DIY Belt driven Brushless Spindle for PCB milling

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Thread: DIY Belt driven Brushless Spindle for PCB milling

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    Default DIY Belt driven Brushless Spindle for PCB milling

    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:


    DIY Belt driven Brushless Spindle for PCB milling-image-314603-original-jpgDIY Belt driven Brushless Spindle for PCB milling-kkdmhdvgsle-1-jpg

    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.

    Similar Threads:
    Attached Thumbnails Attached Thumbnails DIY Belt driven Brushless Spindle for PCB milling-image-314603-original-jpg   DIY Belt driven Brushless Spindle for PCB milling-kkdmhdvgsle-1-jpg  


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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    I'll be using a V-belt or a round pulley belt on metal pulleys for speeds up to 18k RPM, which should be enough for milling PCBs



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    Found a photo of an othermill spindle cut in half with a waterjet. Looks like they use japanese EZO flanged deep goove bearings model F63800 ZZ, not sure about the diameter though. If they are good enough for them - they are good enough for me.

    Looking at the cutaway of the spindle, are those simple washers on top of both bearings inner races (between the inner race and chuck/pulley) or are they retaining rings? Seeing how they are of different width at the cut points tells me they must be latter, but there is no groove on the shaft for them to press into... Maybe there's a washer on top and a retaining ring on the bottom, doesn't make much sense though.

    DIY Belt driven Brushless Spindle for PCB milling-img_1022-jpg



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    No idea, but what if they are some sort of fancy-shaped elastic washers that apply preload...?



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    Quote Originally Posted by HighVoltageLP View Post
    I'll be using a V-belt or a round pulley belt on metal pulleys for speeds up to 18k RPM, which should be enough for milling PCBs
    You want to use a 3 rib Poly-V-Belt, round Oring type belt have problems a V belt is not suitable for these high speed spindles

    Matched pair Bearings sets, the Preload is already set, so this is the easiest part, nothing to worry about for Preloading the Bearings, Deep Grove Ball Bearings are not suitable for spindles if you want any accuracy only use AC Bearings

    Mactec54


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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    I'm trying to build miniature belt driven milling spindle for quite some time - here is my current prototype - version 5 or 6 (i lost count )
    DIY Belt driven Brushless Spindle for PCB milling-frezarka_3540_58589-jpg

    My spindles use cheap bearings (it's just a hobby) most "expensive" combination was pair of SKF 7201BEP in front + 6001 on the back (was not very happy with it since cheap AC bearings have limited max. rpm and my spindle was running hot at 12krpm).
    Current version uses pair of cheap 6902 on front + one 6901 on the back - it can run at 24krpm without problems cutting aluminium with 3mm endmill 1mm deep (surface finish isn't great though). I never had problems with runout (worst spindle 0.03mm, best - under 0.01mm) but all have stiffnes issues - probably time to spend some money on high quality AC bearings.
    PCB milling requires less force than cutting aluminium - i think normall deep grove bearings should be sufficient. Be aware that "10mm dia shank" not necessarily means it has correct tolerance to put 10mm bearing on it.
    For the belt - i'm using MXL tooth profile - not a design choice, just had some spares in the drawer.
    Foto in atachment - a few previous protypes

    Attached Thumbnails Attached Thumbnails DIY Belt driven Brushless Spindle for PCB milling-historia_3540_12361-jpg  


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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    Quote Originally Posted by mactec54 View Post
    You want to use a 3 rib Poly-V-Belt, round Oring type belt have problems a V belt is not suitable for these high speed spindles

    Matched pair Bearings sets, the Preload is already set, so this is the easiest part, nothing to worry about for Preloading the Bearings, Deep Grove Ball Bearings are not suitable for spindles if you want any accuracy only use AC Bearings
    That's what I was thinking, I've read your spindle build thread from start to finish and some books on spindle design as well as the info they have in bearing catalogs, but deep groove bearings can handle some axial loads, surely enough for PCBs, they cost an order of magnitude less than a suitable matched pair of angular contact bearings. And after I've seen them being used in a $3000 machine, I'm convinced they will do for my first try.

    My main concern right now is the straightness and precision of those chinese collet shanks, they are often 9.98 mm instead of 10 or do not have consistent tolerance of 0.01 as they claim. Other thing is the inside diameter of those things, 150mm long have a smaller diameter, so it's possible to thread it (don't know how well the 58C threads though) and use a bolt to push on the pulley on top.

