What is the difference between Helical Rack vs. Ball Screw?
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- čas přidán 27. 07. 2024
- #cncrouter #routing #routertable #helicalrack #ballscrew #madeinusa #cnc
A common question, “What is the difference between Helical Rack vs. Ball Screw?”
The linear motion platform plays an important part in the structure of a CNC machine as it defines the precision, speed, and performance of the machine. In this video, we will show you the different types of motion platform we use.
Three different types of motion platform at MultiCam:
Rack and Pinion - multiple fasteners mounting the rails into our one piece, steel milled frame, it minimizes any vibration and increases secured motion when cutting.
Straight Rack and Pinion - tooth is perpendicular
Helical Rack and Pinion - tooth is slightly angled so the pinion has more than one tooth engaged at one time.
Ball Screw - use for short distance precision, Z axis. Made with a spiral of ball bearings, and only fasten at each end, so the longer the length the ball screw has to travel, the more susceptible to whip.
At MultiCam, we use both ball screw and rack and pinion platforms and here’s why we use helical rack as our linear motion.
Smooth motion - short or long axis, more than one tooth engagement equals smooth linear transitions
Stability of helical - more control of higher accelerations
Accuracy - multiple attributes like gear boxes and excellent servo systems
In summary, helical rack is best choice for large format CNC machines.
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Why put a CNC in your living room, when you could just put your living room into this CNC…
I agree..lol 😄
You would issue a G0 command for the gantry to move you towards your home entrance.
You made me buy helicals years after buying this video .
if this really was the case, RP would be on every DMG
Something I’ve never been aware of. A brilliant insight into the superiority of rack versus ballscrew. Thanks for this fascinating knowledge.
Very welcome!
Sounded very much like a sales pitch.
Great video, thank you. Some suggestions, though: It'd be helpful to clarify pros and cons between both approaches when speaking of (1) pre-loading capability, (2) axial load capability, (3) contact angle aspects associated with rack-pinion approaches, (4) options to shield or seal the driving elements, to keep debris/contamination away, etc. I tend to agree that for 'long-travel' motion systems, helical rack should definitely be considered. However, I'm concerned that the video may be misinterpreted by some as rack and pinion is 'always' better than a ball-screw approach. I've read some of the comments below, and I believe that some people are misunderstanding such details. In any case, great video and reference knowledge. Thank you so much.
Thanks so much! We appreciate the great feedback.
You didn't mention backlash, which is necessary for rack and pinon motion systems to work. You can eliminate whip by turning the ball nut rather than the heavy screw.
There's a reason he didn't. This was a puff piece meant to beef sales camouflaged as unbiased information.
Almost everything he stated was borderline deceiptful. Like the statement that R&P can be more accurate than "Any ballscrew"... BS... If he had been honest, he could have said the best R&P can compete in accuracy with some rolled ball screws, possibly.
Now, what he could have done is talk about how each platform will always be a compromise and the longer the router is, the more R&P starts making sense. And like you said, he could have mentioned rotating ball screws which help reduce whip and then he could have talked about how you need very thick and super expensive ball screws to counter whip. But they are so afraid to play that honest card so they try to make people believe that ballscrews have hardly any advantages. To me, that's just a bad strategy as the honest one is good enough.
Agreed 100%. On the large format industrial machines which cost 200k+ they use rack and pinions but they compensate for backlash using software. They would calibrate each section of the rack using a ball bar by moving the spindle in a circle. Then they store the backlash information for each section of the rack and the controller would compensate according to the stored values in real time. That is to say, each time the x or y reverse directions, the controller would add/subtract the backlash distance nearly instantaneously.
They are able to achieve +- 00005" accuracy using this method. @@AntiVaganza
@@AntiVaganzaNailed it. It's easy to spot sales a$$hole videos like this.
@@AntiVaganza Looking to build a 5x10 CNC router to make cabinets as a side gig. Would you recommend balls screw or this rack? Trying to keep it cheap for the start. Thanks
r p avid drives avid cnc work fine
@@shannonp4037
How could you have this discussion without talking about the main issue of a rack. Backlash. The helical gear contact doesn't change the clearance necessary for gears to roll. Also the drive is likely to have more backlash too as the rack doesn't have any inherent speed reduction like the screw does. So a multi stage reduction is more likely adding places for backlash and compliance to the drive where belts can stretch.
