Shop Built Vacuum Kiln

[@st170ish]

Have you looked into a vac booster pump to help pull initial vacuum, at my old job in a lead smelter part of the refining process used a vacuum dezincing process and they had like a massive super charger before the main vac pump, it would pull max vacuum within about 5min on a chamber 550cf(top section of a 400t kettle)

[@studoran]

Hi mate, very interested in the background research and tech specs for the vacuum kiln. Wondering if we could correspond on that?

[@bricequib]

Sure. I’m no expert but don’t mind sharing what I’ve learned

[@studoran]

@@bricequib Thanks a lot. A few questions: (1) Wondering what your thoughts are about the required strength/thickness of the chamber v the type of pump (or amount of torrs) you are using. (2) Are you able to list the ancillary stuff and what its rough cost was (3) Would you do anything different with the benefit of hindsight (for example, would you get a pump that already has a moisture removal system) (4) Have you had success since the video was made in drying out timber and are you going to build a larger unit as originally intended?

[@bricequib]

(1) I don’t have much data on required strength. I do know that the atmospheric pressure is about 14.6 pounds per sq inch. This can add up over large surface areas. My chamber is made of oilfield surplus from a local machine shop. My chamber was simply a large slip-on pipe flange that was already welded to a 5 ft piece of thick wall pipe. The material is a little more than ⅜inch steel. When I first brought it into the shop I stood it up on end, and It was nicknamed “The Mario pipe”. When sizing the pump, I was advised that the pump CFM should be equivalent to the cubic feet of the chamber. My chamber is approximately 20 cubic feet. My pump is a refurbished Welch 1397 DuoSeal Vacuum Pump rated at 17.7cfm. It is a little under the advised amount but the best pump I could get within budget. My target is to stay below 8 torrs. The pump cannot be used above 10 torr for very long. (2) The total build cost was way more than expected. I spent about $6.5k building it. There were a few things I did not account for when starting the project. You will need a good digital vacuum gauge. I used the Chemtech Scientific Bullseye Vacuum Gauge. Connecting the pump to the chamber requires a thick walled vacuum hose. I used Welch 331080-5 Vacuum Hose. The vacuum pumps are shipped dry so you will need to purchase oil. My oil was contaminated quickly during the initial learning stage, so you might want to have extra on hand. You will also want some good vacuum grease. I purchased the grease and all the fittings from locoscience.com . The heating pad used is a simple heating blanket that I purchased from Amazon. I had to do a little modification to make it stay on. Seems like everything on the market is set to auto shut off after an hour. (3) I would have never welded in the NPT fittings but rather would have used a flange that can use a gasket or o-ring. The video shows me painting the inside. That is proving to be a mistake. I should have opted for a polished surface. Pumps equipped with moisture removal can jump in price significantly. I did look at possibly using a cold trap. At this time I need to recoup some cost before putting more technology into it. (4) I have successfully dried a few pieces that would otherwise prove difficult to air dry. I dove into building a vacuum kiln more out of necessity for two reasons. I had a few really thick pieces of wood I needed to dry quicker than air drying would allow. All of the professional kiln drying services in my area are not set up for small batches. I believe the woodworking community in my area would benefit greatly from a kiln that could do small batches. I do want to build a larger scale but not as large as I was originally thinking. The more volume the bigger the pump needed. If I rebuild another chamber it will be more rectangular and better fitting to a slab to eliminate dead space/volume. I am considering the use of a Turbomolecular pump. They still require a roughing pump because they cannot be turned on at atmospheric pressure. Someone who goes by the handle “seeigecannon” reached out to me via email and gave me this diagram as a suggestion for the next revision drive.google.com/file/d/1N-rNRC5eAKGKKkhenkCEgdDzzxtKm59H/view?usp=sharing. My hope is to make a significant revision to the project this year. My goal would be to have a process that requires less babysitting and could run for a week at a time without interruptions from oil contamination. My full time job does not give me much free time- so as for this journey, I'm writing the timeline in sand.

[@studoran]

@@bricequib Hi Brice. Thank you very much for this detailed reply. Very useful! Sounds like I need to do some more saving before I attempt it. At the same time, it's a fraction of the cost of buying one. Look forward to seeing Mark II when you get around to it!

[@wyatt1486]

Do you have a detailed build? I am having a challenge finding enough details to build one

[@bricequib]

Thank you for reaching out with your question. When I posted this vIdeo I never expected it to receive so much interest. My intention was simply to document the learning process involved. I didn't really intend it to be a how to video but if you look at the reply to @studoran it might help. Thanks again..

[@sebastjansslavitis3898]

does wood shrinks less in vacuum drying or same?

[@bricequib]

I would say about the same

[@waron18]

Where you get that pipe??

[@bricequib]

My chamber is made of oilfield surplus from a local machine shop. My chamber was simply a large slip-on pipe flange that was already welded to a 5 ft piece of thick wall pipe.