Keyway Broaching

[Howard LewisParticipant @howardlewis46836]

To reduce the work required, if you decide to use either the Tailstock or a Toolpost mounted tool (my preference if you cannot access a Slotting Tool or a Shaper ), try this.

I have cut keyways in this manner, but using a depth of cut of 0.010" (0.25 mm) or less

Fit a sacrificial "bung" into the bore.

Drill a hole, say 4.5 mm diameter, on the boundary between the sacrificial bung and the workpiece.

The hole, will reduce the amount of metal to be removed when you slot / broach the hole, and reduce the risk of the tool wandering.

Howard.

[HopperParticipant @hopper]

Posted by Michael Gilligan on 16/12/2019 11:21:42:

Posted by Hopper on 16/12/2019 11:10:03:

Could you even do away with the rather inconvenient long keyway and use instead a dowel pin through the gear and shaft? Make it out of brass and it could be a safety shear pin?

.

Now that’s what I call Engineering

MichaelG.

Yeah, I should do this stuff for a living.

[Norfolk BoyParticipant @norfolkboy]

Just be aware before pinning it as setting the end float or adjusting it with shims is a requirement and not easy to get right first time.

[Howard LewisParticipant @howardlewis46836]

Using a pin in place of a key is intended to provide a location, NOT a drive. They are usually found on a taper, which provides the drive. A pin would not withstand the forces or the torsionals, involved in driving a fuel injection pump. Stanadyne used a pin to locate the driving gear on the tapered shaft, for the DB range of injection pumps.

So if drive rather than location, is required, a key is the way to go, but even then wear of key and keyway is likely to occur. Ideally the drive should be obtained by pressing the faces against shoulders with a nut or other forms of fixing.

Howard

[not done it yetParticipant @notdoneityet]

Using a pin in place of a key is intended to provide a location, NOT a drive.

Dunno about that. ‘Depends’ is what I would say. The drive from spindle to lead screw on my lathe is driven by 1/8” (or less) diameter pins between the compound gears, and the power feed on my mill is driven by … a paper clip. No problems with either – the mill power feed ‘pin’ is, admittedly, not a high torque gear shaft and the power feed does not traverse the table at high speed. The VFD, which powers the drive, may well be a soft start as well.

A diesel injection pump is likely to be drawing kWatts, so a rather different proposition than the few hundred watts (at most) for a power feed such as this?

[DMBParticipant @dmb]

My old Drummond fb had drive pins on the changewheels.

[Howard LewisParticipant @howardlewis46836]

The Drummond was designed in the early 1900s when the power supply was the Mk 1 human foot. The Myford M was a similar machine, produced during the late 1930s when electric motors were only just starting to be applied (Look at Model Engineers of those times Industry relied on line shafting to drive its machines, for many years afterwards. )

They used 3/32 pins to compound gears and the driving collars. Sheared pins were not unknown on M types. The successor ML7 , introduced in 1947 used keys, to withstand the greater power of an electric motor.

Fuel injection pumps impose huge torsional loads on the drive, as pumping starts, and from the reaction as it ends (500 bar on a 6 mm plunger provides quite a kick! ). Hence, the pin or key only provides a location, while the drive is provided by the tapers being very tightly clamped together. To minimise the effect of the torsionals, test machines are fitted with flywheels of a size that would be found on an engine of at least 4 litres. Changing the inertia of the flywheel will affect the delivery characteristics quite markedly.

Relying on a key for the drive will eventually cause it "slog" damaging both the shaft and the wheel mounted on it, if there is any great torque to be transmitted.

Howard.

[John ReeseParticipant @johnreese12848]

I do my broaching on a 3 ton arbor press. Before I had the arbor press I used the spindle of a 21" Royersford camelback drill press. Your frirnd's hydraulic press should work beautifully. Be sure to back off thr ram periodically to allow the broach to re-seat itself in the but. That will prevent the broach leaning outward and resulting in a tapered keyway.

[Martin ConnellyParticipant @martinconnelly55370]

Crude but effective.

I made a bush with 3 different depths to guide the broach. With the broach in position a piece of copper was placed on top and tapped with a hammer to drive it through. Material was aluminium alloy. The workbench helped avoid excess shock to the set up.

Martin C

[BufferParticipant @buffer]

I did this the other day on using the saddle on the lathe. I drilled a small hole first to remove most of the waste but you might not need to do this. Regards rich

[not done it yetParticipant @notdoneityet]

Posted by Richard brown 1 on 05/01/2020 15:23:52:

I did this the other day on using the saddle on the lathe. I drilled a small hole first to remove most of the waste but you might not need to do this. Regards rich ….

OK for a large sturdy lathe, but frowned upon with a small hobby lathe.

The carriage is usually driven by an outboard pinion, supported by a possibly flimsy apron. An expensive occupation if excessive wear or breakage occurs.

Slower, but safer, might be to use the tailstock but still loading the spindle bearings – shapers (and slotters) are designed for this type of machine operation.

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by Howard Lewis on 03/01/2020 16:38:39:

The Drummond was designed in the early 1900s …………………………

Fuel injection pumps impose huge torsional loads on the drive, as pumping starts, and from the reaction as it ends (500 bar on a 6 mm plunger provides quite a kick! ). Hence, the pin or key only provides a location, while the drive is provided by the tapers being very tightly clamped together. To minimise the effect of the torsionals, test machines are fitted with flywheels of a size that would be found on an engine of at least 4 litres. Changing the inertia of the flywheel will affect the delivery characteristics quite markedly.

Relying on a key for the drive will eventually cause it "slog" damaging both the shaft and the wheel mounted on it, if there is any great torque to be transmitted.

Howard.

Hi, very often drives on a taper use a fairly shallow, or slow, taper. The shaft end will have a threaded hole in the end with one or more smaller holes at right angles to it, midway along the taper, the drive component would then be assembled and pushed on with a press and then extremely high pressure oil would injected into the hole in the end of the shaft to expand the gap by a few micros, which will allow the drive component to be pushed on a little further. The oil pressure would then be released before the pressure on the component was. Removal can only be achieved by the reverse process, without cutting the drive component off. The oil pressure involved would be in the region of 30,000 psi or even more for very large shafts. I think one of the blowers in my old day job, had two gears wheels that had to be pumped up to about 70,000 psi to have them removed and refitted, just to change the bearings behind them. Needless to say it went away to a company with the equipment to handle such a job.

Regards Nick.

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