How to Make a Thread Tap

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Introduction: How to Make a Thread Tap

About: Hello, I'm Niki. I like to make things and save money while I am doing it.

How to make a quick and easy tap for cutting a thread.

Supplies

  • High tensile steel bolt
  • Angle grinder (with cutting disk)
  • Bench vice
  • Butane torch
  • Tin can (for quenching)
  • Adjustable wrench

Step 1:

This tool is more of a last resort when you need to tap a thread
and you do not have immediate access to the actual necessary tool.

Step 2:

We take an existing bolt of the exact thread diameter and pitch required.

Step 3:

I recommend a high tensile steel bolt. But mild steel may work as well.

Step 4:

The idea is to make cuts along the bolt threads so that it somewhat resembles an actual thread tap.

Step 5:

Secure the bolt in a vice

Step 6:

Carefully cut the slots with a thin cutting disk.

Step 7:

Your angle grinder cuts should look something like this.

Step 8:

Make yourself a quenching bath, I am using a mixture of salt water.
But I have used old engine oil in the past.

Fire up your burner.

Step 9:

Heat the bolt to approximately 800 degrees Celsius,
or 1450 to 1500 degrees Fahrenheit. Which is expressed as a bright cherry red colour in carbon steel.

Step 10:

Then quench till it is a safe temperature to touch.

Step 11:

The bolt is now hard and somewhat brittle.

Step 12:

Now to test it.
Drill the required size hole in the piece that needs tapping and add some oil.

Step 13:

Start tapping the thread.

Step 14:

There you have it.
This quick tool was able to cut a pretty decent thread in 10mm 3/8 inch mild steel.

Step 15:

This would be a good enough substitute in some situations.

Step 16:

We have more DIY and Tips over on YouTube.

And we would love to see you there.

YouTube - Nikita Maree

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    16 Comments

    0
    oragamiunicorn
    oragamiunicorn

    Question 10 months ago on Step 8

    I'm not saying your wrong at all, but my instinct would be to say that salt would lead to rusting and any kind of oil would be a fire risk when used to quench hot metal. Why would you choose these over just water?

    0
    Left-field Designs
    Left-field Designs

    Answer 10 months ago

    The type of quenching you use is typically determined by the metal itself, for example O1 steel should only be quenched in oil, whereas W1 steel only in water. There are some steels that shouldn't be quenched in liquid and only in air. Water will quench quicker and this generally means the metal is harder but this will also introduce more stress and make it more brittle. Ideally the peace would be annealed to soften it ever so slightly and release some of this stress. Oil quenching is only really risky when you do it too slowly, a quick dip under the surface and the flame doesn't form, slowly and you will set the pot on fire.

    4
    Nikita Maree
    Nikita Maree

    Reply 10 months ago

    Salt water (brine) creates an even quenching. Which reduces the risk of cracking.
    Rusting isn't an issue because once you quench any tool, you would oil it before storing it. Just as you would your regular tools.
    But as the instructions suggests, this is more of a one use tool when you are in a pinch.

    As for the oil. It's only a fire risk, if you aren't taking the proper precautions.
    It's only a small flame on the surface for a short time.
    Obviously you would do this in an open environment, as you would any job with a butaine torch.

    1
    Oldprophet
    Oldprophet

    Reply 10 months ago

    I believe one of the reasons to use oil over water is that water will cool the metal a little to fast, and the metal will contract to fast causing cracking. Maybe its because the water evaporates pulling more heat out vs oil that does not?

    0
    maintann
    maintann

    10 months ago

    Works surprisingly well. Done it a number of times. Works better if you grind the taper at the end of the bolt longer - that way you have more edges taking smaller cuts (like a taper tap rather than a bottoming one.

    1
    jeanniel1
    jeanniel1

    10 months ago

    Really easily understandable instructable. And thank you to the others who contributed to my knowledge now for tapping and quenching!

    1
    JeffCondit
    JeffCondit

    10 months ago

    Actually, oil quenches faster due to the the higher boiling point. What happens is that the iron in steel forms crystals when you heat it up and then it cools. The crystal lattice structure inside each grain is uniform, but where crystals meet the boundaries are jagged. When you bend or machine steel, the atoms in each crystal can slide next to others in the same crystal relatively easily, but when the sliding gets to the grain boundaries the shifting can't be done any where as easily, This is experienced macroscopically as a much harder steel, but one which is more prone to crack and break.

    In the case of a tap, we want it to be much harder than the material we're tapping, so heat treating it by fairly quickly heating and rapidly quenching it in water or oil could be beneficial in making it cut more cleanly and possibly more times before getting dull.

    Of course this is an extremely abbreviated explanation of metallurgy and properties, so you mileage may vary.

    0
    JeffCondit
    JeffCondit

    Tip 10 months ago on Step 6

    Due to the width of the blade and the cylindrical shape of the bolt, the angle of the "cutting" edges for the teeth differ on each side. The ideal angle of the blade with respect to the bolt is such that the cutting side teeth formed by the grinding will be perpendicular to the bolt perimeter (or slightly more acute). This is usually not a problem if the grinding blade is thin and new, but as it wears it could get rounder (i.e. with a larger radius). This can cause binding by pressing the shavings back toward the bolt instead of pulling the away into the grooves in the tap.

    2
    JohnC430
    JohnC430

    10 months ago

    Pretty Damn good when youre in a pinch!
    Thanks.

    0
    Nikita Maree
    Nikita Maree

    Reply 10 months ago

    Absoluitly, Thanks for your comment.

    1
    blenderbender
    blenderbender

    10 months ago

    Trying to harden mild steel likely will not yield any more hardness. Due to its low carbon and alloy elements content, mild steel does not form a martensite structure when quenched after being heated. But handy tip for the "where did that tap go?" situation.

    4
    lorenkinzel
    lorenkinzel

    Reply 10 months ago

    It's called case hardening. The oil provides carbon. The steel does harden in a very thin surface layer. This has never been considered high quality hardening, but rather a better-than-nothing technique. Google "case hardening mild steel with oil".
    If you google "case hardening" you will find several other methods besides using oil.
    Here's a simplistic explanation so that you need not take my word for it:
    https://sciencing.com/how-4579248-harden-steel-mot...

    1
    Oldprophet
    Oldprophet

    Reply 10 months ago

    What bothers me is the fact that a lot of files are now case hardened. They wear out fast and don't cut well, and the worst part is I can't make knives out of them lol.

    2
    lorenkinzel
    lorenkinzel

    Reply 10 months ago

    So true. Case hardened is not quality stuff. Probably why the author recommended high carbon bolts for doing this.

    0
    weish
    weish

    10 months ago

    looks like a solid way to make small,light-duty taps such as for jewelry work, where you're only tapping copper/silver/gold and don't need the sort of toughness and durability tapping something hard like steel requires. i'll be making use of a similar method to make some jewelry taps soon, since proper micro-taps are super expensive and prone to breaking

    1
    Benny the gypsy
    Benny the gypsy

    Reply 10 months ago

    It does not show it in the instructions, but in the video the tap cuts a thread in 10mm thick steel.