Anyone make a plasma/router table?

[bamwa]

Hello I am starting a build and would like to plasma cut as well as switch out to a router. Has anyone seen a thread here regarding that? I know it would need to handle the extra lateral forces. I would be interested to know other's experiences with such a "crossover".

Thanks,
Bamwa

Feelin' fine in 09!

[Torchhead]

What size? For a mixed use table you need to design for the two ends of the cutting spectrum. Plasma needs high speed and high acceleration. Typically you get those from gearing the motors higher and using light weight construction on the gantry. Routers need lower speed and higher torque with heavier and more rigid gantry and Z axis construction. For a mixed use you need a high speed, high torque and rigid design. If you are doing a 4 X 4 consider steppers and rack & pinion with about a 4 or 5:1 belt reduction to the steppers. That will give you good speeds and torque. If you can use a dual drive gantry (motor on each side) to double the torque on the heavy gantry.

If you are thinking 4 X 8 you can stay with steppers (especially with a dual drive) but maybe consider going to servos for the increased torque and speed you will get. At 5 X 10 the servos really start to make sense on a mixed mode machine.

There have been lots of mixed mode machines built. Pick your electronics so they easily support both modes of cutting (aka Torch Height Control) without taking out a home improvement loan!

Then there is rotary axis cutting ...........{:-)

TOM CAUDLE
www.CandCNC.com
Totally Modular Electronics for CNC

[bamwa]

hello tom and thank you for responding to both my posts. My table is sized to cut a 5x10 sheet so my water box is 6x12x1 (currently just finished welding it water tight). My x axis i-beams will be 7' outside to outside. I have already purchased the xylotex 4 axis drive box with 425oz. steppers so I will be running dual drive and saving the 4th axis for lathe style chuck add on. Have you seen any dual use tables in action? I was wondering more specifically how much z axis to give it. I am a welder, so I really despise sawdust or even the sight of lumber in my shop, but thought what the hell if I want to make a sign or flying v guitar body I should be able to (I think).

Peace,Bamwa

[Torchhead]

That drive module and motors is WAY undersized for a large table like that. The Xylotex is limited to using 24VDC. That results in stepper motors that only spin to about 350 RPM. That limits the amount of belt reduction you can use. If you use R & P and direct dive the pinon, you will have enough speed, but not enough torque to pull a sick cat out of bed. The resolution will be poor as well. That rig is made for small tabletop mills and engravers. Plasma HAS to have speeds up to 200 IPM. Moving a large gantry at those speeds with slow motors will be a challenge that is the root of frustration.

The inputs to the Xylotex are not opto isolated so the PC/logic ground is the same as the motor ground , is the same as the plasma ground, etc, etc. You may get lucky and plasma noise floating around won't get into your step & Dir inputs.

After you have all that figured out you will find that the Xylotex offers no input isolation so your table switches will feed your parallel port directly and most likely cause the PC to reset or hang. Running a table without fixed home switches is another level of frustration.

There there is the matter of a THC.......

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics

[bamwa]

Hello Tom, thanks for the news. I would like to use belt drive. I don't know if that changes your opinion about my situation any. Here is my correspondence with xylotex:

"Hi there, I am interested in purchasing cnc equipment to make a plasma
> table and have a few questions I hope you can answer.
>
> 1. What is the lifespan of your stepper motors?
>
> 2.What is the lifespan of your controller boards?
>
> 3. I intend to build a 5'x10' table. Do I need two motors for the x
> axis? If so, how would they be wired? Would they vary slightly and cause
> problems?
>
> 4. Do I need 4 motors or three? ( I would like to use rack and pinion,
> and have a water table.)
>
> 5. Do I need to use a torch height controller? If so, do I need to set
> up the z axis anyway and have both to raise/lower the torch?
>
> Thanks for your time."

The response was:

"Hi,
I don't know the lifespan of the motors. I've been selling them for a
few years and haven't has any "die" of old age.

Same goes for the drive boards, but if mistreated, they can be
destroyed. Damage is mostly caused by overvoltage and over current.
In a properly set up system they will last years. You would need to
make sure that high voltage were not allowed to come close to the drive
board wiring.

I would suggest two motors for the X so you do not have a drive screw
down the middle. Mach3 can "slave" one motor to the other so they get
driven at the same speed, so you would need 4 motors total.

I suppose a THC would be good, but the drive are only stepper motor
drives, and don't have anything to do with THC except provide a place
to get access to extra parallel port I/O.

You would want the 425 oz.in motors for this type of system. You can
see a plasma table here that is driven with Xylotex drives and 425's :

http://www.xylotex.com/Gallery/Gallery.htm

I don't have any experience with plasma tables or cutting so can't
offer any advice about their construction."

Maybe that last sentence tells it all? I was under the impression that the "kickass machines" brand table uses this same equipment. Maybe I should get ahold of them up there in Canada A? And also throw in the towel on routing?

As far as stating I MUST have 200 IPM. I set out a test piece of 1/8" flat bar and average about 10" in 10 seconds. That equals 60 IPM.

Thanks again for your knowledge torchhead.

