Heya,
Been lurking for a little bit and would appreciate some feedback and ideas on a somewhat uncommon "lifting X-axis" gantry mill. Here is a very rough mockup from Fusion360, it's still missing a lot of detail but hopefully it's enough for discussion. General theme is to use scrapmetal and old "leftovers" as much as possible.
Goals:
- Ability to machine parts out of aluminium and steel, softer materials aren't of a big interest to me at the moment
- Not expecting stellar accuracy, but hoping for something like 0,05-0,1mm on the finished part
- I am quite limited on width in my garage, but depth space isn't a problem. Hence one reason for this somewhat deep Y-axis
- Travels of approx 300x400x400
Frame materials:
- Not pictured, but for a subframe and legs I have various 5mm and 10mm RHS available
- For the lifting X-axis "gantry" I could use either 45mm plate steel or 200x100x10 RHS
- For the "table top" that the Y-axis linear rails attach to I have part of an old cast iron paper cutter table, it's about 12mm cast iron with reinforcement ribs
- For the Z-axis uprights I have sourced 220x120x10mm RHS, for the beam between the towers I can use for example 180x180x8mm RHS
- As a fixture plate I was planning to use a 300x600mm cut of 45mm steel plate with a grid of threaded holes. Mild overkill I guess, but reasonably priced T-slot tables are pretty hard to source here in Finland
- Welded table frame, but would use bolted joints in the critical places (Z-axis uprights to base frame etc) to allow shimming/tramming
Spindle:
- I'm aiming for sub-10k rpm so will probably end up with a bt30/iso30 spindle. I have a couple sketchy options lined up, either an aliexpress special bt30 as pictured or I might try to resurrect an old worn out Fanuc Robodrill spindle
- The spindle housing is very much TBD as it will need to follow the spindle. Can be 200x200x12 RHS or something bolted together from 45mm plate steel
Linear motion:
- Planning to use LinuxCNC with a Ethernet Mesa card
- I have 6m of THK HSV25 linear rails with some carts, was planning on using it at least for for X axis as it only sees the weight of the spindle housing, motor and spindle. Could probably also use it for the Y-axis too? I have some Hiwin HGR30 carts so might source some rails to match those for the Z-axis, as that probably sees the most stress having to carry the whole X-axis + spindle parts.
- Planning on using closed loop steppers
- Ballscrews are a bit of a question mark, plan B is to just go with the Aliexpress special "C7" rolled ballscrews, but still seeing if I could dumpster dive something better accuracy wise
Questions/concerns:
- I guess the Z-axis uprights could use quite a bit of gusseting to prevent Z-axis "nod" ?
- Is 45mm steel plate overkill as the X-axis cross-beam? The other option is carving out 200x100x10 RHS to run the ballscrew inside the RHS. This feels like a pretty elegant design assembly wise, but I guess 10mm wall thickness might not be rigid enough for steel milling?
- Could I get away with lifting the X-axis with one central ballscrew on the Z-axis, connected to the beam between the uprights? Or is it asking for racking if the spindle is near one of the extremes on the X-axis? Currently I have drawn two ballscrews on the insides of the Z-axis uprights, but simpler is of course better