Questions on The Kiln Drying Process

[Oli Jersey]

Hello everyone, this is my first thread on a forum but I have been an interested reader for a while.

 

I am looking to find some information out about the process and running of a Kiln, there have been some very good threads on the building of kilns on here, but I would like to find a bit more on the process.

 

I started a small saw mill in Jersey in the Channel Islands about a year ago and slowly have been expanding to cover different requirements. My latest project is the running of a new kiln which I am building.

I am going to be running a Swedish Kiln System sold by Logosol called a Sauno Kiln.

 

My questions if you can help me are:

 

Does it matter about kilning different species of timber at the same time? I understand the some wood need air drying for 6 month to a year before hand like oak.

 

During the drying process you do not want to open the kiln, so my question is knowing when the timber inside is down to the right MC, understand you have to use a Relative Humidity & Temperate sensor on the inside, but for example what RH would give you a 12% moisture content? The guidelines I have with the kiln recommend running it at 40c or lower for hardwoods, so my plan is around 38c which I picked up from a previous thread.

 

Does it matter if you put planks in the kiln which have had their ends sealed, or should this be scraped off or cut off before kilning?

 

Many Thanks for the help.

 

Oli

 

www.lepavtimber.co.uk

[Big J]

Welcome to Arbtalk Oli.

 

First off, I know a fair number of people with the Sauno steam kiln and most seem to operate them without much trouble. I myself prefer a system where I can go in and check on my timber at any given time, so I use the kiln detailed in the kiln construction thread. That said, a furniture making friend with whom I do a lot of work and share a workshop has one, so I intermittently use it.

 

In an ideal world, you would only kiln the same species at the same thickness with the same starting moisture content. Every species takes a very different time to dry and a mixed kiln is going to have a variety of final MCs. Try to avoid mixing Oak with other species as it just takes longer. Also, try to air dry everything for at least 6 months, and Oak for twice as long.

 

12% MC should be achieved at an RH of around 25%, though with oak it would be lower (around 20%). That is at 32 celcius though, so some adjustment might be required for 38 celcius.

 

End sealed boards are fine in the kiln to the best of my knowledge, but I don't do it so can't say definitively.

 

Jonathan

[Oli Jersey]

Thanks Jonathan for your reply.

 

You have answered the questions which were bothering me, i suppose now i just have to give it a go.

I am going to have to mix the loads unfortunately, but i will aim to keep oak separate and kiln that separately.

 

Cheers Oli

[tombo]

Hi Oli

 

I run a small Sauno Kiln, and there are some issues around drying oak. The Swedes are very vague about this, but variously say remove the bark or air dry for six months before kilning oak. Apparently to reduce the corrosive effects of the tannin on the elements during the steaming cycle. Worth checking this out to avoid expensive damage . . . .

 

The Sauno kiln works well enough for me : I find it's OK to open it to pull out a board or two to check MC which varies according to where it is in the stack. More a matter of trial and error : getting to know how your particular kiln works. I'm not an expert, but have a reasonable grasp of timber tech : have been hacking up bits of wood for an embarrassingly long time . . . .

[Oli Jersey]

Hello Tombo

 

Thanks for the info on the Oak, i have been told 6 months to a year before kilning oak. not really sure if that applies to oak which has been down but not milled or only for freshly felled green oak. Logosol seems to think if the oak has been felled for a few years but just milled that will be ok and the tannin would have come out by then.

 

i am still building the kiln, i hope to start it for the first time end of next week. it will be trail and error but will get there eventually.

 

Thanks for the advice.

Oli

[nantmoel]

Take a look here: The Bronze Oak Leaf | Woodworking and Sundry Other Avocations the plans he mentioned I bought but to be honest his description of how he dries his wood are far better than the purchased plans.

 

PM me if you want further details.

[Rob D]

Alright there Oli - nice to see you posting on here and also on a subject that comes up often.

 

 

Oak is a harder one to dry as it just seems to be more temperamental than other timbers i.e. it can start to surface check in raw sunlight after only a couple hours, it takes longer to dry than other timbers, so it can case harden easily. Air drying slowly first can help remove a lot of water without drying defects and then it should be less likely to develop problems in the kiln.

 

 

As Jon said I used to do mixed kilns but if you can same species, same thickness is better... that said I now kiln my neatly stickered timber like this and then put all the odd bits of timber around the outside of the main stack and this works well for me.

 

 

 

 

[timbermillers]

Hi Oli

 

I too have a Sauno kiln, a great bit of kit especially when starting out.

 

I have kilned various species with varying result, but I do keep the species separate if at all possible; especially when it comes to the likes of oak v douglas fir (oak a nightmare and douglas fir bomb-proof!). Ash and beech have worked well together as they both dry at roughly the same rate so if you can match your timbers to the rate at which they dry then all the better.

 

I put some freshly milled oak that had been felled for 2 years through the Sauno and it was a disaster - massive amount of honeycombing on thick sections. In my opinion the problem with the Sauno steam cycle on oak is that it gets too hot and the timber case hardens and then all the problems start. Did the same on 3" douglas and it came out perfectly. I have since dried thick oak in the sauno but I don't steam it first; as a rule of thumb case hardening can occur above 40C so I keep it below this.

 

Everyone has there own little tricks ads a result of their own failures/sucesses.

 

As you say, trial and error is the way forward - good luck!

[tombo]

Hi timbermillers

 

Interested to hear about your Sauno oak drying experience. I've only ever dried a few oak boards mixed in with other loads because of Logosol's warnings.

 

I run an Alaskan mill, and also dry large rough-turned bowls. vessels and other lumps.

 

Recently fried the motor / fan assembly on my kiln ( my fault : I turned it off by mistake during the steam cycle : duh ! ) and had to fit a replacement. Considerable corrosion of the housing, but not the heating elements or the fan, and guessed this might be due to my drying some unseasoned oak.

 

Just wondering how yours has been affected.

 

Interested in your oak no-steam experience . . . . any wisdom to pass on ??

 

All the best

[miller-Ian]

setting up a saruno kiln my self looking at what material to use to make the walls is celotex any good ?