Swingup external threading tool

[bogstandard]

This all started a bit back when I saw the post by Andy here

http://madmodder.net/index.php?topic=1276.msg23777#msg23777

From 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.html

I 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

[Darren]

Very nice start .... as usual ... and comprehensive with all the links 

That reminds me .... off to the shed I go ... later 

[NickG]

Nice start John. This will be interesting and provide me some pointers if I do a QCTP. Gone are the days when I get £100 christmas persents like that so I think I will have to make one.

What is the purpose of the 20 thou relief again?

Nick

[bogstandard]

The dovetails don't need to be in full contact across the bottom face as it would just be too much friction, so by relieving the area and only having it running on the smaller outside face areas, friction is dramatically reduced.

If you look at the dovetails on your machines, you should see the same effect being used.

You can do the same thing by putting a recess in the middle of the male dovetail instead of the female.


John

[NickG]

Oh right, I see. Thanks.

[andyf]

As I said in the post to which you linked, Bogs, the idea is not mine. Credit where credit is due, which is to Mike Cox. By coincidence, he has an article in this month's Model Engineers' Workshop describing a nice way of securing his Norman-style toolpost so he can fit two tools into each block rather than just one.

Andy

[bogstandard]

Thanks for that Andy, I always try to give the due recognition that they deserve for their hard work, as you will see in a lot of my posts. Unfortunately, by what you showed, I didn't know from whom it had originated from, and in a few minutes time, the above post will be changed to give all due recognition.

One thing I really hate is people using others ideas and making out they are their own.

It is for that reason I have gone to watermarking my pics, I know it is only very basic security, but the number of sites I have been to that use them without any recognition or permission at all astounds me.

I did get my own back on one chappie on the HMEM site that basically had almost a complete article of mine on his site about my making of an own design turbine. I deleted the youtube vids to all the links he gave. The article as far as I know is still there with no vids.

Only last week a member on here asked for permission to use my Paddleducks book on his site. No problems at all, as long as no one makes money out of it.

Thanks again

John

[andyf]

Entirely agree, Bogs. Even when people have put their ideas their ideas into the public domain, as Mike Cox did with this one on the 7x12 Mini-lathe Yahoo Group along with pics of his finished product, it's only fair that proper attributions should be given. Once you have finished the device, I'll invite him to view this thread, provided your report on how well it works is  and not 

Andy

[geroli]

Nice work Bogs

Cant wait to see where your taking this one.

Gerhard

[bogstandard]

I got overpowered by heavy eyelids yesterday, so I had a fairly good session today.

I would just like to point out that because I work in both metric and imperial all the time, you will most probably notice that I will be swapping and changing between the two, and will be talking measurements in either. This is just the way I work when I am winging it, and if I pick up an imperial mic, that will be used, even though I am might be cutting in metric at the time. At the very end, when it is all finished, then we can measure up in one or the other.

So lets get on, work to do.

I left it last time with just one side cut, so the first thing that I did was to cut the other side to the same sideways penetration as the other. I am still a way off having the correct width for the dovetail, and because I am copying a known good one, it makes it dead easy, because you can just cut to the right width and guarantee it will fit, whereas normally, you will have to keep trying it onto the male dovetail.




So, what is the right width, and how do you measure it.
I grab a couple of small bars of round stock, as long as they touch both side and bottom of the cut dovetail, then it will do.




Pop them into the original like shown, and measure the distance between the two. Write it down on a bit of paper.




Then do the same with the one that is being machined. Write it down, underneath the reading you wrote down before.




Subtract the lower from the upper and divide the result in two. That will be how much you machine out from each side.




Job done.




Before taking it off the mill, I decided to chamfer all the square edges. This is a true 45 deg milling cutter, not a countersink, which you could use, but this gives much faster and better results.




As I said, it will fit and lock on if you get your measuring and machining right.




So that piece can be put to one side for now, and a start made on the toolholder swinging bit.




Mark out what I want to do with it, but the maching will all be done from datum points, not the markings, they are there as a safety precaution.




The first job was to cut out the tool recess.




Then drill out the pivot hole to 10mm.




Now because this hole has been drilled from this side, I need to make a datum that is perfectly square to the hole, so I took a very shallow cut across the face with a flycutter.




Now when it was turned over and put onto parallels, after this side is reduced down to the thickness I want, the hole will also be perfectly square to this face as well.




This is it after the thicknessing exercise. You can start to see what I am doing.




The holder was marked up again, and was given a bit of profiling.




Not quite there, but you can see how it will fit onto the block.
You might ask why the pivot point has been dropped to lower than the centreline of the cutter.
Anyone who has dealt with swept wing aircraft will understand what is called wingtip growth, where when it turns going forwards, because of the chord length of the wing, the tip starts to protrude further out.
It is the same effect on this, by putting the pivot point as low as possible in relation to the tip, when the tip rises, it will in fact make the tip retract from the job slightly, whereas if higher than the tip, the tip would move towards the job. Only tiny amounts, but everything helps in situations like this.



I gave up at that, I was hurting a little bit too much, so if all goes well, I will get back to it tomorrow.
Besides, I dropped the damned drill chuck when taking it out of the quill onto my little finger, and it is time I went to get a bit of pampering.

Bogs

[spuddevans]

I'm following this with keen interest as i do most of my threading on the lathe by single pointing. This is yet another item that is added to an ever growing list of mods to be made to my lathe.

oh well, better to have plenty to do than to stand in the workshop wondering what to do.

Tim

[bogstandard]

Tim,

Don't be too hopeful, this is experimental, using a few known tricks that I know work. In theory it should work just fine, in practice, things can have a totally different outcome.

It is later, when I get to the very fine tuning that problems sometimes occur.

If it does work, then there are maybe thousands of newbies out there where it could help to solve their problems and make it easier for them to screwcut, if it doesn't, back to the drawing board.


John

[bogstandard]

Only a very short post today.

I decided that I needed to get the main block cut out to see where I need to hack away at to give me clearance and access to the bits.

The first job was to get the main channel cut out.
Using tungsten cutters, this material just gets swept away, and very little heat is generated, so no suds needed, and unlike cast iron, you don't get dirty.




Once the main cutout had been done, I reduced what was left of the main block down to the thickness I wanted.




The main block heavy machining is now basically finished, it just needs lots of holes drilling in it now.




This is how the swinging bit will fit in.
The small thin file in there is to let me see what gaps I have to play with. The only point that the swing fitting will be in main contact with the block is at the back pivot point. The three lower faces, bottom and two sides will be controlled with limit screws, and by doing it that way, should allow the tool to be used for both right and left hand threading, as all cutting pressures will be taken by them rather than the pivot when in the cutting stage.
It also means that by supporting the swing part away from the main block, it shouldn't jam up or get put out of cutting alignment if a tiny bit of swarf gets in there.





Bogs

[chuck foster]

looking good bogs.................i like to see tools being produced in the home shop. 

chuck 

[Darren]

You do get a good finish on that mill John