# DRO Scale on Cross-slide



## lemelman (Jul 29, 2012)

My lathe is a well used Chinese 12x36 geared head that I purchased from Chester in UK some 10 years ago, and a year or so ago I decided to fit a 2-axis DRO.

I met the same problem as everybody has who's done this; where to place the scales? The bed scale was relatively easy; it went at the back, just below the rear bed-way, and doesn't interfere with anything. 
The cross-slide scale was more difficult. If placed on the headstock side it was susceptible to damage from large work pieces, and could compromise turning very short work pieces. On the tailstock side it covered the cross-slide locking grub screw.
A friend had a later model, also from Chester, that came fitted with a 2-axis DRO. I asked him how he locked the cross-slide; he said he couldn't, because there was no locking screw. It turned out that the scale, mounted on the tailstock side, completely covered the locking screw.

To mount my scale, I drilled and tapped two holes on the tailstock side and removed the grub-screw that was used to lock the cross-slide. I then found a set screw with the same thread (M6 in my case), adjusted its length so that there was about 1mm clearance between the head and the cross-slide when locked, turned the end to match the grub-screw, and thinned the hex head to match the thickness of an M6 spanner.  I then inserted the screw and measured the distance from the top of the hex head to the cross-slide when it was just unlocked. This distance, plus about 0.5mm, gave the thickness of spacers to insert between the scale and cross-slide to provide clearance for the M6 spanner used to lock the slide. I then mounted the scale and spacers and checked that I could easily lock the slide by the hex head screw. Because I was concerned that the scale was vulnerable to damage from the tail-stock, I added an M6 screw and lock-nut to the scale reader mounting plate to act as a buffer.

At this point I thought it was finished, but another problem reared its head - I was unable operate the saddle lock bolt. Although I had ensured that the hole for the bolt was not covered by the scale, I had forgotten the size of the special square head - it was too thick to fit under the scale, and too wide to fit next to it. To fix this I used a long M10 socket headed bolt, turned a nut so that it fitted under the scale, and extended the thread of the bolt so that the un-threaded part raised the head just above the scale. The bolt had to be inserted by screwing it through the nut held between the saddle and the scale. I then use an Allen key to lock the saddle.
It all works fine. So much so that my friend modified the mounting on his lathe to match.


----------

