New Plasma build question

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20 Jun 2019 18:54 #137408 by Clive S
With all the talk and discussion on the forum lately you have given me the bug.

So Q1. if have built several routers that hold good accuracy. But with the plasma build, the gantry will be 1500mm long I am thinking of using 50x50x4 box section with this I have put 25Kg in the centre and it deflects 0.3mm is this acceptable for plasma or should I go for a better gantry construction? (I would not do this with a router)

Q2. I waant to fit a water table about 1250x650x!! how deep do I need to make it I was thinking 55-70mm ?



And no I am not using MDF for the gantry sides:woohoo: It will be 15mm ali and it will be taller. (How tall) ?

Thanks.
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20 Jun 2019 19:03 #137410 by AgentWD40
Replied by AgentWD40 on topic New Plasma build question
Following.

Q1: How heavy material are you planning on loading on the table? Are you going to use THC? I get the impression z flatness isn't terribly critical when you have THC constantly adjusting z anyway.

Q2: I'd like to know this too. I'm leaning toward 3" (~76mm) for my build. What ever winds up being convenient with materials I'll have on hand.

"And no I am not using MDF for the gantry sides"... Lol, I am for my plasma! At least until it can cut out it's own replacement parts.

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20 Jun 2019 21:15 #137418 by Clive S
Replied by Clive S on topic New Plasma build question

AgentWD40 wrote: Following.

Q1: How heavy material are you planning on loading on the table? Are you going to use THC? I get the impression z flatness isn't terribly critical when you have THC constantly adjusting z anyway.

Q2: I'd like to know this too. I'm leaning toward 3" (~76mm) for my build. What ever winds up being convenient with materials I'll have on hand.

"And no I am not using MDF for the gantry sides"... Lol, I am for my plasma! At least until it can cut out it's own replacement parts.


I am building this as a hobby as it helps to keep my brain active as I am getting older:) so probably not more that 5 mm plate. Yes I will be using the Mesa THC not sure which one I need though with just a scratch start cut 40.

I have a router so its simple to make gantry sides out of MDF before I cut them for real. The router cuts ali fine.

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20 Jun 2019 21:17 #137419 by thefabricator03
Q1: I would say the 50x50x4 will be fine for a plasma, If the deflection is only 0.3 the THC should compensate for the minor deflection.

Q2: I made my water tray 25mm below the bottom of my slats, I have used 100x6 Flat bar as the slats. For a hobby table you would be fine using 75x6 or even 65x6 and having a smaller gap under the slats.
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20 Jun 2019 21:49 #137421 by Clive S
Replied by Clive S on topic New Plasma build question

Q2: I made my water tray 25mm below the bottom of my slats, I have used 100x6 Flat bar as the slats. For a hobby table you would be fine using 75x6 or even 65x6 and having a smaller gap under the slats.


Now I am a bit confused, I thought the water was to come just under the top of the slats and 65x6 I was thinking about 4 mm is this incorrect?

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20 Jun 2019 21:54 #137423 by rodw
Replied by rodw on topic New Plasma build question
It looks like a mini spaceship already!
A lot of commercial tables use 3mm which is what I used (75 x3) I think I will replace them eventually with 50mm x 3 as its a bit high now. 75mm deep tray and 50mm slat would be fine.
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20 Jun 2019 22:11 #137424 by Clive S
Replied by Clive S on topic New Plasma build question

rodw wrote: It looks like a mini spaceship already!
A lot of commercial tables use 3mm which is what I used (75 x3) I think I will replace them eventually with 50mm x 3 as its a bit high now. 75mm deep tray and 50mm slat would be fine.


Yes it was you ,Phill and Tommy etc. that got me started on this journey.
I have set the shelf for the water table tray to be 70mm from the top of the frame already so will have to go with that now.

I have used the 7i92 before on my last conversion (Novamill that's just been sold on) but this time I want to used the 7i96 but still unclear which THC to get 10 or 300 !!

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20 Jun 2019 22:23 - 20 Jun 2019 22:24 #137426 by rodw
Replied by rodw on topic New Plasma build question
I think for the added cost of adding a couple of resistors, the THCAD-10 gives more flexibility. Also on a small plasma, you can probably get away with < 300 volt full scale to get better signal resolution. (eg 150 or 200 volts)
Last edit: 20 Jun 2019 22:24 by rodw.

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20 Jun 2019 22:51 #137431 by thefabricator03

rodw wrote: It looks like a mini spaceship already!
A lot of commercial tables use 3mm which is what I used (75 x3) I think I will replace them eventually with 50mm x 3 as its a bit high now. 75mm deep tray and 50mm slat would be fine.


I didn't realize that smaller tables used 3mm for the slats, How far are they spaced apart? How many supports do they need to stop them from warping?

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20 Jun 2019 22:51 #137432 by tommylight
Minimum water level under the cut level of the torch is around 40mm, having space under slats is nice so the water can level and escape during cutting, having a bit of water above the metal plate being cut is really nice as it gets rid of the little bit of dust, running it submerged is the best way but not preferable for systems with part time use as it will corrode the torch. Adding baking soda to the water will keep the table in a nice condition for many years as it does not allow corosion while the slats are under water and it also reduces the smell of water wapor.
Scratch start will be a challenge, but I think firing the torch before probing could just make it work, but only with floating head and switch. This will also have the inheritable problem of short circuiting the output of the plasma cutter while probing and while that is required to make it start, doing that very often and for prolonged time might end up in burning the plasma if it does not have provisions for limiting the output current, that can be checked easily by opening the plasma and looking for a choke. Ohmic ( I do not like the term as it has nothing to do with the procedure not is being used for ) can not be used with scratch start as it will send all of the output voltage and power to the sensing equipment, rendering it "on fire ".
As for 10 or 300, in your case most probably the 300 since you do not have HF/HV start and most probably your plasma source does not have a built in divider.
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