Swingup external threading tool

[andyf]

I'm due for a shearing, too, Bogs. Seems to grow faster in winter - must be an evolutionary hangover from a furry Ice Age past. Mustn't complain; at least I get my money's worth at the barber's shop. And he's taken up my suggestion of substituting grey smocks for the dark blue ones against which the cuttings looked so depressingly grey    Now, the silver hairs don't show up and I can take comfort from the remaining mouse-coloured trimmings 

I suppose the simple answer to my misgivings over the tenon is to try it. If it stops the thing working smoothly, just loosen the Loctite with heat, yank it out and see if the device works without it for RH threads only.  I like the idea of the swarf gaps; apart from the swarf problem, they will reduce the contact area, and hence friction, between the parts when they move in relaion to each other.

Next instalment is eagerly awaited.

Andy

PS Might a hairpin-shaped light spring, located with a loop round the pivot, give more positive swing-down?
 

[bogstandard]

Andy,

That was the reason I left the top part on the main channel, if I couldn't get it to go down under gravity, I was going to drill a small hole in the swing block and pop a spring in there.

I seem to have answers for everything anyone comes up with, but what you don't realise, this had been fermenting in my head for over a week, and I had already looked at the thing from most angles. John's suggestion was the one that I hope will get this thing to a finished working tool, and that was the area I was stalling on.

Have a look at the C-o-C, that is now what I envisage a finished, easy to fabricate one would look like. A few easily made bolt together bits with a tiny bit of fine tuning on the block. Nowhere near as complicated as the one I have made. This would also allow for a complete swing away of the threading tool, for measuring the thread with a nut.

Mine had to be made as it was to cater for all known problems that I thought might crop up. It is always invariably the same, the prototype is always more complicated than the finished product.


John

I would just like to add, after all this work, it is still very similar to the original concept by Mike Cox, except for the block, moved pivot point and clearances for swarf.

[John Stevenson]

Devils advocate here 

The swarf gap worries me, if there is a gap then small stuff will be OK as that what it;s designed for but what happens when it comes across thicker swarf?
Some may start to enter then wedge.

Most swarf will enter from the front, what about pushing an O ring over the end of the rocking holder to seal the gaps but still have them ?

John S.

[jim]

just a thought on the swarf, wouldn't it be possible to put a rubber "skirt" around the tool?

i look forward to seeing the end result

[bogstandard]

John,

I already have this in hand if needed. I was going to use a very thin bit of litho plate on the front and side of the tooling with just the threading tool poking it's nose thru. In fact on the trials to come, I was going to stick double sided tape to the outside of the temporary plate to see just where the swarf would be causing a problem, by seeing where it ended up when it stuck to the tape.

Talk about R&D, no flies on me on this one. It all might not be necessary, and the tool stays perfectly clean, but every angle has to be explored initially.


John

[andyf]

How about a thin metal shield, as C-o-C below, attached to the swinging part at points X, and covering the top and front of both the swinging and fixed parts? The top and front of the swingy bit would each need to stand slightly proud of the top and front of the fixed part, and swarf might still get in if the top of the shield had to be narrow so as not to foul the toolpost dovetail and any height adjuster on the fixed part.

Andy

[bogstandard]

Andy,

That is the sort of idea I mentioned.

At the moment, I have to get back into the shop and finish it off, and a shield will only be considered now after I see what is going to happen during the try out.

I don't want things to get too clouded by 'maybe' problems.


John

[bogstandard]

I didn't manage to get into the shop until this evening, so I rushed thru everything, then took some piccy's of what I had made.

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 just didn't have time tonight to get a trial done, and from very early tomorrow morning, I have personal things to do that will leave me incapacitated for a couple of days, so I am sorry, you will have to wait a little longer. I would like to do a vid of the results if they are satisfactory, unfortunately I don't have a camera mount for my machinery yet (another tuit), so you will have to take my word for it.


Bogs.

[andyf]

Looks terrific, Bogs 

It'll be interesting to see how well it works, once circumstances permit.

Andy

[mklotz]

I'm sorry, John, but I'm having an attack of the stupids here.

It looks to me like the tool can only swing up only a tiny amount - a degree or two.  Is that enough to clear a thread while you wind the carriage to the right?  Do you swing it up with your finger - there doesn't seem to be a handle in sight?

Do a befuddled colonial a favor and snap a few pics of it being retracted and/or provide a few words about how it's used in anger.

BTW, it looks stunning.  I wouldn't bother you with these questions but Santa is bringing me a QCTP and I'd love to make one of these assuming I can understand its operation.

[bogstandard]

Not 'stupids' at all Marv. It took a little bit to get my head around it.

The only problem is that it will only work on a machine where you can reverse the the whole machine including rotation of the chuck.

