T8-8 or T8-2 which lead screw should I get?

Most prusa I3 style printers use T8-8 (8mm lead) leadscrews. Would 2mm lead lead screw be beter? It ishould give even higher resolution of the z movement and X gantry would be less likely to fall under gravity and vibrations when not powered.

Are there any disadvantages? Would z speed be painfully slow with 2mm lead lead screws?

I Have used dual Z-Axis T8-2 lead lead screws for a long time and have never had problems.

// Z Axis 3200, / 2mm pitch leadscrew = 200*16 /2 = 1600 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)

Truly hated the T8-8 led screws!!!!

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Computer Programmer / Electronics Technician

What sort of Z feed rate are you using?

I am worried that T8-2 will be really slow which will make things like bed probing take ages.

I have two Cheap chinese 3D Printers, the bed is even warped on one after printing at 100C for ABS.
After straitening the hot bed I continue printing many different sizes models without any problems.

The code below allows me to only level the bed surface when it is required because of being out of calibration, The last time was about a couple months ago/

#define RESTORE_LEVELING_AFTER_G28

I have never had any problem with the bed leveling taking a long time other than the fact that the bed is leveled with a 6X6 Grid.
The data you requested is located in the code block below.

/**
 * Default Axis Steps Per Unit (steps/mm)
 * Override with M92
 *                                      X, Y, Z, E0 [, E1[, E2...]]
 */
 // Typical stepper motors have 200 steps per full step/rev = 1.8°/step, so 1/16 microstepping = STEPS_PER_REVOLUTION_E = 3200 
// X-Y Axis 3200, / 20 tooth, / 2mm pitch = 200*16 / 20 / 2 = 80 :: (STEPS_PER_REVOLUTION_X / IDLER_TEETH_X / BELT_PITCH_X)
// Z Axis 3200, / 1.25mm pitch leadscrew = 200*16 /1.25 = 2560 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 3200, / 8mm pitch leadscrew = 200*16 /8 = 400 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 3200, / 4mm pitch leadscrew = 200*16 /4 = 800 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 3200, / 2mm pitch leadscrew = 200*16 /2 = 1600 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// E-Axia 3200, / (11mm Gear OD * pi) :: (STEPS_PER_REVOLUTION_E * EXTRUDER_GEAR_RATIO / (PINCH_WHEEL_DIAMETER * PI))
#define DEFAULT_AXIS_STEPS_PER_UNIT  { 80, 80, 1600, 94.4962144  }

/**
 *                                      X, Y, Z, E0 [, E1[, E2...]]
 */
#define DEFAULT_MAX_FEEDRATE          { 250, 250, 5, 25 }

//#define LIMITED_MAX_FR_EDITING        // Limit edit via M203 or LCD to DEFAULT_MAX_FEEDRATE * 2
#if ENABLED(LIMITED_MAX_FR_EDITING)
  #define MAX_FEEDRATE_EDIT_VALUES    { 600, 600, 10, 50 } // ...or, set your own edit limits
#endif

/**
 *                                      X, Y, Z, E0 [, E1[, E2...]]
 */
#define DEFAULT_MAX_ACCELERATION      { 3000, 3000, 100, 10000 }

//#define LIMITED_MAX_ACCEL_EDITING     // Limit edit via M201 or LCD to DEFAULT_MAX_ACCELERATION * 2
#if ENABLED(LIMITED_MAX_ACCEL_EDITING)
  #define MAX_ACCEL_EDIT_VALUES       { 6000, 6000, 200, 20000 } // ...or, set your own edit limits
#endif

/**
#define DEFAULT_ACCELERATION          3000    // X, Y, Z and E acceleration for printing moves
#define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration for retracts
#define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration for travel (non printing) moves

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Computer Programmer / Electronics Technician

Thanks

I think I will go for T8-2 then

This means you will have 1600 steps per revolution instead of 400 steps per revolution.

// Z Axis 3200, / 8mm pitch leadscrew = 200*16 /8 = 400 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)

// Z Axis 3200, / 2mm pitch leadscrew = 200*16 /2 = 1600 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)

It also means the Z-Axis stepper motors will have to work less to lift the Z-Axis load.

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Computer Programmer / Electronics Technician

They also make T8-1 lead screws

Quote
witor
Thanks

I think I will go for T8-2 then

It will give enough torque to straighten any crooked frame and overcome stubborn guides A must for most hobby 3D printer.

A good machine will prefer an 8mm pitch.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Why a good machine will prefer a 8mm pitch?

Quote
etfrench
They also make T8-1 lead screws

Did not know this good information for the forum.

Quote
MKSA

It will give enough torque to straighten any crooked frame and overcome stubborn guides A must for most hobby 3D printer.

A good machine will prefer an 8mm pitch.

When I have sticky lube on the Z-Axis smooth rods the T8-2 single start 2mm thread pitch Trapezoidal thread lead screws did not save my 3D Printer from missing any steps.


I had so many problems using 8mm pitch Trapezoidal thread lead screws that will never use them on a cartesian style 3D Printer dual Z-Axis stepper might try on X or Y axis though.

