Z-axis moves down when it jogs

[jfhammond@kwic.com]

I just bought parts wizard to help me use the bot and I wrote a toolpath that looked great on screen. I then took it to the shop and tried to air cut the file after previewing it as correct. The bot seems to creep down as it moves to the first cut position. Previous to this it worked on another file that was exported from Corel Draw.

Is there a setting that causes the Z axis to move even though the program doesn't have a command line in it that asks it to do so?

Another thing, when the z-axis goes up, the screen registers a positive number.
The SK command does similar things. The pg up command actually makes it go down.

I did reverse the wire last time cause it cut mirror images but maybe I screwed something up?

I am a newbie sooo... be gentle.

Thanks for any help,

Jim innerbayboats

[tlempicke]

Reverse wires 4 and 5 on the plug from the Z axis motor into the board. This will make the motor run exactly opposite from what it is doing now. As the Z axis goes down the number on the screen should decrease. Your tool is doing just the opposite.

My guess would be that somehow you have learned to put backwards information into PW in order to make it cut. The normal order of things is to use the top of the work as the zero point. Then a cut that is 1/4 of an inch deep would be shown as -.250 on the screen read out. Any time the tool is above the surface of the work piece it should show as a positive number. Thus when you have a clearance of 1/2 inch the screen should be showing .500.

Whe you press the page up key while using the keyboard the tool should move up.

[tlempicke]

Ya know I just read my own message and need to clarify it a bit.

Remember that -.300 is LESS than -.200.

[bill.young]

Hi Jim,

I agree with Tom that your Z-motor is probably wired backwards...in keyboard mode it should move up when the "page-up" key is hit and down when the "page-down" key is hit.

That doesn't explain your un-expected Z-axis movements, though. This is a long shot, but could you be in RELATIVE mode instead of ABSOLUTE? Make sure you're NOT in keyboard control mode (you're ALWAYS in RELATIVE mode in keyboard mode) and look on the right-hand side of the screen, right below the box that gives your position... it will either say "ABSOLUTE DIST" or "RELATIVE DIST".

If you are in RELATIVE mode by accident it's easy to have the sort of un-expected movements that you describe. Let's say your Z-axis is at 0.5 or 1/2" above your Z-zero position. If your first movement command was...

MZ, 0.5

and you are in ABSOLUTE mode you wouldn't expect your Z-axis to move at all...you're Z-axis is already at 0.5". If however you were accidentally in RELATIVE mode, it would move UP 0.5" in the Z-axis to 1.0 because in RELATIVE mode all movements are added or subtracted from your CURRENT position. And if your Z-axis motor was wired backwards it would move DOWN 1/2"

It would be even move confusing if your Z-axis was at 1.0 and you gave it the same MZ, 0.5 command. In ABSOLUTE mode it would move down 1/2" to a final Z-axis position of 0.5. If you were in RELATIVE mode it would move UP 1/2" and end up at a Z position of 1.5

I know this RELATIVE/ABSOLUTE stuff can be confusing, but if it turns out that it is the problem then just type SA and you'll be back in ABSOLUTE mode.

Good luck,
Bill

[gerald_d]

" . . . a toolpath that looked great on screen. . . . and tried to air cut the file after previewing it as correct. The bot seems to creep down as it moves to the first cut position. . .
Is there a setting that causes the Z axis to move even though the program doesn't have a command line in it that asks it to do so?"

Jim, the z-axis will "creep" towards the first z-value that you have in your file - this is perfectly correct. As you approach the first x,y,z position specified in your file, the SB takes the shortest straight line. (this line is seldom horizontal). You don't normally see much z-movement in your preview screen - in fact, you are probably only looking at the x and y movements.

[jfhammond@kwic.com]

Ok,

So far, the z-axis will move up with page-up & down with page-down command when I request. The readout on the screen says a negative number when it is going up and a positive number when it is going down. My guess is that when I changed the Z hook-up in the control box to prevent mirror image cutting, I probably entered -'ve numbers after that to "fix" it.
I will put things back to their original position and let you guys know what happens.

Also,the machine seems to be cutting deeper and pulling up higher than commanded.

Any thoughts?

Jim

[Curt Bartel]

Jim,
Maybe your unit values are not set right. Do your x and y values move different distances than what you program them to do?
My prt 96 has 20 pinion gears on the x,y,and z axes.
the unit values for these are:
x and y = 127.3240
z=1018.592
You can set these with the [VU] command.
Hope this helps.

Curt

[jfhammond@kwic.com]

When I reset these values, I should be looking at the motors and their gear ratios shouldn't I ?
I seem to remember different values in my manual. I have the newer motors. I can recall that x and y are larger than the z-axis. I'll have to look and let you people know what I find.

Thanks for the info.

Jim

[tlempicke]

It's really a whole lot easier than all of that. Just go into the utility menu and about 2/3 of the way down is the menu to set what you are looking for. Basically you tell the shopbot to move a distance, which you specify, and then tell the program how much the shopbot actually moved. It will then calculate what you need and put it in the program.

[gerald_d]

Tom, that would be the easier, but less accurate, method. Would suggest that Jim goes the easy route, and then verifies his unit values with ShopBot. For example, Jim may be 1% out, but the guys at ShopBot should know which exact value to home him in to.

The machining of the gear racks, and the number of gear teeth and motor step increments are much more accurate than any measuring tool likely to be found in the SB'ers workshop environment.

A mistake of 0.01" over 1 inch becomes a 1" error over the length of the table. In other words, if you want to use the "easy" method, measure over as long a distance of travel as possible.

[jfhammond@kwic.com]

Got it!
Thanks for the help guys! I tried the unit value change according to the thread under set-up and maintenance and it works with a couple of different values than I had.

Can't wait to get makin stuff!

Jim