Author Topic: Swing Up External Threading Tool  (Read 23567 times)


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Swing Up External Threading Tool
« on: October 20, 2012, 06:15:55 PM »
This article is a very abridged version of the development of the first to be shown on the web, a fully operational swing - up tool holder. Many have come later, and in fact, at the very end of this article, there is a sketch to give you an idea how to make a much easier one than I have done. Mine was a wing it job from the very beginning, to prove the concept.

You might find references to other people in this text, don't worry about it, they are references to people who assisted by giving an idea on how to get over a problem.

Before going any further, this toolholder is designed to be used on a machine where the spindle can easily be reversed, and don't worry if you only have a screw on chuck, the forces involved in thread cutting should never be high enough to unscrew your chuck when going in reverse.


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

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.

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.

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.,416.0.html

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.

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 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.

I am struggling at the moment trying to fulfill the two comments criteria placed upon the retracting toolpost and this swing type, namely to be able to cut left hand threads (swing), and the most difficult one, by John Stevenson, to get the cutting tool close enough to the chuck without the holder hitting (retracting). The left hand threading is easy, unfortunately, the easy fix for that compromises the getting close problem.
I will have to see just how much material I can cut away to achieve it, and still retain enough rigidity in the tool. Luckily, single point threading, if done correctly, doesn't require massive cutting loads.

A couple of my rules to making things, what isn't there, can't go wrong, and always try to make things as simple as possible, life is complicated enough as it is.

As was mentioned before, this isn't my idea, but a follow on from a suggestion, and I am sure, if I can get it to it's simplest state, and working correctly, I think we will both be very happy chappies.

I hope that my ramblings help a few people along the way.

We seem to be a bit of a dying breed, with all the latest technology coming along and taking most of the 'hands on' enjoyment out of it, so we need all the help we can get.

Because I am going down the route of a fully machined up tool holder, I have caused myself a problem for access to one area I need to cut a slot into. If you made a much simpler version than this, say with an 'L' shaped backplate, then you would be able to get a normal cutter in.

I had to use a woodruff cutter to solve my problem, so I made a few quick calculations.

Then set to work.

In no time, I had the two slots that I needed.

This is how the two slots lined up.

The uppy downy bit then got a dose of reshaping.
You will notice that I have gaps all over the place with this tool, and I have mentioned this before. This tooling will be working in a swarf producing environment, and unlike normal fixed tool holders, where it wouldn't cause a problem, because this tool is moving, swarf could get in and disrupt the nose setting of the tool and cause major cutting problems. These gaps are to try to give somewhere for the swarf to settle into without affecting the correct operation of the tool.

A quickie calculation gave me the size of block that will be required to give me the gaps I want.

I had certain scoffs when I first mentioned that I used a mini vice, but for jobs like this, they are indispensible. I was able to hold the small component very accurately while I swung the big cutter around, hacking the block down to size.

The block was machined to thickness so that it was a tight fit going into the swingy bit.

The block was then cut to the correct outside dimensions and I got out my secret weapon. A piece of what must be ten year old very worn out fine W&D paper. The block side face was then gently rubbed on it until it fit perfectly into the swing holder slot, with no side play but a nice smooth sliding fit. It took only a couple of minutes to achieve that state

It was then loctited into the main holder.

So very close to being finished. A bit of lathework, a few holes to drill and tap and it will be ready for first trials.
Another point of interest is that the swing block protrudes slightly in front of the main block. This is another one of my attempts to keep swarf out of the operating bits.

The first thing was to get the holes drilled and tapped. I located the swing arm onto the little block and clamped it down onto the block top face, then the pivot position was drilled and threaded. The other holes were just for tool clamping screws and the height adjustment for the main block.

A pair of phos bronze flanged bushes were made up and reamed 8mm. They had flange thicknesses that were in line with the gaps required and the position of the block. I also knocked up a stepped pivot bolt. I made the length so that when it was fully tightened down, the swing arm still had a few thou side to side play only at the pivot point, there was no rock at all at the cutter tip. If this play causes a problem, the bolt shoulders can easily be adjusted to snug things up a little.

A bit of threaded rod and a height adjusting knob were easily knocked up.

These are all the bits now assembled, and the tool completely finished. I had to fine tune the block a tiny bit as it was still a little tight, by removing a few tenths and a dab of oil on the block and pivot, the swing arm now easily rattles up and down, and no sign of side play at all. I'm very happy with the results and how well it went together.

This is now set up for correct height on my machine.

I had set everything up as I would normally set up for threading, using the normal offset method. I set the lathe to cut a 2mm pitch.
A lump of 1" nylon bar was used for the first cuts, if something was going to go drastically wrong, I didn't want my tipped cutting tool damaged.
Everything worked exactly as planned, it cut the thread perfectly and when the lathe was flipped into reverse, the tooltip lifted, wound back to off the job and duly dropped down into the cutting position again. I carried on for a few more cuts, and nothing changed, it behaved perfectly.
This now gave me a little more confidence in what I was doing, so then I thought that it was time to give it a good try out.

Raiding my steel recycle box, I came up with some of the worst crap to thread, a length of 7/8" diameter steel conduit. This stuff is made from the dregs of the steel world. I was expecting major problems.

