Tooling for a spline

Hi,

I am working on a 1951 Formula 3 car and need to make a pair of new drive shafts. The inboard end is a straightforward spline that fits into the Hardy Spicer joint, the outboard end though is more complex.

I think this is an involute spline with 19 teeth that fits into the CV joint in the hub. I suspect that the CV joints are from classic mini.

Can anyone advise how to properly identify the spline form and suggest a source of tooling? I am anticipating machining the spline on the milling machine in a dividing head so I am imagining something that looks like a gear cutter? I don't have any significant grinding facilities to make a cutter, so I assuming I will need to purchase something.

Thanks

Ian

Assuming the spline was made to some standard, machinery handbook might be a good place to look? Not easy to tell from the picture the exact shape of the splines but I would think your method is about right.

Paul.

Machinery's Handbook (21st edition) has a section on involute splines to ANSI B92.1 (1970). It lists 20 tooth splines but not 19. The standard pressure angle is 30 degrees.

Martin C

ANSI standard corrected.

Edited By Martin Connelly on 30/04/2020 13:27:18

May not be relevant (could have been modified over its life), but if it was originally fitted in 1951, it wouldn't be from a Mini.

There is a British Standard for involute splines, BS3550 (pdf copy on Scribd), but it is 1963, so a bit late. However, if you can read the introduction/preamble to it, it may reference an earlier standard from which it was derived or consolidated.

.

That standard [which is now withdrawn] is mind-bogglingly detailed

I have, however, [hoping that BSI will not be offended] copied this introductory text ... which might be useful in that it cross-references American standards.

MichaelG.

.

P.S. ___ I think a definite identification of the CV joints would be very helpful, IanH ...

Hi Folks,

Definitive identification of the cv joint is tricky. The car originally had hookes type joints in the ex BSA three Wheeler front wheel drive hubs, but these were replaced at some point during its life with the cv joints. I think they are likely to be mini (small, cheap and available) but can not be certain.

If I could find some info or a spec of the mini spline form then it would be handy, but my Internet searches are not successful so far.

I have found Sandvik produce some tooling for cutting splines but I need to investigate that option further.

Ian

IanH,

Assuming that there is something amiss with the CV splines, your original post seems to indicate that you are satisfied that you will be able to form the Hardy-Spicer splines, so, unless the half-shafts are overly long, wouldn't it be more straight forward to obtain a pair of Mini halfshafts and machine the Hardy-Spicer splines on the other end, even if it entails replacing the existing CV joints with matching ones from a Mini? It's been about 40 years since I messed about witha Mini drivetrain, but I seem to remember the inner joints are splined anyway. I wouldn't mind betting that the halfshafts you have are retro-fitted items, possibly even complete from a Mini. BMC 1100/1300 (ADO116) would likely be longer than Mini ones, if needed.

John

The problem I have is that the drive shafts that came with the car were too short. I do not know exactly how much too short yet as I have not yet built and fitted the new front driven axle (all machined ready to assemble).

I am assuming that I will use the scrap drive shafts to determine the lengths of the new shafts - essentially by cutting and shutting them in the assembly. There are outfits that will make custom drive shafts to your spec, but apart from the problem of specing the involute spline (other than by giving the machine shop one of the originals as a sample) I am keen to make my own if I can.

Ian

They look similar to the wire wheel halfshafts I once had on an MG midget so something of that lineage may be worth a try, e.g. this from an MGA

https://www.moss-europe.co.uk/half-shaft-axle-wire-wheels-btb153.html

Adrian

Worth noting that the right hand side Mini driveshaft is longer than the left, so if your car is set up more symmetrically, a couple of R/H ones may be of use? Of course the issue could be sourcing them, as the later (and still available) driveshafts switched to an inner pot joint which I think had similar (possibly identical) splines to the outer CV end, whereas the earlier Hardy-Spicer ones are getting a bit rare.

Just a thought........Are you looking at a "Serrated" shaft or a "Splined" shaft ?

I have always described what you have in the photo as Serrations, so you might find more information using that terminology perhaps.

My B.S. A19 from 1941 cover aircraft Serrations, but it jumps from 16 to 20 with no mention of 19.

Serrations are generally straight sided, but your do look to have some curve on the sides, so maybe the involute suggestion is a good one.

The standard method of measurement is with two pins in the grooves and a dimension taken across them, but again with an odd number this does not make life easy. All the one listed in the BS are even numbered.

Sorry I cannot be of more help.

Phil

The original (real!) Mini CV Rzzepa joints at the outer ends of the drive shafts were unusual in that the joint was an integral part of the stub axle that held the front wheel.

Your 1951 car can only have been fitted with CV jointed shafts sometime later in its life, if they are Mini outboard ones then they would be instantly recognisable so from your description definitely not originally from a Mini. Early Minis were often fitted with inboard needle roller type Hooke joints to replace the (Hardy Spicer? made) bonded rubber Hooke joints. I dont know if inboard Mini joints were ever CV type but I think its unlikely.

If you are going to machine the spline yourself I suppose it helps if you can find detailed dimensions but if not you will have to take the measurements yourself.

Ian P

Might be cheaper and easier to just farm the job out.

i had a pair of custom shafts made for a bike engined lotus 7 clone, good few years back and i cant recall the company name, something like GB Engineering.  Think i paid in the region of £160 each

However a quick google brought a few companies up who specialize in such work.

Maybe worth a few phone calls.

**LINK**

Edited By Alan Waddington 2 on 30/04/2020 17:26:16

Thanks for everyone’s input, I am thinking that all things considered, this might be one job that I outsource. The commercial outfits are talking about hardening and straightening after cutting the spline form which is an added layer of complication I could do without.

thanks again

Ian

Although Ian seems to have sorted his problem, it might be worth making a note that DIN 5480-1 lists splines/serrations with 19 teeth. The number of teeth depending on the base diameter of the spline and the size of the Module, (Mod) being used. Straight or Rack profile as well as Involute splines are listed under this specification, but it relates only to 30 degree Pressure Angle(PA).

ISO 4156 Covers 37.5 and 45 degree PA.

Regards

Gray,

Just to close the loop on this, whilst I was getting closer to an answer, 30 degree PA tooling was looking tricky to source economically for a one off job.

Thinking about it again with friends, we concluded that the Morgan has a thin walled tubular prop shaft with inserts soft soldered in each end, and this is well able to handle up to 80 plus bhp in the case of the racing Morgans. The Emeryson has maybe half this power available shared between two drive shafts (no diff), so extending the existing shafts with a length of decent high tensile tube should be fine. I have procured a length of 10g T45 tube and will now set about the job of putting it together. I think I will go silver soldering rather than soft soldering, but with a decent joint area I am pretty sure on reflection that soft solder would do the job. A bonus of taking this approach is that if a joint does fail, it should fail safely in that the shafts will not flail around.

here is the car in period...

If you are not in too much of a rush to complete the machining you could try a single point cutter and fly-cut the splines/serrations.

That's what I thought. I've done that in the remote past for a toothed-belt wheel for Ford. You grind the single-point cutter to fit the profile of the spline, finishing with a hand-stone and checking with engineers' blue. Takes a while, but it works.

Back in the 70's I used to visit one of the Hardy Spicer factories in Birmingham. at that time the spline and threads were rolled not cut so they may have a unique form to their own standard. Just saying that some care needs to be taken to ensure that the mating parts match. Much better to buy the mating parts and modify the rest to suit rather than trying to machine a matching form for the spline.