Tap Titanium

S

Suva

Joined
Nov 6, 2007
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12
Gday Guys,

I am in the process of making my first ever knife, which happens to be a framelock folder. I have been practicing my techniques/methods on 3mm stainless steel and am getting better. I am now ready to make my knife from 6AL-4V Titanium. I have however already encountered a problem. When I was using the stainless steel I was tapping the holes to fit a 4-40 screw by hand with a 4-40 plug tap. When I tried this method on the 3mm Titanium, the plug tap snapped! I have actually snapped all of the plug taps I had ( 5 of them ) and am wondering if its worth purchasing any more plug taps or am I approaching this all wrong. Any advise would be greatful.

Cheers
Paul
 
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4-40 is an awfully hefty tap. I wouldn't expect breakage problems with it. I regularly tap ti with an 0-80 without problems. My guess is you're using too small a drill bit to drill your hole. The usual recommended drill size for 4-40 threads is #43. A lot of guys like to use a slightly larger hole when tapping titanium, as it has a tendancy to gall (grab hold of your tap.) You might try a #42 or #41.

Keeping the tap straight also helps. A tapping fixture is nice, but not necessary. Just make sure you're not angling the tap into the hole.

Unless you're tapping into a blind hole (one that doesn't go all the way through the material) try spiral point taps instead of plug taps. Spiral point taps push the material being removed out ahead of them, so there is less chance of it binding up. Plug taps are designed for tapping blind holes, so there's very little lead in to them, making them less efficient and more prone to breakage.

A little tapping fluid helps, too.
 
I'm not a maker, just worked in a very basic machine shop doing very basic work in college, so feel free to ignore me.

But were you advancing the tap a few turns and then reversing a little to break the chip?
 
If a tap does break in titanium and you can't get it out, I put them in a strong solution of ferric chloride and it dissolves the tap but has no effect on the titanium.
 
It is important to use a good quality tap and tapping fluid. I recommend Moly-Dee as a tapping fluid. In my fairly significant experience with this subject, Moly-Dee is the best.

BTW, WD-40 is a terrible "tapping fluid". High pressure grease works okay.

Figure out a way to keep things aligned. A lot of people tap from their drill press, T wrench held in drill chuck, not powered.
 
Something I do when tapping Ti is to step up slightly in drill size as follows:

1-72 threads= #51 bit

2-56 threads= #48 bit

4-40 threads= #41 bit

I was a bit worried about holding power at first, but have actually stripped a number of screws instead of wrecking the threads (which is what I was worried would happen)

As has been mentioned, good lube, and reversing often to break chips is also a must with Ti.

I have a dedicated 10" drill press with a tapping head, so for the most part broken taps are a thing of the past. With the tapping head I have worn taps out, but have never broken one.

If you break a tap in Ti, you can save the piece by putting it in Ferric Chloride (what I use to etch damascus) overnight. The next morning the tap will be dissolved, and the Ti will be uneffected.
 
Ti will work harden once it gets hot as well. Its more of a concern with cutting it to begin with than tapping though.
 
the taping heads are the way to go.
I broke enough taps in the first year of making that I could of paid for the taping head.
I got the generic one off of ebay for like $150
 
Hi guys,

Thanx for all the feed back. I am using a #43 drill bit and think as some of you suggested that the hole is a little small for tapping with this material, I will try a slightly larger drill bit. For the record I was able to tap into the 1.5mm Titanium sheet, It just went pear shaped when trying to Tap the 3mm sheet. Also the guys at halpern Titanium suggested that I use a Form Tap as this apparently disperses the material instead of cutting it. Do any of you guys agree with this approach ( I just purchased some Roll Form Taps from ebay! ) If worst comes to worst I will counter bore the holes so there is less Titanium to tap through.

Cheers for all your help.
Paul
 
As suggested above:

Bigger hole
better lube
keep it straight-tapping head, hand turn a drill press...


Why use a plug tap instead of a taper tap to start with ?
-on such thin material with a through hole, you could use a taper tap all the way through.

What's the quality of the taps like?
If you have a machine tool supplier available, try to source a spiral point tap made for machine use. I find they are much less fragile on twisting torque and you don't have to reverse them.
 
If you do use the roll form make sure to use the correct size drill (or a little bigger), according to my chart that would be #38.
 
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