1 Topic by pcm81

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Topic: Suggest a Z drive system for homebrew

I am building my own 3d printer. It will consist of 24"x24"x24" aluminum angle box with 16x16x16 (or bigger) print volume. I am looking for suggestions to drive the Z axis. I was thinking of getting a 3/16th aluminum plate, drilling 4 holes in the corners, and using 8mm vertical rods with linear bearings to secure plate in XY plane. I was thinking of buying solid doodles platform bracket and using it with a stepper motor to drive the platform up and down. I also considered using a stepper motor in the center of the plate (motor mounted to the bottom of the box but centered relatively to box/plate) and the stepper driving 4x z axis threaded rods using 4 belts. Rods would go in place of 8mm vertical shafts.

Goal is a rock solid, high quality build. Not going the cheap route, going the quality route on this one...

What do you all think?
Thanks ahead

2 Reply by lawsy

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Re: Suggest a Z drive system for homebrew

If you want quality, then ball screw.

lawsy's Website

3 Reply by pcm81

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Re: Suggest a Z drive system for homebrew

lawsy wrote:

If you want quality, then ball screw.

Thanks Lawsy. I thought about using ball screw and most likely that will be the route i will take. What i am trying to figure out though is if i need the screws on all 4 corners or if 4 shafts with 1 screw will be good enough to move the platform... Concerned about stiffness etc; platform will be up to 20 inches or so...

4 Reply by lawsy

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Re: Suggest a Z drive system for homebrew

The closest thing is probably CNC routers. They have only a single ball screw but thick polished rods with linear bearings to hold everything straight.

Your rods in the corners would do this nicely. Normally I wouldn't advise that because it might be hard to get hands/tools in to access the bed but in your case the area is so big it won't matter.

lawsy's Website

5 Reply by pcm81

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Re: Suggest a Z drive system for homebrew

For ball screws does thread pitch matter or can i just turn it less with stepper motor? I am having trouble finding bigger than 8mm ball screws with fine thread and 500-600mm length...
Considering either:
http://www.ebay.com/itm/1pcs-antibackla … 43bb6039d4

or
http://www.ebay.com/itm/TR8x1-5Dx500mm- … 338b0b00cc

Thanks

6 Reply by adrian (edited by adrian 2014-03-10 01:18:48)

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Re: Suggest a Z drive system for homebrew

Just keep in mind.. Ball screws actually have grease inside the nut and you are supposed to service this.. Often its just lithium grease or might be a specific requirement from the manufacturer for something else of a specific density... Anyway - my point was - There is a maintenance overhead to ball screw long term, AND, you need to be aware of whats used as the grease because if you stick it inside a heated enclosure you will be baking the grease. If its going to be all open frame and such - then this is not as big an issue...  And then you have to have oiler gear to inject it into the nipple

I'd spend some time actually over on cnczone.com myself - and actually study the myriad of pros/cons on lead screws/ball screws etc... Some have advantages over others and the drawbacks are not always obvious. Theres pros to be had from 1, 2, 4 start acme/trap vs ball screw... etc...

Its worth noting, ball screws biggest reason for use in a CNC is more than its smoothness - but its ability to withstand high thrust loads (such as when the end-mill plunges etc...) - This is not really a factor in any 3D printing we are using here - so it comes back to the precision..  And they have virtually no tolerance for misalignment - they need to be dead square as side-loading impinges on their function.

And not to forget - the actual king of kings for 'traditional' linear motion is a Roller Screw, which will cost 10 times as much as a Ball screw but is how things are done in the Aerospace industry due to its high precision, high speed and extreme load capabilities and repeat-ability where precision (or lack of it) with things can cost lives and billions of dollars.....

Personally - in respect to 3D Printing - I'm would hypothesize that a Ball/Roller screw is highly likely not going to do anything more for you than a *quality* trapezoid/acme lead screw would and it'd be 1/10th the cost. Cheap ball screws (most of the stuff on ebay) are definitely no better.

Heres a q&a from Thomson Linear on Ball Screws.. you'll see lots of time is spent talking about lubricants, suitability, and... Noise.. (yes, ball screws are noisy !) and it covers acceleration and loading and alignment...

http://www.thomsonlinear.com/downloads/ … ws_102.pdf

And here is some exploring of the pros/con:
http://machinedesign.com/motion-control … ear-motion

7 Reply by pcm81

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Re: Suggest a Z drive system for homebrew

adrian wrote:

Just keep in mind.. Ball screws actually have grease inside the nut and you are supposed to service this.. Often its just lithium grease or might be a specific requirement from the manufacturer for something else of a specific density... Anyway - my point was - There is a maintenance overhead to ball screw long term, AND, you need to be aware of whats used as the grease because if you stick it inside a heated enclosure you will be baking the grease. If its going to be all open frame and such - then this is not as big an issue...  And then you have to have oiler gear to inject it into the nipple

I'd spend some time actually over on cnczone.com myself - and actually study the myriad of pros/cons on lead screws/ball screws etc... Some have advantages over others and the drawbacks are not always obvious. Theres pros to be had from 1, 2, 4 start acme/trap vs ball screw... etc...

Its worth noting, ball screws biggest reason for use in a CNC is more than its smoothness - but its ability to withstand high thrust loads (such as when the end-mill plunges etc...) - This is not really a factor in any 3D printing we are using here - so it comes back to the precision..  And they have virtually no tolerance for misalignment - they need to be dead square as side-loading impinges on their function.

And not to forget - the actual king of kings for 'traditional' linear motion is a Roller Screw, which will cost 10 times as much as a Ball screw but is how things are done in the Aerospace industry due to its high precision, high speed and extreme load capabilities and repeat-ability where precision (or lack of it) with things can cost lives and billions of dollars.....

Personally - in respect to 3D Printing - I'm would hypothesize that a Ball/Roller screw is highly likely not going to do anything more for you than a *quality* trapezoid/acme lead screw would and it'd be 1/10th the cost. Cheap ball screws (most of the stuff on ebay) are definitely no better.

Heres a q&a from Thomson Linear on Ball Screws.. you'll see lots of time is spent talking about lubricants, suitability, and... Noise.. (yes, ball screws are noisy !) and it covers acceleration and loading and alignment...

http://www.thomsonlinear.com/downloads/ … ws_102.pdf

And here is some exploring of the pros/con:
http://machinedesign.com/motion-control … ear-motion

WOW, Lots of good stuff. thank you. I am definitely going  to dive into some heavy reading.