Introduction: CNC Plasma Table
I do NOT supply kits for these. Give the RAR file + BOM to your favorite laser cutting company to quote then .cut / fold. All parts are cut from 3mm / 1/8" Mild Steel Plate.
So, you've bought a plasma cutter and you wish you could accurately cut your designs in metal. Tracing lines by hand gives disappointing results and CNC Plasma tables are way out of your budget. Sound familiar? Well, that's what I thought anyway!
If you have not bought your plasma cutter yet - there are a few things to bear in mind!
- The cutter must have 'HF Start' (Cheap cutters sometimes use 'scratch start' where you have to touch the torch on to the metal to strike the arc. Sadly, these will not work with CNC, least not this one!)
- If you have the option (can afford it) buy one with 'Pilot Arc'. If the torch moves over a poorly conducting area of metal such as rust, paint or a hole, the arc can go out and it will stop cutting. A Pilot Arc, like the pilot light in your boiler re-lights the arc if it extinguishes. It means you can cut pretty much anything no matter how grotty the surface looks.
- If you can, go for a branded cutter. Hypertherm are probably the best - or at least best known. They will give you the best cut quality and cut thickness for a given quoted power (some of the cheaper ones are a bit optimistic with the quoted power and cut thickness!). I started with a cheap cutter (which was actually pretty good) then upgraded to a used Hypertherm 40A machine which was cheaper than a new 'no-brand' machine.
- Go for the highest power you can afford. My original 30A cutter claimed to be able to cut 12mm thick - but the most it could realistically cut was 6mm. My new 40A Hypertherm claims 19mm cut thickness - and can indeed cut it (not very tidily though). It will cut nicely at 12mm thickness though.
This plasma table has been designed to work with whatever plasma torch
you have whether hand-held or a full blown CNC Torch. The mounting plate has been designed to be adaptable as possible. You can either attach the torch with zip-ties or U Bolts depending on how often you need to take it off.
This instructable really started on a Land Rover forum, LR4x4.com One of the members (RobertSpark) was building his own plasma table but it was a bit complex and needed welding together. I thought "I'd like a plasma table" and thought I could build one too!
I decided to design a table from scratch on Solidworks using Laser Cut parts which anybody could bolt together with no welding. It would also be scalable so you can build a table pretty much any size you like using the same laser cut parts. You need to source lengths of steel box section from a Steel Stockholder and everything else you can buy on eBay / Ali-Express.
All the parts need to be cut in 3mm or 1/8" mild steel A366/1008 Grade (or 304 Grade Stainless). The parts are suitable for both metric and imperial box section / nuts & bolts if you just pick the closest size.
Step 1: Bill of Materials
- 1 x 24v 400W 16A Power Supply
- 1 x 57BYGH56-401A NEMA 23 Stepper Motor
- 2 x NEMA 23 Stepper Motor = 3.1Nm
- 3 x TB6600HG Stepper Motor Driver 5A
- 1 x PC Breakout Board (See Note 1)
- 1 x Motor Shaft Coupler 6x12mm Flexible Coupling
- 6 x 20 Tooth 5M Synchronous belt pulley 21mm width, 8mm centre hole
- M6 or 1/4" Studding (See Note 2)
- 300mm x M12 or 1/2" Studding
- 50mm x 50mm x 1.5wall (2" x 2" x 1/16"wall) Box section Steel (See Note 2)
- 20x20x3mm (3/4" x 3/4" x 1/8") Steel Angle (See Note 2)
- 16 x 6x30x9mm 0630VV 6mm V Groove Steel Guide Pulley
- 8mm Round Section Silver Steel bar (See Note 2)
- 2 x 8mm shaft collars
- 8 x IGUS MCM-08-03 Bushing (See Note 3)
- 15mm x 5mm pitch Synchronous timing belt (See Note 2)
- 4 x 6262RS 19x6x6mm bearings
- 50 x M6 x 20mm Bolts
- 25 x M6 x 25mm Bolts
- 50 x M6 Nyloc Nuts
- 30 x M6 Plain Nuts
- 40 x M4 x 20 Bolts
- 40 x M4 Nyloc Nuts
- 1 x M12 Nut (or 1/2" to suit Studding)
