Rack & Pinion or Leadscrew?- CNCnutz Episode 221
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- เผยแพร่เมื่อ 20 ต.ค. 2018
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Excellent presentation as always, Peter! Can't wait for part 2!
Thanks Mark
Thank you very much. Currently i'm building a cnc milling/plasma cutter. You answered a lot of my question. Very detail explanation.
Great vid bro, very useful! Thanks a lot. Cheers Peter!
That was a great explanation Peter. The next time I'm asked about this I'll send them here to watch your video. Thank you.
Thanks Dave
Excellent, thank you for showing this and also for making the Mach3 macro! Cheers
Thanks Shaun
And here i was thinking everything’s the other way around! You know, like lead screws on milling table and rack and pinion on quill or table lift! Thanks for the enlightenment😀👍
Hay Peter you've got interesting cable management system, looks like simple and efficient, thanks for the idea
Thanks Shakil. It works very well.
Cheers
Peter
Wery good and calm description of different solutions. Thanks.
Thanks Lennart.
I enjoyed the video,many questions in my mind were answered.Thank you
Thanks Jamal
So timely, i've been thinking about switching to r&p so this info really helps me!
Thanks for great video!
Glad it helps out Lyle. I'm sure you will lioke R&P a lot.
cheers
Peter
Thanks Peter great info, nice video as always.
Thanks Geert
You had me in the first 30 seconds. LOL. Yes, that's my kind of humor too. Humour, I guess.
Thanks eggpocalypse
I enjoyed your video. You have helped me immensely.
Thanks
Thank you. Very detailed and informative. Appreciate you sharing.
Thanks Vincent
Excellent content Peter ! For slow - precision movements, one should think about lead screws / power transmission threads.
For fast and enough accurate movements, one should go for non straight pinion / rack types. It applies to any mechanical function design. I have applied that rule since young.
Thanks
I have just watched a group of your videos. Good stuff.
My price for a 2mt ball screw was a multiple of a leadscrew. I then found eithers max rpm was 1/3 of what I needed. I considered holding the shaft and turning the nut, but not easy. A 14mm toothed belt 'R & P' seems to be it for me.
Given that the z axis is gravity loaded, is backlash removal purely for stopping chatter?
Pete EXCELLENT!! explaining my questions between lead screw or ball screw and Rack and Pinion. You have given a very good explanation on the topic and with examples. I am glad you mentioned about the length of the lead screw or ball screw over the rack and pinion. I have read and seen other web sites give there own explanation with out backing it up like you have. I thin the Rack and Pinion would have more torque due to the fact you are using a reduction gear that in itself provides more torque in relation to the gear reduction.
Thanks Dan,
I agree that at the pinion the torque is 3 times more than at the motor but at the same time a leadscrew is a form of gearing itself so it is a tough one. I would probably suffer a melt down if i think about it too hard. I think using the same motor on a leadscrew with a 1" lead would not work as well as my current R&P which also has a 1" lead. It would be interesting to put it to the test because at the end of the day what I believe doesn't really matter. Only practical test results count.
cheers
Peter
Interesting, I have been reading that those individuals that put a Spindle on their CNC machines require compressed air or springs to compensate for the added weight of these cutting motors. If your Z motor is strong enough you could miss steps when it is trying to lift the heavy spindle.
Great video Peter! I do love some Kiwi dad jokes haha
Thanks Mitch
Regarding "whip" in long lead screw, one approach is to not turn the screw but the "nut(s)"
Still not as solid as a helical rack. A rack and pinon will have many more mounting points which gets rid of vibration.
Thanks you for showing and explaining. Is it also possible that the Z-Axis shows a better value because it is vertical and the weight pulls it down? That wouldn't happen in the same way with a leadscrew on the X or Y axis.
WoW I learned so much. Thank You.
