Best practice for tight BK12

I have some BK12 bearings and 1605 ball screws and having a problem which seems to be common.

I cannot slide the ballscrews into the bearing without having to apply a potentially large amount of force.

I don't know if this is due to the end machining on the ballscrew being a little off (hence ballscrews too big to go in the bearing) or if the bearings in the housing are out of alignment with each other (hence the clearance in the BK12 is too small to accept the screw).

Either way, I don't think its a critical problem. I see people online doing one of two things:

1) Lightly sand the ballscrews with 1000 grit sandpaper until it fits.
2) Heat the BK block to cause it to expand enough to accept the screw.

1 involves metal dust being generated. 2 involves potential damage to any plastic components in the BK12 (if there are any!).

I'd love to hear what people think is best. Or maybe there is a 3rd way?

I'm not exactly an expert on this but have a similar problem on one of mine. If the screw won't really go into the the bearings at all, then it has to be a machining tolerance issue - bad alignment between the pair of bearings would make it go in half way and then baulk - and could likely be solved by slackening off the retaining plate on the BK and wiggling. Some gentle sanding might be the cure, alternatively would putting the screw in the freezer and the BK in a warm (50deg) oven enable it to slip over I wonder??? - it would be on for good then I guess so best to get the alignment right.

I had one like that years ago and went for the light sanding option. You should be able to hold the pulley shaft end in a drill and wrap a strip of sandpaper around the journal. If you have a micrometer then aim for 11.97 - 12.00. If not then go by feel.
You will most likely need to take this apart a few times during building plus future maintenance so I wouldn't go the shrink fit route.

Given that bearings are machined very accurately you would think the shaft tolerance would be straightforward to hit.

Thanks for your thoughts guys. I think sanding sounds like the way to go - making disassembly essentially impossible doesn't sound like fun.

Unfortunately my problem is occurring on the pulley end, not the floating end. I'm struggling to think of a way to support the rod so I can use a drill to turn it. I will probably just use a bit of elbow grease - I don't think this will introduce any serious inaccuracy into the machining.

I was hoping I wouldn't have this problem as I have bought good quality Chinese parts from a well respected supplier. They were machined specifically for me as well, not off the shelf. Shouldn't really have happened, but it doesn't seem like a big deal.

Put the plain pulley end in the chuck, point the drill down to the floor, then pull the sandpaper around the journal with the other hand and start the drill.

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Originally Posted by routercnc

Put the plain pulley end in the chuck, point the drill down to the floor, then pull the sandpaper around the journal with the other hand and start the drill.

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Might be a stretch for the 1100mm ballscrew! Thanks for the tip though.

Hi, this is a message to routercnc so I hope it's going to the right person. I read the post from 2015/16 when you were just about to by your Warco lathe. You started out by saying that you had no particular reason to buy one but always wanted one. I am in exactly the same position. I have always wanted to learn how to use one and now I might be able to afford to buy one and to use the Youtube Polytechnic as my learning resource. My question is, after having it for 3 years are you still pleased with the build quality of the Warco machine. I too have looked at the second hand myfords but I would like to start on something a bit more modern and definitely metric. I would really appreciate your feedback before I buy. Please feel free to email me at [email protected]. Many thanks in advance.

See reply in electric kart thread. If you want to continue the lathe questions just add them to the 2015 lathe thread and there is a good chance I will see them. Thanks