I think you are getting the terms "pitch" and "lead" mixed up. It is the "lead" that is important in the calculation. As the picture I posted shows, the number of starts will not change the pitch, but will change the lead.

Bottom line is, your Z resolution is limited by this number. With the 2:1 ratio I have, I can use layer heights that are multiple of 0.02mm. Is that correct?

 

I have not found anything yet to decode the TR values. I have seen 4 start screws labeled as both TR8*2 and TR8*8. The important things to know is the pitch, starts, and lead. Lead is equal to PITCH * STARTS.

With my setup using 40T on the screws, there is not much room between the pulley and the frame. So to get a better gearing ratio, you would need a smaller pulley on the motor. I did find some 10T ones that would give you a 4:1 ratio, or 0.01mm/step. I'm thinking the 0.02mm would be good enough, at least for my work.

 

So, after some calculations based on "Prusa calculator" webpage:

- with a config of "1 Full Step" , 20T - 20T, Pitch 8mm -> I can have resolution of 0.04 (in the slicer I must put a layer height multiple of 0.04)
- with a config of "1 Full Step" , 40T - 20T, Pitch 8mm -> I can have resolution of 0.02 (in the slicer I must put a layer height multiple of 0.02)
- with a config of "1/4 Step" , 20T - 20T, Pitch 8mm -> I can have resolution of 0.04 / 4 from driver (in the slicer I must put a layer height multiple of 0.01)

but the last configuration is in microstepping mode, so in not the correct mode for positioning the Z axis.. and maybe better have the 1st or 2nd configuration using the correct layer multiplier in slicer software

Is that correct?

 

I believe so. At least I will be using the second case of 0.02mm when I get my printer finished.

 

See Keith's previous post. Microstepping on the Z axis doesn't matter (and is even preferable since it's smoother) as long as each layer still lands on a full step! So your calculations are important, but you still probably want to use 1/8 or 1/16 microstepping.

 

Yes, after read the previous post of Keith I think I'll use a 8mm pitch lead screw with 40T/20T pulleys to have 0.02mm/step on Z axis without microstepping.

So my possible configurations in slicer will be multiple of 0.02 as: 0.04mm/ 0.1mm / 0.2mm / 0.3mm and so on...

Or I'm considering to replace my trapezoidal lead screws with regular M8 lead screws with 1.25mm pitch and use 20T/16T for having 0.01mm/step as in the project (with full step)

Now it's CLEAR

 

Clear as mud? Right?

Just to cloud things up, microstepping is fine if used to move from one full step to the next. Just don't end the movement on a non-full step.

 

I had forgotten about the 0.9 degree motors (400 steps). Will have to think about that. But is 0.02mm layer height going to be that much better than 0.01mm? I hate all the extra time it takes to print a 0.1mm layer height version 0.2mm. Not sure I would ever want to do anything less than 0.1mm.

And I am using a Duet. Not sure how to change the microstepping on it. I'm pretty sure it can be done though.

 

I printed my own ACME Nylon nuts (well, PLA) for my lead screws. Seems the nylon nuts I ordered have gotten lost between somewhere over there and here. That is why I switched to the lead screws. If I ever get those nuts, I still have the parts to switch back to them.

 

I've recently discovered (the hard way) that some PLA formulations don't tap nearly as well as others. There was one (with a matte finish) that just turned into a gooey mess and the screws slid right through, whereas others seem to tap fine. I've had more consistent success tapping PLA using larger threads (eg. M5 vs M3). For smaller/finer threaded holes, I've become a big fan of heat-set threaded inserts which are usually made of brass. Installation is much faster than tapping, the only tool needed is a soldering iron, and they're pretty cheap (about $0.05 each). Plus they look nice and are stronger, especially after several assembly/disassembly cycles.

 

I used eSun PLA+ (sometimes called PLA Pro) and it was only for the two nuts on the screw for setting the 30mm length for mounting. Everything else in done in PETG.

 

A question about X and Y microstepping, what configuration should I use with a 20T pulley?

 

I think all of them are manufactured by Penn Engineering:

D.B. Roberts sells four varieties for 5-7 cents each with a minimum of $5 (roughly 100 pieces) per line item:

• D.B. Roberts Company | Search results : IUB-M3-1 (4.4 mm wide, 3.4 mm long)
• D.B. Roberts Company | Search results : IUB-M3-2 (4.4 mm wide, 5.6 mm long)
• D.B. Roberts Company | Search results : IUBB-M3-1 (5.6 mm wide, 3.8 mm long)
• D.B. Roberts Company | Search results : IUBB-M3-2 (5.6 mm wide, 6.4 mm long)

McMaster-Carr sells two varieties of them in packs of 100 for a bit more (12-15 cents each):

• McMaster-Carr (looks to be identical to IUBB-M3-1)
• McMaster-Carr (looks to be identical to IUBB-M3-2)

The IUB ones have slimmer profiles than the IUBB ones so they can fit in tighter spaces.

The docs recommend tapered holes, but they're not strictly necessary. A regular hole that's a press-fit for the very bottom rim of the insert works beautifully. If the hole is too small then melted plastic can obstruct the end of the insert, which is really annoying (if it's supposed to be a through-hole). This isn't an issue if the holes are the correct size though (not too small) and the bottom rim can be pushed in by hand.

 

For the Z Glide Bushings (the part the nylon rod goes into), you mention there being a taper to them. Is it just the bushing part with the taper or both the bushing and the Glide that is tapered? Mine is falling right through so something didn't print right. I am seeing about a 1mm difference between the top and bottom of the bushing.

 

The insides of the glide bodies are also tapered.

 

I was able to scale up the insert so they fit tight. I'll try re-orientating them as you describe and see what happens. Even with the tight fit, I am seeing some wobble on the X axis when changing directions and can see the glides rotating.

 

So you configure 1/16 microstepping for X and Y, but the question is: between 10micron and 12.5micron something would be visible in a printed part??

Thanks for your help Keith

 

Going to reprint the glides and inserts. I used the same layout you have in the STL file and it looks like this...



Is this what you were meaning? Note that these glides are for an ACME lead screw.

 

I used OpenSCAD to cut and paste the original part so there are no changes to the part other than the width in that area.