Old Cutmaster 101 CNC Interface

[kyain]

Hi Folks

Long story short, I picked up an old plasmacam DHC at an estate sale, had some dealings with plasmacam, found software on my own and an old PC and still had no dice, so then began ripping off all the plasmacam stuff to put on new controls

I went with a smoothstepper and tmc3in1, threw some new drives/motors on with some adapters and have the table all moving and doing things like it should. Running into a few snags with the plasma integration though.

I picked up a torch switch signal pretty easily off the main board using E5/E6, as those are normally what's going to the automation board (which this plasma does not have)

Arc OK signal I'm assuming I can just throw a current sensing relay in there on the output leads and use that.

It's getting a divided arc voltage that I'm a bit cautious on. Unsure of what size resistors and how to actually wire it in. I seem to have 2 spades on the output power assembly board that I think I could tie into, or I could just use the same studs that the plasmacam cable was going to. The spades are labeled E1 (-) and E2 (+) and measuring across them I saw up to 300vdc while the pilot was starting, and about 130v while I had an arc going.

Any insight on where to go and what size resistors and stuff to use? Also is it a basic voltage divider circuit (just 2 resistors, signal tapped between) or anything else suggested to smooth out the high initial 270-300v during the pilot arc?

[djreiswig]

According to the manual e1 & e2 are raw arc volts. I'm not sure about the divider, but I'm sure there is some info on the forum about how to make one. Use the search box at the top.

Screenshot_20210821-214443(1).png

[kyain]

any chance you could link me to that manual in particular(or how ya found it?) None of the ones I found online searching for a cutmaster 101 included that.

*** just realized I'm an idiot and if I would have just went to ESAB's site they have a pretty good resources section ***

[adbuch]

For you voltage divider, 1/4 or 1/2 watt resistors should be fine. You are monitoring the arc voltage only, and very minimal current will be going thru the divider network.
David

[djreiswig]

I just googled cutmaster 101.
https://www.manualsdir.com/manuals/5950 ... 100sv.html

[kyain]

yea, when I googled I was searching for the regular plasma (with the standard torch, not the machine torch). The standard manual makes no mention of the E1/E2 pins on the power supply board, nor are they actually shown in the prints. I had found them already because well... it looked right and tested right lol.

Picked up some resistors today. Microcenter unfortunately only had 1/4w resistors so I'm hoping they stick together, I've already ordered some larger ones just in case.

Don't particularly see anything in the prints that I can pickup as an ok to move signal so I'm either going to end up omitting it or ordering a current sensing relay. Any input on getting one with a time delay or just let the controller/cam package handle a delay after signal on time?

[robertspark]

arc ok / transfer signal, using a sensitive reed switch

http://linuxcnc.org/docs/devel/html/pla ... eed-arc-ok

[kyain]

arc ok / transfer signal, using a sensitive reed switch

http://linuxcnc.org/docs/devel/html/pla ... eed-arc-ok

I'm almost embarassed that in all of my years of control experience I have never come across or heard of a reed switch before.

I've already got a CSR incoming but that link still helps. I was goin to put it on the torch leads originally (the pilot arc is a seperate lead from the main arc leads), but putting it on the work lead is a far better option.

[robertspark]

I don't know if the following will be of use to you


what ratio do you want?

50:1 >>>> 100k ohm 1W, and 2k ohm 1/8th Watt or greater.


(300V / 10200 = 0.002941176471A)

I^2 X R (0.002941176471^2 X 100000) = 0.86505190311W

when I have made these up in the past, I used precision resistors 5x 20K 1/4 watt in series (making 100k) a 2K 1/4 watt

you don't HAVE to use precision resistors... but it's nice to know that the number you are reading is accurate... or as accurate as can be presuming that the THC has a very high input impedance

20:1 >>>>>> 100k ohm 1Watt and 5K 1/8 or greater

if I were to make this myself, then again I would use
precision resistors 5x 20K 1/4 watt in series (making 100k) a 5K 1/4 watt

the problem with just buying 1 100k resistor is they are normally 5% and 10% + when you get into the high wattage series.

each to their own, do what YOU are happy with and wear big boy pants..... it is DC and not AC so will kill

when I made these in the past I made them on a tiny PCB and then applied a double layer of heat shrink over the whole assembly so the first layer would protect against abrasion and the second layer provides the insulation.

