To admit defete

[pdentrem]

It was a Ram EDM. Yes if you have one in the area and it is not busy and you are willing to wait and pay they do work.

 

[4GSR]

A set of LETTER drills is also good for the larger size taps. A 1/4-20 thread tap needs an "F" size drill.

I don't think you want to use a letter drill "F"(.257" dia.) for a tap drill for 1/4-20 thread. "F" would be correct for 5/16-18 thread. For 1/4-20 thread, I preferr no. 6 (.204) tap drill instead of no. 7 (.201) drill for the stuff I make.

 

[Tony Wells]

Where I use to work one of the service guys broke some taps in a customers machine that could not just be thrown away. One of the machinist from the factory took some equpipment and went to the customers plant and removed the broken taps without any damage to the machine. As I recall it involved something electrical with a hollow electrode and some fluid. I have thought of trying to build something like it. Maybe some one knows that process and it could be built for hobby use. Need to do some research.......


Benny

Could have been a ram/sinker EDM, or something a little simpler sometimes called a "tap disintegrator" There was one on the market under the brand name Elox. There are still some made. I used to burn out taps pretty regularly with one, but I can't recall the make. If you're into homebrew, try this:

http://mikesworkshop.weebly.com/a-spark-erosion-apparatus-mk-3.html

There are lots of plans online for home-built sinkers. Some are pretty exotic, mimicking the commercial units.

 

[jumps4]

I hope i'm not wearing out my welcome here I'm bored but cant go to my shop today
I have quite a bit of boat shaft brass and it is very tough almost elastic if not heat treating to soften it
I had the problem and almost gave up using it untill I found out how to make it soft
heat it to a red glow and quench it in water
I know it sounded wrong to me also
but i use it on all my salvaged brass now and it really will make it softer and machines fine then
steve
ps i saved that tap-die link
i have broken my share of taps and always makes me wonder why i still tap the holes last :huh:

 

[GK1918]

Thats odd jumps4 I dont have any problems with shafts most are around 1 3/4 - 2". Anyways my defete
was my stupidness. I dont really care about the tap got plenty, I made another thread stop faster,
easy- one side has dovetail the other does not, the one with no dove t. I just use a dowel pin, again I
tapped it for a small screw. takes care of that. A thread stop, I cant live without and not only for
threading I use it for turning all the time, myself I just do better taking cuts with the compound. And
then for me with these eyes, with out a stop internal threading is torture. My guess is people back
in the 30&40s must have had better eyes to read the dials it took S Bend 100yrs somewhere in the
1950s to come up with large dials. Now tell me, say turning, isnt it easy and faster to end the cut, back
off cross, return, slam crossfeed to this stop, and advance compound?? just like treading. Maybe its
just by habit, I feel more control using the compound. thats all sam

 

[Tenn]

Yes a good center punch works good at times to finish busting out a "carbon steel" tap and sometimes a magnet works to pick out the pieces...BUT... it won't work on a HHS tap Been there done that and even broke my carbide end mills trying to drill the HSS taps out. HSS taps are far superior to carbon steel "in some instances" but not when they break.

Below is the chart I use to drill my holes. 70% threads or even 60% threads work good so long as the metal you are threading is at least as thick as the dia. of the bolt or screw you are tapping for. 60% is loose and IMO is best if you have twice the dia. of steel or other material as the dia. of the bolt screw. A little discretion is needed as to the application if you need a tight thread or if a loose thread will do.

Hope this helps ?
BTW the same holds true for drill bits when they break. Carbon steel shatters hew: and will bust out but HSS anic: won't.

Also a High Helix Tap really works great on blind holes. They say "made for soft materials (brass, aluminum) but they work great in steel too and are well worth the little extra they cost.

 

[jumps4]

I was just lately able to thread with my lathe I had to add a tread mill dc motor to my lathe ( chinese 9x20 wannabe lathe ) to slow it down enough I could thread
now I set the compound slide at 29 degrees
run the crossslide in untill the tool touches and zero the dials on both
i set depth of each pass only on the compound
i use the cross slide to back out lets say 2 (this amount is deeper than final thread depth ) turns each time,I reverse the motor after each pass without ever disengaging the halfnut going about 1/2 inch past the end of the work so any play in the machine is gone before the cut starts then turn cross slide back in 2 turns in back to "0"
set the depth of my next pass on the compound and cut the next pass
repeat untill i reach final depth on the compound dial a few spring passes and good to go
the only way this 9x20 will do it is to leave the halfnut engaged the thread dial is microscopic like yours and the slowest speed is just way to fast
but for me to go to dc I just slip the belt on and it turns everything real slow (even the ac motor is turning ) hit stop at end of pass back off and reverse I only use the dc motor for threading but my lathe just would not work right without it
steve