watchmaking

I am a bit new to watchmaker's lathe tools. Is parting off done the same as larger lathes or is there a special tool. I have a conventional top and cross slide fitted to the lathe at the moment with a 'lantern' toolpost and it is quite difficult to set the tool at exactly dead centre. Its fun turning down to 0.1mm - Change from the Boxford .
BobH

I'm not sure Bob but I once bought a Boley of some crooks in London and one muttered at levels he didn't expect me to hear that he would love to see my face when I tried to part off with it. Little did they know that it has adjustable bearings - slight taper on the spindle so has to be set in precisely. Going on that with slides a rather fine parting off tool but I believe a simple pointed tool is used at times. I'll be interested in any other answers.

I have the tool height problem on my Pultra but indexed 4 way tool posts and I don't like using packing. I have used a different type of tool holder on rather large lathes. A holder with a square hole drifted into it at an angle to suite back rake. It struck me that the same thing on lighter lathes could be done with a block with a slot to suite the tool bits milled at an angle in the side. The slot has to be positioned so that the tool tips stick out a sensible distance when on centre. Fine adjustment is made my moving them in and out. The angle saves weakening the tool by grinding on back rake which is often a pain to do while keeping the cutting angle as wanted.

I also came across an interesting tool height gauge. Face of a length of bar. Place it in the cross slide and scribe a line round it with one of the centres. Face that end until the scribed line is split to just remove. Then set height by touch - should be sensitive to microns,

I also needed some decent 3/16 or 4mm toolbits. Cromwell have some in their clearance section. They also list 5% cobalt HSS bits. I could only find M2 on Ebay and that needs real care even when grinding.

John

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Just pare it down with a hand graver and break off the final few thou - see the end of this

Bazyl - interesting video clip. John, yes I bought 3 of those 2mm pieces of HSS, will make good gravers I thought.

BobH

The linked video appears to be 'Maurice' from the South London Branch BHI. If anyone is near the South London area (well, J6 of M25) then you can meet people like Maurice, at every monthly meeting, who I'm sure would be keen to help. There will be an 'open day' in Caterham on 9th April 2016 where things like parting off on a watchmakers lathe should be demonstrated. Not much help now, but worth remembering the date. I'll try and remember to remind people closer to the date

I assumed you meant slide rest tools Bob. I have had a passing interest in watch clock work done that way. Parting off tools look just like the usual type and there is another type where on side is flat and the other slopes back forming a sharp point. There is a google book that can be viewed on the web.

M2 should be ok providing it's not over heated when grinding - the video mentions wet grinding but I suspect we have all used that on an ordinary grinder without tempering it. I've ground silver steel d bits without tempering them further. I wanted the cobalt HSS bits for slide rest tools and larger diameters than typical watch / clock sizes. Due to the once and maybe still use of tool steels for gravers I don't think that the surface speeds are that high really otherwise this type of tool would blunt very quickly. Some years ago there was some argument about even carbide reaching the same level of sharpness as tool steels can.

Nosing around - old book on the internet archive - it reckons tools can be given a high surface hardness by quenching in a KOH solution. It suggests keeping quenching liquid in a glass stoppered bottle which I would assume had a narrowish neck - no one would want to get hot KOH on their skin. It even has problems when cold - sort of soapy feeling due to it slowly detaching skin cells.

John

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John

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