Comments sought on new build: A CNC Router for RC Gliders and Planes

[njhussey]

Just got another bargain bit of Ali on fleabay...20 mm Aluminium Plate | eBay

Might have to think about re-designing my router now to take into account the 20mm thick Ali

[njhussey]

Guys, I'm now in a quandary as to which direction to go in my build. I'm going to have to have the router in a shed (10' x 8' it's grown since my previous post as I've been looking at how much "useful stuff" I've recently acquired!!) so space will be at a premium. As I'm mostly going to be cutting balsa, 3mm thick ply, the odd bit of plastic and thin Aluminium (for control horns etc.) do I go for a bigger design I've been working on or stick with the original design? The original design gives me 700mm x 300mm cutting which is ample for what I need it for (not thinking of future expansion though) with 1000mm 20mm rails and 16mm ball screws and the new design gives me 995mm x 500mm with 1300mm 20mm rails and 16mm ball screws. I've been considering also mounting the new design vertically to save space (after remembering Jazz mounting his, almost, vertically.) For the original design I've already fabricated the base but seeing as I have access to getting hold of cheap steel through work, fabricating a new frame will not be that hard or costly.

I'd appreciate your thoughts as I'm in two (possibly more) minds....

[JAZZCNC]

I've been considering also mounting the new design vertically to save space (after remembering Jazz mounting his, almost, vertically.)

If your space challenged then it's a no brainier to me go vertical. There's no down sides only gains, space being the biggest gain.
My machine mainly (99%) cuts aluminium and other than the space saving the other benefits are below. Wood cutting will be similar and possibly better with vacuum for chips.

Better quality of finish due to gravity helping to clear chips.
Much Longer cutter life due to less re-cutting chips, over 50% less wear.!
Greater DOC can be used for roughing again due to less heat and work re-cutting chips.
Less air required for blown air/mist cooling again due to gravity and less chips to clear. Down from 50-70psi to 10psi and obviously much less volume of air required.
Less chips flung around shop again due to gravity and cut chips being cleared more efficiently so not getting re-cut and thrown about with 80%+ falling into bins below machine.
Much easier access and loading/clamping of material due to bed being directly in-front of you, no more back aching bending over fastening material.
Better access to spindle and tool loading.

Has you can see other than the major space saving there's quite a few other decent quality benefits and I can honestly say there's been NO down sides.

Yes there's things I've learnt from being vertical about design that I'd build into a purpose built vertical machine. These would mainly deal with lessening chip collection on various surfaces.
The Z axis would be one area I'd look at and build more shielding around. Ball-screw bearing blocks would be another and I'd build shielding to stop chip collection.
Both of these are only minor things and don't affect the machine in anyway also my machine has NO protection of any kind for belts,ball-screws so they would be things I'd do anyway if was building again and it was horizontal.

The other thing I'd do with MY particular machine is raise the whole thing up higher than it is now.?
At the minute it's just in the same spot it was when first tipped up, sat on same axle stands. This means the bottom area of the bed lower than I'd like also the gantry when parked at top is not quite above head height and I bump my head on it when removing material. Also it's just makes fitting tools into spindle a bit more awkward than could be.
Both of these things are Still much better than when horizontal but if machine was 12" higher they would be perfect.

Now before folks comment on material holding etc other than requiring holding on first placement until clamped then it's absolutely no different to when horizontal.
This initial holding is easy over come with a simple temporary holding shelf I slide into position to place against material edge, which I then slide out the way while cutting. The slight incline of bed then holds it hands free against bed while I clamp or screw it down.
Just like when horizontal both cut parts and waste material needs to be clamped for safety's sake. To be honest it's actually safer regards waste because it mostly falls away from cutter and off the bed so with thought about placement of material cutting entry IE: always starting/exiting at top then there's far less chance of material being pulled back into cutter. That said I also have and do fasten waste material has it's just best practice.

Hope this helps.!

[njhussey]

Jazz, in your opinion would the router be better at a slight angle (15° in this case) or at 90°?

I can see the slight angle as better for work placement as the work will "fall" against the bed and the chips will still fall away into the collection tray at the bottom. I've added some sheet steel sides (that might need more support to stop resonance) so those will stop the chips from being flung all over the place. Just need to work out some shielding for the ball screw lower bearing mounts, and the stepper mounting arrangements and a few other details and I should be good to go I hope?

[JAZZCNC]

Jazz, in your opinion would the router be better at a slight angle (15° in this case) or at 90°?

Yes defiantly have inclined just helps hold material better while fastening other than that there's no advantage.

Model looks nearly there. Don't think you'll need the tray that wide and If your not using coolant then wouldn't make it part the machine just use removable plastic bins which you then use to take chips to out in. My bins stick out from front of bed about 6-8" when cutting and I just slide them back a bit while loading material.

One thing you want to build into machine is a bump stop at the bottom where you park the machine when not using it. This takes the load off the ballnuts and belts.
My machine doesn't drop when stood without power to motors but only takes the slightest of push to make it drop. Only really required when leaving over night or several hours stood still and in normal use IE: between jobs etc I just park gantry at the top in the home position and it's fine.
I home the machine to top left corner when facing the machine. I have a park button on my screen and it goes to the bottom and rests against the end stops.
I don't use limits only home switches has I never normally get any where near them in normal use and rarely cock up bad enough to get near them these days so it's not a problem with tripping switches. If you where using limits then you'd have to build limit override into the parking routine which is easy enough.

