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Building my own 3D-Printer (Z-Mechanics Question)

Posted by stonecoldfx 
Building my own 3D-Printer (Z-Mechanics Question)
June 25, 2017 07:39PM
Hello Everyone

I dived into the World of 3D-Printing at 18. April 2017 by purchasing a BQ Hephestos 2.
I literally did nothing else the last 2 Months then messing around with my Printer and Fusion360.

Two Weeks ago, I was lucky to get some 50x70 Aluminium Profiles in the Dimensions of 680x680x1000 for free from a good friend. (all mm)

So I started to design my own Big Scale 3D-Printer.

Just to point that out: I am not an engineer or similar. So things could be designed much better or in different ways. I am still in prototyping Phase.
I literally just started drawing directly out of my Head.

Well so here is the Actual Design (It's not finished yet)

Click on the Pictures to enlarge them



Actual Building Process (Takes a while to Print all these Parts with only 1 Printer sad smiley)


Now the Main Question:

Should I use the Z-Axis Carriage as a moving Bed? ( The XY Print volume would be bigger)
Should the Extruder move along the Z-Axis and the bed be fixed at the bottom?

I am using 12mm Precision Shafts H6 and 8mm Threaded Rods (those rods might be little small? since I did not buy the 1000mm rods yet)

Thx for any Answers.

Best Regards


PS:English is not my Main Language tongue sticking out smiley
Re: Building my own 3D-Printer (Z-Mechanics Question)
June 25, 2017 11:27PM
Interesting question...
Depending on the XY gantry you're planning, you could split the Y-movement between gantry and bed. ( I suggest CoreXY gantry )
Both movements are usually slower than X-Axis movement can be ( bed and Y-beam are heavier than X ) and by splitting them, they only need to move half as fast each.
OTOH end supported smooth rods are not the best way to guide such a heavy moving bed. I'd invest in real linear rails, before thinking about a moving bed.

Edited 1 time(s). Last edit at 06/25/2017 11:29PM by o_lampe.
Re: Building my own 3D-Printer (Z-Mechanics Question)
June 26, 2017 07:54AM
Hi there

Thanks for your Answer.

I am not really sure if I understand You right.You thought I want to move to Bed like a Prusa Printer?
If so I never thought of that. I am going for CoreXY for sure.

I just meant if it's better to have the bed making the Z-Movement or the XY-Gantry.

I figured out that I may need 4 threaded rods on each supported smooth rods in the corner to have it stable enough.

Guess like I designed it right now it would be very unstable.

Edited 1 time(s). Last edit at 06/26/2017 05:24PM by stonecoldfx.
Re: Building my own 3D-Printer (Z-Mechanics Question)
June 26, 2017 04:07PM
Little Update

Using now 4 lead-screws with only 2 Motors.

I hope this is working fine? Just need to add a belt tightener. I am lucky the belt needs to be exactly 607mm while my local 3D-Store sells 610mm belts. grinning smiley

Picture of the redesigned model.

(Click to enlarge)

I guess this should work much better than the model in the first post.

Edited 1 time(s). Last edit at 06/26/2017 05:26PM by stonecoldfx.
Re: Building my own 3D-Printer (Z-Mechanics Question)
June 26, 2017 07:12PM
Guide rails provide guidance and restrict motion to the axis of the rails. Lead screws provide motive force, ideally only in the direction of the rails. One round rail restricts motion to the direction along the length of the rail, but also allows rotation around the rail. Adding a second rail, parallel to the first, eliminates the freedom of rotation. Additional rails are unnecessary because the motion has been fully defined by two.
One lead screw placed between the two rails can provide all the motive force needed to lift the bed.

That's the ideal situation, and assumes everything is perfectly rigid and no play in the bearings. Reality is always a little different. The printer's frame flexes, rails flex, the bed support that holds the bearings that ride on the rails flexes, there is play in the bearings. Using two rails and placing a lead screw close to each eliminates the chance of the plate tilting at a single lead screw, but the bed support can roll around the two screws. Adding a third screw, and spacing things apart intelligently prevents the roll. Adding a third rail increases the chance that the mechanism will bind or walk instead of moving smoothly. Going to 4 rails is completely unnecessary and likely to end in the mechanism binding. It can be very difficult to align widely separated, end-supported rails parallel to each other and keep them that way. The more rails there are, the harder it is to align them.

In a printer with the bed moving in the Z axis, if the screws lose sync the bed tilts. Using multiple motors guarantees the screws are going to lose sync unless you have some active compensation. Using a single motor with belt(s) to drive all the screws guarantees that they will remain in sync.

TLDR: It's a bad idea to use 4 screws, it makes no sense to use two motors to drive 4 screws, and using 4 guide rails is begging for problems.

Edited 1 time(s). Last edit at 06/26/2017 07:20PM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Building my own 3D-Printer (Z-Mechanics Question)
June 29, 2017 08:10AM
You're already using fancy extrusions, so maybe you should get fully supported rails instead. End supported rails will work if there is no rapidly moving toolhead on them (so that excludes the Gantry moving in Z already) but supported rails will only flex as much as the extrusions... which look super beefy, so they shouldn't flex much at all...
Re: Building my own 3D-Printer (Z-Mechanics Question)
July 08, 2017 10:35AM
Hey there

Thanks a lot for your Replies!!

Makes totally sense when I have some more time I going for a complete redesign.
But for now I have most of the materials and printed parts and I going to try it anyway. But sure as u mentioned it makes not much sense.
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