After terribly threadjacking Bills thread on doing the Z-Zero, I thought I would start one to document my experiments with making 2 sided coins. I figure this is a good use of time, as it could help me with making 2 sided circuit boards.
Some of this will be redundant from the other threads I've done on the coins and my threadjacking.
The key in doing this I think is that you need to have a reliable and repeatable XY starting point, especially if you want to make more than one item.
So here's an example what I'm working on.
So, After a number of attempts I started thinking through the process and what I could do to ensure that I could get the front and back images placed correctly.
Mistakes I had been making were:
1) Just using screws to hold the material to the spoil board. It did not provide enough support for working the thin metal. I would get chatter and bad cuts.
2) I had been trying to register the position of the workpiece by using the lower left corner. Since I was not ensuring the workpiece was 'in line' with either the x or y dimension, well, This was problematic, not to mention I was not getting what I would call an accurate xy-0,0 with my eyeball.
Also, it's not super easy to get an xy zero by eyeball, at least that is my experience.
Around this time I started using a touchplate to establish the Z-0. I quite liked it and it was giving me a much more accurate position on the z axis.
So I decided I needed to do 2 things
1) Come up with a better way to hold the workpiece, and have that method let me be able to do multiples, if I so desired.
2) Come up with a better way to establish the XYZ-000.
I had also found some information on being able to probe for the x and y zeros using the same command that is used for zeroing the Z. Bill has done a great job of documenting that in his post, so I'll not go over the commands here.
So I designed a jig that would hold the workpiece in place and provide a a way to hold an x/y touch plate a known, fixed distances from where the project origin should be.
The jig consists of a 'pocket exactly the same height of the aluminum bar stock (1/8" thick, so this I made the pocket 3/16" deep). I also included channels along the edges to be able to make sure any swarf would not interfere with the placement of the stock.
I made the touch plate pocket a square, because I originally thought I would use a piece of 1" square al tube, but I had some al angle stock laying around I used instead.
And here's what it looks like IRL...
So that's what I did, I forked their 'Touch Plate' widget which lets you zero out your z axis using a touch plate. I added the ability for it to work in either MM or Inches and and the ability to zero the X, Y, and Z dimensions.
Here's a screen shot of the probe XYZ widget I put together on top of the 3d representation of the gcode to cut my spoil board. You can see that the zero point is where the stylus is sitting on the workpiece.
So, My thought process is
- I have a nice jig to hold the workpiece solidly.
- I have a place to put an x,y touchplate a known distance from the 0,0 point.
- When I placed the spoil board on the CNC, I used a piece of MDF I cut to have parallel sides. I can take this coin board on and off and as long as I use that board to ensure the spoil board is parallel to the X axis, I should be good
So Here's my latest results and I'm pretty close. This is in reverse order of the cut. The front, and the profile cut to cut it out are done last. You can see it all looks 'ok'. I've got some issues I'm working on with quality of the cut, but for this, I'm concerned with placement.
The back side of the coin (which was cut first) is off vertically by about 1mm.
The X dimension though, looks pretty good though, so I'm encouraged.
I believe that difference is due to two factors.
- The offset factor I enter into the probexyz widget
- My machine could use some calibration. I had some issues with the control board and just got everything up and running last week, and I have done a little dis and re assembly. I had only ever done a 'rough' calibration on it to start with any way.
So, That's my story and I'm sticking with it.
What do you all think?