[Spinnetti]

How the H#@@ are you supposed to tighten these things? There's a odd nut that takes some kind of spanner I don't have, and nowhere to grip on the screw.... I ended up grinding some flats, but I tightened the S&^$ out of it and still have end play. How's this supposed to work? Is there supposed to be a crush sleeve inside or?

TIA....

[psykhon]

I didn't have any problem with mines, please tske some pictures and Ill try to help you
Did you bougth it from chai?

[Zach_G]

The angular contact bearings in it are not a matched set, plus on a couple of mine the bearing hole was bored too deep. I had to shim several thousandths using arbor spacers from mcmaster (not the perfect size but close) between the inner bearing races and the outer races/bearing block. Be careful if you disassemble the housing and press out the bearings. If you press on the inner races, you'll likely separate the bearings at which point they're scrap metal. Fortunately VXB sells replacements cheap. The rubber seals also press out.

[cyclemadkiwi]

I assume you are using a "BK" style bearing block!

The last one I got from Ebay was so bad I had to make the whole thing from scratch! As Zack said, the bearing seat was bored too deep (Had a turned down washer as a spacer) The bearing in there were not the correct angular bearings so not matter how tight you do them up there will be end float! It also had no seals in it.

I made a new block, bought some good quality angular bearings and all I used from the one I bought was the nut. To get a matched set of angular bearings is VERY expensive so I used two standard ones and it all worked sweet.

All I can say is buyer beware!

[Spinnetti]

Dam n... thanks for the tips.. I did get from Chai. Such terrible packaging. my z-axis screw was bent Sh*$less. I got it close, but spent more time messing with this junk than it was worth. I always think its me on this stuff, and its just crap that doesn't meet its published spec - not even close!

I don't see how you are supposed to tighten them down at all. On one screw I ground flats (I don't like that) and the other I have quite a bit of screw that's not used - I used a pipe wrench on that - I liked that even less!

My x-axis simply will NOT tighten down, and as you suggest, it probably needs a spacer. I got it to a couple tho, which may be all right. I'm able to force a move, but maybe under my typical cutting loads it might be alright. If not, I'll do like you said and scrap it and make my own end block (GRR).

[millermatt]

Hi all
I have recently purchased the same or similar screws and bearing for a new machine I'm building. I have only had the screws dummy mounted to check my hole positions. I have noticed a few similar problems you guys have mentioned.
First was the complete lack of seals in the fixed end block. I checked my local SKF supplier and was told that there was no off the shelf seal that would fit because of the narrow width and the odd size that the supplied spacers are machined to.
Next was the lack of a greasing or oiling point. I plan to fix both of these by turning up some press-in o-ring carriers, one of which I will put a grease nipple in.
As for the end float, mine seem to be OK, but I haven't put them to any real test....yet.
Oh, as a warning to all purchasers of such ball screw, NEVER , repeat , NEVER take the ball nut off of the screw. You will end up with tiny little balls bouncing all over the floor of your shed and spend the next 4hrs trying to put the wretched thing back together.
So if anyone has anyway of greasing the ball nuts without removing them I'm all ears.

[Zach_G]

It's probably good Chai stopped shipping them with seals. I actually removed them because they were so tight they generated enough friction to start smoking! My fixed end blocks are well protected so I'm not concerned about contamination. The bearings are only like $5 anyway.

You can take the ball nut off the screw, just make cylindrical carrier with diameter matching the ball nut grooves to thread the nut onto. I just rolled up some paper. Also, my ball nuts came with a little package of grease nipples which thread into a hole on the side of the mounting flange. Could also just apply grease directly to the screw.

[Spinnetti]

Good grief.. Finally got my lathe conversion done, and these stupid ball screws have more than .020 backlash in them. That's worse than the Acme screws I started with! Anybody know of end blocks that actually work?

[millermatt]

Oh.
I still haven't put mine to the test yet, but I certainly hope I don't have that problem or I will be pissed off!!!!!
As a possible fix for yours, you could put a shim between the outer races of the 2 bearings in the end block. If you have .020" end play I would put .025" shim between them, effectively giving you .005" of possible crush, or room to set preload.
Cheers
Matt

[Spinnetti]

Oh.
I still haven't put mine to the test yet, but I certainly hope I don't have that problem or I will be pissed off!!!!!
As a possible fix for yours, you could put a shim between the outer races of the 2 bearings in the end block. If you have .020" end play I would put .025" shim between them, effectively giving you .005" of possible crush, or room to set preload.
Cheers
Matt

Yep, I'll try that next.. I can't even set backlash its so spongy. Crappy thing is, I bought this stuff to make it better not worse, and now I've wasted weeks of effort and money to convert the dang thing.

[millermatt]

I feel for you with the wasted time and money. I just hope you can get them working without too much effort. And I certainly hope mine don't turn out the same.
Good luck
Matt
PS let me know how you go

[Spinnetti]

I feel for you with the wasted time and money. I just hope you can get them working without too much effort. And I certainly hope mine don't turn out the same.
Good luck
Matt
PS let me know how you go

I put a .007 shim between the bearings, and it works, but still with .009 backlash. Also had to slow the ramp up speed way down as it has a lot more drag now too. Its horrible. Z axis is the same. The cheap 5/8" screws I got off McMaster with original end bearings on my Grizzly lathe were much better. I'm thinking I'll get some tapered roller bearings in my own block (like car wheel bearings)....

[ninefinger]

Let us know if you do the tappered roller bearing thing. I am thinking of doing the same with my z-axis first and then maybe the x and y. I've shimmed and F'd with the x and y to where they are ok but not great and backlash comp can keep my sanity in check. Z is a disaster and the backlash has cost me alot in broken stuff (small mills and drills don't like to jump down 0.040" mid cut).

I really think the cheap AC bearings are not the right contact angle and can't support the load properly - even the replacements from VXB. They are the shallow contact angle and are meant for a light thrust load and more radial load where as a ballscrew support is mostly the other way round (high thrust and relatively light radial load).

IF anybody has a better design (than the BK type) for ballscrew support they'd like to share I'm all eyes and ears.

Mike

[psykhon]

I bought the ff/fk types from chai and have less than 0.007 with stock bearing. Ill replace the bearings with something better in the future and will post my results in here, maybe in the next 30 days, but so far I think they are ok for the money.
By the way, my screws are 1605 and bougth 2 nuts for each screw but currently use only one,plan to put the seccond with some preload asap