Luthier CNC

[Lee Roberts]

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.

No problem, great that's good to know about the ball count if you ever lose any let me know I can send you some the right size.

Yea that's how I started doing them years ago (dry+screw) I've rebuilt quite a few for people now and found it a little obstructive using the screw (length/weight) so I just use a tube of ali to the right OD with a hose spring clip attached to one side, I slide this in just after I've got the first track filled, it depends on the job though as some people ask for the nut to be on the screw when i send it back because they don't want to risk it again. Both ways though I still use a little grease as a "retainer", they used to ship the nuts with the tube and a clip on both ends but they seem to be a plastic tube with cable tie now.

13mm (1/2") Aluminium Alloy Tube

Best served with some of these: Double Wire Spring Clip

[bluesking]

Equipped with my newly cleaned ballscrews I made substantial progress today.

First I reworked all of the Ali plates. I widened a bunch of holes. The M12 bolts had 13mm holes, now 14mm. The M5 bolts had 5.5mm holes, now 6.5mm. The idea is to allow more wiggle room so I have wider alignment range on all the mechanics. This worked a treat: I no longer need to use any shims, careful and methodical alignment allowed me to find good alignment without messing about with coke cans and tin foil!

I then bevelled most of the holes in the Ali Plate. I was worried that the burrs around the holes were messing with precise mating of all the pieces:



Whilst I was at it I bevelled the edges of all the plates at 45deg on my spindle sander. I was getting tired of the sharp edges opening up my skin and getting blood all over the machine!


Rebuilt the Y axis (major axis) and aligned the hiwin rails. Here is a vid of the gantry running on just the rails. About the same as before, maybe a bit better, seems fine to me.
https://streamable.com/22i2r

I then connected and aligned the Y axis ballscrew. Got the resistance completely even along its entire travel, all the way to the extremes. It is a HUGE improvement due to the cleaned ballscrews and the improved alignment. Here is me turning the ballscrew and moving the whole gantry with one finger, it is this way along the whole length!
https://streamable.com/n26nm

I can even push the gantry and the Y ballscrew spins accordingly. Unlike Lee, I simply cannot do this with one finger, need both arms and a sure footing! Still, this was completely impossible before:
https://streamable.com/sbztv

Here are some vids showing the same behaviour on the X axis, once again over the entire length of travel. Even easier to move (I think mainly because it is lighter, rather than due to any better alignment).
https://streamable.com/yzbnr
https://streamable.com/73cc5

In summary, everything is hugely better. I now believe this machine is set up absolutely adequately for my purposes, belts encounter almost no resistance when turning, my servos should be able to throw this beast around no problems. In fact, it is much better than my little desktop CNC that I have been using to cut guitar fretboards.

I do not think I can possibly improve on this setup. I love the idea that Lee can move his Z-axis side to side with one finger, but that seems impossible to me on my machine - even disconnecting the ballscrews and one hiwin rail (i.e. moving on just a single rail) I cannot get this performance with the rails I have!

I'm very impressed and grateful for everyones help.

Here is a current snapshot of the machine, ready for assembly of the Z axis:

[MikeyC38]

Hi blueskin
Looks a treat and a nice build. It is worth investing in specialised shim stock, because it allows you to shim precisely. see here
Also get you axis nomenclature clear. If you assume that the bottom left corner of your machine (looking top view) is 0,0 then the Y axis is the axis between the gantry sides and the X axis is the longest axis. Z zero is the topmost point of travel on the z axis.

Now start to work out where cable chain will run. This is something I did'nt do until I was at the same stage as yourself. I had to lash something up but luckily the design had space for aluminium channel to be fitted to support the chains

Finally for your spindle mounting, also try and design some means of adjusting for tramming the spindle. It will make your life easier. At the moment I'm using shims and it is tedious!

Keep going!

Michael

[Voicecoil]

Also get you axis nomenclature clear. If you assume that the bottom left corner of your machine (looking top view) is 0,0 then the Y axis is the axis between the gantry sides and the X axis is the longest axis. Z zero is the topmost point of travel on the z axis.l

Surely if you're standing at the front of the machine looking down, (i.e. 0,0 is front LH corner) then this is the opposite to how you'd have X and Y on a normal graph?? I'm with Bluesking on this one :-) Not that it really matters, he's made it perfectly clear what he's doing.

