No such thing as a stupid question - xy datum

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No such thing as a stupid question - xy datum

Postby zeighty » Tue Nov 06, 2018 7:18 am

I think I figured out why some cuts are off. I am not exactly sure how to admit this. I don't think I have been setting the physical XY Datum position correctly.

I understand that if you choose the middle of your project you have to determine the center point and the bit would be lined up with that point. I have not used center point.
I use the lower left corner. Now here is the $64 question: Does the bit, assume it is an end mill, line up with the very tip of the corner?
So the bottom line, as it is very late and I am not sure exactly what I am typing at this point, is:
If I use a corner for my starting position , where exactly do I line of the bit on the machine?

Thanks for not laughing too hard or too much.

Kindest regards,

Robert
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Re: No such thing as a stupid question - xy datum

Postby FixitMike » Tue Nov 06, 2018 7:54 am

The XY datum is determined by the center of the bit. I personally use a V bit or my laser center finder to determine the datum. Then I remove what I used and install the bit to be used for cutting.
https://www.amazon.com/Laser-Center-Edg ... dge+finder
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Re: No such thing as a stupid question - xy datum

Postby vip-klaus » Tue Nov 06, 2018 10:55 am

@FixitMike: this laser center finder sounds good to me. Can you tell us something about the pecision? How width is the spot? If you rotate the router 180°: does the spot move around?

Thank you very much.

Greetings from germany
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Re: No such thing as a stupid question - xy datum

Postby mezalick » Tue Nov 06, 2018 11:33 am

Robert,
If I may add a bit of information.
If, for example you are cutting a pocket, with the vector set to the bottom left of your XY,,, the toolpath created will make sure the bit is within the selected vector.
If, on the other hand, you are creating a roughing or finish 3-D toolpath the program will set the center of the bit to be "on" the vector.
This will cause the actual cutting to be larger, by 1/2 the diameter, of the bit...

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Re: No such thing as a stupid question - xy datum

Postby martin54 » Tue Nov 06, 2018 11:40 am

I use a half round engraving bit for edge finding, depends what sort of accuracy you are looking for but if I use the flat on the side of the engraving bit to locate the x y datum it is close enough that you will never be able to tell by eye :lol: :lol:

But if you have a block of wood & you are just cutting something out of that block then you don't really need to be that accurate :lol: :lol: As long as it looks like the centre of the tool is over the corner then that is probably close enough, you would only set your x y datum for the first tool bit so if using different bits on the same project it isn't going to make any difference :lol: :lol: :lol:
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Re: No such thing as a stupid question - xy datum

Postby Leo » Tue Nov 06, 2018 1:40 pm

The machine "X"-"Y" is what is actually being set - NOT - the tool. The tool is just by chance being held in the machine.

It is the centerline of the spindle, which in turn just by coincidence is aligned with the cutter centerline.

Kinda like the foot bone is connected to the leg bone.

If you think about it, it is the machine that is moving around. It just so happens that it is holding a cutter. It's nothing more than that.

The cutter is determined when you are creating the program in Vectric. The program tells the machine where to move around.
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Re: No such thing as a stupid question - xy datum

Postby martin54 » Tue Nov 06, 2018 2:13 pm

Kinda like the foot bone is connected to the leg bone.

Or in my case, well right leg anyway the foot bone is connected to the 5/8" diameter stainless steel bar :lol: :lol: but that doesn't really roll off the tounge :lol:

Having read your post again Robert you say some of your cuts not all of them so do you have a particular example? Generally people have quite a bit of extra (waste) material around the actual part that they want so setting x y datum doesn't reaaly need to be that accurate, the accuracy only really comes into play when you have a finished size piece that you are working on & then you also need to ensure it is perfectly parallel to the gantry as well :lol: :lol:

Pictures are always helpful so any examples showing what you mean would be useful :lol:
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Re: No such thing as a stupid question - xy datum

Postby Jan.vanderlinden » Tue Nov 06, 2018 2:20 pm

I'm surprised that none has mentioned this.
https://triquetra-cnc.com/
absolutely accurate in all 3 axis
I've learned so much from my mistakes, I'm thinking of making a few more.
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Re: No such thing as a stupid question - xy datum

Postby Adrian » Tue Nov 06, 2018 2:53 pm

There as many different ways of accurately setting XYZ as there are machines. It's whatever works best for you. These days I only cut 8x4 sheets so my machine references everything from the same point regardless of where I cut on the board with the Z zero being set automatically on a fixed point off the board.

