[bluumax]

I'm getting accumulation in X+, Y- & Z+.
I put up a page on my site that might help explain better than words.
http://www.bluumax.com/Taig.html
I've had this problem since I got the mill a year ago, I've tried everything I can think of.
I've checked & re-checked the Mach settings, but still might have missed something.
Hope someone can help with this.


Taig 2019ER
Xylotex 3 axis drive & 269 oz/in motors
CNC4PC C11 Breakout board
Mach3 latest ver 3.037
Mill only PC: P4 266, 724MB

Shawn.

[GeneK]

I'm getting accumulation in X+, Y- & Z+.
I put up a page on my site that might help explain better than words.
http://www.bluumax.com/Taig.html
I've had this problem since I got the mill a year ago, I've tried everything I can think of.
I've checked & re-checked the Mach settings, but still might have missed something.
Hope someone can help with this.


Taig 2019ER
Xylotex 3 axis drive & 269 oz/in motors
CNC4PC C11 Breakout board
Mach3 latest ver 3.037
Mill only PC: P4 266, 724MB

Shawn.

Shawn, it's time to send the part to Q. A. and have them verify all the features. I took both files and concatinated them into one file and imported into Mach 3 and each hole is dead center in each square as best I can see. I'm sure if I cut it on my set up it will cut correctly.
It may help some to have the pads cut in the same pattern as the holes are drilled, i.e. vertical columns. It does seem to be related to back lash, and it is being distributed differently since the patterns are different.
Have you quantified how much back lash each axis has and tried backlash comp in Mach 3?

GeneK

PS
Shawn, I was just thinking some more. I would take my height gage and scribe the grid very precisely on the board and then machine the pattern. That should show what is skewed and an idea of how much.

GeneK

[Stepper Monkey]

I haven't had a chance to go through your website or the problem in detail yet, but I see where Genek is going and I think he is likely on the right track.

The exact same item cut with different toolpathing can show marked difference - no matter how little backlash a machine has, you can write code to unintentionally maximize it, and therefore accumulation error. By the same token, you can take a machine with very large backlash errors and write code to minimize it or almost effectively counter it right out.
I frequently cut low-tolerance items like this to consistently under .001" on a very old and abused Taig showing better than .002" backlash, without any compensation, just good toolpath strategy. By the same token, you can easily cut sloppy parts on an accurate machine with a bad choice of path.
Don't know if this is the answer, but it is a really good place to start.

[cyclestart]

Are you positive the part is clamped squarely on the machine? Also that the pads are equal distance from a datum edge? Judging by that website you do very careful work but the question should be asked.

What does a caliper (and square if needed) read for hole alignment. If the part is very small, maybe not much.

[bluumax]

GeneK: I've checked the & adjusted the BL so many times I can do it blindfolded.
If I tighten the nut anymore it starts to bind.
There's only a couple thousands BL in X & Y, Z is not adjustable.

Stepper Monkey:
The program, PCB Gcode decides the drill & route patterns.
Drill is always Y+ to Y- direction.

cyclestart:
I thought maybe the fixture was possibly moving, that was last year.
This is a problem that has plagued me for a year now.

I just didn't want to start posting until I sure I didn't just miss something stupid in setup, etc.
I don't think it's backlash.
Is there a some type of setting I could have set for lead screw compensation that's hidden?
The only thing I can think of is, somehow I got 3 lead screws that are not exactly 20TPI.
I do a ton of trouble shooting with electronics & mechanical, so I found that to be highly unlikely, but still possible.
Remember Apollo 13? It's possible someone assembled it with rejects or something. I've worked as a temp in industry enough to see some really scary stuff.

[The Blight]

Bl does not acumulate. The only thing that could do this (as far as I can see) is that your X and Y axis is not exactly 90deg apart. A varying pitch in the lead screw can do so too, but I find that unlikely. Because you have had this problem for so long, I doublt that this is the problem. Check if the angle between the 2 axis is correct.

Backlash is added when the axis switch direction. It removes it when changing direction again. It doesn't add the backlash if you continue in the same direction. So the tolerance would then be +/- the amount of the backlash.

[GeneK]

GeneK: I've checked the & adjusted the BL so many times I can do it blindfolded.
If I tighten the nut anymore it starts to bind.
There's only a couple thousands BL in X & Y, Z is not adjustable.

Stepper Monkey:
The program, PCB Gcode decides the drill & route patterns.
Drill is always Y+ to Y- direction.

cyclestart:
I thought maybe the fixture was possibly moving, that was last year.
This is a problem that has plagued me for a year now.

I just didn't want to start posting until I sure I didn't just miss something stupid in setup, etc.
I don't think it's backlash.
Is there a some type of setting I could have set for lead screw compensation that's hidden?
The only thing I can think of is, somehow I got 3 lead screws that are not exactly 20TPI.
I do a ton of trouble shooting with electronics & mechanical, so I found that to be highly unlikely, but still possible.
Remember Apollo 13? It's possible someone assembled it with rejects or something. I've worked as a temp in industry enough to see some really scary stuff.

