This thread is a question about mounting unmatched A/C bearing in a homemade housing, using Belleville washers to achive a so called "Constant Pressure Preload".
I know that this is just another thread in the line many, but I couldn'd really find alot of posts where this subject is discussed in detail.
In the early stage of building my new router, I decided to make my own fixed bearings units, because they were awfullly expensive. How hard could it be just to mount two bearings in a housing? - Now I have learned why
The nuts and screws, which are the heart to accuracy of the system, won't be to any good, without the use of proper bearings. I just mean, that the quality of the bearing setup, should equal the quality of nut/screw. My learning curve regarding A/C bearings have been quite vertical these days.
A week ago, I bought some NSK/IBU 7201 B A/C bearings from Ebay, to use with my 16mm ball screws. As I was digging into the subject of fixed bearings, I got pretty frustrated. I've found out that it is impossible for me to make a decent DB or DF preload configuration. As the more "educated" person can see, there is not given a lot of details about the bearings, with good reason. They are of course unmatched, leading to the fact that it is difficult to preload them properly in either a DB or DF configuration.
I've wrote NC Cams to give his opinion on just setting some preload on the bearings with a torque wrench, but he told me to buy matched pairs and fabricate exact spacers, otherwise I could easily ruin the bearings, because preloading with a torque wrench was too unpredictable.
Problem is, that I don't think it's possible for me to make those spacers precise enough. Another problem is the money required to buy those matched bearings.
Well, here is the deal (and please correct me if I'm wrong)
When reading on the NSK homepage, I saw this Constant Preload configuration and this seems to be my only way out. 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.
The force from the ball screw is around 200-300N, so the preload should be heavy enough to withstand that force in either direction, or?
The nominal heavy preload for that particularly bearing is 78.5N, but I assume that 585N will not be any deal to the bearings? Does that EXTRA HEAVY preload affect the bearings in a negative way? Important is, that the bearings are always preloaded, I guess. This should just be a way to have some kind of control over the situation.
Long thread, I know. Hopefully it can be useful to other members.