Hi everyone !
I have just registered to the Zone. I have read quite a lot of threads on this forum which were quite full of information and inspiration, so I wanted to take part.
I have a freshly retrofitted Sieg SX3 running on TB6560 with mach 3 and ballscrews from linearmotionbearings. This machine runs quite good but I need something with larger dimensions, more rigidity, spindle speed, and off course, axis
I have well in mind what I would like to build, so I will share with you so you can criticize or agree with my design.
The idea is to build a machine which looks like Huron - Graffenstaden fixed table conventional mills. Have a look there :
I suppose you can guess how it works. The only difference is, I want the table to be fixed and the column to travel in X. I had thought gantry at first for stiffness, but I fell in love with this layout.
Now, the special features :
The whole cnc would be made out of granite epoxy mix, with aluminium machined ribs for accurate positioning in the epoxy castings.
I think of at least 1200mm travel in X, 500 in Y, 800 in Z. But as mentionned, I want a 5 axis. So, the 4th axis would be cast with the table on one tip, being parallel to X. The aim is to use the 4th axis as a lathe as well. 700mm diameter capacity would be great. The 5th axis would be a tilting head at the end of the cantilever arm of Y.
I need quality linear rails to ensure stiffness. These would be 20mm Hgw Hiwin guides & rails. Probably fitted with 20*05 ball screws from the same chinese ebayer, with double loaded ball nuts as on my x3. This compensates the small backlash of medium quality ball screws.
Considering motoring, I thought about servos, but I prefer to save money for good rails and get 1200 oz-in steppers for cheap with Gecko drives though. Direct drive for all linear axis of course, with the 10 microstepping mode of the Gecko drives, I would achieve a 0.002mm resolution, no need for less.
About the rotational axis, same stepper configuration for the tilting head I guess, but with a gearhead off course. I don't know which type yet, probably harmonic drive. Backlash is unacceptable here. And quality worm drives cost at least as much as harmonic drives.
I am not sure about the 4th axis though. An AC servo of at least 1kW seemed to be the obvious solution, but a big, direct drive stepper would fit as well. If you think about it, there is no need for speed AND torque at the same time when turning. Torque is required at low speeds. Anyway, a brake would be probably necessary for accurate position holding.
I want to achieve something special about the spindle as well. I think most of the commercial solutions suck. Chinese spindles with a quality VFD for low speeds could be a good solution, with a belt drive for stepping down max rpm and getting some more torque. But it's not that exciting, and I would like something like 5KW for good torque when spinning big mills or attachments. There are awesome inrunner RC brushless motors which are pretty cheap. Have a look at this one :HobbyKing R/C Hobby Store : T5692 Turnigy Pro Comp Brushless Inrunner Motor 1000kv
This little monster is able of 6KW with ridiculous dimensions. Moreover, the price with a suited ESC is just about $250. There is a major drawback though : it will draw at least 150a at 45v for the intended use. The price of such transformer(s) is a no-go. But I would quite like to find a way to use this beast. A TTS-like atc with R8 spindle and 16mm colled would be just riiiight !
Anyway, I hope I made it clear. Feel free to comment upon my ideas, some of which might be utopic or irrealistic. If you think it's great, don't be ashamed to say it as well
By the way, excuse me for mistakes in the language if any.
Greetings from France