New Machine Build- Need help deciding which way to build pls!

[KTP]

Hi guys,

I have finally found a good set of brushless drivers for the tamagawa TBL-S 300 watt brushless motors in the XY-HRS series NSK ballscrew driven slides I have. I want to build a quickie wood/plastic/laser router using these to offload that task from my Shizuoka cnc mill (because it likes to cut metal, but my wife likes things made in wood!). I have come up with 2 easy ways of throwing it together, using 3 slides, for a travel of 20 inches by 37.5 inches by 5 inches. These are the NSK XY-HRS H, M and S series slides. The 20 inch slide is made up of dual thk style linear rails with 2 blocks per rail and the ballscrew inbetween. The 40 inch slide uses a single wide rail (maybe 2.5 inches wide) with 3 blocks on it. Obviously, the 20 inch slide can support more of a moment arm, so idea #1 is to mount the 40 inch slide on top of the 20 inch slide, and have a small single rail with a short block on the far end to help with flexing (but these are very stout slides!).

idea #2 is to mount the 20 inch slide on top of the 40 inch slide, and again, maybe a small single rail to help flexing.

The z axis is just a short S series NSK slide with a smaller (100 watt) drive motor. It still has a 42 lb payload and a 55 lb thrust force!

Here are pics of the 2 ideas...suggestions? I want this to be simple, so I will get it done fast, say 1 or 2 weekends. The cost isn't bad..maybe $1200 total for the slides and drives by carefull ebay shopping over the past 2 years.

[KTP]

A little more info, which might support the less obvious idea#1 (40 inch slide mounted on top of the 20 inch slide).

max rolling moment of the 20 inch slide: 600Nm
max rolling moment of the 40 inch slide: 70Nm

max yawing moment of the 20 inch slide: 350Nm
max yawing moment of the 40 inch slide: 120Nm

where rolling moment = mass(kg) x length(m) x gravity (9.8m/s^2)
and yawing moment = mass(kg) x length(m) x acceleration

The 20 inch slide is 950mm long and has a mass of 23kg

The 40 inch slide is 1420mm long and has a mass of 20kg

Actually, i just had idea 3, which would be to mount the 20 inch slide on top of the 40 inch slide like idea 2, but to put the extra linear rail and carriage very close to the 40 inch slide, thus increasing it's yaw and roll moment significantly. The free end of the 20 inch slide would just hang in the air, but as I said, it is pretty stout for a wood/plastic/laser router

[Med-Pac]

What kind of tolerances do you want to acheive? It looks like you'll be driving the "gantry" on one side? I think you'd be alot happier with drives on both sides of the x though it may cost alittle more.

Mike

[KTP]

Hi Mike,

For wood, I don't need anything better than 0.01" but for when I use the 60 watt CO2 laser with it, I would like to be around 0.002" or better. The slides themselves are rated for 0.0005" or better. They use really nice hardware inside.

Anyway, I scored another of the 20 inch slides on ebay just now. It was brand new, with a 400 watt yaskawa servo motor and a 20mm pitch. Now I am thinking I will just mod the design just a bit and use the 10mm pitch 20" slide as the base in a moving table design, and mount the 20mm pitch 20 inch slide I just bought on a fixed gantry above it. The little z slide will then mount to this. Advantage? All I have to do is bolt a tooling plate to the base slide, make a quicky fixed gantry out of 8020 or something (perhaps with a 45 degree bracing strut on each side), mount the Y to that, mount the Z to the Y, plug in the cables and go! I think 1/2" thick 20 x 20 inch cast aluminum ground tooling plate should be about right. The 10mm pitch slide can move like 200kg and if I really need to hog down on a part I can always place it in the center of the table where it is fully supported by the 4 carriages on the 10mm pitch slide.

The beauty of the whole thing is that all three slides are protected from dust and chips, all have motors, limit switches, etc. and also it will look pretty dang professional. As I guess it should, since it will be using $15,000 (original cost) of parts to make a wood router!