Positive, Negative rake

[Paul ScholeyParticipant @paulscholey17560]

I have just acquired a Secodex 6 tip milling cutter head and noticed that the tips are set at negative rake, looking at my other cutters they are all positive rake. I was told that positive rake is used for milling aluminium? Is this right, if so what would negative rake be used on?

Paul.

[Paul ScholeyParticipant @paulscholey17560]

[Chris TriceParticipant @christrice43267]

Brass and gunmetal mostly but are the tips flat on the top or is there a hollow near the edge? The cutting edges may actually be positive.

[Paul ScholeyParticipant @paulscholey17560]

I see what you mean Chris, had a look and the tips are square all round, no hollow

I take it then you need positive rake for mild steel? 

Edited By Paul Scholey on 08/08/2011 16:18:25

Edited By Paul Scholey on 08/08/2011 16:20:32

[JasonBModerator @jasonb]

I’ve got a set of the “LITTLE HOGGERS” these use tips that are completly flat with no top rake, they are mounted in the holders at about -10degrees and work fine on steel and most other metals as well including aluminium.

 

I really bought them for the radiused cutter, find it very good for cleaning up welds when fabricating things that would originally have been cast or forged to give a fillet particularly as my rough welding is likely to have a few hard inclusions that would soon blunt a radius corner endmill

 

Give the cutter a whirl and see how it goes, maybe in production enviroments it won’t shift the metal as fast as positive rake but thats not really an issue to us.

 

J

[Paul ScholeyParticipant @paulscholey17560]

Thanks for reply Jason, I will give it a go as I have found an arbour for it. I was dead chuffed with it having 6 tips until I saw it was negative rake.

[Ian S CParticipant @iansc]

My milling cutter (3 inserts) was not cutting very well when I first got it, the cutters are at 0 deg or near enough, I made some enquiries when I went to get new cutters, Iwas given (Sold) flat topped plain cutters, the old ones had a groove around the edge, these new cutters worked well.

I use the same inserts on the lathe with 0 deg top rake.

Heres a bit from one of my old (1940s) lathe book “Lathework” by E. Molloy

The following data gives sitable angles for different grades of cemented carbide tools and for various metals and other materials to be cut.

ESCALOY

-3.5 deg for rough cast iron and manganese steel.

-8 deg for light cuts on cast iron and for alloy steels or steel castings.

Negative top rake is advised in some instances, The pressure on the tip causes the tool to be pushed back rather than dig in.

The book also suggests +24 for aluminium, and +24 to 30 deg for copper.

I would suggest that negative top rake would hepl with interupted cutting. Ian S C

[Paul ScholeyParticipant @paulscholey17560]

Thanks Ian, do you mean when the milling cutter is coming off the edge of the material each turn because the cutter head is wider than the material.

[Ian S CParticipant @iansc]

Yes Paul that would be one instance, another is when you have a hole in the middle.

Ian S C

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