[MikeGyver]

I see, so bare minimum I would need a limit switch on the Z axis in order to sense the surface and automatically code in a pierce height of 3/8" (or whatever) above this. Then I could pause for the pierce, then have the THC Z-motor (the 2nd and independant z-motor) do it's thing and bring the torch down and maintain a desired arc voltage.

[C.Michael]

But what are you using to control this servo..to maintain the voltage..If I recall,my THC is looking at the voltage and adjusting it several times a second..

[MikeGyver]

Probably a simple analog regulator type circuit, it'll work in real time with the only lag being the speed of the motor. Think of it like a servo, only instead of using the internal potentiometer for feedback, it'll use arc voltage. So it'll automatically zero in on and maintain the desired arc voltage

[C.Michael]

When it comes to electronics..I know nothing!! Just basic understanding..so your THC would not involve the use of mach,since it is using a separate motor and system to control the height ..I think I am following you..Well,I can say that I had a time adjusting this THC of mine but once I had it,the thing cuts like a laser..Torch height maintenance is super important for a quality cut..A few thousands of a inch and it goes to pot instantly with lots of cleanup with a grinder..

[MikeGyver]

I see.. I could adjust the gearing for greater resolution or even use a seperate stepper for the motor.
But yeah I think I can build a THC that works very well for for mere dollars. It wouldn't interface into Mach3, for all mach knows there is just a Z-axis with no THC, but arc voltage would always be set correctly. It would have it's own knob to set the desired voltage and whatever else. This has benefits though, cheaper, simpler, independant so it'll work on literally any other plasma setup. I just need some experience on a running system so I know what I'm working with so this will come after I have a working table, which is still months out.

Ive got the rails figured out tho I think.

[MikeGyver]

Here's a to scale drawing. The 3/4" 316 stainless angle iron is corner-up, you can see the 2"x3" tubing table frame, the flatbar/angle overhangs the table by 1/2" for the rack gear (which is permanently secured to the flatbar using 3M VHB tape).
Here's the main issue. I need to find a good way to secure the angle to the flatbar under it. Any heat at all is going to warp it over a 4ft run, so no welding. I'll secure each end with an allen bolt, but im not sure how to secure the middle, I've though of epoxy, elaborate ways to bolt it down, etc. The bolts into the 2"x3" tubing will give me adjustability to parallel the rails, so I just need to somehow keep the angle dead straight on the flat bar.
This design has the advantages of hard stainless rails, perfect 90 degrees, cheap as hell, quick and easy to build, packages well...
Ideas anyone?

[keebler303]

If it were me, and since I have a TIG welder, I would weld the angle to the flat. It would only need to be tacked every few inches and I doubt you would see significant deformation from just little tack welds. Thats the best way IMO.

Matt

[mr.riggnns]

has anyone seen or used the hycut nc plasma cutter from china. i found one new for 1800$ usd whats the difference between nc and cnc.looked like it cut good no z axis on the one im looking at but could add one later.also i am a total newby to cnc. how hard would it be to use one of these machine in my home fab shop. what do i need to run one.

[MikeGyver]

has anyone seen or used the hycut nc plasma cutter from china. i found one new for 1800$ usd whats the difference between nc and cnc.looked like it cut good no z axis on the one im looking at but could add one later.also i am a total newby to cnc. how hard would it be to use one of these machine in my home fab shop. what do i need to run one.

You might have better luck starting a new thread than hijacking a random, unrelated one... just sayin

[C.Michael]

Hey Mike,looking at your drawing on post 26, could you put a bearing and v rail on the bottom..this would keep the gantry from tipping forward or back during hard acceleration and braking..just to keep it from jumping off the tracks

[MikeGyver]

Hey Mike,looking at your drawing on post 26, could you put a bearing and v rail on the bottom..this would keep the gantry from tipping forward or back during hard acceleration and braking..just to keep it from jumping off the tracks

True but it would increase complexity and complicate the build and the lash adjustment. I'm going to use a stiff spring to pivot the pinion gear into the rack, and keep the bridge low with a wide stance (2 bearings per rail). I hope it works w/o problems.

[Torchhead]

There is a lot more to plasma cutting than just measuring the arc volts and holding a gap. it sounds simple if you say it fast. You need to be able to find the top of the material (IHS), pierce at the correct height, sense if you have a valid arc (Arc XFR is built into the Hypertherm 45) drop to the correct beginning height (Initial Cut Height) and then keep the cut gap within .020 or better no matter what the material does. The voltage change to hold those type tolerances is a tiny percentage of the actual arc volts. You cut at voltage like 140VDC and a change of 1V needs to be detected by the THC. Mix all of that up with the noise of plasma cutting and it's a challenge. There there are issues like anti-dive. As you slow down a cut or it approaches the beginning of the cut, the arc voltage starts to rise and the THC will see that as the material (or torch tip) getting further away so it moves the torch down (dives to the metal)

The THC300 was good in it's day (I know because I designed it for myself in 2003) but there are better, cheaper, faster more full featured THC's.

If you elect to use MACH3 as the control software for your table and conventional stepper or servos as the motion components then you have the a option to use the LCTHC. It has preset Volts (just dial in your target arc gap using a voltage setting) integrated anti-dive to prevent the head diving, and used with SheetCAM offers all of the touch-off, pierce and things like lead-ins/outs, kerf offset and other plasma specific parameters you will find you need for good cuts. That Hypertherm 45 is capable of really nice cuts but you need a good THC to get the best use of the machine.

Low Cost Torch Height Control (LCTHC) http://www.CandCNC.com/LCTHC.html

If this is your first CNC project and the electronics side is not your strong suit then you might want to look at one of our Plug-n-run systems that have the DTHC (more features, tighter integration with MACH) built in.

TOM caudle
www.CandCNC.com