Setting XY position of material

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Setting XY position of material

Postby Mikehell » Sun Aug 25, 2019 5:34 pm

Let's discuss the pros and cons of various ways to set the XY home position of your material.

One way is to simply place your board at he absolute natural XY of the machine (lower left). If not using the absolute XY, put offsets in the file.

Another way is to put the material on the spoilboard, then jog/move the head of the machine till the bit is where you want it, then re-zero the machine.

Third way is to set your material size to the size of the spoilboard, and then place your cuts within a box (the size of the actual material) placed where you want it.

I teach a class at a makerspace, and I'm more-or-less the guy in charge of the ShopBot. I find it difficult to convince people to use the first method. Everyone insists on putting the board down, then moving the bit to the approximate position of the piece, then turn the move speed of the machine to .1" and keep hitting the button till it's where they want.

I use a ShopBot all day at work, and they get all pissy if I don't set the material size to be the size of the spoilboard, and then just draw my cuts where I want them on it. Using offsets confuses the hell out of the other guy (who happens to be my boss)

So, in the "real world", does anyone actually use offsets, or rely on the absolute home position?.
Last edited by Mikehell on Sun Aug 25, 2019 5:43 pm, edited 2 times in total.
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Re: Setting XY position if material

Postby IslaWW » Sun Aug 25, 2019 5:39 pm

Mike...
In reality all offsets are simple basic math. Although it has the tendency to confuse some, a bit of experience negates the confusion. The software and machine are not capable of making a math mistake, only the operator.
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Re: Setting XY position if material

Postby Mikehell » Sun Aug 25, 2019 5:53 pm

IslaWW wrote:Mike...
In reality all offsets are simple basic math. Although it has the tendency to confuse some, a bit of experience negates the confusion. The software and machine are not capable of making a math mistake, only the operator.


Here's where the problem arises... If you're not used to using offsets, and the person who used the software before you uses them, the default will be set to the offset last used. The other guy never bothers to check the offset because, by habit, he doesn't use them.

There are two things I'd love to see in the next version of V-Carve

1: turn off saving everything as the default for the next time, or at least make a simple way to reset to a default.

2: allow us to set the size of the table, show us the table, and then let us put our material on the table. The way we do it at work, setting the material to the size of the bed, makes the preview more or less useless, without a bunch of hassle.

As for the guys at the makerspace? They all think they are smarter and know what they're doing.
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Re: Setting XY position of material

Postby FixitMike » Sun Aug 25, 2019 6:17 pm

Myself, I zero to the corner or center of the material after I clamp it down. My machine does not have a machine zero, so using that is not an option for me.

I haven't needed to use an offset, but I might if the toolpath size was small and the actual material was large. A small 3D carving in a large piece would be an example.

I have locating bars on my table that have been cut to be parallel to the X and Y axes. The material is located against one or both before I tighten the clamps so I know the material is sitting square.

Yes, the fact that VCarve saves some of what was last used the next time it is used can cause problems. Even for me, although I am the only one who uses mine.
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Re: Setting XY position of material

Postby Mikehell » Sun Aug 25, 2019 6:31 pm

FixitMike wrote:Myself, I zero to the corner or center of the material after I clamp it down. My machine does not have a machine zero, so using that is not an option for me.

I haven't needed to use an offset, but I might if the toolpath size was small and the actual material was large. A small 3D carving in a large piece would be an example.

I have locating bars on my table that have been cut to be parallel to the X and Y axes. The material is located against one or both before I tighten the clamps so I know the material is sitting square.

Yes, the fact that VCarve saves some of what was last used the next time it is used can cause problems. Even for me, although I am the only one who uses mine.


I have a small Chinese 3040 at home that has no limit switches. Iwith that you have to manually set your home. But it's so small that it's always close enough to the computer to make it easy. But on a big machine, where dong an XY home using the limit switches and getting a balls-on accurate home?
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Re: Setting XY position of material

Postby Adrian » Sun Aug 25, 2019 7:52 pm

One of the reasons why I never start a new project by using the New command. I always load a template file or similar job first and go from there. No issues with odd settings then. I don't have anyone else using my machine but I do loads lots of file from different people when helping them out.
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Re: Setting XY position of material

Postby SteveNelson46 » Sun Aug 25, 2019 10:39 pm

I always set my board size to just slightly larger than the project to be cut and x,y zero off of one of the corners or the center. Setting the board size to the size of the spoilboard in the software will result in a lot of wasted space and could have serious resolution issues. Unless, of course, the spoilboard is just a temporary board slightly larger than the actual board.
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Re: Setting XY position of material

Postby TReischl » Mon Aug 26, 2019 1:06 pm

I won't be using the technique of programming all my parts from machine zero, ever.

First reason: My y-zero is in front of the spoilboard outside the frame of the machine. That is so I can attach a vertical fixture for doing dovetails, etc.

Second reason: I often surface warped,twisted,cupped boards on the machine. To do that the machine has to be able to cut beyond the edges of the workpiece.

Third reason: The zero point of the z axis is a line down the center of the spindle. All cuts would have to be a little more than the bit radius away from the board edges.

Fourth reason: I use one or two vises on my machine, it would not be possible to mount them in such away to be able to use them at all.

Fifth reason: When designing/programming sometimes the zero is best in the center. When I use the vises the zero point is in the upper right corner.

Sixth reason: I have a laser attached to my machine. It is offset from the spindle centerline.

Seventh reason: There is a rotary axis on my machine.

There are lots of reasons to use offsets.
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Re: Setting XY position of material

Postby rscrawford » Mon Aug 26, 2019 3:30 pm

TReischl wrote:I won't be using the technique of programming all my parts from machine zero, ever.

