Messages

341

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 05:37:17 PM »

"The low cost THCs DO have the pid loop built in and cost around $500 or less complete ."

Which ones?  Anything that interacts with Mach3 through THC UP/DOWN commands doesn't have a PID loop, or if it does, it doesn't do any good.  The idea behind the PID loop is to adjust the feed rate based on the distance of travel and to control acceleration to reduce/eliminate over-travel.  Most of these low cost THC's simply trigger the Mach3 THC commands, which in turn move the Z at the set THC feed rate with no acceleration applied until the input is turned off. when it's turned off, there is always some over-travel, which is dealt with by reducing THC feed rate to where the "bounce" is acceptable, which as you pointed out, is not as big a deal in plasma as it would be in routing. 

342

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 10:25:20 AM »

Any of the affordable THC's out there (hobby level) do not have built in PID loops.  They simply monitor tip voltage and send THC UP/DOWN commands to Mach.  The lack of a PID loop is exactly why you get excessive oscillation if the THC feed rate is set too high.  If you want to spend some money, you can get a stand alone THC that operates outside of Mach3.  These THC's will have built in PID loops and control the Z axis independently of Mach3.

Which way do you want to go?  If you're looking for hobby level THC that can just command Mach3 to make the THC UP/DOWN moves, you can build something easily.  An stand alone industrial THC with PID capability can cost a few grand.  Thermal Dynamics gets just over $10k for theirs.

One thing to consider is that once you move the Z over to an external THC, you will no longer be able to control it using Mach3 directly.  When plasma cutting, other than setting initial torch height and retracting prior to rapids, the THC controls the Z.  There are no Z feedrate moves in the program.

Are you looking to just measure the material height and apply a Z offset to compensate for variations in material height?

343

General Mach Discussion / Re: MACH as a CMM machine

« on: August 12, 2011, 10:23:28 PM »

OK so use the plasma height controll setup and instead of monitoring the arc voltage level use a sliding reohstat mounted at the head to follow the contour height and generate a variable voltage based on the voltage level as a height input then MACH can adjust it similar to the way it does with plasma. ON THE FLY.

Just a thought, (;-) TP

I will soon be putting together the same thing for my router, as the sheets of material I use aren't always flat! I was going to use compressed air to blow the chip away and help cool the bit, and an ultrasonic sensor to measure the height without touching it. Works an transparent material because it uses sound. Let me know if you would like some info on the ultrasonic sensors we order to use in our products. This along with a Torch Height Controller and it shouldn't be too hard!

Any recommendations on a THC for this application would be great.

Chris

You won't need to buy a THC.  You'll have to build your own using the ultrasonic sensor.  All the THC does is compare tip voltage to a set voltage.  If the tip voltage is lower than the set voltage, the THC sends a THC UP command.  If it's higher, it sends a THC DOWN command.  You'll need to build some electronics to read the ultrasonic sensor, compare it's output to a set constant and output to a second PP on the Mach3 PC.

344

General Mach Discussion / Re: MACH as a CMM machine

« on: August 12, 2011, 10:15:02 PM »

Chip this is a little off topic but can you use a waterjet to cut an automobile windshield?

Yes, you can. I've seen a local shop do it on a 5 axis FlowJet.  The cost to have it done might send them right back to using existing glass though.  The guy running the machine thought it was around $800.

345

General Mach Discussion / Re: what software has this interface?

« on: August 09, 2011, 09:13:19 PM »

Definitely Rhino.  I use it every day.

346

General Mach Discussion / Re: How can I continue g-code tomorrow ?

« on: August 09, 2011, 08:46:05 AM »

If you ever have to explain to an hourly employee how to use 'Run from here", you see why I just edit the GCode.  From a cost perspective, CNC is within reach to the hobbyist, but I don't think you'll ever see a CNC for dummies machine...or controller.  It's easy to train someone to push the proper buttons to achieve a result, but not so easy to teach them what to do if things don't work right. 

CNC machinery is a lot different than you truck.  There are a lot of variables, both in the job setup and in the machine operation...and since most of these machines are home-built, it's almost impossible to document the machine, and since Mach3 is so customizable, it's not easy to document it as well.

The closest you'll come to pushing a button and outputting a part without worrying is to buy a commercial machine and controller, then when things go wrong, you just call the tech to fix it...Kind of like calling the mechanic to fix your truck.  Of course, you'll pay a considerable price for that.  If you want to build you own machine, you have no choice but to learn what goes on under the hood.

347

General Mach Discussion / Re: How can I continue g-code tomorrow ?

« on: August 06, 2011, 08:31:45 PM »

Easiest way is to stop at a logical stopping point, like after Z retracts but before a rapid to the next cut.  Then make a note of the line number in the program where it stopped, open the program in a text editor and delete all of the code that has already run.  Leave the program header and any setup code.  The first rapid move should be to the next part that would have cut had you not stopped the program.  After editing, reload the program and run it from the top.

This assumes you referenced at a point that you can replicate, like the lower left of the stock.

348

General Mach Discussion / Re: G31 Probe problem

« on: August 05, 2011, 10:47:01 AM »

The main reason I would never had seen it is I run all the axis's at the same parameters for accel/velocity.

So do I.  Every now and then I play around with the accel settings.  That's when I notice it.  Other than some random testing, I run all axes at 30.  Stirling tested this and said it was fine on his machine...Z axis G31 followed the Z axis accel settings.  That's why I was wondering is it was a config setting.

349

General Mach Discussion / Re: G31 Probe problem

« on: August 05, 2011, 08:34:50 AM »

So G28.1 fixes it.  Can we conclude that there is a problem with G31?  for whatever reason...maybe a config setting...on my machines, Z axis G31 accel follows the X or Y axis.  If memory serves, it follows the X.   I was hoping to see a G31 fix come out of this thread.

350

General Mach Discussion / Re: G31 Probe problem

« on: August 01, 2011, 09:10:22 PM »

I tested again today.  I set all accels at 50 and did a G31 Z-1.  Motion was as expected for an accel setting of 50.  I then reset the X and Y accel to 5 and did the same G31 Z-1.  Accel was very slow on the G31.  I reset X and Y back to 50 and the G31 returned to normal.  Seems like it's definitely using the accel setting from another axis.  I normally run all accel settings fairly close to each other and fairly high, so this is not an everyday issue.