self retracting screwcutting toolpost

[bentprop]

This seemed such a brilliant idea,I had to have one!
http://madmodder.net/index.php?topic=2323.0

Although John"blogwitch" wasn't the originator of this idea,he put it in pictures ,so the blindingly obvious became clear to even a dumb cloghopper like me :big:
So,after raiding the jun.............err,carefully thrown in a corner,might come in handy one day pile,a start was made.
I didn't have any angle,so used a piece of T profile I did have.One half of the T base was removed,and then the inside squared.(you did know that the insides of angle and T profiles are not square,didn't you?).A5mm hole was drilled 10mm from one corner,and tapped M6.

Then my piece of 20mm(3/4") plate was split into 2 pieces,one for the toolholder,the other for the piece to be attached to the back of the angle as a way to hold the whole sorry mess in a QC toolholder.after squaring up both pieces,the serious business commenced.
Cutting the slot for the HSS toolbit:

Then 3 holes drilled and tapped M4 for the holding screws:

And here we have the finished toolholder:

A short piece of 1/4" key steel was reduced to 6mm,and a couple of bronze bushes magically appeared out of a drawer:

Then it was on to the stepped bolt to hold toolholder to angle.A piece of 10mm shafting retrieved from an old printer provided the raw material.Threaded M6.

This one actually isn't quite right,so I made another with a shorter threaded portion.
The keysteel locator was drilled and tapped M3,and fitted to the angle.

The following bits I have no pictures of,as the camera battery went flat
The bottom of the toolholder was now blued with my magic marker,and clamped on top of the locator.This allowed me to mark the position for the slot the locator will errm,locate in.
This was first milled out with a 5mm slot drill then carefully widened to accomodate the locator snugly.
Not very visible,but I ground a sort of "lead-in" on the back of the locator so the toolholder would slide into the correct position.
This is of course only neccessary when the toolholder is lifted completely clear,say to measure the thread being cut,f'rinstance:

The remaining piece of 20mm plate was made into a 20 x16mm strip.which is attached to the back of the angle.This allows fitting in the QC holder.

A few minor fiddles included a 13mm spacer between the 2 bronze bearings,rounding the bottom rear corner of the toolholder,and milling a couple of flats on the stepped bolt for a spanner.I was to lazy to set up the rotary table to make it a hexagon bolt head.
After a bit of assembly,this sat on the bench looking pretty:

I've never had the courage to do any single point threading on my lathe,but with this contraption it should be virtually idiot proof.
Tomorrow the acid test.Will it work as good as shown in John's video?Will I finally get to cut a thread ?Will my hat still fit afterwards?
For the answers to these questions,tune in later for the next exciting episode.

 

[Twmaster]

Looking forward to your follow up.

 

[Blogwitch]

Hans,

I am glad to see someone has gone for the quick and dirty method as I showed in the sketch.

As you know, I made mine too complicated, as it was a prototype made on the run. By the time it is skinned back to bare essentials, this should work just fine, and as you said, but not believed, that it can be made by 'even a dumb cloghopper like me'.

Best of luck on your first trials, and don't forget, you can put the next cut on as you are traversing back to the start. Take things steady to begin with, and you should soon pick up the concept. and make bigger and better threads as you gain in confidence.



John

 

[Twmaster]

John,

Could this be made from a good hard aluminum alloy if used on say a smallish lathe like a 6" Atlas or 7" Asian?

 

[Blogwitch]

I don't want to hijack Hans' post, but just to answer your question.

Not having the experience of making one out of non ferrous, I couldn't give a definite answer, but I suppose if it was rigid enough, and you weren't expecting to cut very large threads (like the one shown on my vid), then I see no real problems. But it would require good lubrication to stop the parts galling together under the cutting pressures involved.

It would be so easy to make, I suppose you would need to make one and show the results, so people could learn from your experiences. Good or bad.

John

 

[Twmaster]

John, Thank you. I shall make one for my Atlas 618 then. Hans, my apologies. I had not intended to hijack your thread. I'm just eager to make one of these and your post is very much pushing me to do so once I get my workshop back up and running.

 

[bentprop]

Mike,like John said,galling might be a problem.If you could use steel for either the angle or the block,it would probably be ok..Mine was just scrap bits of steel I happened to have.
John,at first I couldn't quite work out how the "locator" was fitted,but the light bulb went on eventually :big:.
I'll fit it on the lathe today and have a go.Unfortunately I won't be able to take a video,as my old fuji finepix is only 2 mp.The video is barely watchable.

 

[Blogwitch]

Hans,

As long as you are happy with the threading results, that is all that matters.

Vids are just a bonus.

John

 

[bentprop]

Sorry,guys,yesterday my time was otherwise occupied by the powers that be.
I got to run a test on the tool today,and it sure does what it says on the tin ;D
My first pic shows the 1/4x28 UNF thread being cut:

the second pic shows the tool returning to the start,although it may not be immediately obvious

next shows a brass nut which had been previously tapped on the cut thread.It was a bit tight on the start of the thread,but ran freely a bit further on.Presumably the shaft was a bit larger at the start.Should have taken a couple of "cleaning "passes after turning the shaft to size.