Thanks Oscar
I'm just so happy to finally see a video that actually explains things as they are! Seen so many videos about why ballscrews are much worse then rack gear setups! It's really been great, love how all those BS "youtube-experts" are trying to tell all the engineers who made all our different high precision CNC machines, from various brands that costs over 150.000€ each, that they are full of crap. Noo, using tech that's only found in several decades old manual/conventional mills are ofc way better then using ballscrews... Even seen a professional "cheap" CNC machine manufacture from USA claim that... Just unbelievable!
Ballscrew setups are often more expensive, but there are dirt cheap versions available, where the ballscrew itself (the bolt part) is rolled instead of being grinded and my best guess is that the ball nut is made the same way. In the end these cheap versions will allow fairly high precision, tho they need to be lubricated and the tension bolt adjusted after a set amount of run time. The life time of the dirt cheap versions can be expected to be similar to cheap gear/rack setups, so there's a trade-off here, either go for gear/rack setup for longer life or for ballscrew for precision.
BTW if you want to avoid backlash in gear setups there's two cheap options, the first one cost ½ of the 2nd. 1st is using spun setup, spun is a certain type of cut that even in straight cuts allows constant contact. 2nd is helic or angle cut, a proper angle will allow more then 2 tooth to be engaged constantly
PS they use the term "a human hair" to visualize what good machinists are talking about to stupid people. (it's BTW 0,035-0,05mm which is far higher then the tolerances i regularly work within)
Is it a good idea to have 2 cheap-ish lead screws and use a similar anti backlash method as the dual pinion drive, that is to have a stiff spring between the 2 ball screws?
did you know that the common lath used in the schools. i have one it a 100 years old some sold in the USA had led screws fitted. i am now in a development sag of of adapting it to run on an ELS electric led screw. it cuts thirds well with it banjo, I suspect it will do as well once i have got it running with an electric gear box .
Well..I went the ballscrew direction..a heavy weight ballscrew..though am thinking if your down for speeds go for rack n pinion if you want extreme precision go for ballscrew..other factors apply
Interesting stuff. Thanks!
Thanks Capi Berra
First 30 seconds were GOLD :))
Thanks Warren
Enjoyed the video, great explanation. I have a 4' x 8' CNC and have chain drive on my y, screws on my x and z. I have checked my machine with a dial indicator and I am satisfied with the results comparable with what you got. I really wished I had went with the chain on the x because of the length of the screw. I get some whipping action because of the length. I feel the chain is comparable to the rack & pinion.
Thanks John,
Chain is a form of Rack but rack has the advantage that it doesn't stretch over time.
Interesting that you get similar backlash results to the R&P using chain.
cheers
Peter
hi Peter, very nice tutorial.
Thanks Max
i love ur cnc chat
Thanks
Very interesting video Peter. With Rack and Pinion it wouldn't be very hard to add an extension to the table for a rotary axis. It could be removable by having dowels to line it up. Cheers Rob
Hi Rob, Interesting thought. So long as you had sufficient length on your cables you could drive it off the current table and entirely onto the extension. What an interesting concept assuming I understand you correctly. Definately can't do that with leadscrew.
cheers
Peter
Yep that's what I was thinking. If the cables / carrier were fed from the front of the table, you could almost double the length of the table. Rob
The other way around leadscrew whip is to keep the screw stationary and spin the nut. This is more mechanically complex, however...
Hmmm. Isn't that kinda what a rack and pinion is?
David Ashenbrener - No, a rack-and-pinion uses a gear with involute teeth; a leadscrew is a helical inclined plane. Mechanically, they’re quite different; and have different characteristics. The axis of rotation is parallel in the leadscrew; and perpendicular in the rack-and-pinion. Rack-and-pinion drives are always in rolling contact; only ballscrew-type leadscrews are (V-thread and acme-thread leadscrews are in sliding contact).
Or with a long lead or ball screw you would have to have it clamped on bearing and pulled so it would not warp. The cost is way too much and it would have many issues not worth investing.
