Ok everything is fine except the X now stops just past the home point when finished with cutting. New stepper motor installed fine. pully tight also. I have been working for hours making adjustment so the X will stop at the homing point. All other axis's work fine just the X likes to stop maybe an 1/8 to a 1/4 past the homed point. Voltage is correct. all motors are cool including the "heavy duty" chips on the controlller. Went from 30 all the way to 70 in the IPS setting. No apparent missing steps. Velocity is around 45 for the X I have actually had it down to 12. Motor works fine and calibrates right on the numers but still likes to stop just past the home spot each time. argh....

 

Frank, changing the acceleration might make the difference. I had to play with mine for a while to get every motor to a "happy state", but I can run my "four corners script" and it will return to 0,0 within 1/16 every time. I've never put a dial indicator on it, so I'm only estimating by how well the router bit goes back into the first corner hole I drilled, but it's never been off more than half of the 1/8 diameter of the hole. I always figured the difference was caused by slippage or slight skewing of the material between the rollers on my PP.

 

Dennis....tell me more about the "four corners" script, and the test fixture for it...sounds like a handy tool for checking your machine!

Tim
AG4RZ

 

Hey Dorsal thanks for the quick reply. I have been messing with that acceleration a bit. I am wondering if it over runs slightly as it makes it's stops and moves. Adds up ever so slightly over time as I cut. I will concentrate on that acceleration setting more. I do test patches myself to make it do some concentrated work. Actually the cuts look nice. Just bugs me how X homes a bit further that it is supposed to. Thanks for the suggestion

Frank

 

Tim, it's really nothing fancy, just a few lines of g-code that I add to the beginning of any cut-file. It pokes a hole at each of the four corners of the 22 X 42 "Safe Area" of a sheet of material, so I can re-register the sheet later (if the need arises) or I can flip the sheet over and align it to the opposite holes. That way, I could cut pockets on the other side if I wanted. I've used it many times to "exercise" the machine to be sure I'm not missing steps with any axis.
Here's the contents of my "Alignment Holes.cnc". It returns the machine to the 0,0 start position, then triggers a STOP with the M00 at the end, to wait for me to hit RESET then PRINT to start the actual cut program.

%
G90
G20
G49
M3 S15000
G00 X 0.000 Y 0.000 F250
G00 Z -0.350
G00 Z 0.050
G00 X 0.000 Y 22.000 F250
G00 Z -0.350
G00 Z 0.050
G00 X 42.000 Y 22.000 F250
G00 Z -0.350
G00 Z 0.050
G00 X 42.000 Y 0.000 F250
G00 Z -0.350
G00 Z 0.050
G00 X 0.000 Y 0.000 F250
M09
M49
M00

 

Frank - Over on CNCzone.com forums, I've learned that you must balance the acceleration with the sharpness of corners in a cut. If the acceleration is really slow (i.e. a large number) then the corners will become rounded, because one axis is slowly getting into position while the other one is zipping along. If the acceleration is too fast (too small a number) then the motors will lose steps. Mine are set somewhere between 8 and 18, but I don't remember the exact numbers.

 

Dennis..that is a great idea! I never thought about having the machine do the indexing! I am going to put that to use. I Had been trying to figure out how I was going to align the foam to do back-side cuts, and it never crossed my mind to let the PP do it...i guess I gotta get out of the "Cut it by hand" frame of mind, and remember that I have the capabilities of the "Machine"

Thanks again!

Tim
AG4RZ

 

Y'know, over on CNC-zone there's been a discussion about the Gecko540's having a problem with one axis that wouldn't return home - occasionally. The reason seems to be that Mach uses a default a 2 microsecond pulsewidth for step signals, but some of the CPLD controller chips need a wider pulse to "see" every step. "In essence, a small percentage of CPLDs ignore the step pulse input signal for 6 to 10 microseconds. "Sherline Mode" cures this because it stretches the step pulse to a 15 microsecond duration. Compounding the strange behavior is this phenomena only manifests itself at low step pulse rates and disappears at higher step rates." http://www.cnczone.com/forums/showpost. ... stcount=27
The solution for the Geckos is to change Mach to using the "Sherline 1/2 Pulse Mode" on the "Config" "Ports and Pins" "Port Setup and Axis Selection" tab. Mariss Freimanis (Mister Gecko himself) says the Sherline mode won't hurt the Gecko controllers under any condition, so a person can either change Mach to use it or send their Gecko540 in for a free replacement of the faulty axis controller card.
Okay, that's a long story, but my thought is: Maybe we should also set Mach to use the Sherline Mode also if these "mystery missed steps" are an issue. I HAVE NOT CHECKED to see if Easy-CNC or any other controller-card manufacturer specifically says NOT to use the Sherline mode, so do so at your OWN RISK. But it may be the solution. :geek:

 

Actually, there is also a place on the Motor Tuning screen where you can set the pulse width. Turning on the Sherline Mode negates whatever was set on the Motor Tuning Screen and uses a Sherline default setting, but I'm not sure what else the Sherline setting does.
So I guess there are a couple different ways to ""patch" the pulse width issue.

btw, I have not turned up any warnings about using the Sherline mode setting from any of the controller board makers, so I'm guessing there are no deleterious effects. :geek:

 

This is similar to what is happening on my MKII, after a cut file my Y and Z are not returning home, but are about 1/2" off every time. I'm using the MKII front tables cut file, from the MKII DVDs as my test cuts. No matter how fast or slow I run it it's always off the same.

I tried the Sherline 1/2 step setting with no diff(and didn't blow anything up either)

Dennis, are you sure lower numbers in the acceleration box = faster acceleration? I tried 15 and everything was smoother, but took about 1/2 min longer to cut.

Jeff

 

Jeff, I dunno. When you look at the graph in the Motor Tuning screen, set accel to 5, look at the graph, then change to 50 and look at the difference. The graph implies a lower number means a faster acceleration.
BUT, if you read the units related to that entry box, it says something like "units or in. per" which would mean a lower number is a slower acceleration.
Just set it to a number and try it. Then set it on another number and try that. Better or worse? Adjust accordingly until your machine is happy. Whatever that setting "means", when your machine is happy, you'll be happy.

 

Hector at easy-cnc.com suggests step and dir pulse set at 15. Didn't work for me, but maybe will for you Frank.

Jeff

 

As noted in another post I made I bought the hobbycnc 3 axis kit. My son built it and it has been very very dependable since. I now have a lot of cutting in and no messing with the board any more. Don't even use heat sinks.

 

Frank, you may want to rethink using the heatsink that came with the HobbyCNC board. I was running a long cut and about an hour into it one of the Sanken drivers on my HCNC board caught fire (smoke, flames and all). It wasn't that big of a deal to replace the driver ($15 each) but it also burned up the parallel port on the computer since there are no isolators. This was running at half power with the aluminum heat sink installed.

 

I am always keeping an eye on the printer when it is cutting. Plus I am in the habit of feeling the drivers as I run it. I have a very direct 4" fan on the board and it is running nicely. But I will remember what you said though for sure.