# Tag Info

16

I am going to answer this as someone who actually did rework their Prusa i3 fleabay clone to use leadscrews for all axes. Before digging into the matter, the backlash issue can be solved easily with spring-loaded brass nuts, kinda like how ballscrews work. That's the simplest problem to solve though as there are a lot of other issues. Short version / tl;dr ...

6

In addition to cost, backlash, which can be experienced in the Z-axis where threaded rods and leadscrews are mostly commonly used, would/could become an issue. The elasticity of GT2 belts generally avoids this issue for the X and Y axes. It would be worth reading Tom's answer to Advantages of GT2 over a rack, which while the question was related to Rack and ...

5

From Accuracy vs Precision and Threaded Rod vs Leadscrews in 3D Printers. I have highlighted the relevant parts: In general, FFF/FDM printers use relatively infrequent, small, precise movements on the z-axis and consistent, fast movements on the x and y axes. A single start leadscrew with the tightest pitch possible (highest thread density, smallest pitch) ...

5

as long as you match the parts that is ok. The m8 rod will give you more stiffness and will be harder to bend. As the result, you will have to calibrate the steps/mm settings in the firmware.

5

Cost would be the primary reason. You can engineer a belt driven system that will be equally accurate, faster, and with longer travel for a lower cost. Lead screws are comparatively expensive. The cost differential dramatically increases with length of travel and speed with equivalent accuracy. Lead screws do have a significant advantage of being able ...

5

I have the Anet A8, I confirm the threads are Tr8x8(p2). This is explained as "Tr" for trapezoidal thread followed by the nominal diameter in mm. The digits after the "x" denotes the lead of the screw (how much does the nut advance per revolution). The value between the brackets "p2" denotes the pitch. This means that the screw has 8 (lead) / 2 (pitch) = 4 ...

4

A lead screw can be fitted with a anti-backlash nut to get past your concern about backlash. Generally, backlash is not that of a problem considering the weight of the carriage (e.g. Prusa), or whole bed (e.g. CoreXY or Ultimaker). Certainly if you're not using Z-hop, the Z screw will only advance in a single direction! GT2 belts are always reinforced with ...

4

Expanding on some previous comments which are probably enough to warrant an answer: What Trish said is completely right. Leadscrews are readily available parts and any dimensional errors in the leadscrews will be reflected in the output of your CNC machine unless you have some sort of compensation for them. Moreover, if the material is not highly rigid, the ...

4

I've not seen trapezoid lead screws with 5 mm lead, you can get 5 mm lead ball screws though. On one printer I use 4 mm lead screws to get native 0.02 mm resolution (so 5 full steps for 0.1 mm, 10 for 0.2 mm, etc.). I also geared down 8 mm lead screws with a 2:1 ratio (e.g. to use a single Z-stepper driving a belt that ...

4

It's probably intentional. Threaded rods are almost never perfectly straight. If the nut is rigidly coupled to the carriage, then the slightest deviation in the screw will either cause it to bind up or appear as artifacts (e.g. z-wobble) in the print. By making the nut slightly loose, it can move around a bit to compensate for wobble. See e.g. this design ...

3

Direct-drive, 8mm-pitch Z-axis screws is a very common configuration. Although it results in low z-axis resolution, apparently it works well enough for most FFF applications. Like you, I noticed this curious design as soon as I got into 3D printing. Based on normal design principles, the resolution of the Z-axis of most printers is technically inadequate or ...

3

Is it possible? Yes. Is it advisable? No Lead screws need to be smooth and have little to no stretch and there can be a lot of tension on them. However, 3D prints are quite rough by the way they are made and super weak on tension forces - and not have a good compression withstanding either. a 3D printed leadscrew is therefore not adviseable, especially since ...

3

No, but the answer could depends on how you set up the lead screws, what kind of lead screws are used and how they connect to the stepper. Also it is important how you transfer the linear Z motion into the X gantry. Note that regularly used TR08 (Trapezoid, 8 mm) lead screws are stiff enough to not flex under the limited load of an X gantry. So, putting them ...

3

Amazon has a few hundred M5 rods listed for sale, so I don't know where or what you've been looking through. If you change the lead screw, you'll have to change the threaded parts on the gantry assembly to match. More important, you'll have to adjust the Z-drive "steps/mm" setting to match the 8mm lead. (with thanks to Professor for pointing out my ...

