Z depth...yet again!

[letterman7]

Hi gang,
PR96 with rack and pinion...running Vectric's software. I've been playing with the thing for a month and have never been able to get a V-bit to cut to the correct depth at any time. Sometimes it hovers above the material, at which point I can manually set the cut height in the 'Bot XYZ percentage panel until it looks right to me. Regular end mills, ball noses and engraving bits work just fine for some reason. I tried to run a job this morning (but running a test first, thankfully) with a 120 degree, 2" bit. Everything I tried still resulted in the bit cutting slightly too deep - see photo:
http://i16.photobucket.com/albums/b31/letterman7/Random/1112081059.jpg (larger image than below)
There's an obvious radius on each straight section of the arrow and "E". I've tried re-loading the SB program, re-setting my Z-Zero plate thickness, checked all my grounds and checked the pinion for gunk in the threads. I even tried it with a 90 degree bit and got the same result. I'm missing something obvious...but I'm out of ideas. Anyone?
3825

[harryball]

Are you zeroing to the table or to the material surface?
If material surface, are you zeroing right over the top of where you are cutting?
If you zero to the material top, then jog Z to 0 over the material does the point of the V bit just almost exactly touch the surface or does it dig in or leave a small gap?

/RB

[letterman7]

RB, I'm zeroing to the surface, trying all over the table. I don't think the surface is warping due to clamping pressure. Now, I've currently have a job running using said 120 cutter. I re-set the Z proportion on that yellow panel of SB to .80, and the letters seem to be the right dimensions. I'll re-confirm that after it finished, but for this job's intended purpose they're fine. I just can't figure why I would need to do that...it must be something in the programming I'm missing.

[letterman7]

Ok..quicky update: the V-carve went well. I changed tools to my endmill to cut the panels free that were carved and...found the endmill also went too deep. Not that it mattered, it went into the spoilboard, but reducing that Z proportion to .80 had the endmill just kissing the spoilboard on subsequent cuts. Now, it's obvious it's a Z measurement error but where do I start? I zero'd all three axis' when I fired up the machine.

R

[ljdm]

If you zero the z, and move it 1 inch up, does it move up 1 inch? If you are getting more or less than that, your unit value for the Z might be wrong. You have to consistently set it for .80 proportion?

[Brady Watson]

What's the condition of your spoilboard? This is the biggest factor with inconsistent Z heights. If you screwed the spoilboard down from the top, I gaurantee that you will have problems. The spoilboard should be glued to the plywood support board (which is attached to the metal X members) and then flattened with a flattening bit. The difference between a glued down spoilboard and one that is just screwed down is HUGE!

-B

[letterman7]

Brady; the spoilboard is screwed from underneath - the support board on this machine (bought used, of course) is 1" MDF; the spoilboard is the same. I surfaced the board when I first purchased the machine, and have done it one other time late last week to rule out an uneven surface.

Lou: DING DING! Winner! I went back to the shop just to check this: a 1" command on screen equalled a 1.25" movement on the Z axis. I located the Unit Values drop down menu, and found that the X and Y were the same default apparently at 733.386 and the Z was 916.7324. Changing the Z to match the X and Y resulted in a perfect Z move via the keyboard - the test will be tomorrow when I run another job. Now, all that said, I can find absolutely nothing in SB's texts or help files concerning all the little parameters that need to be fiddled with, or any descriptions for many of their menus. The default unit value - what is that, exactly? I positioned the gantry so that the carriage was right next to my desk so I could perform the measurements, so I know those values had nothing to do with the position of the machine. Is there somewhere on the site here that defines and describes all the menu drop downs? If not, I think it's time there should be...

R

[beacon14]

Try clicking on the Help menu from the control software. The Command Reference is a good place to start.

[letterman7]

"Try clicking on the Help menu from the control software. The Command Reference is a good place to start."

Yep, it is, so long as you've got a .pdf reader on your processing computer, which I don't on the one driving the 'Bot. I have it here on the office one, though. And reading through the description provides the answer (sort of) as I don't have a complete manual for the machine, so figuring the correct values is going to be hit or miss.

[srwtlc]

Here's a little unit value Excel file that someone posted a few years back.



Unit Values.xls (http://www.talkshopbot.com/forum/messages/26/Unit_Values-35847.xls) (15.4 k)

[letterman7]

Sweet! That'll give me a good reference, Scott. I'll be counting pinion teeth over the weekend...

[mjindustry]

RE: The "Unit Values" sheet posted above...how do you know what you are supposed to be at?

My UV are currently 733.386 on both X and Y. Then my Z is set to 916.732. How do I verify these settings are right?

I'm trouble shooting z axis problems as well here.

[mjindustry]

I think I need to clarify my question above.

The reason I can't verify my UV settings on the UV chart, is because I don't know if I have the...3.6, 7.2, or direct drive? (How to tell?)

Then how to tell if I have...1/2, 1/4 or 1/8 stepping?

If I knew where to find this information about my machine, I could verify that my UV settings are correct in my SB3 program.


3826

Thank you for any assistance.

[richards]

The easiest method is to just zero an axis to a known point and then measure the distance when you give it a command to move 1" (or 10"). If the move is incorrect, you need to change the Unit Value for that axis. Multiply the current Unit value by the number you get when you divide the actual distance moved by the commanded move.

Example: Commanded move = 4 inches. Actual move = 5 inches. Current Unit Value = 916.7324. Therefore the corrected unit value would be 916.7324 X ( 4 / 5 ) = 733.3859.

[mjindustry]

Mike,

Thanks for that info! I didn't run it on my x and y though cause I think those are perfect. However, I did try this test on the Z (it's a little more difficult to execute this test on the z, I think). However, I did the test and it seemed to travel just right up and down during "air excersizes ". This tells me that my z problems are in my file programming or something.

Earlier today I tried a simple part file cutting 3/4" sign foam and I made a simple 2D profile cut to 3/4" depth it only cut to a depth of 3/8". I'm going to do some more testing tomorrow.

[hykambois]

I am new with shopbot and can't yet move it. I need much help from you because I am far from U.S.A and try to start my tool by myself only with your advices and recommendations via this forum.
As recommended, I zero'd all three axis but when I gave command to "1" the move had been incorrect: it jumped up and stopped. then I reduced to "-1": it plunged into the table and broke the cutter.
It seems that something with the unit value for Z is wrong and I have difficulty to program the Z axis.
Looking for help..Thanks in advance.