It would be nice to know........

Why does a milling machine have a reversing motor.... I can't see any reason why I would run the spindle on mine in reverse, but what do i know......

I'm sure there is some logical reason or am i just missing something obvious.

When power tapping would be the obvious one.

Regards.

David.

Hi Me., slitting saws and other similar types of cutters can be used in either direction, is one example, left hand drills and taps another.

Regards Nick.

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

I usually run the cutter backwards in order to locate the edge on the material to be machined. Running the cutter backwards does not remove any metal and give a very clear audio indication when the rotating cutter touches the edge.

Mike

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

… for spot-facing/counter-boring a lower surface, using a left-hand tool and ‘pulling’ in Z

MichaelG.

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

As Andrew says, for tapping - most of my tapping is now done on the manual mill using the VFD to reverse the tap out of the hole at low speed.

And the Hemingway speed increaser kit to improve usage of small cutters in normal mills also reverses the direction, so you need to run the main spindle in reverse.

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

All bridgeports and clones motors have to run in reverse when in low gear... You would have thought than an idler somewhere would have been cheaper than the switch gear; but that's how they are...

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

The obvious reason - apart from tap reversing and LH threads - is that the machine is intended as a general purpose resource where the maker can't realistically anticipate all the purposes the end user may put it to.

Reversing motors are easily available - it would simply be unnecessarily restrictive not to fit one.