The BF side bearing is only there to stop the screw whipping which does not require particularly great rigidity in the mount. This bearing should only be subject to radial forces, so as long as the mount is strong enough in the Y-Z plane it will be fine. I would make it a bit stronger than you have currently drawn, but wouldn't go so far as replicating the other end mount exactly - you can save a bit of material.
If you're buying the Hiwin rails new then there's no need to get 20mm for this size machine - 15mm is perfectly good for the vast majority of CNC routers. This could help with making the Z-axis more compact. If however you find the rails cheap on eBay then by all means use the larger sizes. You shouldn't have much difficulty finding a good deal there at least for the shorter rails.
As irving's said, recessing the motor mounts is an easy strong way to get round the short shaft problem, here's a few examples:
I've drawn my pics with 20mm rails because I had already created them as components under Sketchup, but am seeing more and more comments stating that 15mm is plenty good and that would save some dosh, and might bring Z 2mm nearer to Y.
But, I am a wee bit worried about aligning 15mm rails on this particular profile as the slot itself is 10mm wide and then there is a wee surface rebate on each side of the slot, that looks to be about 1mm, which makes a total gap of 12mm resulting in the rail only being supported by 1.5mm on each side! So am thinking that 20mm would better... supported by 4mm on each side?
You can also get Z closer to Y by milling pockets in the Z-plates for the rails and blocks. That's required anyway if the plate isn't nice and flat...
Yep, I will also need some milling done in the Z/Y plates.
No probsh... My confusion was caused by me not realising the blocks come in that many different models.
Two quick questions please.... I'm considering again how prone the ballscrews and profile-rails are to contamination from chips etc. particularly on the X-Axis.
I'm guessing it might be prudent to get the optional bearing-block scrapers fitted to protect the seals on the X-axis, but that the other axes are far enough removed from the cutting point to not be too much of a worry?
Let's say I am machining small alu parts... would this be best done at the BF end for better accessibility and to reduce contamination, or best at the BK end that is closer to the motor?
Last edited by WandrinAndy; 15-08-2012 at 04:40 PM.
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!
Last edited by WandrinAndy; 17-08-2012 at 11:28 AM.
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.
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.
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