Motor Coupler's

[LongRat]

Originally Posted by Al_The_Man One of the oldest and most efficient (zero backlash) is the Oldham coupling http://www.mechanisms101.com/oldham.shtml They start at about $8 in the Misumi catalogue. I have found that applications that use aluminum Helical with in any kind of medium/high torque servo, they usually end up fracturing due to metal fatigue, and end up putting on a Stainless version. Al.

--Agreed, I have been running oldham couplers on my mill since I converted it. I have thousands and thousands of hours on it, and still zero backlash. Definitely recommended. I run a solid coupler on my z, and that works too. It's a 1/2" shaft... can't see it snapping.

[hoss2006]

Originally Posted by HimyKabibble Hoss, Three years? That's just about how long mine lasted before the first motor shaft snapped. You may have just jinxed yourself! :-) Solid couplings will work, *if* everything is lined up really well. But that is hard to achieve (and even harder to prove you've achieved it), and the couplings I described are cheap and easy to make. Cheap insurance, if you ask me. Regards, Ray L.

3 years and no problems is all the proof I need, the original motors are still in use.
I built my conversion for myself but have had to add other options like the link to "flexible" couplers for all the folks that want something easier.
I'll add a couple new ones from the great tips posted here.
Hoss

[Arquibaldo]

I´ve beens thinking about this problem, and I find HimyKabibble's
recipe for a homemade coupler (post #4) is great - I´m going to
try it.

However, if you are really going to spend around 20 bucks for a coupler,
I always thought that I might opt for 2 pulleys+timing belt instead.
Don't you think this would be a better solution, and probably cheaper too?
With a timing belt you also have another great advantage: you
are free to choose a better position for the motors, avoiding "stiking"
motors, ending up with stiffer motor mounts and a more compact
machine.

Am I overlooking some disadvanges?

Nelson

[fretsman]

Does anyone know where to get these couplers?

I saw them on ebay but they seem awefully salty in price....

Thanks,
Dave

[HimyKabibble]

Originally Posted by Arquibaldo I´ve beens thinking about this problem, and I find HimyKabibble's recipe for a homemade coupler (post #4) is great - I´m going to try it. However, if you are really going to spend around 20 bucks for a coupler, I always thought that I might opt for 2 pulleys+timing belt instead. Don't you think this would be a better solution, and probably cheaper too? With a timing belt you also have another great advantage: you are free to choose a better position for the motors, avoiding "stiking" motors, ending up with stiffer motor mounts and a more compact machine. Am I overlooking some disadvanges? Nelson

Only cost, and potentially a small amount of backlash, depending on what type of belt you use, how well the pulleys fit, and how you mount and assemble it all. You'll have two pulleys, and a belt, which will cost a lot more than a coupling, especially a home-made one. Then there's the extra bracketry, and more complex machining, since it needs to eb adjustable to tension the belt properly.

Regards,
Ray L.

[Riceburner98]

Originally Posted by Al_The_Man Helical with in any kind of medium/high torque servo, they usually end up fracturing due to metal fatigue, and end up putting on a Stainless version. Al.

One of the guys at work here was building a high-speed turntable for product testing, he hit a particular RPM and the aluminum helical coupler he was using hit some resonant frequency and exploded into half-moon shaped shrapnel. Think it was a few thousand RPM, with a large plexiglass platter for the table. Replaced it with a stainless one and all was OK.
As far as "perfectly" aligning a motor with a direct coupling, as long as there's a little float in your motor mount holes, once you clamp down the coupler on the motor and 'screw shaft the motor is automatically aligned as well as it can be, then when you tighten the bolts on the motor it keeps it there. (assuming you don't let the motor "free hang" on the screw after you clamp the coupler down and before the mount bolts are tightened) I don't see any problems with it.. I use stainless flexible couplers only because they already came with my 'screws.. <- edit: this assumes, of course, that your motor mount surface is perfectly perpendicular / square to your screw. if not, then it's going to tweak the shaft of both of them as you tighten down the motor mount bolts...

[project5k]

ok, i've been using the lovejoys for lots of years in different projects, some are high rpm and some are high torque, and neither have given me any issues, or show any signs of wear.. and besides, even if you were able to wear out the spider... youd notice it long before it completely went away, and you can order new ones for cheap, in different materials even. i've tried, and on my cnc machine, i cant measure any backlash on my lovejoys...

further more, if your really that worried about them wearing out, once you have these in, you could allways use the machine to make more spiders, or whatever, but i doubt you'll ever really need them unless something goes very wrong, in which case, your couplers will be the last of your worries.

silly question, oldham coupler? is that like what we used to call a rag joint? like what used to be right above the steering box on cars before rack and pinion?

[Al_The_Man]

Originally Posted by project5k . silly question, oldham coupler? is that like what we used to call a rag joint? like what used to be right above the steering box on cars before rack and pinion?

Not really, the Rag joint was usually a disc of fibre impregnated rubber or similar, and each half of the coupling was bolted firmly to it each half 90deg to each other.
There were slight variations.
The link I showed has the Oldham principle.
BTW Lovejoy is a Manufacturer and of many various types, not just one.
Al.

[project5k]

ahh, ok didnt know about that one.. steam ships eh.. interesting..

rag joint, yea thats what i was thinking about...

lovejoy = Coke in my mind.. they make other flavors, but coke is a generic term used in the south for a carbonated drink, aka soda and pop for the folks up north... we wont go into what a viaduct is.

[SSfab]

wow, i was unaware of how cheap the love-joy's really are. I can do all 3 axis for under $20. I will take your word for it, that they are reliable. I just have a hard time paying $16 for a single coupler.

[project5k]

if i remember correctly, i ordered mine from mcmaster carr, and i didnt pay more than about 8-10 for mine, and so far, i cant find any backlash in them... i've had my machine for over a year now, and being new when i started, i crashed it a couple times, ran it into a hard stop, stuff like that, and even today, i cant find any slack in them..

infact i had my y axis motor off a few weeks back, and i still had a hard time when i put it back together to get the coupler all lined up(its such a tight fit between the 2 end parts and the spider)

i think you'll be very happy with them. I guess you could look at it like this is one of thoes rare times, when the cheaper solution works out just fine in the long run.

The only thing that i will say is that when your putting them on, and then mounting your motors, spend a little time getting the motor as lined up as you can, this can only serve to extend the life of all parts involved. (my mounts were slotted to allow for a little adjustment)