[Iceturf]

Hi,

I recently learned that ballscrew bearing blocks (you know the kind, Bk__) can have regular bearings instead of angular contact bearings inside (especially the cheapo ones from China). I wanted to check mine out before I install them, and I want to do so without messing up the whole thing. Can someone provide some tips and pointers? Is there a 'proper' way to open up a BK10/12 bearing block, does opening one up without the right tools risk messing it up?

[handlewanker]

"regular bearings".....so high tech......you mean radial bearings instead of angular contact type.

Radials won't take thrust for any length of time, so the cheaper CNC routers from China are just fobbing you off with inferior design.......but the small teeny weeny CNC routers that are currently on EBAY for laser engraving etc can have radials on the balls crews (one only) as the thrust forces are minimal

Well, "normally" if you don't have bearings on the motor end of the ball screw that are capable of taking LOTS of heavy thrust,,,,,,ball screws are all about thrust......then you'll push the guts out of your stepper motors apart from having increasing amounts of backlash from the back and forth slop.

The bearings on the other end are a slack fit on the ball screw end that has been machined down to allow the ball screw to float end wise from expansion due to heating while working.

You "can" have 'regular" bearings in conjunction with a pair of "ordinary" thrust bearings, to cater for the ball screw thrust forces, but a pair of angular contacts are the way to go......and seals are a 100% must have.

So, the motor end has the thrust bearings and the other end the "regular" ones.

The bearing block you mention can be opened with "ordinary" tools like an Allen key etc. as the bearings are held in by the end cover plate......getting the bearings out is another matter that requires some experience to know what is in there, but they are probably just a sliding fit in the housing.
Ian.

[Iceturf]

So I opened them up and low and behold, cheap 6000Z bearings. In Every one (I had bought four Bk10 / BF 10 pairs). So now I'm wondering what kind of bearings I should look to replace them with. Angular contact bearings of the right size dimensions, or is there a particular type of angular contact bearings I should be looking for?

[Iceturf]

One of the Bk10's I popped open, I turned it upside down, and a crapload of metal shavings popped out.

One of my four sfu1204 is bent about 0.635mm, but the other three look fairly bend free (~5 thou 'wobble' and as far as I can tell, no visually noticeable bend). A bit of rust on one or two of them (very surprising to see rust).

[handlewanker]

So I opened them up and low and behold, cheap 6000Z bearings. In Every one (I had bought four Bk10 / BF 10 pairs). So now I'm wondering what kind of bearings I should look to replace them with. Angular contact bearings of the right size dimensions, or is there a particular type of angular contact bearings I should be looking for?

Hi, A housing that has angular contacts also needs to have either a shoulder to press against or a circlip groove and circlip with the cover to hold them against that face.

If the Chinese vendors are really cheap they might just Loctite one angular contact bearing in the housing....no shoulder etc...... and rely on the other one to be free to press against it by the nut on the screw end.......to save a penny is practically their total profit margin.

The ballscrew also has a thread on one end and that is the end that is in the Angular contacts......a nut holds the bearing inner races against each other and the shoulder on the ballscrew with the outer race cups facing outwards.

The other end of the ball screw is just a plain turned down section that is a sliding fit in the bearing inner race at the other end......it is to allow the ball screw shaft to float end wise for expansion etc.

You can use regular unmatched angular contact bearings that have the same OD, ID and width as the radials.....you could write an essay on bearing configurations and fitting etc.
Ian.

[Iceturf]

Alright, sounds like a plan - thanks Ian for your input - probably the biggest benefit will be getting angular contact bearings, I'm thinking 7000AC's, of the right size. On an unrelated note, I notice that the 22mm sfu1204 ballnut appears to 'wobble' as it goes down the leadscrew, even though the leadscrew is relatively straight, any clue what that is all about?

[handlewanker]

Hi, just had a browse on EBAY for the BF and BK bearing blocks......no where do they state that there are angular contact or thrust bearings fitted.

