Positive, Negative rake

Advert

New Replies

Report Bug

Help/FAQs

Positive, Negative rake

This topic has 8 replies, 4 voices, and was last updated 10 August 2011 at 11:36 by Ian S C.

Viewing 9 posts - 1 through 9 (of 9 total)

Author

Posts
8 August 2011 at 09:53 #73049
Paul Scholey
Participant
@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.
Advert

8 August 2011 at 09:53 #21913
Paul Scholey
Participant
@paulscholey17560
8 August 2011 at 10:19 #73050
Chris Trice
Participant
@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.
8 August 2011 at 16:17 #73060
Paul Scholey
Participant
@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
8 August 2011 at 16:54 #73061
JasonB
Moderator
@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
8 August 2011 at 17:44 #73063
Paul Scholey
Participant
@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.
9 August 2011 at 14:07 #73076
Ian S C
Participant
@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
9 August 2011 at 20:40 #73095
Paul Scholey
Participant
@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.
10 August 2011 at 11:36 #73114
Ian S C
Participant
@iansc
Yes Paul that would be one instance, another is when you have a hole in the middle.

Ian S C
Author

Posts