Project Plasma CNC

Notes on re-working the existing Grote_CNC_freestafel into a Plasma CNC cutter with our new PlasmaCutter

What are we trying to accomplish?

In general:

• To have a lot of fun while experimenting
• Contributing something very (extremely!) nice to the space

More specific:

• First only to cut metal sheets (2D). 3D cutting may come later :-)
• Doing it safely
• Build something that can be used by the 'generic' maker who knows how to work the CNC for wood, after 15 minutes of additional instruction specific for use with the plasma cutter.

Rough Plan

• Find a proper 8x5 flex-tube to Euro2 pneumatics coupler for the main box.
• Wire up Aart his [plasma torch 'pen' style using one of the spare mounting plates for the CNC machine.
  • It seems to have an extra pilot wire/HF capability.
  • It has a spacer ring.
  • We have no spares yet.
• Re-use the existing pneumatics
  • Current is 6mm OD v.s. cutters 8mm OD -- so we need to check the flow. And otherwise increase diameter for all
• Make it easier to swap heads (wood v.s. plasma).
  • We have nice quick release plates - but the bold is a bit hard to get to
  • We currently do not have easy connectors for the earth-wire; alighnment lasers and the air.
  • The power connectors are a bit of a mess
  • We have several unused wire runs in the flex-chain.
• The current emergency stop buttons pick up interference from the plasma cutting - which upsets the FGPA/embedded CPU and the keyboard of the PC.

Image current cutter wiring

Image of the CNC pen of Aart likely intended wiring:

Todo's

• find out what sort of air/current connector is used on the unit (M12?, conical?)

• figure out the sizes of the solenoid and fittings on the CNC machine - and if it is big enough to carry the flow of the plasma cutter too.

• find out what type of earth connector is used on the unit.

• confirm exact sizes/threads of the current pneumatics used. Including the HBM ones (in at least one case a 1/8 was sold as a 1/4).

• understand how hard it would be to build / use the extra HF /pilot arc wiring we have on the plasma pen:

• • http://mewelding.com/plasma-arc-cutting/
  • http://mewelding.com/images/fig10-72.gif
  • https://patents.google.com/patent/US7615720B2/en

I am a bit confused as to the naming - it seems that the industry now calls the spark-gap starting HF; and the HF pilot arc; and the true pilot arc something like separate pilot arc.

So if we have an expert - or someone enjoys becoming one - yes please !

• find 20-30 meters of shielded cable & rewire all emergency buttons in a ‘star’ configuration (all to one point as opposed to a loop).

• ask our resident electronics experts very nicely to make us some `opto’/something separation for these long wire runs with a relatively solid voltage/current through the switches. (Bonus point if you manage to do the entire thing optical; including the buttons themselves!).

• • Another option -- run a rope round & tie it to a switch - toilet style.

• see if we can get enough flow through the existing 3.2x6mm tubing of the gantry; and if not upgrade that to a 5x8 diameter. Which is not entirely trivial as the current CNC has a solenoid. And it has to be flexible.

• bit of a tedious (but rewarding) task of removing all the old wires/no-longer-used wires from the energy cable trains and feeding the new ones through.

• find a handful of small size quick release pneumatic connectors that match above. And while we do that - also connectors for the alignment lasers and the grounding wires.

• find some flexible wire suitable for 40A / few kWatt / 20m-ish? (and ask our resident electronics / physics experts if it helps if this is shielded).

• move the current dangling connectors to a small box/plate on the Z-axis so we can swap heads. Do something clever with the suction pipe to make it fast/easy release.

Volunteers

Dirk will be looking at the pneumatics, fittings, gaskets, solenoid and the connectors in the next couple of days.

Fulco will have a look at a safety-bed to prevent the table from catching fire. Current idea's

• metal plate 60cm x 60cm, 6mm (just because that is what is available)
• metal walls 10cm hight prevent splattering
• some thermal isolation?
• some thing to have a bit of distance between the object and the bottom of the safety-bed
• some mechanism to make sure the plasma cutter can only be on when it is above the bed

Specs

• Table size: ruim 2m x ruim 1m ?
• plasma cutter
  • max 40A, few kWatt ?
  • trigger switch is wired to 'CB mic' style two prong connector (male on unit; female on end of wire).
  • Around 150 Liter/minuut air usage: implies 5mm tube inner diameter is fairly minimal
• air inlet hose plasma cutter 8x5 (Outer diameter, Inner Diameter) - pressure generally 5 Bar or about there.
• air hoses on the CNC machine now: ~6mm outer diameter
• CNC torch
  • Outer diameter around 29.5mm
  • air seems G1/8 inner thread
  • second brown wires goes to tip -- HF/pilot starter?
• Should get away with 2.5 mm^2 copper wiring: 10m 2.5 qmm Cu is 0,07 ohm -> 2,5V verlies bij 40A according to Aart. May be a bit more if we need to add a connector.
• Kleine perslucht connectors; type Snelkoppeling (DN5) 6 mm slang, schotdoorvoer, Messing

Notes, links

• General notes on safety: https://www.youtube.com/watch?v=WmnqbsjBCM0
• Grounding suggestions: https://xnet.hypertherm.com/Xnet/library/download/?file=HYP103900
• Most CNC heads seems to use magnet easy-come-loose couplings to protect the head as the steel can 'point up' during cutting.
• Exact metric sizes of G1/4, G1/8: https://www.festo.com/wiki/en/Threads_in_pneumatics
• Current pnematics connectors we are using https://www.hbm-machines.com/producten/luchtgereedschap/snelkoppelingen-en-insteeknippels/hbm-euro-insteeknippel-14-uitwendig
• https://www.hf-electronics.nl/CB-Plug-Female-2-Polig
• Torch that is more like 'our' current LIDL torhc: https://nl.aliexpress.com/item/PT-31-LG-40-plasma-cutting-straight-lance-head-40-0-degrees-pen-gun-head-LG40/32674455800.html
• Extension hoses: https://www.amazon.com/Plasma-Cutter-14Foot-Inside-M161-5/dp/B01EZGX4UW

Ordering

• Additional fire extinguisher?
• CB plug; female, 2 polig
• 5mm outer,
• G1/4 outer coupler for 8x5 tube to Euro insteeknippel
• Right euro insteeknippel
• Suitable earth connector (e.g. yellow banana plugs/chassis) 1x female, 3x male)
• Extension hose that is conductive - or hose 5x8 + 2.5mm2 wire.
• Connector for power and for lasers existing head

Ordered

• Small set of spares for head. https://nl.aliexpress.com/item/26-Stks-set-Plasma-Torch-Snijmachine-Accessoires-Tips-Voor-LTP5000D-LTPDC2000-Lastoorts/32835947680.html
• 5mm outer, G1/4 outer coupler for 8x5 tube to Euro insteeknippel

Right euro insteeknippel

• Suitable earth connector (e.g. yellow banana plugs/chassis) 1x female, 3x male)