# Threading thread



## saltytri (Jul 3, 2009)

I've studied up on the new lathe and figured out how to cut my first thread:







So, the next adventure is to cut matching threads in a tube. Obviously, I'm trying to learn the skills to do a light from scratch. My question is whether there is a rule of thumb on how to size the major and minor diameters of matching external/internal threads so that they go together properly.

Thanks!
David


----------



## precisionworks (Jul 3, 2009)

Good looking, especially for the first time. 



> rule of thumb on how to size the major and minor diameters of matching external/internal threads


Machinery's Handbook, any edition including the ancient ones, has tables of correct dimensions for all the commonly used threads. You'll need either a thread mic or thread measuring wires to hit the minor diameter on outside threads.

If you're doing a one off light, cut the internal thread first. Then it's easy to fit the external thread to that one. Problem is, without cutting to standard dimensions, you will not be able to interchange that part to another light.


----------



## gadget_lover (Jul 4, 2009)

There are several "types" of thread, and many sizes within those types.

Most threads you will cut will be Unified (UNC) or Metric (ISO). In both cases, the thread height for a particular TPI is the same no matter how big the screw or nut is. There are tables all over the web with that information.

The major -> minor relationship is determined by the choice of thread. You can start with either the major or minor and calculate from there. You pick a major diameter and a thread, then calculate the minor from that. 

It's worthwhile to read up on the terminology of the thread profile that you will use. Crest, root, pitch thread height (vs thread depth).... 

I have a thread calculator on my web site, but I've never heard of anyone using it regularly. In the last month it got 45 hits.  It also calculates major / minor for you. That URL is http://www.tanj.com/cgi-bin/tpi.cgi

Daniel


----------



## PhotonFanatic (Jul 4, 2009)

Download the threading software from Stellram's website and play with it, along with the Machinery Handbook that Barry suggested. Between the two, you will soon be an expert. :devil:


----------



## saltytri (Jul 4, 2009)

Thanks, guys! I do have a copy of Machinery's Handbook and have used it to get an understanding of thread forms. With that and Daniel's website, I'm off and running. I'll be gone for the next week but will report in when my matching thread set is figured out and cut. :thinking:

The thread in the photo is a little crude. It wasn't done by measurement so much as by trial and error. I just turned the rod to the correct major diameter, .625", set the compound to 29.5 degrees and started making fine cuts with the compound until I could screw a hardware store nut onto it. I suppose real machinists don't do it this way!


----------



## gadget_lover (Jul 4, 2009)

> I suppose real machinists don't do it this way!



You'd be surprised how many people do it exactly that way. It works.... most of the time. The hidden gotcha (at least for me) was that the threads actually have flat (or nearly flat) crests and roots. When you keep threading it smaller and smaller it till it fits by test fitting you may actually have a sharp thread that does not match well. You may also have a thread that deforms as the crest of the screw mashes into the root of the nut, causing it to lock up badly.

Congrats on the new machine and hope you have fun with it. 

Daniel


----------



## saltytri (Jul 4, 2009)

Daniel, you're absolutely right. I did end up with pointed crests. But is it true that if the goal is to cut matching internal and external threads, this doesn't matter as long as they engage smoothly? As precisionworks pointed out, this means no interchangeability but maybe that's not so important for a one-off flashlight.

Don't get me wrong - I do intend to learn the right way to do it, though.

BTW, Happy Fourth to all! I've been a few other places and know for certain that we're awfully fortunate.


----------



## gadget_lover (Jul 4, 2009)

You are right, in that it does not matter as much in a one-off light. But.... 

The sharp crests are fragile and liable to be damaged much easier, making them jam, crossthread, etc. They require a perfect match in order to be tight, so dirt and grit are more likely to be a concern.

I find that with the cut and try method it is much easier to overshoot the desired dimension. It's also easy to get that "perfect fit" where there is zero clearance. When that happens you frequently end up with the two pieces permanently fastened together. Permanently. If you are test fitting and hit any resistance at all, then stop and unscrew it. 

Learning to cut threads to the standards has another benefit. It allows you to cut threads to match parts that you can not test fit. 

