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Internal spline reverse engineering

Internal spline reverse engineering

Internal spline reverse engineering


I am trying to reverse engineer a spline of a 1980's BMW drive flange. I hope you guys can push me into the right direction. I can say i am a newbie to splines and gear engineering

Fabrication of the drive flange is my smallest concern, I have a lathe and also an EDM at my disposal.

The main problem is retrieving the spline geometrics/ standard/ tolerances.

I retrieved the following dimensions:

27 teeth

Smallest diameter (Tooth tip/ Tooth tip]: 27.54mm
Largest diameter (Tooth root/ Tooth root]: 30.68mm
Middle diameter (Tooth tip/ Tooth root): 28.81mm

The teeth seem to be involute

I scanned the drive flange, see attached image. Which steps do I have to take to retrieve the dimensions of this spline? In the end I need a dxf file or similar to edm the spline.


RE: Internal spline reverse engineering

Quote (AldoAldo)

I hope you guys can push me into the right direction.

Send the part to a gear shop and pay them to reverse engineer the part for you.

RE: Internal spline reverse engineering

Haha, o.k. They charge €350,- to create a DXF for me, don't know if this is a reasonable price.

Perhaps you can answer my other questions concerning the fabrication/ hardening of the splines.

Am I correct that I have to measure the hardness of the stub axle and match this hardness with my internal spline to fabricate? Does anyone know which delta between hardnesses is allowable to prevent fretting of the material?

RE: Internal spline reverse engineering

Your spline appears to be fillet root, side fit. Hard to say what the module or pressure angle are.

350 euro seems reasonable for an accurate .dxf CAD file of the existing internal spline. But it will cost several times that amount to machine the hub, heat treat it, wire EDM the spline teeth, and clean up the tooth flanks.

Consider that the guys making the .dxf CAD file will first use a very expensive piece of inspection equipment like an optical comparator or CMM, operated by a well paid technician, to determine the surface profile shape, and then pay some designer lots of money to use an expensive CAD software to create the .dxf file.

RE: Internal spline reverse engineering

Thanks for your reaction.

The costs for machining is not a real problem. I can use an EDM wire cutter and a conventional lathe.

I was planning to do this in the following order:

-Create a DXF
-Pre-machine the new hub on lathe
-Determine original hardness. Match material hardness. Perhaps the material is not hardened? If i need to to harden the base material I am still thinking about the correct order to do things.

If I need to harden the teeth, I can inductive harden the inner diameter of the "new" hub till a depth of 2mm and then EDM the splined teeth or I can EDM the splined teeth first and then nitride harden the teeth with a surface depth of 0.2mm.

Nitride hardening has the advantage that it won't mess with the tolerances but the depth is very minimal. Inductive hardening has a greater influence on the dimensions but also a better hardening depth. What should I do here?

You are also talking about cleaning up the tooth flanks. What does this exactly mean and do i actually need to do this after EDM wire cutting?

Thanks for responding!

RE: Internal spline reverse engineering


Please be advise there are many more considerations than just DXF file.
A metallurgical analysis must to be preformed of the material. what type of steel.
what type heat treat , through harden or case harden.

then there's the actual measurement of the spline criteria.
yes wire cut is great for very low volume but is not economic for high volume.
the exact spline minimum effective size, and the maximum actual size must be known.
for high volume a pull broach would be required. Go & No go spline gages would be required. inspection tools to verify the spline P.D. runout to the ground mating bearing surfaces.
if this is just one part required, then having the mating part at hand will be valuable.
because then an actual fit this part can be accomplished. it will mate for sure.

that is why Gearcutter recommended a gear shop. the reliability issues here are critical for safety.
These are condition where people in the Industry have many many years of experience.
and know to deal with these issues.
what is the stress & torque requirements.


RE: Internal spline reverse engineering

Thanks for your answer. This is a low volume operation. As mentioned before, my production costs are not the bottleneck.

A gear company will measure the internal and external spline of the hub and supply me a dxf with the spline.

So basically the only thing I need to know is the material and the hardness of the original part.

What are your thoughts on my previous post about the order of the hardening proces and the different methods and effects on the tolerances?

RE: Internal spline reverse engineering


It will depend on the heat treat and material.

if it is thru harden cut the spline after heat by wire cut. make a go gauge. to verify the the spline involute is correct. a mating part will work for small qty.
if it is case harden Nitride or carburize, it will require to cut the spline prior to heat treat.
but will require different sizes. what I mean is that a nitrided part will require to be cut at the low end. in size.
(if gas nitrided) the white layer should be removed. thus allowing for very slight stock removal.
where as carburized will require to cut at the high side to allow for contraction of the spline. and to remove distortion will require spline lapping after heat treat. in addition the geometry of the part will require extra measures to prevent distortion. be prepared to find a a heat treater that will run the parts with the best procedure and care.
otherwise the parts will distort like pretzels. what the part looks like prior to heat treat can and will make difference.
the easiest of course is to thru harden, then wire cut the spline.

this of course is not all the possibilities, because one could write a book on the subject.


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