Messages

1

General Mach Discussion / Re: Motor Tuning Math

« on: December 14, 2015, 10:15:27 PM »

Hello All. I had an "Aha" moment. I found my problem. Refer to my previous post about the motor tuning math. My stepper motor resolution is 0.0125 mm. I was trying to get to -0.01 mm penetration depth on the Z-axis. I kept losing track of position.

This attached file demonstrates the fix. When I had the penetration set to -0.01, the problem occurs every time. I changed the value to -0.05 mm because it's an exact multiple of 0.0125 mm. Now it tracks perfectly. Now I don't have to sit and BABYSIT this machine anymore!

My 3-Axis CNC mill is a a "REDONDA" made by "www.DONGDADK.com", from China. It's a great little machine for the money I paid. I just had to work out this issue. If you have one too (eBay), don't be discouraged! I'm using it to make printed circuit boards. I use CopperCAM.

Thank you Tweakie and RICH. I wanted to share my solution with everyone in case the same problem happens to them. Simply put those "micro-steps" get lost! One has to observe the stepper motor / leadscrew step resolution. For me, that's 0.0125 mm (about 0.4 MIL).

Best regards, Richard V

2

General Mach Discussion / Re: Motor Tuning Math

« on: December 14, 2015, 02:55:08 PM »

Hello All. Tweakie, yes; checking the mechanicals is the first thing I did recently. At first I thought this was going to fix it, but it didn't help at all.

I think this "1/8 microstepping" may be an issue. I don't see how hardware can support this. That 1.8 degree/step is fundamental to the motor.

I'm feeling better about going out and spending the money on those drivers now. I just the idea of wasting money on something that doesn't fix the problem. I have no problem investing into the correct solution. I'm looking forward to getting a new Gecko drive! I'll let you all know how it goes.

Thanks, Richard V

3

General Mach Discussion / Motor Tuning Math

« on: December 13, 2015, 10:28:17 PM »

Hello, I have a problem with losing steps. Before I go and buy a new set of motor drivers, I wanted to explore the math behind the motor tuning (or I might end up right back where I am). I am cutting PCB copper to make circuit boards. I only need to penetrated 0.01 mm from the surface (0.05 mm is actually acceptable). Someone pointed out to me that is only 0.4 mil and is hard to control too. That made me think about the tuning parameters.

Okay, here's some math. I used a caliper to carefully measure the pitch of my lead screw. It seems to be very precisely 2.5 mm per turn (used several threads, then averaged). My system seems to have everything in metric, so that's why I chose it.

1 turn = 360 degrees, so 1/360 (turn/degrees) = 1  (unity)
2.5 (mm/turn) * 1/360 (turn/degrees) = 1/144 (mm/degrees)     This is my lead screw

My stepper motor clearly says "1.8 degrees per step", so
1/144 (mm/degrees) * 1.8 (degrees/step) = 0.0125 (mm/step), or 80 (step/mm)     This is my lead screw/motor combination

What's confusing me is that my CNC manufacturer has indicated "640" as the motor tuning parameter for "Steps per". In my case, that's Steps per millimeter.
Using that number: 640 (step) * 0.0125 (mm/step) = 8 mm

The answer should have been "1 mm", not 8. The funny thing is that this 640 value seems to work very well. I have no "scale" issues with X, Y and Z motions using this number. I just don't understand the math behind Mach 3. I think this might be due to the Tonsen controllers then. In the Mach 3 tutorial video on YouTube, the value they recommend is "2000". I've never seen a stepper motor with that kind of resolution.

HERE IS THE IMPORTANT PART:
Most importantly to me, I'm trying to get to "-0.01" mm (repeatedly), but I can see that my step resolution is actually 0.0125 mm/step from the math above. If I repeatedly go to 0, then -0.01, then to 2, then repeat, will I be loosing that 0.0025 mm every time it cycles through this sequence? These are the only values that I ever command my Z-axis to (except to park it at 4 mm when done).

Since my math (theory) shows my steps per mm as being 8 time greater than what practice says, does that mean my resolution is also 8 times better (0.0125 mm divided by  8 is 0.0015625 mm)? Somehow I think not.

I noticed my program (CopperCAM) can't generate values smaller than 0.01 mm. What precision of mm does Mach 3 support?

