My designing is not too complex; collect a couple likely parts and convince them to play nice together. The spindle housing is 3" dia. S-7 die steel machined to accept four 6204RS 20x47mm deep groove bearings. The housing supports an ER-20 collet holder with a 20mm shank that is 200mm long. The ER-20 holder accepts up to 1/2" dia. cutters, and it's shaft is 20mm dia. (.7874" dia.) which should be plenty strong for an under one hp motor. Did I mention that this is going to be an economy build and that all the parts were in my scrap pile except the ER-20 holder which set me back $ 15.68 delivered from china.? So far lady luck is shining on me; The collet holder was of excellent spec. and quality, and the concentricity of the finished spindle assembly appears right on. I'm thanking my Jet 9x20 lathe for that. So under $40 cash spent so far on collet holder and collets, and I have a motor and enough pulleys to complete the drive (if I steal a step pulley from my Gingery lathe). Better get back to work so I can post more photos.
The bearings used are deep groove ball bearings which is what I had on hand (read free). They don't appear to have axial play, at least not yet! I have a couple dozen of them, so if they start to go, I'll put in replacements and thread the spindle shaft for adjustment. Now that you mention it, my cnc 3D engraver has an Enco (lathe) headstock with smaller versions of the same type of bearing, and has an adjustment nut, so I may indeed have to thread the shaft. Alternatives are installing a small taper-lock two part pulley, or switching to tapered bearings (read auto wheel bearings) plus threading the shaft if it comes to that. Thanks for the observation.
You have a good eye. That tool is a Cleveland high speed steel 3/4" counter-bore with a 1/4" pilot which I got in a box lot at auction long ago. It's supposed to be used to cut the pockets to recess cap screws. To bore the housing, I drilled a 1/4" hole, then cranked the c/bore tool through using the tail-stock wheel prior to using a boring bar. It was fast and had very little chatter.
now I see it. I don't own any counterbore tools because I can cut counterbores on my CNC mill with a standard end mill. Nice way to enlarge a hole for boring bar clearance.
This is a photo of the temporary linking of the motor directly to the spindle to cut a key-way for the two step pulleys to be mounted to the shaft between the motor and the spindle. Note the scrap of wood wedged between the spindle housing and motor housing to provide tension. Above that is a closeup of my first object cut with the mill; a 3/8" key-way on a scrap piece of shafting. I think this machine may turn out ok. I know I'm thrilled. The third photo is of the setup for the milling of the actual key-way to secure both step pulleys. It will be one continuous cut. More later as the build nears completion.
