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Just figuring it out
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Discussion Starter #1
I just finished up this oak stool (https://www.woodworkingtalk.com/members/dave-mills-200027/albums/oak-stool/) and one of the areas I'm not 100% happy with is the concave curves on the legs. I had a premonition of this situation going in to the project. The issue is that I haven't been able to get a smooth line on a concave curve. You may be able to see it in the image where the light reflects off the facing leg, or even in the shadow on the wall on the right side. It looks (and more so, feels) faceted. I made them on my router using a pattern on hardboard, and then sanded them on a 3" drum sander. So I suspect these "facets" were in the pattern to begin with, and just duplicated to the legs. The issue I have is that no matter what I did to try to fix them (the legs or the original pattern), I seem to be making it worse. The drum sander drops into a dip, and makes it deeper, rather than skipping over the dips and just lowering the high points of the curve. If I go real slow, I just end up with even more "bouncing" against the drum, making it worse. On an outside curve, I don't have the issue.

In retrospect, the only thing I can think of is manual sanding with some sort of curved block that matches the curve of the leg. I'm wondering if anyone has a better answer to this predicament, though.
 

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where's my table saw?
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never mind ..... concave !
 
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Just figuring it out
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Discussion Starter #3
The drum will find it's own way and make divots. Use a belt sander. Run the belt about 1/2' in from the edge and that's where your pattern will ride, on the bare metal platten. The template should be "belt thickness" larger than your finished piece, or just let the template dictate the finished surface. You will still need to control it by hand and have a good eye to hold a like, but there will be no "divots". :smile2:
Thanks, though I guess the next question is how to make the pattern smooth in the first place. I don't think I would have these divots to the legs if the pattern was smooth to begin with.
 

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where's my table saw?
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my first reply was wrong ....

I was thinking it was convex, not concave. The best way I've found is to make a sanding block with the same curve as the inside shape and hand sand it. You can find flexible sanding blocks or make your own.

Automobile paint and supply shops will have a flexible type.
https://www.amazon.com/flexible-sanding-block/s?k=flexible+sanding+block

If you do want to use a router and a pattern bit, use the flexible sanding plate on the pattern. It will be much easier since it's more narrow. Thin spring steel plate is what I used to make smooth surfaces on wood templates for clay modeling car shapes.
:vs_cool:
 
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Nine Thumbs
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I drilled a 1/4" hole in my drum sander table and drop a 1/4" dowel in it to rest the leading edge of the wood against. Once you run the first inch around the drum and rest it on the pin, it is much easier to control the feed the rest of the way.
 

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make a "positive" pattern - convex so you can make the curve smooth and continuous.

then clamp the workpc on a spacer and use a bottom bearing trim router bit to cut the convex inner...

terrible sketch, but
img20_958.jpg
 

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Just figuring it out
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Discussion Starter #7
I was thinking it was convex, not concave. The best way I've found is to make a sanding block with the same curve as the inside shape and hand sand it. You can find flexible sanding blocks or make your own.
Ah, makes sense, thanks very much. I suspect using that on the pattern will let me get a much better cut with the router!

Thanks
Dave
 

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Just figuring it out
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Discussion Starter #8
make a "positive" pattern - convex so you can make the curve smooth and continuous.

then clamp the workpc on a spacer and use a bottom bearing trim router bit to cut the convex inner...

terrible sketch, but...
Yep, sketch is adequate, and I suspect this would help as well, thanks
 

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Jack of too many trades..
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Wow! That is beautiful!



I also do some of those long gentle curves - on corbels and easing the bottom of radiator caps and bookshelves.

What I was taught (in books) is that you want to clamp all your pieces together as a unit and sand them on an oscillating spindle sander.



I do a lot of craftsman type stuff, so I just upgraded from an old-arse Ryobi unit to a Grizzly cast-iron top unit. But even that old ryobi made a heckuvah difference in my work.
 

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I have a 3" sanding drum with a pilot bearing that I mount in my drill press. I would make sure your template is perfect, put it back on the legs, and use a drum with a pilot that can not dig.
 

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mike44
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Seems that the pattern is the problem. If the curve is a portion of a circle then use a router ,straight bit and an extension to the router base. Pivot point is the radius of the circle minus 1/2 the cutter diameter.
Run the router on a scrap of plywood, mdf etc to make the template. Use a top bearing cutter against the template. I use hot hide glue to install a template if fasteners are not appropriate . Hot hide glue will hold the work as soon as the heat disappears. About 5/10 minutes. Use heat gun to remove the template when routing is done. Let the excess glue get cold and remove with a putty knife or a sharpened piece of hardwood cut on a steep angle. Hot water on a paper towel will remove any residue. There are solvents like Goof Off that should work but may not be compatible with a finish.
mike
 

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I think there's nothing wrong with a little imperfection. But I also respect trying to achieve perfection. I think your stool looks fabulous.

Coming from a traditional woodworking perspective ... you can use a piece of low-grit sandpaper, held in your hand, and take long, even strokes on the legs to even out divots. The process is simple, and not really slow.

I use french curves to make my curved patterns. Another way is to pin down a flexible piece of wood on each end of your curve pattern, flex it to desired depth, and mark.
 

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I drilled a 1/4" hole in my drum sander table and drop a 1/4" dowel in it to rest the leading edge of the wood against. Once you run the first inch around the drum and rest it on the pin, it is much easier to control the feed the rest of the way.
i typically use the biggest drum on my sander, but i'm going to drill my table now
great idea shoprat, i can see me using it more, mine is a harbor fright but it works good enough

good looking stool dave mills 👍
 

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I have done similar stuff like that, I start with a spindle sander not guiet hitting the finish line, then hand sand to the line in long strokes. It is time consuming but works.
 
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