using an expanding auger to make big holes

[adrian]

I'm trying to make a series of big holes (~2.75") in wood about 1/2" thick. I got myself an expanding auger bit and sharpened it and it sort of works. Things seem to start out well, it scores the circle and starts cutting, but then as the cut proceeds it becomes difficult to keep the bit cutting. Eventually the center part of the bit leaves a 1" holes in the middle and the bit won't stay centered, so further efforts to cut are not centered. And I have to give up and saw out the remaining section of material. I also have had problems splitting the work even though I had it clamped from the sides.

Does anybody have any advice on how to use these bits to drill big holes?

 

[Spindle]

Hi

You would be better using a hole saw or router to make your holes.

Regards Mick

 

[Phil Pascoe]

Someone somewhere might make an expansive bit that works - but I've never seen one.
+1 for what Mick says.

 

[adrian]

I need a series of holes that are fairly precisely sized ranging from 2.5" to 3.25", I think, six holes in all. The price of all those hole saws for a one-time use is prohibitive. I suppose this job could be done using the router with some circle cutting jig of some kind. But I hate to use the router. It's not a pleasant process for me. The other option is the fly cutter. I had one of those at one point but the lateral forces worked my drill press chuck loose, and then after that the chuck was constantly falling off. I am not inspired to try that again.

 

[AndyT]

Richard Maguire likes them: http://www.theenglishwoodworker.com/?p=2242

It's hard to diagnose what is going wrong for you, but one thought is that there are quite a few different versions of these, and I expect some designs are actually better than others, so it might be worth trying a different pattern. Also, that's a really big hole - some makes came in a small and a large size and you would be better off using a large one set down small, rather than a small one opened up to the max. Oh and use the biggest sweep brace you can find.

One more thought - if you are drilling horizontally, try vertically, or vice versa!

 

[AndyT]

I just re-read your post and spotted the mention of 1/2" thick wood. I think that's your problem - you need more depth, so the lead screw stays engaged.

Clamp your work to some 1" or thicker scrap and see how that works.

 

[adrian]

It was actually Maguire's post that inspired me to try this approach.

I think I have the largest type bit. The bit's nominal range is up to 3". It includes two interchangeable cutters, one for smaller holes and one for larger holes. I'm using the large cutter.

I would have imagined that vertical was always easier than horizontal. Is it not the case? I have been drilling vertically. I have been using a 10" brace. I have a larger one (14") but I don't think it would make a difference, since the problem is not that I'm getting tired. Am I missing some other advantage of using the bigger brace?

When I tried putting some soft construction lumber underneath to catch the lead screw it didn't help. I could try something harder, more similar to the timber I'm trying to drill through, and see if it makes a difference. Also I think the wood underneath may not have been held in place very well.

 

[Phil Pascoe]

A 70mm hole saw from Screwfix is less than £6, but of course you need the arbour.

 

[Bod]

I'm trying to make a series of big holes (~2.75") in wood about 1/2" thick. I got myself an expanding auger bit and sharpened it and it sort of works. Things seem to start out well, it scores the circle and starts cutting, but then as the cut proceeds it becomes difficult to keep the bit cutting. Eventually the center part of the bit leaves a 1" holes in the middle and the bit won't stay centered, so further efforts to cut are not centered. And I have to give up and saw out the remaining section of material. I also have had problems splitting the work even though I had it clamped from the sides.

Does anybody have any advice on how to use these bits to drill big holes?

You need a thick backing timber, similar to your work piece, very well clamped up.
Start the hole to the stage where the circle is scored, remove the bit, then with a smaller drill remove most of the waste, keeping away from the centre. That is needed to pull the auger in. Now most of the waste is removed, the auger will have an easier time, doing the rest.

Its hard work, but it should do it.
Do you need a clean hole both sides?
If so, work from one side, until the lead screw just starts to emerge, then turn the work over, and continue.

Bod

 

[Cheshirechappie]

I've never had much luck with expanding augers, either.

Another approach, hand tool only. Mark out the circle required on the stock. Using a smallish drill (say 3/8") chain-drill inside the marked-out line. Chop out the centre with a chisel, and chop away most of the waste to near the line. If you happen to have an in-cannel gouge of suitable sweep, finish pare to the line. Chances are, unless you're a patternmaker, you won't have such a gouge - no matter. Pare to the line with increasingly smaller chisels. That'll leave a multi-faceted hole, in effect. Then take a piece of large dowel, or plane a curve on a piece of scrap, and wrap coarse sandpaper round it (a half-round rasp will do just as well, should you have one), and refine the curve with it. Finish with finer grades of abrasive paper.

Not something you'd want to do on a production basis, but for six off it should be quite quick and relatively easy, especially after the technique is refined on the first one. The advantage is that it can be done with ordinary basic tools, though as suggested one or two more specialised ones make it a bit quicker and easier. Works on pretty well any thickness of wood, too.

 

[adrian]

phil.p, since I need 6 different holes that means £36 to get six hole saws. I think it's a bit much for a one time use tool.

I had not thought of the idea of removing some of the waste with a different drill. I would have to leave enough material behind so that the center area is still well connected to the sides and doesn't break off. I'm going to be rounding the hole edges, so the exit hole doesn't need to be perfect, but I could easily imagine a 3cm chunk ripping out the back if I just try to bear all the way through, so I would think that flipping over the work would be essential. That does create something of a challenge with the backer board, though. If I drill down some and then flip the work the backer won't make contact with the workpiece. There were be a gap. Does it matter?

