How to make a vacuum kiln in 20 screwups or less.

Well it seems like that many screwups anyway (G)
Part of the problem was getting the right info and then applying it.
I got a lot of help and some info that does to work. But hell I am not blaming
anyone. I was rushed and had little money so things sometimes were not done
right.
Ok here are some of the things I was told.
First that you need a little fresh air in to move the moisture to the pump.
This is false the moisture makes it to the pump just fine.
Second is you don't need heat. But you do I was told you still need 1000 btu's
per pound of water removed no matter what you use. I found you need atleast
some heat the more you have the faster the wood dries to a point. 140 degrees is
about the max.
I was told you can leave the pump off and turn it on once in awhile. But you
need the pump running the full time to remove the moisture.
First thing that caused me problems was not leaving the pump running. I could
not get a good enough seal for it to hold the vacuum. This drove me nuts and was
a big battle. I put my good pump on a timer so it was not on all the time. This
burned out the motor out. It was a good but slow pump with very old motor.
So I got another pump but I never know how much vacuum you needed to pull so I
only got a pump that goes down to 24" well I finally found out you need atleast
29" of vacuum to boil the water out of the wood and 29.5 to.9 is better.
Though the higher the temp the less vacuum you need though it only goes down
to about 28" when you are at about 140 degrees I think.
Now you need a pump that can handle some moisture this is a tricky one. You
need a pump that can go down to 29" minimum handle a little moisture without
dieing and one that is meant to run continually.
I have a gast saa pump that has two pistons/diaphragms. I don't think the
moisture will hurt it (I will find out soon enough) that seems to work well.
Pumps like this I think will work well
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2545452918 As long as they
have a gas ballast to removed the moisture from the oil.
http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&MfcISAPICommand=GetResult&query=daa&categoryid=&ht=1&st=2&category1=11811&SortProperty=MetaEndSort&BasicSearch=&from=R2&catref=C3
is a good choice too.
Ok lets go to the chamber. I started with using PVC and it works ok. Not the
greatest thing to heat but it works. You just need a chamber that is easy to
seal and to plumb and that can take the heat. Right now my kiln is running at
120 degrees and is PVC with no problems. It will be replaced with metal ones
soon. But it's easy to put fittings on the PVC pipe and to cut it and such.
I seal one end permanently and the other end I make the lip nice and flat and
use a gasket and a lid. You can use sheet rubber between the lid and the pipe
if you make the fit good. If you can't make the fit good you can use a softer
material like closed cell neoprene. The lid needs to be thick enough to stay
flat. The larger the pipe the thicker it needs to be. I glued up two pieces of
¾" and sealed the one face with epoxy.
You can't heat PVC to 140 so if you want high heat you need to use metal pipe.
12" is about the max you can heat from the outside. The center won't get very
warm if you go larger.
Ok now onto heating the kiln. This is a tricky part. Heat does not move well
if at all in vacuum. When I found out I needed heat I tried using these heat
bars I had. With wood laying on them, that piece would get hot but not any
others. Heat does not go up in a vacuum kiln.
You can wrap the wood in a heating blanket but this seemed a real pain to me
to deal with. Getting the wood in and out and plumbing the cord into the kiln
and all. So I decided to heat from the outside. The trick here is to have a hot
enough heat source that will heat evenly the whole length of the pipe including
the end. I found a good deal on radiant heat wire on eBay. It gets me 120
degrees pretty evenly. You can see it in the pic below.
For me this is plenty hot and the wood is drying plenty fast. An old electric
blanket will work fine. The new ones have 10 hour timers. Don't apply too much
heat or a PVC pipe will collapse.
http://www.knight-toolworks.com/web_temp_pics/vacuumkiln.jpg
Ok lets get on with this. You will need to seal the ends of the wood before you
put it in. I use ancorseal but wax will do. Glue will not do. Silicone will do
(G) used that when I had nothing else. Oil based paint may work but I don't
know. Latex I don't think will work.
With ebony I found I needed to seal all faces with the ancorseal or I got
surface checking. I don't know about other woods yet.
You also want to pre heat the wood before you pull a vacuum. This made a big
difference in checking.
It will take some learning how to get perfect wood from the kiln.
One thing that a vacuum kiln can do is dry wood unevenly. So you need to check
the whole board.
A pinless meter may be a must so you can check the whole board fast. I have
found ebony that was fully dry but in the middle or on one face on one end. Even
heat may help eliminate this or help.
Right now I am getting 5 to 10% moisture loss overnight. I may go for less
heat and see if I get less checking.
I think that is most of what I have learned. I had trouble getting enough
vacuum till I rebuilt my vacuum pump. Once I got down to 29" of vacuum I got
water vapor out the outlet of the pump. This was the first time I noticed it. if
you get water coming out of the pump you know it is working right.
I forgot hose. I tried the braided clear hose the Borg sells. It may have
worked without heat. But the inside and outside separated and blocked the flow.
Right now I am using air hose one type collapsed a little way but we will see.
You don't want to reduce the size of the like that what the pump's inlet is.
Larger is better.
http://www.knight-toolworks.com/web_temp_pics/newkiln1.jpg


--
Knight-Toolworks & Custom Planes
Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.