# Cutting threads



## Icarus (Nov 27, 2013)

Do we have a tutorial about thread cutting on a lathe? Thanks.


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## gadget_lover (Nov 27, 2013)

It's in here somewhere.  I don't remember the name of the thread. Did you check the stickies?

If you search the sub forum for "single point" and "threading" you will find a few dozen threads. From there it's a matter of figuring out which one you want to believe. 

It's not super hard. It's a matter of following a few simple rules and not making mistakes. The biggest problem is that there are certain terms you need to know in order to understand the instructions. Look up the terms "Sharp V" and "Full thread form" and all the terms at . Then you really need to study picture at the bottom of http://www.tanj.com/cgi-bin/tpi.cgi and make sure you understand what the terms refer to. 

Post here if that does not give you a good start.


Daniel


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## KC2IXE (Nov 28, 2013)

First - Happy Thanksgiving everyone.

As gadget_lover says, one of the big things to remember is that Metric/UN thread forms (identical forms BTW) are NOT V threads, but have small flats/radii at the top/bottom.

Let's talk "male" threads here (aka outside threads)

Generally, it is FINE (but makes a weaker thread) to cut a V on the MINOR diameter of the thread (the smaller side), BUT, not on the crest (major diameter). The flats at the top are 8p - aka say you are cutting a 1/4"-20tpi thread - the flats will be 1/160" wide.

Next - do NOT start with oversized stock, and remember that the major diameter of a thread is NOT the nominal diameter - for instance, for a class 2A (most common fit) fit thread, that same 1/4-20 thread will have a major diameter of between .2408 and .2489 - a class 3 fit (really tight) will have a major diameter of .2419 to .2500 (where you JUST meet the nominal - this will be a VERY tight thread)

Take it slow, practice on some scrap the first few times, and it is no big deal


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## precisionworks (Nov 28, 2013)

> 13. When the tool reaches the end of the cut quickly crank the tool away from the work using the cross slide crank AND disengage the half nuts.


Profound advice, remember those words even if you forget everything else. The rest is located here:

http://www.google.com/url?sa=t&rct=...CG-tzDIq3V-T_1kDMd8WfRw&bvm=bv.57155469,d.cGU

Reprinted from _Machine Shop Essentials _by Frank Marlow. Earliest lathe cut threads date to 1483 (cut into wood). Nothing much has changed except that today's tooling is better.


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## Icarus (Nov 28, 2013)

Thanks much everyone for your prompt response. When time allows me I will read everything you referred to. I'm sure I will have more questions then and will post them here. At this time I'm especially interested in cutting threads for Maglites and Surefire E-series lights.


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## gadget_lover (Nov 29, 2013)

Icarus said:


> Thanks much everyone for your prompt response. When time allows me I will read everything you referred to. I'm sure I will have more questions then and will post them here. At this time I'm especially interested in cutting threads for Maglites and Surefire E-series lights.



If you are doing a LOT of the smaller lights, a tap and die might be more economical. It's all a matter of spending time VS spending money. 

You would think that manual threading on lathe takes time because you cut progressively lighter threads using multiple passes. 5, 7 or even more passes are required if you are cutting threads according to the manual. In reality, it's the setup that takes the time. Each pass takes only a small time ( seconds ).

Good luck and let us know how it goes.

Daniel


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## Icarus (Nov 29, 2013)

First question, what cutting tools to buy (for the lathe)? Thanks!


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## gadget_lover (Nov 29, 2013)

The Surefire E series are 13/16-20 for the head and 11/16-20 for the tail cap. 

A full form tool for external threads would be this one... http://www.rileyshutt.co.uk/Products/0016000300160002/PO901100 . If that's a bad link, search for an 16ER 20TPI PG PTC2 POSI THREAD INSERT. It needs a special shaft that you will mount it to.

If you want to do sharp V, then use a HSS (High Speed Steel) similar to these from Little Machine Shop. Internal uses http://littlemachineshop.com/products/product_view.php?ProductID=1895&category= and external uses http://littlemachineshop.com/products/product_view.php?ProductID=4115&category= . If the links are broken look for presharpened HSS threading tool. 

If you have a need for carbide cutters, you can also go with the "D-Style" brazed carbide tips as in http://www.shars.com/product_categories/view/2180608/D_Pointed_Nose

Does that help?

Daniel


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## TexasLumens (Nov 29, 2013)

Icarus said:


> First question, what cutting tools to buy (for the lathe)? Thanks!


