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Products => Robotics and Automation => Topic started by: NorthGuy on July 06, 2019, 03:42:52 am

Title: Micro stepper motors with lead screws and their thread
Post by: NorthGuy on July 06, 2019, 03:42:52 am
Have anyone ever bought micro stepper motors from eBay which have a lead screw instead of shaft, like that:

https://www.ebay.com/itm/10PCS-DC-3V-5V-6mm-2-Phase-4-Wire-Micro-Stepper-Motor-moving-Screw-block-Nut-DIY/122247053082 (https://www.ebay.com/itm/10PCS-DC-3V-5V-6mm-2-Phase-4-Wire-Micro-Stepper-Motor-moving-Screw-block-Nut-DIY/122247053082)

There are lots of them, some said to be Cannon, other brands are present.

The thread on the lead screw doesn't look standard. M1.7-0.25 as I can infer from pictures. The nearest standard mertric threads are M1.6-0.35, M1.7-0.35 - all too coarse. Doesn't seem to be US neither - too thick for 1/16, too thin for 5/64, also too fine. But such non-standard thread seems to be very common among these motors - they all come only with this thread. What kind of thread is this? Is it ever possible to buy nuts or taps for this thread anywhere?
Title: Re: Micro stepper motors with lead screws and their thread
Post by: Neomys Sapiens on July 06, 2019, 04:38:09 am
Is the thread trapezodial or more rounded? (Look up trapezodial thread if necessary)
If more rounded, the counterpart ('nut') might be formed by an arrangement of small bearing balls.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: NorthGuy on July 06, 2019, 04:51:56 am
Is the thread trapezodial or more rounded? (Look up trapezodial thread if necessary)
If more rounded, the counterpart ('nut') might be formed by an arrangement of small bearing balls.

It's impossible to see the thread shape on the pictures. I don't think bearing balls can be made that small anyway - with 0.25 mm pitch, the balls would have to be 0.1 mm in diameter.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: chris_leyson on July 06, 2019, 08:10:12 am
It could be a fine metric thread M1.6x0.2 or M1.8x0.2. I don't think M1.7 is standard.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: techman-001 on July 06, 2019, 08:47:59 am
Have anyone ever bought micro stepper motors from eBay which have a lead screw instead of shaft, like that:

https://www.ebay.com/itm/10PCS-DC-3V-5V-6mm-2-Phase-4-Wire-Micro-Stepper-Motor-moving-Screw-block-Nut-DIY/122247053082 (https://www.ebay.com/itm/10PCS-DC-3V-5V-6mm-2-Phase-4-Wire-Micro-Stepper-Motor-moving-Screw-block-Nut-DIY/122247053082)

There are lots of them, some said to be Cannon, other brands are present.

The thread on the lead screw doesn't look standard. M1.7-0.25 as I can infer from pictures. The nearest standard mertric threads are M1.6-0.35, M1.7-0.35 - all too coarse. Doesn't seem to be US neither - too thick for 1/16, too thin for 5/64, also too fine. But such non-standard thread seems to be very common among these motors - they all come only with this thread. What kind of thread is this? Is it ever possible to buy nuts or taps for this thread anywhere?

It looks to me to be a fine thread for very small precision movement inside a camera. It could well be a special thread for this type of task common in the camera industry.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: Fred27 on July 06, 2019, 09:36:40 am
As they come with a nylon nut already on the thread it would seem sensible to just use this. Why worry about replacing them unless you have to?
Title: Re: Micro stepper motors with lead screws and their thread
Post by: NorthGuy on July 06, 2019, 01:56:13 pm
It could be a fine metric thread M1.6x0.2 or M1.8x0.2. I don't think M1.7 is standard.

The pitch is close to 0.25 - it is easy to measure on the picture. 0.2 would be too fine. The diameter is around 1.65-ish

It looks to me to be a fine thread for very small precision movement inside a camera. It could well be a special thread for this type of task common in the camera industry.

I think that's what it is. If many of these motors come from Cannon, they're most likely used in cameras. I guess chances of finding a nut (let alone tap) are slim. It would be nice to figure out the name for this thread, so I could search for nuts or taps.

As they come with a nylon nut already on the thread it would seem sensible to just use this. Why worry about replacing them unless you have to?

This nylon nut has a weird shape and I don't think I will be able to use it.

Some of these are sold without nuts and hundreds of people buy them (according to eBay anyway). Apparently, these people are able to obtain nuts somewhere or cut the thread by themselves. I thought this was a well-known thing among robot makers.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: Domagoj T on July 07, 2019, 10:15:00 am
I have various similar steppers. I can check them tomorrow when I get to work, do some measuring and post some high resolution macro photos.
Off the top of my head, I'm not sure I have that exact model, though.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: Kjelt on July 07, 2019, 11:01:03 am
Yes it looks like a miniature "linear screw" application.
Where you normally would couple the tapped screwspindle to the shaft of the motor with a shaftcoupler they now tapped the shaft.
If you sacrifice one motor shaft and put it in a slowmoving drill you could use it to tap holes in your own POM/Delrin shape. You have to experiment with the pre-drill diameter if the hole but probably 1,5mm woukd be a good start.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: chris_leyson on July 07, 2019, 11:33:14 am
I've seen M1.6x0.25 and M1.8x0.25 in an ISO Metric screw table somewhere but I think 0.2mm is the prefered pitch for these sizes. So it could well be 0.25mm pitch. M3 is available in 0.25mm fine pitch and 0.20mm extrafine pitch, adjustment screws from THORlabs for example. 
Title: Re: Micro stepper motors with lead screws and their thread
Post by: Fred27 on July 07, 2019, 11:38:54 am
Normally I'd say that you could sacrifice one lead screw and turn it into a tap to make your own nylon nuts. This looks a bit small to be able to do that though.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: NorthGuy on July 07, 2019, 02:01:22 pm
Thank you all for the suggestions. Where I could find higher resolution pictures, the screws look more like lead screws rather than a regular screw thread. This would explain why the pitch is different.

I was going to make my own nuts as Kjelt has suggested, but then I found a variety which comes with a neat copper (brass?) nut:

https://www.ebay.ca/itm/5Pcs-DC-5V-2-Phase-4-Wire-6MM-Micro-Step-Motor-Mini-Slider-screw-stepper-motor/122149707478 (https://www.ebay.ca/itm/5Pcs-DC-5V-2-Phase-4-Wire-6MM-Micro-Step-Motor-Mini-Slider-screw-stepper-motor/122149707478)

This one also seems to have 0.25 pitch. Probably some sort of a standard for small lead screws.
Title: Re: Micro stepper motors with lead screws and their thread
Post by: Domagoj T on July 08, 2019, 08:18:19 am
Here are the photos of the steppers I have. I had to upload them to the google drive since they are bigger than max attachment size.
https://drive.google.com/drive/folders/1J1iY5celuFvZdCEQpH3wyoMX76FV0yZI?usp=sharing

I don't have the model you are asking about, but hopefully this is close enough for discussion.
The markings on the ruler are 1 mm apart, so we can count pixels to get a fairly accurate measurements:
For the bigger one I got 1,94 diameter and 0,238 mm pitch which sounds like imperial.

The smaller one is much smaller, so probably irrelevant for the discussion.
Hope this helps.