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I have a large round of wood (horizontal slice of a tree) which is about 20 inches across (circle diameter) and 8-9 inches deep.

I want to take the centre out of the wood, either by cutting a circle which is maybe 4-6 inches smaller in diameter than the piece (thus leaving 2-3 inches of wood around the outside) or by making some kind of cut that follows the shape of the wood (since its not a perfect circle). The second option here would be my preference but I can work with the first.

I'd also like to avoid cutting it into pieces or cutting into it from the edge and then having to re-glue but if thats the only option that might be a possibility. Even if I slice it in half somehow though I still have the problem of hollowing out two very large semi-circles.

Wherever possible I would like to keep the wood inside relatively intact so I can do the same thing to the centre-area I've taken out on a smaller scale (rather than it all being just wasted).

The options I have considered / tried are:

1) Bandsaw - I don't have one of these with a large enough throat I could actually cut the depth of wood on it. Also this would mean entering from the side and manipulating a very heavy and large piece of wood accurately moving it around to place the cut along the side.

2) Drilling adjoining holes - I have tried to drill holes through with a spade bit but have had issues. For one my spade bit is not long enough. Assuming I could get an extender of some sort and get it through to the other side its very hard to keep it 'on track' while drilling an adjoining hole since the rotation of the bit seems to want to pull it into the adjoining hole drilled previously. Once this happens it destroys the 'walls' separating the two touching holes I am trying to drill and makes it near impossible to keep on track. I have a pillar drill that might be able to help with this issue but then I am back to manipulating a very large piece of wood on a drill platform which is much too small for it.

3) Drilling separate holes then cutting through - I have also tried to drill holes which are separated by a small distance (e.g. 10mm). This is much easier to drill the holes and my plan was to use a keyhole saw to cut through from one hole to the other but making these cuts is very onerous, for one its hard to get the pressure required to get the cut through without trying to balance the wood so that the saw is cutting downwards (otherwise I'm trying to cut sideways or in some weird position) and I also have problems with the depth of the wood, particularly if the hole is not drilled all the way through.

4) Jigsaw - I have some quite long bits for my jigsaw but nowhere near long enough. I bought a reciprocal saw as I was able to get a 12" blade for it but it seemed to cut very slowly, suffer from absolutely horrible amounts of vibration, and I still had the problem of getting the blade through (admittedly could be resolved with an extender or a longer spade bit on my drill) and because the blade was so long I had my doubts about it being able to make the turns required to cut the circle.

5) Chainsaw - for a brief time (before I actually handled a petrol chainsaw) I had considered making plunge cuts with a chainsaw through the wood but now see a number of issues. For one oil from the blade might affect the final finish on the wood and plunging a chainsaw into an 8-9" cut just seems to be asking for the chain to bind and then either get perma-stuck in the wood or develop into some unanticipated and likely not very funny distribution of kinetic energy towards the delicate meatbag holding it.

6) Lathe - I don't have one but also I can't imagine it would take the weight of such a large chunk of wood.

7) Circle-cutter drill bit - I once had one of these that went maybe 10-11" across maximum. I haven't since looked or found a larger one but in any case the one I had wouldn't have been able to cut deeply enough to take the entire centre out, so all I would get is a circle groove which isn't much use. My previous experience with hole saws and circle cutters is things get more difficult the deeper you get so I would think this would be problematic.

I'm running low on ideas at this point as to how I get it done. The drill-and-saw-through method might work but it seems an inordinate amout of work. Probably the best I can think of is to spend a lot of money on a large bandsaw with a large throat depth, then build some kind of large adjustable height platform which would allow me to make the cut from one side, turn it round and then exit from another or the same side, then re-glue.

If someone has a solution whereby I can cut it into two halves (also not easy, best I can come up with here is some major elbow grease with a long-blade handsaw or again back to a bandsaw with large throat depth?), and then hollow it out then that would be interesting for other reasons too since I seem to often find myself wanting to hollow out shapes/curves/semicircles of wood which wouldn't be doable on a lathe.

Update for anyone interested:

I wanted to try some of these options before accepting an answer but it's taken me a while to get round to it.

I tried my preferred option by making a bow saw from a modern blade and some custom wood. The saw turned out OK and was able to saw a test piece no problems but because the depth of the cut it had to be able to make to cut the outer ring of the wood was so large it ended up being a very tall saw (around 80cm):

very deep bowsaw

This made it very cumbersome to actually use. If the saw is held higher up then its there's way too much leverage to force the blade along and make the cut and the saw blade just sticks and the whole saw tilts instead. If held lower down then without the wrist strength of Hercules and Popeye combined the saw is just too hard to keep straight. Cutting anything other than horizontally had similar problems of managing the weight and tilt. I did eventually figure out a way around this by hooking a broom handle off a rafter and using it as a slide that I could lift and lower to adjust the angle of the saw. With this I was able to get the saw going but found that for some reason it was very difficult to get it to follow the curve of the wood. The back side of the cut seemed to curve slightly but the front side just wanted to go straight. Even given quite significant torsion on the blade (see pic) there seemed to be no way to get it to curve. Possibly the wood was just too thick for it to make the curve.

squint bowsaw cut

What I did find worked somewhat were auger bits which tracked very well (distinct from forstner bits which I hadn't realised and haven't tried) but which did need a wall-powered drill to have the power to get them through repeatedly and successfully. I also found drill bit extenders which would allow me to get them all the way through although the extenders themselves are quite wide and mean I have to use a wider auger bit than I would like. Even so, drilling so many holes and trying to get them to link up all the way through the depth of the wood is not easy and is very likely to end up needing further efforts to join the holes up from the underside due to them not being perfectly straight.

