sawing a log and reassembling it WITHOUT warping?

[Desmond Bowe]

hello!

I'm building a hifi tube amplifier into a carved tiki head. I start with a log that's roughly 12" wide and 14-20" tall, carve a tiki face into it, then bandsaw the log in half, hollow out the insides to hold all the electronics, and bolt the two pieces back together using machine screws and threaded inserts arranged up the sides.

My problem is that the two sides of the log warp away from each other and my screws no longer line up to the inserts, so the pieces don't fit cleanly back together. Plus, I have unsightly gaps between the pieces. I could use some help and addressing this issue as I don't have a ton of woodworking experience.

--> Waiting several years for the logs to dry is sadly not an option <--
And even if it were, there would surely still be minimal warping of the two pieces that would misalign my screws + inserts.

The amp must be able to come apart for maintenance, but maintenance does not need to be performed often.

What solutions are there for reassembling logs that have been ripped this way? I don't see a ton of examples out there which leads me to believe this is a pervasive problem. One option I've considered is to bolt one side of the pieces together and have all of the warping expressed on the opposite side. The overall damage is worse but I could conceivably cover over the gap with a sliding plate. This option doesn't allow for both sides to be supported during transport, but then these items aren't meant to be moved very often.

Would sealing the wood stop warping? I haven't tried this, but again, even minimal warping would thwart my strategy of machine screws + inserts.

Another option is to leave the shell of the log intact and hollow out the interior from the two ends. This poses some challenges with the wiring but feels like the best option for presentation. I should also be able to cut out an access port in the back and use the cut-out piece as a hinged panel without any warping, correct?

pictures attached. I'm not worried about the little splits/checks in the log, just the large gap that opens between the front and back halves. The second picture is a top view; the small holes are for ventilation, the larger hole is in the center of the pith in a vain attempt to slow the movement.

any other suggestions welcome! thank you!

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[Jim Becker]

You are trying to fight a battle that's going to be extremely difficult to win. "Logs" don't really dry down equally, so you are always likely going to have a moisture imbalance even if you waited for many years. Coating with a sealer (typically on the ends) is to slow down drying to avoid radial cracking in the case of logs. I suspect that about the best thing you can do is joint the faces of the rip line after you hollow and get them gued back together immediately. You may need to do a little hand work to refine the joint to reduce its visibility.

[Cameron Wood]

Hollowing out the log to make a tube with somewhat uniform wall thickness and open top & bottom should work OK. The top & bottom could have separate applied pieces.

Look up 'band saw boxes'. Splitting in half and then hollowing out the halves, or all with one cut- either way would take a very large band saw.

The wood is always going to shrink more around the circumference than other directions, and will continue to move like that after it is dry. Taking away the middle allows the outside part to shrink without (as much) cracking.

In timber framing, sometimes a saw cut is made along the length in to the center, so that the shrinkage happens there instead of other random spots.

Once the wood in your pics has dried more, the seam could be re-cut for a better fit. Maybe the gaps could become part of the design- how about inserting some tiki ears?

[Richard Coers]

Wood moves when it dries and it moves every spring and winter from atmospheric changes. It is a law of nature.

[Andrew Hughes]

Definitely need to wait longer for the log to dry.
At minimum 7 years

[Bill Dufour]

As Norm would say, celebrate the joint. Put some ears, spears or palm leaves coming out of the joint to hide it. Maybe hang a snake or monkey over the joint. Dreadlocks?
Bill D

[John Kananis]

This just isn't going to work. If you absolutely just have to have this look, then start with 8/4 stock, square it, then laminate/carve/stain to make it "look" like a log. You won't have to hollow anything this way either.

[Steve Demuth]

Personally, I don't think you can do what you're trying to do successfully, because of the carved inset where you're hanging the tubes on the outside. If you wanted a whole round log, then hollowing out the log and drying it as a tubular shell would work. But for that to work you need a reasonably uniform thin shell with the interior, small diameter growth rings completely removes, and your tiki head requires that no be the case. If I were given the project as a must do, I would try the following:

1. Commit to building it as a shell, as nearly as possible. That means, removing any wood you can to get the thicknesses down to less than 1" everywhere. It also means that the top and bottom will have to be "floating" inserts into the shell, not integral parts of the piece.

2. Split the log. Ideally, I'd actually split it, not saw it, but either way, get the log into two pieces.

3. Do all the hollowing implied by 1, above.

4. Dry the resulting form. It'll take months, if you air dry it, so if you're in a hurry, get a massive microwave, or build yourself a plastic mini kiln, but get the wood down to 6% moisture. The wood is going to crack to some degree in the face carving when you do this, but it's a tiki log head, so those cracks are just features.

