What mill for best finish?

[meincer]

I am a relative newby and have a mini-mill.

What mill cutter should I use to get the best finish on steel, also on aluminum?

Is an indexable mill better than a carbide or HSS one? If so what is the largest diameter indexable mill I should consider for use with the mini-mill? There are some pretty low prices on import 1", 1 1/4" and 2" diameter ones.

[MikeC]

Not sure what the hp of that mill is, but chances are you will have a hard time pushing any depth of cut with a 1" or larger milling cutter.

If you are looking to get a good finish for slotting, pocketing and such, you will do best with mills ground for the specific material you are working with. Mills for aluminum have higher rake angles to shear and clear chips efficiently, but that high angle means a weak cutting edge that wil chip easily in steel. Steel ground cutters have lower angles to maintain strength for cutting steel, so they may not produce such a pretty finish on aluminum, as they will tend to push the metal off instead of cutting it cleanly. Think of it like the difference in a chisel for metal and one for wood.

If you just want a good faced off finish, get or make some flycutters. Limit depth of cut to just a few thou and spin it fast (1000rpm or so). A 2" flycutter run this way will leave a mirrored rainbow finish on aluminum. Just don't get froggy, as this has the capabilty of beating your mill to pieces.

[meincer]

Thanks for the info.

I am becoming familiar with milling in general but wanted to know how to get a nicer finish (very light cut). I read somewhere that flycutters are not recommended for the mini-mill because if it catches at all you will break a gear.

I also read somewhere that indexable mills make a better finish (let's just talk steel for the moment). Is this true? If so it sounds like I should look at the smaller (1" or so) ones.

[toastydeath]

Indexable endmills leave an amazing finish in larger CNC machines. They can use ridiculously high surface speeds to help with a good finish, speeds you can't work with on a smaller machine. With those speeds comes high feeds, and you can't maintain a 100+ IPM feed rate on a manual machine. If someone is applying them for an excellent finish in a mini-mill, you'll have to ask them how they're achieving it. I have only had moderate success with inserts in manual machines, and then mostly in lathe tooling.

On manual, stick with a flycutter. Even in CNC, flycutters will still leave a more aesthetically pleasing finish (to my eye) than an indexable mill.

HSS tooling all the way for a beginner. As you get better you'll see not only the need for carbide tools and inserts, but you'll be able to appreciate the finer differences between the two. This leads to applying them more appropriately and understanding the pitfalls of each.

[Bill Shields]

A good finish is a function of consistency as much as it is the cutter.

Consistent feed rate
Consistent rotary velocity - with no jarring / chattering of the drive. A big load helps on this, but if you don't have the HP...
Consistent position of the tool - which means no change in clearance - IE a very rigid setup.

All of these are often difficult to attain with a mini-mill that doesn't have lots of iron holding things down, ball-screws on the feed, etc:

Indexable mills, which typically use carbide inserts, require a lot of horsepower and rigidity to attain the desired results.

Do the best you can, but don't be disspointed if you don't get the best expected results.

[kenh]

The belt drive conversion from little machine shop will eliminate the gear problem.

http://littlemachineshop.com/products/p ... uctID=2560

[10 Wheeler Rob]

I have fly cut cast iron and alunimum with very good results on my mini mill. Uaually use a 1/4" carbid tiped bit, becuase thats what works best fwith the cast materials, and one came with the fly cutter I pickup used.

Just take light cuts and works quite well. Pick a speed that cut smoth with out a lot of back chatter form the gears and you will get good results. Due a couple of final passes with like a 1/2 to 1 mil cut at hiher speed and you will get a really smooth finish. Ading a small radius on the cutter is good for smooth finish also.

The tigher you keep the machine ways the better, specially for larger items. I found using real machine way oil lets the ways be tighter and still slide nice. Also clamping to the table verses up off the table in vise works better also, less momnet arm to wiggle the table!

And if you own a mini mill, buy a set of replacement gears, it is only a matter of time until one or more break. My experence is the one on the motor goes most often, but a major jam can take out others. They are very inexpensive to keep on hand. Also get spare motor brushes they wear out too. If you start to notice the motor slowing down, it needs brushes. www.LittleMachineShop.com is a good source for mini mill parts.

Rob

[meincer]

Well I tried the super glue trick and it worked great with one exception: after machining the plate I heated the back of the substrate with an oxy-acetylene torch lightly (Jose, you said about 160 degrees) and nothing budged. I then got it hotter, still no results, I then dropped it into a water bath while hot, still stuck.......

Is there another trick to this that I am missing?

[Gunbuilder]

Well I tried the super glue trick and it worked great with one exception: after machining the plate I heated the back of the substrate with an oxy-acetylene torch lightly (Jose, you said about 160 degrees) and nothing budged. I then got it hotter, still no results, I then dropped it into a water bath while hot, still stuck.......

Is there another trick to this that I am missing?

meincer,
It works well for me, I don't use very much glue at all. I just tap one piece with a hammer, just a light sharp tap and they fall apart.

Thanks,
Paul

[meincer]

Well being the noob that I am I used a lot of glue, I didn't want it coming loose during machining. I might have a permanently stuck together fixture! Maybe I should soak it in acetone?

[meincer]

Gunbuilder: I hadn't tried your suggestion before I posted the last reponse.....

A hammer hit did the trick! Thank you, that should have been obvious but we often overlook that.