Luthier CNC

[Voicecoil]

I'll agree 100% about the HGR20's being a little sticky, but I'd rather they were that way and had no play, than "free and easy" and wobbling all over the place. If you can turn the ball screw end shafts smoothly between finger and thumb then I guess it should be OK - after all, a decent stepper should be giving a good few hundred Ncm torque.

[bluesking]

I'll agree 100% about the HGR20's being a little sticky, but I'd rather they were that way and had no play, than "free and easy" and wobbling all over the place. If you can turn the ball screw end shafts smoothly between finger and thumb then I guess it should be OK - after all, a decent stepper should be giving a good few hundred Ncm torque.

Thanks for confirming my thoughts about the HGR20s. I think I've got the rails sorted, its the ballscrew causing issues I think. I have got it to a much improved state, but I can't quite "turn the ball screw end shafts smoothly between finger and thumb". Whilst the resistance along the entire travel is now pretty much uniform, there is a little patchiness to the motion - there are occasional slight sticking points which require a bit more force than just two fingers can apply. I mainly test it using the belt to move the ball screw and it all operates ok in motion though from a standing start it can be a little "sticky".

It may well be fine with the reasonably overpowered servos I will be using. I'm going to leave it as is and proceed with the other axes so I can compare the motions between each axis.

If its still a problem I can think of only 2 ways forward:
- widen some of the mounting holes so the major extrusions have a little more "wiggle room" so I have broader alignment range
- buy a new ballscrew - I worry I may have subtly bent this one during my initial tests and now it will bind whatever I do...

[Voicecoil]

there is a little patchiness to the motion - there are occasional slight sticking points which require a bit more force than just two fingers can apply

BTW, did you check the ballscrew for smoothness throughout its' length before mounting it?? As I mentioned in my thread here: http://www.mycncuk.com/threads/12524-gritty-ballscrews , although Fred tries hard to please, his engineers don't always seem to adhere to the old saying "cleanliness is Godliness" when it comes to machining ballscrews. Even the replacement parts he sent me needed a clean, strip down, flush through and re-grease before they were acceptably smooth. Try running (twisting) the sticky portions through a piece of clean tissue and then examine under magnification to see if there's any small flakes of swarf.

[bluesking]

BTW, did you check the ballscrew for smoothness throughout its' length before mounting it?? As I mentioned in my thread here: http://www.mycncuk.com/threads/12524-gritty-ballscrews , although Fred tries hard to please, his engineers don't always seem to adhere to the old saying "cleanliness is Godliness" when it comes to machining ballscrews. Even the replacement parts he sent me needed a clean, strip down, flush through and re-grease before they were acceptably smooth. Try running (twisting) the sticky portions through a piece of clean tissue and then examine under magnification to see if there's any small flakes of swarf.

I think you may be right. I need to dismantle much of my machine anyway so best get to cleaning the ballscrews!

In my hurry I didn't attach the nipples to my HIWIN carriages so this is probably a good opportunity to do that as well. I see you have made a post about these nipples: Do you know if the following are a good way to go for greasing the carriages? Are they also suitable for greasing ballscrews/nuts?

https://www.toolstation.com/laser-grease-gun/p29224
https://www.toolstation.com/lithium-grease/p89691

[AndyUK]

I think you may be right. I need to dismantle much of my machine anyway so best get to cleaning the ballscrews!

In my hurry I didn't attach the nipples to my HIWIN carriages so this is probably a good opportunity to do that as well. I see you have made a post about these nipples: Do you know if the following are a good way to go for greasing the carriages? Are they also suitable for greasing ballscrews/nuts?

https://www.toolstation.com/laser-grease-gun/p29224
https://www.toolstation.com/lithium-grease/p89691

Thats what I use, and it works on the ballnuts that Fred has sent me. I think the nipples for the HGR20s are the same, but I haven't gotten that far yet. Highly recommend the flexible extension for the gun, and don't try loading the grease gun for the first time in toolstation's car park when you're inside the car. Not a clean experience. Worth watching a youtube video or two on loading, attaching, and de-attaching grease guns if you've never had the pleasure to using them before, there are a couple of nuances.

This is the flexible bit I'm talking about:
https://www.toolstation.com/laser-gr...nnector/p33147

[bluesking]

Thats what I use, and it works on the ballnuts that Fred has sent me. I think the nipples for the HGR20s are the same, but I haven't gotten that far yet. Highly recommend the flexible extension for the gun, and don't try loading the grease gun for the first time in toolstation's car park when you're inside the car. Not a clean experience. Worth watching a youtube video or two on loading, attaching, and de-attaching grease guns if you've never had the pleasure to using them before, there are a couple of nuances.

