High Speed Machining Tool Holders, Shrink Fit BT30 and BT40

Two popular choices for high speed machining are the shrink fit tool holders BT30 and BT40. These are particularly good when the application calls for high torque or high speed cutting. They work equally well for HHS or carbide, though most cutting is done with precision carbide cutters.

How do shrink fit toolholders work?

Basically, the tooling is heated up in order to expand the bore, the end mill is inserted, then they are both allowed to cool. The cooling allows for the metal to contract, which creates a metal to metal fitting condition, very much as if they were all one piece.

The holding pressure ensures a precise fit with little or no runout. It also eliminates the possibility of tool slippage and the consequent damage to the workpiece. In fact, the holding power for the BT30 and BT40 is up to 10,000 lbs of force.

A special fixture is required to heat up the holder, and the time required varies from a few seconds to a few minutes, depending on the set-up. One complaint precision machinists, CNC operators, toolmakers and injection mold makers have is the time it takes to change the tool.

Because the tools can be set up offline, it makes it possible to work ahead and thus eliminate the time factor. However, this is easier said than done in a real time precision machine shop. Often the lead-times and work load make it very difficult to plan ahead and be tooled up in advance.

Benefits of shrink fit tool holders

• Little or no TIR, less than .0002 in runout

• Solid, one-piece spindle to cutter holding

• Reduced vibration

• Better surface finishes

• Extended end mill life

• Available for carbide or HHS

• Faster cutting speeds and feeds are attainable

• Machine tool spindle life is increased

• Highly rigid for long, hard to reach areas

• Enhances cutting of tough tool steels such as D-2 and inconel

Characteristics of shrink fit toolholders

Shrink fit tool holders are especially good for high speed and high torque machining. With the virtual one-piece, highly rigid tooling, more difficult to machine steels and details can be accurately cut. The spindle will last longer, the end mills will perform better, and accuracies will be more consistent.

Any precision shop should take a serious look at this technology to see if it applies. The increased production, with the increased accuracy will more than offset the initial cost of the set-up.

Used in combination with hydraulic holders, collets and HSK tooling, nearly any type of machining can be accomplished at increased speeds and precision.