View Full Version : BUILD LOG: I need to lose weight !

11-11-2017, 02:05 AM
I have a reasonable stock of short-ish lengths of steel, box section, angle and flat bar and I plan to design and build a welded and bolted machine approx 1100x850 (mm). That is the outside of the frame. I have plenty of 100x50x5 box. My calculation is that the main beam of the gantry would weigh 8.4Kg and you could probably triple that with the sides, rails, screws and motors.

I reckon I could lighten it by cutting out the sides, taking 12 60x60 triangles out of each side, but this would only reduce the weight by 1.8Kg, so no real gain there.

I have also enough 50x50x3 box to make the whole machine, but I would prefer a beefier gantry.

So is a 25Kg gantry stupidly heavy ? I would like to make a really sturdy machine after my experience with my current wibbly wobbly A4 MD butter cutter.

Comments please, so I can start the design off properly. I have attached a dwg file of the cut outs I envisage on the gantry sides.



23185 This is an AutoCAD R14 file, but it will open with most 2D drawing programs.

11-11-2017, 09:27 AM
Rob, for comparison purposes, my machine is roughly1800x1000. The gantry is built from the equivalent of 4m of 50x50x3 box section steel. Then there's a couple of 20mm Ecocast plates, about 450x200, plus weight of ballscrews, motors, spindle, etc. I'm probably looking at around 50kg for that lot - I keep meaning to work it out but haven't done so yet. It's all driven with two 3Nm motors via twin 2005 ballscrews and 1-1 belt drive. The inertia of the ballscrews is a much bigger load than you would expect and makes weight-saving a lower priority. I get 5m/min rapids with reasonable acceleration (important to me as I end up doing a lot of small fiddly work). By bringing the length down you might be able to go to 16mm ballscrews which is a great inertia-saving measure in itself, and I'm not sure I would bother chasing the odd kilo here or there. Unless you want the cutouts so it looks pretty, of course!

11-11-2017, 01:15 PM
Unless you want the cutouts so it looks pretty, of course!

Actually I want the cutouts for bracing fillets for the frame (well, that bit that the frame sits on). 60x60x5 triangles and 24 of them !

I think, however, that the cost of getting the beam laser cut would not justify saving a couple of Kg.