Are Leadscrews Worth it for prusa i3 or m8 Rods?

I have built a prusa i3 recently and everything works except that I get really bad z wobble. I have researched and found out its because of slightly or bent z rods. I'm currently using 5mm threaded rods. I have several Questions. Should I just get a 8mm 300mm threaded rod or a leadscrew? If the lead screws work good for the z i'm going to just change every axis to lead screws including x and y to get rid of backlash. If leadscrews are worth it which ones do I get what thread and what thread pitch. currently I'm looking at these ones. Are leadscrews worth the money. I see allot of people have them. I'm a perfectionist so I cant stand my prints right now.
[www.amazon.com]

The ones you linked should work better than using threaded rods. The nuts should be fine, too. Don't worry about antibacklash nuts for the Z axis- gravity keeps the screws loaded with the weight of the X axis.

For X and Y axis you will need to use anti-backlash nuts with lead screws or get ball screws and nuts that have almost no backlash.

My printer has acme screws (imperial threads) in the Z axis with fully supported round guide rails and a 10 mm pitch ball screw driving the Y axis on fully supported linear guides. It is quite noisy, but produces very high quality prints and is very reliable. I have never had any problems with Z axis quality, including those artifacts commonly attributed to using imperial threads. I use a single motor and loop belt to drive both Z axis screws and never have to realign the X axis because the screws are always in sync. The X axis is belt driven and the extruder carriage rides on a fully supported linear guide.

If you want to see what precision Z axis layer registration can look like, check microscope photos of a fluted vase I printed here: [plus.google.com]

What do you think, are lead screws worth it?

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the_digital_dentist
The ones you linked should work better than using threaded rods. The nuts should be fine, too. Don't worry about antibacklash nuts for the Z axis- gravity keeps the screws loaded with the weight of the X axis.

For X and Y axis you will need to use anti-backlash nuts with lead screws or get ball screws and nuts that have almost no backlash.

My printer has acme screws (imperial threads) in the Z axis with fully supported round guide rails and a 10 mm pitch ball screw driving the Y axis on fully supported linear guides. It is quite noisy, but produces very high quality prints and is very reliable. I have never had any problems with Z axis quality, including those artifacts commonly attributed to using imperial threads. I use a single motor and loop belt to drive both Z axis screws and never have to realign the X axis because the screws are always in sync. The X axis is belt driven and the extruder carriage rides on a fully supported linear guide.

If you want to see what precision Z axis layer registration can look like, check microscope photos of a fluted vase I printed here: [plus.google.com]

What do you think, are lead screws worth it?

Do you have some pics of your printer? I would love to see it.

Some photos of it while it was under construction are here: [plus.google.com]

The third photo lets you see the Z axis drive arrangement pretty clearly.

Here it is printing the green vase in the microscope images. Almost all the noise is coming from the Y axis screw drive.

[plus.google.com]

The printer as it sits today is only slightly different from what you see in the photos. Here's what it looks like now: [plus.google.com]

Edited 1 time(s). Last edit at 05/22/2015 12:32PM by the_digital_dentist.

Looks awesome! Do you feel that you z axis setup works way better then two motors? Your final setup with enclosure and with the drawer covered looks very professional btw, kudos.

Thanks soo much that is one badass printer. I will buy leadscrews for my prusa i3. so for the z axis no ball screw's since there can't be any backlash. For x and y will these work or similar screws [www.ebay.com]. Could you tell me what the specs are for your screws? What type of ball screws did you use? Also will nema 17s be good enough for x and y or will I need a better motor?

I am dead set against using two motors to drive the Z axis screws. If you want to do any kind of precision work, you can't afford to have the axes flopping around on screws that a child can turn with their fingers. Accurately aligning the axes is time and effort intensive. You have to print a rather large object, measure it, and make adjustments based on the measurements. I have attached the STL for my alignment cube. A lot of guys who have these machines will say it's easy to realign the X axis- just line it up with the print bed. The problem is, it's the same print bed that is so unstable it has to be leveled/zeroed after almost every print. That's not a good reference for alignment.

When I first built my printer about 3 years ago, I started with a belt drive on the screws because I didn't want to have to keep realigning the X axis. After I did the final alignment and locked it down I printed for 2 1/2 years without ever touching the X axis alignment again.