 There is no end it seems to single point threading tools. That's the hardest part of threading on a lathe.... picking the tools!! My favorite threading tools are made by Carmex. Go to the Carmex site and do some reading. These are insert style tools. Make sure you pick a tool that will cut the thread / threads you want to do. For instance the insert that I use most cuts from 18 TPI to 32 TPI (I think) . You'll need to match holder and insert as well if you go this route. There are High Speed Steel (HSS) tools available as well.... and many folks grind their own. Just starting out, I suggest a tool that you know is ground properly to cut the threads you want to cut.... that way you know the problem (if there is one  ) with a set of threads you cut you can eliminate the tool. Good Luck! It isn't hard... Just practice! Dan.


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## precisionworks (Nov 30, 2013)

^ What Texas Lumens said - Carmex has a large selection, available almost everywhere, different angle shim seats can be bought to optimize clearance in various materials, etc.

I stopped using HSS anything about 40 years ago but do grind a HSS single point thread tool one rare occasions ... Probably one every 5-10 years. If you run enough odd jobs it will happen & the ability to quickly grind one is essential.


Barry Milton
Precision-Gunsmithing.com
iPhone5 voice recognition


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## gadget_lover (Nov 30, 2013)

I mentioned the other types of threading tools because for someone just getting into it, a $3 HSS tool blank (that you grind down to make the 60 degree tip) can be much more attractive than an Carmex insert and holder. 

FromGrainger, the Tool Bit, HSS w/5 Pct Cobalt, 1/4 In, 2 1/2 is $3.30. They are also available pre-ground.

From Granger the Carmex lay down threading insert for 20 TPI is $28 each, and the holder for it is $120. 

Daniel


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## precisionworks (Nov 30, 2013)

Grainger? I've heard that most of their customers are the same ones awarded the no-bid .Mil contracts & they're using taxpayer funding 

My last Carmex inserts came from Curtis @ latheinserts dot com. $10 or $12 each, three threading tips per insert, so $4/tip. Cheap enough for me.







The holder is a nicely made Israeli knock off - again from Curtis & cheap at $50 IIRC.

Sent from my ASUS Transformer Pad TF300T using Tapatalk


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## DrafterDan (Dec 3, 2013)

+1 on what Precisionworks says. I got my threading tool from latheinserts, the guy there called me up to suggest a different insert because of my "highly refined" insert ordering skills. Good company, that.






The top one is for final cuts/ details/ grooves and the bottom one holds the threading inserts. 
~D


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## darkzero (Dec 3, 2013)

precisionworks said:


> The holder is a nicely made Israeli knock off



Could of fooled me, looks like Carmex to me. 

Both my IR & ER Carmex holders don't say Carmex on them, they came from Enco in Carmex packaging. My ER holder looks identical to yours with the same style & type of markings. In fact the few other Carmex threading tools I've seen in person did not say Carmex on them either. Not sure why some manufacturers do this, I would think they would want their tools to display their name rather than save the cost of omitting. I have a few Dorian holders that don't have Dorian etched on them either but have all the other makings.

Grainger, I'm not a fan of them either but they're great for emergencies. I blew the starting cap on mill on a Thurs night, placed an order online for both caps just after midnight, showed up at the local store at 7 am sharp the next morning when they opened, & I was surprised they had my will call order already picked waiting for me. Went straight to my day job, installed the caps right after work, & was up & running in time for the weekend to finish what I was working on.

Luckily my caps weren't extremely overpriced, I was happy to pay for the availabilty & convenience do to the situation. Large companies like where I work are happy to purchase from them because of the speedy service, kind of like MSC. Of course I'm just a hobbyist but I do shop at MSC.


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## precisionworks (Dec 4, 2013)

precisionworks said:


> The holder is a nicely made Israeli knock off - again from Curtis & cheap at $50 IIRC.






> Could of fooled me, looks like Carmex to me.



Mmm ... searched around a little & found the package Curtis sent it in & it says Carmex. Looked them up & the address is:

*Carmex Precision Tools Ltd. *
*1 Hacharoshet St., 
Maalot Industrial Zone, 24952, 
ISRAEL*


So there we have it, just as you said Carmex doesn't put their name on the tool. Found an identical brand new one for $42.90 + shipping on eBay, same price as LatheInserts. 

Regarding suppliers neither MSC nor Grainger have gotten an order from me this year, pretty certain that's hurting their stock price  McMaster is my go to for most everything as prices are far less than either MSC or Grainger & delivery is next day for actual UPS charges. Amazon is now stocking & selling an amazing amount of tooling & delivery is either next day or second day at no charge (prime member). Still buy some stuff on eBay but not as much as in years past.

Hard to beat LatheInserts if they have the size & style you're wanting. Curt is one of the smartest guys out there & he's really pleasant to deal with.


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