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.

[WandrinAndy]

Yes I know my machine use this setup but that was purely because 1610 or 1605 were not available ...

Thanks Jazz.... that's exactly what was befuddling me... That whilst I was pretty sure that you recommended 1610.... your machine uses 1605... Because it was in the early days of your evolution... Lol.

I didn't actually think that 1610 gave better torque than 1605... thought it was 'tother way around, but it has now finally sunk in! I just hope it doesn't drop out the other side....

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.

That makes total sense.... I will make use of a service that beltingonline offer at a small-ish fee... they machine grubscrew holes... one/two off different sizes. Have just had a mosey at their website and the options available vary depending on pulley size... only M2-M3 for the smallest 12T pulley, M2-M6 for a 20T pulley, and M2-M10 for a 40T pulley. Their website also states that "Position of grub screws will be in hub as standard".... the hubs are only 5.5mm long so reckon that they put two opposite each other.

So.... I will use 1610 1:1 using 20T [o.d=36mm] pulleys with 2 off M6 grubscrew holes in each... and only look at other gearing ratios in the future if it seems necessary for specific tasks.

PS. I think Jonathan had mentioned I might as well use 1605 on the much shorter Z-axis for better resolution.... Is this because torque isn't really needed on this Axis... Unless drilling I suppose?

Thanks again,
Andy

[JAZZCNC]

PS. I think Jonathan had mentioned I might as well use 1605 on the much shorter Z-axis for better resolution.... Is this because torque isn't really needed on this Axis... Unless drilling I suppose?

Yes thats the norm but more for the resolution than the torque. Believe me lack of torque won't be a problem unless you use a tiny motor.!!

[irving2008]

If your drill is sharp enough you need relatively little torque to drill, much of the time the spindle will do most of it under its own weight...

Its all to do with cutting speed, feed rates and chip sizes...

Basically to drill a 6mm dia hole in Ali, needs a drill speed of 5000rpm and a feed rate of about 10mm/min (all nominal values, taken from one of the many online feed/speed calculators)

The force needed to push the drill through the material is roughly 6N, and the cutting power about 10W. (yes its theoretical, Jazz)

That 6N of force needs 5mN of torque on a 5mm screw or 10mN on a 10mm screw... it generally makes little difference so other parameters, such as cost, apply...

Though these are theoretical numbers, even if they are an order of magnitude out from reality, it still makes no difference. The main job of the ballscrew in the Z axis is to support the weight of the spindle, not to make a vertical cut...

[JAZZCNC]

The force needed to push the drill through the material is roughly 6N, and the cutting power about 10W. (yes its theoretical, Jazz)

Not getting into this other than to say my 2.2KW (2200W) WC spindle is rubbish for drilling above 6mm in Aluminium.? WHY . . because where talking about very different things really.!!

When it comes to actual "real" cutting then torque very much does matter but that's not to be confused with pushing force but torque the spindle produces.

So Irving your correct regards pushing figures not being too important but the F/S aren't really practicle in "real" terms because no one would want to drill aluminium @10mm/min.? G-wizzard actually gives 2900rpm and 200mm/min has a conservative feed rate.? . . . . I actually drill aluminium @ 4500rpm and peck drill @ 600mm/min so big difference's here compared to 10mm/min @ 5K rpm.?

[WandrinAndy]

Layout of the pulleys and belts (imaginative) for my X-Axis.... Pretty much as per normal recommendation I think, but have located the motor and idlers to one side as I want the bed to be unobstructed for passing through longer boards in the future when the sides will be mounted on an adjustable-bed steel frame, and the two cross-members removed.

Please shout if the short distance between the motor and RHS ballscrew pulley makes it more difficult to align the teeth on the cogs or align the pulleys.

Think I've found a use for MDF....... to cover the X-axis belts an pulleys!

[WandrinAndy]

Andy is that a fixed rear end bed?

Nope Ant, my van has a double-bed/lounge at either end.

I've thought about using that end as my "workshop", but am so non-domesticated that I can't be arsed making up the bed every day, so just leave it permanently as a bed... And will initially use the area depicted in red for the build.

Doing a build in a caravan does raise some challenges... Later today I will be picking up some 18mm MDF (mostly cut to size) to make this little bench-let/steps/stool thingy that will be further modified with fence-like clamp thingies to help with drilling, tapping, and assembly.

Getting there slowly....

[WandrinAndy]

Am busy "tooling up" for my build and I need to buy some taps for threading alu plate, and [possibly] the cores of alu extrusion... and have a few queries please:

I'm guessing that M5, M6, M8, and M12 should cover my needs.

What type of thread are the bolts that most peeps use... metric coarse or metric fine?

I will be using KJN 45x90 Heavy extrusion which has ribbed cores that I think have an internal diameter of 10mm and outer diameter of about 16-17mm. The core-bolts that can be bought from KJN are M12x30, and I think they have two versions of these, one of which is self tapping. Sadly these bolts don't use normal allen-keys £!*%!.

Wanting the frame to be as rigid as possible... Are these M12x30 bolts sufficient, are the self-tapping version sufficent, or would it be better to drill and tap for using bigger bolts?

Sorry about all the little questions, just need some help.

Andy

[JAZZCNC]

Metric course: Buy spiral flute taps they make light work of hand tapping in aluminium.

Don't use the self tapping things KJN sell they are rubbish stripping heads very easy. Just normal M12 socket or button heads are fine for this profile.