EXACT point of zero XY

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LarryGZone
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EXACT point of zero XY

Post by LarryGZone » Sat Aug 22, 2015 11:54 pm

I have been having a ton of fun with my SO3. Now I am getting into more advanced stuff like 2 sided jobs. I am getting the hang of MeshCAM pretty well. Up until now I really did not worry too much about setting the zero XY point. But now with two sided projects I need to get precise. Here is my question: should my milling bit cutting surface be entirely within the bounds of the corner of my stock when I set zero XY? I originally was thinking that it should be centered on the corner of my stock piece. But my two sided jobs are slightly off on the Y dimension.

Thanks for any input.

-Larry
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WillAdams
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Re: EXACT point of zero XY

Post by WillAdams » Sun Aug 23, 2015 12:38 am

The way I do it is to have the endmill centered — if you register off the edges of the stock, just offset the zero based on the measured endmill (or chucked rod) diameter.

Twforeman mentions this in his write up of work coordinate systems on the G-code page on the wiki.
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LarryGZone
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Re: EXACT point of zero XY

Post by LarryGZone » Sun Aug 23, 2015 12:45 am

Cool, thanks Will. I need to change my search to "coordinate". I did not think of that.
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twforeman
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Re: EXACT point of zero XY

Post by twforeman » Mon Aug 24, 2015 2:51 pm

Where you set your Zero is a highly personal choice. :)

Actually, it depends on what you are doing. For a two sided job I would set my zero somewhere that is easy to pick up on both sides. If that's a corner that is in the lower left on one side and the lower right when you flip it over then that is what I would use.

Using a hole can work too if you have a way to find the center.

I usually make a fixture to hold my parts and I use the edges of the fixture to indicate zero.

You can see some of my fixtures here: http://timf.anansi-web.com/wp/making-sm ... ver-grips/ and here: http://timf.anansi-web.com/wp/milling-r ... iii-grips/

In both of those projects there were features on the back and holes that I could use to locate the front machining operations.
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veng1
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Re: EXACT point of zero XY

Post by veng1 » Mon Aug 24, 2015 3:40 pm

Another option is to use a microscope with a known offset from the spindle center. Drill a hole with the smallest bit you have available, note the co-ordinates of the hole, then carefully move the centering scope to line up with the hole that was drilled and then subtract the co-ordinates to get the 'scope to spindle offset. Then you can use the scope to align with the work you want to center on and add the offset.

So now the question is"where do I get a holder for the scope?" I'm glad you asked that. As soon as I figure out how to get a store front working, I'll offer one for sale. I think it is done and working for a DeWalt611 and a SuperEyes microscope (from ebay) but I'm open to suggestions for improvement. Its a combination air diverter and 'scope mount.
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twforeman
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Re: EXACT point of zero XY

Post by twforeman » Mon Aug 24, 2015 4:22 pm

So one thing that I didn't talk about in my comment was HOW to pick up the zero on an edge.

I use a piece of .250" drill rod (that I measured and is actually .250" in diameter) that I put in my router chuck.

Then I move over .001" at a time until a piece of paper just barely slips in between the rod and the edge of the part/fixture. Printer paper is usually around .004" thick, but you should measure what you use. Then you add the thickness of the paper to half of the drill rod diameter to find the center of the bit. That's where your edge zero is. Set your work coordinate and do the second edge.

For the Z height I chuck up the cutter and lower the bit .001" at a time until the drill rod doesn't roll under it any more. Then I know the tip is .250" higher than the zero.
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apspurgeon
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Re: EXACT point of zero XY

Post by apspurgeon » Tue Sep 01, 2015 7:39 pm

I've been using a sliding length of wood, and when I have my preferred zero adjust the length to fit nicely between the moving X/Y carriage and the end of the frame.
If I change a tool, I manually put back to zero (with power off) using the wood. Works very well for me.

Would be nice to have a better method though....e.g an electronic one...hmm...thinking

James RS
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Re: EXACT point of zero XY

Post by James RS » Tue Sep 01, 2015 10:53 pm

I saw a tutorial somewhere where pins were used for the 2 sided carve, so you could set the zero off off the
holes that were drilled

apspurgeon
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Re: EXACT point of zero XY

Post by apspurgeon » Wed Sep 02, 2015 6:52 am

Now this is smart thinking....worth a watch

https://www.youtube.com/watch?v=BLD4dFoXC7o

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