527,994 active members*
2,407 visitors online*
Register for free
Login
Page 1 of 2 12
Results 1 to 20 of 29
  1. #1
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    CNC plasma setup. Lots of questions.

    I'm getting ready to build a 4x4 CNC plasma table for our in-house production. But the problem is that I know virtually nothing about plasma cutting. I can build the table and controls, no problem. Done this many times. So this thread is directed at the plasma hardware and cutting process.

    I plan on buying a Hypertherm Powermax 45XP plasma unit and a proper machine torch for it. I've not decided on a torch height control yet, or I may build my own integrated into my controls. If I do buy one, it won't be one of the cheap ones on ebay.

    Edge finish is the most important to me. The bulk of our production will be 11ga 304 SS. We are currently having these parts laser cut and I would like to achieve similar accuracy (1) and edge finish. There are 1/4'' holes in some of the parts and they come out acceptable on the laser cut parts, I would like to maintain this. It's my understanding that it is somewhat difficult to make small holes with a plasma system.

    So this goes out to all of you CNC plasma gurus out there. Because I am not educated enough yet to even know what questions to ask, my main questions at this point are what torch and consumables do I need for fine work? Any tips and tricks are appreciated.


    (1) Accuracy is really achieved in the job setup, repeatability is the more important parameter on any machine tool.
    Jim Dawson
    Sandy, Oregon, USA

  2. #2
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Posts
    23452

    re: CNC plasma setup. Lots of questions.

    One of your best bets is to visit one of the well known local welding/cutting suppliers, they can usually provide a wealth of information on requirements and operating details, tips etc..
    Hypertherm is nice equipment, I have never built a CNC table version, but have worked on a few in the repair/maintenance capacity.
    One major manuf. unit I worked on had a PC based system with a Galil motion card in the slot.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
    Member
    Join Date
    Jul 2018
    Posts
    1711

    re: CNC plasma setup. Lots of questions.

    Hi Jim - I have not built a plasma machine but I have been asked to by a few people to do this. My involvement in plasma is observing production machines. I worked at a company that had a "high definition" plasma but they went to laser one they came down in cost. It's my understanding that plasma can't produce the same accuracy or edge quality as laser otherwise why would production shops convert to laser? except for very thick plate but that's changing. Have you seen sample cuts from the hypertherm? cheers Peter

  4. #4
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by Al_The_Man View Post
    One of your best bets is to visit one of the well known local welding/cutting suppliers, they can usually provide a wealth of information on requirements and operating details, tips etc..
    Hypertherm is nice equipment, I have never built a CNC table version, but have worked on a few in the repair/maintenance capacity.
    One major manuf. unit I worked on had a PC based system with a Galil motion card in the slot.
    Al.
    I'll be checking with the local vendors in the next few days. I already have the Galil board for my table Bought it a couple months ago.

    Quote Originally Posted by peteeng View Post
    Hi Jim - I have not built a plasma machine but I have been asked to by a few people to do this. My involvement in plasma is observing production machines. I worked at a company that had a "high definition" plasma but they went to laser one they came down in cost. It's my understanding that plasma can't produce the same accuracy or edge quality as laser otherwise why would production shops convert to laser? except for very thick plate but that's changing. Have you seen sample cuts from the hypertherm? cheers Peter

    I have seen YouTube videos of the Hypertherm cuts and they look not much different than the laser cuts we are getting from our vendor (which are quite good). As near as I can determine, it's a matter of proper setup, the correct torch and consumables, possibly a gas mix, and good torch height control. I would like to have a laser but at about 10X the price, we're going to try the plasma first.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Posts
    23452

    Re: CNC plasma setup. Lots of questions.

    The one I worked on that used Galil, were fairly large tables, they use two X axis motors, one side had a rack and pinion, the other side used the same model motor and was a slaved off of the pinion side.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  6. #6
    Registered
    Join Date
    Sep 2005
    Posts
    1121

    Re: CNC plasma setup. Lots of questions.

    What THC you will use ? A good edge finish maybe need a good THC ...

  7. #7
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by asuratman View Post
    What THC you will use ? A good edge finish maybe need a good THC ...

    I don't know which THC I will use, I am still researching that question. Maybe I will build my own. But I agree, the THC is important for edge finish.
    Jim Dawson
    Sandy, Oregon, USA

  8. #8
    Registered
    Join Date
    Sep 2008
    Posts
    139

    Re: CNC plasma setup. Lots of questions.

