Threaded lid box making....

[Doug Rasmussen]

Here's a little sequence of pictures showing how I make various size boxes in production, 3" diameter in this case. CNC milling machine and CNC lathe being used.

First pic shows the blank being routed to fit the expanding lathe collet in the foreground, 1-3/4" diameter.

Next, the blank is being turned to size in the lathe while held on the expanding collet.

Next, the turned blank is back on the milling machine held in a 3" collet for the thread to be cut.

Same was done for the lid, routed for the expanding collet and turned to diameter, shown here being internally threaded.

Next, the semi finished base and top. Note the base on the left has not been routed to full inside diameter. It has to go back to the lathe for the bottom recess to be cut (forgot to do it when it was first on the lathe.

Last pic shows them screwed together. Single turn to full closed.

The box isn't finished yet though. The top will be domed and could be embellished with a routed design or pyrography with the laser. Likewise the base could be embellished in some way too.

The wood here came from a lumber salvage yard. It's part of a crate that Boeing gets aircraft parts shipped in. It looks like what I would say is Philippine mahogany except much heavier and denser than any I've seen.


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[john lucas]

Very interesting. I do the same thing by hand for turning the box but then remove the chuck and transfer it over to my home made lathe that has a router for the headstock. I do the threading on that with my Baxter threader and then put it back on the lathe to finish the box and do any detailing. I will be making a threaded ornament today using that technique and will post photos later.

 

[robo hippy]

I won't make threaded boxes over about 1 1/4 inch diameter, well, not any more. Went to a show from here in Western Oregon, down to Davis, CA in the Sacramento Valley. Had some up to about 2 inch diameter. At least I could still get the lids off...... I have been starting a box making binge lately while getting settled into the new shop. There was a thread a while back about boxes and I commented about how time consuming they are. Did a couple of the Chris Stott style boxes and went 'Hmmmm'. A few of the 'flutter' lid types, and others. It is another video I always wanted to do... Maybe if I turn as many boxes as I have bowls, I will get efficient at them... They are fun.

robo hippy

 

[Doug Rasmussen]

Robo wrote " At least I could still get the lids off.."

I'm assuming by the above you mean there was enough wood movement that getting lids off easily could become questionable. That's the reason I decided to go with a "bottle" thread profile. They can tolerant way more of a loose initial fit than a 60 degree thread and the lid will still center nicely at final tightening.

The picture shows a 2" diameter white oak box made from a piece of not-totally dry firewood. You can't see it here, the lid developed a crack after a few months which made the lid slightly out of round.

The picture shows the looseness of the threads, As shown the lid is almost half a full turn screwed on. Another half turn and it'd be centered and tight.

I do these on a CNC because i have the machine and it does it easily. Bottle threads could be done an a jig similar to conventional threading jigs with a more complicated mechanism. It'd be expensive and slower to cut the threads. And I'm not sure there's a market.

 

[robo hippy]

Doug, I had to ponder this for a day or so.... So by 'bottle thread' I am guessing a more blunt angle rather than a sharper one? How many tpi are you using? I go with 16 tpi so when I go to time the threads/line up the grain, at most, well most of the time, I only have to adjust the shoulder 1/16 inch. Looking at that box picture, my first guess would be that the threads on lid and box were not parallel. I have seen that a number of times by turners who think it isn't necessary to have the surfaces parallel before you cut the threads because the cutter will fix it. The problem I experienced with my boxes was from them going oval to the point where the movement seemed to be the culprit rather than the fineness of the threads, but now I am wondering... I have considered trying to get some sort of x/y sled cutter for my mini lathe for cutting the tenon and recess on boxes to eliminate the multiple cuts needed to get the tenon and recess parallel. I have an old Bonnie Klein jig for cutting my threads, and took a 3 day work shop with her in Salem some years back. I did like the idea she used of having a 6 inch ruler to line up with the ways rather than just guessing or eyeballing. Have lots of experimenting to do still....

I will be headed to Salem next week because the Box Master guy will be there for a demo. He is going to be taking over for Dave Schweitzer, and I want to see his tricks.

robo hippy

 

[Doug Rasmussen]

robo, this might answer your questions.

