Fixed Bearing w/ Belleville washers

[CNCDevil]

No offense taken at all

I will then try to make this setup and post some pictures of my work.

Thanks to everyone.


CNCDevil

[Mike Everman]

Go go, man. Should be fun. My time in front of a machine is golden, too. Maybe that's because I don't make my living at it. Good luck!

[dpuch]

I have found you can get some matched SKF bearings for pretty reasonable price, and avoid all the trouble. No spacers needed for ball screw (lead screw) applications.

http://www.skf.com/portal/skf/home/p...&newlink=1_3_2

[mackeym]

An alternative to bellevill washers is to use aluminum foil spacers between the outer races (for DB). Thickness tolerance of the aluminum should be adequate. The cheaper the aluminum foil the thinner...the thinnest i've found is about 10um. Alternatively, here is a company that sells various thicknesses of aluminum foil: http://www.lebowcompany.com/foils_list.htm#ALUMINUM*.

The trick is to determine the right thickness for the spacers. One could estimate this from values given for similar sized duplex bearings. Alternatively, you could try to measure the axial stiffness of your bearings (or use the spec. if its given somewhere). It should be noted that the actual preload clearance may not be equal to the thickness of the aluminum foil (since the inner and outer race faces may have some offset due to manufacturing variance). With carefull micrometer measurements of the total width of the inner and outer races under various conditions, it may be possible to get the right preload.

I know NC cams tried this in the past without success, but i don't see why it shouldn't work. It has to be one of the cheapest ways to get a preload. This method also allows the bearings to have zero radial clearance on the shaft.

[dpuch]

Originally Posted by mackeym An alternative to bellevill washers is to use aluminum foil spacers between the outer races (for DB). -snip- I know NC cams tried this in the past without success, but i don't see why it shouldn't work. It has to be one of the cheapest ways to get a preload. This method also allows the bearings to have zero radial clearance on the shaft.

I can see one possible reason why the foil would not give good results. Aluminium foil is typically a pretty soft alloy. With either much axial load, or and minute wobble of the bearing on the shaft will work the foil even thinner over time. Definitely do not try this for anything at higher RPMs

While I do not recommend it... see my comment above. Steel shim stock is probably a better alternative. If you need less than 0.0005" your probably not going to be able to measure it well enough anyhow.

A side issue is getting a good clean circular cut. The cut will leave some minor burr regardless, and needs to be outside the contact area of the race. Otherwise it will potentially throw off the thickness and most likely the alignment of the race a very small amount.

[Belding]

I am not sure if this setup would work. Any tightening of the locknut would cause a loss of the spring pre-load. And if you don't snug the locknut, you may introduce some lash.

Zac

[Maurice Proulx]

CNCDevil, you wrote in your first post:

''.........as you can see on my drawings, the bearings are seperated with two Belleville springs in series. Combusting the washers with 75% of their span, gives a preload of 1170N. The preload is forced onto the two bearings, given that they will each be dealing with 585N. ''

Please correct me if I am wrong, but the preload force on each bearing will be 1170N and not 1170N/2=585N.

Two BW installed as in your attached thumbnail will produce a preload equal to one washer but will double the lenght of the possible compression.

Maurice

[mp3]

CNCDevil

Did you obtain any results, good or bad, from your trials using the Belleville preload washers with the angular contact bearings.

Malcolm