I have been thinking about that option too, but then i decided to go for rack 'n pinion
The rotating nut would be awesome but I can't find anyone how can supply this kind of setup for the home built crowd.
Just looked up acme leadscrew efficiency, only 20-40%, whereas rack and pinion near perfect. So with only that proportion of motor power left over there's less torque on a leadscrew. With a ballscrew you're back up around 90% efficient.
I have just bought the double pinion system for my cnc. Damencnc in Holland makes those. Going to install it soon
Those are the ones I found when looking into this video. Marcel of RoboCNC Installed them on his machine. Very nice looking units. He has videos of assembling and installing them on his channel.
Cheers
Peter
@@cncnutz yes, that's where i found them too. My x-axis is 2860mm long, yes 2860mm. My y-axis are 1870mm long, for that i am currently using ballscrews, but in the future, those will be replaced by that double pinion system too. Expensive, but then i am sure i will be as backlash-free as possible on such a big machine
I never tire of watching your videos, how hard you make it simple!
I have some doubt / query.
I already consulted what type of steeper, you used, but I have some doubt as: What reduction ratio do you use? 1: 5? I will use a gearbox system, since I get something cheaper, (as long as you do not advise me otherwise ...) the rack pinion of how many teeth? And finally, full steps, 1/2 steeps? I feel so much question, but your work is more than perfect. I'm not going wrong, but seeing your work ... I ask. Thanks for your time.
The belt drive reduction is 3:1
Please do not use a gear box as it will have a lot of backlash.
The G540 is 10:1 microstepping.
To see the drive unit i use please look at the link below. It has all the info you need.
www.cncrouterparts.com/standard-rack-and-pinion-drive-nema-23-p-50.html
Tooth numbers are irrelevant, it is the pinion root diameter that is important. Mine is 1"
Hope this helps
Cheers
Peter
For my lead screws I went 3/8-8 4 start. It's a fast screw, but hard to find anti-backlash nuts.
Thank you so much sir
Hi Peter, my name is Alan , i'm total new in this field , i like to build a machine 1000x1000mm , do you have in some video explained the calculation of gears and rack to build a cnc ( gear tpi , diameter ) also stepper motors . thanks for the great videos....
Nice video!
sir . i have one question. can i use ONE SIDE LPT 25DB PIN OTHER SIDE USB TYPE . FOR MACH3 1.1 ??
Sir ..straight rag or helical....which one is better
Acceleration formulas would dictate that there are large differences based on reflected load inertia. The rack has the load at the radius. Also screw fixing being simple simple, Simple fixed, or fixed fixed, will dictate the screw critical speed value.
Backlash presents itself also when decelerating the load while still in motion.
With the rack, cable will move with the load.
While it's true that a rack and pinion mecanism won't change the torque provided by the motor, a ballscrew assembly can move much higher loads because of the transmission ratio.
SO, a rack and pinion amplifies the speed but reduces the maximum forces admisible.
And, one more thing... The reason why the lead screw assembly moves slower is not Friction.... is the transmission ratio
Thanks Gutu
Hey Peter, I am looking to make a cnc router about 1/2 sheet, and I watched your vid about ball screws / rack & pinion. The bit I liked was your spring loaded pinion drive with 3:1 ratio. Could you point me at where you got them made or if you made them yourself any chance of a copy of the drawing if you still have it. Also any info you could give me about the rack size etc. I hope I found you in a generous mood towards a mainlander here in OZ.
Hi Geoff,
The R&P drives are made by www.cncrouterparts.com
They have a couple of different drive unit options. They are nice units.
Cheers Peter
one issue, in looking at speed of a rack and pinion is the ratio is much different than a ballscrew. this leads to why the rack and pinion is faster. it also answers why it is much easier to get behind the torque curve either due to inertia or lack thereof when you are moving the rack and pinion vs the ballscrew The ballscrew has more torque multiplication. accel values seem to be much more sensitive to set, and critical with rack and pinion. good video explaining the nuts and bolts of these types of drives. keep up the good work.
