Hi guys,
So this is my first post on this forum, I've been interested in brushless spindles ever since I saw the OtherMill machine on YouTube, it had a belt driven spindle with an RC motor. And since I was already interested in BLDC motors and control, I've decided this could become a nice project and rid me off all the hassle and mess from the chemical etching process. So I've started googling and collecting all the info on brushless spindles I could find on the Internet, reading books and other literature on spindle design.
Naturally, when milling PCBs we are interested in low tool runouts, so bearing selection and quality is one of the top priorities. In the book designs they are using angular contact ball bearings in matched pairs with a suitable preload. But those bearings are quite expensive, a pair is at least $150 to $200 and require precise preloading to function to their specs.
Lots of commercial and DIY spindles (Paul Jones for example) simply use deep groove ball bearings, similar to those used in skate boards and Dremel/Proxxon tools, they are dirt cheap (anywhere from $1 to $10), but have no precision rating at all. Anyway, those spindles manage to sell for 150 to 200 USD, so they should be at least on par with the dremel tools. Interestingly, though it says on Other Mill's website that they use a preloaded set of bearings in their spindles, it looks to me like it's just a pair of flanged deep groove bearings pressed into the spindle casing:
So anyway, I'm planning to use an ER11 collet 10mm dia shank off ebay (http://ebay.to/2lLSWJr) in 150 or 100 mm length, and I need your advice in bearing selection, I'm thinking a high quality generat purpose double row angular contact ball bearing from a good manufacturer like SKF or Timken on the bottom and a deep groove ball bearing on top, all pressed into an aluminium body with ribs on the outside for better cooling. Would that be a good choice? Would press fit + loctite be sufficient to hold the lower bearing / shank in place?
If using a pair of angular contact bearings, I'd probably need to machine some kind of a sleeve to go on the shank for bearing preload, so I'm thinking of some way to avoid that, keeping costs and performance satisfactory. I'd be extremely thankful for any advice and suggestions from you.