if you make it rigid then your alignment needs to be absolutely perfect and you need to 'clock' the shafts to each other first by putting a DTI on one shaft and rotating it around the other in several places to ensure it is both parallel and concentric. This is not an easy task if your coupling lives hidden inside a bellhousing and even harder if you don't have a shimming/adjustment system. The jaw couplings allow easy assembly plus have a stated acceptable misalignment amount. Any misalignment in the shaft that is forced into alignment by tightening a rigid coupling will cause extra stresses and lead to something failing.
Posts by 57Chevy
1 - 12 of 51 Posts
I'm using direct drive so no. I have used couplings on large engine driven gas compressors and have seen a variety of failure modes due to the things I have tried to outline. Whatever coupling you choose will work as it was intended, if you use it as it was intended. If your guy just has a hunch that it won't work then ask him for evidence/why. Often people can't explain their 'engineering' assessments, sometimes they can and you learn something
Ah, didn't realise he was using a clutch too so yea, those little metal tabs on the periphery of the disc inside of the lining are the flexible coupling. In fact having a flex coupling and a disc would not be a good idea. Otoh, two separate items with average alignment ability joined by a rigid coupling ends in damage eventually.
It is your project, ultimately you have to make the decision, otherwise you are outsourcing it to randoms on the internet.
What are you using on the spline, are you going to weld the centre of a clutch onto a coupling or how are you doing that part? A solid coupling will be preferred but only if the shafts are in good alignment. Any misalignment in the housing that results in stressed applied to the shaft as it tries to rotate where it wants to go will end up breaking something eventually. Use a solid coupling but also know that it is suitable for a solid first.
This is why an automatic transmission uses a flex plate and why a manual trans uses a flex coupling in the friction disc. These are done by design for a very good reason- automotive parts aren't good enough tolerance in the worst case situation out of the factory to reliably use a solid coupling. Solution: chuck a flex in.
What are you using on the spline, are you going to weld the centre of a clutch onto a coupling or how are you doing that part? A solid coupling will be preferred but only if the shafts are in good alignment. Any misalignment in the housing that results in stressed applied to the shaft as it tries to rotate where it wants to go will end up breaking something eventually. Use a solid coupling but also know that it is suitable for a solid first.
This is why an automatic transmission uses a flex plate and why a manual trans uses a flex coupling in the friction disc. These are done by design for a very good reason- automotive parts aren't good enough tolerance in the worst case situation out of the factory to reliably use a solid coupling. Solution: chuck a flex in.
I don't know what the tolerance specs for an EV are but if that is their approach then I'd wager a buck that they don't use the same fit and tolerance bands as an ICE. Just don't assume that a DIY EV with unknown alignment has the same degree of accuracy as an EV OEM.
Given that the input is splined, it kind of rules out a jaw coupling anyway. A solid coupling with a female spline and a mount that has known and predictable alignment would be the best situation. Just don't chuck one in, hope that it will be fine, and then be upset later when it fails
put it on your input spline and spin the gearbox over, does it wobble? Put it on your motor and spin that over, how much does the welded bit wobble? Put a DTI on it and work out how far out it is. It will be out of alignment to some degree, how much determines how long the spline and/or coupling will last
It looks like they bead blasted it, give it a thorough disassembly and clean with brake clean or similar first and then blow out with compressed air
It looks like they bead blasted it, give it a thorough disassembly and clean with brake clean or similar first and then blow out with compressed air
If the weld cracked on the first go then a second go over the top isn't the solution. They need to find out why; is it incompatible materials, incompatible filler rod, contamination, technique... That crater in the end pool looks ominous, it likely has porosity right down to the root and could initiate a crack anyway, even if that line isn't a crack.
Welding axles is an age old practice that often results in failure. Some people have the knack of it, many don't. You are doing a very similar thing to welding an axle, just less torque.
Welding axles is an age old practice that often results in failure. Some people have the knack of it, many don't. You are doing a very similar thing to welding an axle, just less torque.
Maybe it'd be a better shot welding the clutch spline to a stump of shaft the same diameter as the motor shaft, then tighten the coupler on both the motor and the stump shaft how it was intended to work
You can find generic torque specs for the fasteners online. They look about 1/4 unf
![Rectangle Slope Font Parallel Pattern]()
You can find generic torque specs for the fasteners online. They look about 1/4 unf
How much length do you have between the motor and spline, i.e. is there enough room to have a stump sticking out of the coupling with the spline inside? If so then you can get the spline EDM cut into a short section of turned bar and not worry about welding the clutch disc on, that way everything is as good as perfectly true to start with. Broaching or milling a keyway is no drama.
I'm glad you are finding all these little things out early on, far better now than on the side of the road in six months with a thrashed gearbox spline. 0.006" is a lot of runout, you'll likely feel that binding as it rotates. Welding will always cause some amount of distortion, there isn't really any way around it other than old-man skill and knowledge of the welder.
A better way would be to EDM the spline, that way you start with a single piece fully machined and so very little runout.
[sound off]
A better way would be to EDM the spline, that way you start with a single piece fully machined and so very little runout.
[sound off]
Kiwi, the problem with a jaw coupling is that the spline doesn't axially locate the gearbox half and it'll separate. The other issue is that a flex coupling needs both halves to be rigidly secured and the spline isn't very compatible with that. A lightly press-fitted spline in a blind cavity would work. A loose spline will hammer out with a flex coupling if there is any misalignment, so may be easier to use a solid and clock it up properly during install. Btw, I'm up the top end of the islands
1 - 12 of 51 Posts
