[samsagaz]

Hi guys, i purchased a BK12 and BF12 with Ballscrew to use in my Z Axis.

Im trying to figure how mount it, when i roll the ballscrew the nut come very tight, the BF12 come with some spacers but or aim using it bad or dont works.

Can someone know some doc or video about how are the right way to mount it?

Thanks in advance

[samsagaz]

i read this, http://www.rollmannbrgs.com/THK/pdf/...%20BF%20FF.pdf but looks like my BF Support Unit come with two spacers, and in that pdf i just see one, is OK to use one spacer on each side of the bearing?

[louieatienza]

You only need the spacer on the side with the locknut. The screw should slide into the seal in the other side (the shoulder past the bearing journal). Speaking of which, you should be sure that the shoulder is butted up against the inner bearing race.

Now, if these are the Chai bearing blocks, I had a couple and they ran pretty tight. It seemed the locknut was pressing against the seal, causing tightness. If you disassemble the bearing plate, you can find a socket close in size to the seal and "tap" it down a little to get more clearance.

[samsagaz]

thanks i dissasemble the bearing plate and found that the seal are not straight, is that OK?

other thing taht i found are the quality of the bearing not good, try to remove the bearing with hand without luck, try using an screwdriver and not lucky either.

is possible to change the bearings?

[samsagaz]

checked other bf-12 and the seal are straight. looks like its one of the problem of this unit.

[samsagaz]

removed the seal, and put it again in the right way and now are better, but still getting very tight after a few turns of the ballscrew.

[Walky]

Remove the seals, sand the IDs so the spacers don't get caught on the rubber, then sand the lower side of the seals (just rub the whole seal against sandpaper) to reduce its height so it can sit lower and not rub with the locknut either, this is important as the friction can cause the locknut to come loose (just be sure to clean the seals before reassembly so no rubber dust gets into the bearings). I've fixed lots of blocks this way. Even doing this only to the locknut side seal should make a huge difference. If you can't remove the screw side seal, just leave it there; under no circumstances sand a seal without removing it first.

I'd also grease the bearings while I'm at it.

You CAN remove the bearings from the blocks (at least Chai's), but you need to know what you're doing or you risk taking the bearings apart (as they are angular contact bearings the balls can fly off it you push the ID or OD from the wrong side). If you don't feel any axial play in the screw/block assembly you probably shouldn't try to remove them (otherwise you'd have to add a 12mm ID shim between both bearings and/or a 28mm OD shim on the cover side, but that's another story).

Out of all the chinese components I've tried the blocks are the ones which need the most rework, but once they're done they are nice and smooth.

I will make a tutorial for this once I'm able to get components for a new build. I'm writing a document about chinese components and their recommended modifications that should cover most issues people have with them, but there's still stuff to do; once it's ready it will become a thread here.

[samsagaz]

Remove the seals, sand the IDs so the spacers don't get caught on the rubber, then sand the lower side of the seals (just rub the whole seal against sandpaper) to reduce its height so it can sit lower and not rub with the locknut either, this is important as the friction can cause the locknut to come loose (just be sure to clean the seals before reassembly so no rubber dust gets into the bearings). I've fixed lots of blocks this way. Even doing this only to the locknut side seal should make a huge difference. If you can't remove the screw side seal, just leave it there; under no circumstances sand a seal without removing it first.

I'd also grease the bearings while I'm at it.

You CAN remove the bearings from the blocks (at least Chai's), but you need to know what you're doing or you risk taking the bearings apart (as they are angular contact bearings the balls can fly off it you push the ID or OD from the wrong side). If you don't feel any axial play in the screw/block assembly you probably shouldn't try to remove them (otherwise you'd have to add a 12mm ID shim between both bearings and/or a 28mm OD shim on the cover side, but that's another story).

Out of all the chinese components I've tried the blocks are the ones which need the most rework, but once they're done they are nice and smooth.

I will make a tutorial for this once I'm able to get components for a new build. I'm writing a document about chinese components and their recommended modifications that should cover most issues people have with them, but there's still stuff to do; once it's ready it will become a thread here.

Gracias Walky!!!!

Maybe i can help to make some tuts, at least if i can understand all that you type (my english is not very good), now im going to travel for mm 5-6 days, after back will try to get the bk unit working smooth, i have components to build at least 2 machines. I spend lot of money like 1 year ago, and not have time to start working with it.

And yes, tha BK are from Chai.

[Walky]

I'll try to take a few mock-up photos of the sanding procedure, it would be great if you can make videos or something based on them while fixing your own blocks.

Buena suerte en tu viaje

[samsagaz]

Send me the Photo, i will make the vids 1080p =)

[Walky]

Great, I'll post them during the week. :cheers:

[Pplug]

I have also run into the same problem with my Chinese bearing blocks from Chai. I had to put shims between the bearings due to the lateral play. Ive also noticed over time they loosen significantly. I've also replaced those bearings with quality AC bearings and have not had a problem since.

[Walky]

Ok, here are some pictures. I decided to give another shot at removing the screw side seal that was to tightly pressed as to remove by the outer side so I could sand it as well, so I kind of documented a full disassembly.

This is an FK12 block, which internally is pretty much the same as the BK12.

