dry kiln for drying bowls

Greg_Kaldor · February 12, 2004, 02:46:13 AM

Hi all,
My name is Greg Kaldor and I live up in Northern Wi. I want to build a dry kiln for drying my bowls as I am a woodturner. I have everything I need except the de-humidifier. Here is the problem. I am interested in buying it used because the cost of a new one is so expensive. Also my unit would be pretty small. Anybody have any ideas? Any input would be most helpful.

Thanks,
Greg

Jeff · February 12, 2004, 02:49:26 AM

Welcome Greg. You should probably pose this question in the drying portion of the forum. I can move this one over there if you like. I didnt want to move it without notifying you first since you are new to the Forestry forum.

Greg_Kaldor · February 12, 2004, 03:03:26 AM

Hi Jeff,
Thanks for the responce. Yes I am new and yes go ahead and move me.

Greg

Bill_B · February 12, 2004, 04:39:45 AM

Welcome
I have heard of other turners using an old frig or other old appliance for the box. Then you need a small fan to vent it. Also add a light bulb for heat.
Have you ever tried using the soap methed to help in drying?
Have fun

Greg_Kaldor · February 12, 2004, 05:17:09 AM

Hi Bill,
The idea with the fridge, this is to small and I do need a de-humidification unit. Also I tried the soap method and God what a mess.

Greg

beenthere · February 12, 2004, 08:11:01 AM

At what stage of turning (I assume green) are you drying? And are these bowls (species?) turned very thin, or thick in some places? Do you have blanks for turning with (or without) the pith?

There used to be a bowl turner in SW Wisconsin (Mineral Point) by the name of Harry Norr (sp?) and he turned large bowls (20" diam or so) to a very thin thickness (1/8 to 3/16") and worked in epoxy while the bowls were still on the lathe. He then had a clamp arrangement to hold the bowls while he dried them at (I think) 200 degree in the kitchen oven. When they came out (some were cracked, but most were not) he rubbed in more epoxy and polished them. They were always mis-shapen due to drying, but were very nice looking and he sold them for some big bucks. I visited him in the 70's when he was doing his work. He was the retired PostMaster.

Wondering how you are doing yours?

Greg_Kaldor · February 12, 2004, 12:32:18 PM

Hi Beenthere,
I do most of my work in Birdseye, Cherry and Oak. Alot of them are natural edge also. All the ones that are not I turn to
a thickness of 10% of the dia. A 20" bowl would be 2". The
big ones have to sit 1 year... to long for me. This is why I want the kiln. I am also taking delivery next week of the VB36
it is a very large lathe that comes from England. I seen a Demo of a 5 ft. dia. bowl out of Teak being turned. I am told its capability of stock is 600lbs. This is trully a BEAST.

Greg

beenthere · February 12, 2004, 12:49:51 PM

Sounds pretty impressive.

How do you manage the shrinkage of the wood when it dries? Or do you tolerate the cracks in one years' drying, or not get any? Have you been doing this for very long? Any pictures? 2 inches of wood will be tough to air dry or kiln dry, IMO.

All the questions for now - I ran out ;D

Jeff · February 12, 2004, 01:05:47 PM

Greg I hope you can take pictures. I want to see that thing.

Den Socling · February 12, 2004, 02:43:24 PM

Since you sound serious, I suggest a vacuum kiln. Not the type we build but a 'discontinuous' vac kiln. These are fairly simple. They are slow compared to the type we build but a heck of a lot faster than a year.

With 'discontinuous', you heat the wood with warm air. If there is a chance of cracking, you might elevate the humidity. When the wood is up to temperature, pull a vacuum. When the wood has cooled off in the vacuum, repeat the process.

Greg_Kaldor · February 12, 2004, 03:28:24 PM

Hi Den,
I would like very much to hear more about the Vacume Kiln, this whole field is very greek to me. Wood distorts most times in a predictable manner, but there can always be surprises. About pictures I have to go thru my wife for the way to do it. This vacume kiln I would not Know where to go for info, please don't desert me in my time of need. Ha Ha

Thanks,
Greg

beenthere · February 12, 2004, 05:34:32 PM

I found a site for the VB36. That looks like one beauty of a lathe for bowl turning. Congrats.

http://www.hegner.co.uk/system/index.html

(click on VB manufacturing)