5. When it's dry, build the pieces back together using internal backing hardware along the split. Use hardware with slots to allow for inevitable movement. Don't even try to close the strip completely, just tighten it up, and consider the remaining cracks to be features of the piece.

6. Fit the floating top and bottom pieces into rabbets in the log, preferably from a composite material (plywood). Attach only to one of the log halves, or if to both, be sure to attach with slots, to allow for movement.

It's going to move after construction, but all tiki heads do. The cracks are part of the piece.

[Bill Dufour]

12,500 years of proof that wood cracks over time. Not much you can do to stop it. I had never heard of this woodworking. I was looking for ancient Egypt stuff this is three times older.
Bill D.
https://www.smithsonianmag.com/smart-news/earliest-surviving-wood-sculpture-even-older-previously-thought-180977320/

[Tom Bender]

How does sound get out of this log? You must loose a lot of the highs.

As Steve suggests, make it a shell. The top and bottom are going to require some independence if they are going to be compatible with the constantly moving sides.

Put feet under it and leave the bottom open. I'm imagining carved feet but plain rubber feet from McMaster Carr will work. Leave the top open too and put a loose tabletop on it. That'll protect the electronics from spilled drinks and the top from beer can rings.

[Jim Becker]

How does sound get out of this log? You must loose a lot of the highs..
OP states they are installing the amplifier in the carved log, not speakers.

[Bill Dufour]

Still need to vent it to get the heat out.
Bill D

[Desmond Bowe]

thanks everyone for the replies.

At this point I've given up on my initial strategy of split the log -> hollow it out -> screw it back together. I love the suggestions for filling in the gaps with ears, bamboo, etc, but the wood movement makes it nigh impossible for fixturing screws to hold. At worst they crack and the piece is no longer disassemblable without major surgery. For the record, my bandsaw worked pretty well for slicing the logs.

Hollowing out the ends not only provides stability in the outer shell but also gives me more space to install the electronics; now I have the full 3 dimensional space of the cylinder instead of just one wall (pic attached). More and more it seems like an overall improvement.

I generally carve the face first because I don't know how deep I need to relieve the carvings. (This may not have been clear in my first post, but I have several of these amps and they all have different tiki carvings - the one shown was just one example.) Plus I need to cut out holes for the tube sockets and ensure there's enough clearance in the carving for the tubes to be inserted and removed. Perhaps one day I'll be proficient enough to plan everything in advance. Anyway, only after the carving is complete can I know how thick the walls are allowed to be, keeping in mind the walls may be different thicknesses around the circumference to allow for hardware mounting, etc.

After the carving I'll hog out most of the material with a Forstner bit, or perhaps a chainsaw.

Question: what is the tool this guy is using to clean up the edges of this log? https://youtu.be/N4YoxQSjNRc?t=123. Some kind of heavy duty chisel?

Removable top and bottom panels certainly make electronics installation easier. I'm toying with the idea of slicing a 1/4" veneer off the top before hollowing out and using it as a cover. The bottom will likely be a metal panel for mounting transformers. Both with have ventilation holes. I'm currently using rubber feet from Parts Express.

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[Cameron Wood]

Something like this:

https://stryicarvingtools.com/products/large-sculpture-chisel-7-profile-heavy-duty-gouges-wood-sculpture-carving-chisel-tool?variant=40439306649807&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&srsltid=AfmBOopUsVmVTGcBeCHbG5W2H8G8px2QPd01Te7-V0EUKHtuZtlNly3OwAw

[Desmond Bowe]

this is perfect, thank you!

[Maurice Mcmurry]

Cameron Wood has listed the tricks I know of in post #3. Cool Idea for an amp. It is very unique.

[Tom Bender]

You have a lot of stuff in there. Here's a suggestion to ease the crowding.

Carve the face then hollow out the log to a shell with no top or bottom. Make a top from plywood about an inch bigger all around. Paint it or cover it with leather or a grass skirt, something to look nice. Give it 3 ribs to hold it up 1/2" from the log and with stubs to keep it in place. 3 ribs to accommodate movement in the log, 1/2" for ventilation. From the lid hang a board to the bottom and as wide as the opening. Mount all your electronics on this. Just lift out for great access. Put a base on the components board so it will stand up when out. Allow wire slack.

