Zero Z

[matney_models]

I use the C2 to zero the Z and it is still 0.06" into the spoil board.
It is a PTR 96"x48".
Can some one tell me I'm doing wrong?

[gc3]

ck thickness of your plate and the unit value for z axis

[cnc_works]

Don't ask me why, but entering the exact measurement for the thickness of the z zero plate has never been accurate for me. I end up setting it up at the plate thickness, then adjusting that number through real world measurement. Just have to do it once. I don't remember what the difference was, but it was significate enough to cause real issues.

[jerry_stanek]

That is my finding also I had to .130 instead of the .121 that the plate measures.

[danhamm]

I too had that problem, put it down to reaction timing..!!

[cowboy1296]

in the shop bot set up menu under stools on about page three you can change the size of your z zero plate.

how i have been known to not do things correctly but i think this is the correct way, plus it worked for me.

[dana_swift]

I have experimented with a version of ZZero that makes the second plunge much more slowly. That solves the "lie about the z zero plate thickness" problem. After the first contact it only lifts back up a very short distance so the second contact time happens very quickly after the first.

Then on my BT-32 I have it retract to Z max using a prox switch I added. That tells me total available Z with the current bit. A real nice feature!

In any case set the plate thickness value the way Rick talked about.

D

[Bob Eustace]

I have experimented with a version of ZZero that makes the second plunge much more slowly. That solves the "lie about the z zero plate thickness" problem. After the first contact it only lifts back up a very short distance so the second contact time happens very quickly after the first.

Then on my BT-32 I have it retract to Z max using a prox switch I added. That tells me total available Z with the current bit. A real nice feature!

In any case set the plate thickness value the way Rick talked about.

D

Hi Dana
Sounds like a brilliant idea. Would it be possible to post how to do it please particularly where you got the proximity switch and how you fitted it? How do you get Z to retract to say 3" after cutting to make it easier to do a tool change?

Thanks - Bob

[dana_swift]

Bob- the problem I have with "just go up to 3 inches" when finished cutting, is what if my material is 5" thick? The Z will hit the stop, the system will shut down, and all my zeroing in X and Y will be lost. If a tool change is needed, I have probably just ruined the material.

Having a prox switch at max z is just a matter of buy one, mount it in a suitable location on your machine, hook it into a spare input on the control board and then set up a "seek max z" routine to use it.

I wired my prox switch into input number 5, as it is not used on my machine, you setup may be different.

I wrote the following ZMaximum.sbc and set up C4 to call it. Then I have C2 call C4 when the ZZero is complete. Make any sense? You will have to do something appropriate to your installation as C4 may not be available.


'Z Maximum.SBP -- DSwift
'

'Determine whether we are in Preview mode or Move/Cut mode
&modenow = %(22)
IF &modenow = 1 THEN GOSUB Changemode

&start_Zmove_Speed = %(73)
IF %(55) = 1 then goto Done 'already at max z

'----------------------------------------------------------------Read the starting speed values to reset later
VS, ,2 '... move up rapidly
'---------------------------------------------------------------------------------------------------------------

Check_Switch_Status:
'Check status of current inputs to know if we have to clear switches

SA 'Set tool to Absolute mode

'Limits are deactivated here, automatically reset to original state when file ends
VN, 0 'Deactivate the limit switch functionality on input #3
SF, 0 'Deactivate software limits

ON INPUT(5,1) GOSUB ZAtLimit 'this is where we'll go on contact with switch

MZ, 70 ' be sure we go up far enough to hit the prox switch
ZAtLimit:
ON INPUT(5,1) 'this is where we'll go on contact with switch
Done:
VS, ,&start_Zmove_Speed
END

'SUBROUTINES ---------------------------------------------------------------------------
Changemode:
'Tool cannot be detected in Preview Mode. Quit and change Move/Cut mode ...
PAUSE
END 'Exit program now
Thats all there is to finding the prox switch and stopping. Adjust the routine for your bot.

Later I will post a couple photos of the actual prox switch. Dinnertime has interrupted.

D

[donek]

What's been said will most likely be your fix. If you cut material that generates a lot of pitch, a dirty bit can cause the plate be off as well. Be sure to scrape any pitch off the bottom of the cutting surfaces before installing it. It will make the plate more accurate.