I used to use the old copper plumbing cap setup when I used to cut different types of material. Much cheaper than buying a milled block of metal and it can be built into various jigs very easily. There are pages and pages about setting XY zero with different devices on the forum.
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Re: No such thing as a stupid question - xy datum

Postby adze_cnc » Tue Nov 06, 2018 5:42 pm

mezalick wrote:This will cause the actual cutting to be larger, by 1/2 the diameter, of the bit...


Being picayune time: "larger by the diameter of the bit" (half the diameter on each "side").

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Re: No such thing as a stupid question - xy datum

Postby zeighty » Tue Nov 06, 2018 6:46 pm

martin54 wrote:Kinda like the foot bone is connected to the leg bone.

Or in my case, well right leg anyway the foot bone is connected to the 5/8" diameter stainless steel bar :lol: :lol: but that doesn't really roll off the tounge :lol:

Having read your post again Robert you say some of your cuts not all of them so do you have a particular example? Generally people have quite a bit of extra (waste) material around the actual part that they want so setting x y datum doesn't reaaly need to be that accurate, the accuracy only really comes into play when you have a finished size piece that you are working on & then you also need to ensure it is perfectly parallel to the gantry as well :lol: :lol:

Pictures are always helpful so any examples showing what you mean would be useful :lol:


You nailed it. A friend asked me to pocket cut a board that he prepped. He cut two, one for practice and one for production. They were the finished size and he had used his router to round over the edge. After the first try, I adjusted the xy datum point and flipped over the test piece. I then was only off about a 1/16th. Next time I will supply the wood or have him supply a larger piece so it is not a factor.
On some of my own work I had drawn the final desired results on the piece only to have it off by the 1/2 the diameter of the end mill.

So to sum all of this awesome advice - do all cuts on the CNC including the profile, and round over if desired. If the piece is at finished size the xy datum should have the center of the bit (assuming it is in center of the spindle) over the very edge of the corner so half of the diameter is hanging over in both directions.
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Re: No such thing as a stupid question - xy datum

Postby FixitMike » Tue Nov 06, 2018 7:32 pm

vip-klaus wrote:@FixitMike: this laser center finder sounds good to me. Can you tell us something about the pecision? How width is the spot? If you rotate the router 180°: does the spot move around?

Thank you very much.

Greetings from germany
Klaus

The size of the spot can be adjusted. I would guess I have mine at about .005" diameter. The small size is dim. It gets brighter if I make it larger. The spot does not move when I rotate the router. There are screws to adjust it if it gets out of adjustment. Of course this assumes the router chuck itself is free from significant runnout. (I say "significant", because no machine is absolutely perfect.)
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Re: No such thing as a stupid question - xy datum

Postby dwilli9013 » Wed Nov 07, 2018 4:56 pm

FixitMike wrote:
vip-klaus wrote:@FixitMike: this laser center finder sounds good to me. Can you tell us something about the pecision? How width is the spot? If you rotate the router 180°: does the spot move around?

Thank you very much.

Greetings from germany
Klaus

The size of the spot can be adjusted. I would guess I have mine at about .005" diameter. The small size is dim. It gets brighter if I make it larger. The spot does not move when I rotate the router. There are screws to adjust it if it gets out of adjustment. Of course this assumes the router chuck itself is free from significant runnout. (I say "significant", because no machine is absolutely perfect.)


I can say plus 1 on Mikes laser edgefinder. It works extremely well on my machine. And is very easy to calibrate with the give calibration card. :lol: :lol:
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Re: No such thing as a stupid question - xy datum

Postby Leo » Wed Nov 07, 2018 5:24 pm

FixitMike wrote:The XY datum is determined by the center of the bit. I personally use a V bit or my laser center finder to determine the datum. Then I remove what I used and install the bit to be used for cutting.
https://www.amazon.com/Laser-Center-Edg ... dge+finder


I generally use a V-bit, or a pointy tool I made just for the purpose, but I like that laser pointer, I may just go fer that.

Question I have about the laser is --- if the head is not trammed perfectly then the point will be out of location with "Z" height - the more the "Z" the more the error.

I have 10" "Z" and can have the pointer at 11" or maybe 12" above the surface.

Mike have you noticed any of that?
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Re: No such thing as a stupid question - xy datum

Postby FixitMike » Wed Nov 07, 2018 7:08 pm

Leo wrote:Question I have about the laser is --- if the head is not trammed perfectly then the point will be out of location with "Z" height - the more the "Z" the more the error.

I have 10" "Z" and can have the pointer at 11" or maybe 12" above the surface.

Mike have you noticed any of that?


I've not noticed that. But I set my origins with the laser only an inch or two above the material. And for what I cut a small error wouldn't be noticeable.
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