In the Shop

Tuning an Eggbeater Drill so it ‘Spins Real Good’ by Andy Seaman

I love eggbeater drills. They work well for poking small holes in most any material. They’re compact and light, don’t have batteries that need to be changed, are quiet, safe and operate smoothly if you know how to tune them. The other thing that I love about eggbeaters is that they’re mechanically complex relative to planes, spokeshaves and other handtools, yet the classic makers of these tools have done a terrific job of producing elegant designs.

My dad was kind enough to lend me his Millers Falls #77A eggbeater so I could run you through a tune-up.

Actually, I was hoping he’d say, “Keep it,” since he hasn’t used it for quite some time anyway, but I think he wants it back (nuts!)

As you can see, Dad’s drill is in pretty good shape. It spins fairly smoothly, all of the parts are present (I consider side handles to be an amenity since I’ve yet to find an eggbeater that wasn’t missing its original side handle), and there isn’t very much spindle runout (i.e. it spins with minimal wobble on its axis). However, Dad’s drill is a bit grimy, the chuck sticks, and it doesn’t operate as smoothly as it can. By addressing these issues this drill will run more smoothly and will be able to drill larger holes with less effort.

The first thing I like to cleanup is the chuck. This takes the most effort so I like to do it first. Unscrew the chuck from the spindle and submerge it or spray all over and inside with WD-40, my favorite solvent, or whatever solvent or penetrating oil you prefer.

While the chuck is basting, disassemble the rest of the drill and clean it up with WD-40, rags and a toothbrush. Personally I don’t really care about the paint spatters and such (especially since this is Dad’s drill!) but you can go to the trouble of removing all of these if you like. Clean any grime from the spindle threads as these affect how smoothly the chuck will operate. Use a stiff nylon or brass brush to clean the smegma from the teeth of the main gear and the pinions. Spray and wipe out the bearing in the main gear (the central hole) and inspect the journal that it mates to on the frame of the drill. Wipe off the journal and smooth any burrs or raised metal with slipstones or whatever fine abrasive you prefer. You want this journal to be polished and smooth to reduce friction. I don’t recommend removing the pinions (the little gears). These are typically pinned in place and can be removed, but it’s usually not worth the effort. Now that the chuck has soaked for a bit, it’s time to open it up.

I grab the knurled surface of the chuck in my machinists vise. I made up some brass “soft jaws” when I got this vice and they’ve worked well for holding small parts without marring. Try not to go nuts on the vise and make your chuck egg-shaped. You can see that the top of the chuck cap is slotted, as if for a giant screwdriver. I’m fairly certain that Millers Falls used this design for ease of assembly, not disassembly (a common approach amongst American mechanical designs). Resist the temptation to jam something in the slot and twist! You will most likely cam-out of the slot and wreck stuff. I find that Channellock pliers (tongue-and-groove slip joint pliers, Jeff) lined with a bicycle inner tube gives me enough grip and torque without marring the chuck cap. I’m especially fond of the BigAZZ® Channellocks, for what I hope are obvious reasons.

Here I’ve cracked open the chuck and you can see the shiny nickel plating that hasn’t seen the light of day since it was assembled some time ago in Greenfield, Mass. These are right-hand threads mind you, so you’ll want to turn the chuck cap counter-clockwise to loosen (anti-clockwise, Jeff). These threads need to be right-handed because you want them to tighten during normal use, i.e. drilling clockwise.

I remove the guts of the chuck being careful not to scratch the smooth inside surface of the chuck shell that the jaws slide on. From left to right we have the chuck shell, jaws, thrust washer, and chuck cap. This chuck design is pretty common, but there is some variation amongst the different makers. Here’s a quick look at some different chucks that I have.

From L to R, North Bros. 1430A, Stanley POS Defiance Something or Other, MF #5, MF #120A breast drill. The North Bros. chuck is the easiest to get into since it has wrench flats for an open-end wrench (spanner, Jeff). The others are most easily opened with pliers, strap wrenches, vise grips, etc.

The following photo shows the internals of the MF #120A breast drill chuck. This is another common chuck design and is also used in North Bros. drills. Thought I’d include a photo of this style just in case you need it for reference.