This proves that any fool can do it :big:
Flushed with my success,I decided to cut a 40 tpi thread on a piece of 8mm rod .This was not to any recognizable size,but I just wanted to see how well it worked.And work it did:

I'm happy as a sandboy.If you've ever shied away from cutting single point threads on your lathe,build yourself one of these,and you can't go wrong.
I would like to take this opportunity to thank John M"blogwitch,bogstandard"and Andy F for presenting this tool in such a clear manner.Thanks so much,guys.

p.s.The first pic was actually taken after the 2nd one.My initial pics were a bit fuzzy.bp.

another p.s.here's a pic showing the rear view of the tool post,which might help clarify some queries.

bp.

 

[Blogwitch]

I'm glad it worked well for you Hans.

It is very nice to see that a 'roughie' can do exactly the same job as my over engineered one.

I usually prepare the job a little beforehand and make a small runout slot, it can save those brown trouser moments at times, and it would also save your cutting tool point from too harsh treatment when coming to the end of the cut.

Very well done indeed.

John

 

[Twmaster]

Very nice Hans! Applause for you!

 

[Deanofid]

That's a fine shop project, Hans. Pays good dividends, too.
Good job!

Dean

 

[tornitore45]

I know I missed the original post but can somebody explain how the tool workS?
What makes the holder flip up and disengage the thread?
Mauro

 

[Blogwitch]

Mauro,

For the tool to work, you must have a lathe that can reverse the direction of the chuck. The leadscrew is always engaged, so when you put the lathe into reverse, the tooltip goes back towards the start point and because the thread is turning backwards, the tooltip automatically lifts up away from the thread, purely by friction. When the lathe starts to run forwards again, the tooltip automatically drops back into it's cutting position.

If you watch just the first part of this vid, it shows exactly what happens.

[ame]http://www.youtube.com/watch?v=8JFdNaBD5GM[/ame]

the rest is just much of the same except for left hand and small threading.

Bogs

 

[tornitore45]

Pretty kool.
Unfortunately my late coasts for a couple of turns, have no brake. The late in the video runs pretty slow and stops without coasting.

Useful tool for metric where the half nut stays engaged.

As I write I came up with an idea, if I set the acceleration on my VFD high in reverse, I can reverse the drive and should stop fast.

 

[itowbig]

bogs i got a question. how do u get that lathe to stop that fast? does it have a brake of some kind?
my lathe will run on a bit after its shut down and if i could get it to stop that fast that would be great.

 

[Blogwitch]

Itowbig,

I am fortunate to have a powerful footbrake on my machine. It electrically isolates the motor as soon as you touch the bar and only then does it apply the large drum brake.
I wouldn't attempt to use it on very much faster speeds other than for threading, unless it was an emergency. It can be used to gradually slow down the machine from very high speeds, it all depends on how much pressure is applied to the footbrake, just as in a car.

Mauro,

It's for that run on reason your should prepare the workpiece first.

You can see on my workpiece, there is a cutaway section at the end of the threaded portion. This serves two purposes when single point cutting.

The first is that if you don't have the groove there, and the cutting tool goes a little further than normal, it could be trying to cut a whole thread depth in one hit, and that could easily damage the tip on your tool, and the second, and most relevent in your case, it allows for your reaction times and that slowing down period before going into reverse. If you are cutting a fairly long thread, the groove would be cut to the final thread depth, and could be up to say three or four threads wide, thus allowing the chuck to come to a stop before hitting the main part of the bar being threaded.

It does also serve another purpose, it makes your threading look a lot more professional, even if you are hand cutting a thread with a die, but it also has other uses when hand cutting.

Bogs

 

[Twmaster]

John, could you whip up a CoC for grinding the business end of the cutting tip?

 

[Blogwitch]

Mike,

I can do even better than that, and save myself some ink in the long run.

http://www.wikihow.com/Make-a-Turning/Threading-Lathe-Tool-Bit

http://www.wisc-online.com/objects/MTL11402/MLT11402.htm

http://www.sherline.com/grinding.htm

http://www.gadgetbuilder.com/ThreadingTools.html

The first one shows how to grind a tool to give yourself a little extra breathing space when coming up to a shoulder, the leading face is much shorter than the trailing one. As long as the leading face is longer than the depth of thread you are going to be cutting, it can really help out in those brown trouser moments when getting close to the shoulder or towards the chuck.

I purchase my brazed tipped threading cutters ready ground. Blue for general materials, and orange/red for the tougher stuff. They are very cheap (3 or 4 squid each), and not worth the time grinding them up myself. But I have made myself a couple of angle blocks, just for touching them up on the surface grinder.

Hope this explains everything.


Bogs

 

[Twmaster]

John, thank you that is pretty clear.

I seem to recall seeing one edge ground to 55 deg in a post somewhere. That is what prompted my request for grinding angles.

From looking at your 60 deg brazed bits (I have a couple here in my collection) it seems they will work as-is? Other than a touch up when worn some?

The short answer I think I am seeing here is pretty much any bit ground for regular thread cutting will do?

Again, thank you. I'm just about done getting my milling machine back in service after a 1400 mile move.

One of these tools would be a good project foe the rebirth of my workshop.