15m Industrial Plasma Cutter

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23 Aug 2019 20:18 - 23 Aug 2019 20:19 #143004 by rodw
Replied by rodw on topic 15m Industrial Plasma Cutter

Do I need anything when it comes to sensing?

I saw that Rod said he used ohmic sensing on another thread.


You will definitely need ohmic sensing on such thin material as it will warp a tremendous amount.
Ohmic sensing is covered in the Plasma Primer which is part of the main Linuxcnc 2.8 & 2.9 docs.

But you also need home and limit sensors. With Mesa hardware if you use PNP proximity sensors it is pretty easy and you can keep all the wiring located on the moving gantry. My build thread shows the simple method I came up with on the first post. Just make sure the max limit sensor plate is mounted so the high side is on the inside of the limit otherwise if the home sensor is at that end it will think it is near home and move the wrong way and crash!

forum.linuxcnc.org/show-your-stuff/32029...a-cutter-build#84551

So back to material height sensing. Ohmic will be your primary method but you will need to also make a float switch on the Z axis in case it does not activate. This thread which predated my build thread shows some close ups of my Z axis design.
forum.linuxcnc.org/30-cnc-machines/31509...pinion-drive?start=0

The advice from the guys on this thread was really invaluable and this is an excellent design. By purchasing a prebuilt stage, all you need to build is the parts secured to the collar around the ballscrew nut in this photo



eg. the assembly held on by the large black screw.

The only other thing I would say is to be really generous with the Z axis travel. I used a 150mm long ball screw which gave me about 85mm of travel. I think I would use a 300mm long stage and make sure you have a minimum of 200 mm of travel to handle material warpage on thin stock
Last edit: 23 Aug 2019 20:19 by rodw.
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23 Aug 2019 20:37 #143007 by rodw
Replied by rodw on topic 15m Industrial Plasma Cutter
Also, these NEMA 34 reduction mounts will save you a lot of time for the Y axis. They come with a drive belt and have worked well for me with a 1.25 mod helical rack. Much better than the straight rack I used on the X axis
www.aliexpress.com/item/33038138992.html...0.0.0.c16c2e0e8i97dg
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28 Aug 2019 15:07 #143449 by Jarman
Replied by Jarman on topic 15m Industrial Plasma Cutter
Thanks everyone.

I'm leaning towards steppers now (only because I'm pressed for time and I'm trying to keep it simple). I'm not sure that I fully understand what the advantages of servos are.

Is there a good way of navigating this forum/ finding resources? How did you guys find out how things like the z axis worked for your first build? For example, I see pictures of people's designs but I don't really see how they work or what the necessary parts are. Sorry to bug you guys about the boring stuff, normally I'd just trawl through the Internet and figure it out myself but I'm really trying to get into a position where I can place some orders on Friday.

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28 Aug 2019 15:24 #143452 by tommylight
Use google hacking, that is a thing and google teaches you how to do that, just search for it.
Example:
to search for anything related to DIY, plasma, cnc, only on the Linuxcnc.org site you type
diy plasma cnc site:linuxcnc.org

results:


To search for the exact sentence use
"diy plasma" site:linuxcnc.org

results:


Same goes for files, like
diy plasma cnc filetype:pdf
etc.
Attachments:
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29 Aug 2019 14:24 #143558 by Jarman
Replied by Jarman on topic 15m Industrial Plasma Cutter
Thanks for that.

If I'm using tommy's stepper idea and going with a 7i76E + THCAD do I need an additional breakout board? I saw a thread about using a 7i76E and 7i43?

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29 Aug 2019 15:25 #143563 by andypugh
I don't think you _can_ use the 7i43 with a 7i76E. Maybe it was a 7i73?

(the Mesa names are definitely confusing, but they do Google well)
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29 Aug 2019 15:28 #143564 by Jarman
Replied by Jarman on topic 15m Industrial Plasma Cutter
but a 7i76E and THCAD are sufficient aren't they?

They don't need anything else?

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29 Aug 2019 15:55 #143568 by andypugh

but a 7i76E and THCAD are sufficient aren't they?


I would think so, yes.
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29 Aug 2019 16:12 #143573 by tommylight

but a 7i76E and THCAD are sufficient aren't they?

They don't need anything else?

They do need other things, like, power supply, wires, drives, motors, someone to put all that together and a lot of coffee ! :)
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29 Aug 2019 16:58 #143578 by Jarman
Replied by Jarman on topic 15m Industrial Plasma Cutter
I just wish they came with more time!

I'm struggling to see how I can feasibly make the z axis myself in the time frame. I've been looking at some prebuilt z axis stages but they are all from China and most have a 2 week lead time. Does anyone have experience ordering from these chinese cnc companies? Do they tend to deliver when they say? From previous experience with even local manufacturing companies I doubt it.

I'm not too concerned about the complicated stuff like electronics, software and motors. It's the lead times and basic machining that's got me worried. I have to stop in 4 weeks no matter how far I've got so I'm wondering if it's worth investing all this money in a gamble that I can get it built.

I'm also wondering if I can throw together an extremely simplified version eg. no variable z axis height/magnetic breakaway or any of that. And just accept that the quality won't be fantastic, but at least it will get done.

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