    As for belts, I meant a 2 groove V belt, I've already found a source with 260 to 300mm belts, perfect for 3:1 80mm center distance with 16mm and 48mm dia pulleys, don't know where to get those yet, will probably custom order them from a machine shop



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    Quote Originally Posted by grg12 View Post
    I'm trying to build miniature belt driven milling spindle for quite some time - here is my current prototype - version 5 or 6 (i lost count )
    DIY Belt driven Brushless Spindle for PCB milling-frezarka_3540_58589-jpg

    My spindles use cheap bearings (it's just a hobby) most "expensive" combination was pair of SKF 7201BEP in front + 6001 on the back (was not very happy with it since cheap AC bearings have limited max. rpm and my spindle was running hot at 12krpm).
    Current version uses pair of cheap 6902 on front + one 6901 on the back - it can run at 24krpm without problems cutting aluminium with 3mm endmill 1mm deep (surface finish isn't great though). I never had problems with runout (worst spindle 0.03mm, best - under 0.01mm) but all have stiffnes issues - probably time to spend some money on high quality AC bearings.
    PCB milling requires less force than cutting aluminium - i think normall deep grove bearings should be sufficient. Be aware that "10mm dia shank" not necessarily means it has correct tolerance to put 10mm bearing on it.
    For the belt - i'm using MXL tooth profile - not a design choice, just had some spares in the drawer.
    Foto in atachment - a few previous protypes
    Much respect to you for trying to come up with a better design)

    I've done some research on those ebay shanks and I'm not sure I trust them, spent yesterday evening sarching for a better source, preferably with a solid rod or with a smaller hole diameter. I even thought about making a sketch and sending it to local machinists for a quote. I'd be very grateful of you could share some feedback on your sources.

    I will try to stay away from MXL belts, I've heard stories of those rubber teeth getting torn out and flying across the room at speeds about 10-15k rpm)
    As for stiffness - I doubt I'll use this spindle to mill any aluminium, so given the mills used and the thickness of those cuts there won't be any forces those bearings wouldn't be able to handle. And I'm getting decent quality japanese stuff, not $1 a pop junk from ebay.

    BTW, that thing under the lower bearing must be a spring or belleville washer, deep groove bearings do need a preload to get rid of any noise and axial play
    Preloading by springs



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    HighVoltageLP

    You are right if you are just doing PCBs then you could use Deep Grove Bearing these have lots of side play but you could give them a preload of 4lbs that would help with the clearance, this can be set with a wave spring washer

    You will also have to look at what speed the bearings can run at, RS is the your best bet, RS means rubber shielded, steel shielded will let fine particles into the bearings, when you assemble them into your housing you can take the inside seal out, this will allow you to lube the bottom bearings with a few drops of quality oil

    Attached Thumbnails Attached Thumbnails DIY Belt driven Brushless Spindle for PCB milling-smalley-wave-springs-jpg   DIY Belt driven Brushless Spindle for PCB milling-wave-spring-washer-loaded-bearings-jpg  
    Mactec54


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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    Quote Originally Posted by mactec54 View Post
    HighVoltageLP

    You are right if you are just doing PCBs then you could use Deep Grove Bearing these have lots of side play but you could give them a preload of 4lbs that would help with the clearance, this can be set with a wave spring washer

    You will also have to look at what speed the bearings can run at, RS is the your best bet, RS means rubber shielded, steel shielded will let fine particles into the bearings, when you assemble them into your housing you can take the inside seal out, this will allow you to lube the bottom bearings with a few drops of quality oil
    Perfect advice, thank you, I was just trying to google the amount of preload those deep groove bearings need. I was thinking about rubber shielded but figured they would get hot, tried to find if there are any with only the flanged side sealed but somehow the thought of removing one seal didn't cross my mind yet haha. Max speed for them is 37k with grease lubrication, so twice as much as I need.

    Thanks again for your advice, I was hoping you'd come by my thread after I've seen all the good stuff in yours)



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    I've got a question

    Is it possible to replace a shield in a ZZ type bearing with a rubber seal? The shop I'm using for bearings doesn't carry F698-2RS, and I couldn't find them anywhere else



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    Default Re: DIY Belt driven Brushless Spindle for PCB milling

    Quote Originally Posted by HighVoltageLP View Post
    I've got a question

    Is it possible to replace a shield in a ZZ type bearing with a rubber seal? The shop I'm using for bearings doesn't carry F698-2RS, and I couldn't find them anywhere else
    I have taken them out before and put them back in the same bearing after servicing the bearing, there is no reason that would not work, unless where the inner seal lip runs may not be ground the same

    Is this what you where looking for https://www.123bearing.com/bearing-F...+Vehicle+Parts

    Mactec54


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DIY Belt driven Brushless Spindle for PCB milling
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