How to mount bearings?

[jimluu]

I've bought a set of mounted bearing blocks for my ball screw. The fit seems really tight. Before I ruin it by forcing it onto the shaft, does anyone know of a way to slide the bearing without much force?

[mxtras]

Assuming they are correct for the shaft and the shaft is appropriately sized and finished, assembly should be easily accomplished by freezing the shaft and warming the bearings.

Scott

[jimluu]

Thanks for the quick response. My ball bearing is 6fth long, can't stick in freezer. Will dry ice work? Will a curling iron work to heat up the bearing? I take it that once fitted, it's not possible to remove the bearings?

I might as well ask....one of the ends of my ballscrew is 1 inch. My bearing is 25mm. Will this freeze/heat process be enough to fit them together or do I need to grind down the shaft?

[mxtras]

Oh boy.

1" = 25.4MM

If you did manage to get the bearing onto this shaft, it would be completely destroyed.

Producing the correct bearing mounting conditions is every bit as important as selecting the correct bearing for the application. Locate the bearing numbers and dig into the designed mounting diameters for that particular bearing. Too large of a shaft or too tight of a bore will destroy the bearing. Look into the specs.

Scott

[Zumba]

Was 25mm a typo?

You need to get yourself a micrometer...

[jimluu]

Originally Posted by mxtras Oh boy. 1" = 25.4MM If you did manage to get the bearing onto this shaft, it would be completely destroyed. Producing the correct bearing mounting conditions is every bit as important as selecting the correct bearing for the application. Locate the bearing numbers and dig into the designed mounting diameters for that particular bearing. Too large of a shaft or too tight of a bore will destroy the bearing. Look into the specs. Scott

thanks. I found a 1" bearing that would fit in the bearing block. I guess I'm still not sure about how tight a bearing should fit. Do you have to heat/freeze to make it fit? or are they supposed to slide onto the shaft with little resistance?

[mxtras]

What are the numbers and manufacturer of the bearing?

Scott

[jimluu]

Misumiusa bun25 and bsw25

[mxtras]

Ok. It appears that it is a reasonably good grade of support bearing. Good. This means that you need to do it correctly otherwise you could end up destroying the bearing. Mounting spinning stuff accurately requires precision otherwise you may as well just use the cheapest bearing money can buy. You have a good thing - don't ruin it right out of the box.

https://fa.misumiusa.com/gwos/catalo...ODUCT_ID=10338 (takes a while to load, but this is your bearing.)

The bad news - it is Metric. Your shaft needs to measure 25.00MM, not 25.40MM. I cannot find any tolerances on their site for the shafting, so there are two ways to do this:

One - contact them and simply ask for technical service, then ask for the shaft tolerance. They will have this information and it's a normal part of customer service.

Two - have the shaft accurately ground to 25.00MM -0.005MM +0.00MM. Notice these are fairly tight tolerances but if you do not know what it should be then you are best to err on the safe side.

That's the best help I can offer.

Scott

[Zumba]

Hey Scott, do you think the .005mm tolerance is necessary for a ballscrew? The cosine error of a ballscrew is minimal even if the radial runout is 5 times that (around .001"). I would shoot for -.0005" or -.013mm. That's more than enough for ABEC 1 and 3 bearings, which is what I use for ballscrew supports.

Of course, if the ballnut travels all the way to the end of the screw where the support block is, it could load the bearings excessively. That's why I always leave a few inches. That way, the screw is free to flex ever so slightly (half thou) and minimize wear on the bearings.

[mxtras]

Originally Posted by Zumba I would shoot for -.0005" or -.013mm.

You are probably closer to reality. I spent 14 years at a machine tool manufacturer where .01MM was considered sloppy for cylindrical grinding. I am a bit biased towards the tighter end of precision.

I agree the shaft could likely be less w/o issue.

I am guessing these bearings are better than ABEC5 - my guess is 7. At this point, I am doing nothing but guessing!

Scott