I've seen posts about this system once in a while. I've tried to help explain, but without pictures. And found folks were kind of confused about how it works. Tonight I was trying to clean the shop and fix some stuff and decided to mount my TV monitor behind my lathe. Therefore I needed to test it to see if I shorted anything out.
Anyway the purpose here is to show how a video camera is used for hollowing (and yes the chunk of scrap on the lathe is not a closed hollow form, it was just laying on the floor and convenient for this demo). The first time I saw one of these was at the Dalton Ga. Symposium some years ago with Trent Bosch. I immediately found some camera's on Ebay and bought several of them. The only thing I feel is important about the camera is that you can 1)mount it easily and 2)it has a fairly clear view at 12 to 18 inches. Other than that, I don't think it's that big of deal. The monitor needs to be cheap, eventually someone will throw a piece through the screen and you don't want a big $$$$ hit. Besides the shop is a dusty environment, so the monitor needs to be "expendable". You can buy an adaptor off of Ebay and use a VGA computer monitor as well. The rest of the system is just hardware, similar to a laser mount. As a matter of fact, on my Monster hollowing rig, I used the laser mount hardware to hold the camera. All that is important is to make sure it's stable in that it doesn't move. It can shake some, but it has to stay in position, like a laser. Originally I used a piece of mylar over the monitors screen to draw on with a grease pencil or marker. But I found a friend of mine uses "frisket". I bought some and have found I only need enough to cover the picture of the cutter and think I'm going to really like that.
The first picture shows the overall rig mounted on my McEvoy boring bar. Hopefully you can see how all of it is mounted and how the outside of the cutter plus 3/8" creates a kind of halo around the cutter. In the 3rd picture you see when the halo touches the outside of the hollow form, you're at 3/8" wall thickness. The 2nd picture shows the camera, halo and cutter relationship, in that they are fixed. When you hollow with this and watch the monitor, the hollow form seems to be what moving, not the cutter.
Remember the picture on the screen will be most likely bigger, so that 3/8" as measured at the cutter is most likely 1/2" or bigger on the screen. Just make sure you hold a ruler on your cutter and mark your wall thickness on the screen.
This isn't for everyone, but if you like to tinker and want to take the guess work out of hollowing it's fairly cheap to build and easy to set up. I think I paid about $10 each for the camera's, but have since found some we use at our club meetings for $16. The monitor is kind of a wild card. It can be free or up to $100 with shipping. I tried to get mine at about $50 with shipping. The rest is just hardware stuff and should not be much.
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Originally Posted by Grant Wilkinson