I'd not install any filters as these are normally within the thc but I have seen hypertherm install a common mode choke before the divider resistor (ie after the 100k resistor) as this will filter out any HF / AC noise which is common to both lines. consider it the cherry on the cake


https://isteam.wsimg.com/ip/544f515b-f0 ... :600,h:600

[kyain]

I opted for 1% tolerance chassis mount with solder lugs. Bit more expensive but just feels like a cleaner install to me (I'm pretty anal about control wiring).

I played with some 1/2W I picked up from microcenter locally and they got far too hot for my liking. Just felt like a failure waiting to happen. Was fine for a short few test bursts. Even if they didn't completely fail I don't know if I would have been comfortable with the resistance changes from temperature. That has bit me a few times in the past with PT and CT circuits in some of our large emergency power substations. To get a nice matching set these have ended up as completely overkill 10W chassis mount lol.

Thankfully they were in stock at digikey so I'm hoping they show up this week. I did order a couple of those reed switches to tinker with but also found a good used DC CSR today. The CSR requires 24v to operate so I might just make the reed circuit instead instead of running supply power from the control box into the plasma.

Thanks for the tips/info though. Hopefully this thing is making good sparks this weekend. Full control of the plasma is the only thing left to do to bring this old plasmacam back to life.

[robertspark]

the cutting voltage should be in the below 140v range, but it is possible to get open circuit voltages (on some plasma cutters) up to 300 / 350v.... hence you are safer from a long term perspective of going with a higher wattage. imo

the voltage number is not that important as long as you find the best quality cut at a number for the thc, you can track that number for that material thickness + material type + amperage setting

some guys do a series of test cuts....

say 10 parallel cuts (with the thc off!)

4 or 5 inches long

each one 5ipm faster than the last to try to find the sweet spot.... or maybe using some known data from a similar amperage and power wattage rated machine as the central speed and then lower it by 5ipm either side of that central band.

the first pierce can be misleading (sometimes or on some machines) and some will get the machine to do an initial pierce in a scrap section first before beginning the cuts.

if you are not using an air dryer / desiccant dryer then your cuts can vary (optimum federate, thc voltage vary on the day) depending upon the moisture content in the air.... plus your consumables have a shorter life.

i 7t is also beneficial to sometimes do a series of test pierces (say 10 in a series), with different pierce times so you can find the optimum time for dimpling (hole centre marking for later drilling) and for piercing a particular material and thickness and the set amperage..... so you do not get too much more time delay than you require to just pierce the material and then begin the cut.

the pmx45xp does dimpling at minimum current setting of 10A and a dimple (pierce ) height of 0.25".... which is much higher than the normal pierce height of 0.15" (250% of the cut height)

have fun, play with the settings to find what works for you or your setup and materials you cut

[tcaudle]

some power formulas wil help:

the total resistor value (both reisiors in series is th e"load" The formala is E^2 / R so at 200 volts its 200 X 200 or 400,000 / R in watts. So 102k of resistors predicts 4 watts of power. Now a 5Wat resistor burning i\up 4 Watts will get HOT. It won't burn up. To get the power across each resostor its the ratio between the two. So 100K and 2K saws MOST of the power is across the 100K and only about 2% is across the 2K or only about 60Mw (.08 watts). So now it pretty easy to drop in a 2K ten turn pot in series with a 1K and "trim " the output to be exact. You need to consider a low pass filter since the plasma lovage is REALLY ugly with PWM and lots of noise. A twin T LP filter works . Most THC don't have adequate filters for the divided volts at the frequency that plasma runs. You also have to consider that the higher the ratio (like 50:1 or 100:1 ) the more outside noise can effect the reading. Consider that at 50:1 it only \takes 20mv (.02volt) of noise to skew the reading 1 volt. Also couple the fac taht Electrode is POS and workclamp negative (NOT Ground) . You can use normal 5% power resistors also remember that two 5W ins series at 1/2 the R value will share the dissipation . It the same total dissipation but now you have 10Wats of resistors to handle it. We have had an option for many years with out DTHC and the remote PWM pickup to connect direct to raw arc volts uings a Universal connection Kit. The kit contains a non-contact Hall current sensr that slips ove the workclamp and gives you direct amps readout AND an Arc Ok signal. The THC manufacturer should be able to supply ways to connect to rigs that do not have the CNC interface built in. Unfortunate our connection kits are for our DTHC and controllers and are not standard ratios.


also remember that an HF start machine trows a Huge spike onto he like and will kill most conventional difider circuits. I think the TD 101 is pilot arc not HF .