Leveling my bot

[weslambe]

I have been running my bot for about 11 months now and have had some problems with the machine cutting shallower the farther down the x axis it went. I thought I had everything level.....

I bought a Macklenberg smarttool digial 48" level and put it on the bot. Needless to say, both the table and the y-car had issues. To fix them I first levelled the table, then levelled the y-car to the table. I feel sure that this will make a huge difference but will have to see since I have yet to cut anything with it since the fix.

BTW, this level is accurate to within 1/10th of a degree digitally and still has the bubble to gauge with. But the best thing is the level beep. It beeps loudly when you have reached level. No more jumping up to see if it's close.

wes

[gerald_d]

Your digital "levelling" would have nothing to do with a cut getting deeper the further you go along the x-axis. You simply need to "surface" your table top - let the machine cut its own table "level".

"Levelling" in the ShopBot context means to reduce the lumps, bumps, dips, hollows that may occur in parts of your table. It does not need a "level" to measure if it is "level". Maybe "flattening" would be a better word?

[weslambe]

Nope, that's not whats going on. I surface my bot regularly. I screw my material down along the side of my spoilboard so if it was warped or cupped, it would only benefit my cut! i.e. if the material was bowed in the center, my cutter would go farther through. That has never been the case. I did find, however, that my machine needed major tuning. I nearly went insane trying to get the z car plumb and level today.

Thanks for your input though.

[ron brown]

You might want to look at these two threads:
http://www.talkshopbot.com/forum/messages/7/1172.html
http://www.talkshopbot.com/forum/messages/7/1291.html

Ron

[gerald_d]

With the greatest of respect to Wes, who started this thread, I am trying to make it clear that one does NOT need any electronic/digital/laser levelling equipment to set up a SB for accurate cutting. There is an over-emphasis on levelling the SB in this Forum, and that sort of gets us thinking of buying the best level.

The emphasis should be on the following, with decreasing order of importance:
- Rigidness of x-rail supports
- Straightness of rails after tightening down
- Parallelness of rail pairs (the two x-rails and the two y-rails)
- Squareness of y-rails to x-rails
- Squareness of z-slide to table top
- Squareness of router to table top
And if all the above are 100%, then levelness is not even an issue at all - your SB will cut perfectly even if leaning over at 5o.

[weslambe]

Thanks for the kind words. And I agree with you about the 5 degree slant thing. But, it is always much easier (at least for me) to work from a solid, known baseline. For me, that baseline is usually level and plumb. If you can get both level and plumb, you will be square.

Besides, it was one hell of a good way to justify to my wife that I needed to get the digital level. More tools, more fun!

Best to you,
Wes

[gerald_d]

Wes, that certainly is a very useful tool, and I have had one since before our SB arrived. I entirely agree that it is good to work from a "solid, known baseline" and the Smart Tool (http://shop.store.yahoo.com/inspectiontools/48insmtodile.html) will be useful for getting the z-slide plumb to a level table.

[weslambe]

Gerald,

There is one thing that I did notice last night while making my first cuts since truing the machine. The material thickness was .75" and the bot was told to cut .75" deep. It cut about 1.10" inches deep!

I changed bits and re-zeroed the z and it seemed to cut fine.

My question is this; can a dull bit cause the bot to overcompensated and loose its setting? I was wondering if it pushes down and misses steps thereby losing zero?

Thanks in advance.
Wes

[gerald_d]

A lot of us have experienced these occasional deep dives, and we guess about losing steps etc. But, if any steps were lost under load, the cut would be shallower, not deeper. There have been quite a few discussions about this problem.

To us, it happens so rarely that we are willing to concede that it may have been human error.

[stevem]

A too-deep cut can be caused by the Z axis stepper stalling on the up stoke. The software assumes the cutter has been raised to the required position and makes the next down stroke to the programmed depth while the cutter is really well below that depth.

The other possibility is forgetting to re-zero after a tool change. I’ve done that a few times. D’oh.

[gerald_d]

Or forgetting to tighten the collet.

[artisan]

I believe there is a software bug as well. Using the newest SB software, I have on a few occasions seen the "z" dive into a piece also. This seems to happen mostly when I "S" stop the Bot and "R" resume the file and also when I insert commands. I've learned to watch for it and out of habit now jot down the line number of the file on my trusty blackboard.....just in case....D

[chamcook]

I had a deep dive recently caused by a too high Z move exceeding the travel at the top of the Z. The resultant lost steps cause the tool to think it was higher than it really was. These high moves were meant to avoid aluminum clamps on a jig. I didn't allow for the fact that the 3/4" jig sits on top of a 3/4" base jig which reduces my safe Z height. (The tool is zeroed on top of the base jig)
Recently I had an episode of erratic Z movement due to binding of the Z axis. My old PR style Z is getting worn at the lower portion of its stroke where it has done the most work. I tightened up the play in the bearings thinking that I was doing a good thing but when the axis rose to the unworn part of the uni-strut it bound. I have loosened it up slightly until I decide whether to rebuild or buy a new PR style Z.
I have also experienced lost Z position after resuming following stops mid file as Darrell described above.
I guess a person just has to stay on their guard.
David