On Mar 12, 7:35*am, wrote:
On Mar 11, 1:19 pm, _
wrote:
Might be making some bespoke arrangements for a motorcycle project, and was
wondering if there is an available tool to cut the splines on bits to fit
these shafts.
If you fail to locate a ready-made broach, and have a near-death
experience when you see what a custom-made broach will cost, you may
consider making your own broach.
1. Turn the end of the splined shaft down to form a pilot at the
minor diameter of the spline.
2. Turn a long taper along the splined section of your shaft,
increasing the diameter from the pilot section to the major diameter
of the spline. It would be reasonable to figure on a tapered section
three or four inches long, so that each tooth in the finished broach
is required to cut only a couple of thousandths. You can see that to
cut spline teeth .050" deep, you will be needing 25 teeth.
Cylindrical steps, not a continuous taper.
3. At reasonable intervals along the tapered section, cut notches,
forming teeth with cutting edge toward the small end of the taper.
There should be little or no rake and relief on these teeth. Turn a
space between teeth to collect chips cut by the next tooth.
The space should be large enough to allow chips to curl freely, and
undercut enough to grind the faces to sharpen them.
http://picasaweb.google.com/KB1DAL/H...48334136663058
The motorcycle sprocket's center hole had 13 splines. I measured a
tooth carefully and shaped a lathe bit to match on a surface grinder,
then used it to spline the shaft. It's a rubber-hammer press fit.
The OD of the shaft fits the sprocket snugly. I cut the grooves
slightly deep to avoid having to make them concave at the bottom. In
terms of the form tool this meant getting the angle correct but
leaving the end narrower than the sprocket tooth. I machined the shaft
between centers so I could remove it to test the fit, by the location
and thickness of the chips the hardened sprocket shaved off.
That was good enough for a sawmill, which won't fail while
accelerating across a busy intersection. I don't know what's
appropriate or safe for a motorcycle.
The hydraulic pump I salvaged and rebuilt for my tractor had an
involute splined shaft. I shaped a lathe bit to fit the groove and
machined a broach with it to spline the pulley bore. It was a lot more
work to fit the bit to the curved groove than to copy the flat-sided
motorcycle spline profile. Soot from a candle shows up better than
bluing on shiny metal.
Since the pulley is white metal I thought I could avoid hardening the
broach. It cut the first pulley OK, when I needed a second larger
pulley it was dull enough that it bent slightly from the higher
pressing force. The steps on that broach are 0.010" apart so each
tooth shaves off 0.005". Smaller would have been better and I should
have hardened and tempered it.
You could machine your first attempt at a broach oversized to rough
out the hole and make a second one more accurately, with the advantage
of experience. Use the same form tool, rough the broaches when it's
close to shape and finish the second one when it's correct. Then the
chip per tooth could be smaller and the broach less likely to snap
from imperfect home heat-treating. Several short broaches may be less
total work because only the final one has to be accurate and a shorter
one deflects less while you mill the slots with the form cutter.
This is the broach, cutter head and alignment jig:
http://picasaweb.google.com/KB1DAL/T...96150338607922
Those chips are jammed very tightly into the grooves.
Jim Wilkins