Author Topic: How to make a internal/external threading tool on your lathe  (Read 105965 times)

Offline fatal-exception

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How to make a internal/external threading tool on your lathe
« on: August 25, 2010, 12:29:43 AM »
So, yeah, I dont know if this is a new thing or not, but I've never seen another tutorial for making this type of tool anywhere so far, so here goes.

I will show you a simple way to make a threading tool completely on your lathe that can do both external as well as internal threads. I have many pictures of the process, and there's a .pdf of the actual tool with all the critical dimensions that you can download.

First off, i looked for quite some time at buying an internal threading tool that uses inserts, but the cost was rather prohibitive. Not to mention that they tell you that you need different inserts for different pitch ranges. BS I say. I'm not spending hundreds on pro tool holders and inserts. I don't need to do production threading, so I can't justify the purchase. So I came up with this idea. A machinist friend told me that it would undoubtly not work since the design lacks some clearance angles. Being a bit hard headed, I made one anyways. That was 2 years ago, and that original threading tool just failed last week, hence this article. (my bad, broke the tip off not stopping soon enough...)

The steel bar used for this is called drill rod here in Canada. It can be purchased almost anywhere. Bolt supply stores will have it, and steel dealers will know of it. It's sold in 3' lengths here. I'm not sure of the exact composition, but it's similar to O1 tool steel, I'm told. Anyways, it's stringy to work on the lathe, and not the nicest stuff for other processes, but when it's done and hardened, it's a great tool material.

Step 1, get some drill rod that matches your boring tool holder diameter. Here I'm using 5/8". (the drawing shows 1/2", but use any size you want...) Square a T style insert to the workpiece. The edges of this tool will form the v in your threads, so take your time making sure it's good n square.


Step 2, layout the shoulder line. You don't really need to do this, make it as long as you want.


step 3, turn the OD down to whatever you want to start with. I used 1/2" because this tool will be used on large internal threads, 2 inch and over. The smaller you make the tool, the smaller the internal threads you can make.


Step 4, Turn the undercut shaft. Keep this as short as possible, just like short stout borring tools, this follows the same idea.


Step 5, Make the point. Use the side of the insert to make the sides nice and flat.


Step 6, Part it off.


So that's it for the turning. You should break all the sharp edges here, and face the ends of the tool flat if they arent already.


On to the milling. This is the first time that I've done the milling part in the lathe, but it worked OK so I will show you what I did here.  Normally, I would set up the mill, clamp the tool in a vise and mill away the material, but this worked OK. Make sure everything is tight, I had some vibration when I was doing this, and the toolholder actually turned, which is not cool to see when you are hogging off material.

So, put your 1/2 finished tool in your boring tool holder. Make sure it's clamped down tight.

I used a 1/2" 4FL endmill for this, but you can use whatever you have laying around.

I adjusted the height of the threading tool to be cut manually. I started high and took a few light cuts, then just kept lowering the tool by hand, making sure the QC tool post wedged in hard each time, at each height. You can work this anyway you want. It didn't take but a few minutes and I had all the material I wanted removed.




Not the nicest machining but hey, it worked ,especially if you only have a lathe.


So that concludes the machining, that took you about 15 minutes right?  :beer:

Now the hard part, or should I say the hardeneing part? Regardless, it really easy with this steel. Heat to glowing orange, quench in water. Done. Check by trying to file. If you CAN file it's not hard, do the steps again. If the file bounces off, Good job! :beer:

Step 1, get a can full of water, a propane torch, and hold your tool with some visegrips as shown here:
(Pistachio cans make the tool harder, that's why i use them)

Step 2, fire up the torch to high and get the tip of the tool bright orange.


Step 3, be quick as you quench the entire tool and the visegrips and your hand in the can of water, try to cool the piece as fast as cosmicly possible. This will give the best chance of making the tool hard.


Step 4, try to file part of your now hard tool. Do this on an edge that isn't important, because if you didn't get it hard, you don't want to screw up one of the critical edges right?

If the tool is adequately hard the file will not do anything. Stop now or risk destroying your file. (you should use an old file anyways...)

So if it's hard, all you have left to do is hone the top face of the tool. This is the only surface you sharpen, never try to hone the sides or you will change the angle.


Just setup the tool in your boring tool holder and thread away!



Comments are always welcome!