- 1 x Microswitch
- Windows XP PC with a Parallel Port (Something like a Dell GX-280)
- Video Monitor to suit above
- Bluetooth combined Keyboard & Track Pad (Bluetooth means you can use it as a remote control)
- Mach 3 Software (Free Version Available)
- SheetCAM Software (Free Version Available)
- Torch Height Control (See Text)
The breakout board isolates your PC from the stepper motor drivers, protecti ng it from voltage spikes et c. Most of them plug i n to a PC Parallel Port. These are the simplest to set up. www.CNC4You.com supply some decen t boards and include easy wiring diagrams t o make it easy! Have a look at the KK01 board as an example. If you are mo re confident with techy stuf f, a reasonable board can be h ad from eBay for less cost but less good instructions. If you have no Parallel port, there are severa l USB Motion controllers available includ ing the UC100 from the above. The UC100 still needs a breakout board (it just c onverts USB to Parallel. There are a few more USB Motion controllers on eBay from China. The one I bought works fine, bu t took a LOT of experimentation to set up and get working due to the terrible an d misleading instruct ions. Never again! USB boards tend to be sensitive to electrical noise. I had to use clip on ferrite chokes on all the power and USB cabling to m ake it stable. Most boards have one or two relays. Use one of these to switch on the ar c on the plasma cutter. Y ou'll have to figure this ou t for yourself. I just cut the lead from the swit ch on the torch to the plasma and inserted a c onnector block then ran wires to the relay.
Decide on the X, Y & Z dimensions in mm. Make these a little bigger than the size of sheet you want to cut. You can work out the lengths of steel to cut below:
Quantity Description Length
2 X Axis Bars X + 200 mm
2 Y Axis Bars Y mm
1 Z Axis Bar Z + 100mm
1 Bridge Bar Y + 182 mm
2 Bed Support Angle Y mm
6 (or more) Bed Runner Angle X + 245 mm
2 X Axis M6 Studding X + 220 mm
2 Y Axis M6 Studding Y + 20 mm
1 Bridge M6 Studding Y + 202 mm
3 Z Carriage M6 Studding 100 mm
2 X Axis Belt 2 x X + 450mm
1 Y Axis Belt 2 x Y + 400 mm
1 X Axis 8mm drive shaft Y + 300 mm
1 Z Axis Studding M10 Z + 100mm
1 M10 plain Nut
2 Misc 8mm Axle Shafts 100 mm
50x50x1.5 Box Section 2 x X + 3 x Y+ Z + 682mm
M6 Studding 2 x X + 3 x Y + 982mm
Synchronous timing belt 4 x X + 2 x Y + 1300mm
Bed 20x20x3mm Angle (Number of runners) x (X + 245) + 2 x Y
8mm Round Section Bright Bar Y + 500mm
I have used IGUS MCM-06-03 Clip Bearings which on the surface seem very expensive for what they are. However they work very well and have a very long life in dusty & abrasive environments! As an alternative, the IGUS site carries 3D Models (including STL) for all their parts - so you could 3D Print your own! IGUS even sell their special Polymer as 3D Printer Filament - so you can print the genuine part. Other suppliers also sell plastic or Nylon clip bearings - and these might be worth a go too, however, I think IGUS represent good value.
Laser Cut Parts:
I have attached a rar (compressed files) containing all the DXF's and PDF drawings of the laser cut parts. You should be able to send these to any laser cutting company who will be able to cut and fold as per the PDF drawings.
Bill of Materials for Laser Cut Parts:
Quantity Part Name
1 X Motor Mount
3 Pulley Support
1 Side Plate
6 Belt Clamp
1 Y Motor Bracket
1 Side Plate Mirror
1 Y Pulley Bracket
2 End Plate Motor
2 End Plate Pulley
4 End Plate Keeper
1 Z Motor Mount
1 Z Top Cap
2 Z Follower
1 Z Nut Keeper
1 Torch Lift Slide
1 Z Axis Plate
The RAR file below is a Zipped / Compressed archive of ALL the drawings needed to cut / fold the parts. You will need a tool such as 7Zip to decompress / view the files. Give the files plus the BOM (Quantities of each of the laser cut parts) above to your favorite laser cutting company. They will be able to quote and make the parts.
