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Ale
28-11-2020, 02:33 AM
Hi!
I am building new cnc router and it will use nema34 motors and rack and pinion.
Is there reducing gears set with mounting plate that you could recommend? Or should I just buy gears and make mounting plate?
I like those from Avid cnc, but too expensive for me at the moment (about 650 EUR for 3pcs without import and tax).
I am looking for about 3:1 - 5:1 reduction.

Thank you.

Doddy
28-11-2020, 10:39 AM
I've absolutely no knowledge on the subject of rack and pinion... pretty much no knowledge of most other things to be honest, but... am I missing the plot here... if you're talking of gearing the the pinion, then surely the tooth count of the pinion is essentially the gearing component?, If you go from a (e.g.) 60 tooth pinion to a (e.g.) 20 tooth pinion you'd effect a 3:1 reduction.

Or am I being stoopid?

EDIT: Not trying to answer (or validate) the question, and so this response is clearly off-topic, but just casual curiosity. Also, would think the above could avoid introducing additional backlash in a gear chain

EDIT 2: Just reversed the example tooth count above, having woken up a bit.

johnsattuk
28-11-2020, 01:39 PM
There are motors with incorporated very low backlash gearbox. I have used 5 phase 23 motors with a 10 - 1 VLB gearbox on a servobelt system.

JAZZCNC
28-11-2020, 02:51 PM
I've absolutely no knowledge on the subject of rack and pinion... pretty much no knowledge of most other things to be honest, but... am I missing the plot here... if you're talking of gearing the the pinion, then surely the tooth count of the pinion is essentially the gearing component?, If you go from a (e.g.) 60 tooth pinion to a (e.g.) 20 tooth pinion you'd effect a 3:1 reduction.

Or am I being stoopid?

EDIT: Not trying to answer (or validate) the question, and so this response is clearly off-topic, but just casual curiosity. Also, would think the above could avoid introducing additional backlash in a gear chain

EDIT 2: Just reversed the example tooth count above, having woken up a bit.

Yep you'd be Stoopid, but obviously, I'd say that if you were correct but your not:.:joker:

All you would be doing is changing the effective pitch and not applying any ratio for either torque or resolution. For instance, working with a Mod1 rack. 60T pinion would give you an effective pitch of 60 x 3.141 = 188.5mm per/rev and if you used 20T your still at 20*3.141=63mm pitch. Far too large for most machines.
So even with 20T pinion, you'll still want 3:1 for a router or similar. You also don't want to direct drive off the motor for resonance reasons.

Now to the OP, I would just make your own setup using pulleys, etc.
It's often cheaper and comes with the added advantage of easy ratio adjustments but more importantly, it lowers the amount of resonance which affects the motors. Timing belts are also low backlash.
Gearboxes are ok but limiting if you are not sure on ratios and because they are direct drive to the motor they can introduce substantial resonance into the motor. You also need low backlash gearboxes which are more expensive than the run of the mill gearboxes.

Ale
28-11-2020, 05:49 PM
I am talking about something like this:
https://www.avidcnc.com/pro-rack-and-pinion-drive-nema-34-p-226.html

It is advisible to makre reduction, you get smoother motion, better resolution and more torque.

Ale
28-11-2020, 05:50 PM
Yep you'd be Stoopid, but obviously, I'd say that if you were correct but your not:.:joker:

All you would be doing is changing the effective pitch and not applying any ratio for either torque or resolution. For instance, working with a Mod1 rack. 60T pinion would give you an effective pitch of 60 x 3.141 = 188.5mm per/rev and if you used 20T your still at 20*3.141=63mm pitch. Far too large for most machines.
So even with 20T pinion, you'll still want 3:1 for a router or similar. You also don't want to direct drive off the motor for resonance reasons.

Now to the OP, I would just make your own setup using pulleys, etc.
It's often cheaper and comes with the added advantage of easy ratio adjustments but more importantly, it lowers the amount of resonance which affects the motors. Timing belts are also low backlash.
Gearboxes are ok but limiting if you are not sure on ratios and because they are direct drive to the motor they can introduce substantial resonance into the motor. You also need low backlash gearboxes which are more expensive than the run of the mill gearboxes.

Thank you for suggestion. I will follow that path then.

Ale
20-12-2020, 07:42 PM
After some seaching for designs and thinking about it, I have few more questions. I am building cnc router for wood. 2500x1300x20 mm working area.

1. What do you think about this gear reducing assembly? https://www.aliexpress.com/item/4000232951024.html?
I would add tensioning spring to it to allow some play between rack and pinion and would go for straight pinion (I suppose this is preffered).
I am considering this setup because it is cheaper than having it done locally. And it seems decent.

