com. He has a direct drive R & P table (not normally recommended since you end up with 1/3 the motor torque) that uses 300 oz-in motors on a dual drive gantry and he gets upwards of 50 IPS/Sec acceleration (very good) and wickedly fast rapids. The key is the Gantry is ultra light and for non-contact cutting only.

If you don't have access to machine tools to make your mounting plates and brackets you might entertain one of his gantry kits.

It easier to start out with a design that is for the type cutting you are going to do. Adapting a router design to plasma (or vice versa) is not always a quick solution.

There are other considerations as well. The smoke and dust from plasma cutting is abrasive, conductive and gets on everything that is nearby. Even with a water tray. a lot will still drift and deposit so precision components like ballscrews, linear slides and electronics need to be protected. R & P is the most popular drive type for plasma because it is more immune from the debris and offers a cost effective way to get solid rotary to linear movement.

TOM caudle
www.CandCNC.com