I see the BK type have a seal in them and a loose collar........this might indicate that an unsealed angular contact bearing is fitted, hence the outer seals etc.

You would need two angular contacts to do the job properly.

Normal radial bearings are sealed......but can also come as open unsealed etc.
Ian.

[Iceturf]

I guess I had assumed that Bk10 ballscrew blocks had to come with angular contact bearings, because otherwise, whats the point of having a ballscrew?

I was thinking either
2x of: https://www.bearingscanada.com/7000B...-p/Kit8872.htm per block
or
2x of: 1Pcs 7000AC High Precision Angular Contact Spindle Ball Bearing 10*26*8mm | eBay per block
or 2x of: https://www.aliexpress.com/item/10X2...AbTest=ae803_1

which claims it is P0 grade
Do you think its worth paying up for bearings canada ones, it strikes me it may be diminishing returns, but this isn't my area of expertise. I'm trying to make a PCB mill.

[handlewanker]

Alright, sounds like a plan - thanks Ian for your input - probably the biggest benefit will be getting angular contact bearings, I'm thinking 7000AC's, of the right size. On an unrelated note, I notice that the 22mm sfu1204 ballnut appears to 'wobble' as it goes down the leadscrew, even though the leadscrew is relatively straight, any clue what that is all about?

Hi, that's a puzzle.....the nut (if new) should just rotate without a wobble......maybe the wobble will disappear when the nut is in it's housing and supported squarely on the balls crew......if the nut has been used a bit it might have some slackness.
Ian.

[handlewanker]

I guess I had assumed that Bk10 ballscrew blocks had to come with angular contact bearings, because otherwise, whats the point of having a ballscrew?

I was thinking either
2x of: https://www.bearingscanada.com/7000B...-p/Kit8872.htm per block
or
2x of: 1Pcs 7000AC High Precision Angular Contact Spindle Ball Bearing 10*26*8mm | eBay per block
or 2x of: https://www.aliexpress.com/item/10X2...AbTest=ae803_1

which claims it is P0 grade
Do you think its worth paying up for bearings canada ones, it strikes me it may be diminishing returns, but this isn't my area of expertise. I'm trying to make a PCB mill.

Short answer......a ball screw can transmit a load like a ball race without friction and can be backlash free....to an extent.

The plain radial bearings might suffice for PCB making as there isn't a lot of heavy thrust, so you might get away with just using new radial bearings if the others are knackered.

Having bought those housings on EBAY I assume they are unused so should be OK, otherwise new bearings of the same type......don't bother to re-invent the wheel with angular contacts as it can get a bit complicated.
Ian.

[handlewanker]

Hi, on the subject of making a PCB mill have you seen the simple My Sweety brand fixed gantry....moving table.....CNC routers currently on EBAY for approx. $230?.....work area of approx. 200mm X 150mm .....pic attached.

I'd like to build one like this with all welded steel tube.
Ian.

[Iceturf]

I had considered a mill like that - but it doesn't seem practical for me.

If you are able to weld yours together, neat! I don't have the tools / ability to do that. Let me know how it goes for you.

[handlewanker]

Hi, I already have a CNC mill and don't "need" another one, but it looks so cute I just went and started sketching a possible steel tube build on the same lines but without the extrusions to limit the design......welding is second nature to me so that's how I'm orientated.

No matter how simple you design the build, the most cost in the end lays with the electronics......save money there and you end up with no hair.......the cheap stuff on EBAY will cost you double in the end.

The EBAY model was purely designed to be DIY bolt together and once the prototype was established the rest is just stockpiling the components for sale.......my hats off to the originator.

It's designed for cost to run with GRBL......whatever that is, probably the Linux equivalent of Mach3....I don't really know.

Even with a work area of 200 X 150 it's quite respectable and would cover a lot of ground.