Auger bits are probably the best way to get the job done given my original requirements but it seems the only relatively quick and easy option is a bandsaw with a large throat depth, although possibly cutting the whole thing in half with a chainsaw and chopping bits out with that might be a good way to go if the centre wasn't important.

  • somewhat related I think: woodworking.stackexchange.com/questions/866/… – CRABOLO Jul 18 '15 at 13:42
  • #4 -- the sawzall blade might have potential if you went for something with few teeth and open gullets -- might be tagged as a pruning blade. Keep the shoe tight to the workpiece to reduce vibration, and connect multiple holes (18" 3/4 auger bit springs to mind) if you want to spend less time. – Aloysius Defenestrate Jul 18 '15 at 17:28
  • A Forstner bit might be easier to handle than a spade bit. – Pete Becker Jul 19 '15 at 0:48
  • Do they make extensions to router bits such that you could just route it out in passes? – Jeremy Jul 19 '15 at 14:38
  • Lots of interesting suggestions! The bow saw seems to me the most likely solution without spending a lot of money and I think given the bow saw blade is relatively simple I could build my own saw much like the traditional one with a deeper cut if necessary. Also very interesting suggestions from bowlturner on the powered coping saw. I think if manually using the bow saw was too much work I might try to make a powered bow saw along the lines of the coping saw (since a long bow saw blade is easy to find and should be able to cut a large curve). – AntonyM Jul 20 '15 at 23:30
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I think you've already hit on the best way(s) to remove the bulk of the material without going overboard on costs, but aren't using the right tool for the job. Drilling adjoining or adjacent holes I think are the best ways to approach this for the average user, just not using a spade bit.

I'd probably use an auger bit in a brace if I had to do a job like this, since this would be the cheapest option for me. For you, buying a suitable bit for your power drill that's similar to an old-style auger bit may be your best bet. These can be found with lengths in excess of 9" / 23cm (in fact bits longer than 2' / 60cm are available) so you wouldn't have to resort to drilling in from both sides of the round.

If you wanted to go with separate holes followed by breaking through the web between them this type of bit will greatly aid the process because they track very well; their design is specifically to allow the creation of long straight holes, in this regard far far better than a spade bit. So you could go from a spacing of 10mm to just a couple of millimetres. But with auger-style bits you could probably successfully drill the holes adjoining if you go slow, that's how well they track.

Cleaning up afterwards is still going to be a lot of work! Probably best done mostly with hand tools, so this will be a slow, tedious job but hopefully worth it in the end.

  • 1
    Did you say brace and bit? What a concept! +1 – Ast Pace Jul 20 '15 at 4:24
  • The brace here to guide the bit is a great idea. I like the idea of the forstner/auger bits but I have had issues with them in the past where the small screw-guide on the end of the bit tends to bite into the wood and then everything just gets stuck. Not sure if that is because my drill is too weak or because I am often dealing with hardwood but I may post that as another question. – AntonyM Jul 20 '15 at 23:35
  • @AntonyM, "Not sure if that is because my drill is too weak " That does seem a likely reason. If the auger-style bit does not have sharp spurs or leading edges that could also be a factor of course. – Graphus Jul 21 '15 at 7:25
5

What you want to do is uncommon and more of a niche thing. I'm pretty sure most people in a similar situation just hollow out the log and not care much for the inner circle of wood.

Going over your options, A bandsaw with a large enough throat would be the simplest course of action, you should be able to just cut out the center with one cut into the side. to make it easier you could drill a hole (or more) through the log to help with turning the log around the blade. I have a spade bit that is 16-18" long and it did't cost much.

The lathe is certainly possible, but it will likely be the most expensive option. First you need a large lathe. lathe's with a 20"+ swing generally start at $3K. Lathes like mine are cheaper, starting closer to $1800, where the motor can move and can do outboard turning. But at that point you need an outboard piece to actually work the lathe and the cheapest I've seen for purchase is $500 (Family member made one for me from scrap iron). And then making the through cuts will likely need a special tool to make a narrow deep cut through the log.

Just cutting the log in half, a bandsaw is certainly the easiest way to do that though a chainsaw isn't too bad either.

What you really need is a powered coping saw or a scroll saw with a throat large enough to take your piece of wood. You drill on hole through, just large enough for the blade the the blade can go through the hole then be attached to the saw. Unfortunately most I've seen have a max of about 3" throat.

If you don't mind a lot of work, the coping saw could work if you can find one with a deep throat, since the standard one is 6 1/2". You could of course make one specially. You could also make the blades out of bandsaw blades.