    Hi Jim,
    Our shop uses Hypertherm 'Fine-Cut' consumables, but 1/4' holes in 11ga. 304 would be hard to do if
    you want laser quality.
    Good edge quality needs a good drive system, clean, dry air, and settings for speed, torch height etc.
    Plasma cutting is also not to clean and quiet.
    I would look at this system.
    https://www.3dfablight.com/
    Larry

  9. #9
    Registered
    Join Date
    May 2015
    Posts
    495

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by Jim Dawson View Post
    I don't know which THC I will use, I am still researching that question. Maybe I will build my own. But I agree, the THC is important for edge finish.
    I would recommend you use Linuxcnc's Plasmac config
    PlasmaC User Guide
    And read the Linuxcnc Plasma primer I put together
    Plasma Cutting Primer for LinuxCNC Users

    The reason I say this is that if you use a Hypertherm machine with a RS485 interface, Linuxnc can control it for you.
    Plus Linuxcnc and a $69 Mesa THCAD card renders the whole concept of a THC obsolete becasue Linuxcnc knows the arc voltage in real time and can control the torch height using its sophisticated all seeing, all knowing motion controller.

    Plasmac is more than a THC, its a complete fully integrated plasma controller which the Windows controllers with an external THC can't compete with.

    Anyway, I cut a fair bit of 2mm (similar to your 11 ga). You have to remember plasma is a blunt axe compared with a laser cutter. A laser can cut tap ready holes down to M4 (3.2mm dia hole) in that material. At 10mm, I can get a reasonable hole that are great to pop a nutsert in. At 6mm (maybe 5mm at a pinch) I can get a reasonable clearance hole. But the solution is to spot the hole centres with the plasma torch and drill the hole where accuracy is required. Plasmac supports this.

    Just Remember air plasma is not high definition plasma which can compete with laser (aside from the work hardened edges). But then again a 45XP is not a $100k high def system either.
    Rod Webster
    www.vehiclemods.net.au

  10. #10
    Registered
    Join Date
    Sep 2008
    Posts
    139

    Re: CNC plasma setup. Lots of questions.

    Hi Jim,
    Some things to consider on small holes,:
    Pierce Height, Lead-in and Lead-out, Offset, Offset-in, Offset-out, or
    no Offset, voltage, travel speed,torch height
    Hypertherm 'Fine Cut Consumables' have a .040"-.045" kerf width.
    X and Y moving at the same time, belt drive,rack and pinion,lead
    screw or ball screw?
    Clean dry air, and hope no holes are cut on top of the slats.
    I've cut thousands of small holes and slots, but only for sheet metal
    screw clearance, as long as the hole is smaller than the screw head
    it works for me.
    You can also mount a drill motor on the gantry for holes, if the rest
    of the part can be cut.
    Larry

  11. #11
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by rodw View Post
    I would recommend you use Linuxcnc's Plasmac config
    PlasmaC User Guide
    And read the Linuxcnc Plasma primer I put together
    Plasma Cutting Primer for LinuxCNC Users

    The reason I say this is that if you use a Hypertherm machine with a RS485 interface, Linuxnc can control it for you.
    Plus Linuxcnc and a $69 Mesa THCAD card renders the whole concept of a THC obsolete becasue Linuxcnc knows the arc voltage in real time and can control the torch height using its sophisticated all seeing, all knowing motion controller.

    Plasmac is more than a THC, its a complete fully integrated plasma controller which the Windows controllers with an external THC can't compete with.

    Anyway, I cut a fair bit of 2mm (similar to your 11 ga). You have to remember plasma is a blunt axe compared with a laser cutter. A laser can cut tap ready holes down to M4 (3.2mm dia hole) in that material. At 10mm, I can get a reasonable hole that are great to pop a nutsert in. At 6mm (maybe 5mm at a pinch) I can get a reasonable clearance hole. But the solution is to spot the hole centres with the plasma torch and drill the hole where accuracy is required. Plasmac supports this.

    Just Remember air plasma is not high definition plasma which can compete with laser (aside from the work hardened edges). But then again a 45XP is not a $100k high def system either.
    Thank you for you insight on this. I will review the documents you linked to. I won't be using Linux, but I may duplicate that THC functionality in my own software and system. I will be using the Powermax 45XP RS485 interface, I have the communication protocols for it. The good news is that the small holes in question are just clearance holes so some deviation from nominal is acceptable. The goals of this project are: 1) Bring our laser cut parts production in house, and 2) make the most accurate CNC plasma cutter possible without spending $100K plus.

