# Inside threading, can you recommend some tooling?



## WobblyHand (Aug 2, 2021)

I'd like to make a canister, kind of like a film canister (remember them?) that's a little longer.  It would be nice to have inside threads on the canister, with external threads on the cap.  Can someone recommend some tooling for inside threading?  I've done some looking around and find it pretty confusing.  Is there LH tooling available? My chucks are bolted on so I don't have to worry about them spinning off.  Kind of anxious to single point them blind (normal way), that's why I am asking about LH tools.    Only have a mini-lathe, so big bars need not apply.  The largest possible bar I could use is 1/2" and I'm not sure I can guarantee getting a 1/2" bar to center.  I have seen some bars with carbide or even HSS inserts, but am unsure what would be "good enough".  

I have read about inside threading on HM, but sadly there are few if any pictures of setup.  I find the visuals very helpful.


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## SLK001 (Aug 2, 2021)

What size?  What material?  I'm assuming that you will want thin walls, so I would do it with a very sharp HSS tool set in a boring bar.  I would also do it blind.  This is a skill that you will need if you're using a lathe, so practice it now and become proficient at it.


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## talvare (Aug 2, 2021)

I have used the tools from this company with good success:









						THREADING TOOLS | mesatool
					






					www.mesatool.com
				




Ted


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## Illinoyance (Aug 2, 2021)

If you are flank feeding angle the compound 29.5* in the opposite direction from what you use for external threading.  If plunge feeding it makes no difference how the compound is set.

I am with SKL001 on the tooling,  a boring bar with a 60* tool bit.  I prefer this over carbide insert tools.

If you are determined to use carbide check out Banggood for internal threading bars.

Micro 100 sells internal threading tools in HSS.


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## T Bredehoft (Aug 2, 2021)

Threading with the tool upside down, on the inside of the back is less stressful, the tool comes out of the work as it cuts, rather than having to stop before it crashes. With the spindle turning toward you, (conventional) you cut the same direction as when threading outside.

Small bore. Start with a 3/8" HSS  tool blank and remove (slowly) all the stuff that isn't a cutting tool. You'll have to be exceedingly careful to leave the threading tool on the end, but it's worth it. You won't be leaving more than 1/2" of thread, so get a narrow grinding wheel, or spend a lot of time with a 3/4" wheel.

I have made a threading tool from a No 0 center drill, captured in a piece of drill rod for ID work, too.

It's all good experience.


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## benmychree (Aug 2, 2021)

Bokum makes HSS threading tools with 3/8 integral shank, form relieved, grind only on top, lasts for many years with normal use, not sure if they make a left hand tool.


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## markba633csi (Aug 2, 2021)

Wobbly: When you say LH threading do you mean to cut a left-handed thread or do you mean something else?
-M


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## WobblyHand (Aug 2, 2021)

markba633csi said:


> Wobbly: When you say LH threading do you mean to cut a left-handed thread or do you mean something else?
> -M


Not a left hand thread.  Sorry, I meant to use a LH tool and thread outwards.

I'd try a HSS tool "normal" in.  No way for a Micro 100 solid threading tool in normal mode.  I would need a ton of practice with a HSS tool first before using a Micro 100 tool.  The Micro 100 would have a life of less than 5 minutes in my hands! (4 minutes and 30 seconds of trying to screw up my courage to try and 30 seconds of use!)  They snap real easy if you bump the bottom, had a Micro 100 solid carbide boring tool that I used for quite a bit, then a moment of wandering attention and pop!  $40 evaporated in a millisecond.  Need something more forgiving in the beginning.


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## WobblyHand (Aug 2, 2021)

benmychree said:


> Bokum makes HSS threading tools with 3/8 integral shank, form relieved, grind only on top, lasts for many years with normal use, not sure if they make a left hand tool.


I will check that out.


