Clever lady - welcome aboard.

 

I immediately clicked on this as I had had the same idea when redesigning the xcarve.
This looks like a much nicer machine and begged to have the same mods done.
Love your Onshape document (but then again I might be biased as my name is on the Onshape patent )!!!!
My concern about this design is the loss of the direct screw drive when adding belts - I want a machine for some very intricate work.
I am not sure how far your build has progressed, but I am wondering if you would be able to comment on any loss of resolution?
GREAT WORK!
Philip

 

1) There'll be a lot of flex in the structure at that size, probably more than you immediately anticipate, but you can dial back cutting speeds/forces or reinforce the machine as necessary- the torque to drive more weight is readily available.

2) The screws themselves will also be a source of imprecision; potentially up to around +/-0.1mm at any given point. Stated precisions (when they even exist) are often optimistic on hobby-grade parts, which often render attempts to build high-precision machines somewhat futile.

 

Rob - I am new to the 'OpenBuild' machines and note they are using Acme lead screws - is there a drop-in recirculating ball screw upgrade kit or are we pretty much on our own here? Do you think it would make any/much of a difference?

Many thanks - Philip.

 

I don't think any "kits" as such exist, but ball screws will often claim "antibacklash C7" and still have 0.010" of lash and up to +/-0.3mm vs nominal readings across the deck. No different to lead screws, essentially- if anything slightly worse because lash-reduction systems are more complex. The problem is in the rolling method of manufacture, I think. Generally I think more highly of ballscrews, but they're more difficult to use with simple control systems like grbl which don't have backlash compensation. My only grbl machine is belt-based, which grbl excels at (all of these big routers were originally belt driven too, once upon a time. Didn't work all that well, but did spawn some ingenious belt rigidity systems)

The problem is, ground screws of either type typically cost in the low four figures, and will only serve to show up the inadequacies of the rest of the machine (eg. you can push fairly lightly by hand in the middle of a 1500mm C-Beam and get up to a millimeter of deflection).

Hobby grade parts produce hobby grade results, unless extreme care is taken and the appropriate metrology equipment is available. But at the same time, that works just fine for most people. It's just that "precision machining" is typically going to be fairly out of reach.