How to fit a tool into the spindle?

andypugh wrote:

uptown47 wrote:

If I were to change the tool it would be easy to leave more sticking out than the previous tool and your cuts would therefore be deeper (assuming the Z axis moved to the same position)??

This is a more complicated subject than it might at first appear.

I think that from your question we can assume that your spindle uses a collet rather than one of the quick change systems.

Many videos you will see on the internet will be using a spindle with a tapered socket and multiple tool-holders. With this type of tooling the tools are always at the same height as they were last time, and that tool length is stored in the tool table.

Here is a picture I found on the internet of a set of tools set up in their holders: goo.gl/images/9ecxcV As you can see each holder has an ER collet or similar, and the tools are clamped in to that.

If you have a collet built in to the end of your spindle then it is a bit more dfficult.
You can fit collars on the tools so that they always go in to the same depth.
You can set up an automated tool probing system to measure the actual tool length after you have changed tool.
Solid collets exist that will always engage at the same length ( www.cutwel.co.uk/tool-holding/tool-holde...s/shrink-fit-collets ) though the ones at that link are shrink-fit so need an induction heater to change bits.

The most practical solution for a new build is probably to split your machining into a single tool per program, then fit the second tool, touch-off accurately, then run the second program.

andypugh wrote:

You shouldn't need to re-home between tools.

The easiest way to "touch off" is the way that JT described years ago, and which I have copied. Take an accurate dowel (I use a one of my large collection of broken milling cutters, though there is probably a good argument for using something slightly softer).
Assuming that your G-code is set up with Z=0 at the top of the stock, jog the new tool down to a bit less than the dowel diameter from the stock, and then jog _up_ until the dowel will slip under the tool. Jogging down towards the dowel is a good way to chip a tool.
Then "touch off" to tell the system that you are now at the dowel diameter above the reference height. I use a 6mm dowel, so enter 6mm.

For a machine like yours it _probably_ makes sense to keep the tool table all-zeros, and to "touch off" directly in to the work coordinate system.

There are ways to configure LinuxCNC for auto-tool length measurement, and someone has also found a very clever way to allow auto tool changes with your style of spindle. by using the power of the X and Y axes to make a circular move to loosen the collet.