 

[AndyT]

Yet another approach, quite practical in half inch wood unless it's huge, would be to saw the holes out with a coping saw, then tidy up with a rasp or sandpaper.

 

[Phil Pascoe]

Sorry, I didn't see the bit about their being different sizes. My mind was still on the original post.

 

[bridger]

I need a series of holes that are fairly precisely sized ranging from 2.5" to 3.25", I think, six holes in all. The price of all those hole saws for a one-time use is prohibitive. I suppose this job could be done using the router with some circle cutting jig of some kind. But I hate to use the router. It's not a pleasant process for me. The other option is the fly cutter. I had one of those at one point but the lateral forces worked my drill press chuck loose, and then after that the chuck was constantly falling off. I am not inspired to try that again.

I suspect that your bit has a sharpening geometry problem. Regardless, a few things to try:
If the spur has 1/4" or more of length beyond the bottom cutter, sharpen the back of the spur. Drill a pilot hole through your wood and run the bit backward from both sides with considerable pressure. This will cleanly score a deep shoulder close to the center of your board. 1/2" of hardwood is probably pushing it to make it to the center, but should be close enough to waste out the center with coping saw and pare to a clean line.

 

[Jacob]

Yes they do score a nice line before they give up and won't go deeper. I'd wonder about taking out some of the waste (not the centre obviously) with smaller drill holes perhaps, to give the thing less work to do.

 

[adrian]

So your idea is to use the bit to mark the hole edges and then cut out the hole with a coping saw?

I'm not sure which side of the spur is the "back". I sharpened in inside surface of the spur and didn't touch the outside surface, which defines the hole diameter. There are two cutters, one interior one that is fixed and one sliding cutter. I sharpened the cutters on the top surface to avoid disturbing the cutting geometry or reducing the relief angle. The cutting edge was hard to access with my file due to the curvature of the cutter, so I wouldn't claim to have done a great job there. I had to use a round file and work almost parallel to the cutting edge.

 

[AndyT]

If the bit gives up cutting, it could be because the lead screw has clogged up, pulled fibres out, and stopped pulling into the work. You can clear the screw but if there is no wood for it to bite onto, because it has pulled out the fibres, that won't work. That's why I think more pressure might be the answer. If working vertically you might be better putting the work on a low stool or on the floor. Holding it vertical in the vice might be better if you can lean into it, but it depends on how big this thing is.

 

[bridger]

Yes they do score a nice line before they give up and won't go deeper. I'd wonder about taking out some of the waste (not the centre obviously) with smaller drill holes perhaps, to give the thing less work to do.

pare back a bit to make Sellers' knife wall. may be enough to get to the center of a 1/2" board, given adequate spur length

 

[bridger]

So your idea is to use the bit to mark the hole edges and then cut out the hole with a coping saw?

I'm not sure which side of the spur is the "back". I sharpened in inside surface of the spur and didn't touch the outside surface, which defines the hole diameter. There are two cutters, one interior one that is fixed and one sliding cutter. I sharpened the cutters on the top surface to avoid disturbing the cutting geometry or reducing the relief angle. The cutting edge was hard to access with my file due to the curvature of the cutter, so I wouldn't claim to have done a great job there. I had to use a round file and work almost parallel to the cutting edge.

generally, yes, let the spur scribe the circle as it seems to be successful at doing, but remove the waste by other means. the center hole does two things- it defeats the self-feeding screw in the center, so that you control the cutting action directly by pressure on the brace, and it gives you an accurately aligned start point on the reverse of the board. you want to do more than just mark the hole, though. you want that spur to slice as deep as possible, assuming that it is making a clean cut.

the point of going backward is to further defeat the self-feeding center screw as well as defeating the bottom cutter, which is currently not behaving, if I read your original post correctly. to get the spur to cut while the bit is being rotated counterclockwise, the edge of the spur being presented to the wood needs to be sharp. in "reverse" rotation that would be the edge normally trailing. on many auger bits this is beveled similarly to the leading, normally cutting, edge, just not sharpened. you are correct that the sharpening must not disturb the perimeter of the bit- all filing and honing is to be done to the inner faces of the spur.

 

[adrian]

I attempted another hole last night. I used a backer board made of the same wood and tried drilling horizontally instead of vertically. The backer board did not make a difference. The lead screw only made it about 1mm into that board, creating just a small divot.

One thing I noticed was that as cutting proceeded, at times the bit tried to hog off some rather massive chips. Using a 10" brace I had trouble forcing it onward, but furthermore, I was worried about splitting the work. (I could switch to my 14" brace.) I wonder if backing out of this cut disengaged the lead screw and made it less willing to cut. Alternatively it could be that the reason for this is that I wasn't holding the brace exactly square to the work.

Indeed, as cutting proceeds I find that I can force it to cut by tipping the brace slightly to engage the bit at the high spots. But after a while, the hole for the lead screw is enlarged to the point that the bit will not stay centered, so the spur is no longer guided by the lead screw, but only by the existing hole. At this point, it becomes difficult to make any further progress because the bit wanders too much. The bigger center hole doesn't seem to be well enough established to guide the cut.

I worked from both sides and have a well defined hole with about 4-5 mm of depth on each side at the edge. Total thickness of the workpiece is about 16mm (a little thicker than the 1/2" I stated). So I have about 6-8 mm material remaining to remove at the edges. Considerably more material remains in the center: on one of the sides no material was removed.