DIY Build of Aluminium CNC Wood Router without Workshop & Tools

[WandrinAndy]

In my journey so far, you lot... you know who you are... have already warped my thinking to such an extent... thank Thor... that for now I intend using the following components/concepts:

- 20mm supported-rail on X
- 20mm profile-rail on Y,Z
- RM1610 ballscrews on X,Y,Z
- Gear+Belt drive on X and Y, and suppose this may well be used on Z as well... in for a penny.... but this aspect probably worries me more than anything else!

I am now feeling very comfortable with SKP/SketchUp, and how I wish I had used such a tool when designing the odd thing in the past!

I'm starting to make good progress with the design... I think... so have included two SKP pics of my design so far for feedback.

The structure is mostly to be formed out of 6"x2"x3/8" aluminium angle which the Aluminium Warehouse website converts to 152.4x50.8x9.53 mm but let's call it 152x51x9.5 which is what I used in SKP. There are two other materials used so far:

- Blue = 100x50x5 rectangular tube
- Yellow = 45x45 extrusion from KJN

More research is needed before I complete the drive for the X and Y, and do the Y-carriage and the entire Z axis.

Am trying to do the build with standard components, but already need a ballscrew-mounting for Y to be machined and think more will come out of the design of the Y-carriage and Z.

The ballscrew lengths... between bearing blocks... are about 1060 on X and 707 on Y.

When I move on from the touring caravan in the future, this machine will be mounted on a rigid frame with an adjustable bed, so the obviously limited depth below the cutting point is temporary to allow me to get to grips with getting the thing working. Bracing the base of the frame... particularly behind the cutting point is still to be included in my SKP pics.

Please "holler" about the problems... I'm that thickskinned that I cannot recall ever having taken offence at anything!

Thanks,

PS. Is 5mm aluminium sufficiently thick to make a M6/M8 tapped thread reasonably strong?

[JAZZCNC]

Please "holler" about the problems... I'm that thickskinned that I cannot recall ever having taken offence at anything!

Thanks,

PS. Is 5mm aluminium sufficiently thick to make a M6/M8 tapped thread reasonably strong?

Ok I'll holler first but not too much. . Lol

45x45 extrusion is pretty weak so I would consider going larger.!

5mm in aluminium is NOT enough. M6 = 1mm pitch so only 4 full threads M8= 1.25mm pitch so 3 full threads no where near enough and it will strip.!!

[WandrinAndy]

Ok I'll holler first but not too much. . Lol

45x45 extrusion is pretty weak so I would consider going larger.!

5mm in aluminium is NOT enough. M6 = 1mm pitch so only 4 full threads M8= 1.25mm pitch so 3 full threads no where near enough and it will strip.!!

Thanks Jazz.

I had thought that the heavy version of the 45x45 would be strong enough as it is bolted along the back of it's whole length to 9.5 plate. I will look at replacing the top section with 45x90 then. Do you think this will be enough?

I'm hoping that tapping into 9.5mm plate... 90% more threads.... is just ok then?

[JAZZCNC]

I had thought that the heavy version of the 45x45 would be strong enough as it is bolted along the back of it's whole length to 9.5 plate. I will look at replacing the top section with 45x90 then. Do you think this will be enough?

Nah even the heavy version isn't has strong as you think.!! The 45x90 will be better but I'd put it top & bottom and have the wide bit flat.
This way it ties into the sides better and gives more resistance to bending in lateral cutting directions.! It doesn't Add much to the vertical up & down strength plunging will inflict but the 10mm plate will help here and plunging should be avoided if at all possible anyway.! Most of the time the machines cutting and the forces are lateral.!!

10mm is just about ok for threading in Alu.

[WandrinAndy]

The 45x90 will be better but I'd put it top & bottom and have the wide bit flat.
This way it ties into the sides better and gives more resistance to bending in lateral cutting directions.! It doesn't Add much to the vertical up & down strength plunging will inflict but the 10mm plate will help here and plunging should be avoided if at all possible anyway.! Most of the time the machines cutting and the forces are lateral.!!

I would have thought that my design as pictured already provides lateral resistance roughly equivalent to what you're suggesting, as a cross-section of the bottom of the gantry consists of 45x45 bolted close to the backwards pointing 51mm leg of the 9.5 angle? And the 9.5 angle extrusion is bolted to both the base and the uprights of the X-carriage hopefully creating a very rigid joint?

[Jonathan]

9.5mm is definitely fine for M6 since none of the forces on this small machine will get anywhere near the rating of an M6 bolt. I'd advise using threadlock to make sure any bolts don't vibrate loose.

- RM1610 ballscrews on X,Y,Z

Good choice for X and Y but there's no need to use 10mm pitch on the Z-axis. Keep the resolution by using RM1605 on Z.

[Jonathan]

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:

[WandrinAndy]

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.

Thanks Jonathan... Pics really help visualise things... Looks to me like those mounts are milled down to about 3mm? Have you noticed you're missing a bolt in pic-1... or is that one an optional extra... Lol

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?

[Jonathan]

Looks to me like those mounts are milled down to about 3mm? Have you noticed you're missing a bolt in pic-1... or is that one an optional extra... Lol

Yes something like that... you don't need much thickness if there's plenty of material around the motor mount surface to stop it bending. I missed two screws in that picture as it was just a test fit.

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.

The drawings are available from the Hiwin website by the way...
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...

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?

Ahh didn't notice that. With either size rail I would prefer to see them mounted on a strip of aluminium and have that bolted to the aluminium extrusion to spread the load. Hiwin 20mm linear guides are 36mm tall and the 15mm variety are 24mm tall, so if you mount the 15mm rails on a 12mm thick strip the rest of the drawing stays the same. In addition this maintains a good spacing between the 4 blocks which is necessary for good rigidity.

[WandrinAndy]

With either size rail I would prefer to see them mounted on a strip of aluminium and have that bolted to the aluminium extrusion to spread the load. Hiwin 20mm linear guides are 36mm tall and the 15mm variety are 24mm tall, so if you mount the 15mm rails on a 12mm thick strip the rest of the drawing stays the same. In addition this maintains a good spacing between the 4 blocks which is necessary for good rigidity.

The Hiwin pdf I downloaded from Zapp about a week ago gives the height from bottom of rail to top of block as: HGH20CA = 30 and HGH15CA as 28, so much of a muchness. Are you figures for a different model or have I cocked up?

Yep, I will also need some milling done in the Z/Y plates.