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## markba633csi (Aug 2, 2021)

Ok, for threading outwards, RH (conventional thread) two ways: 
1) Spindle reversed,  tool down,  cut inside of bore closest to you  ("LH style tool")
2) Spindle reversed,  tool up, cut inside of bore away from you   ("RH style tool")
I think the second one is easier, better visibility
-M


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## WobblyHand (Aug 2, 2021)

T Bredehoft said:


> Threading with the tool upside down, on the inside of the back is less stressful, the tool comes out of the work as it cuts, rather than having to stop before it crashes. With the spindle turning toward you, (conventional) you cut the same direction as when threading outside.
> 
> Small bore. Start with a 3/8" HSS  tool blank and remove (slowly) all the stuff that isn't a cutting tool. You'll have to be exceedingly careful to leave the threading tool on the end, but it's worth it. You won't be leaving more than 1/2" of thread, so get a narrow grinding wheel, or spend a lot of time with a 3/4" wheel.
> 
> ...


A year ago I ground a trepanning tool and a crude grooving tool to make my led spindle light.  Had a devil of a time with the groover.  Didn't have the correct tools for the job really.  But the HSS tools I made did work and the spindle light was finished. Don't have a small bench grinder or a decent rest for the grinder.  It's the rest for the grinder that makes things easier.  The sheet metal rests on common consumer grinders are a joke, they vibrate like mad, aren't even level, and are difficult to set.

But making a tool and using it is satisfying.  I'll poke around and see if I can cobble something together.


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## WobblyHand (Aug 2, 2021)

markba633csi said:


> Ok, for threading outwards, RH (conventional thread) two ways:
> 1) Spindle reversed,  tool down,  cut inside of bore closest to you  ("LH style tool")
> 2) Spindle reversed,  tool up, cut inside of bore away from you   ("RH style tool")
> I think the second one is easier, better visibility
> -M


I think I understand, but, if you could find a picture it would really help.  Up and down, what do you mean?  

Suppose we have a normal ground HSS threading tool made from a blank and are using it for outside threading.  Up means the flat is on top?  And the relief on the sides is on the bottom?


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## markba633csi (Aug 2, 2021)

Yes, up means flat on the top- like a conventional HSS tool mounted normally


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## WobblyHand (Aug 2, 2021)

SLK001 said:


> What size?  What material?  I'm assuming that you will want thin walls, so I would do it with a very sharp HSS tool set in a boring bar.  I would also do it blind.  This is a skill that you will need if you're using a lathe, so practice it now and become proficient at it.


Size, presume you mean ID.  For what I want, 0.75" and up.  Material?  Workpiece or?  For the workpiece, I'll practice on 6061, but would like to make it out of 304.  Thin walls.


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## WobblyHand (Aug 2, 2021)

markba633csi said:


> Yes, up means flat on the top- like a conventional HSS tool mounted normally


Ok.  I do have a carbide micro 100 like threader, but I have to check if it's LH or RH.  But I really don't want to use it until I am past initial ineptness     But at least I can check the handedness.


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## WobblyHand (Aug 2, 2021)

benmychree said:


> Bokum makes HSS threading tools with 3/8 integral shank, form relieved, grind only on top, lasts for many years with normal use, not sure if they make a left hand tool.


They sure don't make it easy for folks these days.  Their threading tool catalogs are not online, only boring tools.  Looks like their website hasn't been updated since 2011.  Their boring bar catalog uses a URL which is obsolete and has been taken over by an internet squatter.  Weird.


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## WobblyHand (Aug 2, 2021)

Illinoyance said:


> If you are flank feeding angle the compound 29.5* in the opposite direction from what you use for external threading.  If plunge feeding it makes no difference how the compound is set.
> 
> I am with SKL001 on the tooling,  a boring bar with a 60* tool bit.  I prefer this over carbide insert tools.
> 
> ...


What does Micro 100 call them?  Can't seem to find them.  I just downloaded the 2021 catalog and didn't see them.

Where can I find a boring bar with a 60* HSS tool bit.  These are small HSS blanks, like 1/4" square and smaller?  Where do you get them.  Don't know what the correct name is for a search.

For flank feeding (what I normally do for external threading) do you mean -29.5* from the perpendicular to the spindle axis?  External threading would be +29.5* CCW from perpendicular.


