Trying to match bits for old window repair... - Router Forums
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post #1 of 12 (permalink) Old 07-16-2017, 07:42 PM Thread Starter
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Default Trying to match bits for old window repair...

I have an old window I'm desperately trying to repair without having to replace the set of sashes to match. I've built some divided light windows before and have a set that works great - but the profiles of the new sash making bits are very different from what my window has.

The profile of the rails/stiles/mumtins isn't too complicated and I think it's what you'd call a "cove with a bead". I've also seen them as "cove with a fillet". I don't know what the opposite of cove is (ogee?) but I'll need a matching set for the cope side of the cut as well.

Here is the thing - I've tried really hard to measure the existing profile and I'm pretty sure the cure of the cove isn't a fixed radius. In other words the height of the curve is 3/16" while the width is 5/16". The only bits I'm seeing have fixed radius curves for the profile. My picture below isn't great but it should show the basic profile I'm after. The "filets" or beads are 1/16" if that helps.

Any Ideas how to replicate this profile? I think the window was from the early eighties so it's not like it's an antique profile...

Thanks!
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post #2 of 12 (permalink) Old 07-16-2017, 07:53 PM Thread Starter
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with picture...

The grey lines I put in for the "height" and "width" of the radius doesn't show too well but the 3/16 is the drop from the top to the bottom of the radius and 5/16 is the length of the radius.
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post #3 of 12 (permalink) Old 07-19-2017, 10:40 AM
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Dave, Have you looked at the Amana Window Sash and Rail sets?
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post #4 of 12 (permalink) Old 07-19-2017, 12:40 PM
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All that is is a round over bit that is also cutting two fillets. The bottom fillet is achieved by switching to a smaller bearing. A cove bit of the same radius should match if they are well machined. That means I wouldn't trust anything Chinese.
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Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #5 of 12 (permalink) Old 07-19-2017, 01:15 PM Thread Starter
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thanks for the replies....

Well maybe i'm overthinking this or perhaps my geometry is way off. If I use a round-over bit with a 5/16" radius then I get a curve that is 5/16" at its base and 5/16" at its height. The profile i'm trying to replicate is 3/16" at its height which I think means its not a constant radius curve. In other words I will be 1/8" too high on one side of the profile or my curve will look funny.

I ordered a 5/16" round over and i'm going to see if I can get it close. I'm just surprised that this would be such a unique profile for a window from the 80s so was thinking there was a way to get this with one or more router bits...
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post #6 of 12 (permalink) Old 07-19-2017, 01:20 PM
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Your drawing reminds me of a thumbnail bit but you'll be unlikely able to find it's mirror image. They may have been custom ground. https://www.google.ca/search?q=thumb...w=1920&bih=971

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #7 of 12 (permalink) Old 07-19-2017, 01:31 PM Thread Starter
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I think that looks about right - I would just have to find the one with the right dimensions and then figure a way to make the filets. I'll try to see if I can get the 5/16" round over close. I'm thinking I can get the 5/16 curve first and then use a rabbet or other bit to create the filets. Will see...

I've struggled before trying to get sash/muntin profiles for other historic windows and came up empty. I'm couldn't even find them with hand planes. I guess i'm the only one out there building/fixing custom windows these days?
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post #8 of 12 (permalink) Old 07-19-2017, 03:05 PM
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Dave; the original would have been done on a shaper, most likely with custom ground knives. When I needed mouldings to match existing, 'BC Sash and Door' would take my sample, grind the knives, and charge me if I recall correctly $75Cdn. for the process, plus a basic charge for the first X number of ft. of moulding, then a fee of Y for each additional ft. of machined moulding.
I didn't get to keep the knives either.
But you know, it got the job done and the clients were happy.
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post #9 of 12 (permalink) Old 07-19-2017, 03:14 PM
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Just to clarify, Dave; are you saying the curved portion is a true arc, or is it a segment of a parabola? A true arc would have a constant radius. The shoulders at either end aren't relevant to the radius.
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post #10 of 12 (permalink) Old 07-19-2017, 05:10 PM
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Seems to me a few years ago I saw an ad in a mag for a tool that would grind knives for a molder. I can't remember where or how much but it might be something you want to try searching for in your spare time.

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