This is the flexible bit I'm talking about:
https://www.toolstation.com/laser-gr...nnector/p33147

Thanks Andy,
Just got back from toolstation with the gun, but didn't get the flexible hose, looks like I'll be going back!

One question, how do you grease your ballscrews? There is no nipple I can see...

[AndyUK]

One question, how do you grease your ballscrews? There is no nipple I can see...

There isn't a nipple on the screw itself. The bits that move are the bearings and the ballnut - the rest just needs a slight surface coating to protect the metal. The bearings are sealed, so its just the ballnut that needs the gun.

I over-greased the ballnut and then ran it up and down the screw to smeer the grease all around. The other way would be to smeer some grease with a finger all the way along, then run the ballnut up and down a few times.

[Lee Roberts]

Make a new video so we can see and hear whats happening now you've tweaked it some more!

I was about to say the same as Voicecoil re making sure everything is clean, I always suggest people do that with the nut's because I don't think I've seen one yet that didn't have crap inside from the factory.

It can be tricky and the balls will fall out if you remove the nut from the screw, that's OK because your going to flush it all out and clean everything anyway but it can be a little time consuming reloading all the balls back in, to do this pack the nut with some grease first, enough to hold them in place not literally "packed".

The trick is getting the nut back on the screw without dislodging any of the balls, its very doable but equally easy to try and go to fast and knock the balls back out when your trying to thread the nut back on.

While/if your there, count how many balls you've got out altogether, its common for some to be missing from the 17 per track on a 1605 ball nut (even from BST).

Have another read of this thread re nipples and so on, you can include the ball nut: http://www.mycncuk.com/threads/12835

Also (for everyone), if you read the document from Hiwin on the their Linear Guideways it has quite allot of info, Page 27 (2-1-7 Lubrication), shows you info on the grease nipple and ALSO the additional mounting locations built into the blocks so you can move the nipple if you want to: https://www.hiwin.com/pdf/linear_guideways.pdf

[Lee Roberts]

I don't really understand what you mean by moving the mechanism with one finger. Certainly pushing the gantry, it doesn't move, there is enough friction to stop any linear force from being converted to rotational motion. For the vast majority of the travel I can just about turn the pulley with one finger - is this what I should be looking for?

I mean I can move my whole Z axis from the left to the right of the X axis (gantry) really easily, I can push it with my finger and the ball screw on the X axis just spin's like its nothing, its actually amazing that I got it so perfect pre dial indicator to check anything. I think I just got well lucky but it wasn't first time fitting, i went back and forth (literally) for hours loosening the rails and the ball nut and screw fixings until everything just moved perfectly by hand, I used the same method I gave above to do this and at some point you have to say OK that's as good as it gets and start tightening things up as permanent.

I'm really close with the Y axis (bed) but I think its just off a little bit still, like you I still have "sticky points" along the travel, if I push my gantry it is much harder to push along then the X axis for sure but dose go with enough force to get the screw spinning. Still building my machine but i'm going over at the weekend to have another play, I'll get my mate to video me pushing mine about so you can see, maybe the others with more experience can then give their thoughts.

From what I understand, anything less than dial indicator prefect just means uneven ware and tare on the parts and that on a hobby machine used 2-3 times a week, this ware would be negligible because it would take forever to accumulate enough to effect anything a hobbyist would be looking to achieve - Somewhat subjective I know.

[bluesking]

Lee, you are a legend, thanks for all the detailed and helpful responses. I will be sure to post a vid showing some of the machine motion once its rebuilt.

Machine is currently in pieces because today I have disassembled all 3 of my ball screws. Cleaned every part with naphtha and relubed with lithium grease (thanks AndyUK - I just smeared about 3cm^3 on the screw and ran the nut over it, repeating until none was left collecting on the rubber seals at the ends of the nut).

Counted the ball bearings - exactly 51 in each ball screw and I managed to get exactly 17 back into each track when reassembling. I reassembled them dry, using the ballscrew itself to guide the balls into their channels. Found this easy and I think its less messy than using grease to stick everything in place. I used the method in this vid to repack the balls https://www.youtube.com/watch?v=GXdt5M8ZeoE

All I have to show for my work is the following vid. Shows all the nasty stuff left floating in the naphtha after cleaning each ballscrew:
https://streamable.com/up3n4

End result certainly feels subjectively smoother - will only know for sure once the machine is rebuilt. One thing I've noticed is that after cleaning the nuts do not spin as easily - though they do spin much more smoothly. I put this down to increased viscosity of the lithium grease compared to what was in there from the factory.