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## Janderso (Aug 2, 2021)

WobblyHand said:


> They snap real easy if you bump the bottom


Yes they do.......


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## Nutfarmer (Aug 2, 2021)

Joe Pie has a good U Tube video on threading away from the head stock with the tool bit upside down with the lathe in reverse.


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## WobblyHand (Aug 2, 2021)

Nutfarmer said:


> Joe Pie has a good U Tube video on threading away from the head stock with the tool bit upside down with the lathe in reverse.


Watched it a couple of times!  Not sure about the tooling, which is why I'm asking these simple questions.


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## WobblyHand (Aug 2, 2021)

If I were to get something like a SNR0010K11 that is a RH tool, and I'd flip it upside down and reverse the lathe?  Can one get an insert that would work for grooving as well?  Would like to have a thread start area.  Or have I got it all backwards?  This confuses me, a lot!  I could go up to 12mm, or a SNR0012K11.  Is this ok?  SNR0012K11 & Inserts


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## WobblyHand (Aug 2, 2021)

Internal & external threading tool seems like it would work, although it is a bit expensive.  Not sure if possible to flip and thread outwards.  Does have HSS inserts.


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## markba633csi (Aug 2, 2021)

Yes that one looks good, and LMS has a good return policy if it doesn't work out for you
I've seen some inexpensive stuff on Aliexpress also, if you can wait a month
-M


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## WobblyHand (Aug 2, 2021)

I can wait, did I say that?  Yeah, I _could_ wait.  Don't want to, but I can wait.  Is the snr0012k11 style reasonable for my intended use?

Only issue with the LMS item is the minimum bore size is 1.375".  Was hoping to make this be 1.25", but 1-3/8 is ok.  And yeah, it is $109.


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## Nutfarmer (Aug 3, 2021)

This just is calling out for high speed steel hand ground tool bit. For a few dollar piece of steel and a little time on a grinder you can have something that will work for a one off item. I have even taken a broken tap and ground one down so the remaining tooth is the cutting bit. Cost is little and I learned some along the way.


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## Larry$ (Aug 3, 2021)

How about this: make a small boring bar by drilling a hole to hold an 1/8" square HSS cutter. Drill & tap a hole for the set screw into the end of the bar. Grind the HSS to a 60* form, lock in bar with set screw. Do the form grind before cutting the bit free so you have something to hang on to. You can grind another piece of HSS to use for a start groove. Run the lathe so you can cut from the inside toward the outside. For an internal thread the bar is mounted parallel to the ways. Doesn't matter what angle the compound is at since it isn't used, just lock it.  It might be worth making a good rest for your bench grinder. If the grinder is mounted to your bench you can make a rest that bolts to the bench top rather than to the grinder. Make it adjustable in all directions/tilt and put a slot for a tool holder to slide in.


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## WobblyHand (Aug 3, 2021)

Larry$ said:


> How about this: make a small boring bar by drilling a hole to hold an 1/8" square HSS cutter. Drill & tap a hole for the set screw into the end of the bar. Grind the HSS to a 60* form, lock in bar with set screw. Do the form grind before cutting the bit free so you have something to hang on to. You can grind another piece of HSS to use for a start groove. Run the lathe so you can cut from the inside toward the outside. For an internal thread the bar is mounted parallel to the ways. Doesn't matter what angle the compound is at since it isn't used, just lock it.  It might be worth making a good rest for your bench grinder. If the grinder is mounted to your bench you can make a rest that bolts to the bench top rather than to the grinder. Make it adjustable in all directions/tilt and put a slot for a tool holder to slide in.


This seems like a pretty good idea.  I can make a little boring/grooving bar.  Will order some 1/8" square HSS.  Was looking at these kinds of bars, but didn't know how to make the square holes.  Round hole, square HSS and a set screw seem like a good alternative.

Been toying with making a grinding rest.  When I first looked at some plans, 2 years ago, I wasn't capable of making one. Just didn't have the skills.  Think it's possible to do now.


