Tooling Basics for CNC Machining

Below is an article GDP|GUHDO contributed to January 2015 edition (formerly FDM/Cabinetmaker) 
Understanding fundamentals of CNC tooling can make a huge difference in your costs, productivity, and efficiency.  Most CNC machining centers for wood, plastics and composite machining today are equipped with steep taper ISO/SK/BT style, or more frequently HSK style tool holders .  My favorite analogy when discussing tooling basics is the automobile (i.e. the CNC machine), the rims (the tool holders) and the tires (the cutting tool). The most well-designed car won’t go very far if it has bad rims and cheap or faulty tires. Let’s look at the importance of proper cutting tool selection and the outside factors that affect tooling choice as well as other considerations that will directly influence the machining cycle.
CNC Tool Holders - HSK 63F, RDO35 and ISO30

CNC Tool Holders – HSK 63F, RDO35 and ISO30

Start with parameters
Depending on the cutting process that needs to be accomplished, understanding the machine parameters, output, spindle, clamping and tooling options is essential. Material hold-down and dust collection setup will all play a role in the process, as will the quality, density, abrasiveness and surface finish of the material to be machined. Cutting tool selection will be predicated on the basis of understanding the foregoing properties that are already pre-determined, the expectations of anticipated feed speeds to be achieved (capacity) and cost efficiency. These all contribute in making the decision of what tooling is most suitable and cost-effective for the job.
Most CNC machining centers for wood, plastics and composite machining today are equipped with steep taper ISO/SK/BT style, or more frequently HSK style tool holders (Picture 1). The standard HSK tool holders have very high levels of accuracy, with a runout tolerance of 0.003mm (.0001”). A tool holder that is supplied with a ball bearing collet nut, rather than a single piece static nut, is preferred. The ball bearing uncouples the inner ring from the torque/threaded part of the nut (Picture 2) so the circular motion of the nut is completely converted into clamping force without any frictional loss. Advantage: more clamping force, less wear and the tool holder can be used to run both clockwise and counter-clockwise.
The most common versions of tool holders used in wood/plastics/composites utilize ER32, ER40 or RDO35 (SYOZ25) collets and their differences are shown in this chart:
Collet Style Overall Length Clamping Tolerance Max Size Diameter Available
ER32 40mm 1mm 20mm 3/4″
ER40 46mm 1mm 25mm 1″
RDO35/SYOZ25 52mm 0.15mm(premium) or 0.5mm 25mm 1″
HSK63 F tool holders, with any of the above collet types, are interchangeable between machines as long as the same “A” dimension (the dimension from top of the HSK shoulder to the bottom of the collet nut) is the same.
Specialty tool holders
While standard collet chucks are excellent clamping choices for most applications, there are heat shrink and hydro tool holder options for more specialized applications. Heat shrink tool holders are beneficial in high speed machining operations and do not use a collet system as the tool shank is mounted straight into the heat shrink chuck. A heat shrink chuck can only accommodate one size tool shank and generally requires an additional (and sometimes substantial) cost investment for heating equipment to mount and remove the tool from the chuck. It’s a great choice for carbide insert tooling, for instance, where tool and chuck are assembled at the manufacturer and won’t need to be removed for service. See Picture 3.
Another option is the hydro chuck, which also has the advantage of bypassing a collet system reducing compounded tolerances between machine and tool. Hydro chucks are balanced to 25,000 rpm and available in all common metric sizes. (10mm to 25mm). See Picture 4.
Cutting tool options
Moving on to the cutting tool options, it’s important to understand that this is the wrong place to worry about initial tool cost. Accurate cutting tool cost is measured by cost per linear foot machined. Choosing the wrong tool can severely restrict and limit the machine’s capabilities and even give back some of its selling features.
Accuracy, cost-effective production, superior finish quality, waste reduction and maintaining the integrity of machine and spindle all boil down to tool holder and cutting tool selection. Poor quality tool holders or out of balance cutting tools will end up costing far more than might initially meet the eye. Whether the choice is solid carbide spiral tools, insert tools, custom profile tooling or PCD (polycrystalline diamond) tooling, a close look at the pros and cons of each type is something well worth researching and understanding. One company can easily waste thousands of dollars if using ¾” 2-flute solid carbide compression bits to machine table tops, for instance, when a comparable 2-flute carbide insert compression bit will easily out-perform for a small fraction of the cost.
A phenolic fabricator may go through many solid carbide bits every day when a polycrystalline diamond (PCD) bit (special design for phenolic) will run considerably longer and reduce overall machining cost. Someone purchasing a carbide-tipped round-over bit to run on a CNC machine will buy a lot more bits and never maintain uniformity, when an insert tool will maintain constant diameter and hold dimensional accuracy throughout at a lower cost.
Use tools correctly
Whatever tool choice is made, the most important aspect will be using it correctly. The best cutting tool can only perform well if it is used within the parameters it was designed for. The basis of successful cutting tool performance is a synergy of machine quality/integrity, material hold-down, dust extraction, the clamping system (tool holder/collets) and tool and material composition operating under correct machining parameters.
The most important point to consider with any cutting tool is the actual chip load it will generate during the cutting cycle. If the chip load is not within the ideal range for the material being machined, it will result in either overheating of the tool and very short tool life, or, pushing the tool beyond its limits resulting in tool failure (breakage). A very prominent notion is, for instance, that more flutes on a router bit will yield a better finish. This is absolutely not the case. What leads to the best cutting results is the cutting edge moving through the material at the right speed, i.e. chip load. This single factor is probably the most responsible for tool life.
Understanding chip load
So, what is chip load? Simply put, it is the size/thickness of the chip being removed per flute/cutting edge with every revolution of the tool. So, going from a 2-flute bit to a 3-flute bit, the size of the chip is reduced by 33% if the feed rate is not adjusted accordingly. A smaller chip will increase the heat generated during the cut as the chips cannot be extracted out of the cut fast enough and are re-cut into yet smaller particles. Chip load charts found online or provided by tooling manufacturers should all be considered as a starting point/reference range only and it is up to the user to find the ultimate “sweet spot” that provides a combination of the longest tool life, finish and cost efficiency.
The chip load formula is as follows:
                  Chip Load = Feed Rate (inches per minute) / (RPM x number of flutes)
                   Chip Load = Feed Rate 600”/minute / (18,000×2 flutes) Chip Load = 0.017”
Increasing the chip size per tooth will decrease the quality of the cut, while decreasing the chip size per tooth will shorten the tool life, so it’s important to find the ideal middle where both finish and tool life are optimum.