Sorry, I know I've asked a lot here. Thanks to anyone that helps. Tweakie and RICH have been great to me, but I don't want to look a gift horse in the mouth.

Sincerely, Richard V

4

General Mach Discussion / Re: Recommended Encoders

« on: December 11, 2015, 11:17:27 AM »

Hello Tweakie. That's all I needed to know. I'm going to buy a G540 today. It has to be an improvement over the cheap drivers I currently have.

Thank you very much for your help.

Richard V

5

General Mach Discussion / Spindle Motor logic

« on: December 11, 2015, 12:28:37 AM »

Hello RICH. Thank you very much for that part number. I am happily willing to invest in my system (my time is more valuable to me). It's not very much ($300) considering what it can do.

Do I use the "4th-axis" to activate the spindle? If not, how do others?

Explanation:
My spindle motor is activated by a simple digital logic level from the LPT port (not sure if Mach 3 drives this as a PWM signal). The LPT port is connected to a breakout board (one of my pictures shows it) that switches on the spindle motor. 

last question:
Will this controller provide me that logic signal that I need for the spindle motor?

Thank you for your time and advice. I am getting very excited to see my CNC working properly for once!

Best regards, Richard V

6

General Mach Discussion / Re: Recommended Encoders

« on: December 07, 2015, 11:04:55 PM »

Hello Tweakie and RICH. Per your suggestions I have included the .xml file that I am using.

I do not know how to set the motor current with Mach3. I presume you (Tweakie) are asking me to set it directly with the CNC driver. I have attached a picture showing what my controller board for 1 axis looks like (there are 3). I have already tried tuning my motor to run painfully slow or blazing fast. I saw very little change in problem for either speed. Slowing down the motor did not improve the situation. I also made sure to use slow feed rates for the G01 commands to Z axis. This had no effect at all.

I would really like to correct my problem with software if possible, however, I suspect that I have a bigger problem; hardware issues.

My driver boards are a simple cheap boards (picture). I see the name "TONSEN CNC", but I don't know anything else about them. My system is a cheapy CNC from China (you get what you pay for). I took the board off and found that the IC driving the motors is P/N A3977SEDT. I looked it up on Digikey.com and found that it is indeed a stepper motor driver chip capable of driving up to 2.5 amps. There are no adjustments on these boards, so I cannot set the current manually. I see a large 3 watt resistor, but I dare not change it out for a lower value.

I honestly believe that my problem lies with these cheap CNC driver boards (it's a red flag that I can't give you a part number). The X&Y axis' work well, and they use larger motors (Vexta 103H7124-1142, 2.4 x 2.4 inches). The Z-axis motor is slightly smaller (Vexta C8513-9012K, 1.7 x 1.7 inches), but seems appropriately sized for the job. Listening to this motor in action, it does not seem to be struggling with the given load.

Sorry, but I can't identify the motors any better than to provide the part number. I don't know where to find where these motors came from (aside from knowing they came from China). There is no "Vexta" website breaking down these part numbers. The same is true of the driver boards; Another "red flag".

I am willing to replace the motors and motor drivers, but I need a recommendation. For example, do I need a "4th" axis to activate the spindle motor, or can I use my existing breakout board to do that? What do other users do to turn on the spindle? I need to make sure that whatever driver/motor combination I get is compatible with Mach3. I currently use the LPT port to drive my controller. Should I get a CNC driver kit that supports encoders? I'm not sure if Mach3 can use them.

One last thing, I know Mach 3 is open loop. Does Mach 4 support closed loop operation using encoders?

Thank you very much for taking the time to help.

Best regards, Richard V

7

General Mach Discussion / Re: Recommended Encoders

« on: December 06, 2015, 09:12:00 PM »

Hello Tweakie, thank you for your advice. I've explored the options. I found a way to improvise an "encoder" with a Sharpie marker. I set my position to ideal height and then marked the sprocket that drives the Z-axis and a stationary point. I can tell now that I truly am losing position of my Z-axis. I am able to use this to re-zero the Z-axis, and that seems to work well.

