Cutting matching tapers

[old martParticipant @oldmart]

I prefer a much bigger plastic bit on the yoke of micrometers. Many Mitutoyo’s have such a thing. Appologies for going off track, There are plenty of those solid carbide micro boring tools on ebay, but check the sizes available carefully first.

[Neil LickfoldParticipant @neillickfold44316]

Carbide bore bars deflect a very small amount. Even a 1.2mm carbide bar, that is 6mm long, 5d, only deflects less than 0.01mm cutting material at 52Rc.  A 5 or 6mm bar at 5d only deflects  microns.

My normal way of setting the bore bar is to take a cut across the end face on a piece of brass or Al. I have the tool deliberately under the centre line. When faced, it leaves a little spigot of material. Measure the diameter of the spigot. With a DTI on the tool , I move it up 1/2 of the diameter plus 0.01mm. With the very small bars like the Ø1.2 bars, I blue the end of the brass or ali bar, and use the phone as a magnifier to see the diameter of the spot and if the tool went above , below or through the middle. 0.05mm is very visible with the magnifier app.

With my lathes, they all have the same Dickson Myford QCTP. I set the other lathes with a spacer, so that any tool that is correctly set is always on centreline or where I want it to be. Keeping the surfaces very clean is the important aspect of the Dickson holders and main block.

Preparation is the key to any job, and sorting the tooling ahead of time, or job planning is essential. I have several tool holders with the most common tools that cover the majority of work I am going to do. The micro bars, are in their dedicated holders with the adapters. I really like the Iscar Picco series of small boring bars. Readily available, and they have common shank sizes for a series tools that are held by a M4 grub screw or M5 grubscrew. The smaller than 4mm bars are on 4mm shank tools. So a 1.2mm bar can be changed to a 3.5mm bar, and they are on the same centreline still. The Iscar bars are about 4x or so of the import TiN coated carbide bars, but are a lot sharper and I get a lot longer cutting time from them.

[old mart]

On old mart Said:

I prefer a much bigger plastic bit on the yoke of micrometers. Many Mitutoyo’s have such a thing.

And for anyone wondering, the plastic pad’s purpose is to insulate the body of the mic from body heat when it is being held, thus preventing any tiny amount of thermal expansion that might ensue.

[Paul McDonoughParticipant @paulmcdonough43628]

Thanks for the explanation hopper, it is the beginner’s section after all and I need all the help I can get.

whilst I have ordered a few things to try, small end mill, 10mm HSS. to make a form tool, and micro boring bar, I am struggling to find a taper reamer with the specified 7 deg angle though. 5 to 7 dogs would be fine to fit a 6mm hole at the narrow end

[JasonBModerator @jasonb]

You don’t really want HSS to make a form tool unless you have a cylindrical grinder. Assuming you mean a D bit rather than form tool then that is best made from silver steel and then hardened (tempering is optional)

Turn a male taper on the silver steel at the same setting you turn it on the crankshaft. Then mill or file away half the diameter and use this to finish the hole at slow speed after hardening. No need to machine any other clearance angles as as the two were turned at the same setting angles will match.

I don’t feel your hole is really small enough to need a D bit but this is probably a clearer picture than Andrews. Part needing the tapered hole in the middle, finished male part on the left and the d bit/reamer on the right

[Paul McDonoughParticipant @paulmcdonough43628]

I was thinking of grinding the conical shape, and then cutting two flutes at 180 degs to each other, but I suppose I should  try a D tool first as that would be simpler

 

I have some silver steel too and as you say this would allow me to machine it rather than grind it which will be a much more heath robinson effort by me.

[JasonB]

On JasonB Said:

…probably a clearer picture than Andrews.

Ouch, was that really necessary?

Andrew

[JasonBModerator @jasonb]

It was “clear” but the two cutters are a bit dark from heat treating and I thought the OP may not have been able to see how simple they are to make from your image, you can barely see where the tapered one had been reduced to half diameter.

 

[Paul McDonoughParticipant @paulmcdonough43628]

Yes this makes it very clear what a D-bit is thank you.

A D-bit is what I shall make.

when quenching silver steel is it best to use oil or water?

[Clive Brown 1Participant @clivebrown1]

Water! From bright red into the water as quickly as possible. This will give a very hard but brittle cutter. This can be OK for limited use with non-ferrous or even steel if used carefully, but tempering to straw colour will give a more robust tool. Take care tempering, it’s easy to over-heat a thin cutting edge, which is why I don’t bother if I can get away with it.

[Paul McDonoughParticipant @paulmcdonough43628]

Thank you Clive

[SillyOldDufferModerator @sillyoldduffer]

There’s a bit more to it than heating red hot and dunking it in water.

Ideally the steel is heated to the right temperature and held steady at it for about 5 minutes per 1/4″ of thickness of metal.   Holding steady is important, and so is not overheating thin sections.

Conventionally we are asked to heat the metal ‘Cherry Red’, but it’s unclear what that means.  Back when Stubbs Steel was invented, it probably meant dull red – the colour of the fruit skin in a dim workshop, not the much hotter glace red colour.

Stubmandrel, (aka Neil Wyatt) recommends using a magnet to get the right temperature.  I recommend his wise words on the subject.

Dave

[Neil LickfoldParticipant @neillickfold44316]

There is 2 types of Silver steel.

One grade is also called W1 steel. It  is a Water Quench oil. The original Stubbs Silver steel was a W1 steel.

The other grade is O1. O1 steel is an Oil quench steel. Most Gauge plate is O1 grade and there is centreless ground O1 steel bar. Quenching O1 in water will crack the steel if it was at the correct heat before quenching. The magnetic trick works very well for most steels.

When correctly tempered, the steel will be the same size as it was before heat treatment. Temper for 150C a few times and it will retain it’s hardness, but not be as brittle, and will be the same size as before heat treatment. The size change is about 0.04mm per 25mm of section after the hardening part of  the heat treatment.

[JasonBModerator @jasonb]

Well I’m of the simple approach, heat to a cherry red with blow torch no heat treat oven  for me, quench in water and use. Not noticed any of my cocks leaking and my form tools cut the shapes I want.

Not heard of the size change particularly reducing when tempered but is that before or after cleaning off the oxide so you can see the colour change? as that may take the part back to original size.

Water quenched gauge plate untempered cutting brass OK and then modified the shape and it cuts steel too.

 

 

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