Friday, January 21, 2011

Correcting Mistakes with Hollows and Rounds

When I have illustrated the steps for cutting various profiles I have quoted the dimensions in 64ths. I have been asked on several occasions if it's necessary to be that accurate. The answer is "no." My approach is nowhere near as mathematical. I typically lay the profile out on a piece of paper, transfer the profile to the wood and draw my rabbets there. I get it pretty close. I quote in 64ths simply because those are the measurements with which I initiated attack.

Layout, transferring layout, and execution of the rabbets laid out is most of the skill. Work with the profiled planes is dictated by this layout.


Transferred Layout. You can see that the line of the ogee is not parallel to the tips of the rabbets that guide the round. I made my rabbet slightly wider and not as deep. You can see below that I removed the vertical pencil line and left the horizontal.

Note that the tips of the rabbets for the lower portion to be profiled with the round are now parallel to the profile of the ogee. (Roughed out on a table saw, touched up with a rabbet plane.)

Mistakes happen. Recognizing mistakes and correcting them early is crucial. Check your progress.

We have discussed how hollows and rounds are difficult to steer and that steering should be done with the rabbet plane. But what do you do when a chamfer is wrong?



Note that I am intentionally laying out the chamfer for the hollow to follow out of line with the profile of the ogee.


The chamfer is cut at an angle that is too shallow


The profile left by the hollow is out of line with intentions.


I took my rabbet out and reestablished a chamfer that is much steeper and more accurate.


Goal achieved.


Complete

If your rabbets for the lower portion are out of line, a similar correction can be made. It's important to check you progress and recognize errors early. If you don't adjust for mistakes early you will end up pressing the the plane against the profile while trying to cut with only a portion of the iron--a difficult and inaccurate process.

As your accuracy increases your scraping at the end decreases. 

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6 comments:

  1. AnonymousJanuary 21, 2011 at 8:40 AM

    Ahhhh....

    Another light bulb moment.
    The rebates are derived from the profile not vice versa. I've been over thinking this.

    Keep it coming Matt this is fascinating.

    simonm

    ReplyDelete
  2. JohnJanuary 21, 2011 at 8:50 AM

    Thanks again Matt. I too am finding this blog one of the most interesting I have read in years. Hope you can keep up to the orders. LOL

    ReplyDelete
  3. druJanuary 21, 2011 at 1:08 PM

    Hey Matt,
    Is there a good/easy way of getting the profile dimensions from an existing molding aside from cutting a piece and tracing it? Thanks.

    ReplyDelete
  4. Matt BickfordJanuary 22, 2011 at 9:04 AM

    J. Andrew Yang,

    With many pieces you can go to the back of the piece with a circle template and measure. Many moldings only cover three sides. Otherwise, check out something like this...

    http://www.leevalley.com/en/wood/page.aspx?p=32522&cat=1,42936,42958

    ReplyDelete
  5. Matt BickfordJanuary 22, 2011 at 9:04 AM

    John,

    If you like the blog tell a friend...

    Thanks,
    Matt

    ReplyDelete
  6. druJanuary 24, 2011 at 10:07 AM

    Thanks Matt. I tried out the SS version of the profile gauge and wasn't very happy with the result. I was thinking of trying to scribe it using a compass and piece of scrap, so we'll see how that goes. Great blog. I'd tell friends, but none of them woodwork so it would fall on deaf ears.

    ReplyDelete

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