Making lathe chisel - drill/tap issues

[Atabuoy]

Decided to make my own carbide cutter chisel(s). No issues with handle or steel square stock.
So far, one cut thread, two broken taps. the first one broke off in the hole resulting in a do-over.
second one broke after I had fully cut the tap and there was enough to twist it through the hole
with vice grips. I know first problem is I'm using a cheap Irwin tap from Amazon. But I'm chamfering
before tapping, using cutting oil, holding the bar in drill press vise and using the drill press chuck to
hold the tap and turning 1/4 turn forward/backward by hand. Seems to cut easy? Alignment is good?
But still breaking?
I don't expect my 3rd attempt to be any different.
My problem is sourcing a quality 4-40 NC tap.
I'm in the Toronto Canada area and I'm not confident with what big box places have to offer vs Irwin.
I'm no machinist but expect there are specific tap brands out there that will stand up to more than what
I'm experiencing.
My apologizes if this has been discussed in the past….I'm new .
thank you

 

[randyrls]

When tapping, the hardness of the material changes the percent engagement. A 4-40 tap is small with little cross section. Drill the hole *VERY* slightly larger. Look at this printed tapping chart that shows the engagement % for different materials. Look for a tap guide. Drill the hole, then replace the drill bit with the tap guide insert the tap into the end of the guide. The guide keeps the tap straight in the hole. Alternative: Put the tap into the drill chuck, tighten and twist the chuck with the drill press unplugged! Try this out on a piece of scrap first.

 

[darrin1200]

KBC has a location in Toronto

Straight Flute Hand Taps - Results Page 1 :: KBC Tools & Machinery

Straight Flute Hand Taps

www.kbctools.ca

 

[egnald]

What cutting fluid are you using? I used to use 3-in-1 oil and had similar problems with my tap breaking, but since I switched to Tap Magic I haven't broken a single tap. Of course I use a lot of the other suggestions already made in this thread too, but it was the Tap Magic that did it for me.

Cool tool and project, There is something really satisfying using tools that you made yourself.

Good Luck.

Dave

 

[monophoto]

My experience cutting threads smaller than 1/4x16 is that taps wear out frequently. The last time I wen to the hardware store to buy taps, I mentioned that to the guy with the key to the locked shelves, and his response was that other people had told him the same thing.

I think the bottom line is to never force the tap - advance the tap 1/4 turn, back it out, and then move forward another 1/4 turn.

Patience is a hard lesson to learn. DAMHIKT

 

[egnald]

I also back the tap completely out after about 1/3 of the way and use an air gun to expel any chips from both the hole and the tap. Add a drop of Tap Magic and go again. - Dave

 

[carlmorrell]

A few months ago, I broke my first tap, and it happened to be a #4-40 tapping aluminum Small taps do not have a lot of metal. It was an "import". I thought I was being smart by getting a 4 flute spiral tap. Now I use that broken one as a bottoming tap. I went back to my box and pulled out an older USA made and have since tapped a dozen holes with it. If I need another, I am boing to look for a 3 flute, assume it would be stronger.

 

[Curly]

I suggest you try a spiral point tap also called a gun tap. They are for threading through holes and push the chips out ahead of the point. In industry they run them straight into the work without backing them up and they thread a lot of holes. If you have the tool clamped to do the tap drill put the tap in the chuck and a low speed feed it into the tool. Hit the stop button when it comes through. Back it out by hand unless the machine has reverse.

Here are a few examples from KBC from their cheapest to more costly. Several are two flute so stronger than hand taps.

KBC,4-40 H2 HS SPIRAL POINT PLUG TAP,1-359-0440,KBC Tools & Machinery

KBC,4-40 H2 HS SPIRAL POINT PLUG TAP,1-359-0440,KBC Tools & Machinery

www.kbctools.ca

KBC,4-40 COBALT SPIRAL POINT TAP,1-359C-0440,KBC Tools & Machinery

KBC,4-40 COBALT SPIRAL POINT TAP,1-359C-0440,KBC Tools & Machinery

www.kbctools.ca

CLARKSON-OSBORN,4-40 BLUE WIZARD TAP,1-361-0440,KBC Tools & Machinery

CLARKSON-OSBORN,4-40 BLUE WIZARD TAP,1-361-0440,KBC Tools & Machinery

www.kbctools.ca

REIFF & NESTOR,4-40 2FL H-2 R&N CPM-M4 PENTA SP/PT TAP,402VPR-86903,KBC Tools & Machinery

REIFF & NESTOR,4-40 2FL H-2 R&N CPM-M4 PENTA SP/PT TAP,402VPR-86903,KBC Tools & Machinery

www.kbctools.ca

If you are breaking these then the metal you are using may be too hard.