Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

I will try to get some photographs within the next few days (it's in the workshop area I have on the other side of town).

In the meantime this is the motor I am using:

http://www.robotshop.com/en/rs-550-motor-19300rpm-12v-6249oz-in.html

It draws about 1.1 amps with no load and 1.9 amps when drilling with a #65 drill. Using a current clamp on my Fluke multimeter, set to capture the minimum and maximum values, the start up current draw is about 7.6 amps. A 12 volt 4 amp power supply bought from the above source only causes the motor to stutter, a 12 volt 15 amp power supply from the above source works but only if the switch is on the correct side of the power supply (I believe I had it on the output side). The problem with both of these supplies appear to be due to protection circuitry and the initial start up draw. Currently I am using 12 volt 3.5 amp power supply from a Nintendo Game Cube which works well however, I'm a little concerned it may eventually fail due to the large initial power draw.

I think this is the same motor for a couple dollars cheaper:

http://www.goldmine-elec-products.com/prodinfo.asp?number=G21086

This is the chuck I am using:

http://www.amazon.com/Water-Brass-3-17mm-Motor-2-5mm-3-17mm/dp/B00NXSETD0/ref=sr_1_1?ie=UTF8&qid=1456280385&sr=8-1&keywords=Gold+Tone+Brass+3.17mm+1%2F8%22+Motor+Shaft

They are also available on eBay.

The motor shaft has about .00025" runout. There is about a .004" runout with the chuck as measured on the drill shaft. I am unclear why this is since it's a straight through .125" hole so there is no problem with concentricity as there would be trying to connect a motor with a different size shaft to a standard carbide PCB drill. My first attempt at making my own connector drilling and reaming a brass rod and using set screws was only slightly better with about .003" runout. In any case using the guide bushings makes this a nonissue.

I used a linear stage probably by Del-Tron but unmarked. Most of these are not meant to be used in a vertical position but so far it hasn't failed. If it does I will probably replace it with a small linear rail from eBay. Neither of these are cheap but you can find something suitable on eBay for 20-30 dollars, maybe less if you are not in a hurry. The cheaper linear rails likely have somewhat more friction but should still result in a very sensitive feel as long as they use ball bearings and not simple plastic slides. Although you may get by with 1/2" of travel 1" or so gives more leeway in construction.  The finished drill press has a much more sensitive feel than my Cameron micro drill ( http://cameronmicrodrillpress.com/manual-micro-drill-presses/cameron-164-series/cameron-164/ ) or an Albrecht sensitive drill adapter used in a regular drill press.

Craig