Just to explain basically how it SHOULD work.

There is no manual retracting of the cutter at all.

As you know, under certain conditions, you have to leave the leadscrew engaged when cutting threads, on my machine, whenever I cut Imperial threads. When you cannot use the drop in dial.

You take a threading cut as normal, when you reach the end where you usually retract the tool with the cross slide, you don't retract, you just put the machine into reverse, to take the tool back to the beginning. As the tool starts to go back along the thread just cut, because the chuck is running in reverse, the tip of the tool is lifted by the non cutting action. It should only be a few thou lift, that bit has to be tried out yet.

When it reaches the start point again, the tip should automatically drop to the cutting position, so another cut is put on with the compound and run in the normal way. It should work for cutting both right and left hand threads.

If it works, it saves having to retract the tool, and then reset it to zero each time. It does away completely with that part of the cutting regime.

Not a very good explanation Marv, but I hope it strikes a light.

All we need now is to see the work wasn't all in vain. If it doesn't work, shrug shoulders, at least we tried.


John

[Darren]

Like Marv I was wonderin' 

But I gedit now  Ain't that clever thinking Mr B ... 


Fingers crossed it don't chatter during cutting, I surely hope not cos I'd like to copy that little marvel .... 

[mklotz]

Thanks a heap, Bogs.

I've got it now.  My confusion arose because I was thinking of more traditional threading using the threading dial - put on a cut, disengage half nuts, lift tool to run carriage back without retracting cross slide, put in more cut on compound, drop tool, wait for threading dial, reengage half nuts and make another cut.

Now that I see you're moving the carriage to the right under power to avoid losing sync, it's all pretty obvious.

Very ingenious.  I hope it all works under fire.

[NickG]

Looks great John and should work fine - I get it too now! 

Nick

[Divided he ad]

I've just read through all this.... Still playing catch up 



Nice looking tooling there John..... You said it was high on the list...... All confidence in the testing when you get to it 





Ralph.

[sbwhart]

Penny dropped now John 

Great work

Stew

[Stilldrillin]

"I can see clearly now the rain has gone"....... 

Gotcher..... Now! 

Great work John.

David D

[Bernd]

Like Marv, I had the same question as to how exactly it was supposed to function.

What hasn't been mentioned is the backlash or gear wind up in the gearing system of the lathe. When reversing the lathe wouldn't there be a delay from the time that chuck starts to spin backwards to the time the lead screw starts moving the carriage backwards? Seems to me the tool would be cutting the backside of the thread you just cut or even maybe cut the thread in half depending on the gear train backlash.

To me it would see that if there was "0" backlash through the whole gear train a swingup threading tool wouldn't be needed.

Perhaps Marv is right in his assumption that the tool should be lifed clear of the work altogether!

Bernd

[Darren]

Bernd, I believe because the tool can lift then there will be no pressure to do any cutting (even with the back edge) The tool should simply ride the waves.

[NickG]

Bernd,

Good point about the backlash, I've wondered that too but I think as Darren says it will just ride up the thread a little and it's going in reverse so there isn't a cutting edge on the work. Might put minor marks on it but doubt it the pressure will be so light it would just be like a nut going up the thread.

Nick

[bogstandard]

If you had read and inwardly digested my basic description on how it should work, you should have realised that the chuck is running in reverse.

So how could it cut with the metal being turned away from the cutting edge?

Rather than destoying the concept and jumping to conclusions before proven, wait for the results.

Only then should suggestions and criticisms be brought forwards.


Bogs

[andyf]

To my mind, the best way to think of it is that it works like a simple hinged clapper box on a shaper. It lets the tool skid over the surface when the spindle is reversed to run the carriage back, just as the shaper tool does on the return stroke. At least, that's what it's supposed to do - I'll be sorry I ever mentioned the idea if Bogs finds it doesn't work now he has put so much additional thought and effort into it.

Andy

[Darren]

John,

Bernd did say in his post that the chuck would be turning backwards  

On my mini lathe there was no backlash worth mentioning, so reversing the machine without retracting the tool was fine.

On my old Union lathe there was plenty of backlash, if the tool wasn't retracted it would cut the thread off quite merrily even though only the back of the tool was in contact with the work.

I think this is was Bernd was referring to?

[Darren]

To my mind, the best way to think of it is that it works like a simple hinged clapper box on a shaper. It lets the tool skid over the surface when the spindle is reversed to run the carriage back, just as the shaper tool does on the return stroke.

Andy

Nice comparison Andy 

[75Plus]

I'll be sorry I ever mentioned the idea if Bogs finds it doesn't work now he has put so much additional thought and effort into it.

Andy

My guess is that Bogs is NOT reinventing the wheel he is just finessing it a bit.

Joe