Metal or plastic to help the fit of turned box tops.....

[Doug Rasmussen]

Anyone who has turned wood boxes with fitted lids understands the problem. The top fits after turning, then a few months later it may not fit as nicely. Maybe too tight or loose.

My thought is to use metal or plastic rings as the contact surfaces between the base and top of boxes. They should stabilize the wood to prevent movement with humidity changes , etc. They wouldn't be a design element in the boxes and would be as unobtrusive to the design as possible. Some plastics are close to ebony in appearance so that might be better than metal.

This is not an original idea, I've seen boxes done this way. But, I've never heard the pros and cons from anyone who does this.

Any thoughts?

[Tim Boger]

I've used the threads from black or white PVC fittings on boxes that worked fine... don't know why you shouldn't want to take a piece off a pipe and turn the inside or outside to fit.

[Jamie Buxton]

I've used the threads from black or white PVC fittings on boxes that worked fine... don't know why you shouldn't want to take a piece off a pipe and turn the inside or outside to fit.

Don't those fittings use pipe-thread threads? That is, don't the threads taper? (The tapering on pipe threads ensures that the joint tightens up as you screw it together.) I'd think that you'd want non-tapering threads, so the lid itself determines when the lid is fully on, not the taper of the threads.

[Reed Gray]

Fact of life, wood moves... If you want to keep lids fitting correctly, as near as I can tell, there are two solutions. One is to keep them small, 1 1/4 inches or so. That way, wood movement is pretty minimal and even if the fit isn't perfect after moving, it is still close enough. Other choice is to use stabilized wood that is polymer impregnated. That keeps the wood from moving. Other than that, straight grained wood for over that 1 1/4 inch size, and friction fit lids. Even though it goes oval, the lid moves at the same rate so the fit is still good. Not sure if the PVC will over come the movement or not...

robo hippy

[Tim Boger]

Hey Jamie ... that's a good question, I've never considered it as a factor, if in fact the threads do taper.

I'm watching for someone else more plumbing smart than I to answer.

Don't those fittings use pipe-thread threads? That is, don't the threads taper? (The tapering on pipe threads ensures that the joint tightens up as you screw it together.) I'd think that you'd want non-tapering threads, so the lid itself determines when the lid is fully on, not the taper of the threads.

[Dwight Rutherford]

Black ABS fittings designed for drains have straight threads on the fittings. These are so the plug can be removed and replaced for cleaning or flushing. I use them for urns. Got the idea from Brad Adams (SF Bay Area ) turner.

[Doug Rasmussen]

Fact of life, wood moves... If you want to keep lids fitting correctly, as near as I can tell, there are two solutions. One is to keep them small, 1 1/4 inches or so. That way, wood movement is pretty minimal and even if the fit isn't perfect after moving, it is still close enough. Other choice is to use stabilized wood that is polymer impregnated. That keeps the wood from moving. Other than that, straight grained wood for over that 1 1/4 inch size, and friction fit lids. Even though it goes oval, the lid moves at the same rate so the fit is still good. Not sure if the PVC will over come the movement or not...

robo hippy

Okay, wood moves....

So what happens if you constrain that movement with metal or plastic? I wonder how forceful the tendency to oval-ness is?

[Doug Rasmussen]

Black ABS fittings designed for drains have straight threads on the fittings. These are so the plug can be removed and replaced for cleaning or flushing. I use them for urns. Got the idea from Brad Adams (SF Bay Area ) turner.

Have you noticed any long term problems with the ABS? Does the ABS constrain wood movement? Or, maybe the threads are loose enough to allow some wood movement?

[John K Jordan]

Fact of life, wood moves... If you want to keep lids fitting correctly, as near as I can tell, there are two solutions. One is to keep them small, 1 1/4 inches or so. That way, wood movement is pretty minimal and even if the fit isn't perfect after moving, it is still close enough. Other choice is to use stabilized wood that is polymer impregnated. That keeps the wood from moving. Other than that, straight grained wood for over that 1 1/4 inch size, and friction fit lids. Even though it goes oval, the lid moves at the same rate so the fit is still good. Not sure if the PVC will over come the movement or not...robo hippy

One thing I got from, I think, Raffan: when turning boxes with dry wood, turn the box to almost the finished size then leave it overnight. This lets any stresses in the wood. This is a good argument for keeping two chucks with the same jaws.