2. I am having trouble finding 1.5 mod rack with mounting holes. Can you give me some links where these can be ordered?

3. Another option I was considering was rotating ball nut. But I guess that would be more complicated than rack and pinion setup. I will be doing wood carving also with 2mm ball bit. Will rack and pinion be precise enough for that?

hanermo2
23-12-2020, 10:39 PM
There are endless good mechanical options.

But if 650 overall is too much, forget it.
I know you said it for transmission only.

You will spend about 2000 for a decent motion system, and about 2400 for an excellent motion system, for a full-sheet setup.
For 2k you can get excellent ac brushless servos, and should do so, and forget anything else, for a business venture.
Rotating 2.5 m ballscrews with modern 220v ac brushless servos is trivial.
They will provide theoretical accuracy around 2 microns, 0.002 mm, and speeds higher than you want to use.

I use about 1/3 of the max speeds available on my large vmc for cutting metal.
Table is 200-250kg, bridge is 500-700 kg, a 400W servo is ok (marginal) but a 6 Nm servo (750W) runs it all day long.

Woodworking loads are under 100 kgf.

Ale
24-12-2020, 02:36 AM
There are endless good mechanical options.

But if 650 overall is too much, forget it.
I know you said it for transmission only.

You will spend about 2000 for a decent motion system, and about 2400 for an excellent motion system, for a full-sheet setup.
For 2k you can get excellent ac brushless servos, and should do so, and forget anything else, for a business venture.
Rotating 2.5 m ballscrews with modern 220v ac brushless servos is trivial.
They will provide theoretical accuracy around 2 microns, 0.002 mm, and speeds higher than you want to use.

I use about 1/3 of the max speeds available on my large vmc for cutting metal.
Table is 200-250kg, bridge is 500-700 kg, a 400W servo is ok (marginal) but a 6 Nm servo (750W) runs it all day long.

Woodworking loads are under 100 kgf.

Hello!
Thank you for reply.

Well, I was thinking of screws, but still trying to find long and at least 25 25 ones. Do you have source for them? What is your experience with screws that long? Do they sag under their weight? Which ones do you use and what speeds do you get?
If you don not have precision screws, it does not matter how accurate servos are, right?
About servos, are you talking about those cheap Chinese ones from Ebay? I was thinking about them also, but figured that Nema34 with low inductace would be enough since I would need to gear down servos alot.

I am ready to spend about 10k Euros on this project, but would like to get good stuff worth the money. Well, best I can get at least.

JAZZCNC
24-12-2020, 02:18 PM
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.

Ale
24-12-2020, 06:45 PM
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-rack-module-2-q6-high-precision-24x24x2010-6mm/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-drive-antibacklash-diy-includes-gears15t/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.

Ale
24-12-2020, 06:53 PM
Just for reference, this is my (not finished) model of machine im trying to build. Gearbox here is from AvidCNC, just for example.
It will be made of 80x80 80x160 aluminum extrusions from Item24.
292842928529286

JAZZCNC
24-12-2020, 11:06 PM
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.

Those screws where 2525 with 2:1 ratio using 8Nm 3phase closed loop motors and mains drives. They also had fixed ends at both ends of the screws and where preloaded slightly to tension the screws.



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.

I don't think Jonathan does much with DIY CNC anymore as he's working now he's left university. I bought the last 6 sets he made. These are what I used on the 10 x 5 Router.


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.

No probably about it, I'm 100% sure because I've worked on them, only last week I converted a router which used them and it was sloppy as hell. Just about every Chinese router I've worked on uses them.



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.

Exactly, I've built quite a few large machines now that use 3 phase closed motors with mains drives and never had any issues with reliabilty or setting up with more than enough power and speed for even large machines, they are pretty much plug n play fit and forget.

I also have 600w Chinese servos fitted to my plasma machine which are way more powerful than required and nothing but a pain regards tuning.
If I was fitting servos to a router that used Rack n pinion then I'd only fit higher quality servos like, yuskawa, Mitsibishi or panasonic which provide tuning software to help with setting them up, esp with dual axis motors.



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).

In terms of precision then yes 0.05mm will be more than enough for 3D work in woods. If all you are cutting is mostly woods, plastics etc then I wouldn't get bogged down with chasing high precision because it's pointless in materials that can't hold it anyway.

I would pay the extra 100eur and go for 32mm, it will be worth it and lower the chances of whip if your rotating the screw.


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-rack-module-2-q6-high-precision-24x24x2010-6mm/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-drive-antibacklash-diy-includes-gears15t/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 would avoid these, I have worked on a machine that used those anti-backlash untis and was not impressed at all. They where difficult to setup and where constantly needing adjustment. They also caused premature wear on the rack/pinion. The Rack was low quality and wore out within 1 year and as been replaced with helical rack I believe.


