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Old 01-13-2017, 10:32 AM   #31
rodw
 
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With Mesa, you have a choice of either an ethernet solution (my 7i76e for steppers or its cousin the 7i77e for servos) Or a PCI/PCIe solution. In that case, you plug a card PCI in your PC (probably a 5i25) and then you use a 7i76 or 7i77 daughter card which connects to the PCI card via a parallel port cable. The PCI interface has multiple DB25 connectors for the daughter cards.

The 7i76e is basically a 5i25 and 7i76 rolled into one card connected by ethernet. It supports 2 daughter cards so I could add another 2 x 7i76 cards which would let me control a total of 15 steppers. I think then I could add a RS485 interface board that would allow me to add another 4 I/O cards to increase the number of inputs and outputs if required.

Aside from loading a different driver, PCI vs ethernet is totally transparent when you use it.

Tommy my LCNC plasma mentor on the forum says that putting your PC in there with the electronics with plasma is a surefire recipe to spend countless hours troubleshooting recurring random problems due to noise.

Most Plasma system use a high frequency start that generates a high voltage, high frequency spark to kick the plasma off. Mine has a blowback torch where the arc is started in the torch and once established, the tip blows back or retracts and thus does not generate the noise or HF. That style is much preferred for CNC systems as few torch height systems can handle the HF stuff. Mesa's THCAD card can...


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Old 01-13-2017, 10:57 AM   #32
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Quote:
Originally Posted by joco-nz View Post
i.e. no extra card in the PC meaning you should be able to go to a really small form factor mini/micro style ITX board with the associated small case.

Cheers,
J.
Sorry. Did not address this. Yes, I'm using an ULTRA SMALL FORM FACTOR PC (USFF).

The only issue is that to get support for hardware, you need to run a later version of Unix than the LCNC distro. This for me meant compiling a newer kernal and then of course compiling LCNC from source.

The kernel upgrade can be reduced to a single script but LCNC compiling takes a bit of work due to the large number of dependencies that need to be installed.

The onboard wifi cards on these cards cause terrible latency so you need to use a USB wifi dongle to connect to the internet as the ethernet port is in use. IF I built another, I would find a USFF PC with a dual network interface.


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Old 01-13-2017, 06:58 PM   #33
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Thanks Rod. When you get back to posting on build progress I, and perhaps others, would be just as interetsed in the software/electronics side of the build as the medhanical. E.g. Wiring diags, models/versions of MBs/CPUs used, performanc characteristics/jitter/etc, good suppliers you have discovered.

A lot of what you a working through on the LinuxCNC side and associated electronics and controls I'm very interetsted in as I can see its application to any router style CNC table and much that can apply to a LinuxCNCing of mills or lathes.

I just cant let the wife get a hint of another possible project fasination right at the minute.

Hanging out for more build posts.
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Old 01-14-2017, 10:07 AM   #34
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I just cant let the wife get a hint of another possible project fasination right at the minute.

Hanging out for more build posts.
Sorry, but I'm writing this on a Chromebook that crashed and lost my post. Very Annoying!

My wife would die if she knew what I've spent on this project!

The detail is on the LCNC forum here
https://forum.linuxcnc.org/show-your...a-cutter-build

Make sure you follow the links I post as many of them refer to links where I ask a specific question in another sub-forum to make sure the right people see it and help me!

Anyway, today was 36.2 degrees according to my weather station just above my shed which means it would have been 46.2 degrees where I was working in a tiny corrugated iron shed.

I managed to fit the steppers to the 5:1 timing belt reduction drives before I expired in the tin sauna. I emerged in a lather of sweat and was able to plug them in to my control panel which meant for the first time, I had all 4 steppers functioning.





I can't really do much more until I get the gantry ends installed and the gantry up on the table as I need limit switches and homing switches so I can home it. Until I get that done, I can't run any gcode to tune it.

But at least all of the motors run in the right directions.

Off to ebay to order 6 more proximity switches. This time I will make sure I buy the right type (PNP)
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Old 01-26-2017, 09:58 AM   #35
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Well, I have not got any more of the machine built but I have been working on the software side of things which has been quite time consuming



All of the important buttons have been connected to the hardware now which was really hard work. This particular screen has a couple of buttons that I probably don't need (as they are designed to feed into the Gcode but I can set that in the Gcode that is generated from the nesting software. (Usually with plasma cutters, you are cutting multiple parts out of a sheet of steel that are nested and all cut at the one time.) Anyway, I'll probably clean up the interface as time goes on.

I've also installed a new larger (10.5amp) power supply and rewired the NEMA34 steppers to run in parallel mode. This means they use a lot more power but will run at faster speeds so it looks like despite the lower gearing on the reduction gear boxes I bought, they will keep up with the Y axis at 18 metres per minute. Previously, they were flat doing 10 m/min. So I am happy with that!

I've also spent a fair bit of time researching how PID controls work. Now I've got into it, the torch height control in LCNC is pretty basic but people say it works well. I've got some ideas on how to recode this but time will tell if its necessary or if it actually improves performance.