Then the argument of ball screws whipping is easily solved by turning the nut instead of the screw.
You might have multiple gears on the rack with an adjuster to compensate for backlash, and if so seems like it should have come up in here.
I don't know the accuracy of your machines and they may be as you claim, but this video certainly didn't convince me that a rack has the accuracy of a ball screw.
It could happen because the company that sells these machinese which rely on R&P had their own sales engineer do the "discussion". So, it's flawed. They made a sales pitch but camou'ed as unbiased info. Which was plain silly as if they had been honest about it all and explained why as you go to larger machines R&P start making sense, especially from a cost standpoint. Instead, they tried to convince us it's the best thing since sliced bread... Old school tactic. People are smarter that that now (I hope).
This is a sales pitch not science
I’ve repaired their machines before, they are so full of shit tbh
Definitely convinced. Helical for anything over a few feet. Just learning about CNC and this is great info!
Glad it was helpful!
You didn't even mention backlash once
Then which would be best to avhieve precision under 10 microns when rotating a 100 kg part 300 rpm?
"Superior" depends entirely on context - who is building it, how much money is being spent, how large is the axis, it is fully closed loop or not, etc etc. If you're talking about a very large axis and a massive CNC machine like those in the video, then sure you don't have much choice, but for smaller axis it's way more complicated.
Exactly. This is a sales piece and if they had just been honest it would have been a good one.
How would a straight rack perform when two motors/pinions are use? They then also engage at least two teeth, and maybe they can be placed so that it minimizes backlash.
Won't the whipping be mitigated if you have the ballscrew fixed and the nut rotate instead?
But how will you do that? Mount a motor on the nut?
@@mdayaan7573 Why not? I've seen people do that.
@@mdayaan7573 Yes, it's called a rotating nut. Expensive but it's not uncommon.
@@AntiVaganza Not expensive if you have the time.
A ready made rotating one is expensive, but yes you can make your own from a regular nut@@randallsemrau6911.
Crazy how youtube randomly offers up videos like this when I was just discussing this topic earlier today. I think on smaller mills a ball screw setup is perfectly fine. But when you start getting over 8' on a gantry mill you going to get whip on a fast moving machine. A helical rack can match them in accuracy and have a rock solid foundation. We have a 30 year old helical rack machine a work that respectfully runs at least 30 hours per week under heavy loads most of the time. I've just started to notice a slight ammount of play on the end of the table that gets the most use from running small parts. I doubt very seriously ball screws would have held up that long.
preloaded Balscrew= 0mm backlash, helical rack= NEVER 0mm backlash
Finally, someone that actually speaks from the experience and understands the differences.... GREAT JOB !!!
With a ball screw you get a lot more linear force from the same torque motor. It means less acceleration on the axis. It is because one rotation of a screw is typically 5-10mm of linear movement. With rack and pinion it can be from 60-200mm. When you are using stepper motor set to 200 step per revolution you get from 0.33mm to 1mm per step! You can gear down a motor with a timing belt, but you loose the main advantage of rack and pinion - simplicity.
In my opinion using rack and pinion is a reasonable choice only to drive a gantry in machines longer than 2m. If machine is smaller i would always choose ball screw over rack and pinion.
Rack and pinion
-Easier to use on bigger mashines
-Require bigger steppers/servos to get good accelerations
Ball screw
-Dont require big motors
-High forces and accelerations
-More precise than any existing rack and pinion due to pre tensioning and zero backlash
-Slower maximum axis speeds
its 2022 now ,who use step motor? servo system with abs encoder plus a cheap 3 arcmins reducer will beat those same cost ballscrew a lot.
@@joshshen1492 2022 printer still using stepper motors
Yeah, I'm definitely starting to regret going for 2,7m long ballscrews in the Y axis of my CNC router, even if they are 25mm diameter they sag a fair bit, and is a pain to align :P
Hi, but you rotate nut or the screw?
You didn't talk about need of dual pinion. I have seen dmgmori machines that have 3 pinions.
Thats very interesting! Can helical racks work with zero backlash on change of direction like ballscrews? Are building your racks in-house or any preferred supplier? Thank you!