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## markba633csi (Aug 3, 2021)

I was going to suggest making something- wasn't sure if you were comfortable with that.  
I actually made a fishhook tool out of a large nail once, and hardened it with my propane torch. 
Worked fine for a couple threads in aluminum
-Mark


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## JPMacG (Aug 3, 2021)

Keep in mind that that Arthur Warner threading tool has a minimum internal bore diameter of 1.375".   Arthur Warner also offers lay-down style tools that work in a smaller diameter bores.  I have both.   I think the lay-down style lacks rigidity.  My opinion is to stay away from the AW internal threading tools.  Otherwise, the AW tools are great and the company is excellent.


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## xr650rRider (Aug 3, 2021)

I use Joe Pie method and use LH boring bar style holder like this one. That size will get you down to 1/2" thread. I use LH micro 100 carbide for smaller sizes. When you use the LH tool, your on backside of hole and running spindle in reverse. You can set your zero (tool bumps in hole) with lathe off and thread out. You can get pretty small with the micro 100 but usually better to use a tap when you get that small.


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## WobblyHand (Aug 3, 2021)

Nutfarmer said:


> This just is calling out for high speed steel hand ground tool bit. For a few dollar piece of steel and a little time on a grinder you can have something that will work for a one off item. I have even taken a broken tap and ground one down so the remaining tooth is the cutting bit. Cost is little and I learned some along the way.


I agree.  Don't have a grinder that can do this right now.  I have a belt grinder with a rest.  I've done lathe tooling with it.  Also have a horrible pedestal grinder with tin foil rests.  The horrible grinder has nothing solid to bolt to for a rest.  The shields are made of thin sheet metal, rather than being cast.  Hard to adapt.  Sure I could make it work, but I think making a little boring bar like @Larry$ is a much easier task.  I can grind the tooling on my belt grinder.


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## WobblyHand (Aug 3, 2021)

xr650rRider said:


> I use Joe Pie method and use LH boring bar style holder like this one. That size will get you down to 1/2" thread. I use LH micro 100 carbide for smaller sizes. When you use the LH tool, your on backside of hole and running spindle in reverse. You can set your zero (tool bumps in hole) with lathe off and thread out. You can get pretty small with the micro 100 but usually better to use a tap when you get that small.


Does your URL and Joe Pie method cut a RH thread or LH?  Jeepers, I have to set things up in slow motion and watch.  It confuses the daylights out of me.  Compounding this is the fact that mini-lathes are not full featured, so I have to just try it and see if it is possible.

I like micro 100 tools, but they are fragile.  Once I build up some technique I'll probably get some more.  Broke one boring bar.  As a learning beginner, they are unforgiving!  They leave an awesome finish.


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## Larry$ (Aug 3, 2021)

That Shars bar that xr650 linked seems like a fair deal for about $44 total. I didn't check how much a box of inserts cost but it came with one insert. 

I follow Joe Pie and like his methods. Especially when it comes to threading. Threading away from the chuck makes way more sense to me than playing chicken going the other way.


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## WobblyHand (Aug 3, 2021)

Larry$ said:


> That Shars bar that xr650 linked seems like a fair deal for about $44 total. I didn't check how much a box of inserts cost but it came with one insert.
> 
> I follow Joe Pie and like his methods. Especially when it comes to threading. Threading away from the chuck makes way more sense to me than playing chicken going the other way.


The inserts from Shars are kind of expensive, but there's all kinds of choices on eBay, including brand names.  Hope the tool doesn't use a proprietary insert.  Probably going to buy the Shars bar AND make a boring bar.  If nothing else, I'll use the homemade boring bar with a groover, which I need anyways to form the thread relief.


