Tsuka shrinkage

[jezah81]

Hi guys,

 

My friend received his first mumei wakizashi in shirasaya a few weeks back. What he noticed was the tsuka was completely loose, but after a few weeks of being in his room, the tsuka was almost impossible to get off, without a few hard hits with his wrist. I was always under the impression that the cold winter time wood shrink the wooden tsuka core thus causing it to become looser, not tighter. Here in Australia it is winter time, where in Japan at the moment is summer. Has anyone else experienced this problem, where the tsuka gets loose in summer and tighter in winter, i thought it was the other way around. Any explanations how this occurs..??? Does this mean when it is summer time here in Australia that the tsuka will become loose again?

 

Kind Regards,

 

Jeremy Hagop

 

Jeremy Hagop

[Jean]

Hi Jeremy,

 

It is a very interesting topic. I have never experienced this problem living in Paris, but I would like NM members opinion :

 

- Humidity/Dampness makes wood swell, I remember that wooden barrels were filled with water till wood will swell and the barrels watertight

 

- Dryness ===> wood shrinks

 

Too much humidity : difficulty to withdraw the tsuka beware of rust

Too dry : be carefuul because the blade is loose in the tsuka.

 

I would advise a dampness regulator machine (I dont know if it exists)

 

Here in Paris, we have (generally) a very dry atmosphere in our flats, it has adnatages and drawbacks :

 

- Advantages : I never oil my blades

- Drawbacks : I have to put some bowls of water because of my 19th century mahogany furniture which has a tendancy to crack ....

[Eric H]

Hi Jeremy

 

I have best experience with "The tools for tight handle" form USAGIYA Sword Shop. You will be surprised how easily the tsuka comes off.

 

http://www.ksky.ne.jp./~sumie99/

 

Eric

[Grey Doffin]

Sorry, you have it backwards. Wood shrinks when humidity drops and if a tsuka shrinks it will be tighter on the nakago. Thus a sword coming from humid Japan to dry winter will experience tightening of the tsuka, and saya on the habaki. This should reverse next summer. Over time, the wood will shrink a bit more than it rebounds, although if the wood was properly seasoned before the shira-saya was made this shouldn't be by much.

By the way, the movement is only in 2 dimensions: thickness and width. The length doesn't change more than the tiniest bit.

Grey, a furniture maker who lives where it gets bone dry in the winter and humid in the summer.

[Bungo]

same problem here.......sometimes the tsuka ( shira saya ) get so tight, i can't remove it, then seaonal change and it's loose.....

since I don't look at swords that often, I can't recall whether it's tight in Winter or Summer.

So......... I left out the tsuka, problem solved ( I keep them all in silk bags )

 

milt the ronin

[Deron Douglas]

I find mine are tighter in the winter. Living in Canada we have the heat on and it dry the air out, which dry up the wood and makes it shrink. Usually loosens up in the spring when the heat is off and the windows are open.

 

Deron

[Ken-Hawaii]

I guess I'm lucky that I live in Hawaii where the temperature & humidity almost never change. :D My son (a meteorologist) recently moved his family out here, & has been commenting that there's only a few degrees difference between July & December temperatures (less than five). And virtually no change in humidity.

 

Jean, I use a Golden Rod dehumidifier (http://www.dealerease.net/catalog/product.asp?pid=5506&ret_id=139995) in my safes & especially in my Nihonto case. It does a great job of keeping the humidity down around 12%, while the ambient humidity averages 55%.

 

I've obviously never had any problems with things drying out here, but when I lived in Laramie, Wyoming (elevation 7200 feet), almost all the wood items I had shrank & cracked. There were times when I couldn't pull my iaito from its saya!

 

Jeremy, you might have your friend put his sword into a water-tight box with a small amount of water in a bowl; that should loosen things up. But of course be sure that he has first oiled everything he can reach!

[nagamaki - Franco]

If possible, whenever having a shirasaya made talk to the sayaishi about the conditions in your area before hand. Sometimes adjustments are still needed afterwards. Come early winter check the habaki fit into the saya and nakago into the tsuka. For example, here in the NE US, the habaki needs to be about 1/3 of the way out come November, or else it's see you again in the spring.

 

One problem is if it is allowed to get too tight, eventually the saya might split.

[jezah81]

Thanks for the replies fellas. FWIW, i remember back in 2004, i sent my carbon steel blade that i used to use for iaido practise, to get it re-shimmed by Rick Polland. It was June, thus summer time in the US and winter time in Australia. When he received my sword he couldnt find any looseness in the tsuka, so I remember him having to put the tsuka in the refrigirator overnight to loosen the tsuka in order to reshim it tight. Anyways, it is an interesting topic to talk about i guess. Does that mean i can expect my tsuka to get looser come summer time?

 

Kind Regards,

 

Jeremy Hagop

[Jean]

Thanks a lot forthe info, especially for Ken.

 

In fact, I need furher simple explanation, I have got a thickhead (I am not that bright :lol: :lol: )

 

Humidity makes the wood swells : am I right in this assumption?

 

Considering the Tsuka :

 

If it swells it should swell both ways outward the tsuka and inward the tsuka, so it should tighten on the nakago ....

 

UNLESS THE TSUKA WAS MADE UNDER A MAXIMUM HUMIDITY ....

 

Am I still mistaking????

 

 

In fact, my only conclusion is to have, if possible, the same level of humidity throughout the year.

 

Generally, Shirasaya are quite airtight - Do anyone in the board (tricky question from a warped mornin brain) has any idea of the best % of humidity taking into account wood/steel?????

[Nobody]

In fact, I need furher simple explanation, I have got a thickhead (I am not that bright :lol: :lol: )

 

Humidity makes the wood swells : am I right in this assumption?

 

Considering the Tsuka :

 

If it swells it should swell both ways outward the tsuka and inward the tsuka, so it should tighten on the nakago ....

 

UNLESS THE TSUKA WAS MADE UNDER A MAXIMUM HUMIDITY ....

 

Am I still mistaking????

Imagine a doughnut. When its material expands uniformly in each dimension, the shape of the swelled doughnut must be similar in proportion with the original doughnut. So, you can see that the hole of it does not become smaller but larger, when it expands.

The doughnut also circumferentially expands.

[Jean]

Koichi my friend,

 

Thanks to you I have understood

 

Luminous and tremendous example (I love doughnuts :D :D ), that is exactly what teaching is all about : give very simple example/explanation.

 

BTW, I did not have too much time yesterday but I hope everytthing is OK and that you did not suffer too much from the earthquake -