G'day everyone,
Back in the workshop again and this week I need to make another tap. I need a screw with a large pitch which is also good for transmitting power. That rules out a multi start V thread, which isn't great at efficiently transmitting power. The go to solution would be an ACME or metric trapezoidal tap, which can be single point cut on the lathe. However my lathe wont cut a pitch large enough.
That is fine though because I have the helical milling set up, but that only produces square threads. Not my first choice but we can make do with it.
And that brings us here. I have never made a square tap, and I have never made a tap this big - SQ40 x 8. Machinery's handbook advises that these threads are difficult to cut with a tap, which filled me with confidence.
I will be making a 3 set tap set. 3 is the bare minimum for this thread pitch, but I could have gone up to 5. Each tap will have a different diameter to reduce the cutting force. The first one being 34mm to establish the threads, the second tap being 37mm to widen the cut and the final being 40mm to finish the profile.
I will also need to case harden the taps. i used some hot rolled grade 300 steel which is low carbon. Not my first choice of steel, but we can make it work. I will carburize it int he furnace to increase the carbon content then I will quench it in oil to end up with a tap 55 Rockwell C.
The final tap set looks pretty crazy and out of place. I have never seen a tap this large outside of a pipe tap, although the pipe tap had a much finer pitch. And I will also test the tap in aluminium. I don't have the stones to sharpen it yet so I will keep the test easy and use aluminium. Although the end goal is to tap steel. I hope you enjoy the video.
Mill - Sieg x2.7l
Lathe - Hafco Al250g
#machining #diy #tapbuild
Sqaure thread tap
Massive tap build
Making a thread tap
Square threads
Timestamps
0:00 - Introduction to Sqaure Threads
3:24 - Turning Down The Blanks on the Lathe
9:07 - Cutting The Sqaure Threads On The Lathe
12:00 - Machining The Flutes
14:07 - Case Hardening The Taps
18:52 - Sqaure Thread Tap Set Testing
I Had To Make a HUGE 40mm Thread Tap - Its BIG
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