QCTP progress and problems

wawoodman said:
I certainly don't want to start a fight, but the cutter is flat because both Bill Gruby and tomg recommended that I try it that way (unless I misunderstood them, in which case, my bad.) I'll put a little rake on it, and try again in the morning!
Click to expand...

Mike,

You misunderstood...probably because I didn't explain it very well. :thinking:
Here is a pretty good diagram and chart from DiscoverLiveSteam.com showing the various angles for different materials:

Sharpening Lathe Tool Bits

Just ignore all references to back rake because as I said before, it isn't needed. What your tool lacks is side and end cutting edge angles and side rake. Everything else look pretty good.

Tom
 
TomG said:
Mike,

You misunderstood...probably because I didn't explain it very well. :thinking:
Here is a pretty good diagram and chart from DiscoverLiveSteam.com showing the various angles for different materials:

Sharpening Lathe Tool Bits

Just ignore all references to back rake because as I said before, it isn't needed. What your tool lacks is side and end cutting edge angles and side rake. Everything else look pretty good.

Tom
Click to expand...

Tom,

Can you link to or restate why back rake isn't necessary?

John
 
Tom,
A most excellent chart! Already printed, and in The Book. It looks like my misunderstanding was leaving out the side rake. In the flat inserts, that angle would be imparted by the angle of the bed in the tool, right?

Davidh,
Yes, I watch those videos constantly. The issue here is that he shows sharpening for the lantern toolpost (and it works very well!) But I'm dealing with using HSS bits in a QCTP, and so some of the setups for the lantern aren't quite valid. Thanks, though.
 
jgedde said:
Tom,

Can you link to or restate why back rake isn't necessary?

John
Click to expand...


Sorry John, I guess that explanation was in another thread. Here it is:

"Back rake is over rated for high speed tooling and generally unnecessary. I grind all of my tools with zero degrees back rake, use them in a quick change tool post and they cut just fine. About the only time I'll ever use back rake is if I'm machining something soft like wood or rubber or some plastics. Back rake when cutting steel is actually a bad idea because it removes material behind the cutting edge of the tool which allows heat build up. Another plus for tools with zero back rake is you'll get a lot more life out of them since the tool geometry doesn't change as the tool is sharpened."


Tom
 
wawoodman said:
Tom,
A most excellent chart! Already printed, and in The Book. It looks like my misunderstanding was leaving out the side rake. In the flat inserts, that angle would be imparted by the angle of the bed in the tool, right?
Click to expand...

I'm not sure what you are asking, but with inserts, all of the necessary angles are engineered into the insert and insert holder based on it being held in a horizontal position, as in a quick change tool holder.

Tom
 
Mike,

You might want to try a vertical shear bit to get a little better finish. I find they work really well for really fine finish cuts. It makes really small steel threads - almost like steel wool. I can post a picture if you're not familiar with it.

Hope this helps.

Steve
 
You must log in or register to reply here.
Back
Top