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22 Oct 2020 01:30 #186865 by jnwinkie
Stuck was created by jnwinkie
Hi all;

I am at a point where I am stuck with my Plasma CNC build. First a call out to Tommy Light and Fabricator3 for previous guidance and insights. Through their advise/guidance I have got to the point were I have the SheetCAM working and rebuilt my plasma table to have a 4:1 reduction in gearing.

I am using an OOOOLLLLDDD CIG Plasma cutter - bought used 15 yrs ago, and just cannot seem to get a constant cut performance. It will cut thin stuff fine but anything approaching 3mm and it just becomes unpredictable. I have tried differing speeds for cuts as well as maxing out the amps. I have tried fresh consumables and even worked on the air supply to provide dessicated air. All of this to no avail.

I have included some pics to show the set up.

Does anyone have some thoughts because at this stage I am so stymied.

I am using FreeCAD for drawings, SheetCAM for G code and using the LinuxCNC plasma option for post processing and LinuxCNC 2.70 for the machine controller. I am using stepper motors and a Parallel port BoB.

I have tried the 4mm pierce height and 3mm cut height as well as a number of variables and gone from recommended cut speed of 1200mm/min down to 700mm/min with no great success.

I did try to reach out to Jim Colt on settings but the machine isn't a Hypertherm and I am sure he is a busy guy.

I am out of ideas at this stage and hope someone in the community can help give me some fresh inspiration/idea/guidance.

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22 Oct 2020 07:52 #186880 by rodw
Replied by rodw on topic Stuck
I heard Jim retired so is not so active anymore but you have the experts here to help you :)

To me, cutting at 3mm sounds too high for a 40 amp machine. Try 1.75mm
from the look of the cuts, I would guess

1, Too fast
2. Too high
3. poor air quality (water in the air)
4. worn consumables.

Where in AU do you live? I had to buy a refrigerated drier in Brisbane.

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22 Oct 2020 09:30 #186884 by tommylight
Replied by tommylight on topic Stuck
Alll of what Rod said above, plus:
1 belts are loose,
are you using PlasmaC ?
If yes:
Do not use "auto volts"
Set the voltage in the "run" panel or tab
Use a welding mask to check the distance from the torch end to the material, it should look like 2 of distance so adjust the voltage till it gets there
Do not try to cut long cuts at 40A as that plasma source can do that only 40% of the time, so for 4 minutes of cutting it needs 6 minutes of rest, but do make it work properly at 40A.
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22 Oct 2020 09:35 #186885 by rodw
Replied by rodw on topic Stuck
I don't think the belts are loose (unless on the Z) as the circles are well formed.

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22 Oct 2020 10:57 #186890 by Mud
Replied by Mud on topic Stuck

I heard Jim retired so is not so active anymore but you have the experts here to help you :)

To me, cutting at 3mm sounds too high for a 40 amp machine. Try 1.75mm
from the look of the cuts, I would guess

1, Too fast
2. Too high
3. poor air quality (water in the air)
4. worn consumables.

Where in AU do you live? I had to buy a refrigerated drier in Brisbane.


I'm interested in understanding more about the cut height (if it's not taking us off-topic) as I also have a 40A machine meant for hand cutting (GYS 40FV) - the standoff which you can fit to the nozzle to help maintain the distance gives ~4.0mm between the work and tip. I note the TD120 (set at 40A) recommends 4.1mm across all material thicknesses. That said, for thin material (say, 1-5mm) I have been getting good results with 1.5mm height...my main problem being as I move to thicker material I can quickly destroy the plastic nozzle with molten material projecting upward on piercing (and they're ~£15 each!). Toward 4mm height on 10mm material I was struggling to get a good process (yet to try the wiggle pierce as a possible enabler for lower cutting height).

I think around 4.5mm height my system really starts to struggle to make an arc. I appreciate these are all different machines which swirl the air differently/etc.

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22 Oct 2020 15:33 #186904 by rodw
Replied by rodw on topic Stuck
I think thats something you get with the major brands, all that experimentation behind the cut charts.
Its all trial and error. If its not establishing an arc, I would try dropping by 0.5mm at a time. For my Everlast, I settled on about 3.5mm piercing. Pick a height that seems to work well, check some fine adjustment heights too.

Next, experiment with cut speeds by making a series of straight cuts at different speeds about 100-150mm long, 10mm apart. I cut this piece out as part of the file so i could remove it to inspect the underside. Look at the underside and pick the cleanest cut.

So now to pick a cut height, repeat the same exercise at that same cut speed but at different heights. I did from 1.5 to 2.5mm in say 0.2 increments. Pick a range of 2-3 heights and repeat at 0.05mm. Pick the best looking cut.

Then repeat the process again to confirm the cut speed is still good, Pick a final speed and repeat the height test again.
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23 Oct 2020 00:42 #186951 by jnwinkie
Replied by jnwinkie on topic Stuck
Hi Rod;
Great to make your virtual acquaintance and it is nice to know there are people out there willing to help.

So to answer your questions, in no particular order.
I am located in Victoria, and after having lived in Singapore get your concept of humidity. I am using a three stage air filter that I think was one you has deployed at some stage. (see pic).

I have used brand new consumables on most tests (I think the unit maybe a very old rebadged Thermal Dynamics machinebased on the consumable part numbers).

The pierce and cut height were straight out of the manual, but I agree they seem very optimistic and will experiment on height further, but I do not have a THC! (see attached)

The unit says 1900mm/min for 3mm plate but I have slowed it right down to 700mm/min with still no real success.

Thanks again, I really appreciate the assistance.

John
Attachments:

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23 Oct 2020 00:52 #186955 by jnwinkie
Replied by jnwinkie on topic Stuck
Thanks Tom;

You were the one who helped with the gearing on the table and it is now a 4:1 reduction, hence fixing the problems I had with cutting circles etc.
All the belts and pulleys are good ( I have pulled the damn thing apart so many times) :)

I have been pretty conscious of cycle times and don't think I have exceeded these.

PlasmaC, not sure I have been using LinuxCNC with the Axis interface, I don't have and not even sure how I could connect a THC on this machine as everything, including the torch is hard wired.

Cheers

John

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23 Oct 2020 08:00 #186978 by tommylight
Replied by tommylight on topic Stuck
Without a THC there is no way of getting nice clean cuts consistently.
You can remove the stepper motor from Z axis and add a DC motor wired to a two way switch and a power supply so you can manually adjust the cut height during cutting, but that is tedious and requires staring at that arc all the time.
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23 Oct 2020 08:05 #186980 by rodw
Replied by rodw on topic Stuck

Hi Rod;
I am using a three stage air filter that I think was one you has deployed at some stage. (see pic).

John


John, yes, I found that filter woefully inadequate and actually found a pool of water under it one day so bought a refrigerated drier.

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