Gear reducing kit recommendation

[Ale]

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.

Thank you for your reply!
I appreciate your efforts on forum and have been reading a lot of your posts lately. I have also seen vertical cnc machine you have put together, really nice work. I was surprised that that long screws worked that well, until then I thought that screws on machine that big are ridiculous, but you managed it with high pitch screws to avoid whip.

I have also seen design for rotating ball nut made by forum member Jonathan. Those seem really well made and simple. I have sent him the PM if he is willing to sell me 3 of those. But he has not been on forum for about 6 months, so I don't know if that will happen.

You are probably right about those Chinese gear reduction units. They are one piece units, yes, which is bad. And even if I get a high quality rack, there is no sense in getting a low quality gearbox.

My thoughts about servos are the same as yours. They have their place, but for my purposes they are overkill and added complexity (and cost). With proper steppers I should get if not same then very close results. If my steppers are missing stepps while carving or routing, then something else is wrong. And high rapids are not so important to me.

I like the idea of using ball screws with rotating nut, but have trouble finding them. But what is high precision in this case?
I was looking at a C7 grade 2525 ballscrew with machined ends. Price with delivery for 2 of those (3m) is 800 Euro (C7 grade, accuracy 0.05mm/300mm). From here:
https://www.tuli-shop.com/ball-screw-shaft ).
Will this be precise enough for 3d carving? This site does not offer more precise ballscrews with that high pitch. 3232 ballscrews would be about 100 Eur more (C7).

Another option I was looking for were racks. Was looking for Q6 or Q7 racks. Found Q6 racks here (with predrilled holes which is bonus), mod2
https://www.damencnc.com/en/straight...2010-6mm/a2687
They would cost me about 180 Euro/m

I was thinking about using their anti backlash worm gearbox with double pinions (ratio 5:1). But they are quite expensive (360 Euro per piece for gearbox + mounting plates for nema34).
https://www.damencnc.com/en/r-p-driv...15t/a554?c=364

Whole setup with a straight rack from this shop would cost me about 2300 euros for the x and y axis.

I have not looked into helical racks, if you know where to find suitable ones, please let me know. But I see that they are pretty rare in DIY router versions. And so is rotating ball nut.

At the moment, because I am unable to find rotating ballnut, my option is rack and pinion.

I will also look into 3 phase Closed loop steppers with 220Vac you mentioned.

What do you think about rack and pinion setup I mentioned here?

Im stuck here for weeks now :D
Thank you for helping.