3 flute diamond tipped bit for fast feed rates.

Cutting direction
Another consideration is whether to climb cut or conventional cut. With climb cutting, the direction of the feed is identical to the direction of the cutting edge. (As an important side note, this method of cut should never be attempted with a manual fed operation as it can result in very dangerous material kick-back). Climb cutting provides a better finish quality. When conventional cutting, on the other hand, the material is feeding against the direction of the cutting edge which exerts less cutting force on the tool and increases the tool life accordingly.
In summary, cutting tools and clamping systems play a paramount role in a CNC machining center delivering its promise of optimization, capacity, waste reduction and cost savings, as none of these promises can fully materialize without the contributions of high-quality tooling and accessories.
Karin Deutschler, president of GUHDO USA Inc., has been selling diamond tooling since its introduction in the U.S. in 1982. You can contact her and the GDP|GUHDO team at 1-800-544-8436 or
This article appeared in FDMC, January 2015. ©Copyright 2015, All Rights Reserved.

The Importance of Ball Bearing Collet Nuts on HSK/ISO Tool Holders

collet nut

HSK collet nut with and with-out ball bearing

The importance of a ball bearing in the collet nut cannot be understated.  Apart from the fact that it allows the user to run both CW and CCW tools in the same tool holder, it is the solution to eliminating tool slippage problems during the routing process.  Even if tool slippage is not an issue….if you are noticing any collet marks on the shanks of used tools, you have an issue with vibration occurring during the cut.  This leads to poor cut quality and poor tool life.  While these collet marks can also result from a worn collet needing replacement, they often occur from use of a static nut that doesn’t apply the same grip as a bearing nut does.

Case in point:  One Florida customer, lets call him “Carlos”,  bought two 1/2″ diamond PCD router bits from GUHDO and experienced breakage of both bits right below the shank.  When the PCD bits were returned for evaluation, we found chattering to be the problem and upon further investigation, found his tool holder had a static nut and a collet which had not been replaced in years. After replacing the tool holder,  collet and diamond bit the customer called a few weeks later to tell us his problem was resolved and better yet, his CNC machine had never ran as quietly as it was now running, in all the years he had owned it!

At the CNC Cookbook they have studied the effects on precision that come with and without a ball bearing collet nut – the results tell the story on just how important the ball bearing is “…A ball bearing nut has about 14% more static stiffness for surface finish, but a whopping 50% more damping, which helps keep the chatter out when you have to get aggressive with a cut.”   If you’re serious about precision and interested in getting new tool holders, or upgrade to ball bearing collet nuts, you can call us at 1-800-544-8436 to order.

Arbor Tooling for moulders and CNC machinery

double raised panel profile on HSK63F arbor

double raised panel profile on HSK63F arbor

GUHDO offers a wide range of arbors for use on CNC Routers, Machining Centers and Moulders equipped with the Powerlock feature. Depending on the machine and motor connection,  options include SK30, ISO30, HSK63F and HSK63E for CNC routers and HSK85W for Kentwood, SCM and Weinig moulders.  Arbors, especially for CNC routers and machining centers,  allow for large diameter and stacked tooling sets to be used to machine thicker materials commonly seen in the production of doors and windows and large mouldings typical in the millwork industry. The arbors are available with spindle diameters of 20, 30, 40 mm and 1-1/4” with spindle lengths from 40 mm up to 240 mm. Produced from tempered steel and thoroughly balanced, these arbors provide endless production capabilities for your CNC Router, Machining Center or Moulder. When considering arbors and tooling, it is very important to adhere to weight and diameter specifications and RPM limitations as recommended by the machine manufacturer.

For additional information, please contact GUHDO at 1-800-544-8436 or email us at [email protected]  To learn more about GUHDO, visit our website.

double sticking profile cutter set on HSK63F arbor

double sticking profile cutter set on HSK63F arbor


HSK63-F Hydro Chuck for CNC Machines


HS63F hydro chuck by GUHDO

While heat-shrink and power shrink tool holders improve accuracy and increase tool life, the investment in additional accessories required to mount and remove the tool from the holder often makes it cost prohibitive for the smaller shop. A great alternative is an HSK hydro clamping chuck. Precision balanced to 25,000 rpm, the tempered and ground tool holder will provide higher clamping precision than a standard collet and nut are able to since it grips the tool shank absolutely concentrically over the full length of the shaft.

The use of a hydro clamping chuck will improve tool life (less compounded tolerances from collet and nut) as well as the surface finish.  The chuck features a hexagon screw that, when installing a tool, is tightened to the “stop” point. The clamping piston forces the hydraulic medium in the expansion chamber to increase pressure, which first centers the tool shaft and then tightens it securely and accurately for a very solid and secure connection.  They are great choices for cutting composites and other materials that require a precision machining environment.