Grinding a new taper onto a tap?

[pvfjr]

If there was a tap that was missing a few threads here and there toward the tip, and was getting difficult to use...
Could a guy whack the end of it off, and grind a new taper onto the tip? Has anyone ever done this before?

 

[rdn2blazer]

resharpening a tap by hand can be done but is very difficult. it deppends on if the tap is just worn or has actual broken teeth. I will re-gash a tap only at the leed flute area if its worn and I dont want to take the time to go to our tool supplier to get a new one. if it has chipped edges on the leed portion of the tap again it deppends how severe its chipped. it has to be minimal chipping. if its got realitivily large fractured chipping its junk. so if it can be resharpened just remember to keep some "hook" to the leed portion. meaning dont create a flute rake that is flat. you want the chips to be able to curl. also once a tap has been resharpened its on its last leg. use for chasing threads but not for actual tapping. hand resharpened never cuts well at all, but they will chase threads fine. standard taps are pretty cheap now a days even for a good quality tap like OSG, OR Sossner. I will just chuck them when they get dull and buy new most of the time. we use alot of 9/16-18 OSG taps, they cost about 15 bucks each. it cost 13 bucks each to have them sent out for rehharpening, whats the point when for two bucks more I can get a brand new one that allways works better then even a profesionally resharpened one anyways. hope this helps.

 

[pvfjr]

Well I'd just chuck a standard tap, but 7/8-18 is a different story. It has about three or four actual chipped teeth, but it's still tapping at the moment.

 

[rdn2blazer]

Well I'd just chuck a standard tap, but 7/8-18 is a different story. It has about three or four actual chipped teeth, but it's still tapping at the moment.

the bigger the tap the more meat there is to work with. I would try and regrind a tap that big just because of the cost of a new one, especially if its not something you will use on a regular basis.

 

[pvfjr]

That's kinda what I was thinking. I may have to try if it gets any worse.

 

[jarheadk5]

Well I'd just chuck a standard tap, but 7/8-18 is a different story. It has about three or four actual chipped teeth, but it's still tapping at the moment.

Is that a tap for TRE's?

 

[pvfjr]

Yep, that's the one.

 

[mofugly13]

Im thinking, why not? If it's almost useless, then you really have nothing to lose. Grind the end off till you have fresh threads, then grind the first 5 off with a taper, like original. If you have a drill that'll chuck it up, use that and a bench grinder. Just be sure not to get it hot enough to discolor the metal, then you're endeavor will have proved fruitless.

 

[rdn2blazer]

Im thinking, why not? If it's almost useless, then you really have nothing to lose. Grind the end off till you have fresh threads, then grind the first 5 off with a taper, like original. If you have a drill that'll chuck it up, use that and a bench grinder. Just be sure not to get it hot enough to discolor the metal, then you're endeavor will have proved fruitless.

if you do this you will have a tap that does not have ANY leed gash to it and proper clearence for cutting. it will lock up and or wont cut. a tap is a precision cutting tool, you cant just chuck it up in a drill and sharpen it on a grinder. a tap cuts with a progressive manor. look at the end of a tap and how it is ground. it takes skill to properly hand sharpen any kind of precision cutting tool correctly. just try to regrind the factory leed gash back until your chipped teeth are cleaned up.

 

[mofugly13]

OK, to what are you referring when you say 'leed gash'? Are you talking about the 'hook' profile of the cutting edge? I'm not talkin about chucking it up, yanking the trigger and hogging away on the grinding wheel, but using a real slow speed, bracing the drill against something and using it as a 'lathe' of sorts. I'm looking at a tap in my hand right now, I am also looking at a professionally resharpened one. I see how doing it by hand the way the resharpened one would be an excercise in futility, but I don't see why the tap couldnt be shortened past the damaged threads and a new taper ground on the end, making it look 'factory new'.

 

[rdn2blazer]

OK, to what are you referring when you say 'leed gash'? Are you talking about the 'hook' profile of the cutting edge? I'm not talkin about chucking it up, yanking the trigger and hogging away on the grinding wheel, but using a real slow speed, bracing the drill against something and using it as a 'lathe' of sorts. I'm looking at a tap in my hand right now, I am also looking at a professionally resharpened one. I see how doing it by hand the way the resharpened one would be an excercise in futility, but I don't see why the tap couldnt be shortened past the damaged threads and a new taper ground on the end, making it look 'factory new'.

lets start with exactly what type of tap we are talking about here. a 2 flute, three flute, or a 4 flute. there are straight flute taps which are for general purpose applications mainly for hand chasing existing threads that are damaged, then there are spiral pointed taps, these taps have straight flutes and the cutting face of the first few threads is ground at an angle to force the chips ahead and prevent clogging in the flutes. there are spiral fluted taps, these taps have right-hand helical flutes with a helix angle of 25 to 35 deg. these features are designed to help draw chips from the hole. there are many other different types that I wont even get into.


Im talking about a standard spiral pointed straight flute, 3 flute plug tap with positive hook with an eccentric grind which has clearence behind the cutting edges radially which is probably your IMHO most common type of tap. a 3 flute plug tap has a main clearence grind that consists of the "cutting face" and "heel" that serves several purposes. 1, to obviously creat clearence for the chips being cut. 2, for oil or cutting fluid to reach the cutting action. this runs the length of the threaded area of the tap. it can also have several different types of grind clearences ground into the tap. there is negitive rake, zero rake, and positive rake also known as "hook". this clearenced area is NOT for chip evacuation. most three flute taps have a spiral grind which has the first few threads ground on the cutting face at an angle to push the chips ahead. as you can see in the pic with the pen pointing at it.

the eccentric grind clearence is to minimize the cutter contact with the material to keep friction down to a minimum to minimize heat generated by the cutting action. you can see the diameter reading where the mic reads bigger at the cutting edge then is smaller behind the cutting edge.

