Introduction: DIY Threaded Insert (Helicoil) No Lathe

In this instructable we will try to make a M12/M10 Threaded Insert (Helicoil) using a cheap drill press (less than 100€). No lathe required.

The initial thought, it was:
How I can find out the real center of an existing bolt
without the use of lathe or a milling machine. I haven't such machines.

Yes, you can say: why to get in trouble, while they are cheap to buy.

But sometimes, some simple hardware can be a pain to find it... if you can find it at all, and especially if you live overseas.
Not to mention the satisfaction ofdoing it yourself.

What is a Threaded Insert

A threaded insert, also known as a threaded bushing, is a fastener element that is inserted into an object to add a threaded hole.
They may be used to repair a stripped threaded hole, provide a durable threaded hole in a soft material, place a thread on a material too thin to accept it, mold or cast threads into a workpiece thereby eliminating a machining operation, or simplify changeover from unified to metric threads or vice versa.
Thread inserts come in many varieties, depending on the application.
Threaded inserts for plastics are used in plastic materials and applied with thermal insertion or ultrasonic welding machines.
Manufacturers of knock-down furniture often ship the parts with threaded inserts and other kinds of knock-down fasteners pre-installed.
People who use sheet metal or sandwich panel or honeycomb sandwich-structured composite often install threaded inserts to spread shear, tension, and torque loads over a larger area of the material
Captive nut
Captive nuts come in two basic styles. One type, the cage nut or clip-on nut
is a conventional nut held captive by a sheet metal carrier that clips onto the part to be connected. These are generally used to attach screws to sheet metal parts too thin to be threaded, and they can generally be attached, removed and reused with simple hand tools.
The second type of captive nut is a threaded insert. These are either pressed into holes in the material to be joined or moulded in. In either case, part of the insert is generally knurled to get a good grip on the material supporting the insert. One variant, the swage nut, has a knurled portion that swages the sides of a soft metal hole to more tightly grip the nut. Press fit and swaged captive nuts are used in panels that are too thin to be threaded or in soft materials that are too weak to be threaded. They are installed by pressing them in with an arbor press.[3]
Threaded inserts are commonly used in plastic casings, housing, and parts to create a metal thread (typically: Brass or Stainless Steel) to allow for screws to be used in the assembly of many consumer electronics and consumer products. These may be cast in place in injection molded parts or they may be added by thermal insertion. In the latter, the insert is heated and then pressed into a hollow in the plastic part. The heat causes local melting in the plastic.[4] Ultrasonic Insertion is the process used to apply vibration and pressure to install the threaded insert into a molded hollow boss (hole) of a plastic part. The ultrasonic vibrations melt the plastic where the metal insert is in contact, and pressure is applied to press it into position. The plastic material typically reforms around the knurled body of the threaded insert to ensure a good retention.
Externally threaded insert
Externally threaded inserts have threads on the outside and inside of
the insert. The insert is threaded into a pre-tapped hole, or some inserts tap their own threads in a drilled or molded hole. It is then anchored by various means, such as a nylon locking element. Inserts that are anchored via Loctite are more commonly known by the trademarked name E-Z Lok. A thin walled solid bushing insert by the trademarked name TIME-SERT is locked in by rolling the bottom few internal thread into the base material with a special install driver which will permanently lock the insert in place.[citation needed] Key locking inserts, more commonly known by the trademarked name Keenserts, use keys that are hammered into grooves through the threads, permanently locking the insert.[5][6][7] Inserts that are self-tapping and lock via friction are more commonly known by the trademarked names Tap-lok or Speedserts.
Helical insert
A helical insert is an insert made of coiled wire. The helically formed
coils of diamond shaped stainless steel or phosphor bronze wire screw into a threaded hole to form a mating internal thread for a screw or stud. These inserts provide a convenient means of repairing stripped-out threads and are also used to provide stronger threads in soft materials such as aluminium, zinc die castings, wood, magnesium etc. than can be obtained by direct tapping of the base metal involved. Another common generic name is screw thread insert (STI), although many users persist in calling them all by a prominent brand name, the registered trademark Heli-Coil. Applications include engine cylinder head repair after unintentional over-torquing or cross-threading of spark plugs strips the thread of the socket. Kits with matched tap and coil exist for this. The straight radial piece in the photo is the driver tang which is used as a key to grip with pliers for driving the coil into place and is discarded after installation.
Mold-in inserts
Mold-in inserts are internally threaded and have a specially shaped
outer diameter to anchor the insert in plastic. The insert is placed in the mold of an injection molded part beforehand. The mold is then closed and filled with the plastic filling in around the insert. These inserts can also be heated and pressed into pre-made thermoplastics.[8]
For softer more pliable plastics, hexagonal or square inserts with deep and wide grooves allow the plastic to flow and adhere. The process allows large product manufacture i.e. fuel tanks, boats etc., so the torque inserts may be of large thread sizes.
Press fit inserts
Press fit inserts are internally threaded and have a knurled outer
diameter. They are pressed into a plain hole with an arbor press
Wikipedia article:

