El Beast - Initial design phase, comments and critique welcomed!

[rcriss]

Thanks Zeeflyboy for the response on the files. I will be watching till the end!!! I love the design. I would just scale it up to a (work area of 610mm x 915mm). And Specifically for aluminum/Brass cutting. I cannot believe the results you are getting with your current CNC.

[Zeeflyboy]

So chaps, been a while...

Good news is the work stuff is all done with and I got the promotion so happy days - work on this project can soon resume!

While I've been away I've been thinking about designs though (hard to turn off the brain sometimes!) and I was keen to get my ideas for a better z-axis down on paper so to speak. Spent most of yesterday modelling and this is what came out... I'm actually thinking of scrapping my current design and going with this one instead right away as it is in my opinion much improved.

I would love to get some feedback, opinions etc while I'm still refining the design. It's pretty much mostly there, just a few details such as limit switches and grease points to sort out.

It reuses the ballscrew/nut and a few other components from the old design, but will require new rails/carriages.

Headline changes:

- 2:1 ratio belt drive (25mm HTD 5M) to isolate the Z-axis stepper from the hefty vibrations and also give it a better gearing advantage for the now pretty heavy Z-axis.

- Extended rails/front plate which now results in a permanently sealed/protected unit at all positions

- HGH25HA carriages (the size is more convenient) spaced much further apart in all directions for improved rigidity

- Rear mount HGR-T 25 rails for easier installation (increased size also will improve the rigidity of the Z-axis front plate when extended down).

- Ability to tram the entire axis while mounted with only the need to remove the bottom plate to do so.

- Marginally more compact with a reduction of 5mm in stick-out from the X-axis.


will share more details when it's completely finished, but as mentioned I'm keen for any input in the mean time.

[Nickhofen]

Congrats for the promotion.
The Z axis design looks gooood!!!

[Zeeflyboy]

Cheers Nick!

So I fleshed out the design with all the details...

This is the pulley system. I added a manual knob on top as I do find it quite useful to sometimes be able to manually move up the Z-axis while setting up. I also added proper bearing support so the pulley system is properly supported.





Better view of the tensioner idler. I had thoughts of more complicated setups, but this is a simple design - simply an oversized centre bore that allows you to push the tensioner into the belt and then fasten down to clamp it in place.




Moving on, here you can see the seals and the (to be 3d printed) magnet holder on the HD16 ball screw mount






Got a little time to make a start on things too. So first up was modifying the large pulley... I decided to get rid of the ballscrew nut and just make the pulley into the retaining system.

First up I centred the pulley in the lathe and drilled a 10mm bore (the size of the ballscrew mounting shaft).



I then mounted it to a 10mm shaft with loctite to allow me to work on the other side where I needed to open the bore to 11mm to allow me to tap it to m12x1 to match the ballscrew.






Ideally of course the ballscrew shaft would extend all the way into the counter bearing, but I had already ordered my screws for the old design and I'm not re-ordering a c3 ballscrew! To solve that problem I made a small press-fit extension shaft:



end result:

[Zeeflyboy]

I now just need to machine a slightly longer collar for the FK12 so that the pulley doesn't bind on the housing.

With that done, I moved on to the motor shaft extension.

First up, centred the smaller pulley (had to remove the top cap) and bored to 6mm.



For the shaft I centre drilled first as this is going to be quite long/thin so needs support at the far end from the live centre.




Turned down to 6mm





Flipped, re-centred and then did the work on the other end. It's critical that this is a really precise fit on the motor shaft and that it's concentric to the outside as any error will either cause the motor to bind or damage the bearings. To that end I used a 7.8mm drill followed by 8mm h7 reamer and then turned down the external diameter.






I did all this work and then ended up turning down the external dimension a hair too far, so now it's a loose fit in the bearing. Frustrating doesn't quite cover it! Will have to put this on the re-do list once I get back from holiday.

While all this was going on, the 3d printer was at work on the seals.



Who says 3d printers can't be accurate - this was spot on! (I did adjust by 0.8% for thermal expansion before printing)




The big bottom seal next (6hr print!)






Very nice fit - smooth and doesn't stick at all along the rails, but close enough that it should keep the nasty stuff out.

That's all for now. Hope to re-do the shaft extension and get the idler done when I'm back next week.

[routercnc]

Nice work there well done. Those seals are looking great. The ones you made for me work well and are just tight enough but not too tight. You might have seen in the last video I put out that the steppers have no problem moving the axis so a big thank you for that.

Missing a critical dimension is annoying. Sometimes I aim a few hundreds of a mm over size, check with the micrometer and use sand paper strips to get it to final size. Takes a while but quicker than starting again if you overshoot

I assume you didn't fancy slots for the stepper to tension the belt? Also do you have bearings in the top plate for the end of the pulley and the end of the stepper shaft? If so I would make one of them floating in a separate small plate which bolts to the main plate. This will allow both bearings to sit where their respective shafts dictate - otherwise the pockets have to be machined very accurately. Something to think about. Have a good break and don't think about CNC too much.

[Zeeflyboy]

The ones you made for me work well and are just tight enough but not too tight. You might have seen in the last video I put out that the steppers have no problem moving the axis so a big thank you for that.

Glad to hear it - haven't caught up on your work for a while actually... need to go see what's happened while i've been gone!

Missing a critical dimension is annoying. Sometimes I aim a few hundreds of a mm over size, check with the micrometer and use sand paper strips to get it to final size. Takes a while but quicker than starting again if you overshoot

Thanks - that's what I did this time and it worked well.

I assume you didn't fancy slots for the stepper to tension the belt? Also do you have bearings in the top plate for the end of the pulley and the end of the stepper shaft? If so I would make one of them floating in a separate small plate which bolts to the main plate. This will allow both bearings to sit where their respective shafts dictate - otherwise the pockets have to be machined very accurately. Something to think about. Have a good break and don't think about CNC too much.

Cheers for the thoughts. I was originally going to go with slots, but it makes it difficult to use a seperate bearing setup for the stepper motor which I wanted to do for the sake of my motor bearings, and the tensioner has the benefit of engaging more teeth on the small pulley.

I will think about floating the bearing above the ball screw - that's a good suggestion thanks.


So I re-made the shaft extension (it worked this time, I won't bore you with pictures as the process was much the same) and also made the knurled knob that allows me to manually move the Z-axis up/down. My thoughts are this is also an easy place to install a brake if the Z-axis proves heavy enough to slide down on it's own.

So started off by turning the alu stock down to size



Knurled and parting






Meanwhile, 3D printed a drill jig to make drilling the retaining grub screw hole easier.






Pressed into place




To save damaging the collar (plus it's a pretty small thing to clamp) I then mounted a 6mm rod in the lathe and used that to mount the knob to do the top side operations:




Final part:






This is the assembly:

[Nickhofen]

You are a bad guy!!! I have lathe envy now!