Why use Ohmic with DTHC

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Mr. Fixit
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Why use Ohmic with DTHC

Post by Mr. Fixit »

Hi all,

I am in the midst of upgrading from brand X to a Hypertherm 65. I have the candcnc system and I am wondering if there is any advantage to using an ohmic sensor with DTHC? Any help is appreciated.

Thanks,

Steve
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WyoGreen
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Re: Why use Ohmic with DTHC

Post by WyoGreen »

There are pluses and minus. On the plus side, it doesn't deflect thin metal when it goes down to sense it. On the negative side, it won't sense painted or dirty metal, and can be problematic on water tables. (If there is water on top of the plate, the sensor will sense the water instead of the metal.) With all that said, I have a water table and use an ohmic sensor backed up with the floating Z sensor.

Steve
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Mr. Fixit
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Re: Why use Ohmic with DTHC

Post by Mr. Fixit »

WyoGreen wrote: Fri Dec 07, 2018 6:49 pm There are pluses and minus. On the plus side, it doesn't deflect thin metal when it goes down to sense it. On the negative side, it won't sense painted or dirty metal, and can be problematic on water tables. (If there is water on top of the plate, the sensor will sense the water instead of the metal.) With all that said, I have a water table and use an ohmic sensor backed up with the floating Z sensor.

Steve
Sooo, with DTHC it really isn’t necessary other than the cutting of light gauge material in your opinion?

Thanks,

Steve
4' x 4' DIY Table
CandCNC Bladerunner
Hypertherm PM65 Machine Torch
Miller Vintage 250 Mig
Miller Syncro 180 Tig
Bridgeport 2J Mill - Fagor Dro
Southbend 14" x 40" EVS Lathe - Fagor Dro
Brook 18" Metal Shaper
Harig 612 Surface Grinder
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Ironken
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Re: Why use Ohmic with DTHC

Post by Ironken »

Personally, I have used both. As Steve said, ohmic is really nice for thinner gauge materials and thinner gauge material that is distorted. Say you have a piece of 16g that has a bit of a hump in it. Without ohmic, the Z axis will probe and push the sheet flat, set the torch height and move to pierce height....if the sheet springs back .060, .120, etc you effectively have no pierce height. The sheet will be against the torch shield and could blow back and foul a nozzle. If you only cut thicker plate, you probably will see no benefit. It's better to have something and not need it than to need it and not have it. I think CandCNC is pretty reasonable on the ohmic upgrade price.

My buddy actually wears out shields from the plate springing back and rubbing briefly until the THC takes over. He doesn't have ohmic. I do have ohmic and have zero evidence of any scuffing on my nozzle....in fact, I have to scrub the shield to get the soot and schmoo off occasionally.
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djreiswig
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Re: Why use Ohmic with DTHC

Post by djreiswig »

Ohmic and DTHC serve two different purposes. Ohmic is used for IHS to sense top of material before cutting. DTHC is used to maintain arc gap while cutting. They're not really related.
Ohmic is nice for thin material, but as stated above it won't sense dirty or painted material. I have mine wired with a switch so I can toggle between ohmic and touch.
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Mr. Fixit
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Re: Why use Ohmic with DTHC

Post by Mr. Fixit »

Thank you all for the insight. I now understand its purpose and when it is useful. One last question, since dirty material was referenced, will the ohmic work on HRS material?

Thanks again..

Steve
4' x 4' DIY Table
CandCNC Bladerunner
Hypertherm PM65 Machine Torch
Miller Vintage 250 Mig
Miller Syncro 180 Tig
Bridgeport 2J Mill - Fagor Dro
Southbend 14" x 40" EVS Lathe - Fagor Dro
Brook 18" Metal Shaper
Harig 612 Surface Grinder
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Ironken
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Re: Why use Ohmic with DTHC

Post by Ironken »

I have had no problems with my ohmic on HR. The only issues that I have had with ohmic other than those mentioned is standing water on the plate and soot building up on the shield. The standing water bubble issue usually is only on the first pierce. After the first pierce/fire, the torch is in post flow and usually blows the water away before probing. If I allow soot to build up on the shield after many cuts, the soot acts as an insulator and when the shield contacts the plate my machine will fault on probing. A small SS wire brush and a few quick passes over the shield/nozzle and all is well.
Last edited by Ironken on Sat Dec 08, 2018 1:29 pm, edited 1 time in total.
Mr. Fixit
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Re: Why use Ohmic with DTHC

Post by Mr. Fixit »

Got it..

Thank you.
4' x 4' DIY Table
CandCNC Bladerunner
Hypertherm PM65 Machine Torch
Miller Vintage 250 Mig
Miller Syncro 180 Tig
Bridgeport 2J Mill - Fagor Dro
Southbend 14" x 40" EVS Lathe - Fagor Dro
Brook 18" Metal Shaper
Harig 612 Surface Grinder
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