Lathe tool Grinding

[New_Guy]

Tom:
I do not think I have ever seen a chip breaker ground on either. I have seen some pretty funky angles on hand ground tools these may have a bit of a chip breaking effect.
I have seen chip breakers in indexable inserts. This makes sense because the carbide inserts are designed for max production. in the home sop you can always break the chip on roughing cuts by feeding by hand.
If you want to grind a chip breaker the little dremel wheels would likely work well on HSS or a Harbor Freight diamond wheel for carbide.

Tin

WHAT!! do none of you guys grind chip breakers into your tools? i havent seen any info on doing it on the net but its not hard i cant believe none of you guys do it

when i was still in school i did work experience in the machine shop of our rail way and i was asked about what tools we use on the lathe i said we used HSS and they a they were surprised we didn't used carbide, the next week the tool maker brought out a tool he ground after my last visit just to remember what it was like. ti was a big bit 14mm i believe with a chip breaker or curler we gave it a few goes on the Colchester and boy did it love it he then gave it to me and i still have it only been used a few times on the Hercus's at school

if anyone wants a pic i can upload one tomorrow its a nice tool and very easy to grind i think

 

[Tin Falcon]

NG I am not sure there is a real need for chip breakers in the home model shop at least most of the time. Most of our parts are small and of brass and aluminum.
Now in a railroad shop taking a .375 roughing cut on a 3 o 4 foot long steel shaft. Yes you want a chip breaker.
You will find that difference shops have different needs.
Also I find a bit of disparity between text books and what is done in the "real world".
Se la Vi
Tin

 

[kf2qd]

When I grind a HSS tool I leave the top flat. (same with carbide, but I don't have much of that in my shop now...) Cutting steel, aluminum, brass, plastic. If you look at a lot of the chipbreakers on carbide inserts you will see that it is back from the edge as much as 1/32". There are times when a positive angle on the top might be beneficial, but I have seen some ridiculous positive rakes that only made the tool get hot and require sharpening more. And a lot of positive rake makes for a tool that is hard to keep on center after it has been sharpened. I did make a special tool with a lot of positive rake but it was only used on cutting some deep face grooves in UHMW plastic.

By only grinding on the edges, and not touching the top I come up with a tool that is easier to regrind and that holds up well. If you really need a positive rake on the tool why don't you modify your tool holder instead of grinding the top of the tool blank?

I have done lots of cutting on everything from my 7x12 to a 24" production machine. Always ground the edges of the HSS blank and got any positive rake by adjusting the tool in the holder, rather than modifying the top of the blank.

 

[doc1955]

By only grinding on the edges, and not touching the top I come up with a tool that is easier to regrind and that holds up well. If you really need a positive rake on the tool why don't you modify your tool holder instead of grinding the top of the tool blank?

I have done lots of cutting on everything from my 7x12 to a 24" production machine. Always ground the edges of the HSS blank and got any positive rake by adjusting the tool in the holder, rather than modifying the top of the blank.

I agree same here I've been working in the shop for a long time and I've seen a lot of things done to tool bits and really if you keep the top flat or a slight and I mean slight angle like .5 degree plus on the face of the tool no more than 3 degrees I always used about 2 degrees you tool will hold up much better. Specially on carbide the keener edge you put on the thinner the cutting edge gets the hotter the edge will run. Because now the material isn't shearing away from the tool but up closer to your cutting edge. Not sure how to explane it very good without some pictures which I don't have.

 

[New_Guy]

NG I am not sure there is a real need for chip breakers in the home model shop at least most of the time. Most of our parts are small and of brass and aluminum.
Now in a railroad shop taking a .375 roughing cut on a 3 o 4 foot long steel shaft. Yes you want a chip breaker.
You will find that difference shops have different needs.
Also I find a bit of disparity between text books and what is done in the "real world".
Se la Vi
Tin

yeah i know what you mean you guys with Tag and Sherline lathes wont see the need for it but its not hard to do and it would be a good experiment to give it a try i know ill be putting chip breakers on my tools but hey its a bigger lathe

i told a lie before i have seen one guy on the net who ground a chip breaker on a tool that was for a 7" mini lathe he liked it

"If you look at a lot of the chipbreakers on carbide inserts you will see that it is back from the edge as much as 1/32"."

if anyone can get a copy of a Seaco or other manufactures insert catalog/book then i would highly recommend it, its a big book with all there insert range and tables comparing everything about them and yeah they do have a flat on the cutting edge if you had the book it could tell you exactly how much and why.

