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

[njhussey]

Been playing a bit more with Sketchup and added the spindle (see seperate thread for details on the spindle as designed by blackburn mark http://www.mycncuk.com/forums/showth...shless-spindle) steppers, leadscrews etc...

The more I look at it the more I am going to have to re-design the gantry as at the moment it will be too heavy. Will have to apply the KISS principle I think...

Below is a quick walk round video exported from Sketchup.

[njhussey]

Been chopping up some Delrin for lead screw nuts tonight, couldn't find my chop saw plastic blade so used my mitre saw instead :naughty:

Will finish off the round nuts in the lathe tomorrow lunchtime and finish tap them and also drill the white delrin and tap that as not sure which ones I'll use yet.

Hopefully my boring bar also comes in the post tomorrow as I can't wait to carry on with my DIY spindle

Still playing with my design...:whistling:

[blackburn mark]

i always use my mitre saw on delrin that i cant get to with a slit saw, a bit of elbow grease LOL.... id almost forgot what that is

[njhussey]

Well after doing nothing on this for months I'm going to cheat and use MDF to make the gantry sides (yes I know I know!!!) to get the project back under way as I'm spending all my money on RC helis. Then once it's working I'll use the machine to make upgrade bits for itself. The second router is already in the design stage, going to be a supported rail, twin leadscrew design...

[njhussey]

Hmmm seem to have been away for ages again...still now bought a small welder so will start cracking on with the fabrication.



Finally decided to do 2 machines, one for balsa and one for ally...the one for ally will be a small one I can also use for labels etc...

[njhussey]

I really should stop playing about with the design and get on and build the damn thing.....but I keep reading posts on here and changing things. Was going to go with a framed gantry but then everyone says to keep the sides down to a small height to increase the stiffness.

Here's my latest design, can you guys comment on it please? It's going to be predominantly for cutting balsa and ply, the odd bit of plastic, carbon fibre and possibly aluminium components for RC planes, helicopters etc. There's only 100mm of height, but as the thickest balsa I'll be cutting is probably 1/2" it should be fine.

The box frame is 40x40x3 mild steel, the flat plate is 12mm 5083 Ali, the rails are SBR 16, most probably from linearmotionbearings2008. There are a few things which need tweaking to make them fit (Z axis bearing plate needs to be made the same width as the bearings etc.) so I'm aware of them, it's just the basic concept/design.

[Jonathan]

I would make the mounts for the X and Y stepper motors/ballscrew fixed end bearings stronger since they have to support the axial force on the ballscrews, so any deflection in those mounts directly causes inaccuracy in the tool position.
On my machine I have SBR20 and SBR25 rails and it is clear that the 25mm rail system is substantially stronger, presumably (apart from the obvious reasons) because the bearing blocks have an extra row of balls. I urge you to consider at least using 20mm rails as it shouldn't cost that much more, although it does mean increasing the box section size to 50mm.
Have you considered using pulleys and timing belts to drive each axis? This can simplify mounting the motors, reduce resonance, improve feedrates or resolution, among other things.

[njhussey]

Thanks for the comments Jonathan, I'll beef up the mounts and possibly look at pulleys. This router will be used for mainly balsa and ply so I cant see the need for the 20mm or 25mm rails, surely the 16 will be strong enough? The only Ali I'll be cutting on it will be thin stuff for horns, brackets etc. out of 1mm or 2mm thick.

If you look at the below router it's made out of 30x30 Ali and skate bearings and cuts balsa fine for making models! Yes it's not fast or particularly accurate but was fit for the purpose it was built for...



I will be making a smaller stronger router/mill for doing Ali blocks/brackets etc at some stage in the future and this will be made with linear rail and all the other goodies!!

[njhussey]

Just got myself some 10mm Ali plate from fleabay for a (what I think is) bargain price.....aluminium plate 10mm thick 2200 x 950 mm approx 87" x 37 1/2" Pickup floor | eBay Now going to look at the design and get drawing some parts to get made :D Need to invest in a pillar drill now to get all the holes drilled nice and square!

Jonathan, I've been looking at the 20mm rails and you're right they're not that much more so will get them...

[njhussey]

Chai quoted $246 for the rails for my router so I think I'll get them when I've got the money soon. Picking up the Ali plate in a bit and have someone with a CNC router going to cut the bits for me :D

Just one thing to ask. would it be better to have the y axis rails spaced apart and the ball screw (well trapezoidal rod for now) through the middle and have some plate on the back to stiffen it up? This would bring it nearer the spindle and reduce the twisting when cutting?

Very quickly moved things around as per the below (yes I know things need sorting but just wanted to show what I was on about...picture paints a thousand words and all that!!)