    Quote Originally Posted by metalfixer View Post
    Hi Jim,
    Some things to consider on small holes,:
    Pierce Height, Lead-in and Lead-out, Offset, Offset-in, Offset-out, or
    no Offset, voltage, travel speed,torch height
    Hypertherm 'Fine Cut Consumables' have a .040"-.045" kerf width.
    X and Y moving at the same time, belt drive,rack and pinion,lead
    screw or ball screw?
    Clean dry air, and hope no holes are cut on top of the slats.
    I've cut thousands of small holes and slots, but only for sheet metal
    screw clearance, as long as the hole is smaller than the screw head
    it works for me.
    You can also mount a drill motor on the gantry for holes, if the rest
    of the part can be cut.
    Larry
    I haven't decided on the drive system, but given that the design cutting envelope is only 4x4 ft, I am leaning towards ball screws right now. I can position the gantry to +/- 0.001'' or better reliably with any drive system so that's not a problem. From my research, it seems that one of the problems with cutting small holes is being able to maintain the cutting speed on a small circle. It seems that slowing down to make the small circle degrades the cut quality. I think this is a limitation of the mechanics of many machines, and one that I can overcome. I'll have to do some experimenting, but I suspect that changing the power unit parameters on the fly will have some effect, good or bad I don't know yet. With the Powermax 45XP this is possible through the RS485 interface.

    I have a very good shop air system with a refrigerated dryer, and will add additional air filtration/drying directly ahead of the plasma system.

    Funny you should mention drill motor(s) on the gantry. I was having that conversation with my son last night. I just happen to have 2 gantry mount drill motors on the shelf, pretty easy to integrate into my system.
    Jim Dawson
    Sandy, Oregon, USA

  12. #12
    Registered
    Join Date
    May 2015
    Posts
    495

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by Jim Dawson View Post
    Thank you for you insight on this. I will review the documents you linked to. I won't be using Linux, but I may duplicate that THC functionality in my own software and system. I will be using the Powermax 45XP RS485 interface, I have the communication protocols for it. The good news is that the small holes in question are just clearance holes so some deviation from nominal is acceptable. The goals of this project are: 1) Bring our laser cut parts production in house, and 2) make the most accurate CNC plasma cutter possible without spending $100K plus.
    .
    You can't bring the THC up to the level of Plasmac from a Windows Machine running Mach or similar. You are limited by a simple bit bashing up/down interface. You can't sense velocity in real time and vary cut parameters and you can't tell the motion controller the torch voltage.

    BUt I understand you want to stick to what you are familiar with.

    Quote Originally Posted by Jim Dawson View Post
    I haven't decided on the drive system, but given that the design cutting envelope is only 4x4 ft, I am leaning towards ball screws right now. I can position the gantry to +/- 0.001'' or better reliably with any drive system so that's not a problem. From my research, it seems that one of the problems with cutting small holes is being able to maintain the cutting speed on a small circle. It seems that slowing down to make the small circle degrades the cut quality. I think this is a limitation of the mechanics of many machines, and one that I can overcome. I'll have to do some experimenting, but I suspect that changing the power unit parameters on the fly will have some effect, good or bad I don't know yet. With the Powermax 45XP this is possible through the RS485 interface.
    .
    The RS4845 is very slow at 19200 baud and there is no acknowledgement when the requested setting has been made. Its totally not suitable for real time control in that way. There is a new plasma from Telwin that has a 0-10 volt current interface so it might be possible to control the current with the spindle command. (eg S100 = 100 amps). That would give real time control. With Linuxcnc you could control this outside of Gcode based on motion controller parameters, velocity, max acceleration, arc radius etc and you could offset he torch path as well to account for a wider kerf. The bigger Hypertherm controls allow current via the Ethernet bus.

    Acceleration is the key to small holes. I've experimented with rates up to 0.8 G, 36 m/min rapids but you really need to have a very stiff well anchored machine that can handle that sort of inertial force. You cannot allow the gantry ends to flex under inertia. Hypertherm talk about Centripetal Limiting but the calculations we've done indicate this is not going to help much as it comes up with very small radii so I'm not sure if we have the maths right.
    Rod Webster
    www.vehiclemods.net.au

  13. #13
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by rodw View Post
    You can't bring the THC up to the level of Plasmac from a Windows Machine running Mach or similar. You are limited by a simple bit bashing up/down interface. You can't sense velocity in real time and vary cut parameters and you can't tell the motion controller the torch voltage.

    BUt I understand you want to stick to what you are familiar with.
    I agree that Mach3/4 would not be suitable for what I want to do (nor for much of anything else for that matter) which is why I won't be using it. Not sure what you mean by ''bit bashing up/down interface'' I would ask why I can't sense the velocity and torch voltage in real time?


