Vacuum Kiln for Drying Wood

yep so i'm jeff hankinson and welcome welcome once again to my shop and today i'm going to do a presentation on drawing wood with a vacuum kiln that may seem a little science fictiony for a lot of people but actually this technology is a hundred years old at least because physics is known about vacuums and what's happened in those for a very long time and actually all the mathematics and physics were sorted out back in the 80s and 90s not not that long ago so this is old news in the science world but it's a it's a rare victory for the little guy because of their nature and because of the way a commercial wood is dried it really is not worth their while to build vacuum kills wood miser actually made one and was marketing it through the 90s i believe maybe even the early 2000s and they don't make it anymore just because it's too much hassle to load in a big pile of wood and try to get a vacuum seal and dry that way but for the little guy this is a victory so i learned about this after researching all kinds of ways of drawing wood we all know air drying a year per inch of thickness plus a year and i i for one no i'm not waiting that long and i don't know about bert but he probably didn't wait that long either you could buy commercially dried kiln-dried wood and not caution armor leg i like to use our native woods here in alberta birch and poplar and manitoba maple and they're all very amenable to this any wood we'll do with this although i haven't tried ebony that's out of my price range so um i researched this and i researched a small worm box drawing almost built one that's building a box the size of a little cupboard and putting about a 60 watt light bulb in there and that would work very well uh it takes about six months uh and while in the course of my research i came across this book by a fellow called joshua salison who is a ornamental turner in california and i found this book on amazon.com the fourth edition now i got the third edition and i was in a lot of correspondence with him and subsequently said about building one now i'll what i'll do is briefly describe the process and then i'll show you the kiln and how easy it is to build it's it's unbelievable it's so easy and first i'll talk about how quickly it works so a year a year per inch of thickness plus a year so this piece of wood is a couple inches across this should take three years and this is a piece i did for a demo for our club in december of 2015 i went out with a friend of mine and we chopped down about an 18 inch black poplar balsam poplar in the winter frozen we sliced it up on his wood miser and i had a whole bunch of wood from that still haven't and this is one of those pieces i had a longer one this was about uh six feet long so i cut three pieces like this and they're about 16 inches by 18 inches one i kept out two i put in the kiln on january 1st 2016. i had nothing else to do that day so i put it in a vacuum kiln january 1st 2016 at way over 55 moisture it was wet and frozen so i took it out of the kiln three days later at zero percent three days and i turned this platter out of that same stuff one of those pieces on january 6th 2016. so and this is this is heartwood you can see should have cracked should this is the worst kind of wood to dry it's perfect that's amazing so it's it's light magic it's unbelievable until you've until you've done it and uh i've done enough now that typically it'll take me three days to dry wet wood if i'm in a hurry it's right if you get wood that's sealed with wax it's wet guaranteed can you grab me one of those hunks of wood over there bird anyway yep so all of us know that wood is like a bundle of straws literally and the research i've read uh suggests that something like 95 of the drying comes out the end of the straws it doesn't come out the side comes out the end and that's why i think it cracks if you've got a piece of wood that's you know 50 moisture here and 10 moisture here there's a huge amount of stress in the wood just over a very small area they're going to get a crack but it's it's so much faster and so much gentler to the wood to do it in a vacuum kiln that you get very minimal cracking and checking unbelievably the wood doesn't have to be much beyond body temperature heat is the enemy of wood and that's where you get lots of cracking you leave wood out in the sun you're going to see some cracking so i'm convinced it's very simple to implement joshua salison's book talks about it in depth the fourth edition has got some corrections to the science and there's not a lot of science it's just so you understand what's going on so what happens is at sea level water boils at 100 degrees centigrade but here in central alberta i'm at about 2 600 feet and water boils at less than that i think 98 something 99 something like that so if you keep going up water boils at a lower lower temperature so a vacuum kiln takes you way up above the atmosphere so water will boil here at about 36 degrees centigrade so to heat the pieces i have in here i use a simple technology you want to grab that party according to josh's book and that's these heat mats you could use your you could these are rubber you plug them in 110 and they go to about maybe 40 degrees centigrade and that's it and that transfers some heat into the wood there's no point in putting a lot of other heat sources in there because there's no air so you put a little bit of heat in you take out the air pressure that keeps the water in the wood and the magic happens so it's a combination of evaporation and vaporization and the vaporization wave of the wood spreads from the outside gradually to the inside as the wood heats up and i know when i'm done when my when my moisture readings get all screwed up you can see them go down down down down and then they start jumping around it's done and you just need it somewhere around six six to ten percent then it's fine it's stable but uh um i'll take it down 10 12. a lot of times it goes down to zero because i go to bed and forget about it on the last night i gotta fuss about it anymore but i wake it up if it goes down to zero then that would be uh excellent for people that want to