[jamesrnz]

mmmmmmmmmm, i am interested in something similar, i have tried to search for a forum already in place.

i would like to do 4x8 cutting area. so if i were to do this what type and size of motor step or servo, power supplies bearings, low cost or free software..etc...

thanks

[bamwa]

hey james, I think the best place to start is to look around at your favorite designed table and read up on what they are using. I am attempting a belt drive setup with 2 motors on the x axis. I am trying the 4-axis kit from xylotex with 425 oz stepper motors. I might findout I can't use a router because I'm not using gear rack, or the motors are too weak, or the gear ratio is incorrect. That's ok because I mostly want it for plasma. Also my budget may be more limited than yours ( shooting for the under $1000 barrier ). Being a metalworker I have plenty of scrap and leftovers from jobs and whatever to build frames for a water/cutting table.

[Lightfoot]

Gorrilla CNC in London Ontario has a system on their web page . Router/plasma.

[lpbany]

servo driver,servo motor,gearbox,heavy beam
plasma,oxy,drill,and etc is enough
stepper driver,maybe not a good idea

[Torchhead]

We sold a desktop Xylotex 4 axis stepper driver/PC interface product for a couple of years and even ran one ourselves on a small 10X10 tabletop engraver/router. It was slow but reliable. We would not sell one of the units to a customer wanting to build a plasma table since I did not want to have to support something I know would face probelms.

When we introduced the BladeRunner package based on the Gecko250 drives we switched the table top over (using the same 300 oz-in steppers) and got almost 3X the speeds. It went from 60 IPM max to over 150 IPM.

To get enough speeds for plasma you need to be able to hit 200 IPM (250 to 300 is better). A direct drive belt setup will get you that (and a lot more, but you will have low torque at any speed above 100 IPM (low torque means low acceleration and that means rounded corners) It also costs you resolution which a much more critical parameter for routing. You always have to trade speed for torque and resolution (essential component of accuracy) or vice versa. So the more raw speed you have the more you can trade and still keep decent rapids.

The raw resolution of a stepper motor is 200 steps per rev (.005 if it moves one inch in one rev). With a belt drive (or rack & Pinon) the DIAMETER of the driving pulley/pinon TIMES PI (3.1416) gives you the distance you travel in one rev. A 1" drive pulley turns that .005 resolution into over .015...and that is before any other errors are factored in. So in essence you have traded accuracy and torque for speed you can't use.

Plasma has an inherently poor accuracy of about .020 so add that to your machine accuracy and you have the final amount. Regardless of what you hear about microstepping it's for smoothness rather that an increase in accuracy; especially at higher step rates.

To have a rig that does both plasma and router, you need both speed AND accuracy with more torque. The gantry needs to be more rigid for routing and the Z needs to be a lot bigger as well. All of that adds up to more mass to accelerate and stop all while pushing a bit through wood/plastic/aluminum. It's like needing a sports dump truck.

Sometimes the goal to build something as cheap as possible clouds the concept of the overall usefulness.

I would suggest at least a step up to a GECKO540 rig with it's higher rated drives (3.5A @ 48VDC) and it's input opto isolation would end up, in the long run, a solution that has a chance of working up to semi-professional levels. It's capable of driving 23 frame steppers up to 620 Oz-in and moving higher mass gantrys (with a dual drive). Several 4X4 router and router plasma have been done with good results.

The last notation (then I will shut up) is about the plasma cutting process and how much noise is generated when you vaporize metal with a 30,000 arc/flame and blow it out with air. It makes using a system with a shared ground (everything on one ground) a challenge to make work reliably. A few volts of noise on a common ground between systems can cause problems that are tough to find and even harder to fix.

The sour taste of poor performance and wasted material lingers long after the excitement of low cost wears off.

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics

[rgillard]

Hi Guys,

I too would love to build a machine that is capable of both plasma cutting and wood routing and other machining processes if possible (engraving, drilling etc.). However I do understand that to have a good plasma cutting machine you need to set up the drives to suit the plasma torch, which does not suit the router. A plasma torch needs high speed-low torque and the router needs low speed-high torque.

Would it be possible to manually change the gear ratio when changing the cutting tool. What I mean is if the motor was driving the pinion gear via a belt could you have two different size pulleys on the pinion drive shaft. The motor would have to be bolted down on a plate with adjustable slots so that the output pulley of the motor can be moved to either pulley on the shaft. If you had two sets of belts, one for each setup would this work? Its just a thought but it may be worth looking into. The whole trick would be to design it in such a way that the transition is quickly and easily done. I dont know about Mach3 but could you store 2 machine setup/configuration files which would have the different parameters for acceleration etc for each type of cutting? I can do up a sketch if this is hard to understand. It makes perfect sense in my head but that may not mean its understandable.

Any thoughts would be appreciated.


Regards,
Ronan

[Torchhead]

That would work but what a PITA it would be to change over each time. MACH allows as many setup profiles as you want and each can be for different motor/timing setups. If you pick the correct motor driver/motor package and build a machine that can support both then you have the solution without the swapping of belts and added expense of the pulleys, etc. The accepted method is to just power the table via bigger motors and faster drives (speed on steppers comes from voltage). My observations had to do with picking a drive system that offers you the capability to do both high speed and high torque/resolution. It means you have to build a table that will let you get max efficiency out of the new high torque stepper motors like the new 620's at www.HomeShopCNC.com. The core of this thread was about the original post about using the Xylotex motor drives. I don't think that motor driver/motor combo is well suited for larger tables (than desktop) or mixed use designs.

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics