endmill vs slotdrill for facing

[Numb Nut]

Here's a (probably daft) question...

If you only had an endmill and a slotdrill (say both are 10mm dia) which would you use for facing a small block of alu?

I'm asking because I recently read in a book that endmills aren't well suited for facing surfaces - they are designed to cut on their sides. At the moment I only own a few metric endmills.

Aside... I was mowing the lawn the other day and could help but think that the mower was just like a vertical mill... Tried both conventional cutting and climb milling but the finish was equally disappointing, too much moss and weeds.

[PinMan]

A slot drill is essentially just a 2 flute endmill. I have found that if your machine is trammed in well, endmills work pretty decent at facing as long as you arent too worried about the finish (cut marks).

They both should work about the same.

[tobyaxis]

If you hone the edges of the end mill you can get a great finish. A .015 to .025 Radius with the proper feeds and speeds will work fine.

[Numb Nut]

But is a slotdrill really just a 2 flute endmill? One difference for example is that it can be plunged into the work piece. Surely it's cutting edges are quite different?

The book that I was reading is "Model Engineer's Handbook" by Tubal Cain (3rd edition). The interesting bit is in 5.12 Milling - "If an endmill is used as a facing cutter, even with a very light depth of cut, then the corner may break down and rubbing will result. It is preferable to stone a 45 deg bevel or chamfer on the sharp corner, ensuring that clearance or relief is maintained, and to employ a depth of cut not less than 0.006" even in finishing; more is better."

Later on he mentions that endmills are not suitable for cutting full width slots and that a slot drill should be used.

[Aside - found a similar thread asking what the difference is between these two types of milling cutters: When to use slotdrill or endmill.

[Numb Nut]

Here's the book I'm referring to...

[tobyaxis]

The Radii that I mention are in Inches. Also your book is correct but honing a small Radius is a lot easier than honing a 45 Deg.

[Andre' B]

End mill, slot drill is a lot like kerosene and paraffin

In the states they are all end mills, they are then sub divided into center cutting, non center cutting, each of which can have any number of flutes.

In the UK, maybe elsewhere they seem to separate out 2 flute center cutting end mills into a separate class called slot drills.

[Numb Nut]

Ok, although you did say hone the edge with a radius and he said chamfer the corner...

Just to add to the confusion the set of 7 milling cutters that I have are all 2 flute so they could infact be slotdrills rather than endmills but... the receipt definately says endmills!

[Numb Nut]

Ah Andre' B - just saw your post - that makes sense I guess.

That just leaves the corner thing - why does that need to be rounded and why does that help? I really don't understand how it ends up rubbing instead of cutting when used for facing...

[BobWarfield]

The prettiest facing finishes usually come from having a cutter wide enough to face in a single pass. For most, that means a flycutter.

You'll get a decent finish out of an endmill. Slot or otherwise won't matter, because a facing job cuts the entire surface, you won't plunge, you will cut from the sides.

For surfacing, I like more flutes as they equate to more "effective" rpm for a given spindle rpm and feedrate. When surfacing, chip clearance is usually not a problem the way it is when you're down in a hole, so you can use 4 or more flutes.

I've heard elsewhere that a slight radius honed into place with a stone will improve the finish. No matter what, you're going to see tracks the width of your cutter, which is usually what people object to cosmetically.

One last point--tram is really important to your surface finish when facing.

Cheers,

BW

[tobyaxis]

Originally Posted by Numb Nut Ah Andre' B - just saw your post - that makes sense I guess. That just leaves the corner thing - why does that need to be rounded and why does that help? I really don't understand how it ends up rubbing instead of cutting when used for facing...

Look at the End of the End Mill. You will see what appears to be a 90 degree angle which is actually concave if you were to cut it in half.

Here is a pic of an Bull Nose End Mill for reference. This is the edge you will be slightly honing. It is designated with an "R".

[Numb Nut]

Thanks alot for that info, everyone!

My cutters and definately slotdrills, they cutting edges join up in the middle so it would appear to be centre cutting (although never tried it!)

Found a neat pic showing both styles of cutters - mine are like the ones 2nd row down and bottom row.



I've been googling around looking for machining info and found a few websites to share:

http://machine-tools.netfirms.com/index.htm

http://www.frets.com/HomeShopTech/hstpages.html

http://www.finelinehair.com/home/index.htm

BW - your website's one of my faves too!

http://www.cnccookbook.com/