Last year for my long service award I had the opportunity of spending ?750 on myself. The idea of a gold watch didn?t hit the mark so I decided to treat myself to a set of DRO?s for two of my milling machines. This is how I fitted up one of them my Prazimat mill:
The Prazimat is similar to many of the bench top mills you can purchase, it has a substantial cast Iron Table and a round column. Following advice from the suppliers I purchased the mounting plates for all the scales, some of which were purchased much longer than the scales they were for, this was to enable mounting the scales on the machine.
I started with the scale for the X axis. I had decided to mount it at the back of the table, which would reduce the movement by about ?? but was less likely to be knocked or get in the way during use. The first step was to mount the scale cover, first the back plate was clamped in place and the mounting holes drilled and tapped.
With the backing plate in position it was now possible to look to measure up for the head mounting. On the Prazimat the most desirable place to mount the head is immediately in front of the column but with the column in the way it would be impossible. So my answer to this was to make a slightly wider head mounting and to drill and tap on either side of the column using a ratchet tap wrench:
The final job in mounting the scale is to bolt on the glass scale and then using a dial gauge check that there is no run out. Once the scale is level then the head, once appropriately shimmed can be bolted down to its mounting.
The vertical scale mounting presented a number of challenges as the column base is tapered, whilst the head is much narrower. I purchased an over length mounting for the vertical and for the bottom made a wedge that compensated for the taper on the cast iron base. Having measured the resulting off set of this face from the column I then measured the distance from the column to the head which gave me the required depth of the offset piece for the top of the column mount. I then need to check that I had mounted the backing plate vertically:
To enable access to the clamps at the back of the mill head it would be necessary to offset the scale head so that it sat below the clamps. This was achieved using a Z shaped piece of aluminium, which enabled the head to sit here:
Before going any further I wound the mill to its maximum and minimum height and from this worked out where to mount the scale on the backing plate based on the highest and lowest mounting point for the head.
This is the vertical scale in place, hopefully I should not need to put my hand around the back by the head now that it is in place. The red plastic objects either side of the head provide for the correct spacing of the head from the sacle, once the head is bolted down these are removed
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The final scale for the Y axis I decided to fit behind the right hand, it could have been fitted to the left hand side but that would have meant that the cable would have got in the way.
This took a bit of jiggery pokery as I had to offset the scale away from the mill bed to enable the head mounting to pass behind the scale mount:
Finally after two days I had this:
The DRO has transformed this mill, it has gone from being a very expensive drill to being an impressive piece of kit that is very accurate (I had not realised before how accurate it was) that I use for 95% of my co-ordinate drilling and milling
.
I also fitted a similar set up to my Harrison Milling machine
... but that is another story.
Jo