Box Lid Fit Precision?

[Dan Bevilacqua]

I know that woodturning and the term "precision" really don't go well together due to the nature of wood movement. I don't sell my boxes, nor do I ever intend to do so. I don't want a loose fitting lid. I like a good suction or snap fit lid.

Currently, box making is my go to activity on the lathe. I enjoy the opportunity to make the lid fit as precise as possible. However, I realize that the precision of fit probably won't matter because the wood will move, some types more than others. Nevertheless, it gives me satisfaction to make an as "perfectly" round as possible lid to base fit (at least while on the lathe or for a few minutes after I take it off the lathe), I judge this by being able to twist the lid 360 degrees around on the base and the friction is the same all the way around.

I have attached photos of a single piece of maple that is approx. 1.5" x 1.5" (kiln dried). One photo shows tight grain while the other shows wider grain. When the box is rounded, of course, the tight grain and the wide grain alternate.

I have found, in my quest for "perfection" that the tighter grain is slightly deeper than the wider grain portions of the cylinder. In other words, if I lightly touch my tool rest against the wide grain and slowly rotate the spindle by hand the slight sound of the rubbing between the tool rest and the cylinder at the wide grain almost disappears when I get to the tight grain. What causes this variance?

We all try to line up the lid grain to the box grain. Usually, the fit is perfect when the lid and the box grain is lined up. I have noticed, especially when boxes have sat for a little time (some woods longer than others), if I try to turn the lid on the box, the fit will tighten and then loosen up as it rotates. In other words, when the lid tight grain matches up with the box wide grain, the fit is tighter than when all the grain lines up. What causes this variance?

 

[Richard Coers]

I just can't grasp what you are saying about tighter grain being slightly deeper. Anyway, trees grow faster in the spring and early summer. The cells are bigger and this is called the early growth. Then the growth slows and it's called late growth. All wood cellular construction is like a bundle of drinking straws. Early growth are "big straws", late growth is "small straws".

 

[Dan Bevilacqua]

Thanks, Richard. I was having trouble coming up with the correct word choice regarding "deeper". I was hoping the example with the tool rest would be helpful. By "deeper", I mean that when the circumference of the box is rotated (with my hand turning the handwheel of the spindle) against the tool rest, the "deeper" portion (tighter grain areas) is not touched by the tool rest as much as the portion of the box with the wider grain areas. Hope that was a better explanation .

 

[hockenbery]

Dan,

What you describe is consistent with the way wood shrinks as it dries.
The wide grain is the face grain side the close grain is the side grain.
The face grain side will shrink more than the side grain side.
This makes the face grain sides proud.

You can microwave your blanks to get rid of the moisture
Let the hollowed parts sit for a couple days before fitting the lids.

Fortunately the lids are press on pop off so they work when the grain is lined up.

 

[Dean Center]

I've found it hard to predict which box, when finished, will move after I'm done with it. All of the blanks I use for boxes are well aged and dry, but sometimes they still move. It may be that the blanks aren't as dry as they seem, or it may be that turning relieves stresses in the wood and the wood responds by relaxing or moving. Sometimes the change is oval and matches the grain in the way you describe, but sometimes it just gets tighter or looser all over.

For this reason, some of the forum posters here will turn the box to not quite complete and set it aside for a few days, then remount the box and complete it. I'm starting to do that, too.

The important point is that it's not YOU.

 

[Dan Bevilacqua]

...

...

The important point is that it's not YOU.

Thanks, Dean. The thought certainly did cross my mind a few times .

 

[john lucas]

We are turning by hand with hand held tools. You will never get it perfectly round like on a metal lathe with the tool clamped in the tool holder. In fact the wood won't stay perfectly round for even minutes due to stresses in the wood and wood movement. Here is what I do to make a really good fitting lid. Make the tenon and mating surface longer. It's the really close tolerance and air trying to escape that makes a lid feel really nice as you pull it off. This type of lid will take several seconds to fall off if you turn the vessel upside down but still feels really smooth when you try to pull the lid off. I do this on my pill boxes which are long and skinny. Of course I have almost no wood movement on this type of box that is only 3/4" or less in diameter. I have experimented with this on boxes up to about 2 1/2" and it still works. A tenon of about 1/2" works really well.
Or you can go to the snap fit lids that Richard Raffen demos. These actually have a small indentation at the bottom of the tenon and small protrusion on the female half so they snap together when the lid is fully closed.

 

[Mike Johnson]

It helps to rough turn the box and lid and let them dry for several days and "relax" and then finish turning to get a nice tight fit. Any time you hollow out a wood billet you are relieving internal stress inside the wood which will alter the shape slightly as the wood "relaxes" and also dries if it has moisture.

