Project Plasma CNC

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

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

current-plasma-torch

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?)

• 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!).

• 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 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 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.

Notes, links

• 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

• 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
• 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)