So after mounting it up, it was threaded the same way as I had done the nylon, with exactly the same results, except that the finished threads were real rough, but I had expected that because of the material, it is no better when you thread it up with a die when fitting it up in a factory.
There was no chatter, jumping or farting, in fact nothing out of the ordinary, except it only took me a fraction of the time it would normally take.

So after a quickie switchover, I swapped it to 5mm pitch, and carried out the same exercise on the other end of the pipe. I couldn't go any deeper otherwise I would have been thru the tube wall.


This is getting monotonous, exactly the same as before.

Conclusions after this very short trial.

This really wasn't a full trial, but an initial proving run. Until smaller threads are cut then a final conclusion cannot be forecast, but if it goes like these three have gone, it should mean that this concept is definitely a winner, and could be designed to be made much simpler.

I found that when using it, I sat on my stool, with one foot on the brake and one hand on the fwds/rev lever. It was so simple to do, put on cut using topslide, start the machine fwds, stop when at end of cut, flip machine into reverse, run off the end of job then stop, repeat process. In fact it is easier than trying to use the drop in dial, no waiting about or counting. So for me, I will use this method all the time, rather than mucking about with other settings.

I have now to make a camera mount to video the process and to prove the concept on other materials and sizes.

BTW, after seeing how the swarf behaved, I don't think that will be a problem at this time.

I managed to find a lump of 2.5" brass that I could cut a thread on. So away I went and cut a 5mm pitch on it, which is near enough to a 5 tpi thread for comparison. The holder I have made caused a problem in that the top overhang wouldn't allow the tool to come up high enough for really large threads, but that is a problem that can easily be overcome. But with a little coaxing we got it done. Other than that, the cutting action couldn't be faulted, it just went ahead and did it, just as planned.

And for all you video nuts, this is as much as it would record each time, so this will have to do you until I can work out what is wrong with the camera settings. But at least it shows the full cutting and retraction action, just.

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Stew can be my independant witness that the tool really does work (otherwise he doesn't get the free beer at Christmas).

I would just like to thank Mike Cox again for the inspiration to get me to do a bit of R&D on his concept. This has definitely been one of the easiest projects I have ever worked on to get good results so fast. Usually it takes a lot more thinking power. But of course, the clincher was when John came up with the block idea, it got me past the mental blockage that I had. So the glory is nowhere near all my own, but other peoples' inputs and ideas as well.

If it does go on to really prove itself, I honestly think it will transform the way I personally do threading. But that isn't the main reason. Looking at it, and the quickie sketch I did earlier about a much easier design, it could make single point threading much easier for the people who have been scared to try it out before now. This method certainly makes threading at least 50% easier and quicker. It is a shame it can only be used on a lathe with full reverse on it.

In fact, I think a piece of 2" side by 1/4" or 3/8" thick angle iron would be perfect for the main frame.

So now we come to the final part of this R&D exercise. I made up a very complicated camera mount for my machine, it took me ages, about 15 mins of real hard work.

Grabbed a bit of ali from the recycle box (this was a piece from my original slide for the tailstock mounted DRO head).
Two holes drilled, the end one tapped.

Screwed onto the mag base.

Then the camera was screwed onto the assembly.

By doing that, it allowed me to make this vid, all by myself.
I was talking to Stew yesterday about working while other people are in your personal shop space, and nothing ever seems to go right.
This time, no problems, except you will see at the very end of the vid, I ran out of memory on the camera card.
Before anyone comments, I should have swung the topslide the other way for left hand threading, but for this proving job, I left it as it was, set for right hand threading.

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Just to prove I was cutting a 40 tpi thread on that bit of 3/32" (about 2.5mm) brass bar, here is a close up.

Well that seems to be the end of this little exercise. The tool cuts both left and right hand, and John's worry about getting close to the chuck is now no longer a worry.

I honestly don't think that swarf will be an issue. Just keep an eye on it, and if any does get in there, it is dead easy to blow or brush it out.

I was going to make another toolholder, based on the design on my sketch, but because I want to get onto other things, I don't think I ever will. This one will do me just fine for 99% of all the external threading I will be doing, and if I come across something it won't do, then I will just do it the old fashioned way.

I hope you have enjoyed this journey on how I get around to and do things. With plenty of forwards thinking and problem solving, and a little help from friends, you can achieve almost anything.

I do hope that a few of you will be spurred on to make the easier version of this tool, I am sure you won't regret it.

Just to prove I am not all hot air, and that I do use the bits I make, I had a chance to try this out today.

Here is the job ready prepared for threading

Thread cut

Chuck tried and fitted perfectly

The last bit for my interchangeable tooling, a 5c to Myford adapter to fit the spindexer.

I can honestly say that it was the easiest bit of single point threading I have ever done.

As a final act, I have done another rough sketch on how to put one of these together.