Please note again, I do not sell kits - I just made this for fun and thought I'd share it with you.
Step 2: Construction 1. the Z Carriage.
For each of the three lower rollers, pass
a bolt through the laser cut part, secure in place with a nut then secure a V roller pulley to each with a second nut. The first nut acts as a spacer and is important.
Step 3: Construction 2. Z Motor
Bolt the smaller of the motors to the plate
using 4 M4 nuts & bolts. Connect a length of M 12 Studding to the motor using the flexible coupling.
Step 4: Construction 3. Z Follower
The two Z Follower plates are identical
and are fitted face to face as shown. There is a small plate with a hexagon cut out. An M12 Nut is held in place by this plate and sandwiched between the Z Follower plates.
Step 5: Construction 3. Z Follower Continued
Secure the parts from Construction 1 & 2 together.
Cut a piece of M6 studding 20mm longer than your Z post. One end of this passes through the Z Carriage, up the middle of the Z post and through the s quare Z Cap plate. Link the two Z follower plates with a short (100mm) l ength of M6 Studding + Nuts as above.
Step 6: Construction 3. Z-Follower Continued 2
Attach 4 more V Roller pulleys to the folded edges of the Z Follower plates.
Slacken the 100mm length of studding to allow you to sandwich the Torch Lift Slide plate between the V Rollers. Tighten the studding so this plate can move freely up & down, but does not rattle.
Bolt the micro-switch to the Torch Lift plate using 2 x M3 x 40 Screws. You may need to add a couple of nuts / washers between the micro-switch and the plate such that when installed, the button on the switch touches the Z-Follower assembly.
Step 7: Construction 3. Z-Follower Continued 3
You can now loosely attach the Torch Adaptor Plate to the Torch Lift Slide plate. You will need to adjust the height of this later. Adjust the position of the pulley which follows the right hand edge of the Z post in the slots to allow the Z axis to move freely up & down the Z post but with as little rotational play as possible. Once the kit is fully assembled, you can re-adjust these to maximise the rigidity of the assembly. That's the Z Axis complete.
Step 8: Construction 4. X-Axis
Find the part pictured above.
There are two similar looking parts (just to confuse you).
Use the one which has 5 holes cut in the flange on the Right as shown. The other one has only 4 holes - we will need this one later!
Pass one of your two X-Axis lengths of
studding through the middle hole and secure with a plain nut. Pass two M6 x 25 bolts through as well (do not secure with a nut yet)
Bolt one of the bigger motors to the plate above then bolt that to one of the corner brackets as shown.
There are 2 pairs of corner brackets, two being the mirror image of the other two. Bolt one of the four diamond plates (as shown) to the corner bracket. Note the alignment of the L shaped cut-out bottom right in the picture.
Step 9: Construction 4. X-Axis Continued
Pass the X Axis studding through one of your X Axis Tubes, through another corner bracket and through the U shaped bracket as shown above.
The U shape bracket needs to be secured to the corner bracket at this stage too.
Lay this assembly on a flat surface (Table top?) and tighten the nuts tensioning the studding until the corner brackets are held securely in place.
Bolt another Diamond plate to the end of the corner bracket (note the alignment of the L shaped cut-out.)
Insert two of the IGUS plastic bushes in the 9mm holes in the U shaped bracket
Step 10: Construction 4. X-Axis Continued 2
Assemble the other X Axis Bar as shown. In place of the motor at one end, it has another of the U shaped brackets.
This, including the Diamond Plates should form a mirror image of the first X Axis bar as shown.
Take a short length (100mm) of the 8mm ground bar and pass through the Plastic Bushes in the U shaped bracket and attach a belt pulley and shaft collar.
Step 11: Construction 5. Y Axis
Pass the longer length of the 8mm ground bar through the IGUS bushes and attach a belt pulley then insert the Y Axis M6 Studding as shown.
Thread the studding and 8mm bar through the Y Axis tube. Slot the end of the Y Axis Angle into the L shaped cut-out in the diamond plate. This is a bit fiddly - you may need the help of an assistant!