Daniel


----------



## 65535 (Jul 4, 2009)

I prefer flat acme threads. The seem to engage smoother because unlike V threads they have pressure points that are head on parallel to the axis of movement rather than at an angle around 60.

Plus I've never cut myself with acme threads, V threads have sliced me good.


----------



## BoarHunter (Jul 5, 2009)

gadget_lover said:


> There are several "types" of thread, and many sizes within those types.
> 
> Most threads you will cut will be Unified (UNC) or Metric (ISO). In both cases, the thread height for a particular TPI is the same no matter how big the screw or nut is. There are tables all over the web with that information.
> 
> ...



It is in inch ! When you work in metric with a metric lathe, you don't need all this complication ! :laughing:


----------



## precisionworks (Jul 5, 2009)

> When you work in metric with a metric lathe, you don't need all this complication ! :laughing:


I do miss the ability to cut threads used by 3/4 of all the people in the world, but my South Bend won't go there. I've seen a few made with a Metric lead screw, but have so little call for Metric threading that it isn't worthwhile to buy a second lathe. FWIW, I do some work on Jaguar automobile parts which are threaded ... standard USA tpi & pitch 

As Daniel says, you really want to be able to cut threads to a print. If you ever do this for a profit, you will someday get a call, fax or email with a print attached. Then you have to be able to hit the thread spec dead nuts, without the crutch of having a mating part. The talented people here who make the killer Ti parts (like heads, body tubes & tail caps) to fit SureFire E-series have to cut to one standard dimension.


----------



## KowShak (Jul 5, 2009)

precisionworks said:


> I do some work on Jaguar automobile parts which are threaded ... standard USA tpi & pitch


 
Everything manufactured in the UK at one point would have imperial measurements, the Whitworth standard originated in the UK. The slow movement from imperial threads to metric happened at about the same time that the british car industry was losing it's independance, there was an interim period where a UK built car would have a mix of metric and imperial nuts and bolts, subsequently european and japanese companies started making cars in the UK and everything went metric. The current situation is that almost everything is metric and imperial spanners in their various incarnations (BSW/BSF/AF) are uncommon. The US car industry is in a similar situation now, so I think that at some point, the US will go metric too, the future will tell whether I'm right or not.


----------



## BoarHunter (Jul 5, 2009)

KowShak said:


> Everything manufactured in the UK at point point would have imperial measurements, the Whitworth standard originated in the UK. The slow movement from imperial threads to metric happened at about the same time that the british car industry was losing it's independance, there was an interim period where a UK built car would have a mix of metric and imperial nuts and bolts, subsequently european and japanese companies started making cars in the UK and everything went metric. The current situation is that almost everything is metric and imperial spanners in their various incarnations (BSW/BSF/AF) are uncommon. I think that at some point, the US will go metric too....



The UK autombile industry died partly because of the mess and errors associated with the use of the inch. The UK inch was not even the same as the US, that lead to quite some issues during WW2. It is why they came with the Unified standard.
To this you must add the various company standards !

The US automobile industry has been saved once in the eighties by going metric, but now ?
Others have no choice if they want to export and survive, they must work in metric.
Just look at a catalog of supplies and tools, about two third of them are not required if you stick to ISO.


----------



## BoarHunter (Jul 5, 2009)

precisionworks said:


> I do miss the ability to cut threads used by 3/4 of all the people in the world, but my South Bend won't go there. I've seen a few made with a Metric lead screw, but have so little call for Metric threading that it isn't worthwhile to buy a second lathe. FWIW, I do some work on Jaguar automobile parts which are threaded ... standard USA tpi & pitch
> 
> As Daniel says, you really want to be able to cut threads to a print. If you ever do this for a profit, you will someday get a call, fax or email with a print attached. Then you have to be able to hit the thread spec dead nuts, without the crutch of having a mating part. The talented people here who make the killer Ti parts (like heads, body tubes & tail caps) to fit SureFire E-series have to cut to one standard dimension.



Normally you can get a gear to be able to cut metric screw with an inch leadscrew.