do some wood stabilization because it would take the moisture content they like to get for stabilizing get the moisture content as low as possible before they put the resin in yeah so it might be an option for people that do uh stabilization and i don't think it's zero from end to end right i think it's when i get it dried it's zero and i've cut my wood apart doing this at zero at the end and then there's a gradient that goes up to maybe i've found about 12 in the middle and then down so that's fine if i dry it to zero in here it's done so uh that's how it works you put some wood in there you warm it up just a little you apply the vacuum and you make sure the vacuum stays for uh about three days and i automate this i don't have the pump running continuously i have it run for about 20 minutes every hour just for losses and things and and it works it's amazing so out of those two pieces of wood that i showed you that i put in this thing i got three gallons of water wow couldn't believe it so they were more than 50 water there's there's a lot of water 12 liters so what is this made out of you can make them out of a piece of one-inch diameter sewer pipe the real heavy stuff you see around construction sites and i think the best way to do that is have a chunk of pipe that's maybe three feet long and a couple of probably 3 16 inch steel plates to put on the end now mine is a 18 inch diameter steel pipe about 3 8 wall thickness on the far end and on this end i have quarter inch steel plates and on the far end because the fewer leaks the better on the far end i welded it on so the only place i have to look for leaks is at this end and any holes i've drilled in it my gasket is just like anything this is a 18 inch bicycle inner tube and i cut it around the circumference and snip out the valve of course and stretched it over over the end like a sock it's all i need works it's cheap i even have a spare i've had a spare for five years i haven't blown a flat yet and so how do you get the vacuum i use a welsh um vacuum pump these are used in labs they're a piston pump and they are bulletproof i got mine secondhand off of ebay josh salison talks about exactly what kind to use in his book i have used a small one that i got for 80 bucks off of amazon and that's a little oil diaphragm pump and it works it'll pull the right vacuum but there is so much water comes out of these things that the the air coming out of the measure continue to pull a vacuum is just laden with moisture very very high humidity so you're bound to get water in the vacuum pump if you put your 500 gas pump that you use for your vacuum chuck to work you will destroy it in my opinion and the other cheaper ones like i've got one from another place that's that's similar to a gas and i i don't even go anywhere near that so the the welsh vacuum pump like joel describes that works and it's the airflow is nothing it's like 0.9 cubic feet per minute but it just keeps chugging away and it'll pull it down how much vacuum do you need you need about more than 26 inches of mercury so i can pull 27.3 and i i've calculated that that should be the maximum for this altitude as far as i know i'm not great with physics but more than 26 and more than uh 36 degrees centigrade in there the water will boil and i checked that by putting in a camera and a heat plate and a pot with water in it and a thermometer and stuff like that and i could see because i wanted i didn't know who could i ask there isn't anybody to ask uh as far as so that's the the back in the front the gasket i've got one half inch uh pipe nipple that was about uh eight inches long cut it in half drilled a hole for it in the top and welded it on and then i've got some standard half inch pipe fittings on there i've got a vacuum gauge here just a little one and that one goes to negative 30 inches of mercury and out the bottom i've got the the other half of the pipe nipple with a valve on it these valves i got in my local hardware store they're gas rated valves and they work very well they're like eight bucks so the pipe in alberta you can get pipe cheap it's all over the place the steel quarter inch steel this dents in under the pressure probably 16 of an inch on the back here i measured it so you need quarter inch for sure i don't think you can over build these this is all standard stuff i got at my hardware store uh the vacuum line is a 3 8 braided plastic line and that goes to the pump down here now i've got some other things in there i built a little tank underneath you can't see it that is four inch pipe with a pipe nipple coming in and out of it and uh and valves top and bottom because as the water's coming out of the wood uh it condenses on the walls of this uh josh salison talks about keeping his warm i don't keep my more i want a cold i want the water to condense on the outside of the pipe run down and then go out the bottom uh through that half inch pipe and into this little chamber that i built that's four inch pipe like this with pipe welded on top and bottom and then pipe nipples coming in and out with valves so if i can drain the water from here into that tank close off this tank open that one and drain it that water's gone it's out of the equation so i don't have to worry about it and that's that's voted i ran 110 in here so i use the commercially prepared wire and i'll drill a very tight fitting hole here run the run the wires out this way so i've got 110 and i have a usb extension cable and i've got my temperature cable and a few other things in here my temperature sensor cable and uh so i drill a tight fitting hole and i seal that with good old seal all that you can find in any hardware store works like a charm tried silicone doesn't work silicone peels off this thing the only other thing i have is a temperature gauge and that's a specific kind i found is that bert there's a little box over there that's sort of orangish and that's on the right hand side and uh that one is just a little black wire comes out of it and i put that into the end of the wood and you can't quite see it you'll see it on the wood video but i just drill a quarter inch hole stuff the little sensor in there and a little sensor this