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The Humble Hand Brace - A Beginner's Guide to Restoring, Buying and Using #7: Part 7 - Sharpening an Auger Bit

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Blog entry by Brit posted 10-03-2011 12:08 AM 19960 reads 12 times favorited 36 comments Add to Favorites Watch
« Part 6: Part 6 - What to Look for when Buying a Secondhand Brace and more Part 7 of The Humble Hand Brace - A Beginner's Guide to Restoring, Buying and Using series Part 8: Part 8 - Tips and Tricks on Using a Hand Brace »

I know I said that sharpening an auger bit would be part 8 of this blog series, but I’ve taken the liberty of bringing it forward since the ‘Using a Hand Brace’ part isn’t finished yet. After spending precious time restoring a hand brace, you will soon realize that it isn’t much use when drilling a hole if the auger bit you are using isn’t sharp. A sharp auger bit is a pleasure to use and cuts very quickly.

Auger bits have evolved through the years. Manufacturers kept improving their designs and building on previous patents. For this reason, a variety of different designs come up on the secondhand market. At the height of their evolution, there were two types of auger bit that were widely available. They were the Irwin Patent bit and the Jennings Patent bit. Both of these types cut in the same way and and both are sharpened the same way.

You can tell them apart because the Irwin patent bit has a solid metal core running through the business end of the bit into the shank making it very strong in use. The Jennings Patent bit looks like someone took a flat piece of steel and just twisted it. It doesn’t have a solid core and is not as strong where it joins the shank.

Assuming an auger bit isn’t bent or heavily pitted, there are three things that determine how well it will drill a hole. They are:

• The Tapered Lead Screw
• The Spurs
• The Cutting Edges

The Tapered Lead Screw
Unlike twist, lip and spur, Forstner or sawtooth bits, the speed that an auger bit can drill is not determined by the amount of pressure you apply. The speed is governed by the pitch of the thread in the lead screw. Manufacturers made auger bits with coarse, medium and fine pitch lead screws to suit different trades. If drilling a hole with a fine finish was a priority, they used a fine pitch auger bit and if speed was a priority, they used an auger bit with a coarse pitch thread.

Whatever the pitch, the threads need to be in good shape, so if they are packed with saw dust try brushing them with an old toothbrush. Gripping the shank in a vice and cleaning the thread with dental floss is also effective.

So just to reiterate, the job of the Lead Screw is to engage the wood and pull the auger bit through the work, keeping it centered in the process.

The Spurs
As the screw enters the wood, the two spurs score the outside diameter of the hole severing the fibers and preparing the way for the cutting edges to slice the waste. They need to be sharp in order to produce a clean entry and exit hole. Under no circumstances should you file the outside surface of the spurs, only the inside surface. If you do, you will decrease the diameter of the circle that they scribe and the rest of the auger bit will have trouble fitting through the hole and start to bind.

The Cutting Edges
The two Cutting Edges pare away the wood as the bit rotates into the wood. It is important not to change the cutting geometry of the edges. Therefore, you should only ever file the beveled side of the cutting edge and take care to maintain the original angle of the bevel.

The helical flutes of the auger bit carry the waste efficiently to the surface. However, when drilling deeper than about 2” (50mm), it is better if you back the auger bit out and clear out any chips in the hole before continuing to drill deeper.

Sharpening
For all but the smallest auger bits, the best tool for the job is an Auger file. An Auger file is double ended and both ends are tapered. One end has teeth on the flats and none on the edges and the other end has teeth on the edges and not on the flats.

To use it, hold the auger bit as shown below so that the tapered lead screw digs into a piece of wood or MDF. File the bevels on the cutting edges first. Position the file on the bevel angle and push. It only takes about five or six strokes to restore the edge and for all you hand plane lovers, there’s no need for a micro-bevel here. :-)

After sharpening the first bevel, rotate the auger bit 180 degrees and sharpen the other bevel with the same number of strokes.

Next, sharpen the inside surface of the spurs. Again, it only takes five or six stroke on each spur.

The auger file will sharpen the bevel on the cutting edges of smaller auger bits too.

However, you may find that there isn’t enough room between the lead screw and the inside face of the spur for the auger file to get deep enough. You can see what I mean in the following photo.

In this case, I use a flat needle file which has one safe edge.

Notice how the needle file goes right to the bottom of the inside face of the spur.

Sharpening an auger bit is quick and easy and anyone can do it. The following video is in real time and shows how little time it takes.

That’s all there is to sharpening an auger bit. Just remember these few principles:

1. Ensure the lead screw thread is clean.
2. Maintain the cutting geometry.
3. Take the same number of strokes on each cutting edge and each spur.
4. Take as few strokes as possible to extend the life of the auger bit.

In the final part of this series, I’ll focus on how to drill efficiently and give you some tips on improving accuracy when you need to drill deep holes.

Thanks for reading.

-- Andy -- Old Chinese proverb say: If you think something can't be done, don't interrupt man who is doing it.



36 comments so far

View dakremer's profile

dakremer

2491 posts in 1813 days


#1 posted 10-03-2011 01:47 AM

Wow – I was really impressed with how quickly (and seemingly easy) that bit drilled that hole through that junk of wood. I really need to get back on track with this restoration! My school trimester has 2 more weeks left, then I get 10 days off. I will be finishing it during that time! Another great blog, with great explanations! Thanks a lot for all your hard work! If mine comes out HALF as nice as yours, I will be proud

-- Hey you dang woodchucks, quit chucking my wood!!!!

