There are a lot of different geometries involved in making a router bit—clearance angles, grinding angles, hook angles, axle angles, side clearance angles, radial clearance angles, and side rake. For the purposes of our discussion we will only talk about the basics.
Tool size is a determining factorin how fast you can cut and what types of geometries and clearance angles are possible—all major factors in productivity, finish, and consistency of parts.
For stability, choose the shortest cutting length possible. You should have sufficient shank to fill 80% of the collet. Longer router bits will deflect more—run-out is more exaggerated the longer the tool.
The larger the diameterof the tool the faster you can go—up to a point. While a 3/4” diameter bit will be able to handle a much larger chipload than a 1/8” diameter bit, larger bits require slower speeds for safety reasons. The following are general safety guidelines:
Up to 1” Diameter—Maximum of 24,000 RPM
1” to 1-1/2” Diameter—Maximum of 18,000 RPM
1-1/2” to 2-1/4” Diameter—Maximum of 16,000 RPM
2-1/4” to 3” Diameter—Maximum of 14,000 RPM
3” to 3-1/2 Diameter—Maximum of 12,000 RPM
Use the largest shank possible. However, cutting diameters smaller than the shank diameter cause stress points at the transition and can contribute to breakage. Solid carbide tools larger than 1/2” in diameter can be expensive and are designed when extra long lengths are needed. The following are safety guidelines with relation to shank size and head diameter:
1/2” diameter shank—Maximum large diameter is 2”
1/2” diameter shank—Maximum small diameter is 1/2”
1/2” diameter shank—Maximum overall length is 4”
5/8” diameter shank—Maximum large diameter is 3”
5/8” diameter shank—Maximum small diameter is 5/8”
5/8” diameter shank—Maximum overall length is 4-1/2”
3/4” diameter shank—Maximum large diameter is 3-1/4”
3/4” diameter shank—Maximum small diameter is 5/8”
3/4” diameter shank—Maximum overall length is 5”
Free CNC Manual
We cover this topic in more detail in our free to download CNC Manual.
Our free CNC Manual will guide you through selecting the right tool, maximizing machine time, finish, tool life & profits. Here we talk about tool materials and their uses.
High speed steel (HSS). Used primarily on soft woods such as pine, aluminum, and soft plastics. HSS can be sharpened to a very sharp edge and at the appropriate hook and clearance angles “slices” through soft material, reducing pre-splitting. HSS is more impact resistant than carbide but is not wear resistant enough to hold up to many of today’s man-made materials.
Tangtung (TG) A cast alloy material with a high tungsten content. Tangtung retains its hardness at very high temperatures, is more shock resistant than carbide, and resists corrosion from wood acids. Tangtung, like HSS, can be sharpened to a fine edge and is primarily used in hardwoods for a superior cross-grain cut. TG can and has been used in insert tooling for CNC applications. Freeborn Tool has a line of insert shaper cutters available in Tangtung. Tangtung is never recommended for manmade fiber boards or plywood.
Carbide-tipped (CT). Used primarily on hard woods, laminates, composite materials, and for abrasive or resin-based products. Carbide is welded or brazed onto a steel body and profiled to the desired pattern; therefore it is the most common type of material used for profile and custom tooling. There are many different grades of carbide. The harder the grade of carbide, the more likely it is to break during the heating and cooling process in manufacturing—problems overcome with insert tooling.
Solid carbide (SC). Used primarily on hard woods, wood composites, laminates, plastics, aluminum, and other composite materials for longer life and faster feed rates. Solid carbide can be cast into just about any shape. Solid Carbide rods are well-suited for making router bits with spiral geometries and small form or profile tools. Solid carbide blanks are also well-suited for insert tooling and are available in many standard sizes and configurations. Solid carbide is very wear resistant but not impact resistant—strain and deflection often lead to tool breakage.
Diamond (PCD). Polycrystalline diamond is primarily used on composite materials such as melamine. PCD diamond is extremely heat and wear resistant (100+ times carbide) but is not impact resistant, and in fact, it chips fairly easily. Materials must be free of all foreign matter and be homogenous in nature or tool damage may result. Machine condition and maintenance are vital to cost effectiveness. High initial cost but very low operating cost can make diamond tooling a very economical alternative. Diamond wafers are brazed on to a steel body and are not suited to small sizes.
Insert tooling. Insert tooling can provide consistency in production. Using replaceable inserts instead of brazed-on-carbide allows you to maintain a constant diameter. Insert tooling is also able to utilize harder, more wear resistant carbide than traditional CT tooling. While very versatile in nature, the design does not lend itself well to small diameters due to the need to affix the insert with Gibbs and/or screws.
Posted by Kathryn Magendie on | Comments Off on Factors To Be Considered Before Selecting Your Tool
CNC Router Accessories
Many factors need to be considered when evaluating any cutting situation, before selecting a tool. You can find more useful information in our FREE CNC Manual available for download on our site!
