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A Four Facet Drill Sharpener

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Derek Brown's article describing his Four Facet Sharpener for small drills (#42-#80) appeared in "Model Engineer" for January/February 1994; the article was updated and reprinted in the same magazine in May 2000. A version for drills to 1/4" appeared in "Model Engineer" for August 1996. Derek was kind enough to supply copies of all these articles when I couldn't find construction info on the net. My interest originated from a variant of Derek's unit shown on Alan Marshall's site (disappeared since). This hand powered Four Facet Sharpener works very well for small drills; for those who would like to build one and can't find Derek's articles I have provided enough info here to allow construction. A motorized 4 facet grinder is used for larger drills.

The clever thing about the pin vise for the Four Facet Sharpener is that it is rectangular. This makes it easy to get both sides of a drill aligned the same: simply flip the vise over. The vise works in the HoneDrill fixture too although the nut prevents it from registering properly on the back end; this can be compensated by adjusting the fence but I made a longer version of the pin vise so these nifty collets can be used easily in both fixtures.

The article indicates that slitting the collets is the trickiest part of building the unit so I made the collets first - if I couldn't make the collets there would be no need for the tool block. The collets are made from 5/32 drill rod where 4 collets will accommodate drills from #42 through #80. I used a 5C spin indexer to hold the collet blanks for slitting but since I didn't have a 5/32 collet I used a 3/16 split sleeve to hold the 5/32 blank in a 3/16 5C collet. Confusing to describe but it worked well. I stopped the mill to take this picture of the process. The saw is a Thurston 0.015 thick blade, close to the 0.016 blade specified in the article. The collet blanks are 5/32 drill rod, 1.30 long where the body is drilled out with a #42 drill except the last 3/16 which is drilled to size the collet. The drill sizes specified for this are: 42, 49, 55 and 68 -- I didn't make the smallest collet (yet). The end of the collet blanks are tapered at 15° and a 15° reamer is made from the same drill rod to form the taper in the body of the pin vise. The vise body is 1.5" long by 0.250 by 0.220, drilled out to 3/32 then enlarged to #22 = 0.157 except the last 1/8" which is reamed with the 15° reamer leaving about 1/32" un-reamed; I put the reamer in the lathe chuck at low speed and pushed the vise body onto it by hand, cleaning chips out and checking progress frequently. A 9/16 long brass nut threaded 10-32, also through drilled 3/32" completes the pin vise. I added grooves at the rear of the collets to identify the size. This collet and pin vise work really well, little force is needed to solidly lock a drill in place. The collets expand slightly when slit so they must be removed from the pin vise by pushing them with a small drill.

Machining these tiny collets is fussy work; some details concerning this: I made a split sleeve by end drilling a 12 inch by 3/16" brass rod about 5/8" deep, then adding 4 slots with the 0.015 saw. The rod was run through the 5C collet and extended out the other end of the spin indexer. A drill chuck was clamped on this end and used as a handle to move the split sleeve in and out while inserting and removing collets. Slitting was done by approaching from the side of the collet blank with the saw set to clear the 5C collet by about 1/16". The collet blank extends 1+ inch from the 5C so it is gripped by about 1/4" of its length -- this allows slitting about 15/16" of the collet length. My saw blade is small diameter so the end of the collet conflicts with the saw arbor; this forces completing the slit by rotating 180 and coming in again. When slitting, a curl of metal comes out of the side away from the blade and this occurs inside the collet too. This swarf should be removed in place as best as it can be after each cut else the blade will re-cut this swarf and could jam and break. After cleanout, rotate 180° and complete the remaining part of the slit on the other side, clean swarf again, rotate 90° and make the other slots, cleaning after each cut. On completion, the collet will be full of swarf and have burrs so run the #42 drill in by hand as needed to clean things out. In addition, the exterior of the slots will have a burr along the length which must be removed before the collet will fit into the chuck. It takes about as long to clean and debur a collet after slitting as it does to slit it. The collets need not be hardened.

