Helical Couplings

Can anyone who has done this conversion tell me what length coupling I need or the max OD there is room for? There seems to be different OD's and, of course, lengths available.
 
grepper said:
Can anyone who has done this conversion tell me what length coupling I need or the max OD there is room for? There seems to be different OD's and, of course, lengths available.
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Install your motors and make sure you have about 1/8" between the shaft ends. Measure the length from the ball screw shoulder to the face of your motor. This is the max possible coupling length. Realistically the coupling length will be somewhat shorter based on what is commercially available with the bore sizes you need. The max OD is determined by the clearance hole in your motor mount and any other obstructions on your machine. Now search for couplings that meet your criteria with the thought that the more shaft engagement the better. As someone else mentioned the clamp style couplings are better but it doesn't hurt to drill and tap for a set screw also. Hope this is clear and I didn't confuse you.

Tom S.
 
Thanks, got it. Very helpful, guys. Guess I'll have to wait to order couplings until after assembly. I was surprised to see even Amazon stocks a pretty good selection. Free delivery is good. Would have been nice if the Fusion folks had a wider selection of couplings so I could have just placed one order. Oh well...
 
grepper said:
Thanks, got it. Very helpful, guys. Guess I'll have to wait to order couplings until after assembly. I was surprised to see even Amazon stocks a pretty good selection. Free delivery is good. Would have been nice if the Fusion folks had a wider selection of couplings so I could have just placed one order. Oh well...
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You might also try eBay. Shipping time usually is a couple of weeks for items of this size and often free shipping is available.

Tom S.
 
With couplings, you pick your poison. They all have their pro's and con's - and if there was a product/design that was clear winner, the rest would have largely disappeared.
Beam, Oldham, Curved Jaw, and other designs are all used successfully in this hobby CNC market.
Here's a link to just one manufacture's treatise on the topic.

If you are purchasing a kit, then you need to have a dialogue with the kit supplier, rather than second guessing their design.
If you don't agree with their design, design and make a "kit" yourself.
The axial length of a coupling changes with the design of the coupling, and changing the type and size of the coupling will change the geometry of the mount - and not all couplings require an 1/8" gap between the shafts - many require a significantly larger gap!

Have you thought about the possibility of boring the couplings to the size you need??
 
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CNCFusion does not seem to be that conversational. I emailed them yesterday asking what model # coupling they were using and what current lead time looks like but have yet to get a response. They don't list a phone number.

I did think about boring out the coupling, but I'd rather just purchase the size I need if possible. For all I know the inside bore of the coupling has nice machining to enhance it's grip on the shaft. I haven't seen one so I don't know.

I'm just speculating since I have not seen the Fusion kit installed, but I would think that the distance between the motor shaft and the screw would be more or less fixed, determined by the length of the screw, motor shaft, and the thickness of the motor mount. I would guess that the screw position is pretty much fixed, and the only easy way to increase the motor shaft to screw distance would be to cut the motor shaft, or make a new mount, or add spacers, etc., or decrease the spacing by machining the mount. Hmm..., come to think about it, I hadn't thought that various motors may come with different length shafts.

As long as I meet the spacing requirements of the coupling, it fits the shafts and doesn't bind against anything I would think it would work. Aside from getting a zero backlash coupling, simply connecting the motor to the screw can't be that big of a deal, can it? (, said Mark, all the while realizing he might be laboring under a delusion).
 
Jim_Hbar said:
Here's a link to just one manufacture's treatise on the topic.
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Thanks for the link Jim, very informative. In fact I was looking for a summary of the basic different types.

My, my. Look at all the wonderful choices... High angular misalignment capability, Low reactionary loading; low inertia, Fail-safe design :cautious:, Four different types of urethane elastomers available (what more could I ask for?), Highest torsional stiffness! Oh boy! That sounds good. I want that! :faint:
 
grepper said:
I did think about boring out the coupling, but I'd rather just purchase the size I need if possible. For all I know the inside bore of the coupling has nice machining to enhance it's grip on the shaft. I haven't seen one so I don't know.
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A reamed or bored hole would be fine:)

grepper said:
Hmm..., come to think about it, I hadn't thought that various motors may come with different length shafts.
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The NEMA spec sets the shaft length (and the diameter), but some of the NEMA 23 motors have 5/16 shafts and others have 8mm. The actual NEMA spec is 5/16 for a NEMA 23. The lengths have all be pretty much the same. I have seen a number of stepper motors from Asia that have metric shafts.
 
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