Just assemble one end at a time. Trying to line up both at the same time is difficult. So long as you do not tension the studding too much, there is enough flexibility to engage the studding, box section and angle at the other end. Lay this assembly on a flat surface and tension the studding to hold rigidly.
If you are building a big table, you may need to use M8 studding to tension the structure as it will require more force to hold it rigidly.
Step 12: Construction 6. Y Axis Bridge
Assemble the Y motor bracket, Y Axis Studding and bolt as shown then attach the second big motor and bolt in place.
Bolt this to the Y Carriage bracket.
Attach three of the V Groove pulleys spaced away from the Y carriage bracket with one nut. Tighten the top two but leave the bottom (slotted) pulley loose.
Thread the studding through the Y Bridge tube as before. Assemble the other Y Carriage bracket (mirror image of the other side) using a belt pulley, 100mm shaft and shaft collar sleeved by IGUS Bushes.
Pass the studding through resting both Y carriages on the X Axis tubes. Depending on your cut accuracy of the tubes, you may need to use a washer or two behind the V pulleys on the Y Carriages such that they sit squarely on top of the X Axis tubes when the studding is tensioned. A little trial & error is called for!
When you are happy it is sitting correctly, fully tension the st udding then adjust the bottom slide pulleys on the Y Carriages such that the bridge rolls smoothly along the length of the machine. If it tightens at one end, one of your Y axis tubes is longer than the other! I'm afraid you will have to disassemble and adjust the lengths.
Step 13: Construction 6. Y Axis Bridge Continued
Sit your Z Axis assembly on top of the Bridge bar then adjust the V rollers such that it is secure and rolls smoothly. This wants to be fairly tightly adjusted. Take a length of the timing belt and secure one end to the clamp on a Y Carriage bracket. Pass through the hole in the corner bracket, around the belt pulley etc and pass under the other clamp bar. Pull the belt tight using a pair of pliars (some help may be required!) and tighten the other clamp.
You can add the bed / material supports as shown.
Step 14: Construction 7. Belts
Move the Y carriage to one end of the machine so the Y carriages are hard against the corner brackets t hen thread the next piece of timing belt through the other side. You will need to adjust the belt passing t hrough each clamp individually such that the bridge is square and the belt is tensioned.
Repeat this process for the Y axis.
Once all three belts are tensioned, adjust the slotted pulleys again to make sure everything is tight, but moves smoothly.If you still find you cannot tension the belts sufficiently, find some torsion springs (like the ones in clothes-pegs). Put one or two on each belt. These will maintain the tension in the belts as the machine settles in use. In most cases they should be unnecessary.
Step 15: Construction 8. Torch Cable Support.
Using the remainder of the 8mm Ground bar, form one end in to a 'shepherds crook' shape. I bent mine round a lamp post!
You can hook the cable to the plasma torch over the hook allowing the cable to reach the cutting head as it moves.
Step 16: Construction 9. Wiring It Up
There is a great deal of information on the wiring on line. Rather than repeat it here, there the a great set of pages which describes the same components I've used here:
It contains pictorial diagrams of how to wire each of the individual components to the breakout board and that to your PC's parallel port.
The stepper motors have 4 wires - thus you need 4 (or more) core cable to connect them to the stepper drivers. I used 7 core Trailer Cable because it's low cost, easily available and will carry sufficient current (5 Amps). The 3 spare cores were useful to connect the Z-Axis micro-switch without adding a separate cable.
You need the breakout board to switch your plasma cutter on & off - the equivalent of pressing the trigger on the torch. Fortunately, the breakout board includes a relay (normally to switch the spindle on a lathe or mill on & off). I dismantled the plug on the end of my plasma torch which connects the trigger to the machine and attached a pair of wires in parallel to those that connect to the switch contacts. These connect to the NO (normally open) and COM (common) relay connections such that when the relay is switched on, the plasma tries to start cutting.
Some plasma cutters can generate electrical noise on these wires - sometimes enough to crash the PC! If you experience problems, buy some ferrite cores and snap one (or more) over the wires to the plasma cutter. Adding a few more on the mains connection to your power supply, the 24v power connections from the power supply and the Parallel lead to your PC may help too.