little thing this looks like this not anything special this is a stc-1000 these are cheap on amazon and the little sensor wire runs runs down the little sensor in the end looks like that just a little ball little rubber ball it's all rubberized perfect i tried putting in the relative humidity sensor in there and i had an idea it wouldn't work because it doesn't make sense because of physics and stuff but i wondered if i could get some kind of information out of it but you can't so don't bother those stc 1000s are just fine so what i will do is load my wood in there uh i want it up off the bottom so i just built a simple plywood shelf and that's supported here i wanted it somewhere just below center so i got the widest width here and i can put uh whatever i want if i got a bunch of i don't i don't put in already turned pieces uh i like putting in uh just blanks of wood not a really prepared bowl blank for example because you're going to get a little bit of checking and stuff and if you want that size you're going to lose some of the wood you'll be disappointed so i put in stuff that's bigger it dries just as fast the limiting factor is just getting enough heat to rise through the wood once it gets to the center and everything's vaporized it's done and it doesn't take that long so i will load pieces in there on top of one of these rubber mats this rubber mat's uh getting warm we plugged it in a while ago takes a while to warm all up like there's no rush with these things and i'll often put a second mat on top of things that are like this just so i got warming top and bottom then i close it up i'll close it up with this thing i'll put on i have four ordinary pipe clamps that go on here two in the bottom two in the top and these are just to get it started i won't uh oh maybe i'll start it upward while i'm talking sure um so these are just to get it started once it's running there's something like 10 000 pounds pressure on the outside of this tank that's why you don't use something that's not very strong because it won't explode it'll implode and that'll be very disappointing and i don't do these up very tight i've got my uh i've got my bicycle inner tube in there they just have to be tight enough and once this thing's going and pulling a vacuum i could take them off i ignore them but i could take them off now 25 degrees in there right now yeah 25 degrees yeah that's great and that's mostly from outside but it'll warm up now that this is on so i make sure that my valves are open i've got an exhaust valve to atmosphere so i can let the air in when i'm all done that actually goes through an experiment to try to get some of the moisture out of the line but i disconnected it for this demonstration because i think my gasket and that was leaking then i turned it on and that's as noisy as this pump is so it'll run for a while it takes it about uh oh probably 30 40 minutes to pull 26 inches of mercury vacuum and as the temperature is rising then it just slowly warms up the wood and things start happening and as i said i automate this just with the mechanical timer i got from the hardware store so i'll plug in the vacuum and i actually have an inline valve on my usual setup here that runs on 110 that i got from princess and that opens under power so when the motor comes on that valve comes on and i've just got a better seal for the tank and it only has to run for 20 minutes maybe every hour or so over three days so it's not a huge power draw it's not a big deal it's very really not complicated as you see i built this up on a stand because i didn't think i needed to bend over to be doing this stuff and i put wheels on it so i can wheel it around my shop the 2x4 just gives me the right spacing for this thing to go up to the gasket and that's it i make sure the vacuum is started if you've got a leak somewhere you'll hear it pretty quick that's starting to pull the vacuum bird uh looks like it might have just started yeah it doesn't take very long and it's no more complicated than that so you know three days i i don't think i've gone any longer than three days ever if i've got wood that's already partly dry [Music] then you know it's going to take less than that maybe two days and if i'm not sure i'll throw it in there and leave it run for a day or two and then pull it out turn it or something because i don't like turning wet wood i like to get i like to get what i turn i don't i don't like it they move anyway and it's not because of moisture that's more because the stresses in the wood as you know so you might want to talk a bit about what we're seeing here because i see something happening here now so talk about what we set up okay okay so what we did inside was we uh put one of bert's cameras and uh what you see is the end of a piece of mountain ash that somebody gave me and it's green it was about uh 42 moisture just below that hole i drill a quarter inch hole and stuff in that little sensor [Music] and uh bird says we see some action but i don't see much action i seen some whisping happening yeah i wouldn't i wouldn't be surprised just because it's going down and then we've pulled uh about uh six or eight inches of mercury back here so far i've never bothered with a camera in there because i didn't think you'd see anything and it didn't matter to the drying process anyway why did i paint it black because i painted it black that's a black trim cloud and it needed pink i think when i redo it i'll paint it white uh this thing as i said is 18 inch diameter 3 8 wall pipe and it's about 40 inches long because i figured that was as far as i could reach so bert was interested in seeing if there was any any moisture coming out of the wood so i thought i'd give you a little closer up look of this tank and the fittings because it's hard to see with a wide angle camera and these are ordinary half inch pipe fittings i get from the hardware store a pipe nipple as many will know is just a chunk of pipe threaded at each end and i would cut this in half to go in the top and out the bottom of this thing these are gas rated ball valves i got from my local hardware store this is my little vacuum gauge and that's all i need this is my little