----------



## gadget_lover (Jul 5, 2009)

The US has gone metric... sort of.

When I pull a screw out of something I often have to guess at the thread. Was it made in the US? Then I start with SAE. Was it import? Then I start with metric. Once I find a matching thread (tpi or pitch) I will then measure the major diameter and see if it's close to any of the standard sizes on my chart.

Occasionally there will be a screw that can be either imperial or metric based on the thread gages. Sometimes the screw is neither! It's quite possible to do a 1.63 mm pitch screw in the ISO profile, just as it's possible to make a 24.2 tpi thread in UNC profile. 

In the 1970's I had a lot of british motorcycles. Occasionally I'd find that I needed Metric, Whitworth and SAE tools on the same bike. That was fun to work on.


BTW, BoarHunter, thanks for the heads up. I forgot that the maj/minor calcs on my web page are in inches. 


Daniel


----------



## gadget_lover (Jul 5, 2009)

BoarHunter said:


> Normally you can get a gear to be able to cut metric screw with an inch leadscrew.





And even if the pitch is not exactly right, it's close enough for doing short threaded pieces.

And example for the 7x10 lathe crowd: Add a 21 tooth gear to the standard set and you can almost cut a 1.0 mm pitch thread. There are 12 gear combinations that come out to 1.0001 mm but that's close enough for a fairly long thread engagement.

Other pitches are available too. You can almost cut a 1.25 mm pitch (1.2502) 

I understand that a 127 tooth gear will give the larger lathes the ability to cut exact metric threads.
Daniel


----------



## BoarHunter (Jul 5, 2009)

gadget_lover said:


> And even if the pitch is not exactly right, it's close enough for doing short threaded pieces.
> 
> And example for the 7x10 lathe crowd: Add a 21 tooth gear to the standard set and you can almost cut a 1.0 mm pitch thread. There are 12 gear combinations that come out to 1.0001 mm but that's close enough for a fairly long thread engagement.
> 
> ...



Indeed it is a 127 tooth gear. In fact it is also used to cut inch thread with a metric lead screw. This because the inch in fact is defined as 25.4 mm exactly since end of the 19 century in the US and 1950's for the UK.

The amusing thing is that some US companies had devised their own standard ! Guns mfgd and even Caterpillar for examples ! Although most of Caterpillar is now metric, they kept some of these screws for compatibiliy reasons with their older equipments. Same with John Deere.


----------



## KC2IXE (Jul 5, 2009)

BoarHunter said:


> ...snip...The amusing thing is that some US companies had devised their own standard ! ...snip....



Bicycles - many common threads are metric diameter, with inch thread pitches


----------



## darkzero (Jul 5, 2009)

KowShak said:


> The US car industry is in a similar situation now, so I think that at some point, the US will go metric too, the future will tell whether I'm right or not.


 
I wouldn't be surprised. Years ago when working at the shop I remember lots of later GMs with a mix of metric & SAE fastners. I remember the lugs on all the later model GMs were metric. When I first got my own tools I never had the need to buy SAE tools for a while.


----------



## saltytri (Jul 6, 2009)

As Barry suggested, I cut a thread to spec, not to fit. To make a 20 tpi Surefire 6P tail cap thread, the DOC comes out to .0379. Following advice to cut with the compound set at 29.5 degrees, it took .044 of compound dial movement to reach .0379 of depth perpendicular to the workpiece. It seems that a physical measurement of perpendicular DOC using a dial indicator is necessary to pre-determine how much movement of the compound dial is necessary to get the correct DOC. Am I on the right track? Is there a more convenient way to calculate the correct movement of the compound dial? It's all well and good to have a DRO on the cross slide but it doesn't do anything for me when cutting with the compound!


----------



## gadget_lover (Jul 6, 2009)

The technique I've seen described most often (using your numbers):

1) Assuming you've turned the part to the major diameter and have cut the thread relief. 

2) set the compound to 29 degrees.
3) set the tool so that the 60 degree tip is pointing at 90 degrees to the work.
4) move the tool so that it can not hit the work and using the crossslide move it in to the doc (Major plus doc .0379)
5) Zero the COMPOUND slide's dial. This is your final depth. Do not use the cross slide any more.
6) back out the compound to clear the work and start threading. Use only the compound to move the tool in. When the compound dial reaches zero you are at depth.

NOTE: when everything is adjusted right, the right side of your 60 degree tool will be parallel to the travel of the compound.


Daniel


----------



## Mirage_Man (Jul 6, 2009)

gadget_lover said:


> The technique I've seen described most often (using your numbers):
> 
> 1) Assuming you've turned the part to the major diameter and have cut the thread relief.
> 
> ...



Daniel,

That's a interesting way of doing it. I've never thought about doing it that way but will give it a try. The only thing I question is what about a final pass or two using the cross slide to clean up both sides of the thread? I always do this as the 29.5 method will leave one side of the thread a little jagged. Also I would think you'd want to zero your cross slide so you have a reference point for each pass. That is of course assuming you back out of the thread after each pass using the cross slide.

I would also suggest getting some sort of method to measure your threads. I use a thread mic. There are other methods such as thread wires and triangles but I've never used them...yet .


----------



## gadget_lover (Jul 6, 2009)

It's assumed that once you start threading, you will use only the compound, even for backing off for the next pass. It does not hurt to have a reference point on the crossslide too. It helps when you do like I do and accidentally bump the handle mid thread.

Many people advocate doing the last pass with the compound. This should only be a thousandth or so. I'd have to do the math, but the 'jaggies' should be pretty minuscule if properly set up.

Daniel


----------



## Mirage_Man (Jul 6, 2009)

gadget_lover said:


> It's assumed that once you start threading, you will use only the compound, even for backing off for the next pass. It does not hurt to have a reference point on the crossslide too. It helps when you do like I do and accidentally bump the handle mid thread.
> 
> Many people advocate doing the last pass with the *compound*. This should only be a thousandth or so. I'd have to do the math, but the 'jaggies' should be pretty minuscule if properly set up.
> 
> Daniel


 
Just to clarify, you meant cross slide in the statement above right?


----------



## gadget_lover (Jul 6, 2009)

LOL You got me. I meant to say "Many people advocate doing the last pass with the cross-slide"

That'll teach me to type quickly just before leaving for work!


Daniel


----------



## StrikerDown (Jul 6, 2009)

I'm probably all screwed up here but I thought the 29 degrees on the compound instead of 30 (1 half of 60) was to take care of the jaggies?


----------



## gadget_lover (Jul 6, 2009)

Nevermind. Move along to the next post please.
Daniel


----------



## Mirage_Man (Jul 6, 2009)

I don't have the energy at the moment to give a full response but maybe this link and picture will explain what I cannot.

http://www.mmsonline.com/articles/threading-on-a-lathe.aspx


----------



## gadget_lover (Jul 7, 2009)

Thanks! That was the diagram and article I was looking for, but could not find.

Daniel


----------



## gadget_lover (Jul 7, 2009)

Thanks! That was the diagram and article I was looking for, but could not find.

Daniel


----------



## saltytri (Jul 8, 2009)

Daniel, thanks for the suggestion on setting up to correctly cut with the compound. Here's a 20 tpi cut by the numbers in 12L14 (which cuts so nicely that it feels like cheating). The bevels at both ends were cut at 60 degrees. I've just seen some info that says to use 45 degrees, which I'll do next time.








I realized that for a given compound angle, you can just multiply the calculated DOC by a fixed factor to get the reading to cut to on the compound dial. For example, this is 1.13 for 29 1/2 degrees. This is by measurement of the tool travel not by trig, which I had over 40 years ago and probably wasn't any good at even then. :thinking:

Thanks again to everyone for the help and advice!

David


----------



## Fred S (Jul 8, 2009)

saltytri said:


> As Barry suggested, I cut a thread to spec, not to fit. To make a 20 tpi Surefire 6P tail cap thread, the DOC comes out to .0379. Following advice to cut with the compound set at 29.5 degrees, it took .044 of compound dial movement to reach .0379 of depth perpendicular to the workpiece. It seems that a physical measurement of perpendicular DOC using a dial indicator is necessary to pre-determine how much movement of the compound dial is necessary to get the correct DOC. Am I on the right track? Is there a more convenient way to calculate the correct movement of the compound dial? It's all well and good to have a DRO on the cross slide but it doesn't do anything for me when cutting with the compound!


 
It should be

perpendicular depth of cut/sin(60)= compound travel

This and many other thread cutting calcs are in the Handbook


----------



## saltytri (Jul 9, 2009)

Tonight I made interior/exterior matching threads in a piece of 2" 6061 tube. It all came out pretty well except for one minor point. I don't have a tool that does a decent job of cutting the relief groove at the back of the interior thread. Any recommendations, especially for doing lights with 17mm and 18mm bores?


----------



## Mirage_Man (Jul 9, 2009)

saltytri said:


> Tonight I made interior/exterior matching threads in a piece of 2" 6061 tube. It all came out pretty well except for one minor point. I don't have a tool that does a decent job of cutting the relief groove at the back of the interior thread. Any recommendations, especially for doing lights with 17mm and 18mm bores?



I don't have one because I usually don't cut an internal thread relief anymore but these are designed specifically for what you want to do.

http://www.micro100.com/inch/ltr.html

.


----------



## saltytri (Jul 9, 2009)

Thanks for the link to Micro 100, Brian. 

To avoid needing a relief groove, do you thread from the inside toward the outside and gradually feed in depth at the beginning of each cut?

Here's the latest from Beginning Shop Class:











Maybe it's time to make something for real.


----------



## Anglepoise (Jul 9, 2009)

Looks very nice.
One tip. Keep the run out groove width close to the common 'O' ring thicknesses.
When your building flashlights, most will have an 'O' ring for sealing and this just cuts down additional steps.


----------



## Mirage_Man (Jul 9, 2009)

saltytri said:


> Thanks for the link to Micro 100, Brian.
> 
> To avoid needing a relief groove, do you thread from the inside toward the outside and gradually feed in depth at the beginning of each cut?


 
I don't recommend doing this unless you're very comfortable with your machine. I cut an internal thread relief for quite awhile before I attempted doing it this way. When I did I broke my share of inserts before I mastered it.

I thread toward the chuck but roll out of the thread at the same spot each pass based on a zero setting on my carriage dial (Not all machines have a dial on the carriage wheel). IOW I set the carriage dial at a zero point where I want the thread to end. As the carriage moves toward the chuck I watch the dial. When it reaches zero I disengage the half-nuts and roll out with the cross-slide at exactly the same time. the dis-advantage to doing it this way is if you roll out too late you risk breaking your insert or hitting a shoulder if you're threading toward one.

There seems to be many different ways that people thread on this forum. I think each has its merrits. I suggest finding what works best for you.


----------



## gadget_lover (Jul 9, 2009)

I typically use my threading tool to do the relief groove. The groove is usually less than .050 deep and only a few threads wide.


Daniel


----------



## saltytri (Jul 9, 2009)

gadget_lover said:


> I typically use my threading tool to do the relief groove. The groove is usually less than .050 deep and only a few threads wide.



I used a brazed carbide internal threading tool to do this and it pretty well buggered up the groove. Probably a case of operator error! At least there was a groove to work to.

I'm sure that Brian hit the nail on the head with his comment that the best thing to do is what works for each person. The great thing about a forum like this is that it can show a newbie what the various possibilities are - if you don't have experience and/or an experienced teacher at hand, it's hard to know what the different methods are that you should try to solve a given problem. Like with any highly skilled trade, there's an awful lot of lore that you won't find in books.

If anyone cares, MSC has a thread relief tool similar to the one he pointed out:

http://www1.mscdirect.com/CGI/NNSRI...id=13665Pstoreid=1040626Ppagenumber=842Pmode=

Since MSC is having a sale today, I ordered a couple along with one of these:

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1785945&PMT4NO=66794381

I've bookmarked a couple of helpful posts on making cast iron adapter plates for these chucks, so some fun will start when the Brown Truck turns up in a few days.