General advice: Clean the parts as often as you can during the process, especially if you have cat hair all over the place as I do.
Another advice: You might want to reconsider just how much you want to sand if your spindle is heavy enough to cause backdriving when the machine is off. Either way, sanding the lower side of the locknut side seal is a MUST so the locknut doesn't rub so much as to eventually come loose.


The full assembly:


The straightforward part of the disassembly:


To remove the angular contact bearings I place the block over a hole bigger than the bearings themselves (conveniently enough, I used an MDF mockup of a gantry side which uses this kind of block, so alignment was a breeze):


An M8 bolt allows me to gently tap the ID of the bearings with a rubber hammer. It's a good idea to check for smooth rotation on the bearings a few times during this process, to be sure that the screw side bearing is not coming apart (this would be BAD, and if it happens with both bearings in place it would be VERY, VERY BAD):


When both bearings are out (you might only need to take out one of them, which is safer) you'll have this:


The angular contact bearings, with the internal part up. Inside the block, the thicker sides (which most likely has the bearing model and other writing) must be facing outside. Clean and grease!:


The left seal has not been modified yet, the right seal was already sanded:


Put over fine grit metal sandpaper and sand the inner face in circles.


Sand the inner part of the seal, you don't need to sand too much this time, just enough (you can test fit the spacers while at it). After all sanding is done, clean the seals! don't let rubber residues there as they can get inside the bearings later. A fine brush is very helpful to clean the inner part near the spring.


Put the screw side seal back, then the first bearing too. It can actually go deeper than this picture shows because the seal is still not flush with the inside, but once all is assembled the steel cap will press everything in place. Note that I put a 12mm ID shim over the bearing, some grease on the bearing's ID will help it stay in place.


There goes the second bearing. Press it into the block but not all the way trough, otherwise you can trap the shim off center between the bearings. Put the steel cap and put the four small screws in place (don't screw them in yet), then put the screw side spacer and the screw itself, and it will help keep the shim centered. Now press the mall screws alternating between them in a circle manner until you can't tighten them anymore, this will press the bearings further into the block. Now you have this:


Put the locknut side seal back, then the spacer. Congratulations, you've just fixed your chinese bearing block. :cheers:


Now fully grease the ballnut; after moving it back and forth for a while it should move nicely (but, as not all chinese ballscrews/nuts are the same, YMMV):

[Drools]

Thank you Walky, great picture! This does explain a few things.

[samsagaz]

Thanks Walky, will try to follow your steps, looks easy now

[samsagaz]

Ok, here are some pictures. I decided to give another shot at removing the screw side seal that was to tightly pressed as to remove by the outer side so I could sand it as well, so I kind of documented a full disassembly.

This is an FK12 block, which internally is pretty much the same as the BK12.

General advice: Clean the parts as often as you can during the process, especially if you have cat hair all over the place as I do.
Another advice: You might want to reconsider just how much you want to sand if your spindle is heavy enough to cause backdriving when the machine is off. Either way, sanding the lower side of the locknut side seal is a MUST so the locknut doesn't rub so much as to eventually come loose.


The full assembly:


The straightforward part of the disassembly:


To remove the angular contact bearings I place the block over a hole bigger than the bearings themselves (conveniently enough, I used an MDF mockup of a gantry side which uses this kind of block, so alignment was a breeze):


An M8 bolt allows me to gently tap the ID of the bearings with a rubber hammer. It's a good idea to check for smooth rotation on the bearings a few times during this process, to be sure that the screw side bearing is not coming apart (this would be BAD, and if it happens with both bearings in place it would be VERY, VERY BAD):


When both bearings are out (you might only need to take out one of them, which is safer) you'll have this:


The angular contact bearings, with the internal part up. Inside the block, the thicker sides (which most likely has the bearing model and other writing) must be facing outside. Clean and grease!:


The left seal has not been modified yet, the right seal was already sanded:


Put over fine grit metal sandpaper and sand the inner face in circles.


Sand the inner part of the seal, you don't need to sand too much this time, just enough (you can test fit the spacers while at it). After all sanding is done, clean the seals! don't let rubber residues there as they can get inside the bearings later. A fine brush is very helpful to clean the inner part near the spring.


Put the screw side seal back, then the first bearing too. It can actually go deeper than this picture shows because the seal is still not flush with the inside, but once all is assembled the steel cap will press everything in place. Note that I put a 12mm ID shim over the bearing, some grease on the bearing's ID will help it stay in place.


There goes the second bearing. Press it into the block but not all the way trough, otherwise you can trap the shim off center between the bearings. Put the steel cap and put the four small screws in place (don't screw them in yet), then put the screw side spacer and the screw itself, and it will help keep the shim centered. Now press the mall screws alternating between them in a circle manner until you can't tighten them anymore, this will press the bearings further into the block. Now you have this:


Put the locknut side seal back, then the spacer. Congratulations, you've just fixed your chinese bearing block. :cheers:


Now fully grease the ballnut; after moving it back and forth for a while it should move nicely (but, as not all chinese ballscrews/nuts are the same, YMMV):

Una última pregunta, cuanto es el espesor de la arandela? Desarmé, lijé, limpié, engrasé, armé todo nuevamente pero sin poner la arandela y no funciona muy bien, voy a ver si el lunes puedo comprar algunas para probar.

[Walky]

Es de 0.2mm de grosor.

Saludos

[samsagaz]

Thanks

[blitz355]

Ok, here are some pictures. ...

Any chance of getting these picture from you? I can reupload them so the links dont break