Taper grinding a drill bit

**Frank S** · Mar 29, 2022, 10:33 PM

I don't normally use the sides of the flutes of a drill bit to profile a hole, nor to I condone the practice. But today I found myself in need of drilling a tapered hole to 3°ish, through 1/8inch thick brass, instead of drilling a straight hole and running a small boring bar through it to make the angle I decided to just taper the flutes of a drill bit instead. To do this first I checked the side angle of the ceramic sand blast nozzle with a protractor

Taper grinding a drill bit-img_20220329_162314sb.jpg

Then set both sides of my double combination bevel gage made by and given to me by one of my students of bygone years.
Obviously not the best way to check the angle of the flutes but remember this only had to be an ISH angle

Taper grinding a drill bit-img_20220329_215846sb.jpg

the Bevel gage is patterned after the LS Sterrett #49 except it is longer and closed on both ends I believe it is actually a higher quality than A Sterrett if that is even possible

Taper grinding a drill bit-img_20220329_220212dbg.jpg

Taper grinding a drill bit-img_20220329_220314dbg.jpg

**DIYer** · Mar 30, 2022, 05:54 AM

Thanks Frank S! We've added your Drill Bit Taper Grinding Method to our Drilling and Drill Presses category,
as well as to your builder page: Frank S's Homemade Tools. Your receipt:

Drill Bit Taper Grinding Method by Frank S

tags: drill bit, taper

**Paul Alciatore** · Apr 3, 2022, 08:02 PM

That looks like a nice technique. Only problem I see is that the margins on the flutes of a drill bit do not have any relief because they are deliberately made to not cut sideways. For normal drilling that helps the bit go straight. But I imagine it works well for a small taper angle. I have cheated and used a small drill bit in a router to make slots in wood. Some smoke was also made due to those margins rubbing the wood as I proceeded sideways. But it did cut the slots.

That double combination bevel gauge looks like a nice tool to have. Would you care to post some dimensions and angle sizes? And perhaps a rough sketch? I may find time to make one after my present list of about 99 projects.

And just spitballing here, but it looks like a small, fourth piece which would provide a right angle might make a helpful addition. If it were small enough to fit between the other two blades, it could have been used to hold the drill bit in your photos perpendicular to the main beam of the tool.

**Frank S** · Apr 3, 2022, 09:33 PM

Originally Posted by Paul Alciatore

That looks like a nice technique. Only problem I see is that the margins on the flutes of a drill bit do not have any relief because they are deliberately made to not cut sideways. For normal drilling that helps the bit go straight. But I imagine it works well for a small taper angle. I have cheated and used a small drill bit in a router to make slots in wood. Some smoke was also made due to those margins rubbing the wood as I proceeded sideways. But it did cut the slots.

That double combination bevel gauge looks like a nice tool to have. Would you care to post some dimensions and angle sizes? And perhaps a rough sketch? I may find time to make one after my present list of about 99 projects.

And just spitballing here, but it looks like a small, fourth piece which would provide a right angle might make a helpful addition. If it were small enough to fit between the other two blades, it could have been used to hold the drill bit in your photos perpendicular to the main beam of the tool.

I ground a slight relief in the flutes making them more like those of an end mill Just hand ground on a green wheel

What I do for that is I have a 6 inch tri square to push against the back beam but nearly impossible to hold that many pieces and take a picture.
This one was made by one of my mechanical engineering graduate students who minored in machining philosophy, couldn't begin to tell you where he got that idea He also worked in my shop for 3 semesters. He and 3 or 4 others would show up late in the afternoon on days they knew I would there until late. I pretty much left them on their own cognizance in the shop while I was in my office above. if things got too loud or too quiet all I had to do was glance out the window to see what was going on. Danial used the bevel gage as his class project after graduation he gave it to me to show his appreciation for helping him through his years at university. I've had it now for nearly 20 years and have never seen another exactly the same although the LS Sterrett #49 compound bevel gage square comes close.
I have no problem sharing a few definitive photos of it and when Time allows I will snap them and post them in tool talk