Morse taper
It is said Stephen Morse devised the taper system as a way to drive the twist drills he invented because drill chucks had not been invented at that time. When fitted into an identically tapered hole in a tailstock or machine spindle, a tapered drill shank has amazing grip and a lot of power can be transmitted through this purely frictional connection.
In mathematical terms, the slighter the angle of the taper the tighter the grip that can be produced when the two parts are put together with a brisk push. However, we then need to get them apart again without too much trouble.
Back in the 1860s, Morse settled on a taper of approx ⅝-inch per foot (15.8mm per 304.8mm) as the best compromise to give excellent grip yet be relatively easy to separate. Today, this is still the most popular system internationally for manually operated machine tools.
Another once-popular system was the taper made by machine tool builders Brown and Sharpe, although today it is almost unheard of.
CNC machine tools generally use an NT taper system, which is a much steeper taper. It is used in conjunction with a mechanical means to keep the taper pulled hard up into the tapered spindle hole as it will not self-lock. This works best with machines that have automatic tool changers.
Morse tapers come in eight sizes, ranging from the smallest, No. 0, to the largest, No, 7. The actual angle varies slightly from size to size, presumably because standard pieces were less accurate back in the 1860s. The table elsewhere in this article shows the main dimensions.
The tongue at the small end is purely for driving the tapered shank tool out of the tapered socket with a wedge-shaped drift.
equipment designed without any regard to how it would be maintained. I once had a Mk1 Jaguar — I think it had me — and it always needed something attending to under the bonnet. I was convinced the designer had gone out of his way to make maintenance as awkward as possible. For maintenance, if the pipe centre comes apart with the bearings stuck on the static part rather than on the rotating part they will be easier to remove.
If you are going to get this mild steel part case-hardened after machining, it is best to machine the bore just a wee bit larger because the case-hardening process can cause the metal to ‘grow’. This has the effect of making outside diameters bigger and inside diameters smaller.
My guess for this one would be to go for sizes of 32.05mm and 37.05mm where the bearings fit. Don’t even think about using your vernier calipers to measure these bores. You will need telescopic gauges and a 25 to 50mm micrometer.
Before removing the workpiece from the chuck, take a light cut off the outside diameter. This will give you a surface that is exactly concentric to the bores you have just machined and that can be used to ‘clock’ on when setting the part true in the four-jaw chuck. Then you will be ready to do just that.
Once it is clocked up in the fourjaw chuck with the bores facing in towards the headstock, you are ready to machine the conical shape. Set the compound slide around to 45 degrees and start taking a series of cuts until you are left with a flat area on the front face that is approximately 12mm in diameter. Get the best finish you can from the turning tool, then spin it up with some fine emery tape to create a smooth finish and to knock off the sharp corners.
It is always wise to do a check of sizes before sending a part off for heat treatment as it is too difficult to make changes later.
With all parts finished you can assemble your new pipe centre and you’re ready for action. Aah, do you feel more centred already?