 

[robo hippy]

I would like to see the type of boxes you are turning as that can make a big difference. The straight grain woods make for the easiest to turn, make a recess, and tenon, and then they fit together and the grain can line up. If the grain is all over the place, then you need to use a thin parting tool to part the lid off of the body, then turn a collar for making the tenon part of the box. I prefer a contrasting wood. For me, the best fit is the flutter type. This involves making a tenon that is about 1/2 inch long, or longer, and both the tenon and recess have to be spot on parallel. You make the lid first, and cut the recess. I use a 6 inch steel ruler against the recess and then eyeball it against the ways of the lathe to see how perfectly straight it is. I do use a modified scraper with a long straight on the side do I can make a long straight recess. Almost impossible to do with a gouge or even a skew. Note here, with skew, you have to have tool rest and tool above center rather than at center. When at center, you have the square peg in a round hole and can't get up against the wood where when above center, you can do that. After that, then you turn the tenon. I always start with it tapering, and even doing a 45 bevel cut on the top of the tenon. Mostly to prevent making it too small. Get the top of the tenon to fit first, then trim it down till it is parallel. Some times I use the steel ruler to get a better view, but most of the time, I can eyeball it against the ways of the lathe. I use a NRS or a skew to trim the tenon to fit. The difference between a snug fit that you have to pull off, and a fit where you pick it up by the lid and it takes 2 or 3 seconds to fall off is about one trip around the tenon with 400 grit sand paper. You really have to sneak up on the fit very carefully.

As others have already said, rough turn them first and let them 'adjust' to having the bulk removed. With bigger boxes, they have to be made from the same piece of wood. The wood will move, but if both the top and the bottom are made from the same piece of wood, then even when (not if) it moves, you may not be able to spin the lid all the way around, but you can still lift it off. Things that can really change the fit of the lid: leaving it outside in an unheated shop. It is pretty humid here in the winter. I gave a box with a 'perfect' fit, to a young woman who is getting into pyrography, and she left it out in the garage which was not heated. The wood moved to the point where the lid was difficult to remove. Sanding probably helped it, but bringing it back into the house did not. I had one that fell off the table in my booth and sat on the ground for the weekend before I found it again. I was able to get the lid off, but it was difficult, and this one was threaded. Not sure if a short burst in the microwave, or by a light bulb would shrink it back to size or not....

There are some 'snap' fit boxes. Most of the time the customers pick them up, put a little effort into removing the lid, and when it resists, they put it back on the table. The only one I saw that I liked was a 'clam shell' box from Ray Key. Not very tall, maybe 1 to 1 1/2 inch, and where the tenon and recess fit together, they formed a half round cove that you got your fingers into to pry the sections apart. I believe that the tenon and recess were tapered slightly rather than parallel. Some do prefer this type of fit.

Hope to have a video or three out later this summer.....

robo hippy

 

[Dan Bevilacqua]

Thanks for the all the very informative responses. I will certainly attempt to do what has been suggested.

Al's (hockenbery) response led me to do further research. If I understand correctly, the wider grain is referenced "tangential" while the narrower grain is referenced "radial". It appears that there is a difference of movement between tangential and radial grain which may then account for the my experience that when I twist the lid on the box it gets tighter when the radial and tangential grain does not match up.

I guess the difference in movement might also have some effect on why I am experiencing the radial grain having a slight difference in diameter (smaller) from the tangential grain??

PS: Robo, I look forward to the upcoming videos you reference.

 

[robo hippy]

Oh, forgot, some use calipers or micrometers, to see just how parallel the tenon and recess sides are. I found the short steel rule to be far more accurate for the longer tenons, but on a 1/4 inch tenon, they are adequate.

robo hippy

 

[Dan Bevilacqua]

I would like to see the type of boxes you are turning as that can make a big difference. The straight grain woods make for the easiest to turn, make a recess, and tenon, and then they fit together and the grain can line up. ...

...

...

Hope to have a video or three out later this summer.....

robo hippy

Here are two photos of a box turned the same wood blank as shown in the first post above. I did not sand or finish the box since I was mostly turning to try to understand the wood grain. It started out as a square a little less than 1.5" x 1.5" of maple (kiln dried). However, many of my boxes start out about 2" square. I have much more trouble with movement with this wood than I do with my kiln dried 2" cherry. The tenon is on the base, although I have done some with the tenon on the lid

The photos show the lid grain aligned with the box grain (radial and tangential) and when I twist the lid where the grain does not match up, the fit becomes tighter.