Step 1: Tools and Materials


1. Drill Press

2. Drill bits: ø4mm, ø8.5mm & ø10.2mm (recommend HSS-Co from a reputed brand)

3. Taps set: M10x1.5 & M12x1.75

4. Tap handle

5. Square or Flat File

6. Countersink or a drill bit ø16mm

7. Wrench 19mm (2pcs)

8. Bench vise


1. A piece of stock ssquare steel 25~30mm or a rectangular, it doesn't matter the shape, just the height

2. Bolds M12x50mm full threaded

3. Nuts M12

4. Cutting oil

Step 2: Setting Up / Calibration of Drill Press

At first we need to check the setup of our drill press, isn’t needed to be a super expensive drill press..

This one cost me only 69€, has five speeds and 16mm chuck.

The only thing that needs your attention is the correct setup.

So don’t worry and don't hesitate to give a try because you have a cheap drill press.

The tool by alone isn’t God.

As a cheap so and an expensive drill press, can be fall on this process because of a wrong axis setup.

Yes, I know what you can tell me:

my setup, is to factory defaults, I have never changed the verticality.

But how can you be sure that is absolutely on the square?

Are you have checked? ...and how?

I have used for this check/calibration a Hardened Steel Square Block and a Hardened Steel Spindle,

so as to calibrate my drill press to works absolutely perpendicular at Blue and Red axis.

How to Calibrate the Verticality

Mount the spindle at chuck.
Place the block onto the table to check/calibrate as at red axis.
Move the block slowly and gently, till the vertical corner of block, to touch at the spindle.
If the full height of corner crest isn't tangent to the spindle,
adjust the table, till the block is tangent to the spindle 100%.

The use of a light behind the block/spindle, can help for more precision.

Turn the block around the spindle by 90 degrees to check/calibrate as at the blue axis.

My drill press has 1° offset verticality, is it critical?

According the use of the drill press for simple uses at low-depth holes e.g. 10~20mm

isn't so critical and most people maybe to not understand it.

The offset from real center at the down hole center is too small.

1° offset /10mm depth then offset at the down hole center 0.1746mm
1° offset /20mm depth then offset at the down hole center 0.3491mm

For the make of this threaded insert M12/M10 is very very critical.

0.5° offset /50mm depth then offset at the down hole center 0.4363mm
1° offset /50mm depth then offset at the down hole center 0.8727mm
The minor diameter of a M12 male tread is 9.8530mm
so the space between the two threads is too small.

Step 3: How to Find the Real Center Out of an Existing Bolt

Choose a speed between 850~900 RPM. For best performance use HSS-Co drill bits and cutting oil.

Secure the piece of steel at the drill press table.

Do a hole ø10.2mm using at first a ø4mm drill bit and then a ø10.2mm.

Using a countersink or an ø16 drill bit, clean the edge of the hole.

Now we are ready for tapping.

Remember Safety First

Remove the power cord from outlet.

Install a M12 tap at the drill chuck.

Turning the chuck by hand start tapping the first few threads.

Don't forget to use cutting oil.

After we have cut few of the first threads, release the tap from chuck, and using a tap handle complete the tapping.

Do not remove or release the piece of steel from table.

Screw a M12 bolt from the down side, to upside.

Using a file, clean the edge of bolt, so as the surface to be flat and parallel to table.

Secure the bolt with a lock nut so as cannot unscrew, during the drilling process.(needing two Wrench 19mm)

Installthe power cord to outlet.

Using a ø4mm drill bit, start do (touch and go up) 2~3 times till to creating a scribe starting hole.

After you have create the starting hole, use the drill normally to complete the hole.

Change drill bit, and do the hole ø8.5mm

Release the lock nut and unscrew the bolt,

but do not release the piece of steel from table yet.

We will use it to drill a second or more bolts so as to have in stock.

Secure the bolt at vise and start cutting the threads using the First tap of set,

after that the second and finally the third.

(A set of taps usually consists of three taps)

Tapping very carefully and perpendicularly,

The wall between threads is too thin and in some points perhaps and under the limits.

Step 4: Where I Have Use This Threaded Insert

I have make and use this Threaded Insert to fix my 25 years old faforite angle grinder.

By following this way, you can make any threaded insert (helicoil)

with an acceptable combination of threads.

Thanks for your reading.
Good Luck if you try it.
Never say I can't do it.
Necessity is the mother of invention.