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Hollowing with Video

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I just bought a CCTV camera and monitor to set up a video system for hollowing. I've been using a laser thus far, but the video system looks significantly superior. My questions are:
  1. The camera came with 2.5mm and 3.6mm lenses. Does it matter which one I use?
  2. Is there any magnification factor I have to account for when tracing the cutter surface, and then marking the wall thickness line?
Thanks
 

hockenbery

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Is there any magnification factor I have to account for when tracing the cutter surface, and then marking the wall thickness line?

do not measure on the screen because there will be some distortion and that will change with the height of the camera.

be sure to use screen overlay on your screen before drawing on it.
I use dry erase markers. I trace the tool and add the thickness line around the cutter.
When the thickness line gets to the outside of the wall stop cutting.

If I want a 3/16” wall thickness. I keep a folded business card. I traced the cutter on the card and added a 3/16 “ contour around my cutter tracing. Hold this under the cutter with cutter over its tracing then trace over the contour line on the screen. You can glue a small magnet on the card to hold it in place if you can’t reach your screen while holding the card in place.
 
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Thank you hockenbery. Once the image from the card is traced onto the overlay, can that overlay image be used on all subsequent HFs, as long as I want to keep the same wall thickness?
 

hockenbery

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Thank you hockenbery. Once the image from the card is traced onto the overlay, can that overlay image be used on all subsequent HFs, as long as I want to keep the same wall thickness?

I always trace a new image because I switch from bent tool to straight tool and the straight tool tracing won’t be any good on the next HF when I’m using the bent tool. I also want the tool tip close to the center of the screen.

if you only have one hollowing tool and you don’t change the camera height or reach and you keep the tool In the same locked position the traced image should still be usable. Easy to check- look at the video. If the tracing around the tool is in the right position then you would be good to go.
 
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Got it. One last question...I think - when I used the laser, each time I worked on a different area of a vase (e.g. shoulder vs main body) I needed to re-position the cutter, and therefore reset the laser thickness setting. Would I have to do the same with video setup...draw a new trace if I need to re-position the angle of the cutter?
 

hockenbery

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Got it. One last question...I think - when I used the laser, each time I worked on a different area of a vase (e.g. shoulder vs main body) I needed to re-position the cutter, and therefore reset the laser thickness setting. Would I have to do the same with video setup...draw a new trace if I need to re-position the angle of the cutter?
if you move the cutter yes. That would be like me switching from the straight to the bent tool.


While you are using one tool. It doesn’t matter where you cut on that tool edge. the video still shows you the wall thickness.

You trace a thickness contour around the cutter. So no matter where you are cutting on there will be a countour line. As long as you ride the thickness line along the outside edge of you form the cutter will be cutting that exact wall thickness.

With the lazer- unless it is a straight wall vessel you are almost always cutting slightly off from where the laser was set. Small differences are inconsequential. When using the laser on the inside of a curved wall I would always had two conflicting voices in my head.
Voice number One would tell me your not cutting where you set the laser now time to reset it.
Voice number two would say cut a little more you know what your doing wait until you have blow out shavings.
Sometimes the anxiety level would over rule voice number 2.

With the lazer I was always hollowing with a tiny level of uncertainty. Manageable

the tv takes that all away the anxiety. The only thing you have to worry about is the cameras moving. Every time to tool is outside the form you get a positive feedback in the monitor that the camera is dead on.
 

Dave Landers

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Another thing that Al mentioned, but didn't really highlight is having the image of the cutter in the middle of the screen. If it's too far off to one side then the camera isn't looking straight down at the cutter, but off at an angle. And those angles mess up what you think you're looking at.
I went thru the bottom of a couple of pieces with what should be a "foolproof" system before I realized this.
 
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I just sketch an envelope all around the cutter so I don't have to be particular what part of the cutter radius is doing the cutting. Be conservative with your first envelope sizing as the camera lens may not give you a direct 1 to 1 ratio. Make some cuts and then measure the wall thickness. No time to make assumptions with wall thickness until you know what you have.
 

Dennis J Gooding

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I just sketch an envelope all around the cutter so I don't have to be particular what part of the cutter radius is doing the cutting. Be conservative with your first envelope sizing as the camera lens may not give you a direct 1 to 1 ratio. Make some cuts and then measure the wall thickness. No time to make assumptions with wall thickness until you know what you have.

Good point Richard. Some monitors and cameras may support multiple aspect ratios. It is very important to use a matched set.
 
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if you move the cutter yes. That would be like me switching from the straight to the bent tool.


While you are using one tool. It doesn’t matter where you cut on that tool edge. the video still shows you the wall thickness.