Paul
« Last Edit: August 25, 2010, 12:30:16 PM by fatal-exception »

lordedmond

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Re: How to make a internal/external threading tool on your lathe
« Reply #1 on: August 25, 2010, 03:01:59 AM »
the tool should be let down to light blue not left fully hard as it is to brittle

Offline Stilldrillin

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Re: How to make a internal/external threading tool on your lathe
« Reply #2 on: August 25, 2010, 03:39:28 AM »
That's a great little tool!  :bugeye:

Very nicely done, and well shown, Paul.  :clap:  :thumbup:

David D
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Offline AdeV

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Re: How to make a internal/external threading tool on your lathe
« Reply #3 on: August 25, 2010, 04:21:42 AM »
Nice write-up & great photos, thanks! I'll definitely be making one of these.

Does it matter how far over-center you go when doing the milling operation?
Cheers!
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Offline trevoratxtal

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Re: How to make a internal/external threading tool on your lathe
« Reply #4 on: August 25, 2010, 10:27:48 AM »
Many thanks for a well thought out article.
The concept will solve problems I have had with cutting square and acme threads as well.
Well done
Trev :clap: :clap: :clap: :clap:

Offline fatal-exception

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Re: How to make a internal/external threading tool on your lathe
« Reply #5 on: August 25, 2010, 12:27:14 PM »
Does it matter how far over-center you go when doing the milling operation?

Yes, but only really for how much clearance angle there is VS how much meat is left at the cutting edge. The drawing shows how much to mill off. (I've posted the link in the original post)

As far as tempering, yes, if you feel so inclined you can polish the top then gently heat it up till the polished area is anywhere between straw yellow and light blue. Straw yellow will yield the hardest temper with the least ductility, light blue will be the softest but the toughest. If you are going to be threading on an interrupted bar, then go for tough. Personally, I leave the tool full hard as I never take interrupted cuts while threading. Also, the hardness gradient is very short, going from glass hard at the cutting edge to full soft somewhere along the shoulder. Keeping it full hard keeps a keen edge for a long time.

Thanks for the comments.

Paul

Offline andreas

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Re: How to make a internal/external threading tool on your lathe
« Reply #6 on: August 25, 2010, 12:54:21 PM »
Brilliant idea!!!! Well done Paul!! :headbang: :headbang: :headbang:

Offline crabsign69

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Re: How to make a internal/external threading tool on your lathe
« Reply #7 on: August 25, 2010, 03:06:02 PM »
that was a great write up i put it in pdf if its ok with you  :beer:   :mmr:
thanks for the write up and all that  very good

Offline Dean W

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Re: How to make a internal/external threading tool on your lathe
« Reply #8 on: August 25, 2010, 06:14:37 PM »
Nice write up, Paul!  I do have a question and comment.
For brass and aluminum, leaving this dead hard is probably just fine.  I think for threading steel, folks
would be happier if they temper it, as it will be less prone to cracking in the harder metals.

I wonder if the top cutting surface should be more on center.  I mean, mill away less from the finished
end of the cutter, so it ends up closer to centerline on the lathe.  Obviously, if a guy is cutting internal
threads, the "round" part on the end has to fit the hole, so as long as the end of the cutter is a radius
less than the part you are threading, you should have bottom clearance. 
It would leave the shaft part of the cutter that is directly behind the sharp edge a bit larger in diameter,
making it stronger.

I think it's a dandy tool, and next time I need to grind a HSS bit for small inside threads, I'll try this instead!

Oh, by the way, old dog food tins make better quench cans than the ever popular pistachio can.  The tools
come out better, and you don't get the munchies while toolmaking.  This comes from many years of experience
and testing quench cans while making my own tools.   Wash the can first, or you'll have dogs sniffing around the
shop from the smell of  'boiling dog food soup'  ; )

Thanks again for the how-to.  Great job on the pics and text.

Dean
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Offline andyf

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Re: How to make a internal/external threading tool on your lathe
« Reply #9 on: August 25, 2010, 07:20:02 PM »
Nice write up, Paul!  I do have a question and comment.
For brass and aluminum, leaving this dead hard is probably just fine.  I think for threading steel, folks
would be happier if they temper it, as it will be less prone to cracking in the harder metals.

I wonder if the top cutting surface should be more on center.  I mean, mill away less from the finished
end of the cutter, so it ends up closer to centerline on the lathe.  Obviously, if a guy is cutting internal
threads, the "round" part on the end has to fit the hole, so as long as the end of the cutter is a radius
less than the part you are threading, you should have bottom clearance. 
It would leave the shaft part of the cutter that is directly behind the sharp edge a bit larger in diameter,
making it stronger.

Dean, though I agree with you about tempering to make it less brittle, I reckon Paul got it right by milling down to its centre-line. Anything above or below would reduce the tip angle, when viewed from above, to something less than 60o.

