Using a TAP as Thread Boring Tool

hello welcome to another threading tips 2021 long time viewers will know we do a threading tips video every 2021 years this is episode number four turning tools for small internal threads i know it's been a while since that last video so before we dive in let's do a quick recap threads are generally classified as internal or external contrary to popular belief internal threads are not limited to the ones you do in the comfort of your own garage with all the right tools nor are external threads the ones you do under your friend's car with rusty dull flea market taps and a pipe wrench perhaps counterintuitive internal threads are the ones inside of a part external threads are the ones on the outside of a part and to make matters worse you can even have both internal and external threads at the same time i mean you can't make this stuff up today we're talking about cutting threads on the lathe specifically tools to cut threads on the lathe especially specifically tools to cut internal threads on the lathe fundamentally tools to cut internal threads are the same as tools to cut external threads but shaped a bit differently to be able to get inside of a part because this video would be altogether too short otherwise let's recap external threading tools step one we have a something something spinning in the lathe we want to cut threads onto or into it wouldn't look like this because if it did you'd probably be done already but i don't know maybe you want to pick these up because you need to take a little more off or you need to continue this thread whatever you got something spinning in the lathe you need to cut threads into probably your basic tool is a high speed steel blank you or someone else ground the thread form into in this case 60 degree v for 60 degree threads but it could be acme thread or whatever that tool comes in while the lathe is spinning sweeps across the part and cuts your thread usually you have to do that in multiple passes after the high speed steel tool maybe you've got braised tools some kind of a mild steel shank with a little piece of carbide brace to the tip the carbide again has the thread form shaped into it that we want to transfer into the part carbide tip tools are exactly the same as high speed steel except they shatter the very first time you use them then of course there's insert tooling same story here except the thread form the shaped cutting edge is baked right into the insert and usually they have two or three tips you can index to when one breaks or no longer cuts the way you like and lastly perhaps you could use thread cutting dies usually for smaller diameter work but they do come in bigger sizes if you're a masochist i mean machinist you turn your part to the correct diameter for the thread and just simply run them on with a wrench they'll cut your threads in one go though you don't have as much control over these they'll only cut one size thread there are some that you can do some fine adjustments to but moral the story you don't really have as much control as you can with a single point threading tool but then again they work probably 98 of the time internal threading tools i'd have sworn i had more of these but by the looks of them i just regrind the same two or three i have not sound like a broken record broken record broken record but the business end of these are exactly the same as the external threading tools but they're bent or ground rather all add a shape to get to the insides of things external threading tool internal threading tool any viewers out there who've tried to cut an internal thread with an external threading tool knows that things can get ugly pretty fast bry as you might push with all your strength but you'll likely just end up facing your part and scrapping it because it's too short long before you even get your scratch pass on the inside so you need the same thread form but on a tool that's contorted all out of shape so it can get to the inside here's where things get tricky well potentially tricky if the part is big bigger than your turning tool you're golden you just need to grind the shape of the thread give it some relief all the standard fare and you're on your way but as the parts or bores rather get smaller it starts getting harder and harder to breathe obviously you'll need a smaller tool now not only do you need all the same clearance and rake and all around that cutting tip but you're also going to need clearance for the tool itself clearance to get into and move around the hole keep in mind nine times out of eight you're probably going to be working with a square tool blank and making round threaded holes i'm sure you all remember your kindergarten lessons about square pegs and round holes you'll end up grinding all the corners off your tool and more than likely thinning the whole thing out front to back you need space to move your tool out of the threads and be able to retract to come back out and adjust for the next pass the smaller the bore the more the fact that it's circular is going to start to screw with your tool you'll find yourself grinding everything away and according to science the more you take off the weaker the tool becomes now hopefully you can imagine how bad things get as the bores you try to thread get smaller and smaller can you even imagine what the internal threading tool might look like to get inside of a hole like that correct you'd use a tap you'd be a maniac to try to single point tool something like this at all most smartish people under a certain size would resort to using a tap just to clarify i meant under a certain size hole not under a certain size people as you might imagine and probably depending on your equipment experience or i guess size of parts usually make there is a zone of bore sizes that might be a little too small for you to work comfortably with a single point tool but perhaps too big for you to justify the purchase of the proper tap so sit back my friends relax and welcome to the twilight zone okay okay my staff just informed me that we're well over the youtube six minute fluff limit and i should have gotten to the point five and a half minutes ago you can use taps in the lathe to thread holes larger than the tap diameter but of the same pitch of course this is a 24 tpi tap about one millimeter thread pitch the diameter isn't important for what we're about to do but the thread pitch is and i have it brazed onto some scrap so i could hold it in my lathe tool post in fact we should there we go if you can see that that's where it was clamped in the tool post at some point in my illustrious hobby career i needed to cut an internal 24 tpi thread of a non-standard size allow me to demonstrate this is a one-inch hole bigger than this trick warrant since i could easily get in there with a regular internal threading tool but i wanted to use something that's easy to fill something that's easier to see for you unless something changed overnight no one told me one inch 24 tpi is not a standard screw size though knowing me it'd be just my luck you can go on amazon and buy a one inch 24 tap but i doubt it and even if you could i'd be willing to bet the price would be exorbitant allow me now after seven minutes to just shut up and show you what i'm talking about now the lathe is already set up for the thread pitch of the tap that means the carriage will be moving in towards the work 42 thousandths per revolution of the chuck every time this chuck turns once this tap will advanced 42 thousandths of an inch which is the thread pitch of this tap and there you have it just like that a nice 1 7 30 seconds 24 tpi internal thread of course all the same rules still apply here the tool needs to be on center so you have to take some care to clock the tap in correctly when you put in your tool post so one of those flutes is actually perpendicular or tangent to the bore you can't just throw the tap in there any old way i took it i think just a little deeper than it should have gone i didn't bore or face this part i just pulled it out of the scrap pile and threw it in the truck you probably saw it wobbling a little bit when we looked at the side view while we're standing here and since some of our viewers might not still be around in another 2021 years for episode five don't look at me like that i don't make the rules you can do the same thing to cut external threads with machine dies you know those square die insert things you might see in flea markets and stuff you just load one of those up until your two holders come in from the outside not to mention i think you could actually cut tapered pipe threads in one shot without a taper attachment i guess it depends what you're cutting in the power of your machine i chose to braise this tap in place just because that's faster for me but if you'd prefer you could just fill a block of scrap with set screws just make sure one of those screws grabs onto the tap flat as there's usually a ton of torque on these and they could spin on you that would make for a bad day to wrap things up i'm not saying this is the best way to do it but it's another tool in the proverbial toolbox a tool you might even already own and of course the other popular option when you get into a situation like this other than outright buying the tap you need is to make a tap yourself cut a tap from some annealed tool steel i've got two or three of those videos on that subject here if you haven't seen them but sometimes for a one-off maybe you don't want to go through all that trouble for well now for better for worse you've got this up your sleeve that's all i've got for today hope you guys enjoyed that hope everyone's staying safe and thanks for watching

Channel: This Old Tony

Views: 718,641

Rating: 4.9535928 out of 5

Keywords: tap, metal cutting tap, tapping threads on a lathe, tap as boring tool, single point threads

Id: f-YWsgAHR6A

Length: 10min 2sec (602 seconds)

Published: Sun Feb 21 2021