. .
Page 1 of 2 12 LastLast
  1. #1
    Ale's Avatar
    Lives in Vinkovci, Croatia. Last Activity: 1 Week Ago Has been a member for 0-1 years. Has a total post count of 11.
    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.

  2. #2
    Doddy's Avatar
    Lives in Preston, United Kingdom. Last Activity: 5 Hours Ago Has been a member for 7-8 years. Has a total post count of 1,185. Received thanks 163 times, giving thanks to others 55 times. Referred 1 members to the community.
    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.

  3. #3
    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.

  4. #4
    Quote Originally Posted by Doddy View Post
    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:.

    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.
    -use common sense, if you lack it, there is no software to help that.

  5. #5
    Ale's Avatar
    Lives in Vinkovci, Croatia. Last Activity: 1 Week Ago Has been a member for 0-1 years. Has a total post count of 11.
    I am talking about something like this:
    https://www.avidcnc.com/pro-rack-and...-34-p-226.html

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

  6. #6
    Ale's Avatar
    Lives in Vinkovci, Croatia. Last Activity: 1 Week Ago Has been a member for 0-1 years. Has a total post count of 11.
    Quote Originally Posted by JAZZCNC View Post
    Yep you'd be Stoopid, but obviously, I'd say that if you were correct but your not:.

    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.

  7. #7
    Ale's Avatar
    Lives in Vinkovci, Croatia. Last Activity: 1 Week Ago Has been a member for 0-1 years. Has a total post count of 11.
    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?

  8. #8
    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.

  9. #9
    Ale's Avatar
    Lives in Vinkovci, Croatia. Last Activity: 1 Week Ago Has been a member for 0-1 years. Has a total post count of 11.
    Quote Originally Posted by hanermo2 View Post
    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.

  10. #10
    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.
    -use common sense, if you lack it, there is no software to help that.

  11. The Following User Says Thank You to JAZZCNC For This Useful Post:

    Ale

Page 1 of 2 12 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Simple 3D Gear design software recommendation
    By Leadhead in forum CAD & CAM Software
    Replies: 22
    Last Post: 11-11-2017, 01:30 PM
  2. Reducing noise during run with box enclosure
    By Skydeals in forum Machine Discussion
    Replies: 4
    Last Post: 12-02-2015, 08:43 PM
  3. Reducing costs
    By tonygagey in forum Gantry/Router Machines & Building
    Replies: 16
    Last Post: 13-08-2014, 11:33 AM
  4. Reducing 12v DC to 0.5V DC no more than 1A draw
    By AdCNC in forum General Electronics
    Replies: 16
    Last Post: 10-07-2013, 03:01 PM
  5. My first gear, a deadbeat escapement gear for my clock
    By clockman in forum Woodworking Project Showcase
    Replies: 9
    Last Post: 30-01-2011, 11:39 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •