Which twist drill do I use to drill in stainless steelSeptember 13, 2018
You want to drill a hole in stainless steel but don't know which twist drill to use? In this article we explain how to drill in stainless steel and which twist drills to use.
Before we begin with the characteristics for the twist drill, we should first clarify what stainless steel actually is.
What is stainless steel?
Stainless steel is a metallic material which is characterized by its special purity . There are alloyed and unalloyed steel, but only the alloyed variant is also stainless.
In stainless steel, it must be enriched with alloying elements such as titanium, niobium or chromium in addition to iron. Chromium (Cr) is the corrosion resistance of stainless steel and should have a minimum content of 12% and an extremely low carbon content. The chromium content creates a layer on the material surface which permanently protects against water and moisture.
Properties of stainless steel
- long durability
- high durability
- difficult to cut
- 100% recyclable
Features of the twist drill
What features does the twist drill have to have in order to cut stainless steel? The following criteria must be met in order to obtain a good drilling result.
1. Tool steel
Stainless steel is a very hard material and therefore difficult to cut. Therefore, the tool steel of the twist drill should be made of HSSE-Co 5 (5% cobalt content), HSSE-Co 8 (8% cobalt content) or solid carbide.
A tool steel that is too soft would immediately overheat. So since stainless steel is a hard material, you need a twist drill type H. In the course of time, the features of twist drills have been combined differently in order to optimize them for special applications. Thus, mixtures have formed whose naming system is not standardized in the DIN manual. So you will find at RUKO for use in stainless steel types VA, FO, UTL3000, UNI, TL3000, N and UTL.
Due to the fracture susceptibility of hard tool steels, you should better use HSS drills for soft materials.
2. Point angle
The point angle is located at the head of the twist drill. For hard materials such as stainless steel, the point angle should be large and e.g. 130° or 135°. For soft materials, point angles of e.g. 118° are used.
With a large point angle, more of the cutting edge engages in the workpiece when drilling. This also means that more force is applied to the workpiece and higher contact pressure (high feed) is required.
3. Spiral angle
The spiral angle determines the process of chip formation. Small spiral angles are used for hard short-chipping materials.
The spiral angle should therefore be small, between 20-40°, . The spiral is stretched at a small spiral angle.
Spiral angle and point angle are the decisive factors for the application in hard or soft materials.
The twist drills made of HSSE-Co 5, HSSE-Co 8 or solid carbide do not neccesarily need coating . Coated drills are still ideally suited for industrial use. I.e. fast speeds (high cutting speeds), high feed rates and increased heat applications.
If you want to use a coating, e.g. to increase the tool life, it should be at least the TiAlN coating, because it has a high heat resistance. With TiAlN-coated drills, cooling is not necessarily required. In addition, they prevent cold welding on the drill.
You have chosen a suitable twist drill and now you finally want to drill your hole in stainless steel. When drilling, it is important that you
- use cooling, depending on application with cutting spray or compressed air,
- adjust the speed,
- use a twist drill that hasn't already been used for other steels,
- clamp the workpiece real hard,
- do not wear protective gloves and
- put on protective goggles.
In our detailed article "8 features of a twist drill and its functions" you will learn all the important features of twist drills and which functions they have when drilling.
With cooling you ensure that the surface quality is optimal, the temperature is lowered and the chips are swept away. This extends the life of the drill.
If possible, use a pillar drilling machine as it allows you to better control the centering, speed and feed . High feed rate is required and your speed is rather low when drilling.
See the table below for information on the speed and feed settings and the type of cooling. You can download the speed table as a PDF file. Click on the image.
If you do not have a pillar drill available, use the pointed side of the punch and a hammer to make a small recess in your stainless steel workpiece. This gives you better guidance and prevents slippage when drilling. The center punching compresses the material a bit, but mainly the material is displaced to the side and over the top of the material. This does not pose any extreme challenges for the twist drill.
3. Other steals
You should not have used the twist drill on other steels before. The metal particles on the twist drill can attack the stainless steel and make it susceptible to corrosion.
4. Clamp worpiece
Make sure that you clamp your workpiece correctly into your vice.
5. No gloves / 6. protective goggles
You should not wear gloves, because they can get caught in the twist drill. In contrast to the gloves, you should unconditionally put on protective goggles.
In the application table you will find all our twist drills with which you can drill in stainless steel. If you click on the images of the twist drills in the PDF, you will be taken directly to the product page where you can find detailed information about the twist drill.
Conclusion and summary
Since stainless steel is a very hard material, you have to choose the right twist drill. The twist drill should belong to the application group Type H of the DIN 1386 division. Over time, however, mixed forms have been developed whose naming systems are not standardized in the DIN manual. So you will find at RUKO for the use in stainless steel the types VA, FO, UTL3000, UNI, TL3000, N and UTL.
In order to cut stainless steel, your twist drill must
- be made of tool steel HSSE-Co 5, HSSE-Co 8 or solid carbide,
- have a large point angle (e.g. 130-135°),
- have a small spiral angle (e.g. between 20-40°) and
- be coated at least with the TiAlN coating.
When drilling, you should follow these advices:
- adjust speed
- use twist drills that hasn't already been used for other steels
- clamp workpiece
- do not wear protective gloves
- put on protective goggles
If you have found the right twist drill and follow these instructions, you will get a good drilling result in stainless steel.
In each of our product groups you will find a Product finder. Under Products > Twist drills you can filter "stainless steel" in the field Applications. You will then be shown all twist drills that can be used for cutting stainless steel.
If you have trouble finding the right sheet drill, please do not hesitate to contact us.
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