Introduction: How to Mill a Perfect Circle in Corian to Make a Vacuum Seal for a Wood Kiln

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I'm building a Vacuum Kiln to dry wood.  It is made out of 12" PVC Pipe -- See How to tap a large hole in a big PVC Pipe

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

My first solution for an end for the vacuum kiln was to get some 18" diameter 1/4" rubber pieces and glue them to the 1" thick corian  

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

I did not realize how powerful the 360 degree table is until I needed to make this part.

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

The hard part is done!  

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.