Internal splines

That depends on how many you want to make.

Could use one broach indexed 14 times for lower quantity. Or one broach in one shot for lots of pieces.

1/4" probably isn't too much to do in a single pass (although I wouldn't know). I was in another division of our parent company last year which makes transmission components. They had broaches three feet long with dozens of teeth (making splines). I believe broaches can get much longer.

I'd imagine they tend to be *slightly* expensive.

Incidentally, the company was also doing flow-forming. This method could also be used for your application. Not exactly a common technique though.

Regards,

Robin

All the broaches which I have seen have many points, each taking progressively more cut as it is pushed through. A square broach starts out with a round pilot hole which is just a bit larger than the across-flats dimension of the hole being produced. The first tooth cuts out the part of the square corners which is fairly wide, and quite shallow. The next one cuts a little narrower, and equally shallow, until the final one cuts the square corners in the hole.

And -- there has to be chip clearance in front of each tooth.

So -- the broach is quite long by comparison with the hole which it must cut. (As an example, a 1/4" square broach is something like 8" long (says he, without going downstairs to measure. :-))

Hex broaches are similar, except that they cut on six faces, instead of four.

Keyway broaches cut on only one side, and use a bushing turned to fit the hole with a keyway in it to accept the smooth side of the broach. To keep the length from growing to extreme dimensions, the keyway broach sets include one, two, or perhaps even three "L"-shaped shims, which fit between the the broach and the bottom of the keyway in the bushing, so you can draw the broach out, add the bushing, and cut just a bit deeper with the same set of teeth.

The appearance of a keyway broach is sort of like a set of breaking waves on oceanfront property. The gully makes the chip clearance, and the crest carries the sharp edge which cuts the chips.

A spline broach would be similar to the square and hex ones described above, since there is no provision for adding shims to make the broach larger for a second or third pass.

While my experience is with push broaches driven by an arbor press, I do know that there are also "pull" broaches threaded on the end, and attached to a hydraulic system to draw them through the workpiece. There, you would have less chance of the broach buckling as it could if you pressed too hard.

I hope that this helps somewhat, DoN.

The broaches used to do this have many teeth. Imagine a bar turned to the OD of the max ID of your spline. For that size, maybe the tool would be 2 feet long or more. Now taper the bar so that one end's OD is equal to the root diameter of the spline-to-be. Now, cut all around the bar about every 1/2 inch or so. Shape the teeth so formed. Mount the broach and the blank in a broaching machine and push. Every little set of teeth cuts a little--- maybe 5 or 10 thou. Look at broaches on E-Bay to get the idea.

Pete Stanaitis

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Phil Kangas wrote:

When I was serving my toolmaking apprenticeship many years ago back in England the Technical College (Polytechnic)I attended one day a week had a broaching machine and broaching was covered in the 3rd or 4th year of the course (IIRC).

This particular machine used broaches 3-4 feet in length and they were mounted vertically in the machine, the top part of which was basically a hydraulic press. The broaches ranged from single groove types up to roughly 24 grooves/splines or more (again IIRC) and in a range of diameters. They were tapered for roughly 2/3 of the length and had a large number of 'teeth' up the length so that each 'tooth' was only removing a small amount of material (maybe 10-20 thou). The chips came off as small, cylindrical coils and looked a lot like short 'roll pins'. Copious amounts of cutting fluid were needed and this was a straight oil (almost like heavy hydraulic fluid to the 'touch') and not a water soluble cutting fluid (as used on lathes and mills) and served more as a lubricant than a coolant.

I also seem to remember that the 'parts' were not clamped to the table but were allowed to 'float' so that the broach could 'self-centre' in the bore. They were however constrained in the vertical plane so that the broach could withdraw after completing the cut without picking the part up off the table.

Thanks for all the replies so far, the long broach is what I had in mind but was not sure if that is the current approach but I guess it is, eih? What got me going on this is that this part can be had at a faraway dealer for $40 US and the darn thing is now made in India! How can they make this thing halfway around the world and sell it here for $40? Amazing to me. What I found out on a long stroke like this is to make real sure each tooth takes its fair share or else the gullet gets packed full ruining the groove, ask me how I know. Also, each tooth must only have one cutting edge. I learned a lot here but I can't compete with india. That roll forming thing sounds like fun! Might be 'the' way?

Phil

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Phil,

"Roll forming" is the process by which tubes are made from flat sheet.

"Flow forming" is similar to metal spinning. A blank is formed around a mandrel using rollers, but the mandrel has splines into which the blank is formed. This requires a very powerful spindle and a very rigid machine.

The outter surface of the formed part must be machined as the process results in a very rough surface finish. I can't remember if the internal splines require further machining, but any stamping must of course be done after forming.

The part was a clutch housing for Jeep, IIRC.

Regards,

Robin

Pull a broach through it......unless the hole is blind--then a gear shaper would be used instead.

Begin on page 8 of the .PDF document below if you like to learn more about the forming of internal gears and splines :

That is an interesting site, SVL, thanks. Looks like i'm doing it the hard way as usual! At least I'm on the right track here............and only a couple to make. Phil

blind--then a gear shaper

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