Plasma table + 4th axis

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24 Aug 2022 23:39 - 25 Aug 2022 02:30 #250358 by chrisfischer
Hi guys, 
First of all I want to thank all the people who have posted here over the years to make this place such an amazing wealth of knowledge. Then I want to thank all the people who have put in the time on the software to make linuxcnc and qtplasmac so great. Thank you guys so much. I will attempt to stand on the shoulders of giants with my build. 


I am looking to build a plasma table with a 4th axis off the side for cutting and marking tube. Ive been lurking in this forum for over a decade and built my first cnc router back in 2011. Now its time for a new cnc and I'm planning on using servos, stmbl drives, ball screws (perhapse rotating ballnut), 5x5 water table, powermax 45xp, and build it for high acceleration. 

I plan on documenting my progress here to hopefully inspire others. 

As of right now I am planning my z stage to have a sharpie, a scribe, an alignment laser, and a torch with hypersensing and collision sensing.


In my reading this forum I have observed people strongly encourage a floating torch design. Is this still advised when using the hypersensing method with the thcad? 
Last edit: 25 Aug 2022 02:30 by chrisfischer. Reason: spelling
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25 Aug 2022 00:13 #250364 by tommylight
Replied by tommylight on topic Plasma table + 4th axis

In my reading this forum I have observed people strongly encourage a floating torch design. Is this still advised when using the hypersensing method with the thcad? 

Yes it is advised as it will stop the torch going down even of the ohmic sensing fails, but it works without it, i think. <<< i only use float on my machines.
As for ball screws, not preferred on plasma tables due to speed constraints and dusty environment. They can be used for sure though, and rotating ballnut works like a charm from what little tests i did some years ago. Not easy to implement proper rotating nut assembly.
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25 Aug 2022 01:02 #250368 by rodw
Replied by rodw on topic Plasma table + 4th axis
You definitely need the floating head with hypersensing becasue you need some overtravel to allow the torch to come to a rest. I generally run a fast probe speed so its required.

I've got a feeling my float switch sensor is broken so never miss it but need the overtravel.

I don't think roating nut designs are that hard if you have a lathe.  A wheel bearing would be perfect.
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25 Aug 2022 02:29 #250372 by chrisfischer
Wow thanks for the quick responses guys. I'm sold. Rodw, do you have any idea how much overtravel you use? 
Im trying to minimize parts and lengths for lightweight. I've always enjoyed the gram weenie game. 

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25 Aug 2022 09:52 #250390 by tommylight
Replied by tommylight on topic Plasma table + 4th axis
1cm or half inch should be enough travel. My machines have 1.5cm as i use the same part for both sensors for float and home of the Z axis.
More info and plenty of pictures here:
forum.linuxcnc.org/show-your-stuff/38547...plasma-build?start=0

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03 Sep 2022 18:04 #251121 by andypugh
Replied by andypugh on topic Plasma table + 4th axis
You might have trouble sourcing STMBL drives, both the power IC and one of the SM32s are pretty much unobtainable.

So, if you don't already have the drives, you might need to look elsewhere.

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13 Sep 2022 17:38 #251830 by chrisfischer
I understand the power ic is gone. Such a bummer amd i hope the brilliant guys behind the project find a way to get around that. I am lucky enough to have a friend who has some drives i can buy. I understand from him that they work great and interface with linuxcnc via smartserial really well. Im excited to try them.

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13 Sep 2022 17:40 #251831 by chrisfischer
I am plugging away on the design of this machine. Funny how much i underestimated the hours needed for the design.

Another question for the forum, i have seen mention of cutting parts fully submerged but not much info on why. Do any of you fill the water table high enough to do this or is it rare. If so whats the main reason?

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13 Sep 2022 21:03 #251846 by tommylight
Replied by tommylight on topic Plasma table + 4th axis

Another question for the forum, i have seen mention of cutting parts fully submerged but not much info on why. Do any of you fill the water table high enough to do this or is it rare. If so whats the main reason?

I do, but not always. When using the machine every day i fill the table above the material about 1-3 cm, it is a nice showcase, less metal dust and less ultraviolet radiation. Does not last long though as it evaporates quickly if used all day in about two days it gets under the material level.
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14 Sep 2022 01:54 #251864 by chrisfischer
Interesting. That is even deeper than I thought. I originally had the water level stop at the bottom of the material. I will add another inch or so. Thanks for the reply.

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