My favorite method is to not make suction tight lids. Woodturners like them to show off. People who use the boxes don't like them since it takes two hands to open the lid. A looser lid is less likely to bind with the seasons. In fact, lately I have been making tapered connections between the lid and box. This allows an easy fit, a snug fit, and no binding. This is especially important with Beads of Courage boxes that are sometimes opened by children with illnesses.

You might be able to see the taper on the mating surface in the upper left inset picture on the first one, basically a lidded bowl, face turned. The lid fits over the rim of the box. On the second box, the lid is inside and the contact surface is significantly tapered as seen at upper right. It is an end-grain box.

BOC_A_comp.jpg BOC_B_comp.jpg

I've seen PVC inserted into the wood, threaded and not. I have seen brass rings and sleeves on wooden boxes - that looks great.

For threads:
One way is to make the threads a little loose.

Another is to not use too many threads! A wooden box works Ok with just a couple of threads. Fewer threads, less likely to bind when moving.
I've seen PVC fittings for electrical conduit used, I don't know if the threads are tapered like pipe threads. I've seen people turn PVC rings and cut threads into them.


JKJ

[Roger Chandler]

I make a good number of lidded boxes, and seem to sell most every one I make. I remember hearing Stuart Batty say that the only people who like suction fit lids on boxes are the wood turners, and most of the time it is the ladies who purchase them, and if they pick one up and it takes two hands to get the lid off, they will most times set it back on the shelf. Having watched customers in one of the galleries I was in, I found Stuart's observations to be accurate, as I saw the same thing.

I try to make mine with a semi-loose fit, and usually have no problems. That being said, the first dozen or so I made became too tight with seasonal movement. Either kiln dried, or air dried wood to about 6-8% is what is needed for lidded boxes.

[Jamie Buxton]

Black ABS fittings designed for drains have straight threads on the fittings. These are so the plug can be removed and replaced for cleaning or flushing. I use them for urns. Got the idea from Brad Adams (SF Bay Area ) turner.

Hunh! I'd have guessed that they'd be tapered too. After all, you want clean-out plugs to seal too, don't you?

[Clint Baxter]

Hunh! I'd have guessed that they'd be tapered too. After all, you want clean-out plugs to seal too, don't you?

Trap adapters have straight threads while cleanouts, plugs and adapters that go from glue joint to threaded, (male or female), all have tapered threads.

I use use these on my urns and typically only use several threads from the fitting. This does allow the pieces to thread together until the wooden parts contact each other.

Clint.

[Leo Van Der Loo]

To the question of the tapered or straight threads, both exist and are used every day, straight threads rely on a soft washer or o-ring to seal, while tapered treads are to seal by the treads and compounds or teflon tape.

Straight pipe threads are NPSC (National Pipe Straight Coupling) and NPT for National Pipe tapered.

My thoughts on thin walled small boxes, if made from endgrain wood, the changing sizes from moisture changes will be the same on top and bottom parts of the box, the only problem could be, a very small oval change that can occur, so you can’t rotate the halves.

For boxes made of side-grain wood, changes will occur with moisture changes, if you are able to totally restrict this, there is a good chance that either the glue will fail or the wood split IMO.

[Geoff Whaling]

To the question of the tapered or straight threads, both exist and are used every day, straight threads rely on a soft washer or o-ring to seal, while tapered treads are to seal by the treads and compounds or teflon tape.

Straight pipe threads are NPSC (National Pipe Straight Coupling) and NPT for National Pipe tapered.

My thoughts on thin walled small boxes, if made from endgrain wood, the changing sizes from moisture changes will be the same on top and bottom parts of the box, the only problem could be, a very small oval change that can occur, so you can’t rotate the halves.

For boxes made of side-grain wood, changes will occur with moisture changes, if you are able to totally restrict this, there is a good chance that either the glue will fail or the wood split IMO.

Except that the wood movement is far more constrained on the lid/top than the opening in the base. The design of the lid is more like a "C" steel section where the horizontal top resists / modifies the wood movement relative to the amount of movement at the opening of the base - which has a constraining surface much further away.

I agree, purchasers like loose or what I call soft suction fits - the lid settles gently under its own weight as air is expelled and can be lifted off with one hand as the weight of the base of the lidded box is sufficient for it to stay put on the table surface.

[Lee Watermann]

I make a lot of boxes and learned to fit them loose. Roger, and others, has it right. Women love boxes and they want to remove the cover with one hand. If they move from there they will still most likely fit.
Cheers