Copying a window molding

[Nick Keenan]

I have a window where part of the sash is rotted out and I'm going to try to make a replacement, I thought I'd lay out what I'm thinking and see if anyone has any pointers.

This is what the profile looks like:


It's about an inch and a quarter high and an inch and a half wide.

Here's the plan. Cut a piece of stock to size, then cut away one corner using the table saw:



Then use a half inch straight router bit to cut the rest of the depth of that side:


The little lip that remains is at a 14-degree angle, which is the same as a dovetail bit, so I can make that cut on the router table:



Then I can cut out the straight part of the two other cuts with either the table saw or a straight bit on the router table. The big one is 1/8" and the small one is 1/16" so it's not a lot of wood:


Then I just need to cut those two bevels. I could probably do it on a table saw, but I think a chamfer bit on the router table would be safer and more reliable.

How does that sound?

The next question is what kind of wood to use. A carpenter friend recommends Spanish cedar, which I can get locally in 6/4 and 8/4. I also talked to a window-maker who said they're using something called Accoya Wood for window frames now, which is a new treatment. Has anyone used that or even heard of it? It's a new treatment, guaranteed not to rot for 50 years. I don't even know if I can buy it locally.

Thoughts?

Thanks.

[Nick Keenan]

I think I like that better. So I understand:
Step 1:


Step 2:


Step 3:


Step 4, with the dovetail bit:


Step 5:


Then chamfer those edges. I'll have to experiment, it might be easier to do the chamfer with the table saw blade between steps 1 and 2; i.e. before the slots are cut.

[LCHIEN]

Looks doable. A lot of small cuts.
How many feet you needing?

[Nick Keenan]

I'm going to do the whole window, which is 48x24, so 12 feet total.

[Nick Keenan]

I also thought about doing it in two pieces and gluing them together.

[LCHIEN]

That is probably a smart idea. Less waste for one thing, for another, you don't lose all your work if you screw up and have to start over (voice of experience talking).

[mpc]

My concern is the 14 degree bevel cut. If you remove the bulk of the waste as you described prior to making the bevel cut you won't have a good surface to ride against a router table fence. The surface that will eventually get the two 45 degree bevels will have to ride the fence while the skinny leg, that will receive the 14 degree bevel, rides on the router table surface. That is a skinny "foot" to ride on. The fence will be away from the bit, by an inch or whatever the height of the molding is, with nothing surrounding the bit. It's not an impossible cut, just a little less than ideal. You have to balance the workpiece on the skinny foot while keeping it against the fence... and not letting it cock/tip/rotate on that skinny foot. It would be better if there was a second "skinny foot" to straddle the dovetail bit... i.e. don't cut away the big square waste area as step 1.

I think I'd rotate the workpiece 90 degrees counter-clockwise from how it is oriented in your pictures... and then use a table saw dado stack or a straight cutting bit in the router to make a channel in the workpiece; that channel is where the dovetail bit's center/shank will be. It will also be right at the peak of the dovetail in your picture. Before changing the router bit or dado stack, flip the workpiece upside-down and cut the channel at the top that receives one of the 45 degree bevels - one of the cuts you listed in your last step. The 1/8th inch cut if I understood correctly; you can make this wider to match your straight cutting router bit - cutting into the square waste area. You'll have the whole width of the workpiece against the tabletop for a good/wide (and safer) footprint. Then make the 1/16th cut with either the table saw or router. Next, swap in the dovetail bit and make that cut. The dovetail bit will still be "an island" on its own, an inch or whatever away from the fence... but the workpiece will still have a large footprint on the table and against the fence because most of that large square waste area will still be present.

Once the dovetail slot is made, then use the table saw to make a pair of cuts 90 degrees to each other to remove the big part of the waste; basically what you listed as your first step. You could use a dado stack to cut all the way down to the edge of the 14 degree bevel, doing what you described as your second step. And you could use a router bit too as you said; remove the bulk of the waste with 2 table saw cuts as you described, then use a shorter straight bit with a shank mounted bearing to make the final passes. The bearing would ride against the vertical surface cut by the table saw, just below the "channel" made earlier.

All that's left are the two 45 degree bevels which, because they are small cuts, will be easier to make while "balancing" the workpiece on its top. Or use a block plane or other hand plane to buzz the corners to a bevel.

mpc

[Nick Keenan]

I think I like that better. So I understand:
Step 1:


Step 2:


Step 3:


Step 4, with the dovetail bit:


Step 5:


Then chamfer those edges. I'll have to experiment, it might be easier to do the chamfer with the table saw blade between steps 1 and 2; i.e. before the slots are cut.

[mpc]

Exactly. In step 2 you don't need to make the slot 1/8th inch wide either... let it slop over into the "L" shaped waste area. That way you can use the same dado blade/router bit setup as step 1; just adjust the cutting height as appropriate..
Making the step 1 slot wider than the dovetail bit, as your drawings show, is a smart idea. Easier to control if its cutting only along 1 edge.

mpc

[Nick Keenan]

OK, now I'm thinking I can do it all on the table saw:

Cut one:


Cut two:


Cut three:


Cut four:

Cut five:


Cut six:


Cut seven:


Cuts eight and nine would be to clean out the rest, or maybe I'd use the router table for that.

[Nick Keenan]

Does anyone have a good method for making angle cuts like that reproducible? By which I mean changing the settings on the saw and then coming back to where it was. Both the depth and the distance from the fence need to be indexed. The blade angle is easy. I'm thinking of making a reference cut in a piece of scrap and then using that to align the fence and set the blade height, but I wonder if it's precise enough.

[capncarl]

A little design may be in order. The little bevel or trough is probably the reason the window rotted out because of puddling water.

[Nick Keenan]

A little design may be in order. The little bevel or trough is probably the reason the window rotted out because of puddling water.

Perhaps. But it's a window that was installed in 1976. The other ones are fine, which is why I want to fix this one instead of replacing it. If my fix lasts 47 years I'm OK with that.

[Nick Keenan]

OK, I made my first prototype out of a piece of 2x4, using just the table saw. Original is on the left, copy on the right.



I used the original to align the saw, then cut, then adjust. I found it typically took me two tries to get the saw dialed in. I started with eight pieces. Once I got it I cut them all and moved on to the next cut. If I spoiled a piece I'd use it for first cuts unless it was too spoiled to continue.

It's not exact but I think it's good enough to continue. Now I just need to buy some stock.

[LCHIEN]

Looks good!