[Dale gribble]

Hi, I am now on my 4th design for a motor coupling, but I think this last coupling I've made is very simple to make and could be made with just a drill press. If using a drill press I would recommend printing out a cad drawing to dot punch for the drill holes. You will see from the uploaded photo's I've tapped four holes for button head cap screws but these could also be through holes using nuts and bolts. The material I used for the center band was a food preparation mat it's about 1mm thick. This coupling gives good stiffness ( this depends on the band material ) and a lot of angular and concentric misalignment.

Kind regards

Dale

[FandZ]

Haha Kudos to you. Nice job. Do you feel any backlash? I've seen that coupler design before but never thought of it as a diy job.

[Dale gribble]

Hi, back lash is zero, but maybe a little twisting action if there was very high cutting loads. I would guess no more than a Lovejoy type coupling using nylon spider.

I forgot to mention in my first post the heat was to make the plastic more pliable and is not to melt the plastic into shape, A candle would work just as well.

Dale

[skyburt]

Hi Dale ,Nice job I may try that. when you say you got flext at high loads what exactley did you mean. What material were you cutting, and what size tool??
Thanks for passing this information along.
Skyburt

[Al_The_Man]

It appears to resemble an early style automotive Rag coupler used on the steering box?
In fact using the later material now used on Rag couplers, may prove to be less flex prone?
Al.

[Dale gribble]

Hi, I haven't used the coupling when cutting yet, just trials moving my large gantry (50kg / 110pounds) I ran a repeatability prog and run 50 passes rapid moves @ 15000mm/m or 590in/m and repeated fine with no loses in position. I had two Lovejoy type coupling with nylon spider centers on previous to fitting my new band coupling, but they did not give enough run out play, as my lead screw end is running out .002"/.004" I could see this was putting a load on my lead screw and motor bearings. I've just tried twisting the coupling by hand so far and it does resist twisting action well, but this will all depend on the band material used. Due to its shape it allows large run out and angular movement.
I'll update this thread when I get my machine finished. Just the E/stop circuit and vacuum to sort out.

Regards Dale

[skyburt]

Hi Dale, I will have to try that !!! Repeatability looks good, so I cant see a problem in cutting.I work mainly with wood but would like to see how your idea works out. I'm from Sunderland originally been in Canada since 1970.......... how are you enjoying the snow?????

[Dale gribble]

Hi, Skyburt

The snow is nice, and if my router was finished I think I would be making Sledge's right now, but trying to finish my router when the garage is -7c is not much fun.

Regards

Dale

[Dale gribble]

Hi, just an update on the band coupling. After trials I did notice some unwanted twisting on the coupling when machining roughing cuts. I did think of doubling up using two sheets of material per coupling. But opted to make the new band coupling from solid 40mm nylon bar. After a few trails I found that a 2mm ( .08") wall thickness works best. See uploaded images. This design still gives good angle misalignment and some run-out, but resists twisting very well.

This was done in two ops, second op just had to turn the bar 90 degrees.

Kind regards

Dale

[metalworkz]

Hello Dale,
That is an interesting coupler idea and your results seem to show it is working well. Thanks for posting the idea and pictures, and please do some follow up feedback when you have time to see how it works over some time of acutal cutting.
Regards,

[RomanLini]

Radial twisting of the ends causes a diagonal flexion of the center "plate".

If you made the center plate much thicker, it would still allow the desired displacements but greatly reduce the unwanted radial flex.

So I would make the centre plate maybe 4 times thicker than the 2mm thick side walls.

[jjobezo]

If you are making it out of 40mm bar, why not make the whole thing one piece. Include the end connectors as part of the piece.

[Andre' B]

That is called a double loop coupling.
http://www.google.com/search?hl=en&q...&start=10&sa=N

[Dale gribble]

Hi,

Just an update on using my coupling for a few months, so far I'm very happy with them. no visible twisting motion. I don't see a need to change to design as these are working very nicely

RomanLini, you mention making the center thicker I don't thick it's necessary on wood routing machine's maybe on heavy mills.

jjobezo, good idea, it's just the grub screw to lock it onto the lead screw would be I weak area. But maybe it could be made out of aluminum but trials would be needed on the wall thickness to give enough movement.

Regards Dale

[RomanLini]

Good to hear they are working well!

[jjobezo]

Instead of using a grub screw, could you leave the ends square, cut a slot, and use compression?http://cnczone.com/forums/images/smilies/confused.gif