[njhussey]

Cheers Jazz, the tray will be a removable metal one (I’ll get the local tin bashers to knock one up from 2mm steel and run a weld up each corner to seal it and it’ll be loose in between the frame so I can lift/slide it out. I’ve still got to detail things like all the stepper mounts, end stops, limit switches etc. but didn’t want to go into too much detail before getting the basics done! I’ve quickly added a couple of stops at the bottom of the rails and added/changed the stepper mounting brackets for the X and Y axis.





I’ve half a mind to make the leaning frame in one piece and the router bed in one piece and bolt them together. This way I’ll be able to separate them in the event of a move (very likely in the not too distant future) so I won’t need a Hiab to lift it over the back wall to get it out of the garden!!


I now have a few questions to ask before I get going on ordering bits and pieces for the build so again would appreciate the benefit of everyone’s combined knowledge!

I’m going with SBR20 rails for all 3 axis with SBR20UU carriages. X is 1300mm long and Y is 750mm long, Z is 400mm.


Ball screws. I was thinking of 1605 (from Chai) driving them with belts at 2:1 ratio on the X & Y axis and 1204 for the Z being direct drive from the 3Nm stepper. Is the 1204 ball screw OK for the Z or is it better using the 1605? I’d be happier using the 1204 to use the smaller ball nut and therefore getting an extra little bit of length on the X axis.


For the Stepper motors I was thinking of 4 of the 60BYG301B 3.1Nm motors from CNC4YOU? Any others to consider, the SY60STH86-3008B from Zapp? Any difference (I can’t see any in the specs particularly) in the two apart from price?


I’m thinking of going with either the CW-885 Drivers from CNC4YOU or the AM882 Leadshine from Zapp. I’m leaning towards the AM882 but what are your thoughts? I take it that I can drive the 2 X axis steppers from the same driver so will only need 3 drivers? Is the performance of these drivers much better than the 50V drivers? I think I’d rather spend a bit more and have better “future proofing” even though for cutting balsa and thin ply the 50V drivers will be fine I’m sure I’ll be cutting Ali and all sorts after a while!


Which BOB would you recommend?


Power supply. Is it best to buy one readymade, i.e. the PS806-5 from Zapp, or have a go at making my own? Is there a significant saving to be made?


I was going to do this all on a shoe string budget (see first post on this thread!!) but now don’t have to so would rather buy decent equipment (without going completely over the top!)

[JAZZCNC]

Ball screws. I was thinking of 1605 (from Chai) driving them with belts at 2:1 ratio on the X & Y axis and 1204 for the Z being direct drive from the 3Nm stepper. Is the 1204 ball screw OK for the Z or is it better using the 1605? I’d be happier using the 1204 to use the smaller ball nut and therefore getting an extra little bit of length on the X axis.

No wouldn't do that go with 10mm pitch and if around 1500mm then I'd go with 20mm screw, chai now sells these.
Yes 1204 will work ok for Z axis, my machine uses that size. That said I always tend go with 1605 on machines I build has they are more readily available and bit more meat for pulleys etc, they also allow slightly higher tuning.

For the Stepper motors I was thinking of 4 of the 60BYG301B 3.1Nm motors from CNC4YOU? Any others to consider, the SY60STH86-3008B from Zapp? Any difference (I can’t see any in the specs particularly) in the two apart from price?

Either there's very little difference, I've used both.

I’m thinking of going with either the CW-885 Drivers from CNC4YOU or the AM882 Leadshine from Zapp. I’m leaning towards the AM882 but what are your thoughts?

Not used the CW-885 but they will have to be very very good top beat the Am882 so for me it would be the tried and known AM882.

I take it that I can drive the 2 X axis steppers from the same driver so will only need 3 drivers? Is the performance of these drivers much better than the 50V drivers? I think I’d rather spend a bit more and have better “future proofing” even though for cutting balsa and thin ply the 50V drivers will be fine I’m sure I’ll be cutting Ali and all sorts after a while!

NO Bad idea Each motor needs it's own drive. You could in theory run 2 drives from one signal output but don't run 2 motors from 1 drive. I wouldn't recommend using one output has it leads to timing issues and inaccuracy's etc and not worth the hassle.

Couple of reasons for not running 2 motors from 1 drive. The drive ratings are split between both motors so 80V 8A would only allow 80V and 4A for each motor. Most 3-4nm motors are around 4-5A so not enough and plus it's working the drive very hard shortening it's life quite a bit.
BUT bigger reason is the Resonance handling of the drive can not work properly and doesn't know which motor to apply resonance compensation too and gets very confused with result being the other motor gets pushed into resonance.
Believe me you don't want resonance issues they are a night mare, resonance can/does cripple the performance of a machine.
By the way the AM882 are fantastic at handling resonance, you can hear and certainly see the smoothness compared to Analogue and some of the cheaper digital drives.

Another thing to consider when using slaved motors on a Axis is that you will want some way to square the gantry and for this you need 2 Inputs for home switches because each screw needs to be turned individually while homing.

Which BOB would you recommend?

No contest PMDX 126 hands down the best. . . Cheap NO.!!

Power supply. Is it best to buy one readymade, i.e. the PS806-5 from Zapp, or have a go at making my own? Is there a significant saving to be made?

Again no contest build your own this way you can have the exact voltage and Amps required plus it works out cheaper because you'll need 2 of the PS806-5. Will build your own for less than one PS806.