To protect and route the cables, I passed the cables through 'Cable Chains'. Although I've linked to chains on eBay, which are mostly low cost Chinese versions - they have not proven very robust. I wish I had used IGUS chains - which we use at work. These are much better quality and very robust - though more expensive. The choice is yours!
Above you can see a picture of the breakout board. This is how I've wired it up (which may differ a little from the HobbyCNCAustralia site linked above). My wiring is specific to plasma cutting.
The wiring of the Stepper Drivers is exactly the same. However, Terminal blocks 1,2,3,4,5,6,& 7 are as follows. L & R refer to the left & right hand screw as pictured on the picture.
1. +5v Out L is 0v, R is +5v You can use this to power things like the laser cross-hair you may have noticed on some of my photos (very low cost on eBay!)
2. No connection
3. L & R connect to the normally open connections on the torch lift microswitch
4. To the Proma Torch Height Control. L to 'COM' terminal, R to 'Torch Up'
5. To the Proma Torch Height Control. L to 'COM' terminal, R to 'Torch Down'
6. To the Proma Torch Height Control. L to 'COM' terminal, R to 'Arc OK'
7. Connect this to the Plasma Cutter trigger. 7 connects to the relay contacts on the breakout board and you want it so when the relay is energised, the plasma strikes the arc to start cutting.
Step 17: Software
First you need to design the things you want to cut. There are meny options for this ranging from drawing the part on paper to full blown Computer Aided Design.
Starting with an image, scanning it and using software such as Inkscape which can turn a drawing or even a photograph into a vector format called a DXF file. The software can be downloaded for free and although I've only used it once or twice, it works really well!
This would be ideal if, for example you want to cut animal profiles for use on weather vanes or other 'decorative' things. This makes the plasma cutter easily used for artistic purposes without the constraints of traditional CAD software.
You can use a drawing package such as CorelDraw which can export in DXF format - this is a half way house between drawing and CAD. Good for geometric shapes where you are not worried about precision - House Signs for example.
There are many CAD systems available. My personal favorite is Solidworks - but it is too expensive for realistic hobby use. Solidworks has a suite of tools for working with sheet metal and allows you to build, test & analyse assemblies of parts so you can build and run your whole project before cutting any metal. This plasma table is a good example of just that!
At the other end of the spectrum there is Google Sketchup - which is free and if you want to work in 2D only, DraftSight from the same company as Solidworks and is totally free! It's actually quite impressive.
Whatever software you've used, save your design as a DXF. Next you need to turn the design into something a CNC machine can understand. For Plasma Cutting, the best option is known as SheetCAM. There are plenty of good tutorial videos and information on line. SheetCAM lets you import multiple parts and arrange (Nest) them so they fit efficiently in the smallest sheet of metal possible. Once you are happy, you 'postprocess' (convert the layout into GCode which your CNC will understand). If you are going to use Mach3 to control your table, choose the Mach3 PostProcessor.
Step 18: Mach3 CNC Control Software
Mach3 is the interface between your design & the hardware which will make it - it deserves it's own step!
There is plenty of info on line on how to use Mach3. Here I've included the configuration file I've used plus the screen set. The config file will make it talk to the THC, Plasma & Motors if you've wired them up the same as mine. At the very least it will be a good place to start!
Save Plasma.set & Plasma.xml in your C:\Mach3\ folder. When you start Mach3, the start screen should now show 'Plasma' as one of the options - select this.
One top tip! If you change any of the configuration settings (Config Menu), click SAVE at the bottom of the menu otherwise when you re-start Mach3, it will revert to the old settings. This has made me swear once or twice!
With my settings, you can use the PC cursor keys to move the X & Y axis of the plasma table. A & Z move the Z (torch height) up & down.
When you want to calibrate the Torch Height, on the main screen, click 'Ref All Home' next to the X,Y & Z position readouts. The torch will slowly move down until the torch lift microswitch closes, then it will move up until the switch just closes. The Z readout will zero itself. On mine, this is the equivalent of the torch being 3mm too low. In the Z DRO (readout), click in the box then enter -3 and hit return. When you move Z up, 0.000 will be the torch just touching the metal sheet. Yours may be different to -3mm - you need to experiment a bit!
