When power tapping would be the obvious one.

Regards.

David.

So you can use a left hand drill bit to drill out broken or damaged screws – it can help to 'unstick' the screw from the hole.

For when you have fitted the slitting saw the wrong way round

All my milling machines have reverse and all the above apply. I use reverse for tapping on the CNC mill. I have reversing tapping heads for the vertical mill, although I have used reverse and handraulic control when It wasn't worth setting up a tapping head. I also use reverse on the vertical and horizontal mills depending upon which way it is convenient to run cutters and boring heads, like this:

My vertical mill has a single stage backgear reduction, so to keep tool rotation the same the motor needs to run in reverse when backgear is engaged.

Andrew

I think you need to consider cutter heads, that have "screw on" arbours. Running in reverse may cause them to unscrew.

Last time I used mine in reverse was when I accidentally made a left handed cutting tool to create the spaces on an escape wheel.

Didn't realise I had it reversed until I got the whole thing setup in the mil and ready to run – then a bit of a 'hang on… something is not right here' moment.

Glad to have reverse for that – the cutter took a while to make.

Dave

An OTS switch is way simpler and, cheaper, than trying to fit an idler into the head, especially without making the head bigger. Why do import lathes/mills use variable speed drives? Not because they're inherently better but because electronics is way cheaper than gears or belts and pulleys.

Andrew