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.

They are rare in DIY because they are not cheap but most good engineering suppliers will be able to supply them.

Rotating ballnuts are not so common and might require you have your own made. This is the only other place I have seen rotating ballnuts. Use google translate.

https://team-haase-shop.de/maschinenelemente.html

Ale
25-12-2020, 12:45 AM
Those screws where 2525 with 2:1 ratio using 8Nm 3phase closed loop motors and mains drives. They also had fixed ends at both ends of the screws and where preloaded slightly to tension the screws.
Very elegant setup. Just now I noticed that it is rotating nut driven as you mentioned.



I don't think Jonathan does much with DIY CNC anymore as he's working now he's left university. I bought the last 6 sets he made.

Rotating ballnuts are not so common and might require you have your own made. This is the only other place I have seen rotating ballnuts. Use google translate.

https://team-haase-shop.de/maschinenelemente.html

I have found those before, but max nut size is 20mm, while I should look for 32mm as you suggested. So I will try make it locally. I guess 20mm is too low.



No probably about it, I'm 100% sure because I've worked on them, only last week I converted a router which used them and it was sloppy as hell. Just about every Chinese router I've worked on uses them.

I think you are 100% right then. Thank you for saving me money.




I would avoid these, I have worked on a machine that used those anti-backlash untis and was not impressed at all. They where difficult to setup and where constantly needing adjustment. They also caused premature wear on the rack/pinion. The Rack was low quality and wore out within 1 year and as been replaced with helical rack I believe.


Thank you for saving me money, again. :adoration:



3 phase Closed loop steppers with 220Vac mains powered drives are a great choice for a large hassle free machine.

Could you let me know where can I get motors you used?
And thank you again for helping.

JAZZCNC
25-12-2020, 11:42 AM
I have found those before, but max nut size is 20mm, while I should look for 32mm as you suggested. So I will try make it locally. I guess 20mm is too low.

Look again because now they have 25 and 32 versions.



Could you let me know where can I get motors you used?

These are what I use. They are not the cheapest and for not much more money you can get servos, but like I say they are simple and reliable without any of the hassles servos introduce. I've fit dozens of sets so far and never had a single issue.

https://www.aliexpress.com/item/32799243070.html?spm=2114.12010612.8148356.1.7c1f6 f37fvbQyT

Ale
27-12-2020, 07:58 PM
Look again because now they have 25 and 32 versions.

Found it and sent them email. Thanks.


These are what I use. They are not the cheapest and for not much more money you can get servos, but like I say they are simple and reliable without any of the hassles servos introduce. I've fit dozens of sets so far and never had a single issue.


https://www.aliexpress.com/item/32799243070.html?spm=2114.12010612.8148356.1.7c1f6 f37fvbQyT

Those got very high inductance. 18 mH. Is this issue? They operate on high voltage to compensate i guess and three phases. These do not need power supply, right?

On the other forum I was reading that most important is low inductance, because it enables torque at higher rpm. I am not able to find toque curve for these.

Previously I was looking at these. 2 mH, 5 Nm
https://www.ebay.com/itm/Free-Ship-4Axis-NEMA34-Closed-Loop-Motor-710-oz-in-5N-m-6A-Servo-Driver-Kits-CNC/274560683235?

But can't find torque curves for either of them.

JAZZCNC
27-12-2020, 08:51 PM
Those got very high inductance. 18 mH. Is this issue? They operate on high voltage to compensate i guess and three phases. These do not need power supply, right?

On the other forum I was reading that most important is low inductance, because it enables torque at higher rpm. I am not able to find toque curve for these..

It's all relative to the Voltage, these run on 220Vac so higher inductance isn't an issue. Like I say I've fit dozens of sets and I now stock these motors/drives and fit them to all the larger machines I build. They spin fast and have plenty of torque.

For instance, the vertical 10 x 5 router I recently built uses a single 10Nm motor on the gantry (X-Axis) with a rotating ball nut that lifts the Z-axis which carriers a heavy ATC spindle and all the pneumatics, etc. That motor lifted my friend who weighs 120Kg and the spindle etc clean off the floor at 15mtr/min so I wouldn't be too worried about high inductance or lack of torque.

No, they don't need PSU they run directly from the mains supply.


Previously I was looking at these. 2 mH, 5 Nm
https://www.ebay.com/itm/Free-Ship-4Axis-NEMA34-Closed-Loop-Motor-710-oz-in-5N-m-6A-Servo-Driver-Kits-CNC/274560683235?

But can't find torque curves for either of them.

I wouldn't trust that datasheet, I've never seen any Nema 34 motor with 2Mh inductance, most 3-4Nm Nema 23/4 have an higher inductance than that.