This could be compensated by a more obtuse angle, but the  :smart: would be beyond me. I suppose too much resharpening by stoning down the flat top would eventually reduce the angle by an unacceptable amount.

Like Paul said, a purist might argue that such a tool would have zero relief for a tiny distance under the tip when used on the lathe's centre-line. But it works for him, so there's no reason why the copy I'm going to make shouldn't work for me.

The method could be adapted to make boring bars, too, where angles aren't so critical.

Andy
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I've cut the end off it twice, but it's still too short

Offline fatal-exception

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Re: How to make a internal/external threading tool on your lathe
« Reply #10 on: August 25, 2010, 10:40:33 PM »
Dean, thanks for the comments!

I realize that leaving the tool full hard is not conventional, and possibly I should have put in the tempering part even if I don't necessarily follow that concept. All I can go by is experience, and even in tough steels, I haven't had a problem with the tool. I've been very impressed with how well wearing the tips have been. One of the most demanding threading applications that I used the tool for was to cut threads in ACME rod that were just below the root of the ACME thread itself. It wasn't even through the case hardening of the screws, but I did 5 of them and they all came out OK.

Andy, in my example, I DID cut below the centerline of the tool. This is the way I've always made them. There's obviously room for experimentation here, but my rationing is that this gives relief on the tip of the tool. Maybe it could be milled exactly to the centerline...I will try one next week and post the results. And your right about the angle changing, but for the 30 thou that I show to go under the centerline, it is negligible (wish I had the drawing here, I could quantify that statement). Soldiworks still rounded it off to 60 degrees on the drawing. I guess I should check the The Machinery Handbook to see what is acceptable as far as the point not being exactly 60 degrees.

Anyways, I'm off dune buggying for the next 4 days. I just got a GoProHD vid camera so I can get some premium on board footage....Catch you guys next week.  :beer:

Offline Dean W

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Re: How to make a internal/external threading tool on your lathe
« Reply #11 on: August 26, 2010, 06:35:00 PM »

 I reckon Paul got it right by milling down to its centre-line. Anything above or below would reduce the tip angle,
Andy

Andy, what I said was,  Paul didn't mill to centerline, not that he did!  He milled to under C/L.
He confirms this in his most recent post.
If it works well as it is, it's probably just perfect. 
I've made a cutter or two, and on ones similar to this, usually putting the cutting edge right on centerline, or very close,
does just what it's expected to do, as long as the radius of the cutter provides clearance directly beneath the cutting
edge.

All said, I hope I made it clear that I think the tool is a great idea!

Dean
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Offline DeereGuy

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Re: How to make a internal/external threading tool on your lathe
« Reply #12 on: August 26, 2010, 08:15:41 PM »
Yep, I think it is a good idea also...and will try it myself when I get a chance. :thumbup:

Offline fatal-exception

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Re: How to make a internal/external threading tool on your lathe
« Reply #13 on: August 29, 2010, 11:18:27 PM »
Hey guys, I'm back and in one piece. Good weekend for total km's, 300 +/- a few. Sore now, but feel good about the buggy. It has 1600km saying it's reliable....other than brakes...

Heres a shot taken today, after the storm...



Offline Pete.

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Re: How to make a internal/external threading tool on your lathe
« Reply #14 on: November 13, 2010, 02:47:55 PM »
I suppose too much resharpening by stoning down the flat top would eventually reduce the angle by an unacceptable amount.

You could avoid this by always stoning the tip whilst changing the angle radially, so that the flat top always radiated from the same point just on or below CL.

Offline Lew_Merrick_PE

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Re: How to make a internal/external threading tool on your lathe
« Reply #15 on: November 14, 2010, 12:35:42 AM »
First off, i looked for quite some time at buying an internal threading tool that uses inserts, but the cost was rather prohibitive. Not to mention that they tell you that you need different inserts for different pitch ranges. BS I say. I'm not spending hundreds on pro tool holders and inserts. I don't need to do production threading, so I can't justify the purchase.

Please note the qualifier "I don't need to do production threading."  So long as sharp-corner v-threads are what you need, this will work fine.  However, if your work is subject to inspection to any of the formal standards, you will be in a world of hurt.  Each pitch has a specific radius at the root/crest (external/internal) thread that is required to qualify under formal standards.

I realize that I am being pedantic here and that most here would not need to meet formal standards, but the caveat is something that should be known -- even by those who have no need of the formal standards compliance in their work.

