Hdu depth inconsistencies

[signgie08]

We are out of Wilmington, NC and have been in the sign business for less then a year. We have owned the shopbot for several years just for hobbies and now we use it to make money or atleast thats the idea. I mainly cut hdu which seems to be giving me the most problems. When pocketing using a quarter straight bit I get inconsistent depths usually higher say no more then 1/16 of a inch higher in speratic areas. No consistency what so ever. My plenum is made up of mdf with about 10 coats of varnish.Spoil board is mdf siliconed around the edges and varnished on the sides to stop air leaks. Im running two 10hp vacum pumps so plenty of hold down. The room is pretty tight, its climate controled and i have a dehumidifier running constintly. The shop has to make money and im throwing away $220 worth of hdu out every other day. So if any one has any ideas please I ask for your help.

[dubliner]

Keith, wow that sucks. Do you have any flex in the material when the board is being held with vacuum & does it happen in other material too? With 2 10 hp vacs I would think it was machine error. Which model do you have?

[chodges]

Two thoughts - probably stuff you already thought of, but worth a shot ...

1. Have you surfaced your spoilboard lately? If not, it could have just enough raised or depressed areas from previous cutting to give you these problems.

2. Have you checked to be sure the gear on the shaft of your Z-axis motor is tight? There are 2 set screws on this gear, and if they work loose, your machine can't consistently machine at an accurate depth. Our set screws worked loose, and we "cured" a similar problem just by re-tightening them.

Hope this helps!

[myxpykalix]

There was another thread that discussed similar depth issues. Possibly you can get a hint from some of the answers there?
http://www.talkshopbot.com/forum/messages/33572/37352.html?1231001978

[signgie08]

ITS a 5X12 prt with a columbo spindel and a just recently changed the spoil board out. The Z isnt the problem, its square and its pretty tight. This problem has been happening for a while. Been on the phone with shopbot and they even came down, they said its probly the table. I started running the vacumes for a hour to pull any moisture that might be in the table. When shopbot did that I watched the table move. I was just woundering if anyone else has had this issue and how it was resolved. Thanks for all the ideas but i beleive its the table moving so if anyone has any ideas or has a different set up for the plenum let me know.

[signgie08]

I can run the same file 3 0r 4 times and ill get different finished products. Ive got the lattiest software, the unit values are correct. I put a micrometer on the Z and its dead on so im not getting hung on any gears or anything. Does anyone know of any other material that I could use for the spoil board that doesnt move as much as mdf?

[carlcnc]

Kieth
I have a machine that had a similar problem,
ran fine for a long time and then started getting off in the Z, turned out that it was noise from the spindle cable causing erratic steps/movement on the Z axis. I solved it by installing shielded cable from the VFD to spindle and grounding the shield at the VFD AC ground screw.
Carl

[bearcat]

To test the system, set up a dial indicator off the spindle housing/Z-axis to the table. Create a shallow (0.2" deep) drill file to drill every foot in the X-Y. Use a small (0.2") rapid clearance gap and a slow (0.05"/sec) plunge rate. Zero the indicator, run the drill file and record each value. Measure the table and the material/table under vacuum, each with/without the spindle running.

Ed

[jhicks]

Wow Keith, this sounds painful. Ok you say the table is level. How did it get to level? I assume you surfaced it with a flat planing bit. So the surfacing is OK but when you move Z up and down with your design file at the same depth, you come down different depths in different places, correct?
Well assuming the design file data being sent shows the same depths (did you check the code to confirm this?) Then I can think of only three basic possibilities.
1) Mechanical. Since the Z gear is supposedly tight (did you confirm the pinion set screw is really tight?) and V rollers are snug?
Is there anything on the Z rails, V rollers, gears, etc that could be interfering? Chips, rail debris, gear garbage? Did you clean and lubricate the Z rack & pinion?

2) Electrical. As stated by others above, I have experienced problems with interference or noise due to poor ground, ground loops, or external interference. This one is a bear to isolate and solve but it can create intermittent signal interruptions and distort the impulses being sent to the motors. Very ugly problem.
Of course it could also be a partially broken Z axis motor wire, loose or contaminated connection. I have had one weaken and found when I replaced the wires to the motor, all was good. Try having someone toggle the Z up and down while person 2 is flexing, wiggling, and stressing the motor wire and connections. If you can cause an interuption, change the wire or strip and reconnect the conductors to the wago connectors

3) Software corrupt.I have had my windows software corrupted and it started slowly to develop intermittent location and depth discrepancies and stalling that progressively got worse. You can try to "restore" to an earlier date on your PC and see if perhaps that solves anything.

In general if the error is consistently occuring (same error same place) it would lead me to mechanical issues, if its intermittent, it would lead me to software or electrical.
There are many strange stories out there from neon ballasts interfering to refrigerator motors, to voltage fluctuation and more so check one element at a time and carefully document what you change. These can take some time to resolve but try to ask when did this begin and what happened, changed, or occurred around that time period for clues.
Best of luck and post whatever the solution finally is.
I seriously doubt the table, humidity, or hold down is the culprit based on your set up.

[jhicks]

Keith, simple things first. How is your collet? I know it should be obvious but I have scratched my head after a cut and found the bit was loose in the collet? Just a final thought.
Good Luck

[cabnet636]

what drives do you have?

jim

[signgie08]

The pinion and v rollers are tight.
I have a new collet.
The track is clean and lubricated.
I have even changed out the computer.
The wiring is in place correctly.
I ve even used a dial indicator so see if theres any change in the z depth and position in the beginning of a file and after and it goes to the same place. The depth on the files are all the same so no variation there.

[cabnet636]

do you have gecko 210's or 212 drives with the multiplier attached?

we have recently had to convert 9 machines back to 201's because of this.

jim

[jhicks]

So you are saying all movement on Z test is consistent and accurate yet when you cut real HDU files the depths vary from one location to another. Is that correct?
Quite strange?? I would suspect something in your electrical system or file but you say the file is good. Did you verify the code is instructing the Z to cut the same depths everywhere?
a 1/16" variation on the same sheet is huge.
Do you have some large tolerance settings in your design files?
I'm stumped, sorry. But very curious what you finally isolate the problem as.

[signtist]

I have the same problems.
I try to simply not pocket too much.
I try to design with a texture or wood grain so I won't have that problem.