The only reason two motors are used in so many printers is cheapness. Adding a second motor is cheaper than adding pulleys, bearings, and a loop belt. The few dollars saved by using a second motor turns into hours of your time realigning the X axis.

If all you want to print is Yoda heads, dragons, and tugboats, it probably doesn't matter what you do in the Z axis. If you want quality, precision, and accuracy, you have to start with a quality, properly aligned mechanism.

Those screws look OK, though you never can be sure what you'll get from China. Before you order anything, do some calculations. Figure out what your maximum print speed will be and see if you can live with it. Screws are generally slower and noisier than belts. Be sure to put bearings at both ends of the screws. Ignore advice to leave one end flopping around in the air. That only makes sense for bent, hardware store threaded rods on machines with flexy frames and guide rails.

Lead screws are only one part of improving the machine. Look into fully supported rails or linear guides, too. And none of that precision hardware will help if the printer's frame flexes every time you look at it.

As for motors, you need to calculate the required torque and see if the motors you have are going to work or if you need to buy bigger, beefier motors. I like the motor sizing tools at the Oriental Motor web site.

Edited 3 time(s). Last edit at 05/22/2015 10:31PM by the_digital_dentist.

Very impressive print (the vase).

Edited 1 time(s). Last edit at 05/22/2015 10:15PM by JamesK.

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JamesK
Very impressive print (the vase).

Thanks, but not my design.

If you're refering to the vase in this post: [plus.google.com], I reprinted it at 100% scale but this time I turned it upside down. When printing upside down the overhang is much more printer-friendly and the bottom 6-8mm that looked ugly on the first print came out perfect: [milwaukeemakerspace.org]

That's interesting. I actually meant the one you first linked to, with the magnified images. It seems to have deeper, thinner flutes than the second one. Those magnified images are the closest to perfection I think I've ever seen for FDM printing. Those edges look like a single filament looped out and back, and placed with remarkable reproducibility layer after layer.

As an aside, I took your advice about the Z axis layout to heart, and I've ordered the parts for a single motor, continuous belt setup, along with some thrust bearings to build a proper bearing block for the bottom of the Z screws. I've never been keen on the idea of putting all the weight onto the stepper motors, so this solves both issues at the same time.

James

Yeah, that vase is a really nice design for testing a printer's precision.

When you select the belt, make sure you get it a little longer than needed so you'll have room to make the tension adjustable. I adjust tension by either tweaking the Z idler position or by moving the motor mount. IRIC, the belt should always engage at least 90 degrees and at least 6 teeth of a pulley.

I added a page to my printer axis alignment spreadsheet that calculates the Z axis displacement per microstep to allow selecting layer thicknesses in the slicer that use whole number microsteps. It accounts for the screw lead, pulley sizes on the screws and the motor, microstepping ratio used, and motor steps per rev.

On my I3V 12", I have the GT2 belts running x-y axes and the M5-0.8 threaded rods on the z axis. The rods have been lubed with Tri-Flow and are about as straight as they are going to be. Each z axis stepper has it's own driver, which helps immensely and I have had no tracking issues at all. The belts cause resonance issues in the prints whenever there is a start/stop/direction transition and it is seen. Leadscrews go a long way to eliminating that "feature". I plan on moving to leadscrews/ABNs when I upgrade the unit as the belt resonance is irritating and the steppers have enough oomph as to skip teeth if I have the accel/decel rates way too high. I am thinking of doing all three axes with the mod as I have future plans for this that include some light CNC work.

It's very difficult to look at a 3d printer without thinking of adding a milling head for some cnc goodness, but really the requirements for milling and printing are so different I think it would be worth building two separate machines. Laser etching seems more compatible though

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JamesK
It's very difficult to look at a 3d printer without thinking of adding a milling head for some cnc goodness, but really the requirements for milling and printing are so different I think it would be worth building two separate machines. Laser etching seems more compatible though

@James

If you really think about it a bit longer, you'll come to the conclusion that each type of machine has different requirements and so deserves a differently optimized mechanism. IMO and based on my limited experience, there is not enough commonality that a single machine would be any good at any two of these tasks, much less the three of them. "Good enough" for one and mediocre in a second one perhaps, but that's as far as it would go.