On situations where z height is really critical, I use a surfacing program that cuts 6 different surfaces on a piece of scrap. It requests the thickness (measured with a caliper), and corrects for any inconsistencies. If you need really tight tolerances, this is the best way to go in my experience.

[dana_swift]

Bob- second half of my response..

Here are the photos of how I did it.

15686

In the front view, you can see the new prox switch is lined up with the rail. The rail is what is being detected when the Z car travels to its maximum height.

15687

Here in the side view you can see how close it is, about 1/8" from the actual metal. The prox switch was left over from another project and has a long sense distance. There are many other ways to do this, but this is what I came up with.

The wooden mount got cut on the shopbot.. of course!

Hope that helps-

D

[Bob Eustace]

Thanks Dana. Where does one get a proximity switch?

Bob

[dana_swift]

There are several sources that are readily available- first of all ShopBot will sell you one that will be just like the ones on your X and Y axis. They will work fine in Z also..

Most electronics suppliers sell all flavors of "gear tooth detectors" or "bolt detectors". The key words are "NPN open collector" or "normally open" and "inductive". Having a built in LED is nice also. Most of them accept power from 5-24 volts, check the voltage used on your existing prox switches and get one that works from the same power supply. Cylinder, flange mount, etc. That should get you to something you would recognize.

You pay more money for increased "sensing range", which is how close does the steel part have to get to the prox sensor for it to detect. 2mm to 4mm is a good number. The part I used has a 10mm sense distance which is HUGE, but it was recycled from another project which required that.

Frequency rating is not much of an issue as most sensors are so fast you will get good results from any of them. I would suggest 100hz minimum, but almost anything will do that well. Most of them are 1khz or above which are even better.

Several options you might want to consider:
http://www.digikey.com/product-detail/en/GS100102/CH414-ND/361996
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_167020_-1

The Jameco part is probably the least expensive ($20) and should do the job. And if you are not certain, just call ShopBot, they can sell you one.

On my Z I just detected the rail itself, I did not put a bolt on the rear side of the Z extrusion so its not possible to have a collision with anything.

Hope that helps-

D

[matney_models]

in the shop bot set up menu under stools on about page three you can change the size of your z zero plate.

how i have been known to not do things correctly but i think this is the correct way, plus it worked for me.
Were do you find that screen? in your pic?

[cowboy1296]

on the control panel click on tools, then click on shopbot set up, then click "next" 2 times and there is page three where you can change the value of your z zero plate.

[Bob Eustace]

Thanks Dana. I'll try not to get toooooo many new grey hairs fitting it!

Bob

[Bob Eustace]

There are several sources that are readily available- first of all ShopBot will sell you one that will be just like the ones on your X and Y axis. They will work fine in Z also..

Most electronics suppliers sell all flavors of "gear tooth detectors" or "bolt detectors". The key words are "NPN open collector" or "normally open" and "inductive". Having a built in LED is nice also. Most of them accept power from 5-24 volts, check the voltage used on your existing prox switches and get one that works from the same power supply. Cylinder, flange mount, etc. That should get you to something you would recognize.

You pay more money for increased "sensing range", which is how close does the steel part have to get to the prox sensor for it to detect. 2mm to 4mm is a good number. The part I used has a 10mm sense distance which is HUGE, but it was recycled from another project which required that.

Frequency rating is not much of an issue as most sensors are so fast you will get good results from any of them. I would suggest 100hz minimum, but almost anything will do that well. Most of them are 1khz or above which are even better.

Several options you might want to consider:
http://www.digikey.com/product-detail/en/GS100102/CH414-ND/361996
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_167020_-1

The Jameco part is probably the least expensive ($20) and should do the job. And if you are not certain, just call ShopBot, they can sell you one.

On my Z I just detected the rail itself, I did not put a bolt on the rear side of the Z extrusion so its not possible to have a collision with anything.

Hope that helps-

D

Hi Dana

Does your sensor have sirched or transistor output please.

Thanks - Bob

[dana_swift]

Sorry Bob.. I just noticed you asked me a question six months ago.

Here is the answer for all interested:

The prox switch should be "NPN open collector" "normally open" output. That is a bipolar transistor technology which is reasonably robust and should last forever in a shop environment.

"Open drain" outputs will work, but they use a different technology that is easy to dammage with any kind of static discharge. That is a MOSFET technology, and may not be the best idea in the shop environment. But if I had a free one to use, I would hook it up and see how long it lasts! The price for the other kind should be almost identical.

D