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Hi all finally found where to write something on hear .I am looking to build a c n c plasma cutter table looked about you tube all seems to be american or china .I have found xtream plasma but I would prefer something that runs on a rack and pinion .So if there is anyone that can help advise or point me in the rite direction that would be good thanks in advance .
What exactly do you want to know.? Do you want to know more about rack and pinion or more about building the machine as a whole.? Or something else.?
Don't be afraid to ask what may feel like dumb questions, not asking would be the only dumb thing.
HI thanks for the reply the lot from stepper motors gearing, ball screws software the hole thing before I start spending money really..
Ok well, the first thing you need to learn is NOT TO BUY ANYTHING until you understand fully what is required and why you fitting those parts. I CANNOT STRESS ENOUGH just how important this is because if you do buy without learning why then it's 90% likely you'll buy wrong and waste money.Quote:
Originally Posted by ktm530
Ok, here we go, get yourself a drink in a comfy chair because it's going to be a long read.!
The first thing to know is that plasma is very very similar to a router in how it works but does have its own quirks that mean it needs to be specified slightly differently in some areas.
#1 One misconception is that It doesn't need to be built as strong because there are no cutting forces involved, which is partly true in one area, lighter materials can be used for the gantry because there are no cutting forces.
However, depending on the size and thickness of materials you intend to cut and if you fit a water bed or not then the frame may need to be built stronger than a typical wood router. Why.?
Well, my 45A plasma can pierce up to 16mm steel plate and cut up to 30mm steel plate if entering from off the material, so handling and dropping onto the bed a 1mtr x 2mtr piece of say 16mm steel plate will very quickly take its toll if not built strong enough.
If only cutting thin gauge sheet say 0.5mm to 3mm rather than plate then this isn't so important in terms of frame strength but does change the spec of other areas which I'm coming to next.
#2 Speed, Motor torque, and resolution:
The speed at which you will cut varies massively with material thickness in plasma, a thick plate is cut very slowly whereas a thin sheet is cut very quickly. This means the relationship between motor and the system you choose for linear motion ie: ball-screw, belt, or Rack n pinion driven becomes important.
BIGGER is NOT BETTER when it comes to stepper motors so depending on which linear system you choose will determine just how small you can keep the motors.
For instance, ball-screws are very efficient, typically around 90% to 95% so require less power than Rack and pinion which can be as low as 40% so you can get away with smaller motors that spin faster. However, plasma cutting can be a dirty grimy business with water and very abrasive dust which doesn't suit ball-screws very well and wears them out quickly. Also, if the machine is longer or wider than 4ft then ball-screws can start to introduce whip into the equation.
Rack and pinion aren't so fussy and will handle this environment better and far easier for longer or wider machines, but now resolution and low efficiency comes into play. The pinion size determines the speed and resolution of the machine, a large pinion will give high speed but low resolution, the trick is getting the balance right between pinion size and motor torque required.
So you have a choice BIG TORQUE MOTOR with direct drive or LOWER TORQUE MOTOR with a ratio applied.?
Now, the resolution kicks in.?
The direct drive will give a low resolution unless the pinion is very small with fewer teeth, a lower number of teeth means fewer teeth engaged with the rack so less force can be applied otherwise teeth jump and wear excessively, but remember we don't need a lot of force because we don't have cutting forces. But, we do need a certain amount of resolution, or cutting smooth arcs, circles or fine detail becomes impossible.
Now speed, acceleration and motor size come into play.?
If we are only cutting thick material then a large motor that is slower won't matter because we have lots of torque and won't be spinning very fast, resolution still plays its part but to a lesser degree unless fine details.
But if we are cutting thinner material that requires high speeds with high acceleration then large motors with direct drive and low resolution are a BIG problem.
So we need some way to find a balance and this is done by using a reasonably sized pinion with a ratio applied to the motor which can be a smaller size which will spin and accelerate faster, albeit with less torque than a large motor. However, the ratio cancels this out because it increases torque, it also increases resolution, so with the right combination you can have achieved both high and low cutting speeds with good resolution and decent acceleration.
Belt drive.?
This offers an option between ball-crews and R&P. Belt drive is very efficient at around 70% to 85% it also doesn't suffer from the harsh environment as much as ball-screws do. It does still need a ratio like R&P but not quite as much and because it's more efficient the motor power can be less.
#3 Linear motion.?
The type of linear rails you use will become a small factor.? Because we have no cutting forces to speak of and gantry weight is a lot lower, then load ratings are not so important and you will often see plasma machines using V-bearings running on edges of steel angle because all they really need to do is roll smoothly. However, you still have a dirty environment to deal with and personally, my experience of these setups is they don't last very long and become sloppy and troublesome over time. Fitting decent linear rails will pay back over time with less hassle.
#4 THC.? (Tool heigh control) Do you need THC or not.?
This depends on material thickness, if mostly cutting material that is thicker than say 8mm then probably not because the material doesn't bend much with the heat. But if thinner material like 1, 2, and even 5mm then 100% YES because it warps and bends like crazy so you will need the torch to follow this bend to maintain the cutting height as it goes about its business. If not you will get poor quality, lost plasma arc and worn tips, and other side effects as the cut height changes while cutting.
#5 Electronics.?
Plasma is very electrically noisy and will send most electronics into meltdown if not wired and earthed correctly. Also, the quality of the electronics used is very important and if you want to keep any hair you might have on your head then don't buy cheap electronics.
