Thread: Ready Steady Eddy
Whilst we're close to the topic...for a while now I've been dismantling new ballnuts I've obtained from Chai, as it's not uncommon to find debris in them - be that just general dirt or bits of metal.
On the machines I've made to get zero backlash (lathe, mill & router), I preloaded the angular contact bearings using disc springs and shims between the bearings. That way there's less risk of damaging a bearing by over-tightening the nut as you know how much force you're applying from the spring deflection and it avoids buying matched bearing pairs. I also use bearings with a bigger outer diameter than the ones in the BK blocks - i.e. use 7201. They're less delicate...
If you want an easy option for a standard CNC router, then I don't see much wrong with just using double row angular contact bearings (52xx series), as although they have a small amount of axial play, the amount is much smaller than the single ballnut backlash so overall the effect isn't very significant. If you start pre-loading the nuts, then naturally the bearings need pre-loading too.
Also, be very careful with opening out the bearing blocks to better fit the bearings, as going too far may introduce backlash (depending on quite a few factors).
Last edited by Jonathan; 11-03-2014 at 09:55 PM.
The Following User Says Thank You to Jonathan For This Useful Post:
Yes I think you are correct about the double row bearings, I was looking at those yesterday. Getting the nut set right on the BK type is a bit of a fiddle to say the least.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
You make me laugh you lot.!! . . . . Your quite happy to pay peanuts for the parts but then whinge and whine when they aren't top quality.!
WTF do you expect when You couldn't even buy one decent Angular contact bearing in this country for the price payed for both Blocks with bearings.
I strip, grease and shim every BK/BF bearing. It Takes minutes to do and other than that they are mostly fine considering the price payed.
Yes I could make my own better but unless chasing true Zero Backlash like Jonathan mentions then I'd just be wasting time and money because the BK/BF blocks when fettled work perfectly fine for any normal router machine.
Getting all anal about bearing's and whether one came from China and other Japan is mostly pointless unless your chasing very tight tolorences because your own workman ship will introduce a lot more error than a couple of cheap or mismatched bearings ever will.!! . . . . . End of the day it's a router for cutting Wood and provided the bearings are greased and shimmed to remove lateral movement then they last for years.! . . . I've just after 5yrs changed my bearings, yes I've adjusted and greased them couple of times in that period but that's just normal service like any machine needs.
Well, not even that, I just want to buy them and fit them knowing they will work as expected, is that asking too much ? I don't think so.
Anyway I stripped the Y axis ball screw out and laid it on a flat surface, sure enough it was bent about half way. Using a feeler gauge I slid it along underneath to find the bend position, then I put it in a vice with wooden jaws, put a pipe over the other bit and 'leaned' against it until it was straight. Now it's about right however the ball nut is a bit crunchy, I pumped some grease in and the metal particles that came out was alarming, it's still a bit rough and sticks now again so I see no alternative than to strip it out and clean, that's assuming it will go back together.
Last edited by EddyCurrent; 12-03-2014 at 07:56 PM.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
Last edited by JAZZCNC; 12-03-2014 at 08:00 PM.
Been away for a few days, got back and now the PC graphics card has gone ! more expense.
Took the ball nut off like I mentioned earlier, emptied the contents into an old but clean washing up bowl I use for occasions like this.
The ball nut has 3 ball circuits and each ball measured about 3.15mm in diameter, maybe they are 1/8" inch ? anyway the number of balls that came out was 53 so right away you know there is something amiss. Before removing the ball nut the problem was that it felt like it was dragging and looking at grease patterns on the ball screw it looked like the centre ball circuit was stuck because the grease was being totally removed from the ball screw in those threads.
I watched this video on how to repack the ball nut and it was no problem putting it back together.
Linearmotionbearings C7 Ballnut Flipping and Repacking - YouTube
He explains in the video that 16 balls should be in each circuit which leaves a gap, I found that 17 balls left a similar gap so that's what I put back in and it's now nice and smooth running.
Edit: 10/12/2014 It was later confirmed that the correct number of balls for a 1605 or 1610 ball screw is 17 balls per circuit 51 total. (so that's good news for me !)
So the problem was too many balls in the ball nut so that they were jamming instead of rotating.
Last edited by EddyCurrent; 10-12-2014 at 01:43 PM.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
No one wants jammy balls!
Interesting video, thanks for the link.
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