Thanks Layne
Nice video as always.. 👍😊 And thanks for activate me this Sunday afternoon. Now I have to get my “back ass” out to the garage to check how much backlash that my cnc have 🤔
I have managed to motivate you to get out into the workshop to locate a problem you didn't know you had. Which has caused you no issues and will keep you awake at night trying to solve. 😈
My work here is done.
Cheers
Peter
Ha ha I didn't manage to get up from the couch. So right back at you 😜 but serious I will try to check it out during the week. Then I will post the problem I didn't know that I have trouble with here 😉
My Backlash is following Ball screw Z axis 0.00mm Rack and pinion X axis 0.04mm and Rack and pinion Y axis 0.01mm. 😊
Now all you have to do is watch the next episode and see how to fix it if you haven't already sorted it.
Cheers
Peter
Yeah I will, I stared to look on how to calibrate it but the steppers sounded so weird so I will wait for your video 😊
I have never used a Rack and Pinion in any of my builds but I did purchase two 24" lengths of rack and two pinions, so my question is this. Do I need to use two racks to drive each axis or will one rack work for driving an axis?
My X axis uses 1 rack while my Y axis uses 2. I'm using 2 on the Y to prevent racking and if I wasn't using rack I would use 2 leadscrews instead. It depends on the design of your machine Whether you use 1 or 2 racks on an axis.
Cheers
Peter
I used ball screws because at the time they appeared to be easier to set up and align but I can only drive them at about 400 rpm on no load so 1600mm per minute before resonance causes a stall, its about the minimum speed for cutting but the rapids are so slow it is driving me crackers , so on the new one that I am building I intend to use racks on the X and Y axes. I have made the Z/X carriage using a 16mm ballscrew but with my new 2.2kw spindle the Z axis falls down as soon as I power off the controllers so perhaps I might change it to a trapezoidal screw.
You Z axis sounds like the same setup I'm look at for my upgrade and backdriving of the Z is a real concern that I have. One thought is a spring to counteract the weight if the spindle which would also reduce load on the stepper in both directions and should stop backdriving. Just a thought.
Cheers
Peter
Hello, wanted to ask about lead screw. Why do we need bearings while the lead screw is attached to the coupler and stepper motor, isn't the stepper motor and the coupler plus the housing, enough for the stability of the lead screw or in other words, what is the purpose of the lead screw bearing ? to cnc router ?
The bearings act as a thrust bearing to stop the leadscrew moving up and down. Stepper motors are made to turn, not to support the weight of a heavy axis. The dual bearing keeps the leadscrew in alignment.
Cheers Peter
Peter, Awesome presentation!! The only thing I think you should mention with torque is that with a stepper motor as you increase speed you loose torque, unlike a servo that is a constant torque (more or less) motor. GREAT job!
Joe
Thanks Joe.
Thank You Sir
Hey there,
I wonder what brands are reliable when it comes to the cnc motion control belt types 1000x 1000mm? I'm having trouble finding it
I've no idea. I think when it comes to belts stretch is the biggest problem.
Cheers Peter
what the hell are you doing to your cat? That made me LOL
Would you not be able to program your machine to turn certain number of steps to take up the slop when changing directions on that axis?
Yes. It is called backlash and there is a setting for it which I cover in the next video.
th-cam.com/video/CS2rosB_ce0/w-d-xo.html
Cheers
Peter
Would you say that a R & P is compared to a belt drive linear module and a lead screw fits in like a ball screw linear module? Meaning that one is best for perpendicular applications (belt drive) and the other fits parallel applications (Ball Screw) better? Please let me know your thoughts, Thank you.
Belt drive is prone to stretching unlike rack. I personally would not consider it for anything other than perhaps a laser where there is no loading. Ball screw is a good choice for any axis unless it is too long where whip is a problem or the cost is excessive. Leadscrew is like ballscrew except that ballscrew has less backlash and run smoother.