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## xr650rRider (Aug 3, 2021)

WobblyHand said:


> Does your URL and Joe Pie method cut a RH thread or LH?  Jeepers, I have to set things up in slow motion and watch.  It confuses the daylights out of me.  Compounding this is the fact that mini-lathes are not full featured, so I have to just try it and see if it is possible.
> 
> I like micro 100 tools, but they are fragile.  Once I build up some technique I'll probably get some more.  Broke one boring bar.  As a learning beginner, they are unforgiving!  They leave an awesome finish.


it cuts a RH thread.  Joe explains in his first video on threading away from chuck, if leadscrew and spindle rotate same direction, you cut a RH thread, if they turn opposite, you cut a LH thread.

Joe Pie explanantion


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## Larry$ (Aug 3, 2021)

WobblyHand said:


> but there's all kinds of choices on eBay, including brand names


I've wandered about how those brand name inserts can be sold so cheap from China. Suspect something is amiss.


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## xr650rRider (Aug 3, 2021)

I've got some of the cheap ones, they come with the Precision Matthews turning and boring sets, probably $2 each and they seem to work great.  The silver ones intended for aluminum, seem to work great on steel or aluminum.   You'll run into ER (external) and IR (internal) inserts.  The ER will work on a RH outside or LH inside threading tool and IR on a LH outside or RH inside tool.


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## WobblyHand (Aug 3, 2021)

xr650rRider said:


> it cuts a RH thread.  Joe explains in his first video on threading away from chuck, if leadscrew and spindle rotate same direction, you cut a RH thread, if they turn opposite, you cut a LH thread.


Thanks.  Sometimes this stuff doesn't stick, until one experiences it! 

Just spent the last 1/2 hour rigging up a fine point sharpie in a boring bar holder to trace out the threads in a bored test piece. What fooled me was I was looking at the back side and the slant of the threads was unfamiliar.  Had to pick up a RH screw and look at it from the other side, to believe what I saw on the lathe.  So on a mini-lathe it's reverse spindle and left feed.  Both the spindle and lead screw are rotating CW looking into the headstock, and the carriage is feeding away from the head stock.


Ok.  Think I know what to do now.  These 11ER inserts, (for a LH tool, threading outward) any special coating to look for stainless?  (Yes, I know the test piece is aluminum!)  Edit: ack!  answered in previous post.


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## WobblyHand (Aug 3, 2021)

Larry$ said:


> I've wandered about how those brand name inserts can be sold so cheap from China. Suspect something is amiss.


Suspect many are counterfeit.  For the use I am giving them, just learning, probably fine.  Most of the inserts I've bought, even from Hong Kong, have been fine.  Between you and me, I'd rather pay $1 per, than $10 or more, especially since I'm not making a living at this.


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## xr650rRider (Aug 3, 2021)

I made bushings for all my internal threading and boring bars, then use an Aloris BXA-4D holder which has a 1" bore.  you could split the bushings but I put in set screws.  I've got a 1-1/2" OD piece of aluminum bar that is cut exactly to my center position, so setting it on flat way and using a straight edge, quick and easy to set tools on center.  While I have a grooving tool, I rarely cut a thread relief.  I'm using my DRO to set an exact start position, I do NOT use compound only cross slide and feed straight in, so I'm starting in same position every time.  If I had a thread that needed to bottom then I'd cut a relief.


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## stupoty (Aug 3, 2021)

WobblyHand said:


> I agree.  Don't have a grinder that can do this right now.  I have a belt grinder with a rest.  I've done lathe tooling with it.  Also have a horrible pedestal grinder with tin foil rests.  The horrible grinder has nothing solid to bolt to for a rest.  The shields are made of thin sheet metal, rather than being cast.  Hard to adapt.  Sure I could make it work, but I think making a little boring bar like @Larry$ is a much easier task.  I can grind the tooling on my belt grinder.



I tend to rough the threading bits on the grinder and final shape with bench stones.

Stu


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## WobblyHand (Aug 3, 2021)

Found some 0.1875" diameter HSS in my stash.  Ground a flat and a 60* point with 15* relief angles.  That was the easy part. The hard part (for me) is honing it and not destroying it in the process.  It's real hard to maintain the angles with such a small flat, but I'm plugging away at it.  I have some 1/2" 1144 I can use for the bar.  Without making my own boring bar holder, the biggest I can go is 1/2".  I'll drill a hole through the 1144 for the round rod and a set screw.  Guess I will use the boring bar to hold the HSS in place while I grind it off.  It won't be a heavy duty setup, but I hope to be able to internally thread 1/4"-3/8" worth of threads.  At 24 TPI that would give 6 threads, which is plenty.


