It is taking me as long to fit a box top on or in its base as to make the rest of the box. Even taking my time and being patient (I don't have much of either) some of my box tops fall out of the base when held upside down and I have to pretend that's for easy one hand removal. I guess I could morph the bases into small cups, but I hate to throw the tops (or anything else) away. :)
There has to be a better way than cut & try, cut & try, cut & try, cut & overshoot! We can put a man on the moon, etc.
I know and have used several ways for making an accurate "pop fit', but all the methods that I know of end up with the sameole 'cutting & trying' and a miserable success rate.
I don't want to go to the moon, I just want a quick & easy way to fit box tops. What method do you accomplished Boxers find best to fit box tops so they don't fall out?
It's a simple fact: inside-fitting box lids are a problem to fit. In addition to going from too-tight to too-loose in a single cut, they take up space in the box and have a tendency (mine do, yours may be quite a bit better) to move less with humidity than the box itself, resulting over time in a beautiful, tightly-closed, hollow form. Outside-fitting lids, ala Raffin's, are quite a bit easier to adjust to a nice soft "pop!" fit, do not take up space in the box and, since they themselves are hollow, move nicely with the base of the box. As you can probably tell, I am a convert and very seldom turn in-fitting lid boxes any more.
But to answer your question, I'd rather have a loose lid than one I can't get off, so the few in-fitting lid boxes I turn have (slightly) loose fitting tops... for that much-appreciated, one-handed feature that I always point out. To hit the fit it without endless trial and error, I turn the top first, measure the flange with dividers, move the dividers IN a full turn, then transfer the measurement to the box. This gives me a (safe) line (circle actually) to hollow to, which is slightly smaller than what I need. It is then a simple matter of trail and error (more than twice and you are playing with it) to adjust for the (loose) fit I'm looking for.
There may be more sophisticated ways of doing this, possibly adapting Raffin's lid fitting technique. He holds the finished lid to the spinning taper of the mating surface, then burnishes a line on the taper which marks the diameter of the box lid flange, no measuring. Turning to that diameter gives a perfect fit, every time.
You could try treaded lids. The fit could be (and should be) a bit loose, but will still snug up when all the way on. Or go with a "snap lid" as described in the article in the recent "Woodturning Design" magazine.
Other than that...I know of no quick & easy way other that cut & try, etc. Sometimes ya get lucky and nail it in the first two or three tries..oter times it seems to take forever.
Maybe someone here will enlighten us both. Though...I remember a Clay Foster demo and he was fitting a lid and someone asked him pretty much the same question. He answer..."nope...no easy way".
I think that the best book on the subject is Raffin's and if you do boxes you ought to have it. The shape of the tenon (usually on the bottom with the mortise on the top) is important (slightly bellied in the middle). In boxes, organization of the work is important because it is not really possible to accurately rechuck a piece. Again, Raffin.
During the time I was doing boxes (not any more) I had no trouble getting a good fit in a short time via trial and error (the only way) AT HOME. Then I did a day in a store on a Jet
12" lathe and all the fits were, as you have said, too tight on one trial and too sloppy on the next.
The difference -- enough vibration and runout on the Jet to make a really thin cut impossible. At home I turn on a Stubby 750 and there is no vibration nor runout. Even small things go better on a big lathe, I think. I also sometimes do lace bobbins and they also go better on the Stubby than on smaller machines.
I use a locking vernier or dial caliper. You need one that when you lock it the inside and outside readings are the same. Some of the cheap ones are NOT!. Make your lid first and measure the recess with the calipers when it is finished. Now open the calipers another 1/32" inch or so and lock it. Forgot to mention that you need to round the ends of the jaws slightly that you use to measure outside diameters. Now that you have modified the calipers, use them and your parting tool to cut the tenon on the box. I make the tenon slightly oversize, so that I can fine tune the fit, or in case I get heavy handed with the parting tool. Also starting with the tenon a bit larger means that I can make it a very snug fit for the lid, so that I can finish turn the lid using light cuts. To size the tenon I taper it slightly so that the edge is smaller than the body, when the lid will just slip over the begining of the tenon, hold it lightly against the spinning wood and it will burnish a ring on the tenon at the correct diameter for a correct fit.
Lose is better than tight in dry season, tight better than loose in the rainy season.