Shawn, you need to quantify what is happening. just tweaking the adjustments means very little if you don't know what you are trying to fix.
Have you used a dial indicator on one of the axises and programmed to move and see if it moves the *amount* you tell it to move, both directions? In other words, I have a 0 _2" dial indicator. I mount it to the spindle with the tip against a block on the table. If I move the table 1"and the dial winds 1", then reverse and see if it goes back to 0. Any diference is the back lash. Do the same for each axis. (also repeat several times and in each direction for each)

The other thing to do is as I mentioned before, use a height guage to scribe a 0.1" grid on the board and then cut and drill. Now you can evaluate how the squares are drifting in relation to the actual position and the drilled holes also.

If the thread pitch were wrong,( not 20 tpi) the pattern would be ok, but just scaled to a different size.

GeneK

[bluumax]

I square the fixture on the table using 2 pins & one in the collet, running it back & forth on the X, (many times) I KNOW that it's square.
It's not measurable with an MDI by running back & forth a few times.
There is a couple thousands slop, but as The Blight said, It doesn't add the backlash.
I don't know of a way to square up the X & Y as they're not adjustable that I know of.
I don't have many good accurate tools to scribe a pattern.
This is just really weird.


Shawn.

[bluumax]

This is the way it's cut, NOT a goofed scan

[awerby]

First, although backlash itself doesn't accumulate (any slop will be taken up when the axis reverses), inaccurate backlash settings in Mach could very well do that. Essentially, you're telling the machine to add a certain amount to each move in a different direction, to compensate for the distance the screw has to travel before it engages. So if that number is incorrect, you will start to see the sort of drift you're complaining about. I'd start by turning off backlash compensation altogether, and see if the results change any. Later on, when you've eliminated this as a potential problem, you can carefully measure your backlash, put the correct number in the box, and try again.

The other thing that's likely to do this sort of thing is an inaccurate steps/unit setting in Mach. Are you using inches or millimeters? Inches are pretty straightforward, since the Taig is made in the USA, and uses 20 tpi screws (which are quite accurate, actually). 23-frame stepper motors are typically 200 steps per revolution, and (I think) the Xylotex uses 8x microstepping. So you multiply 200 x 8 x 20 to get the number of microsteps in an inch (32000), which should be entered in the appropriate place in Mach. If you're using millimeters, make sure you're converting correctly. You need to divide the figure above by 25.4 to get the number of microsteps in a millimeter; it comes to 1,259.8425. Is that the number you've got set as your steps per unit in Mach? Rounding it off would cause the sort of accumulating error you're experiencing.

Andrew Werby
www.computersculpture.com

[bluumax]

I'm not using backlash in Mach, it does weird things, & I shouldn't need it for less than .005 anyway.
Steps are set correctly, 32000 (1/8th step).
It doesn't matter if I run 2 IPM or 18 either.

[GeneK]

This is the way it's cut, NOT a goofed scan

Ok Shawn that scan shows me a lot. I think you need to check the gib on the Y axis. It is probably moving in and out with direction changes, and in one direction it is binding and causing the Y axis to lose steps. I don't know just how the gibs are set up on the Taig, but it sure looks like a comon problem with tapered gibs that have slop. On the Sherline the gibs is positioned by an L shaped wire and the end can be bent so there is a bias and takes out the backlash *in the gib*.
One thought that I have to test what is happening is to set your 0,0 and run the program several times 'in the air' and then return to 0,0 and see if there is any lost steps. your error should not excede your actual backlash. If there is a greater error after several runs vs only one run you are losing steps.

GeneK

[GeneK]

I'm not using backlash in Mach, it does weird things, & I shouldn't need it for less than .005 anyway.
Steps are set correctly, 32000 (1/8th step).
It doesn't matter if I run 2 IPM or 18 either.

Shawn, Mach does weird things with backlash in
CV mode. Turn off CV mode to run with backlash comp.

GeneK

[bluumax]

I am losing steps then.
I set the step pulse to 2uS before I did this board, also, just incase.
I'll check the Y, but I'm pretty sure it's not binding as I've been @#$%ing with this thing so much looking for anything that could cause it.
I'll check it now.

[bluumax]

It feels smooth, no binding.

[bluumax]

X & Y are the same, Z max vel is 15

Soft limits were off anyway

[bluumax]

I've tried it with CV & exact stop, but no noticeable change

[The Blight]

A wrong backlash value does not accumulate either.

Lets say that the backlash on your x axis is 0.002 and you have set it to 0.003. When moving the axis to X1, you will end up at X1.001 (because you have set it to 0.001 more then what it actually is). When reversing the direction (going to X0), it removes the 0.003, and because there is a 0.002 backlash on the axis, you will end up at X0 again.

Now lets say that you have set the backlash to 0.001. When moving to X1, it adds 0.001 and because you have 0.002 backlash, you will end up at X0.999. When going back to X0, it removes the backlash compansation, and because you have a backlash of 0.002, you will end up at X0 again.

If backlash actually was an accumulative error, my bet would be that several people would end up having problem with their machines. I have seen several industrial CNC machines with a too high or too low backlash compansation (either because its just wrong or because the machine is cold) and it does not accumulate.

You might want to check the couplings. They might be slipping a little. Seems weird. What are you running first? The drill pattern or the routing?

[bluumax]

drill pattern first, then the route

[bluumax]

I checked the motor couplings, they're tight. (but good call!)
If I say I checked something, that means now, today.
Not, I think I did last month, I appreciated everyones help on this.