Milling, routing, drilling - What the difference in the end.

[frugal]

After talking to Phiily about how he cuts out the sides of his infil planes with a milling machine I got to thinking: Really when you get down to it, what is the difference between a router, a pillar drill and a milling machine?

As far as I can tell they all hold a spinny thing vertically and apply it to metal.

If you made up a sliding table for a pillar drill is there any reason why you could not put a milling cutter in the chuck and use it as a simple milling machine? It would not be as accurate as a milling machine (people seem to buy milling machines to do woodwork as they are more accurate, Robert Ingham specifically).

Likewise, if you got a milling cutter with an 8mm shaft, is there any good reason why you could not use it in a router on a slow speed? Attach the metal to a sub-base of MDF so that you were not cutting into the workbench and had a large enough piece of MDF to clamp the sub base down. I can see this one being messy with cutting steel as it would need coolant, but cutting brass does not need a constant feed of coolant.

I am sure that it is a stupid idea, but I am not quite sure why...

 

[Peter T]

Machining metal with an end mill requires a relatively constant feed rate to achieve any sort of acceptable results. So, on a manual milling machine you would set the cut and then wind the metal through at a nice constant speed with the lead screw.

Trying to do that by hand with a slide or by pushing a router would be difficult. At best, the cut quality would be poor, at worst the cutter could break and do some serious damage.

The other thing to consider is the amount of sideways force generated when cutting metal in this way. Milling machines are designed to be robust enough to withstand these forces. Bench drills and routers are not designed with these forces in mind.

 

[frugal]

See, at least I knew that it was going to be a daft idea. I must be learning, normally I would try it out to see what happens first :wink:

 

[newt]

What peter said

 

[9fingers]

Be very careful indeed before applying any side load to most pillar drills.

Their chucks are usually retained by a taper and the combination of intermittent cuts (eg with a milling cutter or router bit) will loosen the taper and the chuck will come out with disasterous results.

Milling machines usually have a hollow spindle through which a draw bar passes to prevent this happening.

Bob

 

[Peter T]

Be very careful indeed before applying any side load to most pillar drills.

Their chucks are usually retained by a taper and the combination of intermittent cuts (eg with a milling cutter or router bit) will loosen the taper and the chuck will come out with disasterous results.

Milling machines usually have a hollow spindle through which a draw bar passes to prevent this happening.

Bob

and that as well

 

[RogerS]

.....and routers are not designed with these forces in mind.

Not sure I agree with that statement. With the exception of plunging, you're always using side pressure with a router.

 

[FatFreddysCat]

Likewise, if you got a milling cutter with an 8mm shaft, is there any good reason why you could not use it in a router on a slow speed? Attach the metal to a sub-base of MDF so that you were not cutting into the workbench and had a large enough piece of MDF to clamp the sub base down. I can see this one being messy with cutting steel as it would need coolant, but cutting brass does not need a constant feed of coolant.

Apart from the fact that the slowest your router motor is going to run at would be circa 8000 rpm - whilst milling machines tend to have speed ranges up to a couple of thousand RPM - there's also the probability that your 1-1/4 HP (900 watt) router will actually only be producing around 300 watts at 8000 rpm so it won't generate enough torque to cut hard metal.

If you are feeling adventurous it is possible to rout aluminium with the appropriate bits and a lubricant. The stuff can give you a very nasty kickback if you try to take too deep or too fast a cut, though.

 

[9fingers]

You might just get away with taking a very fine cut with a small spiral cutter in a router table but the cutting angles for brass will be all wrong. Brass requires a negative rake on the cutter to avoid snatching.

However it is really a case of using the right machine equipped with the correct cutter for the job in hand.

Bob

 

[wizer]

Oddly enough I was just reading one of Paul's old F&C's and it has Ingham using his Mill. I'd certainly love to use this approach but the cost must be limiting for the hobbiest.

 

[Peter T]

.....and routers are not designed with these forces in mind.

Not sure I agree with that statement. With the exception of plunging, you're always using side pressure with a router.

Yes, but with metal the side forces are much higher and, as already mentioned, the router speeds are much higher than normal milling speeds.