Cutting matching tapers

[Paul McDonoughParticipant @paulmcdonough43628]

I have the need to cut matching tapers, one male one in brass that sits on the drive shaft of my engine 1/4″ dia and the other matching female taper has to be cut in a mild steel flywheel.

Because the tapers are quite small, the ‘cone’ of the male part is a slither over 1/4″ at one end and no more than 9mm diameter at the other. The height/length of the cone is no more than 8mm.

My issue is that I am struggling to cut the female taper without the line of the ‘slant height’ curving.

The boring tool, which I have cut from 5mm x 5mm HSS is by necessity quite thin to reach into the bore of the taper and I suspect it is deflecting, despite my very light cuts.

Is there a better way please? Even if this involves buying a purpose made tool, as the need to cut these tapers seems to reoccur a fair bit!

Many thanks P.McD

[Andrew JohnstonParticipant @andrewjohnston13878]

Can we assume that the tapers are being cut with the topslide set over and that the topslide is not moved between internal and external tapers?

The HSS tool shouldn’t be deflecting that much. How is the tool ground and what are the cutting parameters?

For boring, and screwcutting, in small diameter holes I have used these tools:

Tiny Tools

Andrew

[Clive FosterParticipant @clivefoster55965]

Start with a conical blank for your boring tool rather than a round or square one.

Only the tip needs to get into the small end so the size of the shank further down is defined by what will fit in the tapered bore. Starting by step drilling would make a bit more room too.

I know nothing about them but there are “D-bit” style reamers. Relatively easy to make and possibly up to converting a step drilled hole into a taper.

Clive

[Clive Brown 1Participant @clivebrown1]

For a taper of that size, as said above, a  D-bit is much the best way to go IMO. Machine the male taper on the shaft by setting over the lathe top-slide. Machine the D-bit taper at the same setting on a suitable piece of silver steel. Mill or file that taper to half diameter + 1 – 2 “thou”. Harden and temper. Stone the flat to give a cutting edge.

[JasonBModerator @jasonb]

I suspect lack of clearance is pushing the cutting edge off the surface rather than the tool deflecting under load

One way to get better access is to cut the female taper with the big end facing out and with the topslide still set at the same angle run the lathe in reverse and cut on the back side to do the male taper, if you need to use tailstock support on the crankshaft then just mount it with the small end of the taper facing the headstock.

A milling cutter also makes a good boring bar when you get down to these sizes, hold it in the toolpost with one flute on ctr height. Not quite parallel to the angle of the topslide so the side does not rub Not a flywheel but a similar size taper being cut for a venturi. 5mm dia cutter will work for your 6mm min hole. At 5mm it will be stiffer than most small boring bars

This one was cut with the tool cutting on the far side, Crankshaft taper being used to test fit the distance it goes in upto the red line.

 

[bernard towersParticipant @bernardtowers37738]

Definitely D bit territory at that size.

[DC31kParticipant @dc31k]

Would it be possible to cut two matching male tapers?

Then one can be sacrificed to lap the female one to a better fit after boring as best you can by other means.

That avoids the need for heat treating a D-bit.

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