Tap Problems

[Skeeterd5150]

I'm new to the machining world and I have a small dilemma. Back in March my company bought a Trak DPM V5 Bed Mill. Minus some "minor" programming glitches its fine. I want to take more advantage of the Tap function in the canned processes but my problem is I break taps like crazy. I am tapping Bronze bars and plate with a .25-20 blind .201" hole using a tapping fluid called Tapfree. I know I'm not even close to hitting bottom so that is not the problem and the taps I was using were sharp and new. They were 4 flute bottoming hand taps though. I was just looking in MSC and was interested in the 2 flute high performance spiral taps that guhring makes. I'm wondering if I should use powdered metal instead of HSS or stick with it and move up to better suited taps. Thank you guys. This site is a godsend for the amatuer and novice machinist needing advice. I have learned so much about the trade

[miljnor]

Bronze can be a realy tough material to work with.

Taps are a kind of voodoo. I have had tap companies come and demonstrate their taps out and as soon as the engineer leaves the building the taps start f'n breaking.

2flute spiral taps are always a saving grace. I can get an aluminum 2flute spiral tap to work on most metals (the engineer still tells me it won't work! Well for not working I got it to drill 320 holes in 410 stainless plate)

On the negative side they wont do well in bottoming holes. especially a .201" deep one, as the point on the flutes is longer than this.

I have recently started using a tap with alot of promis and its an xl from a company I can't remeber. If someone more knowledgable hasn't givin you some magic bullet by tuesday I will post the name of the tap.

one thing that makes life realy easy as it gives the tap a little extra durability is a floating tap holder. I get about 2-3 times the life out of a tap if I use one.

hope this helps

[Skeeterd5150]

Yeah I forgot to mention that parameter. I do have a Lyndex floating tap holder.

[HuFlungDung]

From past experience, I would say that positive rake tooling does not work nearly as well as neutral (or negative) rake tooling in brass or bronze. A spiral flute tap would be a step in the wrong direction, IMO. Just as a spiral flute drill wants to hog in and overload the tool, so the same thing would happen with the spiral flute tap.

So the hand tap is likely better because one component of the rake face (inside the cutting flute) is neutral because the gashes are parallel to the axis.

However, the other component of the rake face is still high positive and that is the radial face. This give the tap free cutting qualities in steel, aluminum and plastic.

So as an experiment, I would take one of your bottoming taps and grind the inside face of the flute just enough to create a small radially directed flat on the rake face of the flute.

Make sure that your drills are also tweaked with this sharpening tip to prevent work hardening of the holes, which can also affect tapping performance.

[Geof]

"an aluminum 2flute spiral tap"

Now that is something! I have only ever come across taps made out of High Speed Steel.

On a more serious note; I don't like to disagree with Hu (graceful genuflect in direction of Saskatchewan here) but I have found some bronzes do not work with zero or negative rake and need a positive rake.

If your machine has the ability try Repeat Rigid Tapping with a rigid tapholder.

Another thing is go to a slightly larger drill size, this does reduce the thread strength but the bronze is going to be a fairly high tensile material so it may be okay.

[HuFlungDung]

One other thing to check: the depth of the hole was not mentioned, but the chips from tapping may very well be falling down the hole ahead of the tap and causing it to bottom out on the chip pile. This would call for peck tapping.

If the hole is really deep, it might be worthwhile using a plug tap first (in a rigid holder) followed by a bottom tap in a floating holder.

[Geof]

Originally Posted by HuFlungDung ....If the hole is really deep, it might be worthwhile using a plug tap first (in a rigid holder) followed by a bottom tap in a floating holder.

Have you done this Hu? Do you just hope that the floating holder lets the threads line up correctly for the second tap?

[miljnor]

I have done it and it works about 90% of the time. So its not a silver bullet.

I ment to say a spiral Point tap for aluminum! (some ones always got to be the SA! ) Not spiral flute although the one I cant remeber the name of is a spiral flute bottoming tap and kicks the chips up not down. So it will address both problems.

[Geof]

Originally Posted by miljnor (some ones always got to be the SA! )

Expression of cherubic innocence.

[DonRD]

Skeeterd5150
You said "They were 4 flute bottoming hand taps"

I would not recommend using a hand tap. Hand taps are best left for doing threads
by hand. I would go with a OSG fast spiral flut tap that is a high speed steel - elektralLUBE coated tap. If chips are a problem look into using a Thread Forming tap.
Also make sure thst your hole is not undersize as that can break a tap in no time.

[HuFlungDung]

Originally Posted by Geof Have you done this Hu? Do you just hope that the floating holder lets the threads line up correctly for the second tap?

Used to do it all the time on my non-rigid tapping Shadow or Bandit cnc's. I used ER16 floating holders and they are pretty loose, so they don't cross thread.

[Skeeterd5150]

Yeah I was thinking it might be the chips in the hole making the hole more shallow. That happens even when I hand tap the holes. I have to go in and then out and then blow out the hole and retap to get the full length.