View TopamaxSurvivor's profile

TopamaxSurvivor

15020 posts in 2397 days


#2 posted 10-03-2011 07:41 AM

Nice job. Any tips on chasing the feed point?

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Brit's profile

Brit

5284 posts in 1564 days


#3 posted 10-03-2011 08:34 AM

TopamaxSurvivor – Not sure what you mean by chasing the feed point. Do you mean how do you drill exactly on your mark, or do you mean what do you do if the lead screw point is off center? I’m just off to work now, but if you can clarify what you mean I’ll reply later today.

-- Andy -- Old Chinese proverb say: If you think something can't be done, don't interrupt man who is doing it.

View TopamaxSurvivor's profile

TopamaxSurvivor

15020 posts in 2397 days


#4 posted 10-03-2011 08:39 AM

Sharpening the self feed screw. I have worked on some with a tri-file, but they are difficult to do when they get bad. Of course I’m hittiing 16d nails ;-((

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Cobwobbler's profile

Cobwobbler

31 posts in 1208 days


#5 posted 10-03-2011 10:20 AM

Just the info I need to sharpen my Dad’s old bits from the 50’s, thanks a bundle.

-- Martin, Rugby, United Kingdom. Make Tea, Not War. http://thecobwobbler.blogspot.com/

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1837 days


#6 posted 10-03-2011 11:00 AM

great blog Andy :-)
just an exstra note if the bit don´t go thrugh the wood its usualy not the lead that is dull or broken
its becourse the bit itself needs to be sharpened since a dull bit overcome the force of the leading screw
and by then rip the tread the leading screw has made and when that happen … it stop boring
and for those that not knowing it …. you just bore until the center of leading screw is getting thrugh
then you do it from the other side to get a clean hole without splintering on the back

take care
Dennis

View nobuckle's profile

nobuckle

1120 posts in 1483 days


#7 posted 10-03-2011 02:05 PM

Sweet! Thanks for posting this Andy. I wasn’t real sure how I should sharpen my bits, but with your insight I feel much more confident to do so.

-- Doug - Make an effort to live by the slogan "We try harder"

View saddletramp's profile

saddletramp

994 posts in 1360 days


#8 posted 10-03-2011 03:27 PM

A great tutorial Andy. In the past I’ve tossed a couple of bits that I had bought in a group that had obviously been “resharpened” wrong, i.e. they were not sharpened on the bevel. Even though they appeared to be sharp, they didn’t cut/drill worth a hoot. Is there any way to save them (I had tried to reestablish the bevel and proper angle of cut but they still wouldn’t work)?

-- ♫♪♪♫♫ Saddletramp, saddletramp, I'm as free as the breeze and I ride where I please, saddletramp ♪♪♪♫♪ ...... Bob W....NW Michigan (Traverse City area)

View Brit's profile

Brit

5284 posts in 1564 days


#9 posted 10-03-2011 08:36 PM

dakremer – Thanks Doug, glad you’re finding it useful. Topamax – I don’t know of any other method other than trying to restore it by filing it. Sounds like you need to get a Greenlee nail eater a replacable.

Cobwobbler – Bring ‘em back to life. :-)

Dennisgrosen – Very true Dennis.

nobuckle – Its real easy so go for it.

saddletramp – Sometimes you’ve just got to let them go if you can’t rectify incorrect filing. I don’t know of any other way other than trying to file the edge back to how it should be. If someone has filed the outside of the spurs, you can sometime lightly hammer the metal back out to the correct diameter with a ball pein hammer, but it is a bit hit and miss.

-- Andy -- Old Chinese proverb say: If you think something can't be done, don't interrupt man who is doing it.

View TopamaxSurvivor's profile

TopamaxSurvivor

15020 posts in 2397 days


#10 posted 10-03-2011 10:05 PM

I think they are Greenlee, but before the tips were replaceable. I just thought you might have a better trick up you sleeve ;-)

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View WayneC's profile

WayneC

12300 posts in 2819 days


#11 posted 10-03-2011 10:17 PM

Thanks Andy. Very timely. I just picked up about 20 bits over the weekend. Just dropped em in some evapo rust.

Was actually a pretty good drill hunting weekend. I got a wonderful Miller Falls #2. Great shape, nice patina and came with its bits. All for a whopping $3.

-- We must guard our enthusiasm as we would our life - James Krenov

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1837 days


#12 posted 10-03-2011 10:26 PM

that´s a score Wayne … congrat´s :-)

Dennis

View Brit's profile

Brit

5284 posts in 1564 days


#13 posted 10-03-2011 10:29 PM

$3? You should have tried to beat him down Wayne. LOL

-- Andy -- Old Chinese proverb say: If you think something can't be done, don't interrupt man who is doing it.

View WayneC's profile

WayneC

12300 posts in 2819 days


#14 posted 10-03-2011 10:41 PM

LOL – I had been looking for one for quite a while. Not willing to pay the $80 to $125 on ebay for one.

-- We must guard our enthusiasm as we would our life - James Krenov

View WayneC's profile

WayneC

12300 posts in 2819 days


#15 posted 10-03-2011 10:42 PM

Oh and I also added a pointing and tennon bit for my braces. Going to play around with them some.

-- We must guard our enthusiasm as we would our life - James Krenov

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