Messages

311

General Mach Discussion / Re: Physical buttons for plasma

« on: February 04, 2016, 03:09:03 AM »

Yup the Proma is a bad choice... but it was "cost effective" and a starting point on a long learning road ("if I knew then what I know now...")

Basically anything that relies on relays is a bad idea for THC for a start!

the Proma "SD" being direct drive [pass through until Torch Voltage Sensed, then Proma Controlled until the end of the cut) is just an improvement by way of some motion controllers not having THC programmed into them (Chinese USB ones or the USB-SS for instance [started there!, read line 1 above]).... but still uses relays it "looks" like.... (if you read the manual closely).

The SD does not offer the THC Inhibit if blended trajectory drops below "x%" of the feedrate...

And it also does not offer M-code inhibit for corners to turn the THC on & off...
http://www.planet-cnc.com/faq/THC/THCSD.png

If it detects torch voltage.... it controls !




Ohmic has always interested me.... but if you have a working floating head.... is it a gimic or does it really improve the cut?   
All depends I guess on what you are cutting (thickness, surface rust / coating etc) and how you are cutting it (water table).

Could also be considered a "double tap".

I did not know G28.1 ignores limits....   what about if you tie your home and limit inputs together using the same pin numbers?

And put the floating head (or ohmic) on the "probe" input (which is my arrangement)?

Rob

312

General Mach Discussion / Re: Physical buttons for plasma

« on: February 04, 2016, 01:05:30 AM »

Oh... I use floating switch...

Have a look at this table, you can use bits of the idea too.

http://m.instructables.com/id/CNC-Plasma-Table/

Rob

313

General Mach Discussion / Re: Physical buttons for plasma

« on: February 03, 2016, 08:00:35 PM »

Hood, thanks for the too highly rated complement, I'm really just starting out on a very long journey.

I know zero about servo drives, that being said, I like your options, they look very interesting and may have advantages of driving the THC directly.

However... If you drive the THC directly, the z axis DRO will have zero idea where the torch actually is until the next touch off (g28.1).... I don't think this would be a problem with my setup, as I touch off before my torch refires every time.

Another problem you may have if you control the servo directly via the THC.... You won't be able to turn the THC off when blended tradjectory is below x% of the feedrate....

With regards to the rest of the control, I'll try to explain my setup (right, wrong,  works for me).  I use sheetcam, and that goes care of my touch off (I use g28.1, but you can use g31), and also via snipetts, I turn my THC on and off for small circles and corners etc.

Really, consider my setup a little further, I use an ESS, and turn my THC on and off by making and breaking the THCOK signal back from my THC, given THCUp and THCDn are ignored when THCOK is not present.

The THCOK signal is broken by feeding the THCOK feed via a relay which is controlled via m10px and m11px as these are the only mcodes that don't cause a divot and tradjectory to slow for the mcode execution.

The THC is a proma (actually its Dave's old one...) (I am awaiting a new product on the market, .... Since last sept..!!, hence I nearly built my own and have a few times nearly bought the  neuron... If they dropped the pricing back to their introductory price I'd be there like a shot!). I have wasted a great deal of time exploring everyone THC that I could find on the market to try to understand what each offered.

Hence its crude (only settings are hysterysis, torch transfer voltage and target voltage), and its slow... It uses good old fashioned relays... Optoisolators would have been way faster....I would not recommend them, although for the cost it has met its needs as a very entry level thc. (Read:cheap!)

Anyway, the THC is set with a very close hysterysis (2v, the minimum), and an arc transfer voltage of only 5 volts above my target.... The reason behind this is because its acting as an anti-dive function.... Hence the THCOK signal will drop out (or not be enabled until the torch voltage is within 5v of the target voltage, and any spikes the THCOK signal will drop out.   From all the info I've found on the net, 1torch volt is about 0.32 to 0.64mm of torch height... Say 0.5mm per volt.... Hence 2v will be around 1mm of cut height (+/- ~ 0.3 mm).

I leave the THC to control the torch height.

I leave sheetcam to insert my code snippets (which I may hand adjust onscreen) to turn my THC on and off via m10px and m11px, via the post processor.

