Inventables Community Forum

How do you guys cut to your centre line?

Today I’m working with a body blank that is bookmatched halves, and I’m running tests on MDF before I commit.

It seems that using the centre dot under ‘position’ in the ‘shape’ menu is not the way to do it. I thought if I positioned the bit on the middle of the centre line that it might carve outwards from there as a central home position, but it clearly wasn’t designed for that.

So I drew a 90 degree line down from my centre line at the end of the body end of the centreline, then another 90 degree line from that to establish my bottom left corner, and positioned the bit over the intersection. When I did an air carve though, it was off.

Here is a simplified version of the file I’m working on. Before anyone mentions, I know the neck pocket makes no sense- I’m just using the CNC to hog out material, I don’t trust it with my neck pockets, so I finish them offline.

So what mystical technique are you luthiers using to set up your carves to a centre line? I did set up G28 yesterday and scribed a centre line into my wasteboard, but when I entered G28 in my machine controls it crashed it. It was working fine yesterday… so I’m very confused.

Thanks Robert, that was good info… I see I’m trying to work out how to set work zero to a centreline, and cut from there, as opposed to from the bottom left position of the work piece. I know I can jog to it in setup, but how to cut from a centre line work position?

Has anyone else had their G28 suddenly start sending their spindle somewhere other than where they had set it, after a restart?

It is not, these 5 dots provide a reference point for your design.
Say you design a 5x5" square, click Position Center dot, now you can assign a X/Y coordinate to that selected point.

Work Zero can be set anywhere within the workspace of your machine. Work Zero will be where you have your bit when you hit “Confirm Home Position”.

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My workaround for this issue was to create a template file in Rhino/Illustrator, and send it to Easel as an SVG. If your home position is at the bottom left of your machine, this maps a crossed set of lines at 250mm of Y, and 25mm of X that correspond to a scribed line I have in my waste board. I import the SVG into a 1000 x 1000 mm workspace in Easel (don’t let it re-scale it to fit), select all, and select ‘on path’ for everything. Then import whatever I want to cut, line it up with the centreline in the file, and it will line up with the centreline on my waste board in the real world. Once everything is lined up, I delete the workspace elements and just leave the things to be cut, and change any on path items to inside or outside cuts as needed. The workspace file can be used to cut a centreline into your waste board too, so you can use the file if you like. It’s here:

[http://easel.inventables.com/projects/xecgzYnjx0CHPOhTOcGnCA]

I also have the file as a Rhino 3D file, so instead of lining things up in Easel I use it as a template in Rhino, so when I export it to SVG, it will be exactly where I want it to be when I import it into Easel. If anyone wants the Rhino file or an Illustrator file, email me templeguitarco@gmail.com and I’ll be happy to email it to you.

Thanks Haldor, I think I’m just going to leave those dots alone!

G28 use Homing as reference, did you re-home before sending the G28-command again?

I can’t remember as it was a crazy busy day, but I very well may have. Is re-homing bad?

No, Homing provide a relatively fixed reference point and if for some reason your machine loose its position (loosing steps etc) you can re-home in order to align machine to design again.

To use G28/G30 homing is required, otherwise the G28/G30 point may be skewed.

My workflow (not the only one):

  • Start-up machine, hit $H
  • Jog to intended Work Zero position
  • Hit G28.1 (I usually lift Z 10mm before storing G28 position as a precaution)

So if for any reason you need to restart project, failed carve, loosing steps etc you Home again, hit G28 and the end mill should return directly (in a straight line, hence my Z+10 lift) to the same Work Zero position.

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When you say “re-homing”, do you mean changing the home position by moving the switches, or do you mean unlocking the machine at the start of a session and sending it to the home position?

This.

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Ah good. Thank you!