I made the main tool block from scrap aluminum rather than (1x1.5x2) steel as called for in the article (if it wears rapidly I'll make one from steel or HDPE). The article recommends angles of 10° and 25° for the sides; these angles set the relief angles for the facets. Opinions vary on appropriate relief angles, where other sources recommend 6° and 20° so I split the difference and used 8° and 20°. I squared up the stock and scribed lines showing the angles on the end, then used these lines and a parallel laid on the top of the vise to align the part to the vise top and milled the angles into the block. The vise was rotated 59° so the slots for the pin vise could be milled into the angled sides. Each side in turn was set even with the top of the vise and a 1/4" wide by 0.220 deep slot milled so it went through the geometric center of the side - this picture shows a slot being cut. The slot at 59° is appropriate for a 118° drill, the point angle found on most twist drills. To handle a variety of angles the HoneDrill fixture is more appropriate; the Four Facet Sharpener is simpler and faster to use but less flexible in the tasks it can handle. This shows the end and side views; note the slot for the pin vise goes from upper right to lower left - this is true for both slots in a block.

To complete the unit I added black Delrin side plates using 6-32x1/2 flathead screws. The pin vise should be a shake free fit in the slots so make any minor adjustments needed to achieve this. The vise is rectangular to ensure it only fits in the correct orientations; I left the vise square until the side plates were added, then trimmed the vise with the fly cutter and made final adjustments on the bench sander. Chamfer the corners of the vise so they don't interfere with the fitting process.

The plans call for the block to run on rails using a diamond plate for sharpening. Instead, I used sealed ball bearings (salvaged from discarded VCR's) as wheels with 6-32x1/2 button head screws as axles. I use #600 carbide paper laid on a granite block for sharpening, where the wheels hold the sharpener body about 1/16" from the paper. The nose of the pin vise is fettled by placing a small piece of cereal box cardboard on the bottom of the tool block for protection, then filing the tip of the vise in place to within 1/32 of the hole -- do this for all possible orientations/positions.

This sharpener is much simpler to use than the HoneDrill and does a fine job sharpening small drills. It takes some experience to judge how many strokes and what stroke length to use vs the condition of the drill. 600 grit carbide paper cuts rapidly, at least when its new: about 6 strokes 4" long is enough to put a 20° (secondary) facet on a #50 drill and 1 or 2 much shorter strokes adds the primary facet. If a drill is damaged or the chisel is off-center and must be corrected then it would take longer than the 2 minutes it takes for a drill which is only dull. It can take longer to put the drill in the collet and align the flutes vertically than it does to sharpen it (but see the alignment gadget below). Centering the chisel is a judgment call where a couple strokes on the shorter side generally does the trick. Re-sharpening a four faceted drill is nearly instant if the drill is only dull - one or two strokes on each facet.

User Note: The article specifies a diamond plate for sharpening and I found part of the reason: grit from stones or carbide paper sticks to the end of the drill bit and can drop off inside the slot which holds the pin vise, making it difficult to re-insert the vise. My solution is to pick the block up and wipe the drill point with a paper towel before withdrawing the pin vise. I tried using this fixture on an oilstone before I figured this out - the oilstone made the problem obvious although it works well when reworking damaged drills needing more than simple sharpening. To clean the slots push a wad of paper towel through; as with most grinder fixtures, never clean with liquid or apply oil because grinding dust will stick to it and cause trouble.

An optical aid to accurately align the flutes vertically is helpful for the tiny drills sharpened in this fixture. The magnifier in this fixture incorporates a line to help judge when the flutes are vertical. This is calibrated by rotating the (friction fit) Lucite lens to align the fiducial line with the side of the rectangular pin vise. The lens design is similar to the optical center punch lens but shorter; the outside surface is spherical while the side toward the drill is flat and has the line -- the focus is about 1/8" from the lens, magnification is about 4. Magnification and distortion increase as the drill is moved away from the lens. The pin vise is held into the corner of the fixture to center the drill in the magnifier.

To keep track of the tiny collets I drilled storage holes in the top of the main block. Friction holds the collets in these holes and the ID rings allow picking the correct one.