late bits are so boring! help with grinding a boring bit...

Ok I'm rasing the white flag here.. I've tried, and tried, and cannot get the angles right on an inside boring bit.. I don't have a boring bar, and I'm thinking of making one later, anyways, can someone step me through grinding a nice inside boring bit,with some pictures?

What I've been trying to copy is a regular finishing bit but at a 90 degree angle, and I'm failing miserably, and wasted a nice 5" long bit trying.. also is there a depth limit where I should just use a boring bar? still super new to working with the lathe, and boring things has me pulling my hair out. Thanks folks!

If you have a mill or access to one, you could make a boring bar to hold a smaller, shorter piece of tool steel.

Problem with boring is that you cannot snub-up the tool bit short to make the cutting action solid. It take a lot of pressue to penetrate and cut even .002 in one slice..You have to imagine the bit in reverse with the side cutting ege going the other way and all the parts like rake angles and such ground to make chip flow the right way..clearance is the big bugaboo in boring because often the heal (parts under the cutting edge)will drag on the part below the cutting edge..I like to tell new guys to draw the ID and the tool pit at 10X scale and the =measure the clearance on the drawing with a protractor. Later guys often just hold the bit io a Id of near the same size and eyeball the clearance.

Boring bar should be as stout as you dare.. perhaps 3/4 inch diameter to bore a deep 1 inch hole...to avoid twisting and bending under the cutting pressuer

We need more information. What kind of lathe are you using ? What type of tool post do you have ? What material are you cutting ? What size is the bore ? How deep is the bore ?

thanks guys, if it matters its aluminum I'm working with...

Aluminum?.......... then the 3/4 bar for a 1" bore will fudge up the works with strings of material filling the bore.

Boring bars are inherently springy to some degree. When you approach your final ID, do yourself a favor and run the bar in a few times without moving the compound to make sure you have actually removed all the material you think you have. My dad used to call this a "spring" cut when he was teaching me to run a lathe about forty years ago. This will also help in eliminating a tapered cut and very possibly improve the surface finish because of the light cut. You didn't mention what size lathe you have but this will be more of a problem with a light duty lathe. Since I have moved up to much horsier lathes with a lot more rigidity it is a lot easier to hit your ID. I still use a spring cut out of habit and often increase the ID somewhat. I'm just saying that it is harder to sneak up on your intended ID with a boring bar then it is on the OD with a more rigid setup. Just my 2 cents worth.

The problem many new machinists have with boring tools is that they think about cutting the I.D. of the part, but you need to think about cutting the bottom of the hole . . . Z direction, not X direction.

When I started out having to do this kind of shit, I used an already existing and know functioning cutting Tool and modified it to use as a Boring Tool.

I took a 2 flute HSS Endmill and ground one flute off, cleared the other one back enough that it wouldn't rub after the cutting edge, and went from there.

R

Funny I have used an old end mill in the horizontal hole of a boring head with one flute ground for clearance.It will really hog off a lot of material,the only problem is the chip is stringy.