Gauge Length

BigJohnT wrote:

On BT30 tool holders there is a "gauge length" spec. What does that mean?

Thanks
John

Gauge length is some Z distance that is used as a reference for the depth of the taper.
I believe on a BT30 and similar tapers with a flat, that the gauge length starts at the
flat of the spindle nose, where the drive dogs almost seat against.

Jon

Gauge length should always be taken from spindle Flat face (ie if u had no tool in the spindle, where dogs and tool would sit and meet each other) to the end of the holder where the tool goes in ie. the nut or other part of holder.

Then if u have offline tool measuring u can measure this length with a hight measuring device, set the Z distance correct and just enter in the overall gauge length & tool length measured into the tool table.
making it easy to replace a broken tool or the likes..

when you buy holder, most will say ER16120L, the 120 means from gauge length to the nut part. so as jmelson pointed out, how fare you can reach with the holder with no tool sticking out.

so yes andy and jmelson where correct, just wanted to confirm for others..

like andy said every machine is different, due to how much the tool will sit in the taper etc..
some new machines now make the flat of the holder meet the spindle flat, and it pulls up onto this part, giving a more deal lenght, so as the spindle warms up the tool holder can not grow or shrink in length, after few hours of machining