If you want to use Torch Height control, click the THC button (even if it's fitted, you can switch it on & off as required). Try clicking the Torch On button to check your plasma cutter strikes the Arc.
Step 19: Cutting
Once you've set up your software, I would recommend attaching a marker pen to the cutter as the first test. Draw a simple shape and see how well it draws the shape. You should be able to measure it to make sure it's dimensionally accurate. If not, go back to Motor Tuning in Mach3 - you've probably calculated your steps per mm/inch incorrectly (it happens to the best of us!).
The maker of your plasma cutter should be able to tell you the ideal torch height for piercing and cutting. The instructions for my old plasma said 1.5mm for pierce and 1mm to cut - but I found it worked better at 2mm and 0.5mm. Thus - it's worth experimenting!
Hypertherm recommend 3mm pierce & 0.8mm cut with a pierce delay (how long it takes to melt a hole through the steel) of 0.5 sec - which works perfectly for me!
Enter these settings in SheetCAM. Also enter a cutting speed - say 1500mm/min. You can easily adjust this in Mach 3 to fine tune the cut.
The manufacturer may also give a recommendation on cutting speed at different power levels (Current). I would only use this as a guide though. You will probably have to experiment a bit to find an ideal combination of speed & current for a given thickness of metal. I've found that 1500mm/min, 25A works well for 3mm mild steel.
What you aim to achieve is a cut with the minimum 'dross' (solidified molten metal) stuck to the back.
It took me a day of experimentation to achieve results I was happy with - but over the last few months as I have tweaked the settings, the results have got better & better.
Top Tip! Keep a note of the settings that work for different materials & thicknesses!
You will never achieve the same cut quality as a Laser Cut part - but it is plenty good enough for most purposes. You can always sand the edges if you need them to be smooth.
Step 20: Torch Height Control
To achieve the best quality cut, the height of the torch above the sheet needs to be carefully controlled. If the sheet is flat, setting the Z Height using the Microswitch is OK. However, if the sheet is not completely flat (particularly true for thicker sheet), something more advanced can help.
I bought (actually, my wife bought it for me for Christmas - thanks Sarah!) an electronic Torch Height Control made by Proma
However - before you rush out & buy one, there are a couple of things I need to add.
- This THC (others may be different) does not seem to work well on thin sheet (<=3mm). However, 3mm sheet seems to be flat enough not to need it on the whole.
- It does not work at all with my Hypertherm! The reason is that the THC looks at the voltage being sent to the torch and assumes that if the torch is switched off, this will be zero volts. However, when the Hypertherm is not cutting (no Arc) the torch sits at 45V. The THC interprets this as the arc has been struck and starts trying to adjust the height immediately.
The way a THC works is by reading the arc voltage. If it's lower than a threshold (about 120V) it raises the torch height and if it's higher, it lowers the torch. Because it's at 45V, well below the threshold, it starts raising the torch before the arc has lit - and by the time the plasma tries to light the arc, the torch is too far above the sheet and it never succeeds!
Apparently the next version of the THC will allow you to adjust the voltage it considers as the arc being lit - check with them before you buy!
Have a look at the linked video for details of how to attach & use.
Step 21: Conclusion
My plasma table has been revolutionary for me! It has been almost as useful as my 3D Printer - I guess it's a Metal 2D Printer in effect.
I have a mill, lathe, band saw and most of the usual metalworking gear but the plasma has added a great deal to my capability. It's very fast (compared to say a Band Saw), easy and accurate. The biggest single change is that I've been able to add 'aesthetic embellishments' to metal parts - more interesting shapes and lightening holes that are just not worth the time or effort cutting them manually.
I had no idea how much I would end up using it!
I took the Plasma Table to the Newcastle UK Maker Faire in April 2015 and was overwhelmed with the positive comments from visitors (many thanks if you were one of them!) Many of them were members of Maker / Hack Spaces who said the first question members ask about the small laser cutters they have is "can it cut metal" - the answer being "No". They were excited at the prospect of being able to say "No - but this can!"
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