NordicCNC's build log

[NordicCnc]

Thought you said wanted a good surface finish.!!. . . . Any decently built machine will give you that finish.

Hehe, seems like we have different standards! I think that finish is quite good and I would be happy with that. Of course, I will try to achieve the best finish I can with my DIY build. I will not settle with decent, if I can get good.

Also:
If you go with 30mm rails and 25 or 32mm ball-screws then you can forget 180w or 400w servos. The extra inertia will freak a 400w servo motor when trying to stop 25mm screws from 3000rpm that are attached to a reasonably heavy Gantry which is sat on heavy bearings with a heavy ATC spindle hanging off it.

The best machines are those that have the right balance of power and weight which means getting the design and components matched. The choices you are looking at now will give you a very unbalanced machine.!

Yes, I got confused with the advice from jarjar. It seemed quite contradicting to the general advice I've seen on the forums. He mentioned that a 400W would probably be the bare minimum. Anyway I don't plan to rotate any ballscrews with 3000rpm. I will use at least a 2:1 ratio, resulting in max. 1500rpm.

20mm screws and rails are more than enough for a machine this size. Regards the screw size and whip etc then forget whip calculators because they can't and don't account for the whole machine.

As I planned from then beginning, to use 20mm rails. Thanks for confirming!

If you want proof if 20mm won't whip at 15mtr/min then just ask anyone who's using them on similar sized machine.! . . . .

I've seen those builds, which is why I was skeptical and questioned jarjar's advice about the huge ballscrews.

I've built dozens and trust me they don't if properly aligned and with correct end bearings. However, I've told you how to eliminate any chance of whip and still get the speed you require.

Correct. About preloading the ballscrew with tension, using double fixed bearings. Is there any guide how to do this? I guess the applied force by tightening the fixed bearing nuts will be critical?

Regards the weight then I think you must have got something wrong because a machine this size will easily weigh more than 200kg, even 300Kg by time it's all finished.

That is exactly what I said, that I expect it to be around the 300kg mark once finished. Probably above! :)

Also on that note, you have to factor in the Servos and the extra resolution and power they offer over steppers. This means you can use higher pitch screws and still end up with good resolution compared to steppers. Use this along with applying a ratio and the screw speed can be lowered greatly.

My plan is now the following:

- I will build the machine with motor brackets than can be replaced. This will allow me to at least first test the 180W JMC servo motors. If they are not powerful enough even experimenting with ratios, I will have to buy new motors - probably some 400W servo motors or get stepper motors. This will be an expensive learning lesson, but that is life! I will most likely never buy any parts before design is ready again, lol.
- 20mm HIWIN linear rails on all axis's.
- 2010 ball screws on the Y-axis (base frame).
- 1610 or 2010 ball screw on the X-axis (gantry).
- 1605 ball screw on the Z-axis.