A bottle thread is just that, the type of thread used for bottles/jars. Check your refrigerator for condiment jars to see exactly. The whole idea for me is to have a loose initial fit allowing quite a bit of wood movement before thread jamming. Plus I like a single turn to full tightness.

The 4 tpi threads are parallel and the mating contact surfaces are cut parallel (perpendicular) with respect to the threads at the same time.

From the cross section diagram below, there's quite a bit of looseness before the threads contact and pull the lid down onto the base. The looseness is what you're seeing in the previously posted picture. The threads contact only on a point so they self center the lid to the base without much friction that can prevent accurate self centering on 60 degree threads.

I do the threads on CNC, mainly because I have the machines. The whole boxes with threads could be done on the relatively inexpensive CNC routers like Rockler and Woodcraft sell. Thinking about it these could be done on jigs similar to your Bonnie Klein version. Use a double round over router bit to cut the thread profiles, you'd need a coarser tpi than is usually available on threading jigs though. There would need to be some hand clean out where the router couldn't completely finish.

 

[robo hippy]

Well, not sure how you do it, but being used to the 16 tpi threads, in order to time the threads and grain lines, at most I have to trim the shoulder 1/16 inch. I figured out how to use the ruler from a tri square as a spacer block between the cutter and the wood, and a pencil register line on lid and base. Start lid with line at 12 o'clock, and slide up to spacer distance between lid and cutter. For the bottom, start with the register mark at about 7 minutes before 12, and I get just a tiny adjustment to the shoulder to get the grain timed.

robo hippy

 

[Doug Rasmussen]

Well, not sure how you do it, but being used to the 16 tpi threads, in order to time the threads and grain lines, at most I have to trim the shoulder 1/16 inch. I figured out how to use the ruler from a tri square as a spacer block between the cutter and the wood, and a pencil register line on lid and base. Start lid with line at 12 o'clock, and slide up to spacer distance between lid and cutter. For the bottom, start with the register mark at about 7 minutes before 12, and I get just a tiny adjustment to the shoulder to get the grain timed.

robo hippy

One of these days i'll try to align the grain lines. Other than the two boxes I've posted which have noticeable grain I'd rather not deal with that issue by using not so grainy wood. Or embellish the piece to the extent grain is a minor issue.

It shouldn't be difficult to align the grain. Maybe cut the threads, screw them, together measure the angle until they align and remove a calculated amount. But being a single turn you might get into a situation you couldn't align because of the single turn closure.

 

[hockenbery]

Aligning grain has two two components the wood removed between aligning sections and the closed position of the box lid and bottom.

Straight grain can allow more wood to be removed befor the misalignment becomes notice able.

Threaded boxes use at least a 1/4 inch of wood an more likely 3/8. Any grain lines not parallel to the ways or one that change thickness in this 3/8” will never match.

For the best alignment thin bandsaw kerf to separate the parts and some type of insert to fit the lid.
A matching wood is hardly noticeable. It is also a lot of work to make the insert. It can be cut off the piece that eventually becomes the top.

 

[robo hippy]

I have a small lilac branch that I have been waiting to turn into a lidded box. I will have to add a collar to the inside so the bark matches at least a little bit. I don't think there is an easy way to make the collar. For sure, sides have to be dead on parallel... Same process for burl.

robo hippy

 

[john lucas]

If I use an insert, which I do occasionally on wood that needs the tiniest kerf,I often make it out of contrasting wood. I have also made several boxes with epoxy for the insert and/or threads. I cut a groove on both halves of the box. Fill it with epoxy that I will sometimes color and sometimes leave clear. On the male half I wrap tape around the box and then fill the kerf as well as the tape so I have the epoxy proud enough to cut the male threads. this way I can make my kerf as thin as my thinnest parting tool. If I can find one of those I'll post a photo but they may have all been sold.

 

[Bill Boehme]

You can make threaded inserts out of Corian. It is easy to turn and threads nicely. You can often get sink cut-outs for free from companies that install countertops. Typical thickness is ½".