Thread percentage vs broken taps.
Thread percentage vs broken taps.
(OP)
Hello to you. I would like to "pick" your brains about thread percentages. Just to give you some background, I have been employed as a machinist for the last seven years. A problem persists in industry with broken taps. I believe from my experiences that a bigger tap drill would do the trick. But how big of a drill can we go to without losing percentage? I was once told that 51% thread engagement is all we need. Seems like a small percentage to me? Now one will ask what the material being tapped is. I guess lets just say good old hot rolled steel. We "started" the threads at my last shop and finished them by hand. That was done with hss drills and coolant for tapping. The shop I work at now uses carbide drills. I know they drill to the smaller side. So I usually go bigger by a few thousandths on my tap drill. And here we use oil on our taps and tap to depth. Broken taps are a plague when using coolant. It may be a coolant issue? but really? I guess I would like to know what is an exceptable thread percentage based on an engineering stand point. gimme some ideas please. My theory is no oil on taps and tap to depth with no broken taps, There are other variables too. like depth of hole. refractometer reading of coolant, manufacturer of tap etc. Thank you very much. I figured why not go to the source. That source is you guys. If anybody would know it would be you. Thanks again





RE: Thread percentage vs broken taps.
How many threads, or thread length? 1-1/2 to 2 diameters for steel. From engineering viewpoint.
What type tap?
Ted
RE: Thread percentage vs broken taps.
RE: Thread percentage vs broken taps.
RE: Thread percentage vs broken taps.
Software For Metalworking
http://closetolerancesoftware.com
RE: Thread percentage vs broken taps.
RE: Thread percentage vs broken taps.
1- are you checking the concentricity of the tap in the tool holder or are you just mounting it and tapping?
2-Where are you getting the speeds and feeds for your taps at?
1a- your concentricity should be less than .001
2a- you need a book or chart from the tap mfg. that will give you a good starting point in the material your working with.
I would guess that your concentricity is bad and your tapping too slow.
This is from my own personal experience. I have been a machinist / programmer / lead man for 17 yrs in the Milling dept. at my shop. I have seen this a 1000 times, everytime we hire a new guy I go thru this with them and their reply at a later date will be I had no idea you could tap like this.
My .02
Arlie
RE: Thread percentage vs broken taps.
RE: Thread percentage vs broken taps.
RE: Thread percentage vs broken taps.
I agree with the above replies
Must make sure the tool is indicated in.
the right lubrication
the correct geometry style of tap
starting & finishing tap.
the correct feed & speeds.
Mfgenggear
RE: Thread percentage vs broken taps.
Material, hardness, blind hole or through hole, length of thread, tap drill size, cutting fluid or coolant,application equipment, tool alignment, speed, work hardening, temperature, chamfer length, cutting edge design, flute design, web thickness, tap type (cutting/thread forming).
There is no easy button to almost any machining process. Lets talk material for example. Mild steel 15-25 carbon, gray iron, and ductile iron, thread forming only works on ductile material. Gray iron cannot be tapped properly with thread forming tap. Chip control in steel is very important while gray iron not so much. What strength ductile iron has an impact. Now consider 4140 annealed, or normalized or heat treated. Even in the annealled condition the 4140 will be tougher to tap. Then consider "soft" materials which present spell challenges. Aluminum can be very gummy depending on the aluminum grade and condition. Try tapping copper or a composite such as fiberglass reinforced resin or silicon carbide reinforced aluminum. There is no simple answer.
RE: Thread percentage vs broken taps.
A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com