Cheers
Peter
Cat in video --> instant subscribe.
Thanks Haley
I have ballscrews... they are better than acme screws for the most part - unless you have a situation where you need the axis drive to be self-locking... ballscrews can be back-driven. However, for most DIY CNC applications, this isn’t an issue because the head isn’t heavy enough in comparison to the drag of the motor to make it fall when the power is removed.
Thanks. Thats good to know as I want to change in the future.
Cheers
Peter
Why does would pushing the gantry make it go out of square?
shame i never found your video when i stared my cnc plasma build...i have now bought and installed ball screws ..but finding them too slow with direct drive to the motors...so going gear them up with belts and cogs ...
R&P would be my choice for plasma. Less likely to be upset by molten metal as well. Hope the update works out for you.
Cheers
Peter
Nice 👍
Is it me or does it look like he is standing next to a giant leadscrew? I know its just a flexible vent tube, just a funny thought.
"you know who you are... stop doing it" hair hair. ;)
If you're interested I have a supply of rulers in Tad & Whisker graduations.
Thanks for the rack and pinion advice!
But why do you have an anti-backlash nut on the z axis? Surely gravity takes care of that for you?
It doesn't work like that. An upcutting spiral bit will lift the spindle up as will drill into hard material.
Cheers Peter
trapezium tread is allso called acme tread
the split pinion sprocket for taking the play out is a nice idea . never heared of that either but its brilliant unless theres more wear in the middle then on the ends .... maibe springtension the two sprocket against eachother works , connecting two together side by side on the same pinion with a toothed belt and slightly tensioned toward eachother might do the same but is eazier to dyi together
if i ever finish my router i have to think about that system (bought more stuff (gonna be using an acorn controllboard ) but that and the steppermotors i bought for the router are now for the cnc conversion of my bf20 mill)
think for woodworking the acuracy isnt as important as the wood is moving a lot on its own from moisture and stuff a tighter machine might reduce vibrations in the routerbitwish might improve the finish but other than that i dont see a lot of problems with the way youre machine is now
btw if you move youre machine by hand youre creating current wish can blow up youre stepperdrivers if there not as whell build as they should be (had seen that happen with a friends cheap 3d printer the controllboard burned out a driver) just push slowly dont rev the steppers
Actually, Trapezoidal metric thread cannot(well not accurately) be referred to as an ACME thread, ACME refers exclusively to imperial threads.
Do you grease the rack and pinion or run it dry? Seems like running an aluminum gear against a steel rack dry would cause accelerated wear.
Hi Joe,
The rack and pinion run dry and the rack is mounted with the teeth facing down to prevent dust collecting on them.
The pinion is steel and after 8 years of running still show no signs of wear.
cheers
Peter
@@cncnutz Thanks for the fast reply. I bought a CNC Router Parts Pro 4896 with the same setup and asked them the same question. They said they run it dry but their pinion gear is aluminum against a steel rack. I have a hard time being convinced that an aluminum gear mating with a steel rack gear dry is ok.
That's interesting because the R&P drive kit on my machine came from CNC Router Parts and mine is steel.
Cheers
Peter
@@cncnutz You're right. I went and checked again and the gear with the belt is aluminum and the smaller gear on the rack is steel. I feel better now LOL
I'm just at the beginning of the video, so you may address it later, but what about toothed belt dives?
Toothed belt and chain are just different versions of rack and pinion drives. The belt is irrelevant. It is the drive cog that you need to look at just like you look at the pinion on rack and pinion Drive.
Cheers Peter
Thanks for the explanation and pros and cons of easy system.
Sorry but I have an off topic question.
It looks like you have two flange bearings on your Z lead screw, is that right?
Ive used the same flange bearing on my machine for the past ten years, and checking the backlash using the same method you use I have 0.00005” backlash. However I get a lot of concern from other users that the flange bearing is not designed as a thrust bearing. But isn’t the proof in the pudding?
