Hi there,

I've searched through the net and this site to try and find info on making a digitising probe. I know very little about digitising (my CNC mill isn't even running yet...), but it must be possible to make a simple probe that works reliably with reasonable accuracy.

Does anyone know what exactly is 'inside' a probe and what it would take to build one?

Thanks
Warren

http://www.indoor.flyer.co.uk/probe.htm

Karl

Check out industrialhobbies.com

They show instructions on how to convert a edge finder that has an led light to a touch probe. I think :confused: that this type requires that you make contact with a metal surface since it is looking to sink to ground. So, if this is true, it would only be good for digitizing metal/conductive surfaces. If you wanted to do nonconductive surfaces, you would need to build a switch in the probe which when depressed (ever so slightly), would close the circuit.

Chris

I can't remember where these drawings came from. The probe works a lot better than the one MaxNC supply.
I increased the diameter on the one I built, I figured the further apart the balls were the more sensitive it would be.
The tip about tinning the PCB board improved sensitivity a lot.

Regards Mark.
Hughes Tooling.

Thanks for the replies everyone.

I think all this information should get me started on something. My mill isn't even finished yet and I'm already trying to find extra attachments to put onto it. I hope I have time to make something with the mill oneday, other than parts for the mill... :D

Thanks again

Warren

Karl and Mark, nice probe designs.

Thanks also.

Chris

Check out industrialhobbies.com

They show instructions on how to convert a edge finder that has an led light to a touch probe. I think :confused: that this type requires that you make contact with a metal surface since it is looking to sink to ground. So, if this is true, it would only be good for digitizing metal/conductive surfaces. If you wanted to do nonconductive surfaces, you would need to build a switch in the probe which when depressed (ever so slightly), would close the circuit.

Chris


This is true... but in my limited electroplating experience, one may be able to coat the surface of non-conductive items with a conductive "paint" (spray or brush) allowing use of this type of probe. I haven't done any of this with a probe, but have had success in electroplating non-conductive items (years ago).
..of course this all depends if the item to be probed is up for the "paint job".

Could you suggest some products that we would have access to for your conductive spray paint suggestion?

Thank you for the reply!

Chris

Could you suggest some products that we would have access to for your conductive spray paint suggestion?

Thank you for the reply!

Chris


I can't really advise on those conductive coatings....its been SOooo long ago, some of the electroplating companys are non existant now.... I DO remember though that I had made a mixture (to save a few bucks) as an alternative to the comercial coatings by using a medium to hold powdered copper. I don't recall if I fully tested it.
...geesh.. I'm not THAT old...just a bad memory or "too many irons in the fire" at that time. :rolleyes:

Hughesbros, I assume that you are using TurboCNC, since you posted in the other thread I started in the TurboCNC section. Could you please tell me if your probe uses a 'point' on the end or a ball? The reason I ask, is that TurboCNC doesn't have cutter radius compensation and I'd imagine that if a ball were used, then the points written to the text file would be inaccurate. Am I correct in thinking this?

Warren

Hello again,

I've had a good look at all the information that was given earlier and I think I've pretty much sorted out the actual probe design in my head. My attention is now drawn to the 'amplifier'.

Is an amplifier really necessary, or can I simply run 5V through the probe directly to the parallel port? I would obviously like to make it as simple as possible, but if an amplifier is needed, then I'll have to make one.

Thanks
Warren

Originally Posted by itsme
Hughesbros, I assume that you are using TurboCNC, since you posted in the other thread I started in the TurboCNC section. Could you please tell me if your probe uses a 'point' on the end or a ball? The reason I ask, is that TurboCNC doesn't have cutter radius compensation and I'd imagine that if a ball were used, then the points written to the text file would be inaccurate. Am I correct in thinking this?

I'm using a MaxNC CL control on a machine I built. Like TurboCNC there is no compensation for the probe diameter, but I can offset the surface in Rhino. I used a 1mm diameter probe to scan the face in the image attached, the surface on the left has been offset 0.5mm inwards to compensate for the ball.

Mark
Hughes Tooling.

Originally Posted by itsme
Is an amplifier really necessary, or can I simply run 5V through the probe directly to the parallel port? I would obviously like to make it as simple as possible, but if an amplifier is needed, then I'll have to make one.

The MaxNC probe works on 5V, I found it was not very sensitive and you would get spikes in the scan. From what I can remember the printer port does not work 5V on 0V off its something like above 2.75V is considered on and below is off so there's not a big differential. Any bad connection at the lower voltage and the control thinks it is in contact and lifts until the resistance drops and you get a bad reading. Using 12/14v with the amplifier gets over most of the problems with resistance in the switches.

When I get a chance I'll post a picture of the amplifier I built and a drawing of the PCB board. I made the PCB board on a mill so it's quite easy to make if you can get the components.

Mark
Hughes Tooling.

Hi Mark,

Thanks for the information. If (when) I'm going to make the probe, I may as well do it all properly. If you could post pictures of your PCB, that'd be great. The other photos you posted are also awesome. I'm inspired to build a probe!!!

Regards
Warren

I found this Renishaw page that show the innards of their probe:Link (http://www.renishaw.com/userfiles/htm/MTP-WHI-0006.html)

Pablo

Thanks for the link, Pablo. Isn't it strange how the Renishaw innards look so similar to the probes that people build at home??? :p

I've been looking at the amplifier schematic and I've been having a few thoughts on how I can adjust it to suit my requirements. With my CNC setup, I'll have a 35VDC supply. It would be nice if I could put the probe electronics inside my CNC control box and then use my CNC machine power supply. Would the probe be able to handle 35V? I doubt anyone has tried it, but what do you think???

I also have a few questions relating to the actual amplifier running at 35V, but I felt that these would be better placed in the 'General Electronics Discussion', so I am going to start a new thread there (just in case anyone is interested...).

Regards
Warren

well the probe is a simple on-off switch, if the current is not very high I see no problems. the problem is how do you feed 35v back to the parallel port :)

IMHO is easier to use a proper voltage power supply, switching cellphone chargers are a very cheap source of power supplies, they usually have a pot inside that sets the output from 4 to 12v


Pablo

Hi Pablo,

If you have a look back in one of the earlier posts in this thread (from hughesbros), you'll see the plans for a probe and also the amplifier that goes with it. The probe in those plans normally operates off 12V, which is also too high for a parallel port - that's the purpose of all the circuitry. All I want to do is modify that circuit to run off 35V instead of 12V. Why do something the simple way, when you don't have to... :)

Regards
Warren

I don't see why you need extra supplies when you have them in the PC if that is what you are using?
Al.

What about using a piezo as the transducer?
STMs use a piezo tube to move the probe across the suface.
See this homebuilt version;
http://www.e-basteln.de/

renishaw has piezo probes;
http://www.renishaw.com/client/product/UKEnglish/PGP-1070.shtml

Or maybe look at an AFM;

http://www.nano.geo.uni-muenchen.de/external/research/projects/Kempe/afm_detail_english_ppt/AFM-Dateien/v3_document.htm