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Form-Bent Radius Jambs

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This is a pretty simple process for making radius jamb heads. To ensure perfect accuracy, we made plywood form plates using a router and trammel arm. 

The skeleton is made from the MDO fall off, though any plywood will do. The ribs are on 3-in. centers. Formopen95-4-1
formclosed96-3-1 For the finished jamb, we laminated two layers of 3/8-in. bending plywood and one layer of 1/8-in. birch plywood, (bending plywood is too rough for finish paint!) so we allowed a 7/8-in. space between the outer form radius and the inner form radius (plus room for skinning both forms).

We stapled on bending plywood for both the inner and the outer forms so the ribs wouldn’t telegraph through to the finished product.

98-3..innerskin-1 100-3.outerskin-1

Then we covered both forms with wax paper so the glue wouldn’t adhere to the forms.

101-3.waxpaper-1 103-2.waxpaperjpg-1

Once the three pieces were cut to size, we coated both sides of the middle layer with Plastic Resin glue, and sandwiched all three pieces at one time in the form.

105-2.clampedformjpg-1 I prefer using the Plastic Resin glue because it dries harder, holds the shape better than yellow glue, and it reduces spring back. It takes about four people to place the three pieces in the form and get the clamps on. I’ve done it alone, but it’s a ten-round fight.
We made the radius heads wider than the net size needed, so we could trim them to size on a table saw. This method is great for any radius or ellipse, and irregular shapes, too. 110-1.finishjambjpg-1

(This article originally appeared on GaryMKatz.com)

Comments/Discussion

8 Responses to “Form-Bent Radius Jambs”

  1. Craig Savage

    Nice explaination Ed.
    What kind of spring-back should you expect, and do you factor that into the shape of the form?

    Reply
    • Ed Williams

      Craig,

      By using the plastic resin glue and bending luan, we normally don’t experience any spring-back so none was allowed for.

      Ed.

      Reply
        • Ed Williams

          That doll house is a sore subject. I keep it as an expensive reminder. An architect I know drew three doll houses for a client of mine. But in the middle of building the third one, the client decided he didn’t need three – only two because he only had two daughters. The architect said he’d pay for the third one, but when have you ever seen an architect pay for something they screwed up!

          Ed.

          Reply
  2. Joe Dokes

    Absolutely beautiful. Thanks for the heads up about trying to clamp this by yourself. Also the necessity of skinning the forms is very helpful, I would not have realized that the ribs would telegraph through to the final product.

    Regards,

    Joe Dokes

    Reply
  3. Jim

    Nice work! Great explanation to go with the photos. One question; How do you handle to explosed ply with the jamb reveal? Do you use the iron on stuff?

    Thanks

    Reply
  4. Ed Williams

    Jim,

    This particular project was for a 3 light “lay-light” in the floor. It’s basically a skylight, but it goes between floors to let sunlight from a skylight in the ceiling above to filter down to the floor below. We put 1″ laminated glass in it to hold the weight of a person. We banded the jamb – top and bottom – with 2-1/2″ wide poplar set flush to the inside of the radius. The whole jamb system was sized to set 1″ below the finished floor so the glass would sit flush with the finished floor, and the jamb would be flush with the drywall ceiling below. On the top side we made an oak surround that the hardwood floor butted into, and on the ceiling side below, and we moulded the poplar S4S which overlaid the drywall on the ceiling below. So none of the plywood veneers were exposed.

    Ed.

    Reply
  5. Garry Macdonald

    This is a great and very detailed explanation, thank you Ed! It is something I have always wanted to try, but never had the opportunity as yet. I also wouldn’t have a clue how to price for something like this!

    Thanks again for posting,

    Garry
    Glasgow, UK

    Reply

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