[Desmond Bowe]

I'm a little confused at how the ribs and stubs work. I'm picturing three strips of wood, 1/2" deep and say 3/4" wide, running parallel to each other and evenly spread out underneath and running to the edges of the top. Do they fit into rabbets around the inner shell of the log? Which would make them taller than 1/2" to give proper ventilation clearance. I also don't see how the stubs fit into the picture - are they dowels that mount into the rabbets? Wouldn't such a fixed stub warp or crack as the shell moved?

[Jimmy Harris]

One problem you're going to run into is those tubes are gonna get hot. And that's going to quickly want to warp the front of the housing more than the rear. Your best bet is to carve the face, let it dry for a couple of years, then split it and hollow it out. I understand that's not really an option for you. So the next best bet would be to build a frame and mount the face to the frame to allow it to expand and contract. Then use the frame as the connection between the two halves so it can close properly. Or maybe ditch the back half altogether.

Is this a stereo, class A amp with an integrated preamplifier? That's what it looks like to me. Or is that preamp tube a phase inverter on a monoblock power amp or a dual cathodyne PI on a stereo power amp? I ask because if it has an integrated preamp, then with the wood housing and low voltage/high impedance signals in the preamp, you run the risk of picking up radio interference. It might not be an issue where you live, so it might not show up in tests, but if you relocate or sell it, it could become a huge problem, rendering the amp virtual useless. That's why most amps are made with grounded metal housings to create a faraday cage. If it's just a power amp, then grip stoppers and shielded (and grounded) wire are often enough to avoid the issue. So I would want to build that frame I previously suggested out of sheet metal. Then maybe thin out the wood a lot. If the wood is thin enough and attached to a metal support, the metal will likely keep it from warping too much on you. Of course, it'll crack easier, and being as heavy as it is (those OT's are huge!), it might be difficult to move without damage.

[Desmond Bowe]

It's a class AB push pull with integrated preamp. The bigger eye tube is a GZ34 rectifier and the top two nose tubes are 6SL7 dual triodes, similar to a 12AX7, but with larger glass bottles. The circuit is essentially https://diyaudioprojects.com/Schematics/Push-Pull-EL84-6BQ5-6V6-6AQ5-Dynaco-A-410-Tube-Amp-Schematic.htm with a preamp and volume control. So far radio interference hasn't been a big issue; all the signal wiring is shielded.

I'm going to try the hollow cylinder route for the next one. That should not only address the warping issue, but also allow me to install a metal cage on the interior of the log for additional RFI shielding. I'll start a thread in the Projects forum to chronicle the build.

[Jimmy Harris]

Ah. Yes, I didn't notice that the top two "big" tubes were slightly smaller. I thought you had 6 identical power tubes in the nose, and a rectifier and probably a 12AX7 or similar preamp tube in the eyes.

You can get away with just using shielded wire for everything instead of using a shielded enclosure. I've done that before on a true PTP amp. I had some noise issues to work out, but it was really simple circuit, so it wasn't impossible to track down. But it's quite a bit more difficult to pull that off on a turret or eyelet board, as you typically have more wires running everywhere and longer component leads to pick up RFI (and often a more complex design). On a PTP, you can keep your leads short and run shielded wire everywhere. It'll look like a bird's nest, but it can still sound great if you don't get too complex with the design. Since you're using the same shielded wire everywhere for everything, it can be difficult to track down problems versus color coded wire, as you have to manually trace each wire to know where it's actually connected. So minimalism wins here. But, I have a personal philosophy that amplifiers just sound better the less components you use, so I don't shy away from minimalism.

But one of the things I've learned with audio circuits is there can be a lot of philosophy and science behind them. But ultimately, it's your ears and experience that need to do the thinking. Sometimes problems will pop up that make no sense and shouldn't exist, but there they are. And sometimes all logic says you should be experiencing a problem, but for whatever reason, it's working anyway. There's a bit of voodoo involved with audio circuits that defies understanding. More than once I've run into an issue where every tube amp expert and EE I've talked to, said my problem was impossible to have, but there it was. And the fix made about as much sense as the problem, but it worked. So I try not to put too much stock into conventional wisdom and mathematics with this stuff, and focus on what my ears and scope are telling me.

I think you've got a really clever idea going on here, and your electronics look very nicely organized as well. I think it'll be worth it to run through a few "prototypes" to get the bugs worked out and really perfect this idea. And the metal frame and thinner wood should not only add stability and RFI protection, but also lighten the amp a bit. So I think you're on the right path. This will be fun to follow.