I was refering to the spiral point grind when I was saying "leed gash". if you grind off the first few threads you will grind away some or all depending on how how much you grind off the tap. also if you then grind a chamfer back on the tap as you decribed using a drill as a lathe so to speak you will probably grind away the eccentric grind clearence. you might even end up with negitive clearence to the begining chamfer lead of the tap which will not allow it to cut. also if you loose the spiral grind clearence the tap might loose its ability to push the chips ahead and load up and lock up on him. this is ofcourse IF he is actually tapping. if he is just chasing threads its no big deal to grind back the tap and loose some of the spiral point. I just would not want to loose the eccentric clearence tapping or chasing threads.

 

[mofugly13]

Thanks rdn2blazer! It look like you took some time on that 'lesson', I appreciate it. While I have each ofthe types of taps you mentioned, I was assuming that the flutes (of pvfjr's tap) were ground like the 4-flute tap in your photos, where it would seem 'relatively' simple to grind a new taper into the end of it. Thank's again for the learnin'. I am always into learning anything new about any aspect of machine work.

 

[rdn2blazer]

Thanks rdn2blazer! It look like you took some time on that 'lesson', I appreciate it. While I have each ofthe types of taps you mentioned, I was assuming that the flutes (of pvfjr's tap) were ground like the 4-flute tap in your photos, where it would seem 'relatively' simple to grind a new taper into the end of it. Thank's again for the learnin'. I am always into learning anything new about any aspect of machine work.

hay your welcome. it took a bit of time mainly because I forgot my camera at home and I have been getting to work just on time so I didn't have time to type it up. one more thing on the spiral point, when the chamfer leed (or lead) not sure of the spelling, is ground the hook that is positive starts to be lessened by the chamfer so the spiral point does two things, it puts positive hook back into the cutting action and ofcourse because its ground at an angle does the forcing ahead of the chips. hope this helps him with his project.

 

[pvfjr]

Yeah, it's just a regular four flute tap. Everything straight, no spiral flutes or points. I'm not needing it to chase, it needs to tap a few more pieces of DOM tubing for TRE's. I think it had a problem with clogging (no surprise without spiral flutes or points). A buddy of mine used it, and I think he may not have been as liberal with the lube as I have been. Since this is such a simple tap to begin with, would it be impossible start over with a new point on it?

 

[rdn2blazer]

Yeah, it's just a regular four flute tap. Everything straight, no spiral flutes or points. I'm not needing it to chase, it needs to tap a few more pieces of DOM tubing for TRE's. I think it had a problem with clogging (no surprise without spiral flutes or points). A buddy of mine used it, and I think he may not have been as liberal with the lube as I have been. Since this is such a simple tap to begin with, would it be impossible start over with a new point on it?

is the chipping on the chamfer angle of the cutting edge? this is where they usualy chip. if so you can hand grind a spiral point gash grind to clean up the chipped teeth. here is where it gets kinda tough. each grind you make on each flute has to be the same as close as you can make it. remember you want to grind the cutting edge face. its hard to do on a regular bench grinding wheel cause the wheel does not have clearence in it where you need it but it is doable. you need to keep as much hook in it as possible too or it wont cut for crap or it will cut with alot of force and your threads will look like crap too. I will try to take a few pics of what I am trying to decribe, hopefully it will help.

 

[rdn2blazer]

well I just called our local supplier and yes they are not cheap. a straight 4 flute 7/8 18 plug tap is about 45 bucks. I got a price on a 3 flute spiral point plug tap, those are about 100 bucks. I found a 7/8 tap that had the chamfer length completely cut off to make a bottom tap out of it. it was trashed so I ground on it and took these pics one shows a short grind and one shows a long grind, kindof creating a spiral point grind. the problem with a 4 flute is the web thickness of the cutting face to the heel side is kinda thin. if you grind it too thin when you try to tap it will break anyways. there is not much meat to grind away with a 4 flute tap. I would grind a long gash that will hopefully clean up the chipped teeth and leave the web as thick as possible. you can see in the pic how thin the web gets with a steeper gash then with longer gash. you can see how there is still hook to it. and when you do grind you will also be hitting the heel side on the adjacent tooth so this is also thinning out the web thickness. hope this helps

 

[rdn2blazer]

better pics of the grind. in the last pic you can see the 2 teeth on the bottom are the short grind and how thin the web gets, where the longer grind the web is thicker. the thinner web is weak and from the high cutting forces that a tap sees it could and probably will fracture the tap. as I said if you are just chasing its not as big a deal but with actual tapping there is alot of force there.

 

[pvfjr]

Wow. Thanks for going to all the effort, you are the man. The tap isn't in my posession right now, but I may see what I can do if I can get a hold of it.

 

[jarheadk5]

Damn...

It's threads like this that make the $25 a year worth every penny. Cheap education... gotta love it!

Thanks!

 

[pvfjr]

I know it. I just re-upped today so I could see these pics. I figure the $25 savings usually comes around somehow.