First reason: My y-zero is in front of the spoilboard outside the frame of the machine. That is so I can attach a vertical fixture for doing dovetails, etc.

Second reason: I often surface warped,twisted,cupped boards on the machine. To do that the machine has to be able to cut beyond the edges of the workpiece.

Third reason: The zero point of the z axis is a line down the center of the spindle. All cuts would have to be a little more than the bit radius away from the board edges.

Fourth reason: I use one or two vises on my machine, it would not be possible to mount them in such away to be able to use them at all.

Fifth reason: When designing/programming sometimes the zero is best in the center. When I use the vises the zero point is in the upper right corner.

Sixth reason: I have a laser attached to my machine. It is offset from the spindle centerline.

Seventh reason: There is a rotary axis on my machine.

There are lots of reasons to use offsets.



Why not have your machine zero as a useable zero where you would use it most of the time, with the ability to cut in a -ve X or Y direction if you need to machine past machine zero?

I have a table that is larger than my 'most used' 4x8 area (about 65" x 100"). My machine zero is set in the front left corner of my pop up pins, where the corner of sheet goods would get placed. But I can machine to about -4 in the Y direction and -8 in the X direction if I need to cut past my machine zero.

Basically, the offsets are built into the 'homing' of your machine rather than remembering to set offsets in V-carve every time. And you can just leave your zero at the known bottom left corner of the workpiece all the time, and set your job size to be as small as possible to keep the resolution of any 3D models as high as possible (if you absolutely must use 3D models, which I do anything possible to avoid).
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Re: Setting XY position of material

Postby Leo » Mon Aug 26, 2019 4:09 pm

I work in a similar world whereas we have lots and lots of vertical machining centers.

Work offsets are simple and are the norm for this sort of work. CNC routers are no different.

Working in one area all the time will do nothing more than wear the machine in that one spot. I prefer to spread the wear out over the entire machine.

The best answer I can offer is this one thing. Learn what this stuff is and how to work with it.

However - if you do not own it and you are employed by someone that does own it. If they don't want to hear it and demand that you do it their way - then do it their way, and keep the peace.
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Re: Setting XY position of material

Postby TReischl » Mon Aug 26, 2019 8:42 pm

Russel: Maybe you did not notice that I use fixtures all over on my machine, one out the front, a rotary and vises? Setting a machine zero that is inside of the actual machining limits would not help with those items one bit, so I have to use offsets. The vises are rarely in the same spot, sometimes they are spread apart sometimes pretty close together.

Leo said:

"The best answer I can offer is this one thing. Learn what this stuff is and how to work with it.

However - if you do not own it and you are employed by someone that does own it. If they don't want to hear it and demand that you do it their way - then do it their way, and keep the peace."


Amen! And can he get a Hallelujah???

The worst problem I have encountered with using offsets is when I forget to actually set the offset. Came up with sort of a cure for that issue. I modified my post so that the machine moves to zero and then stops. Usually the difference between an old offset and a new one is a lot so it is very apparent to me that I just about did a big OOOOPS!. It has saved me quite a few times since I did that a few months ago. It was really biting me when I was doing things that used the router and the laser. With that I figured out what the distance difference was. Then I modified the laser post to use a different offset (g55 in my case) and so if I am doing a bunch of the same thing I do not have to manually change the offset between operations.

I am with Leo on this one, those offsets are there for a reason, and that reason is LOTS of people use them. Ever see a six sided tombstone on a milling machine with fixtures on each surface? Be tough to program that without offsets.
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Re: Setting XY position of material

Postby rscrawford » Mon Aug 26, 2019 10:19 pm

TReischl wrote:Russel: Maybe you did not notice that I use fixtures all over on my machine, one out the front, a rotary and vises? Setting a machine zero that is inside of the actual machining limits would not help with those items one bit, so I have to use offsets. The vises are rarely in the same spot, sometimes they are spread apart sometimes pretty close together.


No, I did notice that. I do the same, and I use offsets often. It just seems weird to have your machine zero in a spot that you rarely use as your zero, but its probably because you do not use your machine for processing sheet goods. With pop up pins, I guess its just natural to use that corner as machine zero, because sheets index with the pins into that corner every time.

When I use fixtures, I have dedicated spots for them (indexed spots) and I have each of those zeros saved as home positions in WinCNC (under the name of the fixture, I have at least 20 saved at the moment). So I just select each fixture I need and the machine automatically zeros where I need it to.
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Re: Setting XY position of material

Postby TReischl » Tue Aug 27, 2019 1:14 am

rscrawford wrote:No, I did notice that. I do the same, and I use offsets often. It just seems weird to have your machine zero in a spot that you rarely use as your zero, but its probably because you do not use your machine for processing sheet goods. With pop up pins, I guess its just natural to use that corner as machine zero, because sheets index with the pins into that corner every time.

When I use fixtures, I have dedicated spots for them (indexed spots) and I have each of those zeros saved as home positions in WinCNC (under the name of the fixture, I have at least 20 saved at the moment). So I just select each fixture I need and the machine automatically zeros where I need it to.


You are correct that I do not use the machine for processing sheet goods, that is rare for me.

It really does depend on what kind of work you do. In my case, think in terms of a tool shop, no repeating orders, no two things alike. I gave some thought to "fixturing" the vises, but then it dawned on me that I change jaw inserts fairly often so that goes out the window.

Sounds like you have your setups dialed in for the type of work you do. Pays to spend time to do that, no doubt about it.

Here is another thought about having machine zero somewhere in the work area. No real reason to do that because it is easy to just set something like G54 in the header of the cnc file from the post, have 5 and 5 in the offset registers and zero will then be at X5Y5 in machine coordinates.

I guess that is why so many of us like offsets, they are so flexible.
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