broken tap in piece

[bebob1]

Its hard to manual tap small holes where the tap tool cross section is so small. I can literally snap the taps with my bare hands if i wanted to. My tap was also really brittle. I think it failed because of material fatigue since I wasnt really putting too much force on it any different than the other operations.

I bought another brand of tap and tried again, this one 2 flutes instead of 3 so cross section is larger. Its also HSS and not coated. Seems to be better as I now finished all the taps. I also changed the style of tapping, I rotate the tap maximum 120 degrees when hit with mild resistance when tapping, then I back off completely, clear chips in tool and hole and repeat. Small taps require more babysitting.

Yeah, Im gonna throw another carbide at it and then I will give up. I will try the helical approach. The problem is, the end mills dont have enough reach and my threads go really deep. The tap is stuck deep. I think EDM is really the only approach but I dont have a commercial machine. DIY technique works but slow and now recirculating flow to flush dust away. This is quite important as it stains your part. Now my part has brown stains from the eroding of the steel tap.

EDIT: I just got my hands on a 1/16" 4 flute TiAlN coated end mills. This stuff works. My other plain carbide 1mm broke. This one is eating it away, although I can only have enough space to do plunge milling. I lost one of the flutes that broke off but Ive managed to mill out quite a bit. although the threaded parts of the tap is still locked in.

[txcncman]

A final consideration in tapping is that machine tapping is way more consistent in the forces applied than hand tapping. While hand tapping, most breakage occurs, not from chip build up as falsely imagined, but side forces applied and tap alignment not being true to the drilled hole. Use a tapping jig or hand tap machine to reduce tap breakage.

[mcarvey]

So plain and simple, broken taps suck. I have yet to find a good way to remove small taps (4-40ish) that break below the surface. I usually just take some deep breaths, and remake the part. I've tried basically everything except for EDM and that nitric acid stuff. I haven't had much luck with drilling them out (using 140 deg carbide spade drill) or milling them out (although I haven't tried that too many times) I tried one of those finger tap removers and it didn't come close to working. Tried welding something to the tap- no dice.
When I need to tap a 4-40 hole, I'll do the following. fyi I tap pretty much everything using a cordless drill on a low clutch setting. If I need to tap a lot of holes I'll use my tapping head.
-use a larger drill bit (#41 in aluminum, sometimes even larger in steel depending on the depth). I generally will try to make the hole a through hole. Obviously you may not have these luxuries.
-I use a high quality, 2 flute spiral point tap. FYI spiral flute taps break WAY more easily, and are just as difficult to remove when they break. If I'm doing a blind hole, I'll just drill a bit deeper, and the spiral point tap pushes the chips into the extra space.
-use some sort of taping fluid.
-I've also started to grind a groove in the body of the tap- the thought being that if I bend/over torque the tap, it will break there and not under the surface of the part. I haven't had to test this, but one day I came back and found that tap broken in half at the groove. I'd like to think I saved my brother some frustration.

Hope this helps,
-Matt

[cheetahcnc]

...
-I've also started to grind a groove in the body of the tap- the thought being that if I bend/over torque the tap, it will break there and not under the surface of the part. I haven't had to test this, but one day I came back and found that tap broken in half at the groove. I'd like to think I saved my brother some frustration.

Hope this helps,
-Matt

Thanks for the tip. Great .

Jim

[LUCKY13]

Have you tried these before?


JTS Machinery & Supply Co.


Jess

[HorridHenry]

side forces applied and tap alignment not being true to the drilled hole.

This is true.

Use a tapping jig or hand tap machine to reduce tap breakage.

I had to appeal to my feminine side when tapping the other day,well you know what I mean multitasking anyway I put the tap in the benchdrill chuck lowered the chuck and twisted the chuck by hand,lowered chuck,twisted chuck,lowered,twisted till it was done,quite a task using both hands in that way.

I can write me name with both hands at the same time so I quite pleased with the tapping the way it went.

[dak1]

Be very careful with drilling oversize! Gages may work fine, but that doesn't mean you have an structurally sound thread. We've seen a couple cases of this over the years. The one I remember was like some #6 or #8 threads in 17-4 stainless. We had a light head fall in a medical facility. (I don't remember if it hit a patient/employee or anybody). After investigating, we traced it back to tapping issues which the operators "corrected" by drilling oversize. The GO/NOGO's worked fine. The threads didn't.

[HorridHenry]

We had a light head fall in a medical facility. (I don't remember if it hit a patient/employee or anybody).

I guess they musta felt light headed.

[dak1]

I'm guessing so.

I think upper management probably felt so too after the lawyers were done.

[mcarvey]

dak1,
Thank's for the PSA about the dangers of using larger drill sizes- I should have mentioned it in my post. One can never be to careful about these things. Obviously using a larger drill size affects the shear strength of the threads. If you're making parts in a production setting absolutely don't use a larger drill size without consulting with the person who designed the part.

-Matt

[dak1]

Yea. Wish our operators had consulted with with someone. We're quite cautious about minor diameter now. Lawsuit settlements will do that. That also opens up a can of worms about acepptable thread perctentage, especially on formed threads. Formed threads are typically stronger than cut threads, but since the crests are formed, they are more prone to minor variation affected by a number of factors. We occassionally run into issues where one tap drill causes a slight oversize on the minor, but the next size down causes undersize and/or tapping issues. We're still trying to take the gay area out of that debate. We may have to stock e few more metric drills to resolve that. The case of the light head was not a result of this scenario though. It simply lead to the added scrutiny of minors & the visibility of this issue.

[bebob1]

Yeah I decided to remake the part. I couldnt completely remove the bit. It is a royal PITA. The material I think is HSS. Hard stuff. People normally machine HSS by grinding this stuff or EDMing it, but drilling or milling it. Trying to drill it away or mill it away is prone to be more expensive than remaking the part if its like aluminum. i managed to mill away a lot of the HSS tap with my TiAlNi coated end mill but that end mill took a beating. Its blunted and stuff. The end mill costs more than the piece of aluminum. Probably better to scrap the part. Well I had a 100 holes to tap manually and taps broke 30% of the way thru so it sucks. Plus, the hole where I looked to have removed the majority of the tap, wasnt. There was probably a minor wall or scap of it way deep into the thread. As it ends up I couldnt tap it any further deeper because there is probably a HSS remnant left there preventing further cutting after removal, as proved by a magnetic attraction on the aluminum part. So I made a second part instead. It was a lost cause afterall.

I think tapping small threads is a different beast to tapping larger threads because now with the cross sectional area of the tap so small that its strength sometimes cannot cope with the conditions in application. With normal large taps you can probably cut a few rotations worth and have the tap cutting edges taking on lots of engagement, but with a small tap, if you do the same and have a lot of the cutting edges having full cutting engagement, that might be enough to cause resistance that breaks the tool upon attempt to unthread it.

I am thinking I should investigate into thread milling in the future.

Its possible to break the bolt used to thread form also and have that stuck instead of the tap, which is equally a pain, except bolts are probably normally not hard stuff like HSS so its less of a pain.

anyone tried helicoils?

The idea to put a stress concentrator is a good idea. Same concept with crumple zones in cars. But if the tap is really gummed up in there, even if it breaks in the control spot, you probably still cant get the tap out easily without exposing it to stresses that can break it under normal conditions afterwards, so its possible the tap can still be stuck and broken afterwards?