 

[ttrikalin]

I'll grind a chipbreaker and we'll see how it goes.

 

[New_Guy]

I'll grind a chipbreaker and we'll see how it goes.

dont forget to show the tool

 

[ttrikalin]

I'll show it in the BooBoo's and Blunders section --

:big:

 

[Brian Rupnow]

I have an observation to make, based on my own experience. I have been grinding my own 3/8" HSS lathe bits the last 3 months with a 6" diameter grinder. This of course left a "hollow ground" effect on the top and both sides of the tool, which I would "stone" slightly on a flat stone after grinding.---Just the edges, not the depressed area in the center of the ground areas, which were left in their convave "hollow ground" state. These tools seemed to cut very well. I never had a problem with long stringy chips. I bought a 1" belt sander this week, and ground all the "hollow ground" areas perfectly flat.---Now I do get long stringy chips. It seems that the 'hollow ground" area on the top surface of the tool was actually acting as a chip breaker. Chips coming off the cutting edge followed the depression down into its center then up the other side, which caused the chips to curl and break. Now that the top surface is dead smooth, the chips don't curl and break---they just keep coming off in long strings which turn into big balls of swarf still attached to the piece being turned. I have to stop feeding the tool to "break" the chip.

 

[Tin Falcon]

interesting Brian I too use a 6: wheel for tool grinding . I have a belt sander but do not grind my bits on it (too far of a walk to the other part of the shop). I also have some HSS inserts that I use a lot that are dead flat on top can not say I have had a chip problem twith them either.
Tin

 

[cfellows]

As a related question, what are the considerations in using a smaller bit, like 1/4" sq as opposed to 3/8" or 1/2"? Smaller bits are cheaper and easier to grind. What practical reasons would dictate using a larger bit (other than tool height)?

Chuck

 

[Tin Falcon]

the larger bit bit will give greater stiffness and give a smoother cut also a bigger bit can take a deeper cut.
the bit should be sized more or less to the lathe and tool holder. I use 1/8 to 3/8 for my 7x 10 and 9" south bend.for general work I have used 1/2 for form tools where i need the extra width to make my part.
A form tool in my case has the entire profile of the small part ground on it so I get a complex shape with a plunge cut.
The bit size is dependent on preference as well need of the job.

you can make tool holders for small bits I have a couple of tool holders I use for 1/8 bits .It is just a couple of pieces of 3/8 mild steel that I cut a 1/8 wide by about 3/32 deep slot in them one is a Zero angle the other I positioned the piece at IIRC 10 degrees or so . One end being deeper than the other, this gives back rake.This system allows me to grind a 1/16 radius cutter without grinding a lot. I then put the bit and holder in the regular tool holder.
I have a A2Z cnc qctp on the mini and an Aloris AXA on the SB 9.
Tin

 

[Brian Rupnow]

Interesting question, Chuck. The distance from my tool holder to the center of my lathe headstock is some Bastard size, more than 3/8" (I have to use a 1/32" shim) and less than 1/2". About the only reason for using 3/8" tooling other than that its the "closest" size to being correct, is that I can have more tool cantilevered out past the holder than I could with a 1/4" tool without being afraid of snapping the tool off. EDIT--It just occured to me after reading another post that perhaps my machine is sized for metric tooling---i.e. 10 mm

 

[New_Guy]

I have an observation to make, based on my own experience. I have been grinding my own 3/8" HSS lathe bits the last 3 months with a 6" diameter grinder. This of course left a "hollow ground" effect on the top and both sides of the tool, which I would "stone" slightly on a flat stone after grinding.---Just the edges, not the depressed area in the center of the ground areas, which were left in their convave "hollow ground" state. These tools seemed to cut very well. I never had a problem with long stringy chips. I bought a 1" belt sander this week, and ground all the "hollow ground" areas perfectly flat.---Now I do get long stringy chips. It seems that the 'hollow ground" area on the top surface of the tool was actually acting as a chip breaker. Chips coming off the cutting edge followed the depression down into its center then up the other side, which caused the chips to curl and break. Now that the top surface is dead smooth, the chips don't curl and break---they just keep coming off in long strings which turn into big balls of swarf still attached to the piece being turned. I have to stop feeding the tool to "break" the chip.

wow thats very interesting, traditional Japanese chisels and knives have "hollow" grinds down there length the point of is that there is less material to take out while flattening the bottom of the chisel (not the cutting bevel) i notice it to when i hone my lathe chisels but i have a 8" grinder so its less of a hollow anyway thats sort of off topic

have you tried experimenting with leaving the hollow grind on the top and flat sides?