Have you discussed this in one of your videos? If so please let me know the episode number, I’m interested in your feelings on the subject.
Thanks
Hager
I have never thought about flange bearings. That is how it was designed and it works well for me. What issues are you having with your flange bearing that is making you question them other than what others say. If it works and gives you no problem then why worry.
Cheers
Peter
CNCnutz (Peter Passuello) Thanks Peter I appreciate you experience and opinion.
If it ain't broke don't fix it is my motto.
Wouldn't the torque vary based on the gear ratio? It's constant from the motor yes, but on the rack and pinion you have a 3 to 1 gear reduction so more torque. Whether the lead screw has more torque depends on the thread type/pitch to determine what kind of gear reduction it provides. The gear ratio of course is related to the number of revolutions per unit distance of movement. If it needs to revolve more times with rack than leadscrew to travel 1cm, then it would have more torque or vice versa.
Hi Nick
The Belt drive on my R&P unit is a 3:1 reduction which will increase torque by a factor of 3 but the Rack & Pinion ratio is 1:3.14 which reduces the torque by a little more than 3. If we round it off we can say that the R&P drive is 1:1 where in actualy fact it is a little worse off than that.
A leadscrew driven by the same motor will have more torque than a R&P drive but the motor has to turn faster which incurs greater loss and the leadscrew ABnut introduces friction which adds more loss. The result is a lower top speed because of frictional and stepper losses. Each drive has it's advantages and disadvantages and there is no perfect solution. Torques does not equal speed in fact it is the opposite. The more torque you have the less speed you will have for the same motor. You need to choose what is best for you based on price, the machine you are building and degree of accuracy to are trying to achieve.
Cheers
Peter
what are the motor specs you are using for the lead screw?
All my motors are NEMA 23 holding torque of 270 ozin.
Cheers
Peter
I found that repeatability is much more important as super precision (on cheaper machines). If you want to make a square 100mmx100mm and it ends op 100.2mmx100mm then adjust your model. Do run it again at the same spot on the bed. Sure it is not great but a machine that is $3000 cheaper can get great precision. It just needs more tries. :)
Rolled C7 ballscrew maximum lead deviation 0.050mm over 300 mm
Ground C5 ballscrew maximum lead deviation 0.018mm over 300 mm
with other words: a deviation of 100.2 is 0.6mm per 300mm catastrophic failure.
thats not what you think in engineering.
maybe in woodwork, where you squeach da deviances with a hammer.
but in a plane. or just a robot. actually any machine, motor....
i agree,that one must be industrialist or rich man to drive a 6 m cnc for different stuff but wood...
and you might even get richer, if you are taking advantage of this missing 3 mm each 6 m.lol.
by german means: total faceloss.
but hey. the world is big.
isnt there a way to adjust the driver them? adjusting the model sounds like the worst approach from engineering perspectice. thats just messy and not scalable in production. except you start changing your model there as well. just-> tune the machine not the model. thanks. people might become crazy. : ))
Thanks Peter, you’ve made another valuable tool explaining one of the myriad of things going on, on these machines. I’ll download that Mach 3 version and add it to my diagnostic tool box. Looking forward to your next video on this subject.
I use ball screws on my Y axis travel and would like to see you put up a video on the art of using oversized balls in them to lessen the backlash in them, I haven’t seen this approached in a thorough method as you approach things.
Thanks Hager
I have seen videos of people upsizing the balls in a ballscrew but If I get one I don't see myself pulling it apart to do this.
You never know though, stranger things have happened.
Cheers
Peter
What if the one motor is faster than the other, will the axis be tilted? How can you fix that? Thanks
They are stepper motors so cannot run faster than one another. If the axis is out of square or tilted then that should be fixed.
