Luthier CNC

[MikeyC38]

Hi bluesking
When I built mine (see here) It moved by it self once I had pushed gently.The ballscrew was NOT connected for this test so that you can detect any binding in the bearings. However I am using SBR bearings on a supported round rail. These are more tolerant of misalignment than the bearings you are using. With the bearings you are using for the gantry, accurate alignment is a must, I'm afraid, but they are the best you can buy!

[bluesking]

Hi bluesking
When I built mine (see here) It moved by it self once I had pushed gently.The ballscrew was NOT connected for this test so that you can detect any binding in the bearings. However I am using SBR bearings on a supported round rail. These are more tolerant of misalignment than the bearings you are using. With the bearings you are using for the gantry, accurate alignment is a must, I'm afraid, but they are the best you can buy!

Thanks Mikey,
Thing is, even just running a single hiwin hgr 20 carriage along a single rail (hence no opportunity for misalignment), you give it a little push and it moves, but as soon as you stop applying force it stops - no momentum retained. I think this is due to the relatively high pre-load on the the HGR carriages - they just behave that way. Anyway, with no ballscrew connected I think things behave well overall (see my video above). Connecting the ballscrew introduced the problems - though these have been much reduced now - I just don't know what I am aiming for!

[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