Internal Boring Tool Geometry?

[Monk]

I'm working on a project where I need to increase the internal bore on the workpiece by about .250 to .375 or so for clearance of a rotating part for about .750 to 1.0 along a length of the bore. The original bore is 2.375 inch diameter. I've made a 1 inch boring bar drilled to accept a half in round HSS bit that I hope to grind to make a wide grooving tool. Will this work? How much relief angle should I use to allow chip evacuation, etc. Or, would I be better off to make two (L&R) tools. I've had relatively little experience with internal boring etc, and would appreciate any advice. Thanks.

 

[mikey]

I'll chime in if you answer some questions first:

• Is this a through bore or a blind bore?
• What is the material being bored?
• Tolerances or finish requirements?

Being a bit premature, if you're only boring 3/4-1" deep, even a simple brazed carbide, solid carbide or HSS boring bar in the 1/4 or greater diameter will work. If you prefer to grind your own then you will need about 5-7 degrees minimum of side and end relief. Much depends on if this is a blind bore or not.

 

[pontiac428]

Did you say you are using round tool bits? If that's the case, your reliefs will be built-in, assuming you grind a conical grind, profile your cutting edge/tip as needed, and grind a slightly raked flat on top. I know that's coarse as far as ignoring the work I.D., material, and bit diameter, but none of that is very important as long as you have around 5 degrees on the sides (steel) to 7 degrees (alloy). You can use the round to flat corner break on the tool as your cutting edge as-is, or you can grind a slight facet for more uniform performance along the conic edge. I'm sorry I don't have a photo, I packed up my lathe tools and moved them into my new shop where I have many tasks ahead of me before I dig them out. If you look up D-bits for the mill, you will see examples. They're nearly the same grind, minus any offset for the mill bit.

 

[Monk]

Did you say you are using round tool bits? If that's the case, your reliefs will be built-in, assuming you grind a conical grind, profile your cutting edge/tip as needed, and grind a slightly raked flat on top. I know that's coarse as far as ignoring the work I.D., material, and bit diameter, but none of that is very important as long as you have around 5 degrees on the sides (steel) to 7 degrees (alloy). You can use the round to flat corner break on the tool as your cutting edge as-is, or you can grind a slight facet for more uniform performance along the conic edge. I'm sorry I don't have a photo, I packed up my lathe tools and moved them into my new shop where I have many tasks ahead of me before I dig them out. If you look up D-bits for the mill, you will see examples. They're nearly the same grind, minus any offset for the mill bit.

Sorry so long getting back, John. Family health issues kept me very busy for quite a while and when they eased up, I finished the project without getting back to the forum. Thanks again

 

[Monk]

I'll chime in if you answer some questions first:

• Is this a through bore or a blind bore?
• What is the material being bored?
• Tolerances or finish requirements?

Being a bit premature, if you're only boring 3/4-1" deep, even a simple brazed carbide, solid carbide or HSS boring bar in the 1/4 or greater diameter will work. If you prefer to grind your own then you will need about 5-7 degrees minimum of side and end relief. Much depends on if this is a blind bore or not.

I'm really sorry to get back so late mikey. Family health issues kept me very occupied for quite a while and when they subsided, I finished the project without checking the forum. As always, thanks for your input. I'll post pictures of the die filer I was building soon.