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View Full Version : HSS bit geometry for cold-rolled bars, for finish



Elninio
09-05-2010, 01:02 AM
What cutting angles are requires to perform precise nice finishes on cold-rolled, with an approximate tool life of an hour cutting time? I can't go with a large radius tool since I will be doing corners.

Black_Moons
09-05-2010, 01:33 AM
What alloy? Cold rolled is not an alloy. Its a process to produce shapes.

What kinda bit/machine? Shaper? lathe?

If per chance you mean generic 'mild steel' (Still not really an alloy discription I know..), generaly you can not get a really good finish without polishing afterwards with sandpaper.

Elninio
09-05-2010, 02:18 AM
What alloy? Cold rolled is not an alloy. Its a process to produce shapes.

What kinda bit/machine? Shaper? lathe?

If per chance you mean generic 'mild steel' (Still not really an alloy discription I know..), generaly you can not get a really good finish without polishing afterwards with sandpaper.

Sorry, my original question was rather vague.

I will be machining mild steels on the lathe, and shaper, with HSS bits of 5% cobalt. I'd also like to know about how the geometry will differ in solid carbide bits of 5% cobalt.

dan s
09-05-2010, 01:30 PM
I will be machining mild steels on the lathe, and shaper, with HSS bits of 5% cobalt.

What grade mild steel?

Carld
09-05-2010, 02:19 PM
I don't think carbide has cobalt in it's mix. The alloy number of the cold roll steel is what we are looking for. Such as 1018, 1040, 1045, etc. It does make a difference in finish quality with the alloy your using.

For all steels I use a "0" rake with 8 to 10 deg of side clearances. Sometimes I stone the cutting edge for extra sharpness with HSS and on carbide I sometimes use a diamond lap. The DOC, feed and rpm are important for finish on steels. Sometimes a positive rake of about 10 deg helps.

If you want a very fine finish you can use a shear cutting tool as described in other threads hear.

Black_Moons
09-05-2010, 02:43 PM
Cobalt is used heavily in carbide, a quick googleing mentions it and nickle are the two main elements that wet carbide.

Cobalt is the reason you don't wanna grind carbide without a mask on!

Another googleing tells me that Cobalt is the main binder for carbide and the varation in it sets a good deal of the 'strength' code.

However, they are not usally sold as %cobalt like HSS. insted they are sold by a C code, ie C1, C2, C5, C6, etc (those are the main 4)
C1/C2 are very Durable, Soft, Easy to wear
C5/C6 are very Brittle, Hard and hard to wear.

C1 etc is used for cast iron, interrupt cuts in steel, etc
C5 etc is used for Steel, abraisve materials, etc. Easyer to chip the carbide, but much harder to wear.

I don't think you have to worry so much about finish changes beween diffrent grades of carbide or HSS. Its more of wearing resistance and strength and such.

(Note: HSS WILL give a diffrent finish then carbide, but I don't think 5% cobalt HSS will give any diffrent finish then regular chinese HSS, It just might take longer to wear)

Generaly, HSS is considered able to get the 'best' finish on mild steel, although that finish is still considered to be dog turds smeared on a rod compaired to how nicer alloys turn out. Seriously, Except no better then ulgy untill you polish it with sandpaper/polishing compound (could only take a min or two to polish to a shine)

Elninio
09-05-2010, 06:56 PM
Cobalt is used heavily in carbide, a quick googleing mentions it and nickle are the two main elements that wet carbide.

Cobalt is the reason you don't wanna grind carbide without a mask on!

Another googleing tells me that Cobalt is the main binder for carbide and the varation in it sets a good deal of the 'strength' code.

However, they are not usally sold as %cobalt like HSS. insted they are sold by a C code, ie C1, C2, C5, C6, etc (those are the main 4)
C1/C2 are very Durable, Soft, Easy to wear
C5/C6 are very Brittle, Hard and hard to wear.

C1 etc is used for cast iron, interrupt cuts in steel, etc
C5 etc is used for Steel, abraisve materials, etc. Easyer to chip the carbide, but much harder to wear.

I don't think you have to worry so much about finish changes beween diffrent grades of carbide or HSS. Its more of wearing resistance and strength and such.

(Note: HSS WILL give a diffrent finish then carbide, but I don't think 5% cobalt HSS will give any diffrent finish then regular chinese HSS, It just might take longer to wear)

Generaly, HSS is considered able to get the 'best' finish on mild steel, although that finish is still considered to be dog turds smeared on a rod compaired to how nicer alloys turn out. Seriously, Except no better then ulgy untill you polish it with sandpaper/polishing compound (could only take a min or two to polish to a shine)

One of the machinists that did a tutorial on HSS bit grinding on youtube (tubalcain) says "if you're using carbides, these principles don't apply to you"

dan s
09-05-2010, 07:17 PM
One of the machinists that did a tutorial on HSS bit grinding on youtube (tubalcain) says "if you're using carbides, these principles don't apply to you"

what principles don't apply?

Elninio
09-05-2010, 08:00 PM
what principles don't apply?

The cutting angles he describes in the video. http://www.youtube.com/user/mrpete222#p/u/67/hrDr4rYLiAk

dan s
09-05-2010, 08:58 PM
you mean this guy?

http://www.youtube.com/watch?v=hrDr4rYLiAk&feature=related

I have seen his lathe and he has a qctp and an old school Lattern? type, and how you grind a lathe bit depends on the type you have. the old school adds several degrees of back rake if memory serves. depth of cut also effects angles as well.

wooleybooger
09-05-2010, 10:38 PM
top rake makes a lot of difference on generic mild steel. with my square,4 bit post i grind about 5 deg . tip radius needs to be about 1/32". try to avoid a very sharp,acute angle for general turning. use those only for getting into a corner.

Paul Alciatore
09-06-2010, 02:27 PM
The type of HSS does make a difference in the life of the edge and the angles do make a difference in finish.

But for me, the most important factors for a good finish are the speed and feed rate, the cutting fluid, and the sharpness of the edge.

I often will touch up a tool before turning. I like to get an almost mirror finish on the top and faces of the tool. And a razor sharp edge. This finish does not need to extend very far from the cutting edge, perhaps only a distance equal to the depth of the cut. This can often be accomplished with just a few manual strokes on a fine oil stone on a newly ground tool of if there is no obvious edge damage. Use a 10X magnifier to inspect the tool's sharpness. It will show problems that you would never see with the naked eye.