C Beam Expanded

I run a 1000mm lead screw on our C-Beam Y-axis build and there is some slight whip but it is manageable. The two things I did to minimize it is to ensure straight alignment of the nut block and the endplates as well as to make sure I did not tighten the locknut against the acme bearings too tightly. 0.5mm makes a difference, so it took a while to get the perfect tension on the lead screw against the endplate.

I run 2000mm/min rapids currently and the slight whip hasn't caused any noticeable inaccuracy.

Hope that helps! (Our C-Beam is also expanded in size in the X, more info on our build page)

 

The problem of whipping lead screws over longer lengths doesn't have lead to thicker lead screws. Think of it like a piece of rope, taking it to the extreme. Put it under tension and it is going to be straight, put it in compression and it's going to flop around. A solution that some builders are coming up with is to put the acme lead screw under tension instead of compression. Have a look at this video at around 11.30 mark to see the concept in practice.



And to make it tight look at this one at about 13.30

 

Haven't given it a go @boskap but might do in the future. Is to use the standard C-Beam End Plates with the normal 688Z 8x16x5 bearing in the pocket, but stuck in place with some Loctite. Order of assembly is: Flex Coupling > Thrust Bearing 1 8 X 21 X 2mm AXK0821 Thrust Needle Roller Bearing With TWO Washers Each | eBay > C-Beam End Plate > Glued in 688Z 8x16x5 Bearing > to other end and another Glued in 688Z 8x16x5 Bearing > C-Beam End Plate > Thrust Bearing > Lock Collar. Hope that makes sense, I will try to make a picture when I have more time.

 

Have no idea!

 

The Loctite is just to stop the bearing from falling out of the pocket in the end plate. So do these pictures help @boskap ?

 

I can't see why it not working; thought I do not know how long the bearing would last. Give it a try and get back to us on whether it works.

ps. I'm Australian so naturally my english is terrible

 

Applying axial tension across regular bearings is not a good idea as it cross-loads the balls and quickly locks them up. Best solution would be to reverse the end plates and install F8-16M axial bearings in the bearing pockets. You may however need to shave a small amount off the length of the C-Beam to have enough room on the screw to attach lock nuts (or collars) and the stepper coupling.

And note, the budget example bearings provided in the link above may not prove to be a durable solution. Be sure and grease them heavily prior to installation. In the long run you may need to spring for better quality F8-16M bearings.

 

Nice bearing Rick, your wealth of knowledge is a great asset mate

 

Thanks, but I've used a lot of these bearings to the point that they have almost become second nature. The current project I'm working on will have 20 sets in it by the time it comes to fruition.

 

Can't wait to see it Rick, sounds interesting..)

 

You're getting a little beyond my experience level with that one. But I think you are overestimating the amount of tension being applied. I think the goal here is to revise the screw anchorages from where they function in compression only to ones that function in tension only as by eliminating compression you have eliminated the main force causing the screw to bow. Snug tight on the tension is really all you need.

(Note: What is being suggested is just help minimize simple whipping. An understanding of the full extent of whipping caused by imbalances, harmonics, rotational inertia, centrifugal force, etc., etc., etc., is well beyond most forum members including myself. If you really want to get into it, I'm sure there are several Doctoral Theses out there on the subject.)