Hopefully I will have some laser cut parts next week and the fun will really begin!
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Old 02-20-2017, 10:42 AM   #36
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Its been a long time since I've updated this thread but a lot of progress has been made.

My plasma cut parts turned up


and the

parts all mounted up as they should have



very pleased about that

And I got these huge 1.8 metre long 12mm thick rails that had abojut 50 holes I needed to drill and tap to moiunt the gear rack and the 25 mm linear rails. The small part will become the home and limit switches based on my already proven design.



The gantry ends are folded from 6mm aluminium plate



and whilst its hard to see, the pinion clearance was perfect.



Then on Saturday, I borrowed the work ute and grabbed all of the steel for the table



Once it was cut up, it did not look to menacing. The table frame is 100mm x 4mm wall SHS.



and I managed to get one of the gantry ends mounted up and moving.



I had to drill and tap a couple of holes in the stepper mounting plates that are carefully aligned with features in the casting. This let me mount a piece of ally angle to mount the stepper wiring plug to.

I had a lot of problems calibrating the movement but manged to sort it out by trial and error against a 1 metre steel rule. On the previous rack I installed, I just worked out the maths and it worked out perfect. It is clear this rack and pinion was non standard. Anyway, once I got it sorted, I sent the gantry up and down for 20 metres as seen in this video

https://youtu.be/r8YuW3JrFNE

To find I was only out 0.02mm so 0.001 error per metre will do me!



So I think I will call that a wrap!

Today, I went and bought some 330 kg caster wheels and need to work out a couple more things before I start welding up the table. ITs probably going to weight about 400 kg when done so I had to have some casters other wise I would never be able to move it.

Also, on Friday evening a chap from the CNCzone forum tracked me down to see my progress. I think he got a bit of a shock how much work there is in a project like this. (I seem to remember I did too a year or so ago!)

I also found a bug in Linuxcnc and I spent a lot of time sorting that out in the code and on the weekend, the responsible developer released a fix based on the code I had written. I am pleased about that as I did not want to be maintaining code.

I have to say I've become quite a Linux nerd through this and have even checked out different development branches of the code that contained some cool new features that I am sure will work its way into an improved torch height control in time.

Anyway, that brings you up to date.
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Old 03-09-2017, 10:42 AM   #37
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Well, I still have not tackled the table yet as life has been a bit busy. I also have been designing the last few parts for the table because this thing will be so heavy, I need to be able to get it on the 330 kg casters I've bought for it to move it round.



So I made a mount at the stepper end to hold a wiring socket. This required drilling and tapping the stepper mounting plate



I don't think I showed you guys the air regulator with the dessicant to dry the air.



After the air goes though these filters, it will also go through a Motorguard "toilet paper" filter which are often used on plasma cutters.



Which reminds me, I have not worked out how these will get mounted to the table

Somewhere along the line, I found a super cheap welding fume extractor with a 5 stage filter but I don't think it will have enough airflow for the plasma table.



Last weekend, we went to see Adele here in Brisbane. 60,000 people the largest concert ever staged in Brisbane and the first hosted at the Gabba cricket ground since about 1978. It was really enjoyable.



Sunday, I wired in the last stepper driver and soldered up the cables to it.

I did a few CAD drawings in the evenings this week and I checked them last night and thankfully I found the error before I got it laser cut!

One of the things I had to check was the voltage divider on my Everlast plasma cutter. It has the option of raw volts or divided volts at either 16:1 or 50:1. The divider is selected by a jumper on the CNC board inside the plasma cutter.

Plasma voltage maxes out at around 300 volts. My Mesa THCAD card has a 0-10V range so 16:1 was not going to work and 16:1 would not have great resolution as it would only go from 0-6 volts. I had this great idea to use a voltage divider so I could use the 16:1 divider. This would give me a full scale reading of about 9.375 volts so it will be so much better.

Peter from Mesa set me straight on the LCNC forum about how to do this. You don't need a traditional voltage divider circuit, you just need to add a resistor in series with the voltage signal. The value of the resistor is based on a formula in the manual. My Maths was way out and Peter kindly stopped me from buying a 0.1 ohm resistor when the correct value is 100,000 ohms!

It is rare to see a manufacturer to be so involved in a forum and the support Peter offers is simply amazing even building custom firmware for people using his hardware.

Last night, I pulled my plasma cutter apart and checked out what voltage was selected

.

As it turns out, I did not need to becasue it appears to be set to the correct value based on the position of the jumper on the bottom right. I still have to put it together again. This morning, I had to drive past Jaycar electronics to pick up some material for my web site (10 metres of 60mm dia plastic that needs to be cut and faced into about 180 parts). So I stopped and lashed out all of 55 cents to buy a packet of 100k resistors.

So there you go guys, you are now right up to date and I am ready to build the plasma control cable now. I will have no trouble tucking the tiny resistor inside the cable backshell.


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