You trace a thickness contour around the cutter. So no matter where you are cutting on there will be a countour line. As long as you ride the thickness line along the outside edge of you form the cutter will be cutting that exact wall thickness.

With the lazer- unless it is a straight wall vessel you are almost always cutting slightly off from where the laser was set. Small differences are inconsequential. When using the laser on the inside of a curved wall I would always had two conflicting voices in my head.
Voice number One would tell me your not cutting where you set the laser now time to reset it.
Voice number two would say cut a little more you know what your doing wait until you have blow out shavings.
Sometimes the anxiety level would over rule voice number 2.

With the lazer I was always hollowing with a tiny level of uncertainty. Manageable

the tv takes that all away the anxiety. The only thing you have to worry about is the cameras moving. Every time to tool is outside the form you get a positive feedback in the monitor that the camera is dead on.

That was my impression that you didn't have to constantly re-position the cutter; good to get confirmation nonetheless. thanks to the others for the feedback, and thanks to Doug for the Youtube link.
 
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On your lenses, as Doug mentioned, the 3.6 will give you a little closer view. I’d try both and see which is a better view, but keep in mind that the wider angle will have more of a perspective offset at the edges, making it more important to have your cutter centered in the monitor to avoid the edge distortion. The slightly closer view should have less edge distortion, but any difference should be slight.
 
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If you dont do large HF’s, camera distance can probably stay the same. Its easy to determine the magnification factor - lay a ruler at spindle CL under the lense, then measure on the screen. The ratio of the 2 values is the magnification.

Rather than drawing on the screen or overlay I made a target template on the pc, cutter at center and concentric circles for different wall thickness, all adjusted for the mag of my camera. I have different templates for different cutters. I only use a 6mm and 9 mm round cutters for this. Templates can be made for different camera distances. It was funny when I asked around at work for “transparencies” to print on - no one had heard that word in a few years.

When the cutter gets repositioned, the camera the is moved to align the center on the cutter. I use a Jamieson system with the camera mounted to a dowel through the laser clamp. At times the cutter gets 2+ inches off CL. I move the support arm over to keep the lense over the cutter to maintain correct perspective. The center circle matches the cutter so cutting edge orientation, such as around a corner, doesnt matter, no adjustments necessary. The advantage is the template is already made, with concentric line for different thickness, no drawing for different wall t or different cutter orientation. My stack of printed templates should last a lifetime but I can always print more.

Regardless of the method used, always pull the cutter out occasionally to check camera/cutter alignment. The only time Ive lost a piece using the camera was when things shifted and I went through the wall.
 
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Doug:
Let me see if I understand you correctly:
  1. Magnification Factor - are you taking a measurement from the CL of spindle along the vertical, to get the height of the camera above the spindle? Or, are you measuring say 1" along the horizontal and marking that on the overlay, and then putting the ruler on the overlay to see if there's a difference between the 1" seen by the camera and the 1" on the ruler?
  2. Centering camera on cutter - do you use something like a torpedo level to check that the camera is directly above the cutter when the level shows it is plumb?
  3. Why so many printed templates? Since you use a round cutter, can't you reuse each one for each of the different wall thicknesses? I usually have a wall thickness of 3/16" or 1/4". I also use a round cutter, so wouldn't I need just two transparencies to be reused?
Thanks.
 
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Paul:
It's Ed Weingarden from WMW. Below are links for the camera and monitor I bought off of Amazon. After I received them, I had to order an extension for the camera ac power adapter, an extension for the BNC cable for the monitor. I needed them because of the distance to the wall outlet for the camera power adapter. The increased length for the BNC cable is because I now have a cutter bar/overhead bar which allows for hollowing to a depth of about 20". If you need additional info, send me a PM with your phone # and we can talk.

https://www.amazon.com/gp/product/B015MHKJNI/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B07WKG9J35/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
 

hockenbery

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I highly recommend that you measure and mark the thickness contour at the tool tip. Then trace that contour on the screen.
If you do this the Magnification does not matter. The distance contour can be any size on the screen but Remains accurate in the cutting plane.
 
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The 3.6 lens will zoom in a little closer than the 2.5. Be careful changing lenses they are easy to cross thread. Here’s a video I made for setting up and using a hollowing camera.
View: https://youtu.be/6VfHDJrRwq4

That was very helpful, I used your video to setup a similar system. Now I've got to buy a hollowing system, but the cameras setup is all done.

My system, based on Doug's.
 