    The RS4845 is very slow at 19200 baud and there is no acknowledgement when the requested setting has been made. Its totally not suitable for real time control in that way. There is a new plasma from Telwin that has a 0-10 volt current interface so it might be possible to control the current with the spindle command. (eg S100 = 100 amps). That would give real time control. With Linuxcnc you could control this outside of Gcode based on motion controller parameters, velocity, max acceleration, arc radius etc and you could offset he torch path as well to account for a wider kerf. The bigger Hypertherm controls allow current via the Ethernet bus.

    Acceleration is the key to small holes. I've experimented with rates up to 0.8 G, 36 m/min rapids but you really need to have a very stiff well anchored machine that can handle that sort of inertial force. You cannot allow the gantry ends to flex under inertia. Hypertherm talk about Centripetal Limiting but the calculations we've done indicate this is not going to help much as it comes up with very small radii so I'm not sure if we have the maths right.
    Agreed there is no feedback from the unit on a parameter change. And from what I understand you can't change anything while the torch is actually cutting. But you can make a change when you lift the torch to move to the next cut position. That Telwin sounds interesting.

    You can control the motion parameters outside of the G code, on the fly, with other systems also. Just depends on how much control you have with the CNC software.

    Of course the mechanics of the machine need to be up to the task, in this case they will be. My target rapid is 27M/min or better. I haven't finished the calculations to determine the accelerations yet, I may have to increase the axis drive power.

    I have never heard the term Centripetal Limiting, can you provide a link or more information.
    Jim Dawson
    Sandy, Oregon, USA

  14. #14
    Registered
    Join Date
    May 2015
    Posts
    495

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by Jim Dawson View Post
    I agree that Mach3/4 would not be suitable for what I want to do (nor for much of anything else for that matter) which is why I won't be using it. Not sure what you mean by ''bit bashing up/down interface'' I would ask why I can't sense the velocity and torch voltage in real time?
    Most THC's just provide two signals. Move Up or Move down which is a pretty crude method. Thats not how we do it. We use the torch voltage as a process control variable and allow the motion controller to take care of it. Maybe there are other CNC controls aside from Linuxcnc that give that level of control but with Linuxcnc, I can change the motion controller code if I want to (and I have). LCNC has a very rich interface that gives you full control so your custom component becomes as ifg its part of the core code. MAybe other systems allow that but I thought its unlikely that any other system allows you to get to that level. (Unless you wrote it).

    Quote Originally Posted by Jim Dawson View Post

    Agreed there is no feedback from the unit on a parameter change. And from what I understand you can't change anything while the torch is actually cutting. But you can make a change when you lift the torch to move to the next cut position. That Telwin sounds interesting.

    You can control the motion parameters outside of the G code, on the fly, with other systems also. Just depends on how much control you have with the CNC software.

    Of course the mechanics of the machine need to be up to the task, in this case they will be. My target rapid is 27M/min or better. I haven't finished the calculations to determine the accelerations yet, I may have to increase the axis drive power.

    I have never heard the term Centripetal Limiting, can you provide a link or more information.
    I'm not sure of the process when and when you can't change things with the RS485 as I don't have a Hypertherm.
    27 M/min should be pretty easy to achieve. Even my old entry level Chinese steppers could do that.
    Be sure to calculate the inertial forces on the X axis (gantry) and check expected gantry end deflection is within accuracy expectations. I've attached an image of a cut at 2200 mm/min 5m/sec/sec acceleration with a notch to mark a fold line. The leadin was straight into the notch. The ripple is due to gantry end deflection due to the sudden change of direction in the X axis. (I do have an upgrade planned). This is 2mm mild steel, similar to your requirement.

    Centripetal Limiting is a Hypertherm term. Solve this maths problem and I'll elaborate.

    A tool on a CNC machine is travelling at 10.24 metres per minute (0.17067 metres per second) can accelerate at 5 metres per second.
    What is the minimum arc radius it can follow at that velocity?
    Rod Webster
    www.vehiclemods.net.au

  15. #15
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    Re: CNC plasma setup. Lots of questions.

    Quote Originally Posted by rodw View Post
    Most THC's just provide two signals. Move Up or Move down which is a pretty crude method. Thats not how we do it. We use the torch voltage as a process control variable and allow the motion controller to take care of it. Maybe there are other CNC controls aside from Linuxcnc that give that level of control but with Linuxcnc, I can change the motion controller code if I want to (and I have). LCNC has a very rich interface that gives you full control so your custom component becomes as ifg its part of the core code. MAybe other systems allow that but I thought its unlikely that any other system allows you to get to that level. (Unless you wrote it).
    Yes, I write my own CNC software and use industrial class motion controllers. When I write the THC code it will have all of the bells & whistles, I just need to integrate it into my existing software.