Thanks.

 

[Bill Boehme]

Thanks for the all the very informative responses. I will certainly attempt to do what has been suggested.

Al's (hockenbery) response led me to do further research. If I understand correctly, the wider grain is referenced "tangential" while the narrower grain is referenced "radial". It appears that there is a difference of movement between tangential and radial grain which may then account for the my experience that when I twist the lid on the box it gets tighter when the radial and tangential grain does not match up.

I guess the difference in movement might also have some effect on why I am experiencing the radial grain having a slight difference in diameter (smaller) from the tangential grain??

PS: Robo, I look forward to the upcoming videos you reference.

It sounds like you are making boxes with face grain orientation of the wood (grain direction perpendicular to the spin axis). If you are wanting the lid to have a suction it would be better to turn the box in spindle orientation (grain direction parallel to spin axis).

If I understand your description correctly what you are calling "wide grain" is called side grain and what you are calling "tight grain" is called end grain. The trouble with turning a box in that orientation and trying to get a perfect suction fit with the lid is that the shape will always go oval. This is due to the effect of humidity on wood movement along the grain direction versus movement in the cross grain direction.

If you turn a box in spindle (AKA end grain) orientation the wood movement will be uniform all the way around the rim and the warping will be substantially less.

While turning a box with a snug fitting top is a great skill challenge, most people prefer a box with with a lid that doesn't produce a pop when opened.

EDIT: I see from the pictures that you just posted that the box is face gain orientation so the grain direction is perpendicular to the spin axis so you are experiencing the differential movement that I described. That will always be a problem if you want a snug fit.

 

[Dan Bevilacqua]

Thanks, Bill. However, I am in fact turning my boxes with end grain orientation parallel to the bedways. Occasionally, I will turn one with the orientation like a bowl (face grain). Yes, those have much more movement. Is my interpretation in my post that you quoted incorrect?

 

[Bill Boehme]

The box in post #12 above is face grain orientation, not end grain. You might be mistaking growth rings with grain direction.

 

[Dan Bevilacqua]

The box in post #12 above is face grain orientation, not end grain. You might be mistaking growth rings with grain direction.

I thought I had it figured out to some degree . But I thought end grain turning was with the grain running parallel to the spindle and bed ways. I must be missing something because I have no doubt that the box in the photos was turned end grain parallel to the spindle and bed ways . The piece was about 1.5 inches square when I started as shown in the photos in post # 1. The piece was oriented length wise in the chuck and was about 5 inches long with the end grain facing the spindle end and the tail stock end. Please help me with my confusion.

 

[hockenbery]

I think the box above looks to be hollowed through the end grain.
It is sometimes difficult to tell the sidegrain and endgrain apart.
I see that all the time when turning spheres. With there best guess works.

The endgrain does not show rays,

The ovals ar efface grain, the rays are side grain
That leaves the endgrain for the hollowing.

 

[Bill Boehme]

Al convinced me that you are correct, Dan. It should have occurred to me that there would be a pith in the middle of the ovals if it were side grain. I'll go put on my dunce cap.

 

[Dan Bevilacqua]

Bill, it was not a matter of whether I was correct. It was more of a matter of whether I was still confused .

 

[Bill Boehme]

I think that I was the one who was confused.

 

[robo hippy]

Years ago I saw a side/bowl grain box that Kip Christenson turned, maybe 3 inch diameter, and the lid fit was still perfect. No idea how that was possible. I have found with boxes, that I can get a 'perfect' fit lid, and that after sanding and finishing, it will have moved, but it seems to go back over night. Wood has more idiot-syncracies than I do.....

Dan, is the tenon on the lid? That would be the typical box that Chris Stott turned for his 5 minute box. I have been playing with them since it was pointed out to me a while back that maybe if I had turned as many boxes as I had bowls, I could turn a box as fast as Chris.... For that one, I turn lid details, and the tenon. I make the full sized tenon at 3/8 inch wide, which is just perfect for a sizing/peeling/bit parting tool I have. I eyeball the tenon against the ways of the lathe to keep it parallel. When you part it off, you leave a tiny bit of it on the box side, which gives you a mark for the inside of the box.You still have to sneak up on it very carefully....

robo hippy

 

[Dan Bevilacqua]

Robo, the tenon is on the base, although I have made some with the tenon on the lid. The lid is hollowed to a minor degree. Most of the ones I make have more of a delineation between the lid and base such as a bead and/or a groove. This one was just one I was playing with to see about the grain issues I talked about in the original post.

I did make one about a month ago that was face grain turned about 4" in diameter with the tenon on the lid. It is made of Aspen. Much to my surprise, the fit is still very good.

