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Chain Drive vs Lead Screw

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Chain Drive vs Lead Screw

Postby dsailer » Sun Jan 31, 2010 3:03 am

What are the advantages or disadvantages between a chain drive setup or a lead screw setup?

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Chain Drive vs Lead Screw

Postby Awesomeness » Sun Jan 31, 2010 5:38 am

Lead screw setups need to work very hard to eliminate backlash. (Backlash is the small amount that you can turn the lead screw back and forth without actually moving the axis.)

Chain and belt drives let you apply tension, which creates a situation in which there is minimal, or possibly zero, backlash.

Another consideration is gearing, speed and resolution. The lead screw setups typically have numerous threads per inch (TPI), which results in a mechanical gear reduction, which increases the force exerted by the motors several fold, but also reduces the maximum speed by the same factor. The resolution is also increased by the lead screw, since a motor step of one degree (1/360th of a revolution) only moves the axis a tiny bit ( 1 / ( 360 * TPI ) ). Conversely, belt/chain systems [that do not incorporate gear reduction boxes] typically gear up, so all the opposite applies... less power, less resolution, faster speeds.

To combat these issues a gear reduction drive can be added to a belt/chain drive. However, these systems can introduce their own backlash, although in a much more controlled and manageable manner.

Rack and pinion drives can also be considered. They have some hybrid pros and cons, but generally act very similar to belt and chain drives.

There are plenty of other considerations too, such as that tensioned belts and chains will put lateral stress on the motor bearings, and always in the same spot/direction. Screw drives put very little lateral force on the shaft of the motors.

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Chain Drive vs Lead Screw

Postby PHoodDaniel » Sun Jan 31, 2010 7:21 pm

That was an excellent explanation Guido. I would like to add a couple of thoughts. First, the lead screw is actually quite hard to turn in many circumstances and tensioned chain or belt is quite easy. Second, the motor is turining at low speed to travel a great distance in relation to lead screw. Stepping motors have high torque at low speeds and with lead screws, the motor can stall at a moderate speed if there is the slightest bit of torque. Third, drivers can run at mocrostepping mode to increase the resolution. In most cases, manufacturers will tell you to not rely on the driver to gain in resolution, but this conversation is most relevant with lead screws and the fact the the backlash needs to be removed. Drivers can be successfully microstepped to a mechanical system that has little to no backlash. In my experience with roller chain and belt, the performance is quite superior to the traditional lead screw. I welcome any comments and discussion on this subject as this is what drives my motivation.

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Chain Drive vs Lead Screw

Postby dsailer » Mon Feb 01, 2010 4:00 am

Thanks. All making sense somehow... :-)

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Re: Chain Drive vs Lead Screw

Postby NCDave » Mon Jul 10, 2017 2:01 am

While I haven't actually built my CNC project yet, permit me to weigh in on this topic. In years past, I designed and built numerous industrial computer controlled machines for various applications. Some were lead screw based while others were chain drive and rack/pinion applications. Open and closed loop systems, stepper and servo motor driven. My plan is for a machine beefy enough to mill the occasional aluminum part for my car build hobby, durable enough to set it in motion and walk away with confidence...and build it for the least investment possible. I'm leaning toward chain drive and (initially at least) a 2.5 - 3 hp router with a 1/2" collet to handle end mills and a 4'x8' work table. Accordingly, speed and rigidity are important factors. I see all kinds of different guide/ methods on the 'net...not yet sure which way to go. With all of the info on youtube and forums about guide systems, no one talks about run out or tolerance deviation in the setups over a given span. The bearing wear issue mentioned previously is easily dealt with on a chain system. The key to durability there is to not side load the stepper motor. All the other components are industrial rated and can handle the load with no problem. If cost was not object, I'd use acme ball screws & ball nuts, hardened ground rods and linear ball bearings for the guides (the good ones, not the Chinese jobs on ebay). But that's not the case, so I'm very interested in the results the folks on this forum are getting with the various setups.
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Re: Chain Drive vs Lead Screw

Postby Awesomeness » Thu Jul 13, 2017 1:27 pm

NCDave wrote:If cost was not object, I'd use acme ball screws & ball nuts, hardened ground rods and linear ball bearings for the guides...


You have to be careful with that selection being used on CNC woodworking routers anyway. Unlike a CNC mill, which typically makes chips big enough that they don't clog or interfere with the lubricated ball nuts and bearings, CNC routers make fine sawdust, which cakes with lubricant and gums up ball bearings, even when they are equipped with seals and wipers. You either need to hide the bearings under guards and shields, move them to less affected areas such as under the table, etc. That's why you even see so many commercial tables that use open v-groove bearing linear guides. The dry plastic bearing liners, such as those made by Igus, are very well suited to these dirty environments.
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