Cheers
Peter
Do you really need an anti-backlash nut for the Z axis? Doesn't the weight of the spindle ensure that the drive is preloaded downward so that the bottom face of the nut thread is always in contact with the top face of the screw thread, except when the spindle is resting on the bit?
You sure do Mark. Never underestimate the ability of a cutter to lift the axis when cutting especially a downcut bit moving sideways. It will climb out of the cut like a Zombie in the day of the dead. I know what you are saying but all leadscrews must have antibacklash nuts. Cheers
Peter
@@cncnutz ok. Thanks Peter.
I wouldn't really rely on the weight of the Z-axis, a cutter will move your Z-axis, certainly if you are cutting hard wood. Also, when you do 2.5D cutting, you will have lot's of troubles with the backlash.
W#at is the OFF LINE button is for ?
5:30 Couldn't you do the same thing with two nuts on a rod that are pushed away from each other with a spring?
Both are fixed in rotation and only one is fixed vertically. This way the system can adapt when it wears.
If you are worried by accuracy or finish it is probably a no-go. When the cutting tool reaction is through the unfixed screw the fixture can shake to the extent of the system backlash as the spring compresses. The lower the carriage friction and its weight the worse the shudder. To reduce that, spring tension is increased. However that increases the thread loading. Wear and lubrication become an issue. The faster the screw rotation the worse the situation.
My solution is to so shape the nut fixture that the adjusting nut’s far face bears against it, preferable via a Teflon washer. The nut is then attached to a spiral spring. It only needs to be strong enough to overcome the nuts rotational friction. This way there is no backlash and the screw friction is minimal. Too tricky; just hand adjust the slack with a lock screw.
@@andrewdoherty8847 Spot on about the friction and wear.
The way industrial machines handle this is with ballscrews and either beefy steppers or autobraked servos (generally a brake built into the motor that releases whenever it is powering a direction, though an external brake can be used).
Whip can also be countered by spinning the nut rather than the leadscrew.
Why we don't connect the stepmotor directly to the rack , i used rack and pinion but with out any gearbox
Power and resolution.
To get the same power at the pinion I would need a 3 times bigger motor which is inefficient.
Alternatively I would need a 6 tooth pinion which is physically impossible.
To get the same resolution I would need 30 times microstepping. This level of resolution is inaccurate so gearing is the best option if done correctly.
Cheers Peter
What about Ball Screws??
Please tel me how to set my router perameter and how many ways to find the perameter of cnc
Have a watch of this video which explains how to calculate steps per unit.
Hope that helps
Cheers
Peter
th-cam.com/video/rqzlMJevGb0/w-d-xo.html
Can a pinion be directly mounted in the motor? So the r/p is directly driven?
For the same rack and pinion components, If you direct drive the resolution of the axis will suffer. You will also require a larger motor because you loose the mechanical advantage of the gearing. Without gearing my drive would move over 3 inches per revolution of the stepper motor. When you factor in costs you will find that the cost of larger motors along with the more expensive drives to run them far exceed the cost of a smaller motor with driver, a few pulleys and a belt.
Cheers
Peter
@@cncnutz Thank you for the reply. Much appreciated
any software convert LPT 25DB PIN TO USB CABLE FOR MACH3 ??
You can't do it with software. You need a motion control board like a UC300ETH 5LPT board with driver..
Cheers Peter
Soo, the question is which one are better ???
It depends on what you require from your machine and what sort of machining you are doing. How much you want to spend and machine size.
I think you also forgot chip kinking the rack. You need a cover for the rack compared to leadscrew. The profile of the screw is round so less % that a chip will sit on it, and even then, the anti backlash nut would judt sweep it by itself. On the rack instead the chip will stay there and mess the pinion on its way
Racks are always mounted upside down to prevent chips and debris from accumulating on them. Gravity keeps them clean.
Cheers
Peter
R&P is faster because with a lead screw the stepper has to turn faster to move for a given unit of travel and steppers loose torque the faster they spin eventually loosing steps. Basically it's better at converting torque into speed.
