How to place the workpiece in the same place?

[halodri]

Hello vectric forum,

I use a CNC in a makerspace. I would like to carry out milling work on a workpiece over several days.
How can I ensure that my workpiece is in the exact same place on the machine table when I unclamp it and re-clamp it another day to continue?

I am thing of something like this made out of plywood:

I could align the edges/corner of the plywood bracket to the edges corner of the machine table.

This is the CNC I am talking about :

What other methods are there?

[Jan.vanderlinden]

I permanently mounted a framing square to my bed.
Works like a charm.

[RickW3DS]

The gSender post processor has a feature where you can save a "workspace" and return to X0Y0 by clicking on that work space. I have several jigs set up in different workspaces. Works like a charm!

[adze_cnc]

It's important to note that halodri mentions that this is a CNC in a MakerSpace. So permanent fixtures and machines settings are likely to be less useful as others will be using the machine in the mean time.

halodri: you are on the right track. Does that machine have some sort of waste board that you will be mounting your material onto. Or will you be cutting "all the way through"?

[halodri]

I permanently mounted a framing square to my bed.
Works like a charm.

Nice, that framing square looks pretty much like the plywood jig I have in mind.

But as adze_cnc notes, unfortunately I can't mount thing permanently because I am using a CNC at a maker space.

Does that machine have some sort of waste board that you will be mounting your material onto. Or will you be cutting "all the way through"?

Yes, if you cut through you must use a wasteboard, otherwise the grooved aluminum plate will not appreciate it. Actually, a wasteboard complicated the matter because if the height of the framing square is lower than the wasteboard, there is no "edge left" to align the workpiece.

Another way to align could be using painters tape with pencil marks or pencil marks directly on the grooved alu plate, most likely no one will erase the marks and even a broken line would suffice. A pencil line can also be easily erased with an eraser or alcohol. This isn't very accurate though, but should work for most woodworking purposes I think.

I could use a ruler like this:

+ a mechanical pencil 0,5 mm or 0,3mm.

What do you think?

And another method would be to just drill two 4 or 6mm holes in the aluminum table to put alignment pins there, the table already looks pretty battered so the holes wouldn't really be noticeable.

[adze_cnc]

What I'm thinking is take your waste board and attach two strips of similar material roughly in an ell shape as your locator above.

• When you are ready to start or continue your cut mount that assembly to the table as closely parallel to the edges but 100% precision is not needed.
• Jog the machine to just inside the crook of the ell.
• Set your XY zero to the point.
• Set your Z zero to the wasteboard or the top of the ell (depending how you usually do so)
• Cut a file that does 3 things:
  • cuts a hole at XY = 0,0 down to the top of the wasteboard
  • cuts a narrow vertical pocket longer than the Y length of the ell down to the top of the wasteboard
  • cuts a narrow horizontal pocket longer than the X length of the ell down to the top of the wasteboard
• You now have reference edges that are parallel to the X & Y axes and whose origin is the lower left.
• Jam your workpiece against the two edges
• Reset the Z zero to the top of the workpiece (if that's what you normally would do) or leave it at the wasteboard level (if that's what you normally do).

When you need to remount the workpiece at a later date just repeat the steps on the list but jog the XY and set the XY zero on a fresh part of the ell. It will diminish in size the more you need to remount so make it large enough to start with.

The attached image sort of shows what I am thinking of. Pretend that the grey area is the wasteboard and the "MDF" ell is mounted and cut as above.

Steven
 

[halodri]

Dear Steven,

Thank you very much for your detailed answer. I had to read it three times to get what you mean, but I think I got it.

Yes, what you are proposing seems to be a good method indeed and a precise one. So basically I re-cut the ell/corner each time so it's exactly parallel to the x and y axes of the table/machine. This requires me to move the ell slightly diagonally between the x and y axes with each re-cut so that there is enough material left for a re-cut over time this will use up the ell.

Yes, I think I'll try that. Tank you Steven, I really appreciate your help!

Alexander

[adze_cnc]

Yeah, I think that you pretty much have got it. Here's a recent sample. As you can see the alignment jig has been used quite a bit. The clay extruder blank was something that was pre-cut to size for another application.

Also attached is a sample template that I use when I need to make a new alignment ell (or U if needed). I just alter the lengths of the narrow rectangles (leaving the widths alone). I can also use the right hand one if needed otherwise I'd delete it.

Steven
 

[halodri]

Thanks for the picture and the file. It shows that the alignment jig can be made fairly easily from scraps, just two pieces of sheet material, connected with a few dabs of glue, screws or brad nails in your case and it's good to go.

"clay extrusion blank" sounds like an interesting topic

[RickW3DS]

Good point, Makerspace is shared.
I use indexing pins also for everything, square, jigs, etc. Maybe indexing pins no attached squares. JMO to get faster.