Relief for tool ejection on taper spindle

[dalcantara]

Does anyone know about a relief made in some taper spindle that makes easier the ejection of the tool in machine-tools?

With a relief like that is possible to have two points of contact, in the rear and in the front position of the taper profile. However there is no tip in the stardards for that kind of adaptation I think that can help when the drawbar pull force is not enough.

If someone have information or tips on tool ejection please inform. I would like to use that relief.

Thanks

 

[Tmoose]

Tools stick in spindles with steep taper interfaces because of spindle shaft heating > thermal expansion (allowing the tool to be pulled in deeper) or very high speeds that centrifugally enlarge the bore, which also lets the tool be pulled in deeper. The "solution" is a drawbar system with greater ejection force, plus a few seconds extra delay in the tool change cycle.

The relief in the taper is specified in an effort to ease manufacturing, or from a (often desparate)wish to ensure that taper contact will be front and rear for better tool stability. Similarly Taper tolerances that attempt to favor gripping the small end are sometimes used to TRY and guarantee tool stability.

Too low pull force lets the tool wiggle and ruin itself and the spindle taper. Trying to combat tool sticking with low drawbar force would be my LAST choice. With significant side loads you need all the pull force you can get.

HSK and "Big Plus" tooling offer better protection to tool sticking, but their manufacture is often a nightmare.

 

[aamoroso]

Additionally keep your toolholders and spindle clean. Free of chips and excessive oil, the oil will create a vaccum sometimes and hold the tool in place, much like ringing together two gauge blocks.

Fill what's empty. Empty what's full. And scratch where it itches.