Loosing Z in the Middle of a File?

[kevin_morin]

My first plastic engraving project so I used the PW's array text feature to make 'badges' the text moved in well, the tool depth seemed to work OK, got a decent zero at the surface of the plastic instead of using the z-stop switch/auto-Z,0.

First 75% of the file seemed to cut well, the 60DegV single flute seemed to cut the two layered plastic fine, left clear text and all seemed fine.

At about 75% I hear a Z step 'growl' on the Z up from letter to letter and next the Z has been readjusted so the cutter won't touch the work???

As I was doing 110 1" x 2" tags in a 24"x24" sheet I'm hoping someone here has seen this and knows what I've done wrong?

I had taken off the dust skirt since there's little chip scatter, and it seemed to resist Z,neg moves since the tip is so close to the spindle collet. I wanted to get the file 0,0,0 as close to exact as I could.

I'd had this (Z stall or loss of vertical reference location) happen when doing the file earlier as an 'aircut'. At that time, I manually moved the carriage off the table's center, exercised the Z up and down and there was a definite stop - only had about 1" vertical travel somewhere in the middle of the Z carriage range of motion. At that time, an hour earlier than file cut error, the K keyboard control 'page up' and 'page down' keys wouldn't move the Z Carriage very far before the growling stalled motor sound.

However, after the third manual keyboard up and down; the Z motor moved past the 'jamb' smoothly and I went ahead re-zeroed and cut the file. All was well until about the 3/4 mark- then the same Z noise, and re-set reference?

any advice welcomed,

How do I get back to the location I was in the file? and

Why did the Z loose it's orientation?

Am I moving the Z to fast, I'm using default Quick Text parameters?

cheers,
Kevin Morin

[Gary Campbell]

Kevin...
Remove the stepper motor from the Z axis and check the motion by moving it by hand. You may have a bolt in the Z guide roller mechanisms that has worked loose. Also check that there is no lateral motion. There is a document on adjusting these rollers on the ShopBot website if one was not included with your machine.

Another place to check is in the rear of the Z extrusion, make sure that all the rack and stop bolts are properly seated.

This would be a good time to go over all the motion mechanics to see that the fasteners are secure, roller wheels are adjusted properly and all is lubricated.

Reinstall the Z motor and you should be good to go.

You can restart the file using the [F]ile [G] ot to line command. You will need to know where the file ended (hopefully you wrote this down) and will need to move the machine above that cutting point in a place where the next move will not damage material. This is not the easiest of tasks, especially the first time, but is do-able if you take your time. There are a number of posts here on the forum that will give you info on how to do this.
Good Luck, Gary

[erik_f]

I have heard about what Gary is talking about...and there is a good chance that is what is going on. I have, however, experienced a bad driver and it was kind of a groaning sound. I'm not sure if I ever lost steps, but the problem was intermittent and hard to pin down. I guess bad drivers are pretty rare, but its easy to swap the cables at the control box and run the x driver or the y driver to test you z stepper. If you get nice smooth motion you know its most likely the driver...but like Gary said...drop the z motor also and check for smoothness.

[kevin_morin]

Erik, Gary,

Z rollers were tight in one spot vertically. This was the main area where the engraving Z was traveling lifting the tool between lettering toolpath Moves.

Frank, at tech support thought the first idea would be to disconnect motor, and manually move the Z carriage up and dow- within a 1/2" of the test a bind is obvious by hand.

We'll re-adjust the rollers and see how things "feel", then how they run?

Thanks for the advice, I still can't get the cut file to pause so I can use a go to command. Are you implying that I'd do that in the "editor"? Each time I run the file it begins to execute (simulate/preview mode) but when I use pause/spacebar it pops up a very limited dialog box that won't allow other entries- how to I get to invoke the FG command?

Cheers,
Kevin Morin

[kevin_morin]

Erik, Gary,
Well we ended up testing the Z motor, its fine, we removed the entire Z carriage and spindle and found a series of 'lumps' in the Z guides.

Inside the Z guides, on both sides were a series 3/8" long by 3/32" wide 'patches' raised above the V groove's track surface. These patches appeared to be highly compressed plastic, they were only about 0.003- 0.006" thick, like the bearings/rollers may have had a coating a patch of which got 'pressed' onto the Z guide rails? The patches were about the circumference of the Z guide rollers apart, and they would dissolve slightly in acetone.

These raised spots were loading the Z motor much more than it should have to take, it seems they finally added enough torque load for the carriage to loose it's reference?

We finally had to use 3M ScotchBrite(TM) cloth held on a metal bar to smooth these areas. [We didn't test the three axis' carriages without motor prior to use of the bot.] I'd suggest that any new owner personally inspect the guides and rollers/bearing wheels to insure they're clean enough to run other wise these tight spots that may come from any source of plastic particles available could cause a similar problem for others?

Just now reassembling to try running again, hopefully our list of gremlins are all laid to rest?

cheers,
Kevin Morin

[erik_f]

Glad you found your problem...it can be frustrating at best hunting these things down. I had a handful of these sorts of annoying problems when I first got my buddy. The most annoying of all was that the gantry was put on the machine an inch off center so the x car would run out of travel before 24" when the bit was centered at 0,0. Good thing we are a hearty crew.

[Gary Campbell]

Kevin...
It is a good idea to routinely check all the axis' motion. We do this about once a month as part of our normal maintenence. There is lots of vibration from the cutting operation, loads of sawdust can build up, or maybe some other material, like your plastic, can get in the rollers and gum them up. You should be removing the motors to check the pinions anyway... only takes a few second extra to roll the axis around or up and down to see how it feels.

These tools cut great when all is working well, and you are a testament to just how little it takes to throw them off.

Glad you found the problem.
Gary