Thread: Big-ish router concept review
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20-04-2017 #1
Hi,
I've been lurking for some time, this is my first post. I'm considering building a cnc router from scrap parts I've collected over time and I'd like to get comments on the concept, frame mostly - it's a bit different than what I usually see around.
This machine would be used for wood and aluminium work, routing and 3D. Travel area should be 1250x2500x200mm. The idea behind is to use welding and machining only where absolutely necessary, and instead use epoxy putty and bolts for connections and self leveling epoxy for getting everything planar. I'd also like to avoid complicated solutions (like diy rotating or diy dual ball screw nuts) if I can.
1.8kW/24kRPM square spinde would be mounted on "U" section built from bolted alu plates (25mm back, 10mm sides, sides can have extra supports), 460mm SHS15 rails are bolted on the back (Z bed). This assembly would slide through 3 blocks per rail, mounted on 25mm alu plate (X bed) which could also have uprights making "U" section. Z axis would be driven by 400W(3000RPM/1.27Nm) AC servo through 20:30 10mm AT5 belt reduction to 5mm lead ball screw (200mm travel). I haven't figured mounting yet. Total Z sliding mass would be ~25kg, and no counter balance would be used.
X axis would be assembled from 1460mm LH20 rails, and 4 blocks (long, if I manage to repair/reball set of preloaded BN blocks - few balls fell out due to bad packing/shipping and now the blocks jam), and would be driven by 200W(3000RPM/0.63Nm) AC servo through 20:60 10mm AT5 belt reduction to 2020 ball screw. 1250mm travel leaves 210mm width for the X bed. Ball screw will be mounted on the front near lower rail. Total X sliding mass would be ~35kg.
Gantry would be 250x6mm square steel section leveled with epoxy, and instead of welded rail mounts I'd raise X bed on blocks if required. Section would slide on 20mm HG/LG rails with 3 or 4 blocks per rail (400-500mm support length). I have to figure out best solution for the support (currently 25mm alu base plate with 20mm triangle plate), but it should also be bolts/putty solution.
At first I thought implementing rotating nuts for driving the gantry but now I'm thinking that I could get away with rotating ball screws and avoid extra complexity. Total Y sliding mass would be ~120kg, and it would be driven by 2x 150W(1120RPM/1.27Nm) DC servo through 20:40 10mm AT5 belt reduction to 3220 ball screw. Rails would be mounted to epoxy leveled 250x6mm square steel section 3m in length. This again would be bolted/glued to 2 welded "U" sections made of 250x6mm square steel which would allow rough leveling of the rail supports (epoxy putty + leveling screws). "U" sections would be filled with sand or concrete and capped, long rail support sections probably too.
My main consideration is unsupported overhang of Y rail supports (650mm) which would probably vibrate and resonate.
I'm considering UC400ETH controller so I can handle high encoder rates.
What do you think?
Thanks,
Mihael
ps. If someone has experience with repacking balls into NSK LH preloaded blocks, I would appreciate any advice.Last edited by mbele; 20-04-2017 at 11:17 AM. Reason: image source changed from (failed) upload to flickr url
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