To answer your questions:
No, my motor is not getting hot; it's cold to the touch. I also measured the temperature of the driver boards for all three axis'; They each measured about 83.6 degrees F (using an IR thermometer).
In the motor tuning section, I set the delays to maximum (5 uS for each). I can't say this helped, but it seemed that I did not have to "re-zero" the z-axis as often as before.

New Question:
Just to rule out Mach3, I'd like to know if the system waits for a command to finish being executed before moving onto the next line? Maybe this is what "Dwell" is for?

Please look at the following made up code below (an example similar to my actual code). Some of my commands are short moves in X-Y, then Pen-Up, Pen-Down. I'm wondering if my Z, axis is being RE-commanded to another position too fast. For instance, I do "G00 Z0", then "G01 F4 Z-0.01" immediately after.

Also, some of my Pen up commands come after only doing a short X, or Y translation, then another Z translation (pen up). For example:
G00 Z0
G01 F4 Z-0.01
G01 F60 Y40  (presume it was only a short move from Y=39)
G00 Z0.5


This is just simple Made-up code:
G00 Z0.5
G00 X23.6 Y36.2
G00 Z0
G01 F4 Z-0.01
G01 F60 X30
G01 F60 Y40
G00 Z0.5
G00 X25.2 Y39.5
G00 Z0
G01 F4 Z-0.01
G01 X26 Y35

8

General Mach Discussion / Recommended Encoders

« on: November 30, 2015, 02:13:06 PM »

Hello, I've read that one can buy a stepper motor driver with a built-in encoder to ensure that we can close loop on a target position. I've seen "Gecko" and "Romax" mentioned in these posts. They cost somewhere around $200, or so. I don't mind the cost, but I don't want to experiment and buy a controller that won't work with Mach3, or my system. I saw a 4-axis controller that is compatible with Mach3, but I only need 1 axis (the one giving me trouble).

Can someone please recommend some Mach3 compatible encoders/motor drivers? I'm using a 1.8 degree/step stepper motor (24 V, I think). My system is very small, so I don't want to buy one that is more expensive than necessary.

Thank you, Richard V

9

General Mach Discussion / Re: Z-Axis Repeatability: Small Changes

« on: November 28, 2015, 10:46:47 PM »

Hello Tweakie. What you suggested is a good idea: halving the speed, and checking the mechanicals. I took apart my machine and thoroughly cleaned the moving parts. I also tuned the motor to give me a slow response to G00 commands (rapid move). I also made sure my feed rates were set low (like 20 mm/min). I even tried using painfully slow speeds, but that didn't help.

Despite all of this, I still keep losing counts. It's always in one direction; my cut depth is set to z = -0.01 mm. I can hear that something is going wrong as the milling takes place. At first it is good, but after repeated up and down commands, it keeps cutting deeper. If I pause the run, and re-zero the Z axis, I see that my Z axis is off by 0.23 mm (roughly). So instead of cutting to z=-0.01 mm, I'm going to z = -0.23 mm (or so). If I were to let it go, it would probably get worse.

In reviewing Part 3 of the Tutorial on YouTube, I saw a configuration for extending the pulse duration. The video explains that that older controllers might have problems with reversing the direction a lot, as I do in Z axis (making a PCB). The video explains that 99% of users don't need anything other than a "0" entry. Does anyone think this will help?

Thank you, Richard V

10

General Mach Discussion / Z-Axis looses steps

« on: October 29, 2015, 11:00:12 PM »

Hello All. It's been a while now, but I'm back trying to make PCBs with my machine. I've just read my old post and I am having the exact same problem.
I know how to tie down a collet,
I know how to zero my Z axis,
I know the resolution isn't perfect; I get -0.094 rather than -0.01 mm for my Z axis.

I believe the problem that Mach3 looses track of the Z axis. In fact, it looses track in the same direction; Z always goes deeper. I notice this because it bores down into my PCB surface, wiping out the copper that I needed to stay behind. MACH 3 never looses track of X & Y. If it were a "motor power" as someone suggested, it takes more power to dig deeper into my PCB material. Maybe it's when I lift the Z axis?

I do think this may be a speed related issue traveling in Z axis. I was wondering if anyone has figured out a good way to deal with this problem? I wish I could add an encoder to my Z axis, but does Mach 3 support it now? In the older version it doesn't. I look forward to any good responses to this post.

Thank you, Richard V