For instance motion controllers, don't buy USB-based motion controllers because they are flaky at best of times and in a plasma environment they just crumble unless specifically designed and shielded for plasma. Ethernet is the only way to go if you want a stable controller.
The rest of the electrics like stepper drives and motors are less affected by plasma but they must be wired using shielded cables and earthed correctly otherwise they will lose steps.
So here's what I would recommend.
R&P for X & Y-axis. using a Module 1 or 1.25 rack with 20 to 25 teeth pinion. Mod1 is = to 1mm pitch between teeth, so 20T would give a DP (diameter or diametric pitch) of 20mm, likewise Mod1.25 = 1.25mm so 20T = 25mm DP.
Now this DP becomes important because to give the true pitch or distance traveled for each revolution of the motor we need to apply good old "pi" so 20 x 3.141 would give a pitch of 62.84mm which if directly driven would give low resolution, ideally a pitch of about 20-30mm is what we want. So in this case we would apply a ratio of 2 to 1 between motor and pinion giving roughly 30mm per motor revolution.
When used with a typical stepper that can reach 1000rpm this would give in excess of 15mtr/min travel speeds with a 2:1 ratio and a realistic resolution of around 0.1mm or better.
For the Z-axis a 5mm or 10mm pitch ball screw directly driven will do the job.
Stepper motor size 3 to 4nm Nema 23 or 24 with 70Vdc drives with a 50 to 60Vdc PSU will do the job nicely for X and Y-axis, the Z-axis would get away with 2Nm as it's not carrying a lot of weight.
Linear rails I would use either supported round rail or better still profiled linear rails size 15 or 20mm.
Motion controller, any ethernet-based controller like AXBB-E or UC400 from CNCDRIVE will do the job.
THC: Then I'm not sure as I use a Linux CNC mesa card THC setup (which I don't recommend for a beginner) and have never used windows based THC.
However, there are several THC setups like the Proma Compact, etc.
Other than this then just use shielded cable on all motors, limits, E-stop, and signal cables also make sure you use a Star grounding system and pay careful attention to how you run wires around the machine trying to avoid any signal wires running alongside or close to high voltage power cables.
Hope this helps.
Wow that is a lot of info thank you very helpful. I was thinking same balls reward for z but never thort of pitch so that was very helpful. And open carriage linner rail tracks for x y. The motors thinking of closed loop motors 2x 34 for y and 1x24 for x and a 24 for z. A stand alone singalong border computer. But now the software????? Any suggestions I am playing around with fusion 360 but mach 3/4 seems to crop up a lot on videos again many thanks for your advice so far.
Some more reading for you:-Quote:
Originally Posted by ktm530
https://forum.linuxcnc.org/plasma-la...g-in-one-place
https://forum.linuxcnc.org/plasma-la...info-and-guide
Don't need 34's for the Y-axis because like I say bigger is not better. NEMA 23's will give you better performance and still have plenty of performance. I'm not getting into why because don't want to cloud things with technical details just trust me 34's would be a mistake.Quote:
Originally Posted by ktm530
All PCs are kind of stand-alone unless you are meaning a stand-alone controller with PC built into it.? I don't know any stand-alone controllers that are not USB and like I said you will regret using USB for plasma unless the stand-alone controller is specifically designed for plasma and even then I wouldn't trust it.!Quote:
Originally Posted by ktm530
Also, stand-alone controllers don't usually have toolpath display or features for seeing what's going on. a PC based setup with a separate controller are much better to use and see what's happening.
F360 is CAD/CAM software where you design the part and program the toolpath. Mach3/4 is the control software that runs the machine, they are completely different and not to be confused.Quote:
Originally Posted by ktm530
However, I don't think F360 does plasma CAM, I may be wrong as I don't use it, but most people use a program called Sheet CAM for generating the cutting tool-paths. This software is designed purposefully for Plasma with features exclusive to plasma.
The process goes like this. Design the part in the CAD side of F360 then program the tool-paths for cutting the part in the CAM side of F360 and use what's called a post-processor to save the file in a G-code format which mach3 can understand.
Then load the G-code file into mach3, set your X, Y zero points, usually, with plasma, you don't set Z-Zero as you have a touch sensor that sensors the material and lifts the torch to pierce height then drops to cutting height.
From what you are saying, again I strongly recommend you DONT buy anything because you have a lot of learning to do and will buy wrong.
The best advice is to start researching and reading any plasma builds you can find to understand the process of how it works in regards to CAD/CAM and control software. Also, the difference between a router and Plasma regards the Z-axis and THC, with plasma you have a Z-axis but as mentioned above you need some way to sense the material because each time the torch lifts to go to a new area of the part it needs to sense the material surface and retract to the pierce height, often this is done with the torch attached to a plate on the separate rail on the z-axis. Also, this separate plate is designed to break away from the Z-axis and stop the machine should the torch snag on a piece of material while cutting, which can happen often with plasma.
OK thanks again for your advice. Do you build these machines, or have plans, parts kits etc. If so have you got any pics/ videos you could send/ show me many thanks.
We don't build plasma's at the moment which we offer for sale but we are going to at some point in the not too distant future.Quote:
Originally Posted by ktm530
We do have parts like a Closed-loop stepper system, Ethernet motion controllers, linear rails, drag chains,s and other electrical components like proximity switches, E-stops, etc. which we fit on the routers we build and do offer for sale. All of these are suitable for a plasma machine.
When you are ready and know what you need then get in touch and I'll give you a price
Quote:
Originally Posted by JAZZCNC