I have two 3D Printers both with the 8mm thread pitch lead screws, every time I had any vibrations close to either 3D Printer I would have to realign the Z-Axis again.
As the dual Z-Axis steppers on the Z-Axis would vibrate out of sync from one another causing me constant re-alignment of this axis.
The symptoms that it caused was prints would have one side the correct thickness the other side would be too thick or too thin.
The calibration that had to be made before most new prints was to align the right and left side to be level, or as I say to be in sync with each another.

This included the vibrations of my 3D Printer printing a new model sitting next to a 3D Printer that was powered off, the vibrations of the active 3D Printer would cause unused printers Z-Axis sync alignment issues. After changing out the T8-8 Trapezoidal thread lead screws with the single start 2mm thread pitch Trapezoidal thread lead screws this issue has never re-occurred since.

Do not get me wrong the T8-8 Trapezoidal thread lead screws would work perfectly on other 3D Printer designs, though was never proven to work on my cartesian style 3D Printer.

On my MPCNC Single stepper motor Z-Axis design either lead screws works, to raise and lower my heaviest router without any missed steps when correctly aligned...

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Computer Programmer / Electronics Technician

I had the same problem. I solved it by mechanically linking the 2 lead screws with a timing belt. This is of course not ideal as stepper motors should not really be linked like this. Well I gave it a try and it worked quite well.

i have replaced the main board now so I am able to run Marlin 2. with BLtouch so I will be able to perform auto z aliment if needed. 2mm pitch screws should make it needed less often

Quote
witor
Why a good machine will prefer a 8mm pitch?

I rephrase: If it works with a 8mm pitch, the machine doesn't bind and is therefore either well designed/built or has plenty of sloppiness, flexibility, play in the guides and bearings. In case of the latter, it will show with other issues.

1mm pitch is very common, one of the most common metric fine pitch. For ex; in small mill, and many similar equipment as it gives 1mm displacement for 1 dial turn .
Most common standard pitch for gun "silencers" too

BTW GT2 belt with the common 20t pulley is equivalent to a 40mm lead screw pitch !

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Just a little update.

I switched to T8-2 lead screws and I don't see any benefits so far. I don't see any improvement of the print quality. Surprisingly they are harder to spin than 8mm lead screws and often make annoying grinding noise while spinning. I did align them as well as possible. Another think that I kind of miss is the ability to move z axis by hand. It is still possible but it takes forever. with 8mm lead I was able to move both z sides to the bottom and with Auto bed leveling sides getting out of sync was not much of a problem.

I think i am going back to 8mm lead screws...

So ? Why did you expect to get an improvement by just changing the pitch ????

Furthermore, if it is harder to turn, that means you just worsen your machine built or these TR8 are either of poor quality and hard to turn or very good with minimal play and therefore bind due to poor alignment..

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I was hoping that smaller lead will result in smaller error in z movement caused by inaccuracies in a single motor step angle.

I mounted them the same way and following the same aliment procedure as for the longer lead.

Shorter lead nuts were not particularly tight on the screws, but tighter than longer lead nuts. I think the reason why they did not work particularly well for me is the number of starts.

I am thinking that 1 start might result in 1 point of contact on one side of the nut which might push the screw to the side and cause a bit of binding. With 4 starts nut is more evenly supported by the screws.

That's just my theory I am no expert on lead screws, but 8mm lead just works better for me.

Left - 2mm lead Right - 8mm lead. There is very little difference and I would say that right is tiny bit better (I know I still have a bit stringing going on)

8 or 2 mm pitch makes no differences in term of "accuracy" !
8mm pitch is just more suitable here. The resolution is plenty enough and still 5 times the X and Y.
When I read about micron resolution for this kind of machine built the way most are, I just smile ! A heavy glance bent them more than a few microns !

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I have learned my lesson an at least now I know that 8mm lead 4 starts lead screw is probably better for I3 style printer.

Just to discuss the accuracy error. I think it can be assumed that after the whole rotation motor will return to the starting position. With 1.8 degree stepper and 8mm lead it takes 200 steps to move z axis by 8mm. If inaccuracy of a single step is let's say 0.2 degrees then inaccuracy of a move corresponding to a single step is 0.0044

With 2 mm lead and the same stepper the inaccuracy of a move corresponding to a single step is 0.0011.

So, it would seem to me that 2 mm lead screws should allow higher accuracy, but the difference is just not significant for a 3d printer application.

Is my reasoning correct?

I think the model on the right looks better than the 2mm lead.

Yep... That's why I went back to 8mm lead screws

How much did that detour cost you?

Not too bad, about 7 pounds and some wasted time....

thats cheap(maybe thats the problem) I bought two or 3 for the mill, 400mm, 200 & 150, cant remember if it was 1mm lead or 2mm or how many starts, and the same for a shorter one...they cost more that equiv 4 start 8mm, but are sitting dormant, I think the 400mm was about 12 quid.

Are you using springy couplers, short motors, I suppose its hard to know the cause, I bought my leadscrews for less backlash & round numbers, rather than for speed, I wonder if the more steps you have, means more chance of missed steps, especially with speed or heat, and because of the tighter constraint it shows more of the errors?

Edited 1 time(s). Last edit at 05/27/2020 10:21AM by MechaBits.