 

[john lucas]

When I saw Chris Stott he turned a box in 1 minute. We started the demo and he said OK anybody got a watch lets get this over with and then he proceeded to turn a box like described by Reed in 1 minute. Blew my mind. I'm too picky I guess but I spend longer than that just trying to clean up the inside to reduce my sanding, and that's after hollowing. Still his point was, he could make boxes fast enough to sell at a low enough price point that he made more money selling those than he did larger things like bowls and platters.

 

[robo hippy]

Is Chris still around? I thought it was a 5 minute box, but that may have been because he was talking while turning, still pretty fast.

robo hippy

 

[Dan Bevilacqua]

Another question arises for me related to this thread.

Can chuck runout cause the spigot of a box to be out of round?

I seem to recall a post explaining that even if there is runout of the chuck and/or spindle, that the tenon will always still be round because of the wood turning on the axis, or something like that. I could be wrong; but, if I am on the right track or not, could anyone please explain and elaborate upon this.

 

[Dean Center]

Dan, I'm not sure I understand your question. Can you please restate it?

Assuming the box is turned end grain, as is usual for boxes, and the wood is truly dry, the tenon should not go out of round, except for the possible internal wood stresses which might be released as the box is hollowed. The latter effect would be pretty small on a typical end grain tenon, in my experience.

 

[Dan Bevilacqua]

Dean, I have done some research since posting yesterday. What I was trying to understand, and was having difficulty phrasing, was that even if the chuck and or spindle has runout, the object being turned would not follow the runout; rather, it would be round (no runout) because it would be turning on the axis of the center of the spindle. I hope this was more clear.

I think I may kinda understand it now; however, I still am having difficulty grasping the concept. For some reason, I have it in my mind that chuck and /or spindle runout will result in runout (out of roundness) of the object being turned. I'm having difficulty envisioning this "axis" concept.

Of course, further elaboration and examples might help me understand it more, and get my mindset correct.

 

[John Jordan]

Another question arises for me related to this thread.

Can chuck runout cause the spigot of a box to be out of round?

I seem to recall a post explaining that even if there is runout of the chuck and/or spindle, that the tenon will always still be round because of the wood turning on the axis, or something like that. I could be wrong; but, if I am on the right track or not, could anyone please explain and elaborate upon this.

Chuck runout cannot result in out of round work. The spindle spins on a single axis-doesn't matter if the spindle or chuck wobbles-unless you are mounting/remounting. Its hard to put something back in exactly the same place.

John

 

[Dan Bevilacqua]

For further clarification, the correct word I am looking looking for to replace the phrase "out of round" is "eccentric".

So the question is, why would a chuck and/or spindle that is eccentric, not affect the turned box flange and create corresponding eccentricity in the box flange? For example, if the chuck and/or spindle is eccentric by .004" (random #), then why would the box flange not also be .004" eccentric?

 

[Dan Bevilacqua]

Chuck runout cannot result in out of round work. The spindle spins on a single axis-doesn't matter if the spindle or chuck wobbles-unless you are mounting/remounting. Its hard to put something back in exactly the same place.

John

Thank you, John. Looks like your response was posted while I was writing my further clarification. I understand your response. However, I am having difficulty grasping the concept.

 

[Dennis J Gooding]

Thank you, John. Looks like your response was posted while I was writing my further clarification. I understand your response. However, I am having difficulty grasping the concept.

Dan, try this thought experiment. You have turned a perfectly round cylinder between centers with a perfectly round chucking tenon on one end. Then you chuck it carefully in a chuck that is off-centered; that is, it holds the center of the cylinder a bit to one side of the spin axis of the lathe. If you now bring up the live center you will find that its point does not quite meet the old center mark on the cylinder. If you rotate the wood you will see the old center mark rotate around the live center point. Now, bring up the tool rest and with the lathe turning slowly hold a pencil against the end face of the cylinder and scribe the largest circle that will fit. You will find that part of one side of the cylinder does not fit in the circle. If you then proceeded to turn the cylinder down to eliminate the overhang, you will find that you have a true cylinder, although a bit smaller than the original.

 

[Bill Boehme]

Thank you, John. Looks like your response was posted while I was writing my further clarification. I understand your response. However, I am having difficulty grasping the concept.

If you do any multi-axis turning the concept will become clear. A chuck, drive center, or faceplate is merely holding the wood ... it's the lathe spin axis alone that determines how the wood rotates.

 

[Dan Bevilacqua]

If you do any multi-axis turning the concept will become clear. A chuck, drive center, or faceplate is merely holding the wood ... it's the lathe spin axis alone that determines how the wood rotates.