Lets just say it could be a lot better, but it's what I can do right now.


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## Larry$ (Aug 3, 2021)

WobblyHand said:


> Between you and me, I'd rather pay $1 per, than $10 or more


I've never bought the high end inserts so I don't know what I'm missing. I prefer using HSS though I have a few inserted tools that I use when it happens to strike my mood. I've got a D bit grinder so I can (sort of) easily sharpen lots of different tools. I also have an 8" G Bear bench grinder that is terrible. Our shop has a nice Baldor 8", huge difference. I just free hand on the bench grinder.


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## Larry$ (Aug 3, 2021)

WobblyHand said:


> Found some 0.1875" diameter HSS in my stash.


When I use round  stock for the tool I grind a small flat along it's length for the set screw to always hold it at the correct angle. 
You can use tool holders with a V in the bottom to hold round boring bars or mill flats on the bar for a regular tool holder.


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## ericc (Aug 3, 2021)

Hi Wobbly.  Here's mine. It uses a broken drill bit.  You have to be careful, since the shank is soft (gouges visible).  I used this to make my chuck back plate thread to attach to the spindle (1-1/2"x8).  It worked just fine.


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## Larry$ (Aug 4, 2021)

Ericc, you proved that function doesn't require beauty. But it is beautiful in it's own way.


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## WobblyHand (Aug 4, 2021)

@ericc nice tool!  Looks like it will do the job.

Thanks to some great ideas graciously donated here, I'm nearly complete with the bar and tool.  The bar was pretty easy, just chopped off some 1/2" 1144 and drilled a couple of holes.  One was reamed to 0.1878" since the HSS miked out to 0.18755" and the other was drilled and tapped to 8-32.  I ground an 8-32 SHCS to the approximate length.  Might go with a set screw, we'll see if the screw gets in the way.  While I had the bar in a collet block, I milled a flat in the top and bottom faces, enough so it can be grabbed and turned.



The threading tool was previously ground but there was no flat on it for the screw.  I really don't have a good fixtured way to grind things.  So I decided to sacrifice an 1/8" carbide end mill.  Since these end mills were incredibly inexpensive, (I got 10 for $3 due to an eBay snafu,) I thought it might be worth a try.  I didn't want to try a good carbide end mill.  So put the 3/16 HSS in the toolmakers vise vee and indicated the flat I had ground at the tip.  


Got it as level as I could, about 0.0002" over the 0.15" area I could indicate.  I then used an 1/8" carbide end mill to make a flat.  Was surprised it worked as well as it did.  Is it good?  Not really, but it is good enough, especially with a little touch up with a hone.  Haven't dared to look at the end mill yet, suspect it is in poor shape now.


Have to cut off the tool bit, as it's 3.5" long!  Be back in a little while with the completed assembly.


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## WobblyHand (Aug 4, 2021)

Took me a while.  Not to cut the HSS, but to find the little bugger when it bounced on the floor and rolled away.  Flashlight chose to work for 15 seconds at a time.  Eventually found it.  I cut it too long, but that's ok as the plan was to grind it off in the tool holder after a bore test fit.  Set up to work in the smallest bore of about 1".  What I want to eventually thread is larger.  The SHCS head is too high, it hits the bore for an 0.84" ID.  Think I will turn an 8-32 set screw to length.  It needs to be around 3/16" or so.


I had ground off the 8-32 SHCS but didn't get it flat,  This is slightly turning the bit.  If I do the set screw in the lathe it will be reasonably flat.  

This all has been an interesting and fun diversion.  Never made something like this before.  I'm liking having this capability, gives me the giggles.


