[willheg]

Hi people, wondering if anyone could help me with a question or two i have about a machine i'm building.

I am looking at chain driving it with something like BMX bike chain.
what i'm wondering is that if i go this way would i need to run a gearing ratio or just direct drive the chain and micro stepping the driver??

If i was to go this way what would people suggest for a gearing ratio if i need to use one and what micro stepping ratio to use.

Or if i was to not need a gearing ratio what stepping ratio to use??

also while i am posting, would you use a ball screw on the z/axis or would it be ok too use the same idea on it to, althought i'm thinking the weight that that axis will be holding up it might not stay in position well, where as ball screw would be better, but if i do not ask the questions to find out info and get other peoples views.

[ger21]

I'm not a fan of chain drives, but I'd recommend gearing it so that 1 revolution of the stepper motor gives you 1" of travel.

For a Z axis, it's probably easier to use an acme screw or ballscrew.

[Christian Knüll]

Hello,

I also wouldn't use chains - even though it is possible of course.

First: using a chain without gearing means coarse step resolution and very little force. If you compare for example a screw with 5mm pitch and a sprocket with 50mm effective diameter you get 0.0125mm step size for the screw and 0.39mm step size for the chain (with a standard 1.8° motor). Also force is about 20 - 30 times lower for the chain. Microstepping will help a bit to improve resolution - but microstepping angles are "soft" - the more torque needed the higher the deviations and it won't help to improve force. You'll need a very strong motor or need a gearbox.

With this in mind you can select a gearing ratio depending on sprocket diameter. At first it would be reasonable to keep it to something that is more or less comparable to a spindle. In this case with a 50mm wheel it would be something around 30:1 - quite hard to make - you'll likely need 2 gear stages. So if you have a strong motor you may use a lower ratio - this will also increase speed but precision will be worse. Next consideration: your gear should be more or less backlash free or you'll have a lot of backlash to compensate especially with 2 stage gear drives. Timing belts may be a good and reasonable priced choice.

There is one last especially bad thing about sprockets with low tooth number: "polygon effect" -> the travel your chain will make with each step is different depending on actual sprocket angle. With a 10 teeth wheel it is about +-2% - with 30 teeth only about +-0.25% - so a large diameter wheel is more precise but also needs higher gearing ratios than a smaller one.

My personal conclusion: unless you have very good reasons to use a chain (extremely long travel of several meters / a lot of dirt / very high forces) - don't use them. You won't save money and precision won't be too good.

Christian

[willheg]

Thanks for the replys guys,

I have seen a few done this way and they look like they work ok, but like you say they have a big gearing ratio which i maybe able to do but will need to look into how i drive it and all, i have some quite big steppers to put on this machine, 4.2 amps and 48v power supply.

Might just have to redesign the machine i have starting building a little bit to work it with this if i go this way.

If anyone else out there has any info they would like to supply that would be great, in the mean time back to the drawing board and rethink what i'm doing.

Once again thanks to those who have replied and to those that do reply your information is welcomed.

Will

[louieatienza]

You might want to consider timing belts in lieu of chain. Would run a lot quieter, more accurate and possibly cheaper than chain. Or even rack and pinion, which may be easier since there are ready=made components available.

[willheg]

Thanks for the reply, I have thought about belt, but where I live it is not that commen and not very cheap, also I cannot manufature the pullys myself where as where I work I can make sprockets easy and cheap as.

I also felt that the belt way might strech fast over time than chain wear.

i undersatand about the presion and all but i have found some cheap chain which i could use.

my machine is x of 2000mm, y of 1800mm, and z of around 250mm
still open to everyones points of view and gearing ratios and anything else.

also anyone that could point me in the direction of the best/highest microstep setting to use that would be great.

[MillworkMike]

Chain drive works!!! Its not the best in the world but it works!
It will require constant adjustment so be ready!

I ran my diy 4 X 8 machine for a year with pretty good luck before swapping over to rack and pinion.
I made over $10K in a years time making raise panel cabinets doors on the side using chain drive.

I used fulling nema 34s with 7.5:1 gear boxes, 9 tooth #40 sprockets, #40chain, and 1/8 microstepping which gave a resolution of 2666.66.

I did not read the entire thread word for word and im not sure what you plan
to do with your machine but if you are on a budget or have limited resources
chain drive will work. :-)

[willheg]

Thanks for the reply, good to hear from someone that used it and had pretty good success with it.

Sounds like a pretty good resolution but to buy the gear boxes would be a cost i'd hate to think about, so the thinking continues.

I thought of gearing it with extra sprockets and chains but but to get the resolution i'm looking for will take a lot of extra bearings, chain, sprokets and work.

Will still have to think about this some more.

How did you work out your resolution MillworkMike, just out of curiosity.

Will

[louieatienza]

Thanks for the reply, good to hear from someone that used it and had pretty good success with it.

Sounds like a pretty good resolution but to buy the gear boxes would be a cost i'd hate to think about, so the thinking continues.

I thought of gearing it with extra sprockets and chains but but to get the resolution i'm looking for will take a lot of extra bearings, chain, sprokets and work.

Will still have to think about this some more.

How did you work out your resolution MillworkMike, just out of curiosity.

Will

You need the root circumference of your drive sprocket. To simplify, if you direct drive, or use no gear reduction, and your sprocket circumference is 2" and your steppers are standard 200 steps/inch, then your mechanical resolution is .01" For example, a GeckoDrive can do 10x microstepping. But you shouldn't rely solely on microstepping since it is not exactly linear, and the torque drops when microstepping. A GeckoDrive will morph to full stepping at speed to increase torque at speed. Microstepping "smooths out" the stepper movements at slower speeds.

