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Thread: Advice on how to cut thick Victorian corbels

  1. #1
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    Jun 2018
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    Default Advice on how to cut thick Victorian corbels

    I am replicating several exterior Victorian corbels. 2 of them are 3 or so inches thick and can be made with a 2D cut, one is closer to 5 inches thick and is more complex.

    First question: how should I achieve the thickness?
    1. I could buy a 4x6 and cut it out of that, but that seems intimidating -- I'm not sure how to attach it to the SB bed, 6" might be too thick for SB, it requires a trip to specialty store with difficult hours. The wood choices were some really light weight wood that I think was Cedar but they claimed was Douglas Fir, or man made stuff like soggy PT or LDL. I also worry about cutting out pieces just to find a huge knot in the middle. Might be expensive, prices were unclear.
    2. I could glue together several Douglas Fir 2x12s (and maybe a 1" white pine in the middle for the 5" corbel) and cut corbels out of them. May be a little awkward to work with.
    3. I could cut many corbel-shaped slices out of a 2x12 then glue those together. This seems the easiest, however I fear the pieces will warp after I cut them and gluing them together might be a pain and may require hand planing to get them to line up. I know when I rip a 2x12 it twists and curls, I'm not sure if CNC cuts will do the same.


    (I also tried laser cutting a pattern in plastic and following it on my router table with a flush cut bit at home, instead of going to the makerspace. The result was the router ripped a huge chunk out of the Fir and tried to take my hand off with it. I'm now leaning away from that method.)

    Here are the cross sections for all 3. I painted the originals white, scanned them, and cut them out of 1/4" plywood for comparison since VCarvePro won't just let me print them...
    20180504_190149.jpg

    The 2nd and 3rd in the image are 2D designs, but the 2nd one has tight cuts I might need to to with a coping saw or something. Unless someone has advice on how to make those tight cuts.

    Note the 1st design is 3D, only the widest 2D cross section is shown above. The top front and sides are beveled, and the front face has flutes:

    20180905_091910.jpg20180905_091856.jpg

    To cut the 1st corbel, should I:
    1. Just cut it 2D then taper it with a chop saw and cut the flutes with a chisel?
    2. Extrude it to 3D, add the tapers and flutes, then carve it with a ball nose or something? I've never extruded a shape and I've never done a 3D carve, so I have no idea if the results would be good or how long they would take.


    Thanks in advance for your help, and sorry if this is excessively wordy. Everything has gone wrong with everything this week, so I may be overly stressing over this.

  2. #2
    Join Date
    Oct 2009
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    Elgin Illinois
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    Seth, because those parts can be well supported by their connections to the house, I would use PVC for all of the parts you have pictured. It won't warp or rot, ever. If some of them are too thick for your machine, you can slice the model in Aspire (I forgot what software you are using, but it wasn't Aspire.... and I'm late for something, so I can't go back and look) and then glue them together. This is a slam dunk. Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  3. #3
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    Quote Originally Posted by Chuck Keysor View Post
    Seth, because those parts can be well supported by their connections to the house, I would use PVC for all of the parts you have pictured. It won't warp or rot, ever. If some of them are too thick for your machine, you can slice the model in Aspire (I forgot what software you are using, but it wasn't Aspire.... and I'm late for something, so I can't go back and look) and then glue them together. This is a slam dunk. Chuck
    Yeah that would probably be the most logical material choice... However home is "historical" so technically I am only allowed to use materials available in 1865. Fun fact: plywood was first imported to America in 1865 so I used MDO plywood for my huge brackets I read somewhere that PVC expands and contracts a lot and might shed it's paint or something, and most of these will be in direct sunlight, so wood might be a better choice.

    But hypothetically if I did break the rules, how would you suggest I cut those flutes? Would that be part of the slices? Would I use a bullnose bit?

    Thanks!

  4. #4
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    Hello Seth. We have 5 historic districts in my home town, and a "preservationist" on the city staff. She has been presented with some work of mine to be cut from PVC, and she accepted it after examining the material.

    Of course every preservationist is different, but present her with some of the PVC, and tell her you won't be using the fake grain side (lots of it here has fake wood grain on one side, and is smooth on the other side). And she will hopefully be impressed that it will never rot. And it paints well. And in this application, it is not structural.

    Joe Crumley will attest to how good PVC is for painting. As to expanding and contracting, these are fairly small pieces, not like 18 foot long boards, so I don't think that would even be an issue. Though you'll need to read the specs, and first convince yourself, then you'll be better able to convince the preservationist.

    And PVC machines very well. Coming from it as an Aspire user, making these parts is all straight forward, no tricks required sort of stuff. The flutes could be cut with a ball-nose endmill, or a bullnose bit. I have used bull nose bits for making such large grooves and they work well.

    Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  5. #5
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    Given that these things are not going to fit on your Shopbot in the orientation desired, if you want to use it you'll need to do them in two parts. See if all the carved detail can be contained in a piece of material that will lay on the table face up with clearance for cutting. Once it's carved, glue that piece as a face block onto a triangular-section piece of the same material that makes up the rest of the corbel. If you match up the grain directions well, you can do it with natural wood, but it would probably work better with plastic, since differential expansion won't be an issue.

    Andrew Werby
    computersculpture.com

  6. #6
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    Lancashire, UK
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    Default Slices

    Dear Seth

    If I'm making these 'corbels'. I'm splitting them half way down the fluting. Giving what looks like 25 or 30mm thick slices. I'm cutting them in pairs and then gluing and screwing them back together face to face and back to back until I have one completed.

    Slices.jpg

    I think eight pieces each corbel. With them only being 25mm or so thick I don't need any special tooling, An 18mm ball nose for the fluting and the smallest diameter straight bit that will cut through, will help to keep the 'internal corners' tight.

    Anyway that's my two penn'orth
    Sincerely and in good faith
    Martin

  7. #7
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    Jun 2018
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    Quote Originally Posted by Chuck Keysor View Post
    Hello Seth. We have 5 historic districts in my home town, and a "preservationist" on the city staff. She has been presented with some work of mine to be cut from PVC, and she accepted it after examining the material.

    Of course every preservationist is different, but present her with some of the PVC, and tell her you won't be using the fake grain side (lots of it here has fake wood grain on one side, and is smooth on the other side). And she will hopefully be impressed that it will never rot. And it paints well. And in this application, it is not structural.

    Joe Crumley will attest to how good PVC is for painting. As to expanding and contracting, these are fairly small pieces, not like 18 foot long boards, so I don't think that would even be an issue. Though you'll need to read the specs, and first convince yourself, then you'll be better able to convince the preservationist.

    And PVC machines very well. Coming from it as an Aspire user, making these parts is all straight forward, no tricks required sort of stuff. The flutes could be cut with a ball-nose endmill, or a bullnose bit. I have used bull nose bits for making such large grooves and they work well.

    Chuck
    What end mill would I used to make all the other cuts on the 3D piece? Would it come out smooth or have a ton of lines and ridges that needed sanding? Would it take an hour to cut or be quick? I've never done a 3D shape or even seen it done, just some pictures of a model and it had lines all over it...

    True about the paint. Might be an issue on my giant brackets but not these corbels.

    The historical board rejected me replacing a few fascia boards on the porch with PVC, though I was a rebel and let the roofers use some because there is no way I'm climbing up 40ft to repaint every few years. The board has worked with me a little, like they let me get my chimney lined even though technically the cap is against the rules... They also let me buy faux-slate shingles instead of spending $150,000 on slate which was nice of them. Everything else must be wood or metal. I think the entire commission is a knee-jerk reaction against a wave of house flippers that ripped out a 2-story stained glass window on a Victorian mansion and covered it with vinyl siding.

  8. #8
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    Jun 2018
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    Quote Originally Posted by Martin Reid View Post
    Dear Seth

    If I'm making these 'corbels'. I'm splitting them half way down the fluting. Giving what looks like 25 or 30mm thick slices. I'm cutting them in pairs and then gluing and screwing them back together face to face and back to back until I have one completed.

    Slices.jpg

    I think eight pieces each corbel. With them only being 25mm or so thick I don't need any special tooling, An 18mm ball nose for the fluting and the smallest diameter straight bit that will cut through, will help to keep the 'internal corners' tight.

    Anyway that's my two penn'orth
    Sincerely and in good faith
    Martin
    Wow those are corbels almost exactly like mine! I'd have to do 8-10 slices, each 12mm or so... I'll do that math, but if it requires wood of custom thickness it might be faster just to hand-carve the flutes.

  9. #9
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    Nov 2012
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    Default Just a thought

    Quote Originally Posted by skintigh View Post
    Wow those are corbels almost exactly like mine! I'd have to do 8-10 slices, each 12mm or so... I'll do that math, but if it requires wood of custom thickness it might be faster just to hand-carve the flutes.
    Dear Seth

    I hear what your saying, but if you have the machine there why would you not want to use it? Besides from the machine they will all exactly the same - no messing.

    Best of luck, post a picture when they are finished.

    Sincerely and in good faith
    Martin

    PS you must be able to find some 12½ mm thick poplar, it grows over there!

  10. #10
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    Elgin Illinois
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    Default

    Seth, I'll agree with Martin. You have a CNC router, and it is good at these types of projects. Using a CNC router for some tasks makes no sense, but what you are describing is made for CNC routing. I just assume you are on the steep/beginning part of the learning curve, so most everything seems harder than it will later become.....

    Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

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