Pre-set CNC Mill Tooling System
Bertho Boman


Commercial CNC milling machines have the tools mounted in tool holders and the length is preset. Being able to quickly switch tools without recalibrating tool length is of course a requirement for automatic tool changing but also very desirable when manually changing the tools. Adding interchangeable tool holders on a small mill is very expensive and often seriously limits the available Z-height. This system is used on a Taig mill with ER-16 collets.

An alternate low-cost and efficient solution:
By using pre-calibrated tools in the ER-16 collets it can be fast to change from one tool to an other without any calibration steps. It is even faster if the same size shank is used on the tools since the ER-collet only needs to be loosened in that case. It will further speed up the process if a spindle lock is available like:
www.Spindle lock

Tool Holder


Cone Cone

I laser cut the tool holder but of course it can be CNC drill or even manually created. By using the removable labels it is easy to update or change the tooling. In some cases I mounted drill bits in custom tool holders so they can be quickly switched too.

By using fixed stops on the individual tools, and keeping track of the tool number, an efficient setup can be achieved that allows fast tool switching without any calibration steps. This type of tool length control is used in the PCB manufacturing with the little colorful rings pushed onto the PCB drills.

There are several ways to obtain the stop rings, the PCB drill bit rings are perfect for 1/8 inch tool bits, suitable sized tubular sections are sometimes available, and it is easy to custom make the little rings. The metal ones are typically held in place with Loctite or super glue.

The individual tool lengths are entered into the Mach3 or Mach4 tool table or other system used.

Tool Length Definition

The easy way to visualize the definition of the tool length would be the distance from the top of the ring to the tip of the tool. The tip of the ring is of course the clamped position against the ER-16 collet. Unfortunately that is a very difficult to use surface to calibrate the vertical axis to the top of the table surface or material.

Instead a very short tool bit, labeled #0, with a smooth rounded tip is used as a reference and its length is defined as zero. To measure the individual tools, first the #0 reference tool is set to touch the table and the Z-axis set to zero. Then the next tool number is inserted and the Z-axis is adjusted so it just touches the table. The displayed Z- height is the tool length entered into the tool table for that tool.

Setting Z-axis Efficiently

Besides using an electronic tool setting option there is a much better way than gradually lowering the tool bit to the table or work piece and sliding papers under it to judge the position. The movement has to be done very carefully and it is too easy to damage bits or work surfaces.

A much better way is to reverse the process using a known size diameter round short rod. An ideal one is a tooling pin. Lower the Z-axis quickly to about 7 to 9mm above the table and then try to slide an accurate 10mm rod under the bit. Rise the Z-axis until the rod just slides under the bit. Set the Z-axis to 10mm. It is much faster and much less chance of damages.

With a round rod it is easy to feel when it is getting close to sliding under the tool and the Z-axis can then be raised slowly the last few steps. Sliding a flat piece will not give that gradual feel.

Note that mixing collet brands might result in different offsets, so be sure to use only one collet set with the calibrated tools and tool table.

Hopefully, this will help newcomers to this field. Old-timers already know what to do.

Bertho Boman
Vinland Corporation
Fort Lauderdale
Florida USA
(954) 475-9093
Email: Boman33 at Vinland dot com