A drawbar force gauge is a

gauge Gauge ( ) may refer to: Measurement * Gauge (instrument), any of a variety of measuring instruments * Gauge (firearms) * Wire gauge, a measure of the size of a wire ** American wire gauge, a common measure of nonferrous wire diameter, especia ...

designed to measure forces on a

machine tool A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, Boring (manufacturing), boring, grinding (abrasive cutting), grinding, shearing, or other forms of deformations. Machine tools employ some s ...

's drawbar. These types of machines are found in

metalworking Metalworking is the process of shaping and reshaping metals in order to create useful objects, parts, assemblies, and large scale structures. As a term, it covers a wide and diverse range of processes, skills, and tools for producing objects on e ...

woodworking Woodworking is the skill of making items from wood, and includes cabinetry, furniture making, wood carving, joinery, carpentry, and woodturning. History Along with stone, clay and animal parts, wood was one of the first materials worked b ...

, stone cutting, and

carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers ( Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon comp ...

fabricating shops. Many modern machines generate well in excess of . Measuring and maintaining this force is an important and necessary part of a

machine shop A machine shop or engineering workshop is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tool (machining), cutting tools to make parts, usua ...

preventative maintenance plan.

How drawbar force gauges work

Modern drawbar force gauges typically are based on a force sensor that uses bonded strain gauges and

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

to convert the resulting output into a digital display for the user to view. Earlier versions of these gauges sometimes also used a sealed hydraulic cavity with a

pressure gauge Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of press ...

to measure and display force. These hydraulic gauges are generally considered less accurate because of the physical limitations of the indicator.

Why drawbar force is measured

Drawbar force gauges allow early detection of problems with the spindle's Belleville spring stack, verification of performance of the clamping system as a whole, help prevent damage to spindle taper and other machine features critical to machining accuracy, and ultimately help to keep the machine operator safe. Drawbar force measurement has been made much more important in recent years with the introduction of radically higher RPM machines. These machines are necessary to work the modern materials required in a multitude of applications—new types of

composite wood Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, wood veneer, veneers, or boar ...

material, carbon fiber, and high strength materials such as

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

. High speed machining of these materials is considered to begin at 10,000 rpm and may reach as high as 50,000 rpm. The need for regular verification of the spindle clamping system becomes obvious. As the required machining speeds become higher, the need for machines to be built with smaller diameter spindle components increases. When the spring pack, bearings, and hydraulic units become smaller, the stresses placed upon them become greater. As a result, the clamping system will remain in good shape for fewer and fewer "cycles", or "clamp/unclamp" procedures. Again, this requires gauges and routine procedures to monitor this process. Many operators do not realize that this is something that has changed over time. Any metal or wood working machine that takes advantage of the HSK taper system should be routinely checked. The slightest stroke mis-adjustment, dirt, or slight wear of the drawbar system can result in significantly reduced holding force. A preventative maintenance schedule, with a strict timetable for testing is a necessity when operating any type of high speed machine utilizing the HSK system.

Retention knob

Drawbar force gauges are able to detect broken or weakening components of the drawbar clamping system, can give indications that the unit needs

lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubr ...

, detect gripper mis-adjustment, or demonstrate that the incorrect retention knob is being used for the machine. A retention knob is a device screwed into the narrow end of a tool holder, enabling the drawbar to pull the tool holder into the spindle. With a highly accurate electronic gauge, deficiencies can be noted and corrected. Many hours of expensive machine operating time can be put to use while avoiding fretting, chatter, "stuck" tool holders in a spindle, etc., by employing proper preventative maintenance techniques using an accurate electronic gauge and other spindle health management tools.

Drawbar force gauges in tool holder standards

The following tool holder standards specifically address tool retention force as measured by a drawbar force gauge: *HSK standard ISO 12164-1: Hollow taper interface with flange contact surface—Part 1: Shanks—Dimensions *Steep Taper standard ASME B5.50: 7/24 Taper Tool to Spindle Connection for Automatic Tool Change *Capto Taper standard ISO 26623-1: Polygonal taper interface with flange contact surface—Part 1: Dimensions and designation of shanks

External links

Don’t Forget The Drawbar, Modern Machine Shop magazine, March 2006, By Peter Zelinski
{{DEFAULTSORT:Drawbar Force Gauge Machine tools Metalworking measuring instruments