    I'm not sure of the process when and when you can't change things with the RS485 as I don't have a Hypertherm.
    27 M/min should be pretty easy to achieve. Even my old entry level Chinese steppers could do that.
    Be sure to calculate the inertial forces on the X axis (gantry) and check expected gantry end deflection is within accuracy expectations. I've attached an image of a cut at 2200 mm/min 5m/sec/sec acceleration with a notch to mark a fold line. The leadin was straight into the notch. The ripple is due to gantry end deflection due to the sudden change of direction in the X axis. (I do have an upgrade planned). This is 2mm mild steel, similar to your requirement.
    Yeah, 27M/min is not very fast, but I need to run the numbers to figure out if 0.75KW servos are capable of the 0.85g or so acceleration I want at the planned gantry mass. If needed I can increase the servo power because I have not ordered them yet. My work area is only about 1200x1200mm so crazy fast rapids are not needed.

    You must be using a cantilevered axis to get that much whip. I started down that path then realized that as the speeds and accelerations I want to run that it would be difficult control without a massive structure. So I decided to go with a more conventional moving gantry system. I'll build a very solid base frame and try to keep the moving gantry down to about 50Kg

    Centripetal Limiting is a Hypertherm term. Solve this maths problem and I'll elaborate.

    A tool on a CNC machine is travelling at 10.24 metres per minute (0.17067 metres per second) can accelerate at 5 metres per second.
    What is the minimum arc radius it can follow at that velocity?
    R=0.00582 M (5.82 mm)
    Jim Dawson
    Sandy, Oregon, USA

  16. #16
    Registered
    Join Date
    May 2015
    Posts
    495

    Re: CNC plasma setup. Lots of questions.

    Well, thats your guess of the Centripetal Limit. Its the third different answer. I got 7.8mm, one engineer came up with 0.15mm and another thought I was on the right track. So I'm still confused
    The formulas I solved for are below. I think I see an error in my calcs now so it would be great if you could share your working.
    Rod Webster
    www.vehiclemods.net.au

  17. #17
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013
    Posts
    4436

    Re: CNC plasma setup. Lots of questions.

    R=V^2 / Ac(celeration)

    V=0.17067, V^2 = 0.0291282489
    Ac=5

    so,

    R(in meters)=
    0.0291282489 / 5

    I'll admit I used my friend Google

    https://www.symbolab.com/solver/cent...3D0.17067m%2Fs
    Jim Dawson
    Sandy, Oregon, USA

  18. #18
    Registered
    Join Date
    May 2015
    Posts
    495

    Re: CNC plasma setup. Lots of questions.

    Yeh, thats the trick. That was my original attempt. You have linear acceleration set in the motion controller (m/s^2 and radial acceleration is in radians/s^2) so you have to solve for 2 equations. This maths stuff does my head in these days. Its 40 yrs since I did this stuff!
    Rod Webster
    www.vehiclemods.net.au

  19. #19
    Member
    Join Date
    Jul 2018
    Posts
    1711

    Re: CNC plasma setup. Lots of questions.

    Hi Rod - In the image with Omega = v squared/r thats wrong. Omega is usually the angular velocity. But Ar does equal V squared on r. Ar also equals omega squared x r. Is the 5m/s/s tangential (linear) or radial acceleration? Peter

  20. #20
    Registered
    Join Date
    May 2015
    Posts
    495

    Re: CNC plasma setup. Lots of questions.

    Yeh, I saw an error in my working today. Its a while since I've looked at this. 5 is the linear acceleration
    Rod Webster
    www.vehiclemods.net.au

Page 1 of 2 12

Similar Threads

  1. Another guy with lots of questions......
    By Rit in forum General Laser Engraving / Cutting Machine Discussion
    Replies: 1
    Last Post: 12-31-2014, 08:31 AM
  2. Lots of questions
    By bhurts in forum Dynomotion/Kflop/Kanalog
    Replies: 59
    Last Post: 05-30-2014, 12:56 AM
  3. MWT RF-45: Lots of questions
    By mattmark in forum Benchtop Machines
    Replies: 442
    Last Post: 03-08-2013, 08:02 PM
  4. A few questions on building a cnc plasma setup...
    By LSX in forum General Waterjet
    Replies: 2
    Last Post: 08-31-2012, 05:53 PM
  5. I'm new, Please help with lots of questions
    By I'm_Lost in forum Surfcam
    Replies: 4
    Last Post: 04-25-2007, 08:08 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •