DIY Vacuum Chamber

I've been getting into pen turning (making 100 pens for our clients at work), and a local sawyer gave me a huge slab of spalted sycamore. The problem is that it's pretty soft, so any pen blanks cut from it need to be stabilized. The best method I've seen for stabilizing is using a product called Cactus Juice. The problem is that you need a vacuum chamber to do it.

So what do people like us do? We build our own vacuum chambers.



It was surprisingly easy to do. Here's a list of parts and sources:

Pressure cooker - $6 - Salvation Army

12" x 12" x 1/2" cast acrylic plexi - $11.29 - EstreetPlastics

Vacuum pump - $58 - Amazon

1/4" Ball valve - $4.80 - Zoro

1/4" Brass hose barb - $.79 - Zoro

Brass T - $3.04 - Zoro

Vacuum gauge - $9.82 - Zoro

Flare to hose barb fitting - This was the most difficult piece to figure out, but I was able to find it at McMaster-Carr. It's part #5670K21 - $1.50

1/4" ID braided PVC hose

Another thing I wanted to try with this setup was to dye woods all the way through. Back when I was first prototyping my straps, I was going to try to dye the Originals, so I purchased some fiber reactive dye from Dharma Trading Company. Well, the cotton my straps are made from was apparently treated with something, so it wouldn't hold the dye, so I've had several jars of this dye just sitting around.

This type of dye is for any natural fiber and can be used on wood, so I thought I'd give it a try. I mixed up a batch of Pagoda Red according to the directions and dropped in a couple of pieces of apricot wood.



I ran the vacuum to the max for 20 minutes and then released the vacuum and poured in the fixing agent. I then let everything set under vacuum for another 2 hrs, and it came out like this.



This was right out of the water, so it was still pretty dark. I'll let it dry for a week or so and then try turning them to see how well the dye penetrated the wood.

My chamber kept losing vacuum pretty quickly, and I'm not sure why since it held so well in the first test. I've removed all the plumbing, and I'm going to redo it all and try to get a better seal on everything.

 

The biggest is about 1" x 1" x 5"

 

That's what I thought at first as well, but vacuum is actually a much better method.

when the air is removed from the wood, it's replaced by the liquid in which it's submerged.

 

I just put a couple of nuts on the wood to keep it submerged.

Wood is essentially a bundle of air-filled straws. When you create a vacuum, all the air is evacuated and replaced with the water, resin, or whatever else it's placed in.

 

True, but you really wouldn't try to dye ebony or katalox or pau ferro or EI rosewood, etc...

I'm not a scientist. I'm just a guitar builder with an English degree, so if you want to know the exact mechanism of how it all works, send an email to Bill Nye

 

Ok, so at Jup's urging, I went ahead and cut into one of the blocks...



Aaaaaand it was a complete failure.



Again, since I'm not a science guy, I'm not sure why. I just assumed that this method would work for dye since it's how the stabilizing resin is infused as well.

I don't know if it was a matter of my chamber not holding vacuum, so it would drop down to about 20 in Hg (according to my gauge, which I believe is faulty as well) before I'd run it up again. My gauge doesn't appear to be measuring accurately because the needle never drops back to 0. It's stuck at 3 in Hg, so I may not be getting enough vacuum also.

Or maybe it's as @trev333 is postulating and as Rick just stated above — maybe I need to apply pressure as well.


Ok, I typed all that above and then went to Turntex.com and found the info below. Turns out @Jupiter had it nailed. Just how to use that information to help get better penetration of dye is another story:

Explanation of Vacuum and How it Relates to Stabilizing
Vacuum is a totally different animal than pressure! With pressure, given the right equipment, the amount of pressure is infinite. Vacuum, however, has a limit. The definition of a true vacuum is the absence of all molecules. This, of course, is unobtainable, even in outer space or the perfect laboratory setting. However, we can get fairly close with a good vacuum pump.

The 2 most common measurements for vacuum pump ratings of the amount of vacuum in the US is "inches of mercury" ("Hg) or microns. With "Hg, the higher the number, the higher the vacuum. With microns, the lower the number, the better the vacuum. A perfect vacuum (remember, this is not obtainable!) is 29.92" Hg at sea level on a standard atmospheric day (59° F) or 0 microns. For every 1,000 feet above sea level you live, you loose roughly 1" Hg of vacuum. However, since the air is thinner and the atmospheric pressure is less the higher you go, you still get the same effect at the lower vacuum reading since there is less air to begin with. It is really better to think of vacuum performance as it relates to stabilizing in terms of % of vacuum.

For example, at sea level, a 29" Hg reading on your vacuum gauge indicates a 96.9% vacuum or removal of air inside your blank (29/29.92). A 25" reading on your gauge at sea level indicates an 83.6% vacuum or removal of air inside the blank. However, in Denver, which is 5,000' +/- above sea level, the maximum theoretical vacuum is 24.976" Hg so a reading of 24.5" Hg on your gauge indicates a 98.09% vacuum or removal of the air inside your blank. In other words, make sure you know your elevation above sea level before you freak out that you are not getting enough vacuum! One person's reading is not necessarily the same amount of vacuum as another person's! Calculate your maximum theoretical vacuum with my new calculator!

Now, the big question...how much vacuum is enough? Get as much vacuum as you can get and you will get better stabilized blanks! It only makes sense. The reason we use vacuum when home stabilizing is to remove the atmospherically compressed air that is within the material, thus making room for the Cactus Juice. The more air you can remove, the more Cactus Juice you can get into the blank and the better the blank will be stabilized.

Here are some pictures I took of rubber shop glove that I tied off without any air in it to speak of. This is in my shop at 800 feet above sea level. My maximum theoretical vacuum is 29.055" Hg.



0" Hg 25" Hg (86.04% vac) 26" Hg (89.48% vac)

27" Hg (92.29% vac) 28" Hg (96.36% vac) 28.5" Hg (98.08% vac)

As you can see by the photos above, there is a huge difference in the expansion of the air between 25" Hg and 28.5" Hg. How is the amount of inflation of a shop glove relevant to stabilizing? Well, a piece of wood, in very simplistic terms, is like a bundle of straws that are filled with air. The air inside the blank is compressed by atmospheric pressure. When you pull a vacuum, you are removing most of the atmospheric pressure that is compressing the air which allows it to expand. When it expands, it flows out of the blank and into your vacuum chamber and then is extracted by your vacuum pump. The more air you can remove, the more room there is inside those "straws" for your Cactus Juice!

Since the blanks are submerged in Cactus Juice and the fact that nature abhors a vacuum, when you release the vacuum, the space inside the blank tries to fill back up but instead of air, it fills up with Cactus Juice! Basically, the blank sucks up the resin with the help of atmospheric pressure. Then, the atmospheric pressure continues to hold the Cactus Juice inside the blank instead of allowing it to run out all over the shop floor! All you need to do now is cure the Cactus Juice and viola!, you have a Cactus Juice impregnated blank!

 

So now the question becomes, if the vacuum chamber isn't able to get the dye to penetrate, how do I get a good dye on my pen blanks? If I turn the barrels down to the proper size and then dye them, they'll expand when submerged in the dye solution, which means I'll need to sand or turn them back down to size, thereby losing my dye...