Ok, back to the matter at hand. The inside of the chuck shell is coated with some schmoo that’s been softened by the WD-40. I suspect that the MF assemblers lubricated the chucks with lithium grease, a lubricant that’s notorious for drying out over time. Add to that decades of metal chips, sawdust, and storage dust and now we’re beginning to understand why the chuck sticks.

But I’ve seen and fixed a lot worse. That chuck from the Stanley Defiance was so rusty it was pitted on the inside – but now it works like buttah. I wipe out the inside of the chuck shell with a rag. My intention is to remove as much of that schmoo as I can in about five seconds. Now we move on to my technically advanced chuck-cleaner-outer (patent pending) available for three easy payments of $19.95 plus S+H.

Yep, a dowel with a wide saw kerf will hold a piece of non-woven abrasive pad wonderfully. I use ½” dowel to stiffen things up. Jam the piece of Scotchbrite into the kerf and chuck the dowel in a breast drill. I put the chuck shell back in my vise and insert the end of the chuck-cleaner-outer so that the Scotchbrite kinda folds over onto itself. Then I spin this gizmo as fast as I can for about 30 seconds, angling the breast drill all over the place to polish the entire inside surface. There, now check the result.

Looks pretty good, eh? The tapered surface is smooth and polished. If your chuck shell isn’t in good shape like this one then just keep working it with the Scotchbrite. Use coarser grades if necessary but make certain to finish with finer stuff. Now let’s take a peek at the cleaned-up jaws.

These are also in pretty good shape. We’re primarily concerned with the tapered round surface that is in contact with the inside of the chuck shell. Make sure these surfaces are smooth and burr-free. I touched up the corners of mine on a fine India stone for good measure. When I’m ready to put the chuck back together I put a *small* amount of synthetic grease inside the chuck shell where the jaws will slide, clean and grease the male threads of the chuck cap, and apply a touch of grease to the tip of the spindle threads.

Less is more here, so take it easy with that grease!

Here I’ve jammed the jaws back into the chuck shell. The thrust washer sits on top of the jaws as shown in the second photo. The underside of the washer is flat and smooth (yours is smooth, right? No? Make it smooth!) so that the jaws can slide across it easily. The chuck cap has a counterbore that centers the thrust washer; you can see this in the earlier photo of the disassembled chuck. Grab the chuck cap and screw it back into the chuck shell. Reassemble the entire drill and admire your handiwork.

Alright. Everything is clean and your chuck operates smoothly. There’s one more important thing to take care of before we’re done. We need to lubricate the journals. Any place that you see an oil hole is a great place to lightly lubricate.

Light machine oil like 3-in-one works great for journal lubrication; you want to avoid the heavy, high viscosity stuff here. You also want to avoid lubricating the gear teeth. That’s right, don’t lube the teeth of the gears! You may be thinking, “But hey, isn’t there contact and friction and moving parts and stuff?” Well, there’s some contact and friction, but not nearly as much as the journals experience. The gear teeth are often nickel plated, which is a low friction, long wearing coating. I’ve also seen brass, bronze, and nylon (yuck) gears to reduce friction and wear. I’m quite certain that the eggbeater manufacturers didn’t lubricate the gear teeth. Have you seen lubricated gear teeth? I have. It wasn’t pretty! Lube on the gears attracts dirt and sawdust like you wouldn’t believe. If you feel you must lubricate the gear teeth I recommend paraffin or paste wax since they tend to attract less grime.

Ok, now try out your tuned-up eggbeater. Unless there was something drastically wrong with it (e.g. somebody used it as a hammer), your drill should be running smooth and easy. If your eggbeater worked ok before this tune-up, it should work great now and should be able to drill larger holes with less effort. Don’t be afraid to put a squirt of oil in the oil holes now and again. Proper lubrication will keep your drill running smoothly. Wipe off any excess oil with a rag to avoid attracting dirt and grime. That’s it for now. Lemme know if you have any questions.

Hey Dad, thanks for the eggbeater!

Andy Seaman
April, 2006