3

You'll need to do some calculation to figure out how long of a lead screw you need. The best solution would be to mock up the entire printer in CAD so you can visualize how everything fits together. Not only is the coupler going to take up some space, but the nut also takes up some space, and perhaps (due to design constraints) you won't be able to have the ...

3

Longer lead Pros: Faster movement (mostly benefits homing) More standard Weak motor friendly Might be slightly more stable (sideways) than shorter leads because of more starts creating more contact with nut (?) Cons Backlash Less resolution (unless using 0.9 degree motor but see note1) although this is ignorable since it's still very high. It's already ...

3

Based on what I've learned over 8 months of printing: What matters the most is getting a very accurate zero relative to the bed surface. An offset of 30 or 40 microns can strongly affect first-layer adhesion. Now, unless you put in some of the advanced auto-levelling sensors, the repeatability of the Z-axis limit switch may outweigh the precision of the ...

2

I agree with Tom about looseness. I would suggest 2 solutions: Use grease which will reduce friction (and vibrations as a consequence); Use better clutch (coupling). Full aluminium couplings are prone to conduct noise (vibrations) from the threaded rod. You can use Oldham coupling with a plastic floating member. This will definitely reduce noise on Z axis....

2

I don't own the printer, but the intertubes identify it as a "TR8X8 T" (8mm diameter / 8mm offset per revolution).

2

Yes and No Let's start with the obvious: Flex couplings or rigid couplings are a deliberate choice in designing the printer. Each has its benefits and drawbacks. So let's look into the 4 types of drive-train setups that I know to be possible: Spiral couplings make it possible to operate the machine with a slightly misaligned motor to the shaft (<1°) but ...

2

The motor is mounted in a fixed position no matter if it's on top or bottom. You can imagine the lead screw as a rod hanging down and supporting the bed in the Z direction only, because all of the XY rigidity comes from the Liner rails the bed is attached to it works just as well if the stiff rod is under compression instead of hanging from the rod. Any ...

1

First of all, let's look at the geometry: We have a static XY and changing Z on our build plate. This mitigates several problems we might have faced in a different setup, mainly that our lead screw has loads changing from one face to the other: all loads always go into $-Z$, so the lower surface of the Trapezoidal threads in the brass nut of the bed carrier ...

1

Your lead screw nut advances 8 mm every complete rotation of 200 full steps, so a single full step would change the height by 8/200 = 0.04 mm. This implies you need to set the layer height a multiple of 0.04 mm. The gear ratio of 4:1 (a reduction) is required to get to your desired 0.01 mm layer height, but that is a very uncommon and a ...

1

I expect a T8 with 8 mm pitch to be cheaper (in large quantities) than a T8 with 2 mm pitch (which also exists). I think that if you have T8x8 you can use 4 milling heads (the screw has 4 starts) and therefore cut away the material faster. With a T8x2 mm you can use only a milling head at time. This is speculation, since my local supplier prices them the ...

1

This is a work in progress - I'm still plugging in the numbers A couple of issues: You appear to be mixing Force (effort) and Inertia and comparing them directly - this mistake seems to have come from the first link; You used 8 mm diameter, instead of 4 mm radius, to calculate the torque You haven't calculated the holding force, which would provide the ...

1

Update: To answer your question, you could use either metal ones or printed ones. Metal housings are way more heavy that printed parts. The housing you refer to is not attached to the platform, but a static part connected to the frame. Weight is not an issue, stiffnes, strength and temperature stability should be of higher importance. For metal housings ...

1

You can use the screws and rods you can find easily, of course some dimensions will change and is needed to adjust parameters. I used in my first 3D printer and standard screw of 9.5mm (3/8) the main problem was the coupling available in Mexico that werer none on that time. You can buy the bearings on Ali Express, they can send from there to Mexico, I ...

1

I do not agree with the answer of Tom. In a proper design, the nut is supposed NOT to be loose, especially in the Z-direction. All options of the nut to move can cause imprecise layer heights and Z-wobble. There is also the possibility to introduce Z-wobble by bent rods and good contact of the nut. However, Z-wobble is not what I want to address. Yes, to ...

Only top voted, non community-wiki answers of a minimum length are eligible