There are no dimensions shown as you can make it as large or as small as you want it to be. I am sure the members on here can cope with something like that. The things not shown are the pivot point bits. If you drill a plain hole to use, then a washer will be required between the swing up and the main body. If you fit bushes, as I have done, then the top hat flange will give the stand off required. You should make the step bolt to give a couple of thou side to side clearance. I would suggest giving the locating block a small chamfer on each of the top edges, to assist the tool in relocating itself if it has been completely lifted off the block as it was being retracted to the start.

Get in there and enjoy your screwing.


Offline smfr

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Re: Swing Up External Threading Tool
« Reply #1 on: October 20, 2012, 07:04:15 PM »
Thanks John, that's a great writeup to make what looks like a very handy tool!


Offline zeeprogrammer

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Re: Swing Up External Threading Tool
« Reply #2 on: October 20, 2012, 08:21:04 PM »
Very interesting John. A lot of work in posting...thanks. Also appreciated the videos. Very helpful.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Zee-Another Thread Trasher.


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Re: Swing Up External Threading Tool
« Reply #3 on: October 20, 2012, 09:07:57 PM »
Thanks for doing this John, you've come up trumps again. I'm sure many folks are going to find this very useful.



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Re: Swing Up External Threading Tool
« Reply #4 on: October 20, 2012, 09:46:19 PM »
Sorry it was all one long post, but the original was 6 pages long and it was easier for me to do it this way.

As I tried to explain, mine is too complicated for what it has to do, and if you follow the C-o-C at the end, you should easily be able to knock one up. But one thing you mustn't leave out is the small locating block at the front, it is that which takes the side loads associated with the cutting, stopping any loads reaching the rear pivot point.

John Stevenson actually uses the dies out of a die head for his, instead of a single point tool, and I will be doing the same thing some time in the future, as he says it does a perfect job, acting just like a thread chaser. I managed to get a full set of Imperial and metric for 10 pounds, and all I have to do is make up a swing up holder for them.
They will then give me the correct profile to the threads as well, with rounded tips and roots.


Offline tel

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Re: Swing Up External Threading Tool
« Reply #5 on: October 20, 2012, 09:56:13 PM »
Glad to see you put it up here John, as you know, that tool has my seal of approval - a wonderful bit of kit!
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Offline Don1966

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Re: Swing Up External Threading Tool
« Reply #6 on: October 20, 2012, 10:53:25 PM »
Just finished reading your thread John, great work as usual. It was a very educational thread and I thoroughly enjoyed reading it. Also a very useful tool to boot. Thanks John for all of your efforts and time. You are an inspiration to all.   



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Re: Swing Up External Threading Tool
« Reply #7 on: October 20, 2012, 11:42:28 PM »
John, do you think you could use a pin instead of a block as a location device? Just thinking it would be easier to drill through both parts once assembled. If tapering a pin is not suitable them maybe a (parallel) pin and slot.

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Re: Swing Up External Threading Tool
« Reply #8 on: October 20, 2012, 11:59:49 PM »
Well done John!   glad to see this one again!

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Offline bp

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Re: Swing Up External Threading Tool
« Reply #9 on: October 21, 2012, 01:24:33 AM »
This is really good John, I made a swing up doofa earlier this year, and was intending to make it integral with the toolholder, to suit my pillar style QCTP.  In the end I didn't have the right size bit of material, so I made it to fit in an existing toolholder, which is a shame as there isn't a lot of spare space on a mini lathe!! 
Arbalest ... I used a vertical 5mm diameter dowel pin in the swinging part of mine, this engages beautifully with a slot.


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Re: Swing Up External Threading Tool
« Reply #10 on: October 21, 2012, 07:35:08 AM »

As BP has said, it can be made with a pin, but NOT tapered.

If you used a tapered one, you risk having the swing up bit ride up the taper when side cutting loads are added.

The pin really does need to be a fairly good side to side fit, as it is that which takes the cutting loads, not the pivot pin at the rear.


Offline bp

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Re: Swing Up External Threading Tool
« Reply #11 on: October 22, 2012, 12:20:06 AM »
Again John Bogs is spot on.  I lined the moving part and stationary part up, then clamped the two, drilled hole for pin, then reamed said hole.  Fitted the pin to moving part with Loctite, turned the hole in the stationary part into a slot so that the pin could just engage the slot and accurately locate in the reamed part of the hole.
I also put a lifting handle at the operator side of the moving bit.  The swing up function works beautifully, but a lot of the threads I cut are very fine (0.5mm pitch or finer) in Al Alloy, so this "lifting handle" prevents any damage.  If I can persuade The Boss I'll see if I can post a picture or two.


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Re: Swing Up External Threading Tool
« Reply #12 on: October 22, 2012, 08:12:47 AM »

You are doing the right thing, making something that suits your needs, but still retaining the original specs for working correctly. That is the correct way to do things

I made mine grossly over complicated and ended up where I couldn't lift the tool completely away, so I have to back the tool way past the end of the job just so that I can check for fit with a nut.

So even the designer has lapses at times.


Offline Peewee

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Re: Swing Up External Threading Tool
« Reply #13 on: October 22, 2012, 01:17:57 PM »
Great little tool holder.  it was one of those posts where i was reading it all through thinking WHY and then i watched the video and it suddenly made total sense.  definatly on the tools to do list.

Still sane?  definitely not but enjoying life more