Great Video Mr You get what you pay for! ha,, one thing you did forget to mention is that most rack n pion set ups? your project STILL relies on THE MERCY of a BELT!!!!!! yeah its a long toothed steel track but those 3 pulleys that house in the motor are belted together! lol!!! hey but they are people out there running machines On Toothed timing belts on its own orbit of thought! So its really a double edged sword in a way, Another option are chains!!!! for the individual that feels that kevlar or steel belted rubber Either way you will still have to keep on eye on it! Rest assure you will still have to service and maintained the unit regardless of what you choose!!
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No mention of the sideways forces on the pinion, thus an unfair and incomplete comparison.
nice knowledge to have. i never know Helical gear always engage more than one teeth...
thank you for sharing
Except you can get as close to zero backlash as you will ever get with one while the other requires that you build some in just to keep it from destroying itself in short order. Didn't need the marketing wank, its simple, want to move really fast or cover distances over about 6-8 feet then you probably want rack and pinion. Whip isn't even an issue, your screw is either bent or you're trying to spin it way faster than the ball nut bearings are going to tolerate for long anyway, turning the nut is a solution also. A lot of mechanical advantage is lost with a rack vs screw, so more expense in bigger motors to meet the demand but that also means a likely reduction on positional resolution, or you gear it down which is an expense that likely adds more backlash yet. No silver bullet here.
celiturbo said 'A lot of mechanical advantage is lost with a rack vs screw'. What are the disadvantages of increasing mechanical advantage at the pinion through gears or pulleys or some other means? .
rack and pinion is the cheapest and easiest way to create numerical machines, it reduces components and you can use fiber reinforced performance concrete instead of metal for the structure, so this makes cnc routers, printers, tapping affordable to anyone. also if you install a contact layer in the rack and pinion , you can replace it regularly after wear saving materials
Ball screws are easier to install. Also the accuracy of ball screws are very high. The price of ball screws is also less due to higher production volumes
@@arbjful i can make a precision fiber reinforced thermoplastic (even self lubricating) rack with wax milling and molds, however making a screw is only possible with metal rods and it has to be forged metal with plenty of treatment, and after this metal has to be precision milled in all the 360º degrees compared to 3 axis milling of a rack. precision is more about the pitch and lead of both systems
@@crapisnice we use 10mm pitch ball screws for our centering application. An open loop stepper motor easily handles our accuracy requirements, we used a timing belt system, but apart from speed, there were accuracy issues here
@@arbjful yes but rack and roller pinion is more reprap friendly, more accessible to be done diy and spreaded, that the reason i have chosen it anyway beside the bending stresses of screws, however fiber reinforce composite screws can be done as well (and applied in vertical z axis with no problem)
@@crapisnice do you make rack & pinion? Maybe i can consider for some applications
Ball bearings and bearing balls are different things.
There are no ball bearings inside a ball screw but there are bearing balls.
Ball bearings and bearing balls are indeed different. However, rotating nuts for ball screws have both.
thanks for the useful information
i like your ring
Hmm it’s a ballscrew but not a conventional one.. but yeah the helical rack for these maschines makes sense as of there work room.
Others go even further by either using magnet based rails or air cushions.
Ball screw Passion as well.
I call absolute bullshit on helical rack being anywhere near as accurate as they are claiming.
I think we all learned something about our new savior Helical Rack.
,🙏 Thanks for the knowledge.
thanks for your explanation very good information
Thank you for the info
very important
If rack and pinion is so superior then why don't you use it on your spindle axis? Backlash on R&P is insane - fine if all you are doing is making signs but otherwise, I'll stick with my ball screws.
First of all, don't mix measurements. Either Imperial or metric. Also in machining 0.0002" is a large. I built a macro to l rail in my spare bedroom with a theoretical resolution of 0.0000118" (that 0.0003mm for places that aren't America). The next one in currently working on could potentially have an even higher resolution.
Hello CV thank you for your work and thank you very much for your work. Is what you can do me a favor
How can I help you?
Why dont you Rotate the nut. Not the screw.
the best solution may be for a fixed and minimal length, but to add extensions it is worth nothing
The explanation is inclined to rack and pinion and it does not give genuine difference rather a biased
Well
Что за бред?)))) Допустим мы используем ШВП с шагом винта 10мм. Получаем 1 оборот=10мм. Чтобы получить такое же соотношение на зубчатой рейке, на редуктор. Редуктор если не свехточного исполнения это люфт зубьев в 2х местах.... компенсация на реверсе это однозначно ударные нагрузки при смене направления движений...
Not more miss information to the public 🤷♂️👎🏻