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

[Anonymous]

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.

[bernard towersParticipant @bernardtowers37738]

If you go the D bit route the tapers will match no need for lapping and heat treating a small D bit is something we should all be able to do with some degree of success, enough to work once anyway.

[Anonymous]

The tapered valves and the D-bit used to make the tapered, blind and flat bottomed holes are show along the bottom of this picture:

The valves and D-bit were machined at one setting on the lathe, although to get the best surface finish they were then ground on the cylindrical grinder. The tapered seat was stepped drilled before using the D-bit to form the taper. Internals shown here:

Andrew

[HopperParticipant @hopper]

I would be tempted to use a standard tapered reamer. A No1 Morse might be a little large for your purposes but one for reaming tapered dowel pin holes would certainly do the job.

Then set your topslide to match by trial and error on a piece of scrap material before machining the male taper.

[HopperParticipant @hopper]

Or you could treat yourself to a new solid-carbide or cermet micro boring bar. I have seen them down to 3mm. Ready made for the job and not expensive if you shop around.

I have a 5mm one and it works  brilliantly.

[bernard towers]

On bernard towers Said:

…heat treating a small D bit is something we should all be able to do

Why the “should”?

Many roads lead to Rome and Highway number O1 (or Interstate W1) are just a few options. Others may prefer the scenic route.

It would be remiss to pretend the Country Road leading to home does not exist and more so to attempt to prescribe use of a particular route.

[David George 1Participant @davidgeorge1]

I have a selection of taper reams which were used to make tapered holes for investment casting sprue holes. These are available and cut a smooth tapered hole.

David

[Paul McDonough]

On 27 August 2024 at 17:19 Paul McDonough Said:

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

I’ve not heard of ‘slant height’ before but have highlighted what I think the OP has identified as the cause of the taper mismatch.

Particularly at small diameters the tool tip height is extremely critical if a conical bore is not going to end up barrel shaped.

Ian P

[Paul McDonoughParticipant @paulmcdonough43628]

Thank you everyone.

i have not heard of a D-bit, but I can picture what it might be, I was going to try to grind a  taper shaped form tool in HSS cutting some relief in by hand! and keep the top slide angle to cut the matching male taper.

i like the idea of using an end mill, didn’t think of the one!

and yes I think you are right Jason, I suspect it is the lower edge of the tool fouling on the lower part of the hole causing it to deviate.

I have since found that it is possible to buy pre machined cones, but then I have the hassle of getting the internal taper to match.

[Neil LickfoldParticipant @neillickfold44316]

I bore the backplates with a carbide bore bar that has a min diameter of 6mm. It has a 6mm shank and about a 80 deg included angle from the front to the side of the bar. I use an angle block to set the top slide with. Make sure that the tool is very close to cutting on the centre line, to no more than 2 thou above. Don’t have it below. Check that the top slide is not loose. You don’t want it wobble as it goes along the cut.

Making  a plug gauge first, and then using that plug gauge to get the depth or diameter of the taper correct. If you over bore the taper, you can measure with the gauge, the distance too far it is, then just take that length off to make them very consistent in size. So any backplate/Flywheel will fit any shaft.

Make a gauge flywheel as well. Then all the parts will interchange. Bearing blue can be used to confirm the fit of the parts.

You can also make a split collar, that then connects the shaft to the flywheel, and the collar fits onto the parallel shaft. It works well when there is a front ball bearing for example. If its a plain bearing, then the taper on the shaft works really well.

[Paul McDonoughParticipant @paulmcdonough43628]

Thanks Neil,

 

With all of this advice  I can seen that I need  to have another go

cheers P. McD

[HopperParticipant @hopper]

Micro boring bar. Less than a fiver a shot. Solid carbide or cermet.

They even have a little chip-breaker ground on the tip. Cute as a bug.

 

[Paul McDonoughParticipant @paulmcdonough43628]

Thanks Hopper I might do this, just need to figure out what size I need/will fit, I don’t understand the codes for these things, but as you say quite economical.

[Paul McDonough]

On Paul McDonough Said:

Thanks Hopper I might do this, just need to figure out what size I need/will fit, I don’t understand the codes for these things, but as you say quite economical.

Many of the sellers on Aliexpress have charts showing the dimensions and code numbers. You might want to look at something like an MUR 5xxxxxxx series. The 5 denotes 5mm width across the head, so it should work in a 6mm hole. They come with different length reduced shanks so make sure to get the one long enough for your job. Once you figure out which one you want, you can buy it from your favourite UK supplier for quicker delivery.

[derek hall 1Participant @derekhall1]

Neil said…

“Make sure that the tool is very close to cutting on the centre line, to no more than 2 thou above”.

Not a criticism Neil, but how would you measure that the centre height of the tool tip is within 2 thou?

I would have thought that even if you were able to measure that, a very slender, small boring tool at its extremity of cut would be deflecting more than 2 thou anyway.

[Paul McDonoughParticipant @paulmcdonough43628]

Thanks Hopper, I am quite partial to a rummage on that site.

[derek hall 1]

On derek hall 1 Said:

Neil said…

“Make sure that the tool is very close to cutting on the centre line, to no more than 2 thou above”.

Not a criticism Neil, but how would you measure that the centre height of the tool tip is within 2 thou?

I don’t know how Paul does it but very soon after getting the 280 I established that the ctr height above the cross slide at 3.389″ so I know how much to pack up work when mounting on the cross slide to bore etc. I also use the height gauge on the cross slide to mark things such as the throw of an eccentric. So no problem if I wanted to use the same gauge to measure tool height.

I have also seen that a lot of people make a gauge for setting tool height, so just stand that on a 2thou feeler gauge if you what to set a tool 2thou above what it is set for. If you don’t use a setting gauge then use whatever method you usually do to set a tool on ctr and once it is there just loosen the toolpost screws and slip a 2thou feller gauge under the tool.

10-12mm stick out on those carbide bars combined with the small DOC when sneaking up using the male taper a sa gauge won’t see much deflection

[noel shelleyParticipant @noelshelley55608]

Like Hopper I would think about a taper pin reamer of suitable size, then trial and error for the male part. Just checked a No6 = .27″ to .35″  Good luck Noel.

PS how many people ever wonder why there is a plastic bit in the yoke of a Mitutoyo micrometer as shown in Hoppers photo ? N

[noel shelley]

On noel shelley Said:

 

PS how many people ever wonder why there is a plastic bit in the yoke of a Mitutoyo micrometer as shown in Hoppers photo ? N

I know why it is there. Was explained to me as a first year apprentice when that particular mic was issued to me.

[Author]

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