The homemade coping saw is likely your best option, and if you did this a lot I'd think about putting a motor on it. In either case, I would buy one or two long spade bits to drill through the depth you need.

5

You tagged powertools but, much like you, I don't own the the types of tools that would do this.

While you might have a hard time getting a uniform curve I would suggest you use a bow saw. You could just follow the natural curve of the log which would look just as well. Traditional or modern bow saws should both work. Using a wider blade with deep gullets would be advised for this method. Bow saw are used for crosscutting but you can also use them for curves. Below you will see picture of a traditional bow saw and then a modern.

Traditional Bow Saw

Image from LumberJocks

Modern Bow Saw
(source: benmeadows.com)

Image from topoequipos

The advantage you would be getting here is that you just need to drill a hole large enough for the blade and then you could assemble the blade inside the hole. No welding needed!. The blade won't even curve that much as you move around the log so you should have no problem.

Side Note

You don't mention how green this wood is. Removing the heart wood from the piece in question should help reduce the chance of splitting but just know that if your wood is still not at a regulated moisture level (which is possible with a piece that large) I would expect cracking to some degree.

  • 1
    A traditional bow saw would work well, but I don't think the second one pictured would work nearly as well for curved cuts. You need to be able to rotate the blade relative to the saw frame so the frame doesn't interfere with your cut. – rob Jul 20 '15 at 4:25
  • @rob I only own the second one and it actually cuts curves quite well. I found that out when I got to vigorous with sawing and motion caused a curve in the log I was working. – Matt Jul 20 '15 at 10:05
  • 1
    I guess what I should have said was that I don't think it would work as well for the type of controlled cut AntonyM wants to make, since it was designed to make straight(ish) cuts in small trees and logs. A traditional bow saw is more like a large coping saw in that it lets you rotate the blade to move the frame out of the way. Also like a coping saw, its design gives you more control when making curved cuts. – rob Jul 20 '15 at 14:04
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In the shop I worked in, we welded our band saw blades together from a big roll of blade. The band saw was also big enough to easily fit your workpiece. It was in a primarily metal workshop but we did have the big toothed blades for woodworking. This setup would allow you to drill a through hole to fit the blade, then weld the blade while through the wood, install the blade, cut the wood, and then cut the blade off. So if you can find a big shop near you they might have a similar setup and be willing to help you.

3

Would it be possible to split the log with an axe and wedges, make the hole somehow, and then glue the pieces together again?
You will demolish the wood at the axe's and wedges' entry points but the rest should, with some care, be ripped apart along the grain. Carefully gluing together again should be invisible.

3

Someone with an industrial CNC laser- or water-cutting machine might be able to do this for you at a reasonable cost. 8-9" is thicker than I have experience with, but might be possible.

If you had a blade welder, you might also be able to drill a hole near the circle you want to cut, thread a bandsaw blade through it, weld the blade together, and then install the blade (with workpiece already on it) into your bandsaw.

2

Would try to get a hole in the middle and then work with a hammer and chisel (best a round one) towards the edges. If precision is not that important and you want to follow the outline rather than have a perfect circle, that should be good enough.

Carving chisels sounds most like what I would use but my English is bad:

You could also try to create the initial hole with a chisel. Sounds like a lot of work, but you learn to use the tool and you don't need to go to the gym. ;-)

One of the wiki images says:

A sharp wood chisel in combination with a forstner wood drill bit

That might be a good way too, drill as deep as you can, then chisel away the rest.

  • This method was one that I had actually tried but had problems with it. For one I think I drilled the holes too deep which caused problems trying to chisel between them but also the nature of the wood being a round slice of a tree means its end grain so I can't get the wood to peel out like I would normally if I was chiselling along the grain. Instead it seems to just crack at the point of chiselling like a broken tree and then is quite hard to actually split off entirely and remove. That may again be down to a lack of technique, there may be better ways to chisel end grain? – AntonyM Jul 20 '15 at 23:38
2

The best way to do this is to use a router with preferably a plunge base and a makeshift circle cutting jig. There are many plans available online for free. Some routers come with an edge guide which can be pinned on one end.

If you don't have a plunge base, you'll have to drill a hole on the inside tangent of your circle so that you can start your cut easily. Make sure you take shallow depths for each complete revolution.

You may want to fix your work piece on a substrate using hot glue, pin nails or double sided tape. It will prevent the inner circle from breaking lose during the final passes.

1

An option could be to burn it. I haven't tried this, but it might be of help. It is a technique used to hollow bowls in spoons and in other tasks, but I can't see how it wouldn't work here. The idea would be to build with some rebar a curved shape, such as a circle (or a quarter of a circle), then to heat it in a fire or with a welding torch.

When red hot you press it into the wood and it will burn out most of it in the direction of the grain (like in a swedish torche). While it may take some time it might come in handy and is a cheap way to do what you want. And in the bargain the charred wood is protected. You can then finish to pare the sides of the wood with a brush and enjoy a smooth surface showing the grain of your wood.

See for inspiration those videos on youtube:

Fire hollowing a didgeridoo

Shou sugi ban

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