50w chinese laser keeps firing during cutting process

Hi People, I am a complete newbie to laser cutting/engraving and am not so technically minded. so, please be gentle with me. Let me set the scene. 3 months ago I bought a 50w CO2 "Chinese" laser cutter/engraver., for my wife to use for her crafting shed. initial setup and alignment went better than expected, resulting in good cuts/engraving. 3 weeks ago the laser started to arc, after watching YouTube videos I had the confidence to purchase and replace the laser tube. After installing the new laser tube, realignment went well and to be honest I surprised myself with what a good job I had done. However. When I tried to cut/engrave a piece that had good results with former tube I found that I was left with marks where the former laser didn't leave marks previously. It's as if the laser is not "loosing/dropping" power between cut lines / engraving lines resulting in unusable projects. If anyone could help with anything to try / ideas could they please reply to this post. I understand this is a rambling post, but as mentioned am a newbie and do not understand the "rules" of forums...... sorry in advance for my ignorance, but, please help if you can. Thank you.

... your best source for detailed information would be the vendor ... but, as this are chinese (extreme low quality) products, gettig usefull infos for them could be an adventure on its own

My bet is, that the new tube needs different specs for the voltage levels for the threshold (below threshold voltage the laser would be OFF, above ON).

But could be too, that your power source and driver can't be adjusted properly for this tube ...

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Viktor
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Hi Viktor, Thanks for the information you have supplied, I have emailed both the vendor and the seller of the new laser tubes for full technical specifications. I will post again once the replies have been sent and hopefully someone will be able to give me some advice on resolving this issue. Thanks for the speedy reply, very much appreciated.

Hi, after 7 days I still have had no reply from laser cutter vendor regarding power supply technical information, however, the company that supplied the new laser tubes replied instantly with the tech specs of tube and is attached to this message. I still cannot find an electrical engineer who is willing to assess the laser cutter as they don't know anything about them. I've got £2000 worth of cutting machine and cant do a thing with it. Frustrating. any help would be very much appreciated.

You say that the old laser started to arc. Where exactly was the arcing, and what did it look like? If it was on the outside of the tube but the tube was otherwise working, that should be fixable. I can't imagine how you would get arcing on the inside of the tube, because it is at low pressure and there is a continuous discharge in the laser tube whenever it is operating. If the tube cracked then I could imagine that it would arc along the crack and not work at all.

If the problem is that the new laser tube is staying on for too long when commanded off, then that is an issue of matching the power supply with the laser tube and probably also the firmware. There will always be a delay in starting and stopping the laser because of the power supply capacitors. I would expect good control firmware to compensate for this delay. If the new tube draws less current than the old one, then it will take longer to discharge the power supply capacitors when the power supply is turned off.

I built CO2 lasers when I did my PhD many years ago. In case you are anywhere nearby, I am in Langport, Somerset.

Edited 2 time(s). Last edit at 06/24/2017 11:19AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for the reply dc42, I have attached some pictures to this post, they have been taken from a short video showing the arcing process, if I am correct, they are coming from the "negative" connection (black wire) end of the laser tube and not from the focal point? (red wire) firing end where the laser exits the tube to the first mirror. As you suspected, the arcing was external. The noise was a very high pitched "screeching" sound. To be honest it was quite frightening. I hope I have supplied information within the pictures to enable other users to help me. If I need to supply further information, please do not hesitate to contact me. dc42 I live north of Manchester U,K. The offer of help is very much appreciated, however, I would imagine that unless you are planning to visit Manchester, in the near future, an "on site" visit ...... well, you know the rest lol. I really do appreciate the help this forum has supplied, I am learning lots.

... this "arcing" looks like the isolation of the HV-wire is broken, so it shorts against the housing (normally GND) - this could be repaired by removing all the old isolation and isolate it anew ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

I agree, it looks like a high voltage insulation issue - but check first that it isn't due to a connector or wire having come loose.

If the insulation hasn't actually fallen off then it may be repairable by first making sure that the high voltage has discharged completely, removing dust, and then sealing the place that the arcing is coming from with this [uk.rs-online.com] or this [uk.rs-online.com]. If you use the aerosol, make sure you don't spray it anywhere near external mirrors or windows in the laser tube.

Regarding the new laser tube, my guess is that the power supply reduces the voltage to turn the laser off, and it isn't reducing the voltage enough to turn the new tube off completely. There may be an adjustment in the power supply for this. If the power supply is a separate module, it may be a standard unit, in which case look for the model number on the outside and then search for instructions on the web.

Edited 1 time(s). Last edit at 06/25/2017 03:17AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].