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View Full Version : How to zero the Z with a full sheet loaded



Ed Lang
10-27-2007, 8:38 PM
Well, I have a full 4'X8' vacuum table with 5 zones on it. From time to time I would like to zero my Z axis on the bed of the machine, but I have work covering the entire surface. What am I to do? Well...... here is what I did today and it works great.

I got a 1.5" aluminum rod about 9" long. I used the laser to cut a sturdy bracket to mount this rod to the end of the machines table. I wrote a file to move the spindle over the rod, zero the cuter on top of the rod, move away a bit and start the spindle. Then it will lower 0.005 below the surface of the rod and surface it. Then the spindles speed is changed to a speed to cut the Ultralite I use for a bleeder. The cutter is moved to 0,0 and plunged 0.005, to the same height it just cut the aluminum rod to. Then the surface of my table is cut the same height of the aluminum rod.

Now I have a smooth table and a contact point off of the table that I can use to automate the z zero process, as long as I am happy to zero at the machine surface. Next I will add some code to allow me to measure the exact thickness of the material on the table and calculate cut depths from that.

Fun and useful for me all wrapped up in one project.

Here is a quick picture of it.

http://www.mvww.org/autoz.jpg

Keith Outten
10-28-2007, 7:40 AM
How about using aliminum angle? Screw the horizontal leg to the bottom of the table and machine the vertical edge true the top surface of the table. This would have less material sticking out and you wouldn'r need a jig to hold it to the table edge.

An excellent idea Ed.
Thanks

.

Ed Lang
10-28-2007, 10:50 AM
Keith,

I don't think I am following you on the use of angle.

I wanted a large surface to be available to contact with. If I have a sheet loaded to the edge of the table, there is only a small distance between the sheet and the edge of the rod. If I needed to zero a large cutter, say 1.25" surfacing bit, I would be real close to the sheet as it is now. I could not zero a 1.5" cutter because the outer edge of the cutter would contact the sheet and never get down to the contact surface.

Maybe I am missing something here.

My original design called for U bolts and holes drilled into the steel table of the machine. I cut PVC pipe for insulators around the rod with a slit up the sides so it would compress with the U bolts. U bolts as in muffler clamps.

But I didn't have them handy and the laser was running so you see what I did to try it out!

This is holding real tight and strong, but I like iron!

I have been thinking about your angle idea. If the angle is put on so it makes a shelf away from the table, that would give a larger amount of area to have the cutter hit. You would need a thick angle so when you surfaced the table it would still have metal there. I run a 3/4" Ultralight Trupan bleeder and need to have 3/4" of rod to surface away with the bleeder. When I put a new bleeder on, I slip more rod up and continue.

Let me know if I missed your idea.

Tom Galzin
11-26-2007, 11:50 PM
There is an easier way. I find it easier to zero my machines of the TOP surface of the part, not the table top. As a benefit a "cutting" move is always a -Z number.

Secondary benefit if a want a .375 deep dado I always get it dead on, even if my board is over (or under) thickness.

Ed Lang
11-27-2007, 9:24 AM
There is an easier way. I find it easier to zero my machines of the TOP surface of the part, not the table top. As a benefit a "cutting" move is always a -Z number.

Secondary benefit if a want a .375 deep dado I always get it dead on, even if my board is over (or under) thickness.



Your first example where you say to Z zero at the top is made not valid by your second example of material thickness changing across the sheet. Your depth is not the same depending on where you Z zero and the thickness of the sheet at that spot. So, Z zeroing at the table surface will solve this problem. It does not matter where you Z zero or the thickness of the material. The cut will be correct.

In regards to your second example, if the material thickness changes so will the finished outside size of your cabinet. I would rather have the depth of the dado change and not the finished size of the cabinet. Imagine cutting your dado exactly .375" deep but having the outside of the cabinet wavy as the material thickness changes from place to place.

If you only care about dado depth, then Z zero on top of the material. If you care about final outside dimensions then Z zero to the bed.

No back to my example, I V-carve signs. I use a V-cutter Z zeroed at the top of the material to do the lettering. I change cutter and Z zero to the bed of the machine and cut the sign out of the material. Best of both worlds and a lot more exact than using the top only. My original post showed how I automated the Z zeroing process which is quite easy.