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driftspin
25-11-2017, 08:10 PM
Hi guys,

I would like an opinion on Z ballscrew 1605 1:1 vs 1610 with 1:2 reduction.

I cant decide.

Will a Z axis 1610 run down under its own weight when not under power?

Setup:

Fixed float.
Pully/belt
length 350mm





A few other questions.

Do i need more resolution then 0.025 mm on Z per full step?

Do i need to aim for 0.01 mm per step for some reason i dont know yet?


What is to be expected from a stepper in lets say 4 microstep setup... can a stepper hold position and or will it return to for example 1/4 step position after it is pushed out of position a little.. lets say 1/8 step.... Looks like it would but this is just my gut feeling.

I think i am comfortable with 0.025mm full step resolution.
(1610 reduced 1:2 stepper 1.8 degree)
but unsure if micro stepping adds anything useful for resolution.

I know resolution is not the same as repeatability.


I have been looking around for these info's but did not find a satisfactory answer to this.


Grtz Bert.







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MartinS
28-11-2017, 01:51 PM
I was interested and waiting for replies to this question............surprised there are no comments yet:upset:

Neale
28-11-2017, 02:05 PM
Not a lot of theory here, but this works for me...

I use 1605, 1-1 belt drive from stepper. Z feed rate is generally lower than X and Y, so you do not need 10mm lead ballscrews. I have never had any problems with downward creep of Z, even with power off, and that's with a big chunk (500x200x20) of tooling plate for the spindle platform and a 2.2KW spindle. I use 8x microstepping. This is not so much for resolution (I have a theoretical 0.003mm step increment) but for motor smoothness. Something around 8x seems like a good compromise between smooth running (fewer microsteps runs more roughly) and loss of torque (with too fine microstepping). However, testing with my touchplate, I have seen +-1 microstep (i.e. +-0.0003mm) repeatability. I doubt if the machine is that accurate when cutting, but even with intricate 3D machining, I have not seen any problems.

Nr1madman
28-11-2017, 04:51 PM
I was also interested ;)

I got 1610 delivered from China but ordered 1605.. solved this with pulleys 2:1 ratio.
My z axis plate is 300x160x15 in steel and 2.2kw spindle.
Just got a belt mounted on the pulleys and the motor supports it from dropping without power.

How it's working under power remains to be seen :D

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driftspin
28-11-2017, 11:26 PM
Not a lot of theory here, but this works for me...

I use 1605, 1-1 belt drive from stepper. Z feed rate is generally lower than X and Y, so you do not need 10mm lead ballscrews. I have never had any problems with downward creep of Z, even with power off, and that's with a big chunk (500x200x20) of tooling plate for the spindle platform and a 2.2KW spindle. I use 8x microstepping. This is not so much for resolution (I have a theoretical 0.003mm step increment) but for motor smoothness. Something around 8x seems like a good compromise between smooth running (fewer microsteps runs more roughly) and loss of torque (with too fine microstepping). However, testing with my touchplate, I have seen +-1 microstep (i.e. +-0.0003mm) repeatability. I doubt if the machine is that accurate when cutting, but even with intricate 3D machining, I have not seen any problems.Ok this answers the question... i will change my bomlist..
1605 for z 1:1 pullys.

I have zero hands on experience so...

Grtz Bert.

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komatias
29-11-2017, 07:32 AM
For a Z I would belt drive and reduce to 2:1. As Z motions are not always as long as the X and Y you can live with a slower speed.

The 2:1 will also ensure you do not drop as easily when the motors are off. It may not be a concern of course if you are using bog standard screws.

(I know on my little CNC conversion kits, because I am using ground screws, you can easily backdrive them. Then again the head weighs around 30kg there)

Neale
29-11-2017, 07:54 AM
I reckon that my moving Z components weigh around 15kg and that seems OK with 1605 and 1-1 pulleys. However, one of the great things about belt drive is that you can always change ratios if you need to without too much work.

routercnc
29-11-2017, 10:13 AM
My Z is also 1:1 with pulleys on 1605 and works fine

driftspin
29-11-2017, 07:51 PM
Ok guys thanx for the infos... i send a final rfq to Fred...

Maybe i will have parts before new year.

Grtz. Bert.


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