Cover for the Z axis belt drive - and front drag chain support bracket.

I need to finally devise a cover for the Z axis belt drive. 

And here's the actual installation, including the linear encoder. I don't recall why I modelled the encoder on the back of the ballscrew whereas it's installed at the front. Lost in the mists of time, that one...

From the main machine assembly, here are the critical components. The belt itself isn't modelled, as Fusion doesn't manage that yet. Solidworks and Inventor do but it's not a big deal:

Something like this should work:

Section view:

But with some lugs to secure the cover to the ballscrew bracket:

Looks good.

And fits like a glove. I barely need to use the M6 fixing screws, as it's a nice snug fit over the motor bracket.

While I'm in Fusion and running the printer, here's a bracket for supporting the front drag chain:

Wow, that turned out well. In fact I will print out another one, so there are 2 of them supporting the lower section.

I think we can say the front drag chain is done now.

Assembling the carriage (front) drag chain and finalising the sensor wiring

Due to the way the carriage and cross slide assembly are constructed, there's no sensible means of getting the front mounted linear encoder and limit switches for the Z axis passed over to the rear, so that they can use the drag chain I've just implemented at the rear of the machine.

It only has to convey the 3 small signal cables, so the size of the drag chain is mainly dictated by the requirement to be large enough for robustness. Igus don't do anything that looks appropriate and certainly nothing that would be described as "fully enclosed".

This Chinesium drag chain from Amazon looks like a possibility, so I got myself a length of it and went from there.

I need to make u some brackets to mount the ends on the machine. Here's what we have currently:

This is the read head for the linear encoder:

Yes, those are threaded M4. Very handy.

Something like this should work for the moving end. This would attach to the moving head of the encoder using those 4 spare M4 threaded holes.

And perhaps something like this for the fixed end, which would attach to the bracket that supports the Z axis ballscrew and servo motor assembly.

Ah, but this would force the lower section of the chain to sit below the lowest reach of the bracket due to the bend radius, so a slight adjustment is required. 

With some thought and refinement, I can provide a route for the cables to emerge without needing to thread the connectors

Looks good:

Clear out the M4 threads:

And wop it op. I should provide a support under the lower section but otherwise it looks like a success from here. Obvs I could have terminated the chain just under where the current fold is but I'd then have needed to either provide a conduit for it or make another hole through the chip tray.

The various signals cables (limit switches, encoder read head, servo motor etc) are all different lengths - some too short, others too long. So this is the time to make them all the same length. Messy and slow but it needs to be done.

Combined X and Z axis limit switches:

Z axis limit switches:

Z axis encoder read head:

It's a good thing I took photos of the wiring before chopping off the connections and extending them. When printed out on the new Kyocera printer, the green and blue wires come out the same (blue) colour. Some manual notation is required! Here's the printed copy held up against the same image on the screen.

Almost done now. Then mount the cabinet on the machine and check to see if my wiring modifications were error free. And get the machine running again.....

Butchering the chip tray - mounting the drag chain tower

The drag chain tower (aka the base for the fixed end of the drag chain) is a fairly simple concept - a lid holds the chain in place, as well as sealing the tower. The channel down the middle of the tower is big enough for me to drop the encoder and limit switch connectors through without needing to disassemble them. I should be able to run those cables without majorly dismantling all the neighbouring components.

Some dimensions, for when I come to butcher the machine:

Let's try a mockup:

And check the movement (450mm) will be accommodated without clashing:

Mark out the positions of the holes:

After some stich drilling and die grinder action, it's done. So I then got a bit carried away and cleaned away the swarf and gunk from the chip tray. I'm not about to paint the thing but this seems like a good time to get rid of that nasty muck.

From the front as well:

The machine is old and tired but having stripped it back, adjusted the myriad gib strips and fitted the Linuxcnc system with closed loop servos, it should be good enough for the likes of me. And it can do stuff the Tree CNC lathe can't, like faceplate work and larger, odder shaped workpieces. The Tree was really intended for repetitive machining of bar stock, rather than jobbing work.

When the drag chain tower is done (tomorrow), I will assemble the cables, drag chain etc and hopefully move on to mounting the cabinet and routing the cables in a semi professional fashion.

Designing and printing the drag chain tower - and testing various filaments

I have some 3.4mm diameter o-ring cord(?) - the groove dims shd be around 4.5mm x 2.5mm for about 25% compression.

And I shouldn't forget to put some tiny o-rings around the 4 fixing screws. You might argue the screws would be better placed within the large o-ring but that's where I ended up.

Printing this in PA-CF (carbon fibre loaded nylon) didn't look like an option, having tried to print out some of the drag chain covers using the stuff. Apart from the surface texture (rough as a bear's arse), the things snapped along the layer lines without much provocation. They were also pretty feeble in terms of stiffness - all in all a complete disappointment. No amount of fiddling with the slicer settings is going to help. Perhaps it's best suited to large, structural parts.

It fits - but distorts if you so much look at it. And it looks (and feels) shit:

Let's try some PETG and see if that's any better. I'm rather hoping for something that is reasonably rigid, with a clean finish and possibly even a degree of solvent (coolant and way oil) resistance.

Well that is shit - but in a different way to the PA-CF.

Let's try the Creality ABS and see if that's any better:

Well, it looks better - but isn't a whole lot stronger (snaps in half easily). I may simply revert to the PLA, which actually worked well, if you can forgive the fact it's grey, not black. I could always get a reel of black of course.....

However, for the drag chain tower, it may be well suited, given that strength isn't a big issue there.

So, back to the drag chain tower. Let's print that out in ABS and be done with this part of the task. ABS is more fussy when it comes to printer settings, requiring a heated bed, hot chamber and various additions such as extended bed, multiple base layers etc to prevent it lifting around the base.

Well, this looked OK to start with:

The base is lifted at the edges ie it won't sit flat on the table. NVM, I will bugger about with the settings - but in the meantime, let's check out the other features. Those M5 holes for the lid seem to tap out ok:

The lid(s) are both badly warped.

This is with a raft, 5 layers at the base, hot bed, fan almost off. I stopped the print to check how it looked. 

This is a lot better. Pretty decent finish and no warping at the edges. I will now print the tower, noting that it estimates about 10 hours. Ideally it will be ready in the morning then.