How to get the best from your router cutters

 

If you use incorrectly selected or poor quality tools you can’t expect to get good quality, reliable results from your cutting or engraving process. In this flyer, the team at CNCRouterBits.com.au will provide you with information that will enable you to get the most from your CNC router or engraving machine.

 

Cutting Tool Selection

Choosing the right router bit for the product you are cutting is paramount. Choose the wrong one and you end up with poor edge finish, slow production rates, tool breakages and wasted time and money. There are a number of factors you need to consider when choosing the right bit for the job. Here we will only discuss solid carbide router bits as they are best suited for use on CNC routing machines.

Material to cut

Different materials require different router bits manufactured with geometries specific to that material. For instance, a router bit designed for cutting veneered board will not cut aluminium. Similarly, a router bit designed for cutting acrylic will not successfully cut composite panels. If you don’t know what router bit to choose ask your material supplier, or do some research online. Our online store allows you to choose the right tool by selecting the material you want to cut or you can choose to shop by cutter type if you already know what type of bit you want.

Depth of cut

The depth to which you need to cut will determine the diameter of the router bit required. As a general rule, you should not cut deeper than 3 times the diameter of the bit. So with a 6mm diameter bit, you should not cut deeper than 18mm. You should always opt to use the shortest possible bit for the job. This will reduce the likelihood of premature tool wear and breakage, improve edge finish, reduce vibration and allow you to run at higher feed rates since the bit will not be subject to unnecessary flexing.

Bit diameter

The diameter of the router bit you choose is influenced by a number of factors.

• smallest required internal radius of the job
• depth of cut
• required edge finish

Rigidity

As well as the above you need to consider the overall rigidity of the system since this has a direct bearing on vibration, edge finish, cutting rate and router bit life. You need to consider;

• machine construction. Is the machine solidly constructed with heavy duty materials? A welded frame and gantry is always going to be more rigid than a bolted construction as it has the ability to absorb vibration.
• work holding. Is the piece being cut held securely? Ensure that flat sheets are not buckled resulting in space between the machine bed and the work piece.
• is the router spindle in good condition? Worn bearings will introduce resonance into the cutting process.
• are tool holders, collets and cover nuts well maintained and not worn? Contrary to popular belief these are consumable items that become worn through use. If any of these become excessively worn they will become a source of vibration.

The correct selection of router bit is always a trade off between the above factors. Sometimes one factor will have more bearing than the other, for example, edge finish over speed of cut, or cutter radius over tool length. You need to decide what is most important and focus on that when making your choice. Just as importantly you should always choose quality router bits. All router bits available on CNCRouterBits.com.au have been tested for performance and suitability in real world applications on Australian CNC routing machines.

 

How to avoid bit breakage

Router bits will break for a number of reasons however, the vast majority of CNC tool breakages are caused by incorrect or faulty colleting.

A router bit spinning at 18,000rpm is at risk if it is as little as 5 microns off centre. That is about how thick a deposit of resin or dust is when it's squashed inside your collet. Collets are manufactured to exacting tolerances and when they are 5 microns out of round both the collet and the router bit are strained because the distorted collet cannot grip the tool shank perfectly.

This results in;

• Poor component edge finish
• Less than optimum tool life
• Metal fatigue and eventual breakage of the tool
• Increased noise

Other factors that can cause tool breakage are surprisingly obvious.

• Replace chipped or worn bits before they break
• Use the shortest possible bit for the job
• Use the largest possible diameter bit for the job
• Don’t drop the bit. Carbide is hard and brittle and does not like being subjected to sudden loads or impacts.

Tools should be changed at the first sign of edge deterioration causing finish degradation or an increase in operator effort to maintain feed rates.

Never allow the tools to dwell in a cut.

The router bit should be fed in such a manner so that in moving through the work, it has a chance to bite or cut its way freely. If the feed rate is too fast, strain and deflection will occur. If fed too slowly, friction and burning will occur. Both decrease the life of the router bit and are common causes of breakage.

The router spindle must be well maintained for any cutting tool to perform properly. Routinely check the collet for wear. Inspect tools for collet marks, indicating slippage due to wear or dust buildup. Check the spindle on a dial indicator for run-out. Collet and run-out problems cause premature tool failure and associated production difficulties.

Do not use adaptor bushings to reduce the size of the collet on a routing or production basis. Tools will not perform properly in bushings over an extended period of time. Bushings are for prototype, experimentation, test and evaluation and not for production.

Wherever possible, use a coolant when routing. Heat buildup caused by action between the tool and workpiece will lead to premature tool failure.

Heat is a function of surface area per unit of time, thus, the more dense the material, the faster the feed rate to minimize heat. However, a compromise must be reached between finish and heat.

Tool life is affected dramatically by tool geometry. Rake and clearance angles, as well as cutting edge length should be examined.

Router bit breakage is most often caused by a misapplication of the router bit. Do not assume the proper router bit is being used.