mach 2, xylotex and homemade digitizing probe

[gun_mike]

Hi All,
I have just finished building my touchprobe, and now I need to hook it up to my computer. I have a 3-axis xylotex control board, and Im running mach 2 (computer to slow for mach 3).
My probe is wired NC (normally closed) this being said, in mach 2 under ports and pins, I need to set the digitizing to "active low" is this right?
My second question is, how do I hook the probe up to my xylotex board. I have an idea that it goes in one of the unused pp pins and the other end goes to gnd? I read in another post that resistors need to be installed to prevent the computer from being fried. Would anyone know what size this resistor needs to be?
Is there anything else I should be aware of before hooking up the probe?
thanks for your help,
Mike Grobowsky

[tooManyHobbies]

I don't have any experience with any of the Xylotex boards, but here's how I would hook it up:
- The Xylotex manual says that there are available pins on the I/O screw terminals. I'll leave it up to you & Mach2 to determine which one to use.
- The picture shows how I would connect it. If your probe is Normally Closed, then you need to set Mach2 to active high (the probe keeps the port shorted to ground until it opens when 'touched' and the 10K resistor pulls up the port to VCC). You could make it active low by switching VCC, but I've always preferred to switch ground and pull-up VCC through a resistor. Slightly safer in some cases.

Does your probe have electrically isolated connections? If not you could have tricky connections to consider.

Any plans to publish or produce your design? Let us know how it turns out!

Hope this helps.

tom

[gun_mike]

Thanks for the diagram, it makes set up much less complicated.
The probe is not isolated. Could this cause a problem?
I could probably take it apart and cover the copper clad with something to isolated it.
The prob is not my own design, I modelled it after Shaun Wainford's probe
http://homepage.ntlworld.com/shaun.wainford/Probe.html

It wasnt as complicated as I thought. Pressing the 3 pins into the hub was the most difficult part, as they have to be exactly 120 degrees apart and square to the hub or the point will not be centered.

I'm going to make a separate circuit (from the xylotex board) for my limit switches and the probe. I can't stand a mess of wires.
I will post pictures as soon as I finish making it.
Mike G

[Wainford]

Hi I designed this probe, although the example above appears to be the earlier version, I have since updated it to make it easier to manufacture, and to allow for centering adjustment etc, the original design is posted on the Mach site ( http://machsupport.com/forum/index.php?topic=1196.0 ) in PDF format simply to show a possible method of producing a probe that can scan 3d, and was never intended for production, having said that, going by the emails I get, lots have been made to this earlier design, It works as multi directional NC switch and uses a spare pin on the parallel port, the updated version is available as a set of drawings in PDF format or as a 3D-Model in E-Drawing format, if you contact me shaun_wainford@yahoo.com I will email it to you.

Best regards

Shaun

[MRM RCModels]

Wainford,

Sent you an email.
____________________________________

Gun Mike,

Did you turn the aluminum housing on a lathe (I don't have one yet)?

[maxboostbusa]

Email from me also.

[gun_mike]

Gun Mike,

Did you turn the aluminum housing on a lathe (I don't have one yet)?

MRM,
Yes, I did turn the housing on the lathe. If you have a rotary table, or a cncmill with little backlash, you could make the probe with no problem. The only thing that might be troublsome, is the stem. The plans say to press fit the stem into the housing. You may be able to use a broken 3/8" endmill shaft (or whatever size EM fits your mill) as the stem, and then accuratly mill a circular pocket on the backside of the housing for it to fit in. Idealy, you want the stem to be true to the prob tip. If you are using the probe for digitizing then, its not as crucial. But if you plan to use the probe for setting origins, then your parts will allways be out as much as the tip to the stem.

Mike Grobowsky

[Wainford]

If you make the stem removable or make a small block/Holder, you can invert the probe body sit it on the Mill table remove the probe tip and use it to set tool height, I do this and it works well.

Shaun.......

[gun_mike]

Had a little extra time on my hands, so I made up the G-code for the probe's aluminum housing.

cnc milling machine,
.500" 2 flute endmill (must be long enough for 1.709")
origin is the center of the probe
stock surface: 1.709"
feed rates: cutting 7 and plunge 2
DOC: 0.05" (rough), 0.01" (finish)

I've tested the program on cnc simulator and all is well.
I would recomend drilling say 1/4" hole through to the other side at (0,0) so you have a reference point for the stem.

see post below for file!

Mike Grobowsky

[gun_mike]

NT