I started designing early in 2013, as I wanted a larger machine than my first one. I built the Z-axis and gantry beam in march and april. Then there was a long pause until november, when I made the gantry side plates and the gantry parts under the table. I spent all christmas making the table and was able to fire it up for the first time in the first week of january.
The work range is 2030x710x180 mm, and it's more rigid than my old router in all directions, based on simple measurements with a baggage scale and a DTI. I used a single 25x10 ball screw under the table, and was a little worried that I'd have racking problems, so I made the ratio between the X bearings length/width spacing 1:2, and I think I have achieved negligible racking. I made holes in the aluminum bearing plates by the gantry side plates so that it would be easy to upgrade to a twin ballscrew drive, just in case. The reason for the odd shape of the side plates was to make it possible to cut them in my old router, which is just 1000x300mm.
Regrets/problems:
-I should have made a rotating nut assembly for the X. Not a big problem though, as I'm getting 6000 mm/min without whipping, but it would be nice to jog at 12000 with such a long axis.
-I should have gone with profile rails and trucks instead of supported round rail. The drilling and straightness of supported round rails were much worse than I had expected.
-The main beams of the table are a little lightweight. I should have used steel for those instead of aluminum, as the table will bow a few 1/10 of a mm in the center with full weight, but it's probably not going to cause any problems.
-The Y ball screw was bent and turned offset when I got it. I was able to turn it undersize in my lathe, but it doesn't sound good, so I'll replace it later.
Plans:
-Make a housing that moves with the gantry to contain chips and dust, and extract fumes from the alcohol coolant.
-Sturdier feet.
-A rotational 4th axis.
-A belt drive spindle assembly with ER20 collets.
The almost finished Z-assembly. Spot the mistake?
Attachment 219202
The backside of the Z. Room for a 16mm piston pneumatic actuator on the left to help lift the assembly:
Attachment 219204
The main gantry beam. A heavy duty channel profile:
Attachment 219206
Gantry side plates. Skinny but strong. 2024-T3/MDF sandwich. Pockets for the accordion dust protection:
Attachment 219208
The complete gantry:
Attachment 219210
The table during construction. Making all those gussets from square tubing was a pain:
Attachment 219212
DIY mist coolant:
Attachment 219214
Dust shoe:
Attachment 219216
Almost ready to run:
Attachment 219218
Backside with the cover off. The expansion tank for the pneumatic actuator is visible inside. Dust covers on the Z:
Attachment 219220