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That's pretty much what I'm doing, and I've gotten close. But with the small size of the workpiece, there's not a lot of room for error. Picture doing a shallow vcarve circle on one side, then flipping the workpiece, doing another circle, then using and end mill to cut the workpiece out. I know it sounds simple enough, but after all the experiments I've done, I can assure you that setting that center accurately is the hard part, which is what led me to look for a better way of finding the center (x-y) of the jig I'm using to hold the workpiece. All too often, that back side is offset enough to either ruin the piece completely or to be very noticeable.

I apologize for my egregious threadjacking. I'll go and start another thread and describe my process and problems and maybe you guys can help me see the error of my ways.

:threadjacked:
 
Hmmm.. I'm thinking maybe 2 x stops and 2 Y stops bracketing the coins position would give you a known "square" and then because the workpiece is at a known position within that square you can use that to interpolate the "true" center of the workpiece.

You could do it with one x and one y stop if the position of the hold down never changed, but if you need to remove/re-add it then two each allows you to re-center the entire workspace and not have to work about aligning it as precisely in the x/y coordinates.

I think you could make something reasonably easy to have the coins in a sub holder that you simply flip over as well so the coins aren't rotated.

Here's roughly the layout I'm thinking of:
xy.png

Perhaps I'm over complicating things.. :D I'll be curious what the CNC guru's say.
 
Ryan Mooney said:
Hmmm.. I'm thinking maybe 2 x stops and 2 Y stops bracketing the coins position would give you a known "square" and then because the workpiece is at a known position within that square you can use that to interpolate the "true" center of the workpiece.

You could do it with one x and one y stop if the position of the hold down never changed, but if you need to remove/re-add it then two each allows you to re-center the entire workspace and not have to work about aligning it as precisely in the x/y coordinates.

I think you could make something reasonably easy to have the coins in a sub holder that you simply flip over as well so the coins aren't rotated.

Here's roughly the layout I'm thinking of:
View attachment 94171

Perhaps I'm over complicating things.. :D I'll be curious what the CNC guru's say.
Click to expand...


I'm putting together another thread on this. I'll have details on my current process there, a little later today. I will be interested in the ideas that it generates.
 
Yeah, I haven't done s sided yet, but I do know it is critical. In that case I would be more precise.

Well - I did do it one time but it was not critical

In a machining center I would use an edge finder, but in the absence I would touch off the side of the work with a straight round pin of a measured diameter, say .250 with a piece of paper. I would then move my axis above the work and towards the work the radial distance plus the paper then set zero. Of course that is to the edge. Same deal for the other edge. That would give me the corner.

Another thing I do as I want to align an edge is to "tram" the edge with my machine axis. I run a straight pin along the edge I want to tram and adjust the edge to be touching the pin the entire length.

On the vectric forum and in one of the tutorials on two sided machining, they talk about a dowel location hole to align the two sides. The hole does not need to be in the actual work - it can be in an area in the material that will get cut away.

Again, I have not really done it yet. It is one of those things on my list.
 
I just read all this after posting my method in Brent's other thread.

Using locating pins works WAY better than any other method i've tried -- though, i don't have any probes, yet, so ... but i like the process better anyway -- operation 1 cuts features that operation 2 aligns with - this guarantees they flip accurately and all you have to do is make sure your machine zeroes on the fixture properly (i do this by homing and saving a fixture offset)
 
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