Plasma table + 4th axis

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14 Sep 2022 02:45 - 14 Sep 2022 02:50 #251868 by chrisfischer
Here is a teaser of the design so far. Im sure a fair amount will still change.

-5x5 table
-4th axis on the side big enough for 6x6 square tube (so far)
-I havent drawn this but I plan on indexing a full size tube for cutting every 5 feet so I can process a whole tube in one setup. 
-scribe, sharpie, crosshair green laser, and hyperthem mini torch on the z axis (I plan to add a bolt on 20w diode laser someday... maybe)
-4 to 6 inches of z travel (going back and forth... probably 6)
-hypertherm 45xp with finecut consumables and shop air
-rotating ball nuts on x and y
-carbon fiber tubes for linear bearing on the z axis (provided I can get the od more precise using an od grinder... total experiment)
-chicago scribe and retractable sharpie deployed by steppers (as opposed to stuffmadehere's pneumatic example)
-torch collision detection
-designed for 2g acceleration (this is arbitrarily high and I am pretty loosely estimating things other than mass - like friction)
-mesa 7i96, thcad torch height control, thcad ohmic sensing, stmbl drives, 60ST-M01930 servo motors
-QTPlasmaC, touch screen monitor, sheetcam
-$6k budget

This machine will help me take on job shop work as well as prototype designs for a business I am building to manufacture motion simulators. 



 
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Last edit: 14 Sep 2022 02:50 by chrisfischer.

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14 Sep 2022 12:25 #251892 by tommylight
Replied by tommylight on topic Plasma table + 4th axis
Forgot to mention, if you do not use the machine daily, avoid dipping the torch i water as it will rust pretty quickly.
I have about 10 seconds of post flow on all plasma sources, so not an issue really, but shuting down the plasma while it is still wet is not good as it stops the air drying the torch.
Just leave it on untill the post flow stops.
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16 Sep 2022 16:27 - 16 Sep 2022 16:29 #252086 by chrisfischer
Thanks for the tip tommy.



I made an attempt at making commodity carbon tubes into linear rails lasts night. In the end, it was more trouble than its worth.

The tubes i bought were 1.5mm wall 25mm od tubes off amazon. My hope was to bairly scratch the surface to true in any change in diameter so I could slide an igus bearing on it smoothly. I already purchased 25mm igus bearings and they slid with slight changes in friction along the length.
 

I figured since they are made on a mandrel the id would be concentric but it was pretty out - like .4mm. This meant that I would have to drop the tube down to the next igus bearing size of 24mm. Of course that meant I could grind off a good amount of carbon. The grinder handled this really well. With coolant the wheel didnt load up at all. 

 


Unfortunately the layers under the top are all pulltruded layers rather than a weave. I should have guessed this would be the case. Since there was only pulltruded fibers they were fraying in places rendering this tube useless.

 


The way to do this right is lay up your own tube with plenty of carbon past where you will grind it back to - all with a weave fabric. This doesn't sound appealing to me so Im changing the z bearings to linear rails. 



 
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Last edit: 16 Sep 2022 16:29 by chrisfischer.
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06 Oct 2022 14:11 #253610 by CarterKraft
Replied by CarterKraft on topic Plasma table + 4th axis
This is going to be fun to watch. You seem capable of doing some really high quality work.

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19 Oct 2022 19:46 - 19 Oct 2022 19:51 #254555 by razplaz
Replied by razplaz on topic Plasma table + 4th axis

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.


Tommy,

Do you have any issues with excessive dross, since the sheets are underwater?

I watched a video with Jim Colt who said cut quality can be better if the water level is slightly below the bottom of sheet.



I was also wondering if the water level affects the THC readings in your experience?

Thanks!
Last edit: 19 Oct 2022 19:51 by razplaz.

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19 Oct 2022 22:11 #254562 by tommylight
Replied by tommylight on topic Plasma table + 4th axis

Do you have any issues with excessive dross, since the sheets are underwater?

No, and the dross that gets left is easier to remove when cut with water touching the plate or under water, it cools down much faster so has no time to stick to the rest of material.
In general, no amount of videos will help with cut quality, been there done that, the only thing that really helps is testing and more testing and writing the results.
Get some scrap sheets, set the plasma to say 50A, set the feed rate to 1500mm/m for say 3mm thick plate, check the air is sufficient and do 500mm cuts in a straight line, then do 1600, 1700, etc.
Look under it, get a small hammer and smack the dross see where there is the least dross and comes off easiest, write those settings.
Never ever change 2 or 3 parameters at the same time, that always leads to bigger mess than stared with! :)
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19 Oct 2022 22:27 #254569 by tommylight
Replied by tommylight on topic Plasma table + 4th axis
Oooops, forgot this:

I was also wondering if the water level affects the THC readings in your experience?

Not in any noticeable way or form. The current is way to big for the minuscule amount of current that passes through water to cause issues.
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22 Oct 2022 10:12 #254741 by andypugh
Replied by andypugh on topic Plasma table + 4th axis

Does not last long though as it evaporates quickly if used all day in about two days it gets under the material level.

Why not plumb a float-valve to the table? (And an overflow pipe in case that fails) 
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22 Oct 2022 10:29 #254744 by tommylight
Replied by tommylight on topic Plasma table + 4th axis

Does not last long though as it evaporates quickly if used all day in about two days it gets under the material level.

Why not plumb a float-valve to the table? (And an overflow pipe in case that fails) 

I like to suffer! :)
That is easy to add, but never though of it, thank you.

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01 Feb 2023 22:36 #263474 by Dah-Lih Llama
This is exactly what I want to build. I was looking at just buying a 3 axis table, but then I saw a laser machine that had the 4th axis on the side like this. I've got a healthy budget as this isn't for hobby use, but I'm not sure I have the time. I know whatever time I think it's going to take, I might as well multiply by 10.

So, ever make it anywhere past design stage?

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