It would be nice to have one as a fun thing to do some fine small carving work.......I "need' another project with all the others I must do

BTW.....a half hour learning curve with a simple basic Mig or stick welder and you can open doors that were previously closed as far as design is concerned.....and steel is cheap too.
Ian.

[Iceturf]

..the cheap stuff on EBAY will cost you double in the end.

Ain't that the truth. I was looking carefully at the bearings, and I noticed huge backlash. Which despite their axial nature, seemed high. Upon closer inspection - there is a 0.22mm gap between the bearings and the bearing shelf or "shoulder" as you described it. 0.22mm!!!! Of just empty air the bearings can bounce around in - and they aren't in there tight either, a 26mm bearing inside of a 26.08mm wide slot.

Amazing - money well thrown away I guess. Too bad, I'm something thinking that three of the ballscrew leadscrews themselves seem reasonable, even with the 5 thou wobble, but everything else, total garbage. And total garbage if I have to purchase twice. You are right. ahh.

[Iceturf]

bleep

[handlewanker]

Well, you could get "crafty" and try to recover the cost by a bit of redesign work.

I puzzled out the design and why it's so cheap.........they rely on the fact that radial bearings "can" take a small amount of end thrust for light duty work but eventually become quite sloppy when used in that manner.

So, if you have a bearing block with 2 bearings you could fit a large "O" ring inside between the 2 bearing outer races ......this will exert a small amount of end force to make the 2 bearings act as angular contacts.

you will need to have a shoulder inside the bearing block for one bearing to push against and a cover plate to keep them pressed together against the "O" ring.

The cover plate will then be slightly away from the face of the bearing block by the thickness of the "O" ring.....add some washers behind the cover plate..... and the nut on the end of the ball screw will allow you to put pressure.....not too much...... on the two bearing inner races to push them together........that is a quick fix

That would make a cheap alternative to a sophisticated angular contact design proper......the radials will still be good for a long life as they are lightly loaded in that configuration but normally would develop end slop without the springiness of the "O" ring to apply constant back pressure to stop end play.

The "O" ring is fairly hard rubber but still resilient enough to not be compressed by the end thrust of the ball screw.

The bearings MUST be sealed type to stop crap getting in and lubed for life etc.
Ian..

[Iceturf]

Hi, I already have a CNC mill and don't "need" another one, but it looks so cute I just went and started sketching a possible steel tube build on the same lines but without the extrusions to limit the design...

My design is similar to the photo graph you posted - how ever I'm planning on a gantry that moves back and forth. Also out of aluminum (light duty) because its only for PCB's. Steel and aluminum parts hybrid is my plan. We'll see how well it works out I guess. I'm thinking about aliexpress HGR15 450mm linear rails with 2x blocks per rail - do you think china HGR15's are enough quality for this task?

[Iceturf]

So, if you have a bearing block with 2 bearings you could fit a large "O" ring inside between the 2 bearing outer races ......this will exert a small amount of end force to make the 2 bearings act as angular contacts.

Yes - I agree this sounds like a good plan. I don't know how well the axial bearings will do long term, but if it works for a few years of light use, then I can slowly replace the bearings or bearing blocks to something better. I hate that I feel ripped off right now though. I can "make" something work, but I don't like re-inventing an all in one solution.

[handlewanker]

Hi....we might have solved the simple thrust bearing housing for mills and routers like this using cheap radial bearings as they come with seals.

BTW, you still have to mount the stepper motor on the bearing block, so the design must take this into consideration........some of them have 4 stand offs to mount the motor against.
Ian.

[handlewanker]

Yes - I agree this sounds like a good plan. I don't know how well the axial bearings will do long term, but if it works for a few years of light use, then I can slowly replace the bearings or bearing blocks to something better. I hate that I feel ripped off right now though. I can "make" something work, but I don't like re-inventing an all in one solution.

Well, providing the work load is light the radials will last for a long time,. and the "O" ring solution will allow this to happen......worth a try.
Ian.