Don’t forget that it doesn’t matter how to grind the round broach file only: in case of flat, triangle, etc. the “plank” surface must be strictly perpendicular to the working surface of the broach file. We are going to grind with the flat side, not with an edge as the fretsaw does. In some time of processing you must get such result:
The last thing we must do is to move the support roller in such way that it would support the broach file from the opposite side: specificity of using fretsaw as a file consists in the fact that vector of typical pressure turns to 180 degrees (to hold fretsaw upside down is inconvenient). You can rearrange everything in initial position if it’s necessary. In original this roller is fastened in the following way:
As you see, it can be easily moved forward; you just need to bore the mounting holes.
This is what we get as a result:
You may not put the platform to its place; in most cases it only impedes normal operation. In my case I had to grind a bit the roller holder as the connecting rod rested against it in the last millimeters of its run. That’s all; the electro-file is ready for operation.
This device is indispensable when you need to make some grooves (for example, for wires) or improve an off-centered drilled hole. The advantage of this device over dremel tool and other turning devices which are used in such cases consists in the absence of running in rotation direction and, as a result, high accuracy. There is only one drawback: full-sized file can’t be fitted in the fretsaw; this means that when you need to take off a thick layer of material you’ll have to think over another way out. For example, you can take a thicker and rougher round file and fit it into the usual hand drill obtaining a kind of rotozip.
Update: I found out more information about electro-files. It turned out that I’m not the only wise man. Bosch manufactures similar ready-made nozzles for fretsaws and reciprocating hacksaws…
… moreover, there is a class of devices which people call – electro-files. They represent a hybrid of chainsaw and belt polishing machine:
Unfortunately, they are expensive and I suppose that change belts can be not available.