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dsalihi2
06-06-2012, 01:57 AM
I just received a 1605 ball screw and bk/bf bearing mounts. My question is how tight of a fit should the bearings be on the machined ball screw. Testing the fit the amount of force required to slide the screw into the bearing seams is quite large after it is inserted a couple of mm. If this is meant to be a tight interference fit? What is the best way to drive the shaft thru the bearings without damaging the bearings?

Walky
06-06-2012, 02:30 AM
I usually use fine sand paper to make it easier to fit (wrap the shaft with it and spin the screw uniformly), it has worked great so far.

Also, if the blocks feel too tight (quite common with chinese blocks) you can sand the inner side of the seals (so it rubs less), and the outer side of the metal spacers. Just try not to get rubber dust into the bearings. This usually makes a BIG difference.

If you feel axial play on the blocks (the screw moves back and forth when mounted) you might need to add one or maybe two shims to the blocks (OD shims go between the seals and the internal bearings, while ID shims go between the angular contact bearings (in most cases all play would be gone by adding one there to add a light preload, as two might create too much preload and make the bearings even harder to spin), never use an OD shim between the bearings, as it can damage them.

Those modifications will allow you to get the most performance and precision out of your ballscrew/block assembly.

Also, try not to get the nut out of the screw (the balls will fall). When spinning the screw for sanding it's common for the nut to move along the screw, and it can go dangerously near the end of it if you're not careful.

dsalihi2
06-06-2012, 10:01 PM
Thanks Walky a small bit of sanding worked. Nice and tight but not excessive. I don,t feel any play so I don't think I need shims but just in case I have a couple of questions. Where are typical places to find bearing shims? When you say between the bearing, I assume you mean to disassemble the block and remove one of the bearings. Do the bearings come out of the housing easily when the 4 screws are removed or are they a press fit?

Thanks

Walky
06-06-2012, 11:00 PM
Thanks Walky a small bit of sanding worked. Nice and tight but not excessive. I don,t feel any play so I don't think I need shims but just in case I have a couple of questions. Where are typical places to find bearing shims? When you say between the bearing, I assume you mean to disassemble the block and remove one of the bearings. Do the bearings come out of the housing easily when the 4 screws are removed or are they a press fit?

Thanks

I get them in a local place that sells stuff for car repair (bolts, screws, taps, drill bits, hoses and stuff like that), I think mine are about 0.2mm thick. I guess McMaster Carr must sell them in the US.

The bearings are a press fit, but they can be removed (you can safely remove the cover). The bearings are a pair of angular bearings placed back to back. Depending on you tight are the bearings on the housing it might be harder to take them out, because the balls can fall off if forced too much (it happened to me, and it took me a while to put them together). The ID of the bearings can get loose if pushed towards the center of both. This means that if you only have one AC bearing and hammer the ID towards where the other bearing is supposed to be, it can come apart, no good!

To get both AC bearings out of the housing I hit the ID from the closed side (you need to remove the metal spacers first), very carefully and lightly using a rubber hammer and a bolt (a proper spacer would be better), it's very important to do it carefully to prevent the deeper bearing's ID from coming loose (the one you're hammering); it would be safer to press the OD, of course, but on the bottom side of the block it's not accessible. The harder the bearing is press fit into the housing, the easier it is for it to come apart (with the balls falling off) when hammering it. After installing the shim between the bearings (you'll want to put something through the center so it doesn't go off center when reassembling) you'll need to press/hammer the OD of the front AC bearing (the one near the cover), you can even use the cover itself to some degree since it has a border that makes contact with it. After certain point of reassembly you can use the four small screws to press the bearing the last mm or so, alternation between them while turning them lightly, so the cover presses the bearing evenly. Hammering the cover side bearing on the ID to press it back in would be the worst idea, since it could come apart and then the ID would fall between both bearing and you'll need to somehow pull the OD out to be able to reassemble the bearing.

Might be a little hard to visualize without pictures, though. I plan on making a tutorial next time I make a machine using those.

All of the above is based on chinese blocks. The "real" BK/BF/FK/FF blocks are said to be really good out of the box and not supposed to require any modification (but cost much more).

Walky
06-06-2012, 11:05 PM
Thanks Walky a small bit of sanding worked. Nice and tight but not excessive. I don,t feel any play so I don't think I need shims but just in case I have a couple of questions. Where are typical places to find bearing shims? When you say between the bearing, I assume you mean to disassemble the block and remove one of the bearings. Do the bearings come out of the housing easily when the 4 screws are removed or are they a press fit?

Thanks

I get them in a local place that sells stuff for car repair (bolts, screws, taps, drill bits, hoses and stuff like that), I think mine are about 0.2mm thick. I guess McMaster Carr must sell them in the US.

The bearings are a press fit, but they can be removed (you can safely remove the cover). The bearings are a pair of angular bearings placed back to back. Depending on you tight are the bearings on the housing it might be harder to take them out, because the balls can fall off if forced too much (it happened to me, and it took me a while to put them together). The ID of the bearings can get loose if pushed towards the center of both. This means that if you only have one AC bearing and hammer the ID towards where the other bearing is supposed to be, it can come apart, no good!

To get both AC bearings out of the housing I hit the ID from the closed side (you need to remove the metal spacers first), very carefully and lightly using a rubber hammer and a bolt (a proper spacer would be better), it's very important to do it carefully to prevent the deeper bearing's ID from coming loose (the one you're hammering); it would be safer to press the OD, of course, but on the bottom side of the block it's not accessible. This pushes both AC bearings. The harder the bearing is press fit into the housing, the easier it is for it to come apart (with the balls falling off) when hammering it. After installing the shim between the bearings (you'll want to put something through the center so it doesn't go off center when reassembling) you'll need to press/hammer the OD of the front AC bearing (the one near the cover), you can even use the cover itself to some degree since it has a border that makes contact with it. After certain point of reassembly you can use the four small screws to press the bearing the last mm or so, alternation between them while turning them lightly, so the cover presses the bearing evenly. Hammering the cover side bearing on the ID to press it back in would be the worst idea, since it could come apart and then the ID would fall between both bearing and you'll need to somehow pull the OD out to be able to reassemble the bearing.

Might be a little hard to visualize without pictures, though. I plan on making a tutorial next time I make a machine using those.

If you have the proper tools to pull the ID of the cover side bearing to remove it, all should be pretty straightforward and safer than what I do.

All of the above is based on chinese blocks. The "real" BK/BF/FK/FF blocks are said to be really good out of the box and not supposed to require any modification (but cost much more).

dsalihi2
06-08-2012, 08:21 PM
Got it. Sounds like a job I dont want to attempt unless necessary.

Thanks for the very helpful information.