I'm using the solid surface counter-top material Corian since it is not porous and it is relatively strong and a 1" thick slab will not deflect / fail (crack shatter) when under a vacuum. You can glue it together and the epoxy glue welds it so that it is strong as heck.
My first attempt at making an end for the kiln was a failure. I had to go back to the drawing board and learn how to use a new tool for the vertical mill --- the 360 degree table. It is so versatile, I wanted to do an instructable on it.
Step 1: Rubber and epoxy failed -- Solution use a O-ring
I thought that this would work like a charm! At first glance, it seemed to work. Unfortunately, the vacuum pump that I'm using is so powerful, it is pulling the rubber from the corian when under 28" Hg.
I decided that I needed to go a different route -- I needed to make a giant O-Ring and route a channel 1/2" into the corian to mate with the 12" PVC pipe.
This was not a job for a hand-held router. The solution is to use a vertical mill and the attachment for the mill that allows you to make a perfect circle -- the 360 table!
Step 2: Use the vertical mill and the 360 degree table
The table allows you to rotate an object around a center-point an set number of degrees. You can also make a full circle if you want to do so. This is ideal for what I am trying to do.
I sometimes say that I'm going to write -- "Nothing is ever easy" on my tombstone. The vertical mills that TechShop has will accommodate parts that are normal sized for machines -- 4 - 10 inches, no problem. When you start trying to do something with a 12x12 part, the issue is that you need to make a hold down extender for the table.
If you look at the silver plate underneath the corian, you will see that it is aluminum. Fortunately, I was able to borrow one from another TechShop member who had already made one -- so I did not have to make it also. This is the beauty of TechShop -- If they don't have it, you can make it. Sometimes, another member already has -- it's a great community! Thanks Tony!!
Using the digital read out (DRO) on the mill, you can determine exactly where the X axis of the mill is. I determined the center point of the corian square, then zeroed the DRO.
The 12" pipe has a wall thickness of slightly less than 1/2". The ID of the pipe is 11.87" The OD is 12.75. I placed 1/2" bit into the collet and moved the table so that the DRO read 6". This put the inside edge of the 1/2" bit at 1/4" less than a 12" circle. I then moved the X axis and added 0.2" to the DRO reading.
You move the table by turning black handle of the table. After lowering the bit into the corian 1/8" and making sure that the cut was in the right place, I milled out a 1/2" channel. I then had to move the x-axis and add the difference to to the cut to accommodate the wall thickness of the PVC pipe. This is a second cut using the 1/2" bit.
The last step was to take a 1/8" ball end mill and make a channel that is in the center of the 1/2" groove that is 1/16" deep ( one half of the 1/8" ball end mill). The reason for this is the O-Ring material is 1/8" in diameter.
Using the mill made this a hyper accurate job. The first time took me two hours to figure out. The second end took me 15 minutes to do. Practice makes perfect!
I also had a small piece of 12" pipe that I was able to use to make sure that the channel was in the proper width to accommodate the pipe.
Step 3: Make the 12" Diameter O-Ring
I ordered 10' of Soft Viton Fluoroelastomer Oring Cordstock 1/8" Fractional Width, .139" Actual Width, part number 7643K75 from McMaster-Carr. It's $2.61 a foot. They sell it in 3' and 10' lengths. I needed enough to make two of these. 10' seemed like the right amount.
I overlapped the O-ring material in the channel and made sure that I had the right length. I also overlapped the material and cut it on an angle.
I used small amounts of RTV Silicon to glue the Viton to the corian.
This part worked like a charm! I was able to increase the amount of vacuum that I'm pulling by 1" of mercury. That's significant!
I made it at TechShop.