Cutting a blind keyway

[TomG]

You misquoted me Ken. I didn't say "never", because I know there are many different way to do the same job. I actually said "I would never".

Tom

[RobWilson]

Quote:RobWilson 

I have some very short flute TC slot mills that  due to being short and rigid cut bang on 1//4 with no ruffing out .  

I must have the same  good quality cutters Ken    , as I said earlier  I have some 1/4 and 6mm stubby TC that hold bang on ,a key is a nice snug fit , maybe its a machine rigidity/setup  thing .


Rob

[mcostello]

I was taught to do it in one pass, anything else made it bigger-how much , depends on lots of things. Company also bought around .0005-.001 under size cutters to allow for run out etc.

[Pete O]

Well the working week is done and I have had time to read through these replies properly and follow the links, thank you all and as always the more I learn, the more I realise that I don't know. With a bit if reading, it seems there are a whole lot of forces interacting to make a cutter do things that you don't want it to do. Probably the most confusing thing is the terminology relating to cutters, I have no idea whether what I have been using is a slot drill or an end mill, will have to give it a close inspection when I get a chance to get back to it. Seemed to plunge cut without any difficulty, but then without a quill on my machine it is impossible to get a feel for how much force I am applying in the Z axis, cranking the knee up with the hand feed is heavy whether there's a cut happening or not.
I have a heap of garden and lawn work to do before I get back to the shed and figure out what cutters I actually have.

[Pete O]

I finally got a chance to get back to the mill this afternoon and make another attempt on the keyway. I am pleased to report that the second attempt turned out spot-on, thanks to all the advice from here. I used a 5mm slot-end-mill-cutter thingamajig to rough it out, then finished it with a 1/4" cutter that i found amongst my stuff that has 2 very short flutes. A close inspection under the magnifier revealed that the corners of the cutter were very slightly chipped, so I took a couple of brave pills and sharpened it on the bench grinder- came up a treat. As did the keyway. The key went home snugly with a little tapping.
The cutter I used has 2 flutes, with different length edges on the end so that it centre cuts. Does that make it an end mill or a slot cutter? Pretty much all my cutters have been bought in batches from clearing sales so I have never actually ordered them by name.
I have to admit that I cut the second keyway at 90 degrees from the first attempt, rather than start the whole job again. Please don't tell anyone .

[Mayhem]

Glad to hear it worked out well Pete. You could always fill the practice run with a weld and then turn it down but depending on the diameter and how much heat you put in you may find that you bend the shaft...

[PixMan]

Over here the term slot drill is not used. It seems they're all just end mills. Some are center cutting, some aren't. There are two flute, three flute, four flute and more flute, some with corner radius and some sharp. And all are listed as end mills.

We seem to get along fine without knowing what a slot drill is.

[Mayhem]

I'll go with the American nomenclature on this one then

[Highpower]

Everything I have read says to use a 2 flute (only) end mill for slotting / cutting key ways etc., so that is what I have been following. The reason given was that it keeps the tool pressure equal on both sides of the slot. I'll buy that for a dollar. I can see where 3 flutes would flex back and forth between the sides because of the offset cutting contacts, but what is the problem with using 4 flutes?  

Something I've always wondered about, but never thought to question WHY?  

[EdK]

(09-18-2015, 07:42 AM)Highpower Wrote: Everything I have read says to use a 2 flute (only) end mill for slotting / cutting key ways etc., so that is what I have been following. The reason given was that it keeps the tool pressure equal on both sides of the slot. I'll buy that for a dollar. I can see where 3 flutes would flex back and forth between the sides because of the offset cutting contacts, but what is the problem with using 4 flutes?  

Something I've always wondered about, but never thought to question WHY?  

Chip clearance, possibly.

Ed