Help Identify this spline please?

[Martyn Hogg]

I am trying to make a knuckle to fit on this splined shaft. It is the kickstart shaft on a Honda CR250 motocross bike so it could well be a bespoke Honda spline.

I managed to get it to show up on the shadowgraph (which surprised me as I don't know how the light managed to get  past the big lump of metal attached to the shaft!) Bear in mind that the shadowgraph image may not be 100% accurate and this is a photo of a suspect shadowgraph!

There are 32 teeth and the OD is about 16.45mm but could be a worn 16.5mm. When I measured the tooth height on the shadowgraph I got 0.75mm.

I am assuming it is metric not imperial sizing as that's what the Japanese would have worked in.

I need to work out how to draw this in a 2D format like .DXF that I can then use to wire EDM the spline. The wire is 0.25mm diameter with a 0.1mm spark gap which means I can't make anything with curvature less than that of a 0.175mm rad.

If anyone can identify this spline it would be a big help...

The second question is can Gearotic generate this spline? If not any ideas?

I have a Grasshopper plugin for Rhino that can generate gears so I'm looking into whether this can generate the spline too.

[ArtF]

Hard to say..OEM could have used any toothform or module.. but if I try to get close its a module .49 , suspiciously close to .5Mod.
A .5 mod woudl be too large tough.. Try this dxf to see if it looks close..

Art

[BobL]

Hi;

Maybe this is a dumb question, but would an envolute curve tooth work as a spline?  I thought spline teeth were more of a straight edged thing with a slight curve at the tip? I'm no expert on this, however having dealt and worked on motobikes and snowmobiles, I noticed splines in general to look very different than a gear tooth, I just assumed it was designed to stop backlash between teeth, yet allow lateral movement. I agree the shadowgraph does come close to Art's dxf, my question is will it work?


Cheers
Bob 

[ArtF]

Splines come in a few flavours...

  Small splines are often just V shaped grooves  , others are involutes, and still others are crowns.
Crown splines are just radial grooves really, and their more typical on larger shafts. There is no real
mathmatical reason to use an involute, there is no true rolling action which typically defines the need
for an involute, but for some reason they still get used. Take note though, that most splines have a fairly high
tooth count, so the involution of the tooth may not easily be seen, the more teeth a gear or spline have , the
flatter the tooth gets and they start fairly quickly to resemble pressure angled flats.
  If the tooth has no flat portion on top, its likely a V gouge type of spline, which are the cheapest to produce,
and probably the easiest to strip due to a narrower tooth thickness than the other methods.

  GM's gear outlines are about the cloest it will do to a spline. so far anyway..

Art

[Martyn Hogg]

Thanks for the replies and thanks for the dxf Art.
I will check the dxf against the shadowgraph image when I get back to my Rhino PC and I will probably just round off some corners and try and get the spline close enough with a little bit of clearance.
I had originally thought these splines were straight V-Type grooves and hadn't even realised splines could be other shapes until I got the part on the shadowgraph.
I'll keep you updated on how this goes. Next step will be to wire some splines out of gauge plate to test on the shaft!


Martyn

[Martyn Hogg]

Attached is a dxf with the following layers...

1. Orig - I worked out a way to create curves from the image from the shadowgraph. Its wobbly! *
2. Gearotic - Art's spline
3. Grasshopper - a gear generated using a Grasshopper model (a plugin for Rhino)
4. Spline - made from 32 circles of radius 0.393mm on a PCD of (7.817mm)x2 to form the peaks of the teeth and 32 circles of radius 0.238mm on a PCD of (7.747mm)x2 to form the troughs between the teeth, and the tangent lines between them.
5. OffsetSpline - I offset the spline by 0.02mm which should just about give a nice fit over the original splined shaft.

Hopefully I can get this wired on the EDM tomorrow and see if it fits... I'll probably also do a couple at bigger offsets to see what works best.

Looking at the values I used in 4. above, perhaps this is a crown spline made on a PCD of (7.75mm)x2 with 0.5mm rad tops and 0.25mm rad troughs? Does anyone know of a standard that might be close to this? Or should I be looking at the angles between the tangents to match a standard pressure angle?

*[The curves created from the shadowgraph image was quite interesting... I created a mesh of points and used an image sampler to get the brightness of the image at each mesh point. I used this value to move the mesh points vertically to give a heightfield of the image as another mesh. I then used a mesh-plane intersection to give intersection curves of the heightfield and a flat plane and adjusted the height of this plane until the intersection came out looking like the spline profile. If you zoom in, you can see its a bit wobbly but good enough to draw something around.]

[ArtF]

Yes, I think your on the right track. There are no real standards for that type of thing that Ive seen, each engineer
comes up with what works for him in that application it seems. Goo dluck, looks lke your close enough for government work! :)

Art

[Martyn Hogg]

Ended up having to add an 0.05mm offset for it to fit but it fits OK!

[ArtF]

Martyn:

  Glad to hear it worked out. Looks like a nice fit too. Congratz..

Art