Offline Artie

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Re: How to make a internal/external threading tool on your lathe
« Reply #16 on: November 15, 2010, 12:57:48 AM »
Ive had a thought, if we can make this thing turn in a half circle while being used internally, we can use it like the swing up tool Bogs wrote up.... the head is spinning this over.... I might investigate this further... liked the concept, but fo rexternal threading I cant se a benefit over a 60 deg tool... internally though.... oportunities.... :proj:  :nrocks:
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Offline Bogstandard

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Re: How to make a internal/external threading tool on your lathe
« Reply #17 on: November 15, 2010, 01:42:03 AM »
Artie,

I have already come up with an easy design that 'should' work for as a swing up internal thread cutting tool, both left and right hand, and it would use a cutting tool made similar, but not quite the same design as this one shown here.

Unfortunately I can't see it being put into metal for a fair while as I have a massive backlog that needs to be cleared up first.

When eventually it gets to the top, unlike the other one, it will all come as a one lump post, just to make sure the idea and concept isn't pinched and put into production before it is finished and proved on here.

Maybe someone else would like to come up with an idea and preempt me by showing it on here.


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Offline Divided he ad

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Re: How to make a internal/external threading tool on your lathe
« Reply #18 on: November 15, 2010, 03:04:21 AM »
Quote
Maybe someone else would like to come up with an idea and preempt me by showing it on here.


Hehe.... I could just use the design you told me about when I was over at your house last month John   :poke:    :lol: 


Obviously I won't, not that kind of chap :thumbup:   

Upside is.... I know what people are talking about on this whole thread due to the multiple conversations Bogs and myself have had over my fear of threading issues   :beer:



Paul, nice work as far as I see.... Not upto some standards apparently, but if it works....  :thumbup:   Basically I'm liking the whole thread  :doh:   What a loverly pun for 8am  :)








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Offline Artie

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Re: How to make a internal/external threading tool on your lathe
« Reply #19 on: November 19, 2010, 06:23:40 AM »
Pssssssttt...... Ralph.....  :wave:
South Wales, wait...NEW South Wales... Batemans Bay.

Offline bob ward

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Re: How to make a internal/external threading tool on your lathe
« Reply #20 on: November 21, 2010, 08:30:03 PM »
Thanks for the tip fatal-exception, you've enabled me to do a little job that would otherwise still have me scratching my head.

I needed to make a weird internal thread 26TPI x 0.65" or 21/32" or 16.4mm (suits a Lucas dashboard warning light bezel, 40's, 50's), no taps available for that one of course. Made one of your devices out of 8mm drill rod/silver steel and it worked a treat.

Not too long after that I needed to make a short blind 3/4" x 16TPI internal thread, I've only got a taper tap, and my 16mm internal threading tool won't quite fit down the hole. Your device rescued me again.

Offline crabsign69

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Re: How to make a internal/external threading tool on your lathe
« Reply #21 on: November 22, 2010, 01:16:44 PM »
i made one and i must say it works pretty dam good.  now onto making different sizes .
thank u for this valuable tool making stuff.   :headbang:   :beer:

Offline Divided he ad

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Re: How to make a internal/external threading tool on your lathe
« Reply #22 on: November 22, 2010, 03:27:39 PM »
Quote
Pssssssttt...... Ralph.....   :wave:

Not going to happen Artie. Else this would be Bogs and me  :wack:   !!!


 :lol:



Looks like a few people have had a roaring success with this design Paul, I think that gives it a Madmodder approval rating... Anyone else think that it gets one?   :nrocks:


I'm still not a threader.... I'm going to have to do some some day  ::)




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Offline Bogstandard

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Re: How to make a internal/external threading tool on your lathe
« Reply #23 on: November 22, 2010, 04:03:05 PM »
Ralph,

I like this one as well, and could be put to other very good uses, boring bars for example, they are usually a PITA to make up, but as long as you don't require one too long, then this method is ideal, but would require a bit of handwork afterwards to put the correct clearances on. :nrocks: :nrocks:

With ref to your not single point threading, I have been threatening to show you for far too long, maybe next time your over, I will explain and show you just how easy it is to do.

In fact this evening, I cut some 4mm fine in about ten minutes. To buy the die would have cost me around 20 squid, and may never be used again for years. It was the same last week, when I needed to cut some 5mm coarse left handed, it was sorted in no time.
So it does really pay to know how to do it.


John
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Offline compspecial

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Re: How to make a internal/external threading tool on your lathe
« Reply #24 on: January 15, 2011, 02:35:23 PM »
What a great idea, works a treat too! the excellent results speak for themselves! I don't ever recall seeing anything like it before! :clap: