View Full Version : Shaft couplings??

06-25-2003, 06:46 AM

What kind of couplings did you use for the motor to the ballscrew?
I was going to use solid couplings I made out of brass but I heard somewhere that it was a no-no :(

I saw a dealer online that sells helical couplers, but at $27 a pop I know there has to be a cheaper solution. I thought about using vacuum hose that JK uses (on that other site ;) ) , but I just don't like that route, want something a little more professional looking.
Any ideas?

Almost forgot, here's the machine I currently building.

06-25-2003, 08:35 AM
helical couplers are the only way to go.

06-25-2003, 03:45 PM
I second that. There is a fine line that sometimes you can't cross. I

06-25-2003, 04:15 PM
I don't see too much wrong with a solid coupling if the alignment is perfect. In a face mount situation, this is usually not too hard to accomplish, if the mounting surface has been machined perpendicular to the screw. In such a case, then the motor can be mounted on the screw, supported only by the coupling, and then the motor screws can be tightened.

If you cannot guarantee the perpendicularity of the face, then use the helical coupling.

For driving an encoder, I'd always use the helical coupling because of the possiblity of damaging the delicate instrument bearings in it.

06-25-2003, 06:16 PM
I used solid couplings for the motor to screw, helical for the screw to encoder. The screw is not supposrted at the motor end, other than by the coupling.


06-25-2003, 09:42 PM
Hmm, I don't know if I could machine the motor mounts accurately enough to go with the solid couplings. I mean if I could get my mounts to within .006" would that be enough? :confused:
Somehow I doubt it. I'll probably go ahead and layout the cash and get the helical couplings.

Forgot to mention, I'll be building a wooden cnc router first for making some of the components of the aluminum one. Almost have it finished and I've got most of the materials for the aluminum one already. How's that for ambitious :D

Electronics I know really well and I'm also a cabinet/furniture maker so most of what I'm doing isn't too far out for me, but machining metal is something I've never done. Wish me luck

Thanks to all for the help and I ALWAYS appreciate comments or crits. We all have to learn somehow.

06-25-2003, 10:12 PM
These are pretty good, It,s what I am using 3 piece design


06-26-2003, 07:32 PM
If you can use 1/4 to 1/4 couplers, try http://www.meci.com and do a search for couplers. They have a 3 piece aluminum and rubber one there for a rather good price. I used 3 of these on my machine and they work pretty well.


06-27-2003, 01:29 AM
Any problem with backlash on couplings from MECI? Being as frugal (cheap) as I am that would be perfect.

I also like the three piece couplers with the spider insert.
Thanks guys for all the help.

06-27-2003, 01:26 PM
I bought a bunch of those and they work great.

06-27-2003, 01:33 PM
>Any problem with backlash on couplings from MECI?

As far as true backlash, there seems to be none. The picture on the website doesn't do the design justice. The rubber part of the shaft coupler is probably about a half inch long. Each aluminum collar extends nearly 1/4 each or so into the rubber sleeve. The part of the aluminum collar that extends into the sleeve has deep grooves that match deep grooves in the sleeve, so there is no slop.

I have not tried to measure if there is any 'twisting' of the rubber sleeve itself, but there appears to be virtually none.

Verdict: I think this coupler does a good job of directly translating the rotational forces of my 135oz/in steppers on to the rotating "leadscrew" -(in my case, 1/4-20 threaded rod)

Additional Note: At least one of the axes on my machine has less than perfect alignment between motor shaft and leadscrew. The coupler seems to do a good job of handling the mis-alignment.


06-27-2003, 02:18 PM
No way .006 perpendicularity is going to be close enough for solid coupling. You need in the neighborhood of .0006.


06-27-2003, 05:22 PM
Try McMaster-Carr P.N. 6208k14... it is a great solution at $27.58 ea. Can be configuree 3/8" in 5/8" out. All these others being suggested look more expensive and less capable.

Smaller ones are even less from MC. If ya haven't checked outhe MC online catalog, it's great.

Not nessarily the cheapest always ,but they always seem to have the part!!

07-01-2003, 01:43 AM
I just ordered a set of these http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=MEC-002

They are made of steel and appear to be more robust.

07-03-2003, 02:40 AM
I don't know if anyone else has tried this?

I am using universal socket joints (the kind you put on a ratchet) and I made solid couplers (clamping type) to fit on each side of the uni-joint. My motor mounts are 3/8" and the uni-joints are 1/2'' Dia. So I made two solid couplers. The first one is 3/8" on one side and 1/2" on the other side to accomodate the uni-joint. The second coupling is 1/2" on both sides. This accomodates the uni-joint on one side and the lead-screw on the other.

The uni-joint cost me $4.00 and I made the couplers out of scrap round stock in my shop.

I can post some pics if any one is intereasted.


07-03-2003, 02:51 AM
I'll be interested to see the pics of the setup as I'm still searching for low cost ideas for couplings. I'm still using solid coupling for my setup.

07-03-2003, 03:20 AM
I saw a picture somewhere, though I don't remember where, of a coupling like a solid one but he had made several saw cuts part way thru in different places. Seems kind of crude now that I think about it. Maybe to the point of getting hard and soft spots as it is rotated.:rolleyes:


07-03-2003, 10:29 AM
An interesting solution. Pics would be great.

I am backing off my solid couplings. Going to get some other couplings today. Even when acurately made, the setscrews induce some wobble/missalignment.


07-04-2003, 02:03 AM
Here is the coupling together with the two solid outside couplers and the uni-coupler between them


07-04-2003, 02:10 AM
Here is the coupling connected to the lead screw and the motor. The assembly is setting on top of my uncompleted cnc mill.


07-04-2003, 03:57 AM
Now that all the mechanical building in done on my machine,

I will offer you this,

I debated on the used o solid vs Flex...

