As the holder for my spindle could be removed so that I could replace it with a laser module holder, or a pen holder, I sometimes found that this arrangement could very often cause inaccuracy issues. This was because the spindle holder could shift position slightly, depending on the clearances between the attachment bolts and the holes. This was especially so for the angular position. This resulted in the spindle tool not being exactly vertical to the work piece.
I found this inaccuracy when I did tramming of the z axis.
In most machinery, in order for the various parts to be matched exactly, the manufacturers would drill accurate holes and drive cylindrical or taper pins between the matching parts so that there would not be any clearances for movement. In my case, the matching part was one of aluminium alloy and another of wood. Wood is soft and of uneven material composition. It would be difficult to drill accurately without drifting, so it would not make much sense to follow the same countermeasures. However, I found that a block of wood, fitted perfectly into a machined pocket of the aluminium alloy part could become an effective stopper for any lateral movement.
That’s what I did.
Having positioned a perfectly fitted block of wood in the aluminium holder pocket, the spindle holder was bolted in place and its position was adjusted for accuracy by tramming the cnc machine. Once accuracy of the spindle was achieved (when the tool was deemed perfectly vertical in relation to the waste board), a set of screws were tightened onto the block of wood through the spindle holder, thus attaching the block of wood to it.
The block of wood thus became part of the spindle holder. Whenever, the spindle holder was removed, it had to be moved a little at a time because of the friction fit. Similarly, when installing the spindle holder, it also needed some amount of pressing in order for it to fit in position. But when everything was fitted in place, the accuracy of the spindle remained perfect.