Usually, a burr-free screw hole (tapped hole) is created by using a drill bit, a countersink and a tap. Most of the taps do not have drilling function. As a result, it is necessary to drill a pilot hole for tap to place into before tapping, a process of cutting threads inside a hole.
This article is going to compare Traditional and New ways of how to drill a screw hole in sheet metal (with video).
Traditional Way to Drill a Screw Hole by 3 Cutting Tools
What is a Drill Tap?
How to Use a Drill Tap?
Features of Drill Tap
Benefits of Drill Tap?
Application of Drill Tap?
Easy-understanding Drill Tap Chart
Notice
Watch the Drill Tap Video
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After determining the screw or thread size you need, follow the tap drill chart to find what drill bit and tap size to drill the screw hole. The diameter of drill bit for pilot hole will be smaller than the major diameter of tap. This will form the thread for screw to grip into.
If your work piece is not fastened, please secured it by clamping on a stable place. Otherwise, it may move or spin or even rise up by the forward power of drill bit which can damage the cutting tool, object or the operator.
After knowing the drill bit size that matches the hole size from tap drill chart, create a mark by a center punch for your drill bit to grab. This can prevent the drill bit from slipping when starting drilling.
Apply some cutting fluid to your drill bit to make your drilling easier and can also cool the drill bit. Then, put your drill bit into the center mark and start drilling at a slow speed rate.
Before tapping, use a countersink to chamfer the surface of the cutting hole. The chamfer edge will become a guide for the tap to place into the hole in the center. This also can help the tap start tapping more easily.
Besides, the chamfer edge provides a place for screw with countersunk head to enter, so that the screw can flush with the surface of the work piece.
In a factory, machinist can tap the thread by machine automatically. Also, you can tap by power tool or various tap handles (wrenches) manually.
According to the hardness of the materials, you need to use a set of taps to tap the thread. If tapping manually, please check that each tap uses an appropriate tap handle size to make sure they fit correctly.
Taper tap (first tap) – 8 to 10 chamfered thread with incomplete teeth.
Intermediate tap (second tap) – 3 to 5 chamfered thread with less complete teeth.
Bottoming tap (final tap) – 1 to 1.5 chamfered thread with complete teeth.
Insert the tap into your power tool and twist the chuck until tightened. Make sure the tap is straight and does not shake by giving squeezes to the trigger before tapping.
Don’t forget to check your power tool if it has a reverse function to back the tap out when tapping finishes. Please tapping at a very slow speed to ensure the tap on the center vertically and prevent over drilling.
To begin tapping, place the tap into the pilot hole vertically with some tapping fluid. Start rotate the tap handler slowly clockwise. When you feel resistance and the cutting becomes harder, untwist the tap counterclockwise and clear the chips.
Turn the tap back a little for a full rotation can break the chips. Repeat the process until you finish the tapping work.
Follow these steps, you can drill and tap ONE screw hole. Repeat this process until finishing all the screw holes you need. Feel tired even before starting? Don’t worry, here is a special cutting tool able to complete drilling, countersinking and tapping in one operation.
Drill tap is a special cutting tool designed to drill, countersink and tap for a through hole in one quick step. You can create many common screw holes for machine screws and bolts by inserting the drill tap into impact driver without switching cutting tools which really saves lots of time and money.
With a thinner and sharper cutting point, the split point tip helps the drill tap grab the work piece without drifting when start drilling. Additionally, because of its self-centering feature, there is no need to use a center punch for center drilling.
Compared to other brand, our drill tap has a 2-step or 3-step (for larger diameter) pilot drill design in the front part. The function of first drilling step just like a pilot hole which can reduce power needed to turn the next step. This stepped design also lowers the breakage risk of drill tap to longer its lifespan. Additionally, the chamfer edge between two drilling steps makes the transition much smoother.
This design comes from our popular product – Step Drill.
For more information, please see the article: What is a step drill/ step bit/ step drill bit?
