Broach for motorcycle gear/brake splined shafts?

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.

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_
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The phrase 'serration broach' looks promising.

Matching to an existing spline might be the tough part.

Dave

Reply to
spamTHISbrp

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. You can probably make one on your own if you have a milling machine and indexing fixture. Basically, you make a splined shaft to match the hub you want to mate to, and cut teeth in it. Many of the serration splines use a groove pattern which can be cut with the edge of an ordinary end mill, cutting a 90-degree- bottom groove in the shaft. You will need to make a splined section several inches long. After cutting a facsimile of your shaft spline, you proceed to turn it into a broach by these routine steps:

  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.
  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.

An article on how to make such broaches appeared in either Home Shop Machinist or Machinist's Wrkshop a couple of years ago, and makes it look quite doable by an inexperienced machinist. In selecting your material, consider how many pieces you expect your broach to produce, and the hardness of the hubs to be broached. For a few hubs of aluminum, you could get away with a broach made of 4145 steel or other popular shaft material. The 4145 can be oil hardend to make a very durable broach for use in softer materials. If you want a real production broach, select drill rod for your material and harden it to full tool steel hardness.

Reply to
jwdoylejr

Cylindrical steps, not a continuous taper.

The space should be large enough to allow chips to curl freely, and undercut enough to grind the faces to sharpen them.

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:

Jim Wilkins

Reply to
Jim Wilkins

Thanks - I was considering that. What I didn't know was whether just tapering the splines, which would result in a flat-topped cutting tooth, would be ok, and whether having no relief would also be ok. Yes to both makes it much more do-able.

I need to make about a half-dozen bits from some kind of stainless.

Reply to
_

You may consider finding someone with a shaper or slotter, which could make quick work of it.

Don Young

Reply to
Don Young

Or lacking one you can use a lathe, with the work in the stationary chuck and the shaping tool on the carriage. If the lathe has a threaded spindle you can make an index wheel that fits behind the chuck. This is MUCH slower than a real dedicated machine and you still need a very sharp form tool.

Reply to
Jim Wilkins

You might consider finding a shop with a wire edm machine to cut the spline.

Water jet would probably be a little to inaccurate.

John

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john

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