One of my pet hates in the workshop is blunt drill bits. Unfortunately this does occur so the blunt bits need to be re-sharpened occasionally, unless you want to spend a fortune on buying new bits all the time, which I do not.
Over the years I have struggled with trying to sharpen bits by hand, with varying levels of success. It is extremely difficult to get the technique and the angles just right and trying to do this on a grindstone is also tricky. Previously I have owned 2 different devices that attach to a power drill and spin a small cylindrical grindstone which the manufacturers promise will give perfectly sharpened bits every time. Yeah, right! The one broke and the other was absolutely hopeless, so both ended up in the bin. Back to square one.
Thanks once again to the internet, after some research I have considered the pros and cons of various devices and sharpening techniques. Not wanting to buy another exorbitantly priced sharpening machine, I decided to make a jig that will allow me to hold the bits in exactly the right position while using my belt sander to do the work.
I knew that the optimum angle for the cutting tip of a drill bit is 118°, but that's not all. What I always struggled with was rotating the bit just the right amount to get the other angles and surfaces correct. I learned that I could avoid this by tilting the bit upwards at a constant 22° angle in front of the belt. So this is what I did. See the photos below.
The work table on my belt grinder is adjustable for position and angle, so I tilted this to 22° relative to the vertical belt surface. I took a scrap piece of wood and secured another wooden strip below it so that it can slide sideways when slotted onto the top of the work table. On the top surface I secured another strip of wood at exactly 31° off perpendicular in the horizontal plane. So together I now have a positioning jig that will hold the bit at an upward angle of 22° and 31° to the side. The last detail was to file a groove in the top strip so my fingers can get up close to hold small bits nice and tight.
So far it seems to do the job just as I need it to. I have sharpened all my bits with consistently satisfactory results.
From the side. Work table tilted up at 22°.
Guide block on the top angled at 31° to the side.
10mm drill bit for illustration purposes. (0.4")
When sharpening I need to hold the wooden jig and the bit tight in this position with both hands.
5mm drill bit in position. (0.2")
Note the use of the finger groove.
1.5mm drill bit in position. (0.06")
I would not typically try to sharpen such a small bit, but it's nice to know I can.
Nice, clean tip surface.