Zeroing question

[joelinkous]

I saw this method used with a tool changing system I saw at Mr. Forney's shop a while back. How many people have mounted a secondary zeroing plate on their machine? Instead of pulling out the zero plate and zeroing to the table surface every time (which may become warped or otherwise unlevel over time), you could zero to that plate using a custom routine which is already perfectly calibrated to the table surface?

Assuming you mounted it correctly, you could use that point in a zeroing routine which would zero the machine to where the spoilboard surface *should* be, regardless of any minor imperfections the surface has, which may otherwise throw off a normal zero plate by even .01" in certain locations.

The only problem that could occur is that since the machine is zeroing to the exact same point every time on that secondary plate, it could cause a little pock mark/impact point of you zero V bits on it too many times. That could be fixed by making the software pick a random point within the area of that zero plate, assuming you can ensure the surface of it is completely level to the table. You could solve that by initially planing down the surface of the plate with the cnc after mounting it (assuming it's made of something soft, like aluminum/copper/brass/etc), so you can guarantee that the plate/spoilboard/machine is all completely aligned together.

Has anyone had any experience with this? Is it worth the setup time for such a simple modification, or has it seemed to help with accuracy/consistency?

[thewoodcrafter]

You are describing what I witnessed on a recent startup of a new Thermwood 3 axis machine that a friend bought. Quite a machine.
The pad is a switch with a plastic cover on it. The machine is always zeroed to the top of the vacuum table. A 1/4" spoil board is placed on top. You enter the measured thickness of the spoil board into the controller. Zeroed perfectly. You can run the tool measuring routine and it zeros each tool on the pad. It enters these measurements into the controller and subtracts the spoil board thickness.
It was very interesting to see how Thermwood does this on a "Big Iron" machine.
But I was surprised to see that after you surface the spoiler board you need to manually enter the spoiler board thickness again. It does not account for this automatically. The 0,0 location was the same as our machines but HOME was the opposite corner (96,48). Easy to the load material and close to the tool rack at that end of the table.
VERY, VERY fast machine. 2400IPM jog.

Anyway I think I will try this separate pad with a switch.

[mrdovey]

Joe...

I took a long, hard look at doing this on my 'Bot.

I frequently zero to the top of a workpiece and set a &WORKZ variable in addition to zeroing to the spoilboard, and thought that if, following a bit change, I could zero to a permanently mounted plate/switch, I could automatically re-zero to the top of the spoilboard and automatically recalculate my &WORKZ variable value.

I actually wrote and tested the software to do the job - but:

[1] I needed to dedicate some real-estate somewhere in the workspace to mount the plate, and decided that I didn't have a place that'd always be available when I need it.

[2] While it would be a great idea if I had a tool changer, it didn't buy me much time/convenience for manual bit changes.

I did actually carry the idea one step further, and tried a plate like my SuperZero plate so that the zero points for my x- and y-axis could be reset at the same time.

But none of the above saved me any time or improved on the accuracy of the SuperZero used in the ordinary way.


...Morris

[ed_lang]

Hello Joe,

My December article is exactly what you are talking about.

http://www.shopbottools.com/getting_started.htm

After you, and others read the article, feel free to ask questions if I didn't explain something clearly.

I get around the pock marks from zeroing in the same spot by cutting 0.005" off of the rod each time I surface the spoilboard. I have a custom Zzero.spb file to move to the location of the rod and zero. I must say it is neat to watch when I run my custom surfacing routine too. The tool moves to the rod and zeros the Z. Then starts the spindle and surfaces the rod down 0.005". Then the tool moves to the 0,0 of the table and changes spindle speed and the move speed values. Then it cuts the same 0.005" from the spoilboard.

For V-carving I still zero the Z with the zzero plate on top of the material. When I go to cut something out, I change tools and zero to the rod.

I have been thinking about adding the ability to zero to the rod and then measure the thickness of my work by using the zzero plate and some custom software. I have not gone beyond the thinking part due to other things I need to get done. Maybe next week while I have some time I can work on that.

[sagreen83]

Ed,

Awesome idea!! I would love to give this a shot. I have never worked with aluminum, but I just did a google search for "aluminum rod" and this is the first thing that came up...

http://www.smallparts.com/products/descriptions/zhsa,%20zra.cfm (http://www.smallparts.com/products/descriptions/zhsa%2C%20zra.cfm)

I have no idea which type to use, but to get anything bigger than 1" diameter you have to go with Type 6061-T6 ASTM-B211. Would this work? Is there a better source that I could go with?

Thanks!
Scott...

[joelinkous]

Ooo, nice idea Ed. Now that I look at it, my machine may not have sufficient room near 0,0 to mount such a device, so it may need to wait until I resurface the table again and can move the tabletop a few inches along the x axis.

I also thought of the ability to measure the exact thickness using a custom routine. Very neat stuff! There's nothing worse than trying make cutouts and not being able to cut through the whole thing (or vice versa, cutting into the table) on the first try. When I first tried zeroing to the table before starting the cutouts, it cut cleanly through the material and left ZERO marks in the tabletop! It was ecstasy! If I could only get that kind of precision all the time.

[ed_lang]

Scott,

Sorry I didn't see your question before now.

I don't see any reason the rod you spec would not work.

I have no idea what I have and I cut slow and easy without any problem. I am sure I can surface it much faster, but I am not trying to push to the limit, rather get the best quality.

Sorry I don't know much about metal.