Preferred thread size for 2-3” boxes

[Webb Willmott]

I would like to give it a try at threaded boxes. What would be your preferred thread size?

 

[John K Jordan]

I used 16tpi on the Baxter Thread Master for the Ebony boxes in the picture.



I also have 12tpi, 16tpi, and 20tpi hand thread chasers. 20tpi is almost too fine. 12tpi is pretty coarse, ok for larger things.

Some things about threaded boxes

• It's sometimes better to use fewer threads than more. It's nicer to twist a lid on with 2 turns than with 6.
• Hard, strong, fine-grained wood cuts cleaner than some softer and coarser grained wood.
• It can be tricky to calculate the diameters.
• Threading end-grain boxes is recommended. And from very dry wood.
• A different wood for the lid eliminates the effort of perfectly aligning the figure.
• If chasing threads, Mark StLeger recommended practicing on PVC pipe. Mark hand chases hollowed halves to make a clever baseball box. https://s3.amazonaws.com/cmwt.production/paperclip/files/145/StLeger.pdf?1328369689

JKJ

 

[john lucas]

I use 16 mostly fir bixes upnton2 1/2" orv3". I have courser threads i use on larger boxes. Allows me to make a looser thread to compensate for wood movement. 20 tpi is used on boxes ear rings under 1".

 

[Ed Jarvis]

John,
What is Ear ring on boxes under 1".

 

[Bill Blasic]

For a 1/4" threaded hole I have 24 tpi for my Baxter threaders. I have yet to try one of that size but do have the tooling to do so. My normal thread is 16 tpi but I do have 8", 10" and a few others for the Baxter Threaders.

 

[William Rogers]

Most wood turners seem to prefer 16 tpi threads. They look “prettier” than a say a 10 or 12 tpi thread. However I made two boxes one with 16 tpi and one 10 tpi. My wife didn’t like the 16 tpi saying it took too many turns to open. That of course is just one opinion. 10 tpi threads would be more robust in softer wood in my opinion. You didn’t say if you were considering a threading jig or hand chasing. I tried hand chasing and wasn’t successful most of the time and you need wood with a high hardness. 16 tpi threads are a little easer to hand chase than 12 tpi threads as the feed is not as fast. I made a threading jig (posted in the project forum) what I did. You can user soft or hard woods using a jig. I have been successful every time using my jig. I can do 8,10, and 16 tpi. Mostly I do 10 tpi as these threads seem to work well. Alan Batty’s video is a good resource and I use his sizing method for my threads.

View: https://www.youtube.com/watch?v=-0iEd0kD0S4&t=1363s

 

[robo hippy]

The advantage to the 16 tpi threaders is that when you are getting the grain to line up, you have to remove at most 1/16 inch of shoulder on the base. At least I always adjust the bottom of the box rather than the top. I don't make them more than about 1 1/2 inch diameter, mostly because there is the possibility of wood movement and not being able to get the lid off. One thing you can do, well should ALWAYS do is rough turn them first and let them sit for a month or six before you finish turn them. All woods "adjust" to having bulk removed....

robo hippy

 

[John K Jordan]

Alan Batty’s video is a good resource

Thanks for the reminder on that video - been a while since I watched it. I like the way he uses the hooked armrest tool to use a scraper on the end grain - much better than rotating the tool rest 90-deg for such operations!

JKJ

 

[John K Jordan]

One thing you can do, well should ALWAYS do is rough turn them first and let them sit for a month or six before you finish turn them. All woods "adjust" to having bulk removed....

The last part, "all woods adjust to having bulk removed" reminds me of the advice which I always follow - even when finish turning a well-dried roughed end-grain box I ALWAYS turn it almost the finial size then leave it in the chuck at least overnight, maybe longer, before truing up any stress relief movement in the wood, hopefully the last. It's not always there but I can often feel and see it.

Can't remember where I first heard this. From Raffan?

I do it for other turnings too. It sometimes amazes me how much internal stress can be in dry wood. Mounted a dry blank once and did the initial outside shaping. From the sharpening station I heard a loud "crack!" as the wood split from released stress. Even dry spindles blanks can harbor evil stresses - I encountered this earlier this week in a 14" spindle blank just over 1" square - showed itself overnight.

JKJ

 

[robo hippy]

I do tend to think that kiln dried woods have far more stress in them than air, vacuum kiln, or solar kiln woods have. Rip an air dried piece of wood on your table saw and you get shavings, same with vacuum and solar kiln dried wood. Kiln/kill dried wood, well, you get dust.

robo hippy

 

[Jeff Jackson]

I use 16 tpi up to 2 to 2 1/2", and 10 tpi for larger. For 16 tpi I add .040" to the tenon and .070" for 10 tpi. This ensures there's sufficient clearance for wood movement. I've lost count (over 200) of the number of threaded boxes I've done and this has always worked for me.

 

[Webb Willmott]

Sometimes a little CA is used on the threads near completion on softer woods. Curiosity has me asking if using some thin on the area to be threaded before starting the chasing would be a good idea.

 

[Doug Rasmussen]

When I built my threading jig years ago I found a very coarse thread like 4 tpi was a favorite with users. Just a turn or two to remove the top. Coarse threads can have a great deal more looseness to accommodate seasonal changes in fit.

Grain matching between base and lid was something I didn't care much about. Too much trouble having to be careful getting the lid just at the right tightness or looseness to grain match. Better IMO to use different woods or embellishment at the contact area to avoid the mismatched grain appearance.

I don't know why commercially made threading jigs only offer finer threads. Unscrewing a fine thread with many turns can drive you crazy although somebody told me it can increase the anticipation of what treasure might be in the box once the lid is off.

 

[John K Jordan]

Sometimes a little CA is used on the threads near completion on softer woods. Curiosity has me asking if using some thin on the area to be threaded before starting the chasing would be a good idea.

I haven't done that, but I do often use thin CA glue to strengthen wood fibers when threading the outside of a cylinder with a die or threading a drilled hole with a tap, sort of the same idea. Drill/turn hole or cylinder, add thin CA to the wood surface, tap, maybe add more CA then run tap again.

But it doesn't make much difference for hard, strong, fine-grained exotics like this Pink Flamewood:

That said, the CA doesn't matter too much for things like bottle stoppers since after tapping the wood I epoxy the stainless steel threads to the wood.

For hardware with fine threads that need to removed often, for example for cleaning or to swap with other hardware, I generally use brass inserts that cut into the wood.



I find the CA is especially helpful with softer wood or wood with coarser grain to keep the tips of the threads from crumbling, especially with coarse wood threads for like things threaded for the 1-1/4"x8 lathe spindle and custom wooden adapters to fit the 3/4"x10 Oneway-type live centers.



JKJ