We all know that when tapping the thread by a tap, it is important to clean chips frequently or the accumulation of chips inside the hole will cause damage to the tap. The fluted shape helps the chips remove smoothly out of the hole which makes tapping easier. Besides, the removal of chips decreases the friction heat to avoid overheating to extend the service life of the drill tap.
The countersink part is used not only to make a burr-free and smooth edge of the screw hole on the surface but also to provide a space for countersunk head screw to flush with or sink under the surface.
The 3 in 1 design combines drill bit, tap and countersink with a smooth transition design. Therefore, you can drill the screw hole at a constant speed during the whole drilling process to increase work efficiency.
Instead of straight shank or 3 side shank, the hex shank provides a strong connection to the impact driver to ensure a stable drilling process and excellent drilling precision.
Since drill tap can drill, tap and chamfer in one step, there is no need to switch cutting tools with different power tools while manual tapping is powered by your human power. Impact driver and drill tap are the tools you have to prepare for drilling a screw hole. This can significantly improve the tapping efficiency.
The special design of drill tap allows it to create a pilot hole, tap the thread and chamfer (deburr) the surface by the same impact driver in one easy operation.
You don’t need to use traditional tap drill chart for finding sizes of 3 cutting tools. We have already calculated the diameters of each part for you. The only thing you need to know is the screw size so you can choose a corresponding drill tap for the targeted screw hole.
-For use with materials of steel, copper, aluminum and plastic.
-Mainly Used in Electrical box for electrical working
Telecommunication fields
Electronics industry
-Ideal for ON-SITE Tapping
Maintenance and repair jobs
Assembly and fabrication works
Production drilling
General industries
-Also used in Home renovation
| Drill Tap/ Screw Size | Major Diameter (X) | Pitch (Y) | Minor Diameter (X-Y) |
| M3x0.5 | 3.00 | 0.50 | 2.50 |
| M4x0.7 | 4.00 | 0.70 | 3.30 |
| M5x0.8 | 5.00 | 0.80 | 4.20 |
| M6x1.0 | 6.00 | 1.00 | 5.00 |
| M8x1.25 | 8.00 | 1.25 | 6.75 |
| M10x1.50 | 10.00 | 1.50 | 8.50 |
| M12x1.75 | 12.00 | 1.75 | 10.25 |
| Drill Tap/ Screw Size | Major Diameter (X) | Pitch (Y) | Minor Diameter (X-Y) |
| 6-32NC | 3.51 | 0.79 | 2.72 |
| 8-32NC | 4.17 | 0.79 | 3.38 |
| 10-32NF | 4.83 | 0.79 | 4.04 |
| 10-24NC | 4.83 | 1.06 | 3.77 |
| 12-24NC | 5.49 | 1.06 | 4.43 |
| 1/4-20NC | 6.35 | 1.27 | 5.08 |
| 5/16-18NC | 7.94 | 1.41 | 6.53 |
| 3/8-16NC | 9.53 | 1.59 | 7.94 |
| 1/2-13NC | 12.70 | 1.95 | 10.75 |
Example1: M6x1.0 drill tap is for M6 screw
X = M6 means the outside diameter of the screw and the tap = 6mm
Y = Pitch of the screw (distance between threads) = 0.5mm
X – Y = Diameter of pilot drill and inner diameter of the screw and the tap = 6 - 1.0 = 5mm
Example2: 8-32NC drill tap is for size 8 screw with 32 threads per inch
X = the outside diameter of the screw and the tap = 4.17mm
Y = Pitch of the screw (distance between threads) = 0.79mm
X – Y = Diameter of pilot drill and inner diameter of the screw and the tap = 4.17 - 0.79 = 3.38mm
3keego provides straight fluted drill tap and spiral fluted drill tap made of high speed steel for durability. You can search more information on our product page of DRILL TAP.
If you have any further questions, please do not hesitate to CONTACT US.
Spiral Flute Drill Tap