Mickey mouse touch pad

(Paul Musgrove) #1

Had a bad few days with my Z-axis, but it seems to be more or less under control now. Turned out there were several problems, including stock bulging up a few hundredths of a millimetre. (Wouldn’t be concerned about this amount of error were I not trying to get parts to fit together perfectly). Anyhow, adjusting belt tension and securing the stock properly solved some of the difficulties, but one remained – touching off. I was using paper from a roll of double sided tape (Nicely waxed so it slid out easily from under the cutter) and a piece of really soft plastic stock (An Ikea breadboard, actually) and I finally came to suspect the cutter was depressing the tape and plastic to produce erroneous readings. In an effort to eliminate that I designed a mickey mouse touch pad which can be assembled for less than $10 and seems to work fairly well. Hook the alligator clip onto the collet nut, hold the copper plate tightly down against the stock, lower the bit (.01 mm at a time when close) until the LED lights. Take that Z value and subtract the thickness of the copper plate. (Thickness actually varies by a few hundredths of a millimetre across the board, so pick one spot and stick with it. In my case the number to subtract is 1.38 mm.) If anyone wants to play with one of these things, they’re easy to assemble… Here’s a component and price list (all prices in Cdn $ at Lees Electronics in Vancouver B.C.)
copper clad board $3.40
100 ohm resistor 70 cents for 10
wire 22 or 23 gage (85 cents per foot, get two feet)
red LED $1.00 for five
alligator clip about $2.00
copper tape (but any decent tape will likely do).
small prototyping board (but it isn’t really needed).
holder for two AA batteries, 90 cents
Here’s a picture of the mickey mouse apparatus…

The result. Tabs show Z axis is working properly (at last)

For those not into electronics, here’s a really crude Photoshop drawing of the hookup