[cropwell]

Most 2D/2.5D drawing packages use the normal mathematical convention that the X axis is L -> R as you look at the paper, the Y axis is at right angles to it. How you orient your paper or machine is irrelevant. My machine is in portrait mode and it just makes it easier to visualise if it is the same as the drawing. My Z zero is at the top of the workpiece, but my Z homes to the top of travel. X and Y homes to Left and Nearest me respectively. I just find it less confusing this way and therefore mistakes are less easily made.

[MikeyC38]

Hi Guys

Sorry everyone, this is what I meant - standard landscape graph mode.But I of course it does'nt matter which way you do it providing you know what to expect...

[bluesking]

Wow, what a controversial issue my axis labelling has turned out to be! I'm happy with my system, long axis Y, short axis X, corresponding to a portrait graph as you guys call it.

[bluesking]

Z axis build today.

aligned the hiwin carriages first of all as I can't get to them after anything else is assmebled


then finalised the fit of the hiwin rails


then ballscrew aligned and attached the spindle once I was happy there was no binding


entire travel moves smoothly, it is easily pushed down by hand, not so much up for obvious reasons. My biggest concern here was that the Z axis would fall under its own weight. Well, I got lucky, there is just enough friction to keep the axis from falling down so I won't need to bother with a brake. Here is a video of how it behaves as it is - this is without the belts/servo connected, so after connection there will be even less chance of it falling after powering down:

https://streamable.com/z05b9

bolted on the reinforcement struts to the base to improve rigidity - seems to make a noticeable improvement


quick measure up of the drag chain - I'll cut some Ali Plate to support this - one end will be attached to the gantry, the other directly to the table - not pretty but I think it'll work just fine - I liked Wal's build that he had his chain under the table, but I have my reinforcement struts there and prefer rigidity over neatness!



finally, a quick test fit of the servos to see if there is enough pulley adjustment range (broadly planned that there should be throughout the build!) and to check whether the belts I have are of suitable length. I need to buy a slightly longer Z axis belt, you can see that the servo doesn't quite mount properly as is - I had to shorten the support extrusion for it during the build as I couldn't be arsed to cut an indent to go around the ballscrew bolts.

[Lee Roberts]

I can even push the gantry and the Y ball screw spins accordingly. Unlike Lee, I simply cannot do this with one finger, need both arms and a sure footing!

I love the idea that Lee can move his Z-axis side to side with one finger, but that seems impossible to me on my machine - even disconnecting the ball screws and one hi-win rail (i.e. moving on just a single rail) I cannot get this performance with the rails I have!]

Just to clarify mate, I can only push my Z axis across the X (gantry) left to right with hardly any resistance, watching your video of you moving the gantry up and down the Y axis (bed), I would say we are very close in terms of effort required to make it move and the screw to spin.

You should note I'm using supported round rail, I thought I mentioned that in my other post, if I didn't sorry about that. Your rails are far superior to the ones I've used on this machine, overall I think your now on to a winner and agree you should move onto the next parts.

What pitch screws have you used on your longer axis's ? I've used 1610 ball screws on both X and Y, I think that may also be why its a bit easier for me to make things move. The rails on this machine will be making the most difference.

Well done, keep going looking forward to seeing you push the Start button

[bluesking]

What pitch screws have you used on your longer axis's ? I've used 1610 ball screws on both X and Y, I think that may also be why its a bit easier for me to make things move. The rails on this machine will be making the most difference.

Nice one Lee,
I'm using 1605 throughout and various gear ratios. As I'm using servos my main goal is to slow everything down enough rather than to speed it up like most stepper guys are doing.

Between that and the round rails you are using I'm feeling confident that I've managed to squeeze out all the performance I'm likely to get from my machine. Thanks again, you've given me really helpful advice about what I am aiming for and now I can move on with confidence, its a good feeling!

I'll mainly be focusing on the electronics and software from now on.