My thinking is to get the best mechanical resolution you can, and the microsetepping is icing on the cake. You have to be realistic about resolution; as I feel it's more important to have positional repeatability. With steppers, accuracy will come at the cost of speed, and you can only spin them so much before the torque drops off big.

In short - don't worry about resolution too much with chain drive, as your backlash will exceed the microstep resolution.

[MillworkMike]

You need to know the pitch of the chain/sprockets you will be using.

The #40 roller chain and sprockets that I used has a 1/2" pitch...
9 tooth sprockets gave me 4 1/2 inches of travel per rev. 9 X .5 = 4.5
My steppers are 1.8 degree steppers 200 Steps per one full motor rev.
At 1/8 microstepping that is 1600 steps per rev and my gearboxes are 7.5:1
Sooo... here goes the math...

1600 steps X 7.5 gearbox ratio = 12000 steps per gearbox shaft rev.

12000 divided by 4.5 = 2666.666XXX Mach 3 resolution.

Hope this helps! :-)

[willheg]

So from what i can understand mike your machine moved .00038 per each step move. Cause that is about what i would be looking for.

I'm not really to sure what you mean by the mach resolution but i guess i'll find out in time.

But thanks for the information so far it is rally good that guys out there that have been there done that a keen to help other people like us newbies.

[Orion13]

So from what i can understand mike your machine moved .00038 per each step move. Cause that is about what i would be looking for.

I'm not really to sure what you mean by the mach resolution but i guess i'll find out in time.

But thanks for the information so far it is rally good that guys out there that have been there done that a keen to help other people like us newbies.

He is saying the 2666.66 is the calculated number you first put in Mach3 to tell it how many steps per inch on that axis. It isn't till you actually calibrate the machine do you know the true number.


Orion13

[willheg]

Ok then thats good to know, thanks for that i'll keep working and see what i can find out to aid me on my way to finish my build.

[metricengr]

I Have been using #25 Roller Chain with my 260 oz Steppers to drive my heavy Gantry along the X axis with great success. I have to constantly make sure everything is adjusted and correct though, because too much tension on the chain causes the motors to bind not enough i get horrible accuracy problems. It is doable But i would suggest being sure it is not cheaper to go with something else first because once you start to build and get V1 done you will never want to stop making it better and faster and bigger, and for this reason it might be more money in the beginning to get rack and pinion but it will pay off.

[wildwestpat]

Hi
Before investing in chain or effort consider the main problem with chain drive and that is the number of links each of which has a minute amount of slack due to the clearances in the link pins. Over a length these all add up to make what for most purposes is way too much backlash. The chain also needs lubricating and that attracts dirt and generates more problems. Most precision uses of chain drive are unidirectional so that the issue of backlash does not arise (timing chains in combustion engines etc.) Try toothed belting either as a loop or a single replacement for a toothed rack.

regards - Pat

[PaulRowntree]

Hi
Before investing in chain or effort consider the main problem with chain drive and that is the number of links each of which has a minute amount of slack due to the clearances in the link pins. Over a length these all add up to make what for most purposes is way too much backlash. The chain also needs lubricating and that attracts dirt and generates more problems. Most precision uses of chain drive are unidirectional so that the issue of backlash does not arise (timing chains in combustion engines etc.) Try toothed belting either as a loop or a single replacement for a toothed rack.

regards - Pat

Pat, I think that the real failing of chains is the cogging caused by a rigid set of links trying to roll around a circular sprocket, which causes the motion to be slightly irregular during a rotation of the sprocket : reproducible, but irregular. I can tweak my chains to be tensioned at the sweet spot, but it is not for the faint-hearted. I am going to ACME on #2, although I know I will miss the speed.
Cheers!

[willheg]

Hit guys i'd like to thank you guys for the information as it has be great to get some more.

I decided a while ago after this topic died the fact i had brought some chain at a bargin price even before i started asking questions that i will go ahead with it to get this off the ground and upgrade later on when money/time allows.

Anyway once again thanks for the valuable input and info on what you have all learnt.

Will

[wildwestpat]

Hi

Paul There is a type of chain known as silent chain that avoids the problem you describe as cogging with small numbers of teeth. However silent chain is expensive compared to standard roller chain. Starting with a clean build I agree there are other motion drive methods that can be more appropriate depending on the operating requirement.

Will So you have the chain you need to make sure the sprocket tooth gap geometry is correct for the sprocket wheels. The ANSI standard specifies five different cutters for cutting the tooth gaps for making sprockets by non generating profile processes. Just as for making meshing gear wheels and pinions the standard is for a range of pitches and correct at only one! I suspect that racing cyclists have sussed this out and have chain wheels and sprockets of the correct tooth form. You can even feel the 'cogging' Paul is flagging up with cheap imported cycles by rotating the pedals with the back tyre off the ground.

For a wood cutting machine chains would have the advantage that they would be resistant to fouling with wood chips with little or no protection.

Good luck with the build just work back from the accuracy you require in the finished parts you intend to make to check that the axis drives will deliver.

regards - Pat





All in all IMHO you have made a good decision to use

[willheg]

Hi Pat, just like to thank you on your info this is really great of you.

It has opened my eyes a bit more but i might do what everyone else does.

Ask questions, get answers, ask more questions, try to prcess it all and make head/tails of it. Then just start somewhere and do it then mod and update as money/time/funds come along.

once again thanks Pat

Will

[PaulRowntree]

Hi

Paul There is a type of chain known as silent chain that avoids the problem you describe as cogging with small numbers of teeth. However silent chain is expensive compared to standard roller chain. Starting with a clean build I agree there are other motion drive methods that can be more appropriate depending on the operating requirement.

Thanks Pat, I had never heard of silent chain.
Cheers!