st 1000 temperature gauge and that that is routed into the tank they go along the top of the tank here and then into some holes that i've sealed with seal underneath is my little vacuum pump this is a welsh duo seal it's got a little bitty motor driving it and then the piston pump itself next to it is a tank i made to try to dry out the uh air coming out of the the kiln and it comes from the kiln over to here and then out the top of this and around and into the top of the vacuum that thing is filled with a bundle of straws just to try to increase the surface area and grab hold of some of the moisture next to it is my little exhaust line with a closing valve and then a chunk of four inch pipe with 18 steel top and bottom i built a simple sight glass another valve at the bottom where i can drain it i have a simple shelf on the front to catch the lid and then over here i have a 110 valve that opens when it's powered and that just gives me a better seal in the tank when the pump is not running because the pump itself doesn't seal very well the usb line that i that i mentioned before comes out and inside the tank i'll hook it uh to some alligator clips and these will be attached to some colored nails i just shrunk some some heat shrink for wiring on there and i'll use them as pairs or i'll have a common ground and then four different sample sites on the outside i have a matching set these usb cables have four wires plus a ground so uh five potential connections so if one is a common ground then i got four others i can use i use a common commonly found mechanical timer to switch on the pump and the valve in line to the tank and that i got at home depot wasn't much i used these moisture meters one or the other uh i think i got this one at busy bee and this one probably lee valley and these uh alligator clips i can use a pair at a time and just clip them on to the the connectors for there to seal the pipes i found that this great white pipe joint compound works the best the heavy teflon stuff is okay the light stuff doesn't work very well this stuff gets all over everything but does it ever seal well so that's uh that's about all i can tell you about that so hopefully that gives you some idea of drying wood in a vacuum kiln typically i'll layer the wood in here on top of that shelf i'll have a heat mat then a layer of wood maybe two three inches thick then another heat mat another layer of wood and then finally a final heat mat on top of that second layer that fits inside the narrower top of the tank here i'll come out three or four times a day and check the moisture settings and see how i'm doing i'll empty the little drain tank if need be make sure there's a decent vacuum but it really isn't much more complicated than that when it's all done i'll slowly let the atmospheric air in and that's over about five minutes or so and uh because there's no point in you know you're in no hurry after three days really and then pull a wood out i'll double check the moisture content to make sure that it is what i thought it was and that the nails weren't registering funny usually the readings start getting a little odd when it's getting close to the end i had a paper by a french research scientist that i found they i found a reference to it on the internet from a conference they had in the early 90s but i couldn't find the paper so there was an email for the guy i emailed him and he was kind enough to send me the paper the next day in english it was great and it talked about all the physics and stuff which didn't really interest me too much but the economic analysis at the end pointed out that it really wasn't feasible for a commercial operator because they can't put a forklift load of wood into a vacuum kiln that's big enough to be economically viable they want to do entire warehouses full of stuff and that's how our typical two by fours and stuff are done so that's why it ends up being a victory for the little guy it doesn't end up costing all that much to reproduce this today would probably cost me about 500 and half of that is the cost of that welsh dual seal pump if you had a smaller setup and got away with one of the smaller 80 diaphragm and oil pumps off of amazon you could probably do it for a lot less if you already have a vacuum pot and it was a decent size you could use that you'd have to figure out how to get power in there and get a drain valve perhaps but power for sure so that you could wrap a heating pad or something around the wood i have not found that trying to dry entire logs works that well because you don't get very good heat transfer from these mats to a log you just have a small area of contact so typically i'll split them in half and that's often what's done with bowl blanks and things anyway uh i with a if i had a vacuum pot i would probably just get another piece of steel to put on the top instead of the usual lid and then you could play with that piece of steel and not screw anything up using a chunk of one foot sewer pipe as i mentioned earlier is quite doable i would put a chunk of 3 16 plate steel on each end and clap them with pipe clamps using a inner tube from you know one inch bicycle or one foot bicycle wheel and that would probably work fine i would run the fittings through the the end plate because it's easier to weld them on and seal them and that kind of thing but it's all quite doable it's not complicated as you've seen and not everybody has space to do a big pump like that i did find a canadian government circular that talked about uh drying wood with vacuum kilns and it was buried of course in the federal archives but it was quite interesting and glossy and all that kind of stuff for me this is a practical very very fast way of drawing wood the warming box that i mentioned would be just about as good it just takes four to six months and i'm too impatient for that and i think that's about all i can tell you about drying wood in a vacuum kiln it's easy it's fast and not that expensive so with that happy turning

Channel: Edmonton Woodturners Guild

Views: 54,998

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Id: -I9DygHrLCo

Length: 32min 6sec (1926 seconds)

Published: Thu Aug 06 2020