I used Solid....


This is the way I set up my motors,

I made a mounting block for the motor,
4in X 4in the motor is mounted/ screwed down to the block then bolted to the Granty/ or X supports with Four - 1/4 in Bolts,

I made the 4 mounting holes over sized by about 3/16 that allows me to move the mover up down ect...(If needed you could make the holes bigger.. but there was no need on my Y axis I almost need no adjustment... ( I just cut out the support peaces together to make mirror Images)

My machine is made of MDF, I did have the lead Screw turned down to fix the coupling 1/4 ID.

I used the same method for the support bearing on the other end, of the all thread.

Worked out good they move very smooth... just feels like you are threading a nut on them...( even with the weigh of the z axis and the Gantry )

Luis ( good luck)

07-04-2003, 05:32 AM
Wow, I didn't realise there were so many options available. I like the universal joint idea, but I'm limited to a few woodworking tools and I know that would be beyond my capabilities.

I bought ballscrews and linear bearings on eekbay for my machine and I used Rhino to model the machine I'm building down to the finest dimensions. I got a sample helical coupler from Helical Products and will probably go ahead and order two more from them.

I have another newbie question to pose for all the experts out there:D

My X axis ballscrew is 10" too long and it will need to be turned down to 3/8? I caled a local machine shop and they weren't interested enough to even give me a ballpark figure as to what it would cost to cut and turn it. All the info I got from them was that it was air hardening:confused: and would take extra work to do a good job of it. Being in a small podunk town this doesn't leave many options:mad:

Now I had an idea, and I know it's way out there , I can see the machinist out there cringe:eek:

What are my chances of mounting this ballscrew in a fixture whereby I could turn it with a motor and take a right angle grinder to it and turn it down a little at a time? Do you think the shaft will still be concentric when I'm through? Is this crazy or what :p
Hints? Suggestions? Straightjacket?

Like I said before, I'm a woodworker with alot of woodworking tools and that's as close to metal working as I ever got. What does it usually cost to turn a ballscrew down? I know there are alot of variables involved, just interested in a ballpark figure.

Thanks all for the replies

Lanny in Podunk

07-04-2003, 12:48 PM
What I would do is cut off the screw with a cutoff saw, you might get a usable piece of ballscrew for another project.

Make sure the ballnut doesn't come off the screw, as it is very inconvenient to measure each ball and reload the nut ;)

Weld an oversize stub on the end, using C1045 shafting (ordinary medium carbon steel). Then, machine the stub straight in line with the rest of the shaft. Of course, I'm a professional with a shop full of tools, so this wouldn't be hard to do.

07-04-2003, 01:26 PM
I would think a machine shop could turn the end down for you with a carbide tool or maybe ceramic. I would hope it would not cost more than $20.00.


07-04-2003, 02:11 PM
The easiest approach is to anneal the end of the screw so that it can be easily machined. As for keeping the nut from falling off the screw, use a shaft collar of the appropriate size (www.reidtool.com page330 of their paper catalogue). This will let you remove the nut if you have to, and is far less expensive than welding and turning..

07-04-2003, 03:09 PM
If the screw is an air-hardening grade, it will be very difficult to anneal.

The extreme length and small diameter required forbids accurately turning the shaft in the hardened condition.

The salvaged end could be worth something, too. 10" of thread is enough for another Z axis drive, if the same weld-on-stub technique is used. It depends on what the screw cost initially. I did this exact sequence (cut, weld stub and turn) for a retrofit I did, but the screw and two ballnuts cost $1200.00 so it was worthwhile.

07-04-2003, 04:18 PM
Take a file and try to file a little off the edge of a screw. If you can file it, it won't be a big deal to turn the end down. if the file just rubs....


07-04-2003, 05:12 PM

I agree with balsaman you should be able to turn it down with a carbide tip.

If you were in california I would turn it for you.

Have you thought about couplers with different diameters on each end. It would be easy to make such a coupler that is what I did above on one of the solid couplers.

07-04-2003, 07:27 PM
Hu, you’re right about the accuracy problem in turning the screws in the hardened state. Mine are a little wobbly, since that’s what I did. Although, once you get through the hard skin, the core is easy to machine with a sharp carbide cutter. I hope the flexible couplers I ordered will take care of the wobbles.

07-05-2003, 12:23 PM
Solid coupling ! Not a good idea, if youre machine crashes theres more chance of bendind something.
Also alignment maybe perfect but when under cutter load that will not be so.
Three peice spider couplers can have quite an amount of backlash,helical couplers would probably be great on this light machine other wise i would go for toothed pulley wheels.

07-09-2003, 08:49 PM
Follow-up on these couplers http://www.herbach.com/Merchant2/me...ct_Code=MEC-002
Just received them. The couplers are aluminum, not steel, and have 6mm holes, not 1/4" holes. The customer service of this company may be a topic for a future post.

07-09-2003, 10:39 PM
Ouch. Those details would make a difference! Aluminum would be OK but the 6mm thing could be a problem. How are they for backlash? Can you drill them to 1/4"?


07-09-2003, 10:51 PM

They appear to be back-lash free and I can ream the hole in my lathe, but I ordered these particular couplers because they were descrebed as "steel".
Interested in some new aluminum couplers?


07-10-2003, 01:01 AM
What's the O.D. size? Can they be bored out to .375? How much? Where are you in Ontario?



07-10-2003, 06:53 AM
OD is 15.63mm. Boring them to 3/8" would no leave enough meat for the set screw thread. I can ream them to 1/4". Price is CAN $28.00 indluding shipping.
I'm in Toronto.

07-10-2003, 08:29 AM
I can't use them. Hang tight, I am sure someone here can.....Can you send em back to Herbach?