This all started a bit back when I saw the post by Andy here
http://madmodder.net/index.php?topic=1276.msg23777#msg23777From an original idea by Mike Cox.
I will be using his great idea and putting a few of my own mods onto it.
It has been nagging at the back of my mind since, and if I could get it to work satisfactorily, I think I will be happy having a tooling holder that will do just external threads, as internal threads are so few and far between, I can easily cope with the normal methods of doing them.
Having picked up on a few pointers, like John Stevenson's issue of being able to get close enough to the chuck, I think I have a design in my head that will work and allay a few fears in that department.
This would have been posted last night, if I hadn't had a late night gumbeating with Darren on Skype. How time flies.
Just a warning, I have nothing down on paper for this one, as I am designing and making as I go along, so please don't ask for sketches just yet. I will be showing how it progresses gradually from raw materials to hopefully a fully operational bit of tooling, warts and all.
I make no excuses about using the tooling I have, at times like this, I use whatever is available to me. If you ain't got it, you ain't got it, full stop, no arguments.
So belt and braces on, hitch up your pants, away we go.
A quickie order to Chronos (if you could ever say Chronos was quick) had a couple of cheapo 10mm square brazed tip threading tools in my grubby claws.
http://www.chronos.ltd.uk/acatalog/TWINW_PACKS_OF_BRAZED_TCT_THREADING_TOOLS.htmlI have thought ahead a bit on this part, and almost any shape or size of threading tooling can be used with a slight mod. More on that later.
The next bit was a toolholder for me to copy from, and a lump of cast steel that was originally cut up for making the retracting toolpost out of. The square is there just for checking things out with. I have a set of engineers squares specifically for bench only use, and others that are used around the machines, they are so cheap, it pays to do this sort of thing, a 'best' set, and general working ones.

The very first thing I do is check my machines out, it only takes a few minutes, and it saves you chasing your own tail feathers trying to get things square and flat.
Set up the tramming tool first. The collet is loose, and I made sure I had double zero on pressing against the table top.
Making a tramming tool is here.
http://madmodder.net/index.php?topic=822.0
Lock the tool into the collet and take a reading, as you can easily see, it is a little out (BTW these are metric dials, so those using imperial, this reading would look a little on the high side. This is about 0.006" in imperial money). It is dead easy to knock the tram out on your machine, even one as heavy as mine. So it always pays to check before starting an important project.

A couple of minutes later, the tram was back to spot on.

Next, the vice was checked for being square to the table run.
Ready to go.

First job was to flatten and square up the block on all faces.
I tried to use my preferred method, the flycutter, but it was struggling getting into the metal.

Then tried it with some coolant, no joy, it was still not happy.

So out came the heavy brigade, and that went thru it as though it didn't exist.

The ends needed to be squared up next. The cutter wasn't long enough to do the whole face in one go.
So I went as deep as I could, as long as it went some way past centre. The block was then flipped over and the backstop set onto the centre of the material, onto the freshly cut face.
It was then a matter of doing a cut across, rotating the bar around the x axis and skimming off the uncut bit. Then flip the block over and do the same to the other end.

The block was soon square and flat on all points of the compass.
I haven't measured up the block, as long as it is somewhere near to what I want, it can be fine tuned to size later.
I now needed to get the dovetail in so that it can be mounted to the toolpost.

I did a quickie measure up of the original, and marked up roughly where I wanted the mounting to be. As you can see, it isn't central to the block. You will see why later.

The area that I marked up is where the piston on the toolpost operates, and is on a different level to where the dovetail goes, so this depth is rather important.
The marked up area was cut away until the 'lines were split'.

The depth was then finely cut down to a certain figure.

Which just so happened to be the same as the original holder.
If you go too far astray on the depth, you can find that you can have trouble getting the holder locked on tight to the toolpost, especially if you go a little too deep. The critical part is the distance between each dovetail face, and I will be showing that sometime soon.

It is now time to break out the secret weapon.
I bought this 60 degree HSS dovetail cutter over 20 years ago, to make a new topslide for a small Myford, from the same chappie I get my specialist cheapo tooling at the shows nowadays. It has cut many dozens of dovetails since, it is the best 5 squid I have ever spent on a cutting tool.
Isn't it funny how you can easily get attached to a favourite bit of kit. I have brand new ones waiting in the wings if ever this one decides to retire, but it will still be used until it decides to do so.
The cutter was 'touched on' the bottom face, then lifted 0.020" upwards. This is to allow the correct working of a dovetailed slot.

They make a funny 'rattling' noise as they cut, and you can soon pick up when it needs to have the cut reduced and/or a squirt of oil.
There is a bit of a secret to using dovetail cutters, you start off with a fairly deep cut, in my case about 0.025" @ 800 RPM and as the cuts gradually work their way up the cutting edge, so I gradually reduce the load on the cutter by adjusting the depth of cut and speed. The last cut I took was 0.005" @ 500 RPM. Of course those figures were my own for this size of dovetail and material type. On brass or ali, the speeds would be higher and the depths deeper.

So that is as far as I got last night.
If I don't overstay my power nap this afternoon, I will see if I can get a bit more done later.
Bogs