----------



## tino_ale (Jul 17, 2009)

Interresting... thread :naughty:

Does anyone has accurate major diameters of E-series compatable bodies and minor diameters of heads and tailcaps? I'm looking for the nominal dimensions.

Also E-series parts are 20TPI right?


----------



## darkzero (Jul 19, 2009)

saltytri said:


> Since MSC is having a sale today, I ordered.... along with one of these:
> 
> http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1785945&PMT4NO=66794381
> 
> I've bookmarked a couple of helpful posts on making cast iron adapter plates for these chucks, so some fun will start when the Brown Truck turns up in a few days.


 
Congrats on the new chuck! :twothumbs As the others told me, you are going to love it, they were right, I know I do. It's absolutely the best accessory I got for my lathe.

I'm sure you will have no problem making an adapter plate for it. When I made mine I had zero experience in making one but it came out pretty good IMO. I posted a thread on it too. I enjoyed making it & it was a great feeling when it was done but the mess of cast iron dust was not fun.


----------



## tino_ale (Jul 19, 2009)

Won't the 6" set-tru chuck be too big and heavy for the Wabeco? Most people here got the 5" for these reasons on small lathe...


----------



## saltytri (Jul 19, 2009)

darkzero said:


> Congrats on the new chuck! :twothumbs As the others told me, you are going to love it, they were right, I know I do. It's absolutely the best accessory I got for my lathe.
> 
> I'm sure you will have no problem making an adapter plate for it. When I made mine I had zero experience in making one but it came out pretty good IMO. I posted a thread on it too. I enjoyed making it & it was a great feeling when it was done but the mess of cast iron dust was not fun.



Will:

When the Bison adapter blank showed up I said, "Holy C**P!" There's a lot of cast iron dust that is going to come off of that thing! I think I'll set up a vacuum nozzle to pick up as much as possible.

I've had your thread bookmarked for some time. I'll be going over it carefully before I start. Thanks

David


----------



## saltytri (Jul 19, 2009)

tino_ale said:


> Won't the 6" set-tru chuck be too big and heavy for the Wabeco? Most people here got the 5" for these reasons on small lathe...


The D6000 is factory spec'ed with either 5" or 6" so I'm not concerned. The machine seems pretty robust and has quality bearings. If you always started it at full RPMs, I can see how it might be a strain but I doubt that anyone does that.


----------



## tino_ale (Jul 19, 2009)

You're right, the D6000 can come with a 6" chuck.

Did you choose the DIY path for the adapter for fun/cost reasons or is it because there is no readily available option on the market?


----------



## saltytri (Jul 19, 2009)

There's no ready made adapter that I can find. The D6000 uses a spindle disc that is about - I'm doing this from memory so don't quote me - 4" in diameter with a raised 70mm registration boss and three 10mm bolts on an 83mm bolt circle diameter. This is apparently a European configuration but there don't seem to be a lot of chucks available that are a direct fit. One exception is the Bison 5C collet chuck, which bolts on slick as a whistle. When I talked with a Bison/Toolmex rep on the phone, he was unfamiliar with this mount/spindle configuration and surprised that the had anything that fit it.

"Fun" would be just bolting on the 6-jaw and making chips. But if there's one thing I've learned lately about machine tools, it's that one of their most important uses is to make parts for themselves!


----------



## tino_ale (Jul 20, 2009)

What a bummer. Frankly while I can understand the fun of making your own parts yourself it really suck there is nothing available for such a basic need :tired:

Camlock seem to be really cool for this. Bison makes adapter plates to mount your chuck to a camlock spindle nose.


----------



## sdman (Feb 17, 2010)

saltytri,

Do you have a D6000?

I'm thinking about getting one.

What do you think about them?

sdman


----------



## saltytri (Feb 17, 2010)

Yes, I do have the D6000. It has worked out very well for me. You could certainly make an argument that it is an unusually expensive machine but there is a lot of satisfaction in using any excellent quality tool. I also have the new electronic lead screw kit. I haven't installed it yet but it promises to really amp up usefulness and efficiency.

No regrets, no buyer's remorse. Just a big smile on my face!