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## WobblyHand (Aug 4, 2021)

Tool is done, but I must be tired, because I'm not cutting a good thread.  Trying for 24 TPI.  Used chart on side of mini-lathe and did a scratch pass, which seemed ok.  When I measured the sharpie "thread" it was 24 TPI, or so I thought.  Chart setting is one of the _allowed_ settings for 24 TPI.  A,B,C,D = 40, 65, 45, 60.  This is a valid setting according to littlemachineshop.  I'm backing the tool into the workpiece using a stop for a reference.  Then advancing directly into the piece.  I wait for the thread dial to hit 1 and start the feed.  I'm getting multiple threads.  Seems I'm missing something obvious.  Am I not taking up the backlash of the leadscrew properly by starting without thread relief?  I tried multiple times, and wiped out the thread entirely.  Good thing this is a test piece!  Almost positive I'm not shaving off the back side, but will check again.


Have to say, this is good practice, and I don't feel bad about this piece at all.  Rather make my mistakes on junk, rather than expensive stock.

Edit:  thought of something.  Do I need to drop the tip down of the tool bit?  Most other tools are rotated below center to gain additional clearance.


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## Larry$ (Aug 4, 2021)

WobblyHand said:


> The SHCS head is too high, it hits the bore


Put the set screw in from the end.


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## WobblyHand (Aug 5, 2021)

Of course!  Can't believe I didn't think of that.  Oh well, I cut down a set screw in the lathe.  Good thing, since the flat was ground on the top of the bit.  Next time, I will try the screw from the end.  Soon, I should have some square HSS which should give me more options.


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## WobblyHand (Aug 5, 2021)

Tried two things.  1) lowered the bit so the point was closer to center line & 2) used a different gear combination.  The little machine shop gear calculator creates some settings that, at least for me, were physically impossible.  Found a different combo that worked for 24 TPI.  60, 45, 40, 80.  Checked the scratch pass with a gauge and it was correct.  I also slightly extended the bit outwards.  Think I will back that off as I got a tiny bit of singing.  (High frequency chatter)

Things progressed ok for a couple of passes.  Then it seemed everything had gone wrong.  What really had happened was a bit of tearing.  I then made a light pass of 0.002 at slightly higher spindle speed which cleared up the thread.  Here's an inside right hand thread 24 TPI in 6061 made with a home made inside threading tool using a "left feed" and reverse spindle.  Focus is not as good as I'd like, but at least it is a picture, and it did happen!  


Thanks for everyone's help.  Now to make a matching plug.  To match this I turn the male blank down to ID + 0.5/tpi ?


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## Larry$ (Aug 5, 2021)

Aluminum is prone to thread tearing. I've tried several different tapping fluids and varying speed. Seems like a higher speed often improves the finish. It certainly cut the time. 300+rpm works.  Requires feeding away from the chuck to be safe. Square bits work fine in round holes. The set screw against the flat of the bit keeps them from rotating. Only disadvantage is, you need to have the grind oriented to the flat since you can't just rotate the bit like a round one. 

I've got a D bit grinder which makes sharpening somewhat easier. The grind is also smooth enough that I don't fool around with honing. It took me a while to figure out how to get all the angles set. Not all that hard once you've done it a few times. Using a commercially made bit as a reference helps. There is a lot of information about what exact angles each grind should be. I'm sure there has been lots of testing to come to those #s. If I manage to get in the "ball park" and the bit cuts OK, good enough. 

I've got lots of 1/4" & 3/8" round, dull, carbide router bits to make into cutting tools for metal. HSS is a lot faster to grind so it is the choice for short term use. There is a lot of difference in various HSS formulations. Some grind easier but usually don't hold up as well. I don't see any difference in the cut quality of a sharp HSS VS a sharp carbide.


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## WobblyHand (Aug 5, 2021)

The matching plug I made is loose.  Apparently my formula is wrong.  It fits but could be a lot snugger.  
Correct formula for male OD = ID of threads in tube + 0.866/tpi.  It kind of feels like there's 0.016" of slop in the thread.  Which is what the difference is between 0.866/24 and 0.5/24.  No problem, I'll make another.  That's why we practice and learn!


