Author Topic: Cheap focus axis, maybe  (Read 2442 times)

Stonemull

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Cheap focus axis, maybe
« on: June 08, 2017, 04:28:04 AM »
Just noticed a few cheaper possibiltys on banggood.

This one looks the best option ..

https://www.banggood.com/DC-4-9V-Drive-Stepper-Motor-Screw-With-Nut-Slider-2-Phase-4-Wire-p-964613.html

I can't see an advantage of this one over the first, but you never know..

https://www.banggood.com/Drive-Stepper-Motor-Screw-With-Nut-Slider-Small-Stage-2-Phase-4-Wire-p-956344.html

The ultimate in cheap, this one might need a lever advantage.

 https://www.banggood.com/DC-5V-2-Phase-4-Wire-Micro-Step-Motor-Mini-Slider-Screw-Stepper-Motor-p-997700.html
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Niezam

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Re: Cheap focus axis, maybe
« Reply #1 on: June 08, 2017, 07:54:34 AM »
Actually I already have 1 (your 2nd link) few months ago but not test it yet since i dont have 5v stepper driver.
It look like too small to mount spindle with 775 motor, maybe 550 saiz or smaller can.
For mounting laser module (to make motorized focusing), I think this little thing will make it. I should try it, but my question, how to wire it to standard 12v driver board, for example 3axis mana board.

ggallant571

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Re: Cheap focus axis, maybe
« Reply #2 on: June 08, 2017, 11:13:13 AM »
Please don't take this as a negative or criticism, but you/we need to find a way to maintain a perfectly vertical orientation. Any slop will cause the laser beam to strike the work piece at an angle. Then it spends (requires) energy to burn the wall surface and creates a wider cut path. I have not found a method to test for vertical orientation other than cutting a square and examining the edges.
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Stonemull

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Re: Cheap focus axis, maybe
« Reply #3 on: June 08, 2017, 11:40:10 AM »
Actually I already have 1 (your 2nd link) few months ago but not test it yet since i dont have 5v stepper driver.
It look like too small to mount spindle with 775 motor, maybe 550 saiz or smaller can.
For mounting laser module (to make motorized focusing), I think this little thing will make it. I should try it, but my question, how to wire it to standard 12v driver board, for example 3axis mana board.

Plug it into the stepper driver the same as a Nema, they say 5v, 500mA, which indicates the resistance is 10 ohms or so, this is normal range for a large stepper as well, all you need to do is turn down the reference voltage to around 0.35V or so (0.5V / root(2)) then for the first 10 minutes of use, see if it is getting hot at all. On 12V if the pot is turned up too much, this would be 1.2A .. this will cook the motor but the driver can handle that current ( though it would need a heatsink).
So it will get warm at 0.35v as that is max current, so you just keep on dropping till it does the job without overheating.
Safer option is too start low and turn it up till it does the job.

 I have some large stepper motors here that are rated at 3.5v and can easily destroy a pololu .. I use them at 24V no problems without anything getting warm.
The voltage is what they can cope with as constant DC, we never use constant DC if the current is being regulated, the pololu is turning the current on and off to maintain a lower current.

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Stonemull

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Re: Cheap focus axis, maybe
« Reply #4 on: June 08, 2017, 11:56:52 AM »
Please don't take this as a negative or criticism, but you/we need to find a way to maintain a perfectly vertical orientation. Any slop will cause the laser beam to strike the work piece at an angle. Then it spends (requires) energy to burn the wall surface and creates a wider cut path. I have not found a method to test for vertical orientation other than cutting a square and examining the edges.

No thats good info.
They probably are quite slop free so long as there is some tension, I mean the entire machine has to put the laser back over the same spot as well, it manages to do a reasonable job of it though.
Interesting problem that vertical alignment. I wonder if there is an optical solution, some little mirrors or prisms mounted to the frame off to one corner that can be used as an alignment tool.

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mrehmus

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Re: Cheap focus axis, maybe
« Reply #5 on: June 08, 2017, 12:23:47 PM »
I think the solution is to actually change the focus of the lens (when you have one that will adjust). I have the little stepper motors, the gears and everything but time. I think I'll set it up to run off a separate Arduino for the time being. The steppers are so small they probably could be run directly from the Arduino although I will use a shield to drive them. Later, a focus signal in the G-Code can be inserted to adjust the lens.

I have several of those small slider/stepper combos and they are not mechanically stout enough to handle the bulk of the laser.
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ggallant571

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Re: Cheap focus axis, maybe
« Reply #6 on: June 08, 2017, 01:18:12 PM »
My experiments with setting the Z and manually focusing the laser ruled out that technique very quickly. The focus dot rotates in a circle with a 2mm radius. Could be my lens or the threads.
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Stonemull

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Re: Cheap focus axis, maybe
« Reply #7 on: June 08, 2017, 08:39:01 PM »
Mine does that too, also does not have any O-rings in the grooves, U dan rock the lens side to side when focused close.
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mrehmus

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Re: Cheap focus axis, maybe
« Reply #8 on: June 08, 2017, 09:54:22 PM »
I was planning to make a new focus mount since I've purchased some aftermarket lens for the laser. If the axis of the laser and/of lens is off-center, I think it will move the spot.
Otherwise, I will print a carbon fiber Z-axis setup I think to keep the setup light and I will also try to balance it on the carriage rather than cantilevering it off one side.
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kibodwin

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Re: Cheap focus axis, maybe
« Reply #9 on: June 09, 2017, 03:04:49 AM »
the small DC 4-9V Drive Stepper Motor Screw With Nut Slider 2 Phase 4 Wire things like in your picture can be found in diskette drives and I think in cd /dvd drives... I have seen some longer travel ones online though.
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Stonemull

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Re: Cheap focus axis, maybe
« Reply #10 on: June 09, 2017, 06:07:37 AM »
the small DC 4-9V Drive Stepper Motor Screw With Nut Slider 2 Phase 4 Wire things like in your picture can be found in diskette drives and I think in cd /dvd drives... I have seen some longer travel ones online though.

Bingo !
I knew I had seen them before but could not think where, I know they aren't from CD/DVDs ..  they are from 3.5" floppy drives.
Maybe someone still has 5 1/4 ones ?
I think the 8" ones are sold out by now :)



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ggallant571

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Re: Cheap focus axis, maybe
« Reply #11 on: June 09, 2017, 09:06:48 AM »
Nuts!! I threw out 3-.5 about 5 years ago, the 5.25 about 15 years ago, and the 8 inch about 25 years ago.
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kibodwin

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Re: Cheap focus axis, maybe
« Reply #12 on: June 25, 2017, 10:48:02 AM »
you can find 3.5" diskette drives on ebay for less then 10 / euros/ $....
=)
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Stonemull

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Re: Cheap focus axis, maybe
« Reply #13 on: June 29, 2017, 07:50:08 AM »
My el cheapo maybe focus changing doohickey stepper arrived yesterday with cable chain, nearly threw out the envelope with it in it, only a double check before rubbish bin saved it.

I knew it was small but damn..
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kibodwin

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Re: Cheap focus axis, maybe
« Reply #14 on: July 31, 2017, 05:41:03 AM »
hey stonemull,
I have been tidying up my parts bin and have a few cd rom drives to recycle. Do you want me to take out these little motors for you? I dont mind sending them on to you.
K.
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