We are often asked if it is possible to fit a DRO to small lathes, and in short it is possible to retrofit a DRO system to the majority of lathes and milling machines often found within the model engineers workshop. To go about demonstrating this, we acquired a 1954 Myford ML7. This being one of the more common machines we encounter and set about preparation for installing the Digital Readout.
Step 1: Linear Scale Selection
Traverse the cross slide to its maximum outer position (photo 2). Be aware that on our ML7, we can wind the lead screw right out of its nut. Measure between the two marks to give the cross slide travel. We then repeat this for the carriage travel along the bed. Armed with these measurements we started the linear scale selection process.
We had a choice of three ranges of glass linear scale. These include the GS300 standard with reading lengths of up to 1 metre, the GS500 slim for limited space installations, for example our Myfords cross slide and the GS600 long length with reading lengths between 1 metre and 3 metres. All the linear scales are categorised by range and reading length, so the GS300-420 standard scale will measure 420mm (16 1/2) of travel and its total length will be 526mm (20 1/2).
Our Myford has the standard 4 tee slotted cross slide found on the ML7. The ML7S has the longer 5 tee slotted cross slide fitted as standard, which can be retrofitted as a common upgrade to the ML7. We measured 145mm of cross slide travel on our Myford, which gives us two possible scales, these being the GS300-170 Standard or the GS500-170 Slim. Generally we would always suggest the slim scale as this gives more options when coming to fit.
Our ML7 has 510mm (20) between centres and we had measured 450mm (17 ¾) of carriage travel. Based on these two measurements we opted for the GS300-520 standard linear scale. The standard scale can be fitted, as we don't have the same restriction with space on the bed as encountered on the cross slide.
Looking at the linear scales there are two mounting blocks fitted, one at each end of the scale body, both of which are slotted for adjustment. The reading head has two mounting holes with a grub screw in each corner to act as a jacking screws for mounting to a stepped or uneven surface. A selection of mounting bolts of either M3 or M4 depending upon the scale type are part of the fixing kit.