In article 20050515130041.558e8894.MyForeName@TheLast4CharsO fMySurname.net,
Tim Angus wrote:
On 14 May 2005 23:04:56 -0400 DoN. wrote:
How many do you need?
Only the one initially.
And what other tools do you have?
In addition to the mill and lathe, I have a relatively substantial drill
press, but no shaper.
The small ones tend to be too expensive -- even so, I did get
one eventually. :-)
A CNC
mill isn't much help for this. A lathe could be used to emulate a
shaper, if the number of splines matches a sub-multiple of the number
of teeth on the bull gear, but it would be tedious.
The actual number of splines is not important, nor is the precise
profile of the splines. The purpose of this part is as an internal
ratchet, used for a gear shifter on a bicycle. The spline profiles must
be symmetrical as there are two pawls, one for each shifting direction
(the pawls are disengaged at rest).
O.K.
I am intrigued by your suggestion of using a lathe, how might this work
exactly?
Mount it in the lathe -- either in a 3-jaw chuck, or a 4-jaw
chuck and take the time to center it well. (And you may wish to use the
lathe to bore it to a nice concentric and smooth ID.)
Then -- take the boring bar for the lathe (one of the old ones
which accepts HSS lathe bits ground to shape for boring), and grind a
new bit for it -- with the tip as wide as the grooves in your splines,
and with whatever shape you want. Mount it so the profile is end-on to
your workpiece.
Next, turn off the power to the lathe, open the headstock cover
(if you have back gears), pull the pin but don't engage the back gears,
and clamp on a makeshift indexer which fits into the teeth on the bull
gear. Use this to lock the spindle so it won't turn.
Crank the cross-slide so the tip of the tool is just barely
touching the ID of the workpiece, and using the carriage handwheel,
crank it towards the headstock, drawing the HSS tool along the length of
the ID, cutting a shallow groove. Withdraw it, and crank the
cross-slide out about 0.001" or so, and repeat (Aluminum would probably
tolerate more, steel probably not. Keep repeating this until the groove
is the depth which you want.
Then crank the cross-slide back in to where it was before,
withdraw the indexer which is restraining the bull gear, and rotate one
or two teeth (depending on the width of your spline grooves and
spacing), and re-lock with the indexer. (Best if you make it so it can
be returned to precisely the same place each time.) Now, cut another
spline, just like the first one.
Keep repeating until you have the full collection of splines
made. They will be some sub-multiple of the number of teeth on the back
gear -- divided by two or three, or possibly even four for a coarse
spline.
Does the number of splines matter? What about the shape? Your
image looks like square splines, but the most common ones are about
the shape of gear teeth. You might even be able to find internal
tooth gears.
I feel quite stupid that this never occured to me. I had come across
drive shaft coupling splines, but they tended to have too few splines
for my purposes.
Hmm ... how about the spline in the clutch hub on a car? Some
of them are square splines, fairly coarse, but others (e.g. the British
MGB) have a fairly fine triangular toothed spline. The trick is
extracting it from a dead clutch plate, and machining the OD to fit your
needs.
Good Luck,
DoN.
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