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Paul:
It's Ed Weingarden from WMW. Below are links for the camera and monitor I bought off of Amazon. After I received them, I had to order an extension for the camera ac power adapter, an extension for the BNC cable for the monitor. I needed them because of the distance to the wall outlet for the camera power adapter. The increased length for the BNC cable is because I now have a cutter bar/overhead bar which allows for hollowing to a depth of about 20". If you need additional info, send me a PM with your phone # and we can talk.

https://www.amazon.com/gp/product/B015MHKJNI/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B07WKG9J35/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

I thought that was you Ed, no avatar so wasn’t sure. Thanks for the info.

Paul
 
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Doug:
Let me see if I understand you correctly:
  1. Magnification Factor - are you taking a measurement from the CL of spindle along the vertical, to get the height of the camera above the spindle? Or, are you measuring say 1" along the horizontal and marking that on the overlay, and then putting the ruler on the overlay to see if there's a difference between the 1" seen by the camera and the 1" on the ruler?
  2. Centering camera on cutter - do you use something like a torpedo level to check that the camera is directly above the cutter when the level shows it is plumb?
  3. Why so many printed templates? Since you use a round cutter, can't you reuse each one for each of the different wall thicknesses? I usually have a wall thickness of 3/16" or 1/4". I also use a round cutter, so wouldn't I need just two transparencies to be reused?
Thanks.
1. Ruler lays horizontal at spindle CL, then measure length of 3” on CL ruler on the screen, which = 9”, 3x mag factor (what mine happens to be). If the height of the camera changes, the mag factor changes. So for my template, a true 1/4” is 3/4” on the screen and on the template.

2. I center it by eye. The spindle/bed axis alignment is “fixed” by the camera being mounted perpendicular. The side to side, or turning dia axis, is controlled by rotating the mount around the support bar or moving the bar over. Small adjustments are made rotating the camera, but more then ~1” cutter offset I move the bar out, so the lense is parallel to the ground and the cutter is centered on the template.
3. I only use 1 template for a cutter, with concentric circles marking a wall thickness of 1/8, 3/16, 1/4, 3/8, etc out to 1”. I made a lot of copies of each template in case one gets damaged - why I said lifetime supply. I mad to make a shorter upright for the laser mount to get under my steady rest, so I have 2 sets of templates, 1 for closer camera/shorter support, and 1 for standard support height.
 
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Pics of 2 of the templates I use, 6mm cutter and 8.9mm cutter. These are created in MS PPT and printed on transparencies. Use painters tape to hold them on the monitor.
6mm3-1mag.jpg 8-9mm3-1mag.jpg
 

Dennis J Gooding

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I use a technique that is generally similar to Doug’s. however instead of using concentric circles I have drawn images for a. wide range of of wall thicknesses, each containing a 3/16” reference circle corresponding to the size of my cutter tip tip. Each image was replicated many times and printed clear acetate sheets. The individual images are cut out as needed. To increase the durability of the product (the ink scratches off easily), I seal the ink side of each row of images with clear tape. I affix the image directly to the monitor with a piece of masking tape. Note that this method is indifferent to the focal length or height of the camera lens and to the monitor size.

One note of caution with any of these techniques: paralax. It has already been pointed out that the cutting point should be for carefully centered on the screen. This is particularly
important if the camera height above the cutting point is not many times the diameter of the work.

A second consideration is cutting height. Like laser guidance, camera guidance presumes that you are cutting at center height and underestimates the wall thickness otherwise.
 
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Doug:
Thanks for your reply and the pictures. I've now got a good idea of the concepts discussed. Now it's a matter of trial and error, but I'm confident that I'll be much happier going this route, in contrast to the laser.
 
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Just in case - I want to point out that the printed template actual size is screen size. The 1" circle line is actually ~3.3" from the cutting edge. Depends on the magnification you end up with from your camera lense and mounting height.
 
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Doug very good video, thanks for sharing. Exactly what are you using for a camera, and monitor? Thinking of building one myself


Paul
I attached a pdf of my camera parts and how it's wired. The parts list is a couple of years old and probably not available, but you can easily find substitutes. I sell them assembled for $175, including shipping.
 

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My technique is much more basic. I cut a piece of masking tape about 1/8 inch wide. I place this on a steel ruler so one end is at the desired wall thickness (say 1/4 in), and the rest of it overhangs the ruler. I take this to my cutter, and gently touch the end of the ruler to the side of the cutter, and press the tape to the top of the cutter. Remove the ruler so the tape protudes the desired amount, and then draw my line in the screen so it is that same distance from the cutter all around. Takes less time to do it than it does to explain it. This works on a hooded cutter as well, but you have to fiddle with the tape to make sure it is perpendicular to the camera.
 
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