Thanks Oswyn,
The lead on my R&P is about 1" per revolution of the stepper. It would be interesting to get a leadscrew with a 1" lead and compare them side by side.
Cheers
Peter
The other way to drive an axis is with timing belts (a.k.a, cog belts), the way that 3D printers and machines like the X-Carve and Shapeoko do.
True but that is a can of worms that I'm going to avoid opening. I would use belt on a laser or 3D printer but not on a CNC.
@@cncnutz what would you prefer using on a plasma cnc
@@AS-ug2vq
I would personally go rack and pinion myself.
If I understand it right, and you use an 4 start 2mm pitch leadscrew, that gives you 8mm per rotation of the screw. A 1inch pinion has a circumference of about 80mm (79.79mm) and after your reduction you have a movement of about 27mm. That's why R&P is "faster", it's doing three times the distance for the same amount of rotations as leadscrews.
As for torque, I believe leadscrew wins. For holding torque leadscrew definitly wins.
If you cut for tolerances, R&P is only workable with some serious reduction and then you still have to overcome backlash. At the end of the day your motor will do the same amount rotations so it's all basically relative. Ballscrews are just easier for fine work, leadscrews work well enough as a compromise and chain, belt and rack drives are designed for greater distances. All have their place and their application, I have just always wondered why people don't just do two narrow racks against each other and springload them. Same as springloaded spurs just way less work. I can also tell you that if you are still reading, you have the same amount of time on your hands as I do.
No Jaco. I am using a 2 start 8 threads per inch leadscrew. Or 4 turns. Per inch. Or 6.35mm per revolution for the screw. Other than that the rest looks about right. As always you need to ask how much accuracy do you need and go from there.
Yes I do have time on my hands so I read to the end.
Cheers
Peter
There is also helical racks that engage 2 teeth at once.
I think I've seen photos those somewhere. I wonder if the opposite pointing teeth reduce backlash.
Cheers Peter
What about ball screws? You keep saying lead screw, but wouldn't you use a ball screw instead ?
Hi Mark
A ballscrew is just a different type of leadscrew. They are interchangeable in this context and ballscrew is an excellent choice. The video is really about screw vs rack.
Cheers Peter
@@cncnutz I was wondering because as far as backlash, isn't a ball screw better than lead screw, and possibly depending on length R&P?
Hy peter
Imran here
I want a opinion
I am going to make 6 meter long and 40 cm wide laser engraver for brass tube ( mm graduation )
What process I adopt
Question 1
Is i travel engraving head or bed
Question 2
I both situations upper said rack and pinion or ball screw
Question 3
What is the size of a pinion
Reply as soon as possible
Live healthy life
Dear engineers grant me your opinion
Ballscrew all the way baby!!!!
with a double ball nut!
There is another version of rack and pinion. Which is roller pinion this is supposed to have almost zero backlash
Thanks Ian
I saw pictures of that type of rack but didn't take much notice. It looked a strange setup.
Cheers
Peter
If memory serves me, I remember seeing one or more supporting nuts that move with the leadscrew at half speed therefore the drive nut only catches up to it at the ends.
Long nuts often have a lot of slop...
Nexen Rack and Roller Pinion system
Trapezi-oidal? XD
Northwood Cnc ball screw all axises all day baby
Thank you very much for the video, it was very informative! Just one minor point, there are a couple of pauses which are a bit unexpected. Better do a cut there
The 3:1 reduction gives you more torque that's a fact
It sure does. I'm not sure if this is true of a pinion but the 1" pinion moves 3 inches so that to me is a 3:1 increase. Does that sound right?
Cheers Peter
Poor cat
I don't know about that. I wouldn't mind changing places on occasions. Spend all day sleeping, waited on hand and paw. A conformable lap to sit on and the occasional stroll outdoors to catch a bird and disembowel it on the carpet.
What a life.
Cheers
Peter