DIY Build of Aluminium CNC Wood Router without Workshop & Tools

[WandrinAndy]

As I've never made much of any mechanical rotating thingies before, the whole aspect of Timing Belts and Pulleys was a worry. But now that I've absorbed the relevant postings on the forum... particularly thanks to Jazz's pics... it seems quite simple.

I am again thinking of using RM1605 ballscrews for maximum possible resolution and torque and then gearing 2:1 to achieve "longer pitch" and speed. I understand this will increase load on, and reduce life of, certain components... but it somehow still gels better in my grey matter than doing it the other way around. Please persuade me if the other way is really the far better balanced solution... afraid I can't quite get my mind around that... yet?

On the X-axis will use 5mm pitch 15mm wide HTD Timing Belts and HTD5M-15 Timing Pulleys - 16T [o.d=28mm] and 32T [o.d=54mm] from http://www.beltingonline.com/5mm-htd-timing-belts-4575.

On the X-axis the Ballscrew pulleys will be 16T and Stepper pulleys swappable between 16T and 32T as a start :

- Stepper pulley bores modified to be 8mm and with 1 off M4 grubscrew hole
- Ballscrew pulley bores modified to be 10mm and with 1 off M4 grubscrew hole

Each idler will be made of two bearings 8mm i.d x 28mm o.d x 9mm wide from http://stores.ebay.co.uk/xtremesportandleisure-uk-online?_trksid=p4340.l2563 sandwiched between large washers serving as guides on each end.

Two quick questions please -

- Apart from asking Chai to machine F increased to say 30mm for coupling, does Chai grind the small flat on the shaft for the grub screw to grip and stop the pulley spinning or is that something I would have to do?
- Are M4 grubscrews about the right size for 8-10mm diameter shafts?

The costs are mounting... but after my massive shock at the cost of profile-rails and bearing-blocks, these components seem comparatively cheap!

Thanks,
Andy

[JAZZCNC]

I am again thinking of using RM1605 ballscrews for maximum possible resolution and torque and then gearing 2:1 to achieve "longer pitch" and speed. I understand this will increase load on, and reduce life of, certain components... but it somehow still gels better in my grey matter than doing it the other way around. Please persuade me if the other way is really the far better balanced solution... afraid I can't quite get my mind around that... yet?

No no no wouldn't recommend that route.? Yes I know my machine use this setup but that was purely because 1610 or 1605 where not available from Chai and at that time ballscrews from anywhere else were very expensive and out my reach. Even 2nd hand they were more than Chai wanted for new ones. Thankfully things are very different now days.!

It's always better to obtain the required speed from the using correct pitch screw so 1610 is far better option if you need the speed. Plus you'll have more torque from the motors has they won't be spinning has fast and in a much better area of the torque range while cutting which is where it matters most.
If you need resolution then you can always gear down, yes you'll lose speed but the torque will double. Still use belt drive even if your running 1:1 because of the fringe benefits of resonance dampening and flexibility to gear if required.

Two quick questions please -

- Apart from asking Chai to machine F increased to say 30mm for coupling, does Chai grind the small flat on the shaft for the grub screw to grip and stop the pulley spinning or is that something I would have to do?

No it's DIY but turned portion is soft so a decent file and it's done in 2mins

- Are M4 grubscrews about the right size for 8-10mm diameter shafts?

Use the largest you can fit in the boss of the pulley.! If going between teeth on pulley then just make sure you sink deep enough doesn't foul belt and no sharp edges.
I mainly use M5 and M6 some times M4. Bigger the better because the larger allen key means you can get good purchase for tightening plus more surface area on shaft flat.

If you end up using 1610 1:1 then I'd use 20T pulleys has it's a nice radius and the belts aren't quite so prone to cracking from the tight radius smaller pulleys give.