Flexible Coupler wont go on

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Auarhau
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Flexible Coupler wont go on

Post by Auarhau » Mon Mar 24, 2014 8:06 pm

It's too tight to fit my nema 17 shaft it seems. How tight is this supposed to be? I'm afraid to force it harder..
ShapeOko 2. Nema 17 74 oz·in. GAUPS shield on Arduino Uno. DRV8825 Drivers x4 . Kress 1050 FME-1. Z Acme Screw. Threaded inserts table.

WillAdams
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Re: Flexible Coupler wont go on

Post by WillAdams » Mon Mar 24, 2014 8:10 pm

Did you loosen all of the set/grub screws? You might want to completely remove them.

It's a solid chunk of aluminum --- I don't think you're likely to damage it --- just be careful of the motor.

One other thing to try would be to put the coupler into boiling water (dry it carefully) and hold the motor shaft against a piece of ice (w/o letting the motor mechanism get wet, or condensation run down the shaft).
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edwardrford
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Re: Flexible Coupler wont go on

Post by edwardrford » Mon Mar 24, 2014 8:11 pm

Sorry you're having this problem. here are a couple of possible solutions:

1.) make sure the screws are all the way loose on your coupler
2.) Start from a slight angle and try to rock the coupler onto the motor shaft
3.) make sure there are no burrs on the inside of the coupler
4.) With some finesse, use a straight blade screwdriver to slightly open up the coupler end

-Edward
Shapeoko 1 #0 - a couple of upgrades.
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Auarhau
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Re: Flexible Coupler wont go on

Post by Auarhau » Mon Mar 24, 2014 8:28 pm

Yeah I did remove all the screws. I measured the shaft and the coupler now (4,99mm shaft diameter and 4,89mm coupler diameter). It's 0.1mm off. I tried to pry it open at the end with a screw driver, and pressed and rocked it on as hard as I dare. I can see the motor shaft has widened the coupler at the opening. Seems like I almost got it in 0.5mm and the result is tiny thin aluminium rings were shaven off the inside of the coupler.

I am tempted to try to drill it larger, or turn some sandpaper down there.. Bad idea?

How far am I supposed to press the coupler down on the shaft by the way? Docs only say to put it on.
ShapeOko 2. Nema 17 74 oz·in. GAUPS shield on Arduino Uno. DRV8825 Drivers x4 . Kress 1050 FME-1. Z Acme Screw. Threaded inserts table.

RobCee
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Re: Flexible Coupler wont go on

Post by RobCee » Mon Mar 24, 2014 8:32 pm

If you can get access to one, a reamer would be better (more accurate) than a drill. But maybe you could gently twist a drill in it by hand?


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WillAdams
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Re: Flexible Coupler wont go on

Post by WillAdams » Mon Mar 24, 2014 8:36 pm

Compare it to the lengths of the M3 stand-offs.

The length of motor shaft inserted should be:

- enough for the coupler to grip firmly
- less than half the length of the coupler

A drill would be my inclination as well --- I believe the whole assembly is flexible enough that it'll ``just work'' once you're done, but agree w/ RobCee that doing it carefully and slowly by hand would be best.

Before you do so --- have you checked to see if the M8 rod fits as well?
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
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edwardrford
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Re: Flexible Coupler wont go on

Post by edwardrford » Mon Mar 24, 2014 8:39 pm

The other thing you could do is run an M5 screw through it. I'm thinking the threads might knock off/down any burrs that could be preventing the motor shaft from sliding in. It would be akin to a small file :-)

-Edward
Shapeoko 1 #0 - a couple of upgrades.
Shapeoko 2 #0 - a couple of upgrades.
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Auarhau
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Re: Flexible Coupler wont go on

Post by Auarhau » Mon Mar 24, 2014 8:40 pm

Yeah the 8mm rod threaded in as far as the 5mm neck on the opposite end, so that's good:) I haven't got a reamer, but I will try to improvise then
ShapeOko 2. Nema 17 74 oz·in. GAUPS shield on Arduino Uno. DRV8825 Drivers x4 . Kress 1050 FME-1. Z Acme Screw. Threaded inserts table.

Auarhau
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Re: Flexible Coupler wont go on

Post by Auarhau » Mon Mar 24, 2014 9:10 pm

Got it on now!

What did the trick was a combination of the suggestions here and some MacGyver'ing 8-)

I roughed up the back end of a old 5mm drill bit with some coarse sandpaper and made my own ultra ghetto "reamer". With a flat screwdriver inserted in the slot on the end of the coupler, and gripping my ghetto reamer with some mole grips I was able to turn it back and forth until I got through. It worked kind of like a very round very fine file. And I could use more force with the stepper motor out of the equation.I just hope it's still straight enough. I don't think I will have problems with the coupler slipping on me though:p

Thanks for all the helpful suggestions!
ShapeOko 2. Nema 17 74 oz·in. GAUPS shield on Arduino Uno. DRV8825 Drivers x4 . Kress 1050 FME-1. Z Acme Screw. Threaded inserts table.

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