Gear reducing kit recommendation

[JAZZCNC]

Regards the ballscrews, yes at this length they do bend under there own weight and you can't spin them very fast because they will whip. This is why rotating ballnuts are a better choice at this length because you put them under tension to lessen this. However, even with a rotating ballnut and the screw under tension the screw can vibrate when traveling at higher feeds. I recently built a 10 x 5 machine using 2525 screw which where put under tension and above 20mtr/min the screws would vibrate slightly when the gantry was at either end. If doing again I would consider using 32mm screws.!

However, it can be done using a rotating screw but requires careful selection of the screw pitch and using a ratio to lower the screw speed. Also, you can add spring loaded support tensioners to support the screw which get bumped out the way as the gantry travels past them.

Those Gear reduction units you linked to are not very well made, they are what come fitted to most of the Chinese Routers. The pinions are one piece untis and wear very quickly, the castings are very brittle and easily crack. The bearings are usually poor quality which don't last very long, these I would replace before fitting to avoid doing at later date.

Regards servo's then personally I prefer the simplicty and reliabilty of Closed loop steppers for wood routers in a Non or low production enviroment. Only if you need the extra speed or power they offer would I consider using them.

Yes they are faster, smoother and quiter than steppers with much more pwoer but they are also like High performance Cars in that require more tuning and setup to get the best from them and the rest of the electronics and machine needs to match otherwise it's wasted expense. Also, they will actually hold the machine back rather than make it better as you'll struggle to tune them correctly if things are not perfect as they are not very forgiving of low quality workmanship or vibrations in the machine.

This is why you'll often see steppers fitted to lower spec Rack n pinion router machines because the slop in the machines makes tuning servos a nightmare, esp the cheap Chinese servos which don't have any fancy software to help with the tuning.

3 phase Closed loop steppers with 220Vac mains powered drives are a great choice for a large hassle free machine. The 220V means you get plenty of speed and power from them and they offer very good level of positonal accuracy and while slightly lower resolution they work exactly like a servo does in terms of maintaining positional accuracy and keeping the loop closed between Motor and drive. Only if you go to a fully closed loop setup do servos offer more.

If it was me building this machine I'd use 32 screw with 32mm pitch and rotating ballnuts with 2:1 ratio if using steppers or 3:1 if using servo's.

If using Rack n pinion I would only use helical type as it's much smoother with lower backlash. I wouldn't spring load it into the rack as it's too easy for it jump and chatter, esp with high power motors. I would just buy precision ground rack and accept that you will have a certain amount of backlash to deal with, which for most wood routers this is often more than good enough.
If you are wanting higher precision then you really have no option than to go with ballscrews and use a rotating nut setup to avoid the hassles of long screws.