Knurling is a manufacturing process, usually performed on a lathe, in which a pattern of straight, diagonal, or intersecting lines is embedded into the material. It is a process performed on screws or knobs that are intended to be turned by hand. The embossed patterns aim to eliminate slippage. The grid pattern of the machined object can vary. Thanks to knurling, the machined material of the object will slip less, and a simple layout of grooves and grid pattern will make the object more visually attractive.
Currently, there are several types of knurling:
- A – straight (knurling lines are parallel to the axis of the shaft),
- B – right-hand helical (tilted at a 45° angle to the axis of the shaft),
- C – left-hand helical (tilted at a 135° angle to the axis of the shaft),
- D – cross helical (convex),
- E – cross helical (concave),
- F – cross (convex),
- G – cross (concave).
We write about its wider application and its advantages below!
Knurling- where to apply
Why is it worth using knurling? For several reasons:
- Perform this operation to create a groove in the part of the workpiece. Knurling allows the hand to grip the knurled object better than a smooth metal surface. Sometimes the pattern of knurling is rather a series of straight spirals or ridges, rather than the more typical cross pattern.
How does the knurling process work?
Embossing is usually done using one or more very rigid rollers, which contain the opposite side of the pattern to be applied. "Straight" embossing (not cross) can be pressed with one roller, however, the material must be properly supported to avoid distortions. The cross pattern can be obtained using any of the following methods:
- Arm yourself with a single roller containing the complete reverse of the desired pattern. You can create "male" or "female" patterns from them.
- Roll the element straight to the left, then straight to the right (or vice versa), one or more scrolls to the left are used simultaneously with one or several scrolls to the right.
- Use a flask with a pitch that is a multiple of the circumference or a pitch with a diameter larger than π. The diameter of the semi-finished product is crucial for high-quality knurling. An improper diameter of the semi-finished product will result in double knurling, as a result of which the pattern will be finer than the knurling was designed. For the knurling to look correct without double tracking, you need to match the diameter of the flask to the pitch of the knurling. This is very similar to having two matching gears of the same diameter. Each time a tooth is added, the diameter increases by a discrete value. There is no intermediate diameter that will work. The same applies to knurling and knurling flasks, although fortunately, knurling tolerates a certain amount of errors before problems arise. The total number of knurls for a given diameter will usually be repeated three times from the bottom to the top of the pattern. Unlike knurled notches, the spaces between the notches are not set and can be adjusted to allow for the creation of a total number of patterns around the workpiece, regardless of the diameter of the workpiece.
- The provided tool for manual reaming is similar to pipe cutters, but instead of cutting wheels, it contains reaming wheels. Typically, the tool is transported on three wheels: two left and one right, or vice versa.
- Scraping cutting often adopts automatic feeding. The equipment for scraping cutting is similar to that for scraping turning, except that scraping has sharp edges and corners and is set at a certain angle to the workpiece to allow sharp edges and corners to cut the workpiece. Corner, diamond and linear scraping are not possible because lathe wheels cannot withstand such longitudinal speeds, and because reasonable cutting speeds cannot be achieved.
Hand vs Machine Quilting
There are two basic methods of knurling: manual or machine. The first method involves using a roller that creates the desired pattern when pressed onto the surface of the workpiece, while the second involves using a lathe to cut the desired pattern on the workpiece. Manual knurling is the most basic method and only requires a small turning tool. As the worker moves the tool across the surface of the workpiece, it leaves a textured surface in the pattern of the tool's indentation. On the other hand, machine knurling is a more complex process that requires a lathe. Unlike manual knurling, machine knurling does not create a textured surface through pressure. Instead, it uses a drill to cut material from the workpiece.
Benefits of Riddling
Knurling can enhance the aesthetics of a product by introducing an attractive pattern on its surface. Most people agree that textured finishes are more appealing than smooth ones. However, manufacturing companies have several practical reasons for knurling beyond appearance. Products requiring grip, such as hand tools, are often knurled to improve performance and usability. If a hammer has a smooth handle, the user's hand may slip while holding and using it. Knurling prevents hand slippage and creates a more grippy textured pattern.
What are the methods of knurling on a CNC lathe
To reduce problems associated with traditional knurling processes, macros can be used for the production of CNC knurled parts.
- Multi-head lathe for cross knurling threads
The principle of this method is to treat the moire as a long line with positive and negative interweaving. The traditional processing technology involves generating programming other than knurling and the φ1.6 hole, and then performing knurling. Due to the high requirements for the position tolerance of CNC knurled parts, additional fixing leads to a long construction period and a high defect rate. The new processing technology completes all part processes at the same time through fixing, which is easy to ensure processing accuracy.
- Use random cross dithering
During thread turning, there is often a thread disorder in the form of multiple impacts. This phenomenon can also be used for knurling. However, this method is more suitable for knurled parts with a small number of thread heads and a small angle of the helix line, which can increase the spindle speed, depending on the specific situation.
- Simple knurling using spindle lock function
The principle of processing this method is that after locking the spindle, a longitudinal groove is drawn on the surface of the workpiece, and a continuous groove creates simple knurling.
How to finish the knurling process on a CNC lathe?
The knurling process uses a tool to create patterns on the surface of the workpiece. These are straight lines and grid patterns, and the thickness of the patterns depends on the distance.
1. Form of knurling and pattern of knurling
The thickness of the knurling pattern should be selected according to the diameter of the knurled surface of the workpiece. The larger the diameter, the larger the module pattern.
2. Knurling process
- Secure the object to be processed as firmly as possible.
– When securing the object to be processed, the length of the protruding handle should be as short as possible.
– Long objects are handled by the end piece.
– When rotating the external wheel of the knurled part, its diameter should be about 0.25 mm smaller than the final size.
- Ensure proper installation of the knurling tool holder.
– Check if the knurling tool is free from dirt, clean with a wire brush if necessary.
– During the installation of the knurling knife, the rotary pin should be leveled.
– Securely mount the tool.
- Knurling of details.
– Choose a low cutting speed and high feed rate.
– Start the spindle of the machine and apply a sufficient amount of coolant to the knurling tool.
– Insert the knurling tool into the object being worked on and apply pressure until a full diamond pattern is formed.
– Use longitudinal feed, then infeed, until the desired length of knurling is achieved.
– Move the knurling tool to quickly drop the object being worked on.
- On the surface of the object being worked on, deburr by cutting a 45° chamfer at the bottom of the knurled groove.
- Visually adjust the grooving tool to tilt it at a small angle.
Knurling provides the ability to decorate surfaces with various patterns. The groove of the machined object, the shape of the pattern surface, or the elements of straight line turning, are a few of the plastic mass elements that influence the entire process. Additionally, proper lubrication of the machined surface is important, as improper moisture will destroy the shape of the pattern surface. Damage to the pattern caused by improper knurling process is rather rare. Let's remember to minimize them through a cross arrangement of grooves, a grid pattern wheel, or by installing a flower wheel.