angular contact bearing selection

[ShentParticipant @shent]

Hi All, hope you had a great Christmas.

I am starting to draw up the designs for a cnc conversion of my mill, I have most of the purchased hardware but I am sketching out the plates and ballnut mounts now and have hit a bit of a wall so need some expertise.

1. I know the likes of SKF are the best ACB's but has anyone used another (preferably cheaper) manufacturer such as dunlop etc?

2. Can I use a double row ACB instead of 2 single row ACB's? I have an x screw which can take bearings at both ends but the y and z can only take bearings at one as the other end just floats.

Any help would really be appreciated.

Thanks

Mark

[ShentParticipant @shent]

[Ex contributorParticipant @mgnbuk]

IIRC "proper" ballscrew support angular contact bearings are a different contact angle to "regular" versions – 40 degrees springs to mind, versus 25 degrees for the standard types. At my last employment we used to specify IBC cartridge bearing units that came in a housing with a flange like these

Similar units of Chinese manufacture are readily available from Ebay & the likes at far more hobbyist friendly prices like these

Be aware that the "fixed" end bearings are the ACs – the "floating" side is just a standard single row ball bearing.

Both flanged bore fitting and flat surface pillow block mounting types are available. At the kind of pices these go for I wouldn't bother trying to make my own.

Nigel B

[ShentParticipant @shent]

Thanks Nigel, never knew about the difference in angle needed for these. Due to the limitations that I have regarding the length of the ballscrew I need to make my own housing for them, no issue (in theory) with getting that done, just didn't know if I could get away with 1 double row instead of 2 singles. Good to know that I dont need a third at the floating end though.

[Ex contributorParticipant @mgnbuk]

If we were battling space limitations we used INA ZARF or ZARN bearings ZARF

ZARN

but not hobbyist friendly prices. You could make up something similar with a drawn cup needle roller bearing for radial support & back to back needle roller thrust bearings either side. This should give a more compact arrangement than angular contact bearings.

Nigel B

[HOWARDTParticipant @howardt]

Having designed linear waxed ballscrew slides over the most of the last 30 years, my twopenerth for what it is worth. I will say that obviously working life was the most important factor along with rigidity and positional repetition as the machines we built were heavy high production machines cost was not too important.

As a hobbyist cost can be the most important, but the final design needs to give satisfactory results. The ballscrew needs to be mounted such that the drive end maintains concentric running with the motor, within any couplings allowable deviation. It also needs to run so that the axis is true to the ball nut, some require greater accuracy than others. The tail end can either be unsupported or supported, depending on length/diameter/speed. Look at the manufactures catalogues for guidance, you only need to look at one toggle you the idea, SKF, THK, Thompson etc.

The easiest way is to mount a standard ballscrew bearing block and directly mount the flange of the motor to it with a servo class coupling between. Mount a single sealed ball bearing in a block to support the other end of the ball screw. To fix the nut to the slide, make a block with a slot that will fit over the ballscrew and a bore through that is clearance on the nut. That way you can drop the slide over the ballscrew with it all aligned to the ways. The face of the block should be mounted to the slide with a key across it, this ensures that the block is square to the sideways.

Bt all means use what ever angular contacts you want, just make sure the assembly is stiff and adequately sealed for the environment. The biggest test will be making sure the ballscrew is mounted parallel to the ways in all directions and remains there when the slide is mounted. So you need to ensure that you can mount all three parts and fix in position before amy slide is mounted.

Read the catalogues and it may make sense.

Howard

[old martParticipant @oldmart]

I have dealt with Simply Bearings in the last six months and can recommend them. They have a huge variety at all prices and unless your machinery is going to be used for production, the premium ones will not justify the expense.

**LINK**

[KW56Participant @kw56]

I used cheap angular contacts from Simply Bearings but I had to use a 0.2 shim between the bearing outer rings to achieve close to zero backlash. The housings I machined myself.

[ShentParticipant @shent]

Thanks for the resonses all. It's only a hobby machine Nigel so couldn't justify commercial grade prices but thanks for the link bud, figured out a way to reduce the depth of the whole assembly, i'm going to thread one end of my coupler. Think i have the design down decentlyl for the x axis Howard, Left some movement when screwing the bearing plate to the table by the way of slots as I wont be able to get everyting bang on…..especially first time around. Using some couplers that will allow for some misalignment of the stepper shaft and ballscrew so should hopefully be ok and took all measurements from ground, mating suraces only. Thanks mart and KW56, just been looking at simply bearings, if i need to get some more bearings in the future could upgrade but i think what's on that site will be fine for now.

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