[taskman]

Hi

The ballscrews that I ordered arrived today. Actually the second batch because the first batch was cut completely wrong. The guy thought 14 is the same as 41

So my question is, this new batch is 50 micron or so out and doesn't fit in the ball bearings. I started sanding them off to make them fit. Is this normal?

The BK bearing, the big one that is closest to the motor, has 2 metal inserts. Do I leave the inserts in there or take them out?

I have a sleeve that screws onto the top of the ballscrew. It seems it will sit on the one metal insert I mentioned in the above paragraph. It might touch the rubber part that the metal insert sits inside. Is that right? Should the weight of the ballscrew be balanced between the sleeve that you screw on and the adapter between the ballscrews and the motor? The ballscrew will be used for the Z. It is a 20mm ballscrew and I will attach it to a Neva 23. Can't imagine it can be good for the motor to have maybe 10kg hanging from it. Since the BF bearing allows the ballscrew to expand and it doesn't take any of the weight

[wendtmk]

Are you sure the ballscrews weren't machined to be pressed into the bearings?

Mark

[louieatienza]

I'd have to agree that the bearings are normally press-fit or the inner races heated. For the fixed end you only need one spacer, at the end, and the lock nut rests against that spacer. The motor is usually placed at the fixed (BK) end.

[taskman]

How do I press fit the BK? I will burn the rubber if I heat up the BK in the oven. Do I need to buy dry ice to cool down the rod?

I am building a machine I want to kickstarter and it will be a kit. Not sure I can expect each customer to press fit the ballscrews and I have heard horror stories where someone received a ballscrew with the bearings already fitted, but the ballscrew was completely bent

[Spk64]

Hi
The BK bearing, the big one that is closest to the motor, has 2 metal inserts. Do I leave the inserts in there or take them out?

Some of the fixed ends we get from Misumi have a spacer on each side that provides the sealing surface for the seals mounted in the blocks.


Steve

[taskman]

What is supposed to carry the weight? The pressed fit bearings, or the spacer or the adapter to the motor or will they all just share the weight over time?

All I can think of is to sand off the ballscrew and then at the last 10 micron or so, bind ice packs around the tip for some time and hope the ice can reduce the last 10 microns to 0 before it melts

[ger21]

The bearings are not pressed on. The nut holds the bearings on the screw tightly, and the block holds the bearings

[taskman]

So if I sand off a micron or two too much I am not going to ruin my whole machine then. How much weight can a 20mm ballscrew with a BK and nut normally take before it deforms seriously? I assume at the start thigns deform anyway a couple microns and stay there. So you should probably let everything stand for a day or two before you calibrate the machine?

So all the weight actually sits on the inside diameter of the bearing? Since the ballscrew hangs off the nut, the nut sits on the spacer and the spacer sits on the inside of the bearing

[taskman]

Another question. Can I just place the BK on top of the rod and then the nut over it and screw the nut in and while I screw it in, it will press the BK down or will I damage something like that if it is an extremely tight fit as it is now?

[Spk64]

I would just polish it some with 400 grit. Mine were a little snug took very little polishing to get a nice fit.
You will regret not doing this if it has to take back apart or you get it half way on and it will not budge any further.


Steve

[louieatienza]

So if I sand off a micron or two too much I am not going to ruin my whole machine then. How much weight can a 20mm ballscrew with a BK and nut normally take before it deforms seriously? I assume at the start thigns deform anyway a couple microns and stay there. So you should probably let everything stand for a day or two before you calibrate the machine?

So all the weight actually sits on the inside diameter of the bearing? Since the ballscrew hangs off the nut, the nut sits on the spacer and the spacer sits on the inside of the bearing

Well if you can sand the bearing journal concentrically, you'll be fine. I guess with a C7 ballscrew it should be fine. The two angular contact bearings under preload are what keep the inner races (and ballscrew) fixed axially.

As far as calibrating, if you do a lot of 3D where there will be a lot of Z movement, the screw can actually grow in size as it warms up (which is why the free end is designed as such.) You may want to run a "warm-up" routine on your machine, before calibrating....

[louieatienza]

How do I press fit the BK? I will burn the rubber if I heat up the BK in the oven. Do I need to buy dry ice to cool down the rod?