Does "spin axis" have anything to do with spindle runout (eccentricity)? I'm feeling kinda dense here for not being able to grasp the concept .

 

[Bill Boehme]

Does "spin axis" have anything to do with spindle runout (eccentricity)? I'm feeling kinda dense here for not being able to grasp the concept .

No. I suppose that by spindle runout you mean something akin to the nose of the spindle being bent. The axis of rotation is determined by a line that passes through the center of the two headstock bearings. Since the radial play in a bearing is essentially nil unless the bearing is completely shot and that the two bearings are usually several inches apart and that we're not making parts for the International Space Station, for all practical purposes the spin axis is rigid. There are other things that can move such as the headstock if it isn't firmly locked.

 

[Dan Bevilacqua]

Thanks, Bill. I think I might be understanding it. The axis of rotation or spin axis is an imaginary line that goes right through the center of the spindle morse taper?? Is that correct?

If so, then regardless of what the outside of the spindle is doing (running eccentric), the imaginary line through the center of the spindle morse taper (spin axis) remains centered and governs the object being turned so that it is turned concentric?? Is that correct?

Edit: Bill, when I refer to spindle runout, I am referring to putting a dial indicator on the circumference of the spindle, and any movement of the indicator as the spindle is rotated by the hand wheel would be runout (eccentricity). I guess that would be "something akin to the nose of the spindle being bent."

 

[Bill Boehme]

Thanks, Bill. I think I might be understanding it. The axis of rotation or spin axis is an imaginary line that goes right through the center of the spindle morse taper?? Is that correct?

If so, then regardless of what the outside of the spindle is doing (running eccentric), the imaginary line through the center of the spindle morse taper (spin axis) remains centered and governs the object being turned so that it is turned concentric?? Is that correct?

Edit: Bill, when I refer to spindle runout, I am referring to putting a dial indicator on the circumference of the spindle, and any movement of the indicator as the spindle is rotated by the hand wheel would be runout (eccentricity). I guess that would be "something akin to the nose of the spindle being bent."

I think that you understand. Just to make sure, suppose we have a cheapo faceplate made by welding a big washer to a nut, but I'm not a good welder so the washer is tilted and not centered. Now we fasten a rough lump of wood to the faceplate and proceed to turn it round, it should be clear that despite what is used to hold the wood the shape that we turn will be symmetric about the lathe axis of rotation. Next, suppose we chuck up a square piece of wood so that the corners of the square are between the jaws. Then we proceed to turn a cylinder. Whatever problems the chuck might have, we will have a cylinder that rotates about the lathe axis of rotation. Next, let's turn a tenon and shoulder on the far end of this cylinder that just happens to be the perfect circle diameter of the chuck jaws. Now let's remove the cylinder from the chuck, swap ends, and chuck this nice perfect circle diameter tenon in the chuck. Turn the lathe on and ... &%$@*! The cylinder isn't running perfectly true ... why? No scroll chuck is absolutely perfect and woodturning scroll chucks have to strike a balance between cost and precision. There's another lesson to be learned here ... if you have to remove a turning from the chuck temporarily then mark the jaw positions next to the tenon so that it can be reinstalled as closely as possible to where it was previously.

 

[Dan Bevilacqua]

Thanks again, Bill. One more question, please. Is there anything that can cause the axis of rotation to be out? I would not think so, short of a significantly bent spindle which would result in so much runout (eccentricity) of the spindle that you wouldn't need a dial indicator to see it. Is this correct, for my final test of whether I do indeed understand?

 

[Bill Boehme]

Thanks again, Bill. One more question, please. Is there anything that can cause the axis of rotation to be out? I would not think so, short of a significantly bent spindle which would result in so much runout (eccentricity) of the spindle that you wouldn't need a dial indicator to see it. Is this correct, for my final test of whether I do indeed understand?

No. Just as my example with the lopsided home made faceplate tried to illustrate, the axis of rotation is completely independent of anything that leads to off axis mounting.

Back to multi axis turning ... if you had an Escoulen eccentric chuck, it changes the angular orientation of the wood, but when you start cutting after the angle has been changed-you are still cutting about the same axis of rotation. The only thing different is that the wood has been repositioned.

 

[Dan Bevilacqua]

Darn, I thought I had it figured out. So what, if anything, can cause the axis of rotation to be off?

 

[Bill Boehme]

Darn, I thought I had it figured out. So what, if anything, can cause the axis of rotation to be off?

Nothing. Well, if the balls fall out of the bearings, but then that is outside the scope of normal operation.