Making a slotted flexible shaft coupler

Having received some sub-standard shaft couplers for a CNC conversion I'm now thinking about making some rather than waiting another 4 weeks for replacements.
Is there any particular advantage to the fully spiral (like a spring) kind over the easier to make alternating slot type? It would appear that the spiral kind are usually made from aluminium and the slotted kind is usually used with harder material such as stainless etc. I don't know why this should be the case.
At the moment I only have a (manual) rotary table, a vertical mill with a single motorised X axis (Y and Z need the couplers) and a Dremel cutting disk which can do deep cuts into bronze.
Mike.
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The helical aluminum couplers cannot transmit as much force as an Oldham(alternating slot) coupling. The Oldham coupling will have a tiny amount of backlash, the helical coupling will not. The helical coupling allows for angular as well as off axis error whereas the Oldham coupling only allows for a tiny amount of angular error. The Oldham coupling allows more off axis error though. All that said, I like Oldham type couplings. Eric
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wrote:

I do not think Mike is talking about an Oldham coupling which is made from three separate pieces (and in some case is combined with a flexible coupling). I think he is talking about a single-piece flexible coupling with multiple slit cuts instead of a single or double helical cut.
The specs of the two types are generally very similar, but of course depend on the design details. Both types are made in aluminum or steel or even plastic, but the split type concentrates the strain on a smaller cross section of material, so steel may be needed to get the same misalignment range as an aluminum helical coupler. There are various designs of slit types where the multiple slits are not just at right angles to create larger sections that bend to spread out the strain. Another difference is that helical couplings have a bit more rotational springiness which often is a good thing for absorbing shock. It is not quite as good if you want to decellerate something nearly instantly with no overshoot and springback (but that kind of motion would probably put excessive strain on other parts anyway).
There are a whole bunch of places that stock and sell couplings. Mike, have you tried searching other vendors?
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wrote:

Sorry, I forgot to mention one more very imprtant thing. The helical couplings allow for much more axial movment which may be need as the shaft and motor heat up.
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wrote:

Yes, I was thinking of a one piece like this
http://source.theengineer.co.uk/pictures/633xAny/8/3/8/2013838_ABSSAC-Plastic-shaft-couplings.jpg
The slots are perpendicular to the axis and end at the mid point.
There are various slot patterns, some almost meet in the middle, others are offset along the axis so there is no chance of accidentally cutting through the entire work piece.
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http://source.theengineer.co.uk/pictures/633xAny/8/3/8/2013838_ABSSAC-Plastic-shaft-couplings.jpg

The type with offset slits can be made to accomodate more axial movement if the slits go past the center, but then the torsional stiffness is not quite as high.
If you can not find one with the correct shaft diameter, maybe order the next smaller size and drill it out.
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wrote:

I decided to make one, and all went well until I tested the flexibility. The bronze I was using just wasn't springy enough. It deformed, quickly fatigued then broke.
http://25.media.tumblr.com/54d11bed58a68d71c4881dfcb2c7ba39/tumblr_mg7361zOX61rnlkmeo1_500.jpg
As you said, all the bending stress is concentrated in a small rectangular zone where the slots overlap.
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http://25.media.tumblr.com/54d11bed58a68d71c4881dfcb2c7ba39/tumblr_mg7361zOX61rnlkmeo1_500.jpg

The slots also have to be thin enough, or the outer diameter large enough, that the joints can not bend close to the point of fatigue.
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what are the dimensions of your shaft sizes. I have some couplers and can suggest alternative sources for others.
Call these people up Monday morning, with your shaft sizes..and they will likely ship the same day.
http://www.rocomcorp.com/
http://www.rocomcorp.com/products.aspx
Good people and they take care of the customer
Gunner
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4.5mm to 6.35mm (1\4"). 4.5mm is a non standard size with 4mm being the closest I can find. (I'm in Australia)
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Ouch. Well, they do custom sizes.
Gunner
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wrote:

=====In order to minimize fabrication time would it be possible to use an actual heavy [relatively] compression spring [section] with adapters/spring clamps on the ends, possibly even epoxying the spring into the adapter? You can probably buy much better spring material as actual springs rather than as bar stock. If you have space, I can see a larger spring with internal adapters in each end possibly retained/clamped at several places by small button head set screws.
--
Unka' George

"Gold is the money of kings,
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On Sat, 05 Jan 2013 15:53:20 -0600, F. George McDuffee

No..a spring will get longer or shorter as it loads and unloads...and it does that by winding up or down. In fact..a spring is probably the worst thing one could use
Gunner
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