I am building a machine I want to kickstarter and it will be a kit. Not sure I can expect each customer to press fit the ballscrews and I have heard horror stories where someone received a ballscrew with the bearings already fitted, but the ballscrew was completely bent

No, you would disassemble the bearing unit, keeping track of the orientation of the bearings. You slide the bearing housing in first, then the bearings are put on a heater that heats the inner races, and then they just slide right on. You then pull the housing back on, and replace the clamp plate.

Since you're trying to make a kit, you could likely specify the tolerance on the bearing journal for slip-fit...

[taskman]

Is everything supposed to rest on the nut? I screwed on the nut, the side that seems to have an integrated washer towards the bearing housing. I held onto the bearing housing and turned the ballscrew. There seems to be alot of friction doing it this way. It doesn't seem like the right way of doing it

[louieatienza]

Is everything supposed to rest on the nut? I screwed on the nut, the side that seems to have an integrated washer towards the bearing housing. I held onto the bearing housing and turned the ballscrew. There seems to be alot of friction doing it this way. It doesn't seem like the right way of doing it

Without looking at a picture of what you have done it's hard to tell what's going on; we're just running around in circles guessing. I have found that the seals on these Chinese ballscrew supports are really tight. I do have some C3 class Chinese ballscrw supports, and when mounted to some precision ground ballscrews, do not exhibit any excessive friction. But as to the nut. It tightens against the spacer, which rests against the inner race of the outer AC bearing, which rmay or may not rest against a shim, then the inner race of the second AC bearing, and finally the shoulder of the bearing journal of the ballscrew.

[taskman]

This is the design. I am wondering if I did it wrong with the motors at the top and the rods hanging off them
Attachment 223934

The photos show how I attached the nut and how the nut looks. I screwed it on with the washer side pointing towards the bearing assembly
2014-02-15 15.21.47 | Flickr - Photo Sharing!
2014-02-15 15.22.19 | Flickr - Photo Sharing!
2014-02-15 15.22.12 | Flickr - Photo Sharing!

[tahustvedt]

Looks like you should have bought FK bearing mounts. They are already adapted to axial mounting like you have modified the BK for.

You tighten the nut enough to achieve the required pre-load on the bearings. Tighten the nut until it touches the bearing, and takes up the play, if you don't need very high stiffness.

Why is the BK mounted to a thin strip of sheet metal? The BK should absorb all the load, not the motors. Stepper motors aren't designed to absorb high axial forces.

[taskman]

You asked "Why is the BK mounted to a thin strip of sheet metal?"
My BK's have holes front and top BK 10 bearing fixed side | Flickr - Photo Sharing!. I wanted to keep the back of the machine clean, because I still want to attach a removable skin to the machine there so I didn't want to attach the bearing to a back plate that could cause issues for me when I design the skin and might then need attachment points at the back. It also means when I attach the skin it will be clean and no holes and no bolts coming through it. So I decided to design brackets for the bearings that will sit between the profiles. It means it is out of the way for future upgrades.

My BK's are at the top and the BF's are at the bottom

Should I turn things around so that the motors are at the bottom with the BK's and then the BF's at the top? Then the rod will rest fully on the bearing and have no load on the motor or should the rod always hang? Then I also won't have the friction

When I tighten the nut so that it is against the bearing there is alot of friction when I turn the ballscrew. Is it just bad quality bearings/nut? I don't know if the spacer is maybe not long enough. Should I maybe add two washers between the nut and the bearing so that they can turn and I will have less friction? Isn't the nut or spacer going to wear out with all the friction? As it wears out it will move microns down every day you use the machine to the point where the ballscrew will start pulling on the motors, or not?. Am I thinking about something that will only happen in a hundred years now?

If you look closely you will see the nut is at a bit of an angle. When I hold onto the bearing and let the ballscrew hang like it would in the machine can turn the ballscrew with 2 fingers and then at a point I need to turn it with my hand and then it is loose again and I can turn it with my fingers. All 3 of the ballscrews with nuts attached act the same way
2014-02-21 03.31.50 | Flickr - Photo Sharing!

BK's
bk screenshot | Flickr - Photo Sharing!

BF's
bf screenshot | Flickr - Photo Sharing!

Complete back
full screenshot | Flickr - Photo Sharing!