Shopsmith Forums

A while back my power coupler died on me and while waiting for a new one I got bored and got my digital calipers out and drew the required dimensions into a CAD program to make a model. I did this with the intention that I could design a better one.
When I had mentioned that my coupler broke on the site a couple of people mentioned alignment issues... I felt that you really shouldn't need to have your machines and motor perfectly aligned.

Anyway I designed a part that looks like a socket from a socket set but the 'socket' part goes on to where the coupler normally slips onto. I sent it to Shapeways to get it printed and they fitted perfectly and is working beautifully so far... more testing to come tomorrow.






This will work at an angle up to at least 20 degrees I would think .. I realise that the whole idea of having it plastic is so that it will break if there's some serious obstruction problem with the machine so you can put any square piece of wood in between and that is what will break instead of the actual coupler parts. I put mdf in there to test this theory and shure enough it broke nearly straight away.. swopped a piece of pine in instead and ran a couple of things through the bandsaw and no problems. As a 3d printed prototype it works out kinda expensive but it was fun to design something to very fine detail like that and have it arrive in the post .. first time I got something 3d printed!
Interested to know what ye think...

What little I understand about 3D printing is that you can specify different materials and strength requirements, do you feel that your design is strong enough for use with other SPTs? I am also wondering what was the cost to get 1 printed?

I love the ingenuity shown here BUT I'll just wait for new couplers! I would not want to rely on these universals at the rotational speeds involved in this application.

Well you're right you can specify materials and strength.. I could have them printed from stainless steel but the cost is way up there for that. 3d printing is primarily used for prototyping something that will be produced in greater quantities later on. The cost was 20 dollars for each one including postage to Canada which is quite cheap for testing a design but is obviously more expensive than buying the shopsmith official coupler.

As to whether I trust it's strength... honestly I should have made it slightly beefier. Maybe made the walls another 1 mm thicker but I still think the pine will break a long time before the plastic will.... I have absolutely no data to back that up though and the wall thickness is still more than the SS coupler. Like I said I will test it with something like the jointer that will put more pressure on it and over the next month or so I should be able to say with confidence it's unlikely to break or confirm that I should make the walls thicker on the next prototype evolution!
Thanks for the comments

I think it is an awesome idea and prototype. It completely removes the problem I always ave of getting the SPT perfectly lined up with the headstock. When I used to turn wrenches professionally I broke some universal joints on many occasions using different size ratchets and to be honest the torque involved to break them was significant as in I had to really over torque them to break them. Sometimes the actual metal of the socket broke before the pins holding the universal together broke so they are very strong. I too would only be concerned with the possibility of the rotational speed causing the universals to go flying. I think though that as long as you make sure you connect everything together nice and tight that the possibility of that happening is lessened.

dusty wrote:I love the ingenuity shown here BUT I'll just wait for new couplers! I would not want to rely on these universals at the rotational speeds involved in this application.

I am in 100% agreement with Dusty on this one.
These were never designed to be universal driveshaft joints
If you do throw caution to the wind, I would recommend a shield for when they eventually explode at speed.

wiredone wrote:I am in 100% agreement with Dusty on this one.
These were never designed to be universal driveshaft joints
If you do throw caution to the wind, I would recommend a shield for when they eventually explode at speed.

I would vote for a shield and am looking at a couple of possibilities even for the standard coupler more to keep from doing something stupid (I try to do at least one stupid thing a day ) than protection from the standard coupler failing.
Actually we kind of just had this discussion about a week or so ago. I forget which thread. For me the failing here is not the joints. I have impact wrench universals that have taken a beating since about 1958. I also assume that we are not talking about anything as silly as running with the thing seriously out of alignment. Even on farm equipment PTO drive shafts that take maybe 100 HP we always try to run them as straight as we can. A decently aligned universal gets very little wear... Harsh angles will eat them up.
For my purpose and the purpose of the other thread the failure with this one is not being able to telescope the ends together to connect / disconnect without having to move the headstock. If I am going to move the headstock (disturbing a second setup) I will just stick with the standard couple. I have never had one fail.
Interesting project though.


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robinson46176 wrote: For my purpose and the purpose of the other thread the failure with this one is not being able to telescope the ends together to connect / disconnect without having to move the headstock. If I am going to move the headstock (disturbing a second setup) I will just stick with the standard couple. I have never had one fail.
Interesting project though.


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Actually one of the things I wanted from this was the ability put a sliding system in or have the headstock further away if I wanted. Because they are standard 1/2 inch socket drives you can put whatever wooden (or aluminium or whatever) mechanism in the middle that you would like, you could do a sliding dovetail type thing or make something simlilar to the PTO shafts on the back of tractors where you have a sliding joint.
I should mention for people talking about universals going flying that the socket I designed has the little dimple inside for the drive ball-bearing to pop into. When I ran the mdf to destruction last night the sockets/univeral joints did not come off the bandsaw or motor side. They just spun around at 1000rpm roughly.

I never even thought of the universals failing .. it's an intersting point but I would have thought they are more durable than a piece of plastic? I wonder what the actual torque involved is when the machine is running.... I would imagine it's quite small. If I post a picture of me with a universal joint embedded in my forehead I will have no problem admitting i was wrong..

I never even thought of the universals failing .. it's an intersting point but I would have thought they are more durable than a piece of plastic? I wonder what the actual torque involved is when the machine is running.... I would imagine it's quite small. If I post a picture of me with a universal joint embedded in my forehead I will have no problem admitting i was wrong..

Trust me, they will fail at speed and it will not be pretty.
They are not designed to spin quickly, they have no bearings and are basically just pinned together.

Although they technically spin they don't really spin in terms of something with bearings. Bearings are only used when one thing spins and the other stays stationary which isn't the case here. Anyway the only true way without getting come awfully complicated maths done is to go ahead and try it. Will put it to the test over the next few months..
thanks again for everyone's feedback.