Tool table progress

I think I'm sort of starting to understand what tool tables, tool lengths, tool length compensation etc are about. Spent a fruitless hour or so trying to get the controller to show that it had accepted the tool lengths and was actually doing something with them.

I thought that simply populating the tool table with some tool lengths would cause the spindle to change height when I asked it to go to G54 Z0. That's one of the many problems caused by not knowing what you are doing. 

In fact, you have to issue a G43 and accompany it with the appropriate H command. Seems the tool lengths are defined as H01, H02, H03 etc and although you should always associate (height) H01 with (tool) T01, height H02 with T02 etc, you are not forced to. And the G43 looks at the H** value, not the T** number. 

So you have to say G43 H02 for the tool length 2. Ideally, H02 is associated with tool T02. Then, when you ask for G54 Z10 with tool 2 active, it will bring the tool tip to Z10, allowing for the length of tool 2. I think.

During my recent extended stay in the armchair workshop I acquired a Mahr 3D touch probe. That's a me-too, cheaper version of the Haimer probe that is much used by Tormach owners amongst others. The drawback of this device in conjunction with a turret mill of limited Z axis movement soon becomes apparent. By the time you've mounted it in a toolholder, it sticks out far more than any tool, so the notion of setting G54 zero with it and then setting offsets for the other tools doesn't work so well. I thought I might be able to use the thing by setting G54 with an offset instead of zero but with a little bit of thought that clearly won't work. Unless I can think of some other way of making use of this device, it will have to sit at the back of the cupboard. I can't even see it being much use on the Blidgeport when that is finally converted, as it is also a turret machine with even more limited (120mm) quill movement.

You can see what I mean here. The red Mahr tool is reading zero with G54 set to zero. 

If I now swap the Mahr for a typical tool in a toolholder, the spindle has to be extended almost to the extent of its travel to reach the same G54 zero. There is almost no travel left, so unless I plan to do some engraving, I won't be able to machine anything of any height:

  Anyway, I managed to make a dummy tool (about 125mm gauge length) with another piece of 6mm aluminium rod in a 50 gauge length tool holder. This will be longer than any tool I currently own. I then numbered it #1 and with the machine coordinates at Z-1.0 (mm), I zeroed the Baty DTI and set the tool length in the tool table as tool #1. 

Next I used an ancient 1" end mill that I found in a scrapyard in Ripon when I was about 15. It's got buggered corners but it's the only tool I have that fits the toolholder that came with the Shiz - and as it's buggered, I have little to lose playing around with it. I knew it would be useful some day!! Anyway, that became tool #2. 

Tool #3 is the face mill and finally, I made the Mitsubishi indexable 12mm cutter tool #4. 

For each tool, I jogged the Z axis until the DTI read zero again ie the tip of the tool was at the same height as tool #1 had been. Then set the tool length for that tool in the table (go into "redeem", highlight that row and press "A"). The numbers look right and when I issue a G43 H* (where the * signifies the row in the tool table), the spindle moves so that the tip of the tool is at the zero defined by the DTI. 

If you add up the gauge length of each tool and the corresponding tool length from the table, you end up at the gauge length of (the master) tool 1, which is about 125mm. I suppose that's progress!