# gSender probing question

I’ve been looking at gSender, and like what I see. It seems to handle almost all of what I normally need, and looks like it does it better than my existing machine control program.

One possible exception is a probe routine to find the center of a hole. I have a technique where I use a simple copper plumbing fitting as a dowel. I can solder a wire to the dowel, then use it to register the machine to the hole center, since the plumbing fitting is just a thin wall cylinder. This is all done with simple electric conduction, though I’m thinking of buying a 3d touch probe for \$100 to simplify and generalize the process.

Anyway, I didn’t see a probe routine to find the center of a hole in gSender, after watching an in depth video. Is there such a routine, or could it be easily added. I use this technique quite a bit.

Been a few years, but you could start with this.

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@NeilFerreri As usual, Neil, your stuff boggles me. One question, though. The code assumes that the hole itself is bored in a material that is a conductor, yes? In other words, this cannot work to find the centre of a hole bored in wood??

Tks for the education.

I would assume that as well. That’s why I use a copper plumbing fitting as a hollow “dowel”. I can insert it into a previously cut dowel hole and I’ve got my conductor. However, 3D touch probes are now affordable, so I could skip that step and use any hole!

@jandyman Understood, tks. I guess to be accurate, the hole and the OD of the pipe must be pretty much exactly the same. Do you mind explaining when and why you use this? Tks.

Yes, I cut the hole to be exactly the diameter of the fitting (.565") . I’ve used this system because I need to flip over parts like bass bodies and necks, and location is critical when doing that. Whatever system I use to secure the stock for the first side cut, I create two dowel holes in the top of the stock and the spoil board at each end of the work. It might be days later when I finish the top cuts or get around to flipping the piece over, and I don’t trust the homing switches to find X and Y accurately, so I just the probing routine and the plumbing fitting to locate X and Y zero, whether it be using the spoil board holes or the holes in the piece, depending on whether I’ve flipped it or not. Hope this make sense. I am thinking about other ways of doing this, but it has worked well so far.

@NeilFerreri Reading your reply made me realize just how much is possible with G code itself, and gave me an idea about solving a problem I’ve been thinking about for a long time - how to create a precise relief curve for an electric guitar or bass, even with the strings on. Let’s imagine we are talking about a 48x30 MK2 mill, and we are assuming that the gantry is perfectly straight. If we could use a 3d touch probe and probe the top of the neck at a few different points along the neck (between the strings and avoiding the frets), and gather that data, it would be easy to figure out the exact relief profile. This is sort of a holy grail, as measuring with a straightedge and feeler gauge is really error prone. The numbers we are talking about are small - the maximum deviation from straight (the “relief”) on a properly set up bass guitar neck is between .015" and .025". But as long as the 3D touch probe is sensitive enough and the gantry is completely straight, this could really work. The trick is being able to save out the measured points somehow. How would one do this, and does this sound crazy?

@jandyman Thanks for the explanation. I do a lot of two sided machining. I use 1/4" aluminum “dowels” in 1/4" holes to ensure that the top and bottom are precisely aligned. The technique is well described in both the Vectric videos and those of Mark Lindsay. I’m sure that you’ve seen that technique and found yours to be better, though.

As to 3D probing, there are commercial probes available, like this one for example

https://www.nextwavecnc.com/shop/DIGITAL-DUPLICATOR-FOR-CNC-SHARKS-AND-PIRANHA-p114869869

For DIY, you may want to look at Bill Korn’s efforts here

From what I can tell, 3D probes are getting even cheaper than the ones posted above. Here’s an interesting video:

It looks like that is this class of probe, for about \$100:

https://www.amazon.com/PGFUN-Anti-roll-Waterproof-Measuring-Compatible/dp/B0B3XMFDX5/ref=sr_1_1_sspa?keywords=cnc%2Btouch%2Bprobe&qid=1664586478&qu=eyJxc2MiOiI1LjMwIiwicXNhIjoiNC42OCIsInFzcCI6IjQuMTkifQ%3D%3D&sr=8-1-spons&ufe=app_do%3Aamzn1.fos.006c50ae-5d4c-4777-9bc0-4513d670b6bc&smid=A1S6QHOHFESIR0&th=1