# Belt driven v rail Vs 20mm shafts



## LAMEIII (Oct 31, 2010)

Newbie here. I'm trying to make some decisions prior to purchasing a CNC router. I'm only a hobby nut; I want a decent system but have no plans on opening a business. I don't want to build a system either, just buy a complete system. I've been looking at a K2 machine that has unsupported 20 mm shafts and a Romaxx that has a belt driven V rail system. I know nothing about the various drive systems so I'm looking for some basic info. What are the pro's and con's about the various systems?
I'm looking for comments on these two machines and shaft Vs V rail.
Any information that would help me in making a decision would be greatly appreciated.

Jim


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## john4153 (Dec 1, 2012)

LAMEIII said:


> Newbie here. I'm trying to make some decisions prior to purchasing a CNC router. I'm only a hobby nut; I want a decent system but have no plans on opening a business. I don't want to build a system either, just buy a complete system. I've been looking at a K2 machine that has unsupported 20 mm shafts and a Romaxx that has a belt driven V rail system. I know nothing about the various drive systems so I'm looking for some basic info. What are the pro's and con's about the various systems?
> I'm looking for comments on these two machines and shaft Vs V rail.
> Any information that would help me in making a decision would be greatly appreciated.
> 
> Jim


Same question, same use here, maybe this bump will get some attention. Obviously, it is too late to be of much help to you, but the use of belts vs. ballscrews is an engineering question that I have not seen answered very well anywhere.

John


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## Phil P (Jul 25, 2010)

john4153 said:


> the use of belts vs. ballscrews is an engineering question that I have not seen answered very well anywhere.


There's also rack and pinion, John. I suppose it depends on the speed, accuracy and loading. Industrial CNC routers all seem to use a combination of rack and pinnion and ball screw drives (or sometimes ball screws only). Ball screws are expensive and it's difficult to drive them at extremely high speeds. Rack and pinnion, whilst not as accurate (accurate enough for many uses, though) are much faster and will take heavy loadings. The only place I've seen belt drives used industrially is in lightweight applications, such as pick and position systems for small component handling where a slight degree of inaccuracy is allowable. Industrial machines are generally capable of exerting a lateral thrust of up to 25kgf (sometimes more on machines designed to handle dense plastics) on the tooling. Can drive belts handle that?

Regards

Phil


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## bloomingtonmike (Dec 13, 2011)

I have a R&P machine and K2 Z axis that uses the ballscrew. No way would I want belt drive on my machine. The load while cutting wood with a bit would not be something I would want on a belt. 

Soon I will build a stand alone 3d printer and it will use a belt on the X and Y axis but not much load will be on the head beyond its own weight. Belts can be very fast if designed correctly. Tensioning has to be done correctly.


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## john4153 (Dec 1, 2012)

Specifically, I am looking at the Romaxx. I do need to do light aluminum milling; although, most of my work will be 1/4" or 1/8" plywood.

It is my understanding that a good ballscrew does not take up much of the working forces. Thus, both belt and ballscrew would be limited by the steppers. If I were converting my Bridgeport, I would not think twice about the question and use ballscrews.

Another way to put this question, is comparing the Romaxx with lower-end American made and higher-end Chinese made CNC routers, do rolled ball screws offer a real advantage overall. My target is <$4,000, and of course, lesser is better so far as price goes for the bare machine.

I left off rack and pinion as that design seems to be for larger machines. I am looking at "desk-top" machines of < 24"X24", and in the import nomenclature, a 3040 is as small as I want to go.

Regards, John


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