Recently I decided to attempt to produce a couple of
splined couplings out of steel. Dim's are: length 3 inches,
id to fit 1.250 od 14 spline 25 deg p.a.male spline! Somehow
to make indexing tooling and using a pair of custom ground
I was able to do it but sure learned a lot on the use of
So my question is, how would this part be done in a
situation? Most surely not the way I did it, one spline at a
_many_ passes each! I don't see how a cut that big can be
one pass through a three inch tube, that's a big chip to
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.
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,
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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.
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
dealer for $40 US and the darn thing is now made in India!
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
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
cutting edge. I learned a lot here but I can't compete with
That roll forming thing sounds like fun! Might be 'the' way?
"Larry Green" wrote in message >
"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
The part was a clutch housing for Jeep, IIRC.
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.
"PrecisionMachinisT" <> wrote in message>
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