Let me know if you want specific information and feel free to PM me if you want to visit on the phone.

David


----------



## Tom Anderson (Feb 18, 2010)

Very informative thread! :twothumbs

I just got one of these the other day. Has anyone here ever used one?


----------



## StrikerDown (Feb 18, 2010)

Tom Anderson said:


> Very informative thread! :twothumbs
> 
> I just got one of these the other day. Has anyone here ever used one?




Whatcha going to thread?


----------



## sdman (Feb 18, 2010)

Love to have one but out of my price range for now.

Probably looking at 6K plus not counting the electronic lead screw,tooling,etc.

Maybe an used one will show up sometime.

sdman


----------



## KC2IXE (Feb 19, 2010)

Tom Anderson said:


> Very informative thread! :twothumbs
> 
> I just got one of these the other day. Has anyone here ever used one?



Yep, I've got a die head - love it when I have to do production threading


----------



## Tom Anderson (Feb 19, 2010)

I make a lot of special titanium screws and have been using an APT round die holder in my tailstock. 

When I found this, I thought I'd give it a try. I just need to figure out how to mount it in my lathe. (I don't have a turret - just a quick change toolpost and standard tailstock.)

In case anyone is interested, here is a link I found that has some general information on geometric die heads:

https://www.pmpa.org/files/bulletin_file/Pages_B168-178.pdf


----------



## gt40 (Jun 21, 2010)

I have been at the learning the lathe thing now for only a bit but can make external threads to spec that look nice, smooth and are actually within tolerances. 

Internal threads however are giving me fits. I got the compound setup like in most manuals and stuff but my inside threads are all angry no matter what I do. I tried varying the compound and even using the threading tool upside down like I read somewhere but even with taking small cuts, it is jaggy. Any help would be appreciated.


----------



## gadget_lover (Jun 22, 2010)

I guess I'll be the first to say we need a little more info.

What technique are you trying to use (compound at an angle? Straight? What is your cutting tool? What material are you trying to thread? Are you using the threading dial? What size thread are you going for?

All problems will eventually yield to careful examination.

Dan


----------



## precisionworks (Jun 22, 2010)

> Internal threads however are giving me fits.


Try starting the thread at the headstock end & threading toward the tailstock. You'll need to cut an internal groove just before the thread starts as that's where your threading tip is located when you engage the feed. At least you don't have to worry about stopping at a certain point, just let the tool cut until it exits the bore.

The rest is much like OD threading - tool point on center, shortest possible projection of the tool from the tool block, correct speed for the material, etc.

This article was published years ago but is still worth reading: http://www.mmsonline.com/articles/threading-on-a-lathe


----------



## gt40 (Jun 24, 2010)

precisionworks said:


> Try starting the thread at the headstock end & threading toward the tailstock. You'll need to cut an internal groove just before the thread starts as that's where your threading tip is located when you engage the feed. At least you don't have to worry about stopping at a certain point, just let the tool cut until it exits the bore.
> 
> The rest is much like OD threading - tool point on center, shortest possible projection of the tool from the tool block, correct speed for the material, etc.
> 
> This article was published years ago but is still worth reading: http://www.mmsonline.com/articles/threading-on-a-lathe


 
I haven't tried cutting starting at the headstock but I made some improvements. My problems were getting greedy with too big a cut and having the tool not perfectly on center. I tried both 29 degree and zero degree and with small cuts of .008 to .01, getting decent results with just advancing with the cross slide. I was trying initially to take .015 to .02 a cut and that was the largest cause of my problems. I am now working up to the .0406 thread depth for 16 tpi with a series of progressively smaller cuts. I do .008 till I get to .032 and then go to .005 or so to finish. 

I like having the dro tell me exactly how much I have advanced the tool cutting straight in vs using the compound. For aluminum, I am going to take small cuts and do it this way for now. The best part was I was finally able to cut an inside thread to 1.182" with a .0406 thread depth as per spec to fit the 1.25" male thread.

Here are some pics:







Inside thread:






Still need to clean up the relief part at the start of the thread but it is getting better. This shot was right off the lathe without going over with scotch pad or anything.


----------