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## WobblyHand (Aug 5, 2021)

Made a reasonable plug cap for the inside thread.  Using the formula in the previous post, turned it down to a few thousandth over the formula value.  Externally threaded it.  Now the thread fits properly and isn't loose.  Knurled it to make it look a little nicer.  First attempt at a straight tool knurl.  May have over pressured it and got some flaking.  Learned another valuable lesson about holding the workpiece.  (That's we call screwups!)  Had made a spacer for the lathe so the plug cap would just stick out of the chuck.  Then used some aluminum shims to prevent marking the workpiece.  Since the cap was not very thick, there wasn't much of the jaw holding the piece.  While facing the piece it grabbed the cap, dug into it and pulled out the piece from the chuck and jammed it into the tool.  Made some pretty deep gouges.  

Decided to thread the piece into the lower half and chuck that into the lathe.  Put an o-ring into the thread relief to act as a buffer. Then faced off the cap.  The cap wasn't perfectly concentric, but it worked out ok for facing.  With the cap screwed all the way in, the container should be waterproof.


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## JPMacG (Aug 11, 2021)

Aluminum threads against aluminum threads have a propensity to gall.  When this happens it is like they became welded together.  There are lubricants that help...   molybdenum disulphide is one.


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## SLK001 (Aug 11, 2021)

WobblyHand said:


> Tool is done, but I must be tired, because I'm not cutting a good thread.
> View attachment 374370



If you're trying (still) to thread left-to-right, it looks like your tool is not upside down (which it needs to be).  If you cut that way, you did little cutting and a lot of dragging.


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## WobblyHand (Aug 11, 2021)

SLK001 said:


> If you're trying (still) to thread left-to-right, it looks like your tool is not upside down (which it needs to be).  If you cut that way, you did little cutting and a lot of dragging.


Can you explain this, please?  The lathe is in reverse, (CCW) the flat is pointing towards the backside and is upright.  Why is this incorrect?  Basically it is a LH tool, not a RH tool turned upside down.


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## WobblyHand (Aug 11, 2021)

Thanks for the tip on aluminum galling.  The aluminum was only a test piece with stock that I had on hand.

When I get a chance, I'm going to do internal threading on 304.  I have two ways to do it, either a LH threading bar with carbide inserts, or my home made tool (with HSS), which is ambidextrous!  It can be right or left handed, depending on how I insert the tool.  When I cut threads towards the tailstock, it was left handed.


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## SLK001 (Aug 13, 2021)

WobblyHand said:


> Can you explain this, please?  The lathe is in reverse, (CCW) the flat is pointing towards the backside and is upright.  Why is this incorrect?  Basically it is a LH tool, not a RH tool turned upside down.



Okay, I had to think about the geometry and you have it correct.


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## WobblyHand (Oct 5, 2021)

An update:  The 3/8" LH threading bar I bought from Shars is ok for smaller stuff, but not so good for bigger stuff simply due to its diameter.  Even choking up on the tool leaves quite a bit unsupported, almost 3/4".  It chatters a bit.  I used my 1/2" bar that I made and it is ok for easier to machine materials.  It was chattering in thin walled 304.

A few days ago, I tried the 1/2" bar on some 4140.  The wall thickness was 10mm, still got a bit of rough cutting.  Have a bit stick out which is as small as I can do, and the tool stick out from the boring bar holder is 3/4".  The OXA boring bar holder is made of 7075.  The quality of the cut isn't that good.  There's some chatter marks on both sides of the thread.  I also found the tip of the top seemed to have broken off.  There is a small flat spot on the tip, which didn't used to be there.  Unfortunately this is not obvious in the photo.  Some of this is reflective of my tool grinding skills, which apparently needs improvement.  Perhaps other parts are the rigidity of the platform, being a mini-lathe.  Thought I would show the photos to see if anyone can think of some changes to make.






My LED flashlight is apparently strobing.  I was trying to use it as fill light.  Won't do that anymore.  Male thread cut with SER1010 + AG60 insert in 1144.


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