I leave sheetcam to inset my pierce pause by setting up the relevant tool settings  (pierce delay, pierce height, initial cut height and do my touch off before every pierce)

Code snippets in sheetcam reduce my feedrate for circular cuts to 60% of the straight line feedrate automatically also for circles less than 1.5" dia (most of my metal is under 4mm)

Hope some of that is for use to someone

Rob

314

General Mach Discussion / Re: Physical buttons for plasma

« on: January 31, 2016, 09:08:36 AM »

Thanks Russ for the offer, much appreciated.

1/5" lead is about a 5mm pitch, and 5/8 is about 16mm dia... So unless I got it wrong they are approximately eqivelent to a 1605 ballscrew although using delrin/acetal etc nut.

I'm presently running a 2mm pitch 10mm trapezoidal leadscrew.

I'm in the UK and may take you up on the offer if it's still available after a bit more advice on leadscrew + plasma + z axis.

315

General Mach Discussion / Re: Physical buttons for plasma

« on: January 31, 2016, 04:15:06 AM »

Thinking about designing a better plasma z axis...


Anybody used anything like this for a z axis leadscrew?

High helix leadscrew, 10mm dia, 12mm lead, with a delrin nut (22mm of)

http://www.igus.co.uk/wpck/7001/DryLin_Steilgewindemuttern

Was looking at 1610 or 1616 ballscrew as a faster response zaxis for a plasma as well.

Why the 10mm leadscrew you may ask, smaller, lighter, easier to couple, no need to have ends machined for bearings or couplings, especially when I would be only after a short length (150mm)

Open to comment, thanks

Edit, drive by stepper, with programmable digital drive, hence choice of microstep resolution.

316

General Mach Discussion / Re: Physical buttons for plasma

« on: January 29, 2016, 09:34:29 AM »

I think the two z axis were to have a slower positioning axis (to touch off) and a high speed low inertia high acceleration THC axis..

Probably back on page 5...

317

General Mach Discussion / Re: Physical buttons for plasma

« on: January 27, 2016, 01:25:32 PM »

Another interesting investigation is to be able to Directly TALK to the THC without a COM link to the THC. That way teh THC could be  adjusted on ANY controller ON THE FLY and without a COM link. A universal fully programmable THC without teh need to create a normal Com link to talk to it.

You have lost me there??

The best method would be to run teh entire THC function directly from inside of the Motion Controller itself ( ESS, UC300,etc) . Just give it the reference voltage or frequency and the Ark OK signal and it handles everything internally.  There is one that can do that currently.

can I ask which one? CISMO I thought did it and purelogic does something, but I'm not sure how much is shared from their THC to their motion controller?

318

General Mach Discussion / Re: Physical buttons for plasma

« on: January 27, 2016, 01:19:26 PM »

Keith as you said.... why could you not use PID instead of bang bang control for THC?

(totally external to M3 or M4 of course)

That way accel and vel is proportional to the error and increased relative to the error time and decel used obviously once you get closer to the target voltage (D).... or PI control?

I guess in theory the intergral "I" part with a fast Z should be near zero?...

319

General Mach Discussion / Re: Physical buttons for plasma

« on: January 27, 2016, 11:29:05 AM »

Thanks Terry on all the previous items covered, following the thread closely.

I know mach3 is not up to the imposed acceleration, but did wonder about Mach4 as the scripts run much faster....  I'm still waiting for the new ESS plugin (no jokes please!!).

As posted previous, the Neuron THC and the CandCNC both directly control the Z axis so should be able to attain higher z axis motion with a very steep accel and deceleration, I'm also aware of another product that I'm eagerly awaiting to hit the market which will do the same.

What does everyone else do to turn THC on and off via gcode on the fly (I use sheetcam as I'm sure most probably do), before corners or small circles etc?

320

General Mach Discussion / Re: Physical buttons for plasma

« on: January 27, 2016, 09:43:14 AM »

the 13º is from the arctan (tan-1) of (1.4 / 6)  (opposide / adjacent)

sorry... post corrected... muppet!