I use a double taper, myself. The bottom tapers gently into the top, which still has witness marks from the parting tool to give me a starting point, and the top is tapered gently in at the bottom, to fit inside a deeper area outside the "tenon."
I do the lid, including sanding, before I begin the bottom. When the top of the tenon fits inside the bottom of the lid, I do my tapers. Good thing about it is if you get a little too loose, no sweat, because you're going to taper it to fit it in a tighter place at the last, anyway.
I'm not turning boxes much but the simplest way I have seen is to layout the wood giving room for the amount of lid and shoulder that will have to fit in PLUS a little for the parting tool (and a little more). Now turn the outside first, lid and body, make a groove between what will be the lid and the body, AS DEEP AS YOU WANT TO MAKE THE WALL THICK, and a little wider than the parting tool and the shoulder, sand and finish now if possible, then part the lid off, but LEAVE A SMALL SHOULDER ON THE BODY, hollow the box, do NOT take that shoulder off yet, sand inside if needed, now VERY CAREFULLY open up the opening till that shoulder is gone, and your lid should fit just right.
I turn a lot of boxes, and over the years have settled on a tenon on the box with the mortise in the lid. I watched videos from both Richard Raffin and Ray Key, but I got a better fit after taking a class with Alan Lacer at the local Woodcraft store. Here's what I do:
- Turn the inside of the lid, holding the outside with a chuck. I cut the mortise recess back to a slight dovetail - the rim at the base of the lid is the smallest diameter.
- Turn the outside of the box base holding the bottom with a chuck. I turn the outside to shape, and hollow and finish the inside before I fit the lid. (Someone told me that if you fit the lid first, and then hollow, removing all that interior mass may allow the shape to shift due to stresses in the wood.)
- With the base shaped and hollowed, I use a 3/8" beading and parting tool to cut the tenon at the top. (Allow for this recess when you hollow!) I cut the tenon at a slight taper towards the front, then test my fit with the mortise on the lid. If the tenon is still too big, I cut it back parallel to the ways of the lathe (this cylinder will still be too big to fit he mortise), then taper again towards the front. With a little care, I get a taper where the front fits into the mortise, but the base is still too large. I carefully cut the bottom of the taper back so the lid friction fits onto it. I turn the outside of the lid using only friction, so it has to be pretty tight. Them with the lid complete, I carefully sand the tenon back to get the fit I need.
All that said, remember: - wood expands when its hot. If you sand a lot, what fits tightly on the lathe, may be loose later in the house. - Only other turners care if the fit pops. Many of my customers tell me they want a lid they can lift with one hand, particularly for wider boxes. I don't want the lid to rattle, but a slightly looser fit often sells first.
How do Arch? I've learned to stop the fitting process before I get the fit I want. I'll explain how and why later.
With the tenon on the lower portion and the mortise on the lid, I cut and finish the lid first. Then trial fit the tenon to the morise. I sneak up on it and stop even if the lid is too tight. As long as it fits all the way on without undue (as in palm pounding persuasion or mallet) force, I'm done with the tenon on the lathe. I go about working the rest of the box to completion.
(When sneaking up on the tenon, I will make a superfine adjustment cut on only half of the outer end of the tenon. This gives me a reference as to how much I've removed (or left on the untouched portion) as well as an opportunity to test fit the lid without the risk of taking the entire tenon down. If the lid will mount on the smaller diameter portion of the tenon, I'll just pare down the untouched portion - if the lid still doesn't fit, I'll pare the untouched portion to the same level and trial fit the lid anyway just to be sure - and start the 1/2 paring process again. I start and stop the lathe a LOT during the process.)
After the whole thing rests for a couple hours I lap the lid to the base. Making up my own homaid lapping compound as such: I skillfully shape and build an aluminum foil tray. Then using two small sections of wet/dry 320 sand paper, I rub the grit faces together over the tray so that it catches the dust. Then mix in some furniture wax to make a small amount of slurry and spread a bit on the tenon and mortise. Working the lid on and off and twisting it in complete revolutions will, after a few minutes, yield a perfectly fit lid. You can stop at the suction-pop stage or else go just a bit further and stop at a fit that is a nice friction fit but won't allow the bottom to drop off if the box is is picked up by the lid.
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