What is the desired finish? Chip-free, hidden part, some minor chips ok, etc. Are both sides (top, bottom) of material of equal importance? The desired finish will often dictate not only what type of tool we can use but also how fast we can cut and whether we must make multiple passes.
Which is more important, speed or finish? While striving for both, sometimes we must assign priorities or make compromises. Higher quality finish can mean higher machining costs (multiple passes, use of more expensive tooling, slower feed rates, etc.). However, ironically, most people run their tools at too slow a feed rate at too high of a RPM, resulting in heat buildup and premature tool wear.
What are the machines capabilities and limitations? It is important to know your CNC’s capabilities and limitations. If your machine’s top feed speed is 600 IPM as opposed to a machine capable of feed speeds of 1200 IPM, your tool selection and setup will be quite different. It is important to note here that just because your machine is capable of running at 3400 IPM does not mean you can cut at that rate. When programming any cut for the first time, it is important to ascertain at what feed that part is to be cut. Part size or geometry alone may preclude you from running more than a few hundred IPM.
Do you have sufficient ability to hold the material you are cutting? If you can’t hold it, you can’t cut it. This is one of the most common problems that I encounter. I am continually amazed how many people will accept minimal feed rates and quality because of chatter and movement. Your ability to make a clean fast cut is related to your ability to hold the material firmly without vibration. Insufficient hold-down can be responsible for everything from premature tool wear and breakage to sub-standard parts, chatter marks, chipping, and material movement. A little planning and effort will give you huge payoffs in productivity and cost savings. When purchasing a CNC router, don’t skimp on the vacuum system. I have never met anyone who said they had too much.
What is the material you are cutting? Raw particle board, plywood, MDF, single-sided laminate, double-sided laminate, etc. Different materials have different cutting properties and may restrict your tool selection and will often dictate geometries, feed, speed, etc.
Are there any operations after this one that will cover, conceal, or change the shape of the part being cut? For example, the top edge will be rounded over or the edge will be covered in such a manner so that a small chip would be of no importance.
Is exact size important? Does another part rely on the accuracy of this part? Maintaining exacting measurements may require multiple passes after a tool is serviced or if the size is non-standard. Edge of Arlington offers insert and diamond tooling designed to solve these types of problems.
Free! CNC Manual
Part configuration and size are important considerations. Small parts can be hard to hold. Intricate parts, parts with holes, curves, and short cuts can be challenging due to heat generated because of a machinery’s inability to make instantaneous speed and directional changes. Advances in machine capabilities have greatly improved the speeds associated with travel time and the ability to change direction. However, a bit turning at 18,000 RPM still turns at 300 inches per second and a good Boy Scout can start a campfire with a stick at a much lower RPM.
Posted by Kathryn Magendie on | Comments Off on Collets & Tool Holders Maintenance
Collets & Torque Wrenches
One of the most critical and most over-looked parts of the CNC router is collet and tool holder maintenance issues
Collets and tool holders are critical parts of any CNC; they should be thoroughly cleaned and inspected during every tool change. Collets are inexpensive and expendable, especially compared to the cost of the tooling that relies on its accuracy.
Edge of Arlington carries Techniks collets and holders and parts. Guaranteed accurate.
Collets are made out of spring steel and should be replaced at least every six months of daily use (400-600 hours of run time), or when there is any sign of wear or damage.
Tools should be tightened with the aid of a torque wrench. Over-tightening can cause distortion and runout, leading to tool wear, breakage, and finish degradation. Under-tightening can lead to bit slippage and twisting in the collet. Torque wrenches should only be used to tighten; using a torque wrench to loosen a nut can lead to miscalibration.
When using full grip collets, whenever possible the tools should be chucked to fill 80% of the depth of the collet. Fillers are available to prevent collet collapse in the event the 80% rule cannot be maintained. Full grip collets have slits running from the top and bottom.
Never chuck up on the cutting edge of the tool but always just below the fade of the flute.
The tool holder is also subject to wear and should be inspected regularly for wear and damage.
Techniks Spindle Wipers
Collet brushes are available for cleaning. Clean using a nylon or brass bristle brush only. Use alcohol after cleaning to ensure there are no chemical residues remaining.
Spindle wipers are available for cleaning the spindle where the tool holder mounts. Real lambskin provides the best cleaning.
Recommended torque is based on the style of collet used in the tool holder. An HSK tool holder for example is available with several collet options. Torque has been calculated based on the unique properties of each collet style.
While changing the bit, it is important to use a set-up fixture or similar device to hold the tool holder safely. Damage to the tool, holder, or operator can occur if the holder is dropped or clamped improperly.
Remember! Over-tightening can distort collets, causing runout problems and premature failure of the collet, tool holder, and cutting tool. Improperly tightened tool holders are a safety hazard. Always use a tightening stand and torque wrench to tighten collet nuts and pull studs.
Cutting tools last longer when you … Torque it right!
If you have a question, feel free to ask us in the comment area, or contact us and we’ll be happy to assist you. As well, we look forward to your comments! Thank you for reading.