Wobblycogs CNC Mk1

[Wobblycogs]

So size does matter! ;-)

Yep, and as with everything bigger is better :-)

I'm having a love hate relationship with the legs where they are.

The two upsides that I can see are that I can have a more rigid gantry without losing X travel that wouldn't have been lost anyway and it gives me a 50mm recess each side that I can move the Z-axis into. I'm hoping that will allow me to achieve 800mm of workable length on the Y axis but I'll be happy with 700. The downside of course is that the machine has to be that bit longer in X. The longer X is though the small the loss is as a percentage of the total length - yet another reason bigger is better :-)

[Jonathan]

You should be able to fit the gantry into 280mm, maybe 300mm, quite easily, especially if you let the Z-axis stick out at the front. On my machine the X-axis bearings are 300mm from end to end, which is adequate. It's certainly good to increase that if you can, but not absolutely necessary. The same is true for getting the centre of mass to lie precisely between the bearings on X.

You can make a sufficiently strong Z-axis 160mm, maybe 150mm, wide so the frame doesn't need to be wider than the Y-travel plus 160mm. Again, if you want to make the Z-axis wider and space the bearings out more that's a good idea to get better rigidity.

Nema 23(/24) motors will be fine for the Y and Z axes. For X, try using irving's spreadsheet:
http://www.mycncuk.com/forums/faqs-p...do-i-need.html

[Jonathan]

Hmm, just read the beginning of this thread again. You're after 1220mm travel on the X-axis but we're discussing buying 1800mm ballscrews, so did you suddenly decide to increase the travel?

300mm is a good width for the gantry, so to get 1220mm travel you could easily use 1550mm(ish) ballscrews. If you're slightly more imaginative with positioning the bearing mounts then you only need the travel plus the length of the ballnut and end-machining, which for RM1610 is 57mm for the ballnut and 76mm for the end machining (including 10mm extra for the pulley). That makes the required length 1220+57+76=1353mm. Call it 1400mm just to 'be safe' and suddenly the motor and ballscrew choice becomes a lot easier as the critical speed is much greater...

On my machine the rails are 2000mm with 2094mm ballscrews and 1700mm travel. The new rails I got are 2200mm, but I'm keeping the travel the same and using the extra 200mm to increase the bearing spacing (among other things!) and using the same ballscrews. This is a similar situation since the frame and rails will be a fair bit longer than the ballscrews.

If you're after more travel then you could get about 1650mm travel with the 1800mm ballscrews.