Tool Height Touch Sensor for Techno-Isel

[mikkojay]

Hey-
I had a minor breakthru with my machine today (luckily not the kind of breakthru where the bit goes thru the board!) I FINALLY figured out how to set up a touch sensor and make it work with the software I am running. I am using the older MS Dos G-Code stuff- not by choice, that's what talks to my machine.
The machine is servo with the srv400 ISA card and srvbox2 controller. I made a homemade sensor out of some bits and pieces I had laying around the shop. If anyone has a setup like this and wants any of the details, feel free to send me an email. It looks crude, but it I would bet that it will accurately gauge the surface height of whatever material I am cutting to at least .005 or so.
Mike

[Madclicker]

Post some details and pics.

[mikkojay]

It turned out to be really simple- don't ask me how I figured it out- I just tried it and it worked. Actually, I did see somewhere that a Techno machine used its 4th axis encoder plug for a tool position sensor, but nothing specific.
I ended up using a single wire going to pin 6 on the 4th axis encoder input.
This pin is supposed to serve as the home switch input for the "A" axis, but since my machine only has XYZ, the 4th plug was empty.
I did not have a 15pin male connector, so I pried the shield off of a 9pin serial cable and removed the "right hand" thumb fastener (see pic)- yeah, I know, cheezy but it works.
Here is what happens:
1) you set up your config with an "X" in the "TOUCH KIT" setting.
This will make visible a new button that starts the touch off process while in the jogging screen.
2) Pressing this new button will make the z axis start to slowly decend.
What the machine is looking/waiting for is pin 6 on the 4th axis encoder plug to be sent to ground.
3) The little wood block that I made has the aluminum cover from a Radio Shack hobby box on the top surface. To this is soldered a wire that goes to pin 6 on the 4th encoder plug. I sandwiched semi-rigid foam between the plate and the wood block. I used the 4 screws to adjust the height to exactly 1.6" in all 4 corners. This was for an "oh my God" scenario- the plate will "give" upto 1/2" to allow emergency stoppage if the switch fails to stop the z axis decent. I am new to this so I need failsafes like this!
4) When the tip of the router bit touches the metal plate, the program stops the downward decent, and returns the z axis to its original position. The program then sets current Z zero position to the place where it touched the plate, MINUS the pre-configured thickness of the touch sensor (in this case 1.6".

Now when I need to start the machine at exactly 0.000 Z, I will use this method to set the tool before I run a job.

I just got it working yesterday, and I am really new to all of this- so that's the plan at least!
I just needed a good way to accurately tell the machine where the Z axis was in relation to my material surface, and since this semi-documented, outdated, etc.. software isn't actually supported by Techno, it is up to the user to try to get it to work.

Thanks, Mike

[sploo]

Simple, and by the looks of it, very effective. Nice work Mike!

I'm assuming that the pin is being grounded through the bit, router and machine. I thought that most routers were double insulated? Or is that just the can (i.e. the bit will be electrically connected to ground)?

I could just go into my workshop with a multimeter I guess, but it's twenty past ten at night here, and I'm enjoying a beer

[mikkojay]

Yep, the bit is at the same ground level as the ground in the controller's power supply. I think the term double-insulated might apply more to the motor's windings in relation to the motor body/frame. I tried it out for the first time tonight and it worked really well. If I have time, I might make another one that is a bit more pleasing to the eye, but I will have to put it at the bottom of my to-do list since this one seems to be doing the trick.
Have a good one-
Mike

[sploo]

Originally Posted by mikkojay Yep, the bit is at the same ground level as the ground in the controller's power supply. I think the term double-insulated might apply more to the motor's windings in relation to the motor body/frame...

I had a play with a PC892 router and a multimeter, and, as far I can tell, there's no connection between either pin on the plug and the collet.

At least as far as it's used here in the UK 'double-insulated' refers the following (found on a website): "Electrical power tools with parts that carry current being insulated from the person using it by internal insulation in addition to a non-conducting outer casing.".

I believe these tools don't usually have an Earth connection, and certainly the PC892 plug only has live/neutral.

K2 CNC are building machines using these routers, and they have a height indicator, but it looks like it might be some form of mechanical switch: http://www.k2cnc.com/Indicator.asp

Interesting...

[mikkojay]

The router I am using is a Makita-
I am not home right now- I am actually sitting in the waiting room of my ISP- my cable internet conn has been down!

[mikkojay]

Just got back (with a new cable modem)
Mine is a Makita RF1101 like this:
http://www.toolpartsdirect.com/cgi-b.../makita/RF1101
It has an aluminum body and a grounded (3 prong) plug.
This configuration might prove ineffective if a person's router body/collet were not at earth-ground. You might be able to just make an alligator clip type of ground that you could clip onto the shaft of the bit while performing the tool touchoff procedure- it might be cheaper than using a different router. It wouldn't take but a few seconds to clip it on and off.
Mike

[sploo]

Originally Posted by mikkojay ...You might be able to just make an alligator clip type of ground that you could clip onto the shaft of the bit while performing the tool touchoff procedure- it might be cheaper than using a different router. It wouldn't take but a few seconds to clip it on and off.

After finding the PC892 wasn't grounded I was thinking of how to do it, and that was my first idea.

You could make some sort of switch, or use a floating piece of grounded metal (of a known thickness, which is pushed onto the block by the bit), but the ally clip would be so much simpler.

Cheers!