Den Socling · February 12, 2004, 06:13:20 PM

Greg,
If you want to build a vac kiln. I'll lead you through it here. But it will take some money. do you weld? The expensive parts are the chamber and vacuum pump. The chamber can come from something like a propane tank but it needs to be cut. Then flanges, hinges and clamps need to be welded. Lots of metal work.
Den

Bill_B · February 13, 2004, 03:51:53 AM

Den
What would be a ballpark drying time say for 2 inch wall thickness?
Thanks

Den Socling · February 13, 2004, 04:38:32 AM

There's a lot of variables. I'd guesstimate around one week for 2" to get it to about 10%. It takes continuously heated vac kilns about 5 days to get 2" to 6%. The nice thing about vacuum for bowl turners is that you can dry from under the surface with vacuum. So very thick pieces can be dried.

Greg_Kaldor · February 13, 2004, 04:49:58 AM

Hi Den,
I do not weld but enough people owe me favors. I would just have to know ahead of time just how big a project this is going to be. Also how long would it take to dry bowl 2" thick.
maybe you can send me some more info. I am most
grateful. one more thing how much money would you think.
Greg

Jeff · February 13, 2004, 05:54:53 AM

I would like to see this discussion continued here and not off forum. Valuable information for others.

ronwood · February 13, 2004, 06:25:59 AM

Den,

Does a 'discontinuous' vac kiln dry a load of wood quicker than dehumidification kiln say from Nyle or Ebac. Would you get less degrade?

Thanks
Ron

Fla._Deadheader · February 13, 2004, 10:31:33 AM

I too hope this thread goes the distance. We are very fortunate to have Den advise us. He has so much 'sperence to help those of us that are seriously looking at small kilns.

Being that we ARE welders, this info will be most valuable. Thanks, Den ;) ;)

Greg_Kaldor · February 13, 2004, 11:08:44 AM

Hi Den,
There seems to be a great deal of interest regarding this subject. I know that woodturners such as myself have always searched for a quick safe way to dry our rough turned pieces. I agree that this would be best searved by keeping this thread open so that everybody now interested may still
benefit. My only intention for asking you direct was for clarity. It is quite difficult to gage this project on the whole by
this method though. I see that the vacume kiln might be the Holy Grail for me if it is not to expensive.

Greg

Den Socling · February 13, 2004, 03:06:08 PM

Discontinuous vac kilns used to be built by an Italian company and VacuTherm tried to sell them. With thick stock, they are probably 5 or 10 times faster than conventional kilns. But they are slow compared to continuously heated vac kilns. I've worked on them and the wiring, relays and timers needed for automation in the 'old days' are a nightmare. The patent has expired and one might be built by an enthusiast.

The basics are as follows: You heat the wood by blowing warm air over it. Lumber gets stickers. Blocks would just take time. When you heat the wood, you increase a property of the water in the wood. This property is called vapor pressure. If you heated until the vapor pressure was (for discussion) 50 and then you pulled the chamber pressure down to 50, all of the water would instantly evaporate. This doesn't happen in reality because, when water evaporates, it takes heat with it. The remaining water cools and it's vapor pressure is lower - say it's 40. Then too, the evaporating water fills space and eliminates some of the vacuum so the chamber pressure might become 60. Instead of all of the water evaporating, only some can and then the 50/50 doesn't exist anymore.

With discontinuous vac drying, you heat with air and then pull vac. Repeatedly. You could do it by hand. You could do some automation. You could make it completely automated. The cost, for the most part, depends on how much you will scrounge for parts and how much you want automated.

shopteacher · February 13, 2004, 03:15:18 PM

Ya got us all setting on the edge of our seat Den. Please continue.

Greg_Kaldor · February 13, 2004, 03:26:19 PM

I have a good friend where I work who is an instrument man and I am sure will give me tech. advice. Most of this is all Greek to me. But I will try very hard this is very important to me. I will be watching for more. Thankyou.

Greg

Den Socling · February 13, 2004, 03:27:52 PM

It's been a long day with a DanG 50 HP freq drive blowing up in my face, it's dinner time and I'm ready for a beer.

But you need a chamber. I'm always wondering about propane tanks. They come in all sizes. They are stronger than needed. If you could just cut the end off and turn it into a door.

etat · February 13, 2004, 05:18:04 PM

careful cutting into a propane tank. first remove the valve, then either fill full of water and cut, or hook up a hose to the exhaust of an engine and cut while co2 is pumping into the cylinder. Otherwise you might find you head going into orbit, along with the tank