yet more questions on making round edge profiles

Re: Routah not worthless

William Duffield, on the Cohansey

>You can use a router. I've done so for such things as thumbnail profiles, using quarter round bits with a bearing on the end. The router is not the last step in the process, by any means, but it should get you close. The main issue is that once you have taken one side down, and flipped the piece over, the bearing now rides on this curved surface, and you end up with a step right in the middle of the edge. You have to understand, with practice on scrap, just how close this first approximation is going to get you to the curve you really want, and choose the depth and radii of your router bits to compensate. Then, it is fairly simple to work the step down to a finished, pleasing profile by hand, using rasps, files, scrapers or spokeshaves, or even sand paper. Getting a consistent profile with a fair curve just means some careful work, and lots of checking of the profile with your finger tips as you do the shaping. The first couple of times you do it, you might not be sure when you've got it good enough that there will be no visible problems after you've got the finish on. To check yourself while you are learning and training your fingertips, just squirt some mineral spirits (odorless, for your health) on the surface and look at the surface with various lighting conditions before the OMS evaporates.

Re: Routah not worthless

Paul M. in San Diego

>Hmmmm...

Router = #71

Quarter round = moulding plane

Bearing = carrying lumber from the shed

Ya lost me for a while until you got to the part about the scrapers and spokeshaves. Why didn't you start there in the first place? ;-)

Re: Routah not worthless

Frank D. in Montreal

>I thought the same as William, what you are looking for is a true bullnose profile, which, at least where I come from, is a section of a circle, not a half-round. There are true bullnose bits, but you can do the same with a quarter-round/beading profile, just don,t extend the bit all the way up and you'll have a section of a circle like in the pic.

If I'm not mistaken, although I'm the farthest thing from an expert, the cutting edge of a hollow (the sole) is 1/6 of a circle.

Frank

I'll bite *LINK*

Ed Mulligan, Cape Cod

>Edges … wind up fuzzy, no doubt a result of poor technique or ill prepared tool.

Another possibility is end grain – very likely to fuzz if scraped.

When using a scraper on an edge is the scraper tilted forward from 90 degrees?

Yes

About how much?

Depends. Tip forward until cutting action is obtained. Not much tip is needed if no hook. If you’ve added a hook, more tip will be needed to engage the hook edge.

Is the whole profile scraped at once, ie scraper hole matches profile desired,

No. The cutting geometry won’t work well.

or does one work around the edge a section at a time with a scraper hole larger than the desired profile of the edge?

Yes.

2. In preparing a scraper for a round profile does one make the hole in the scraper a section of a circle or an ellipse.

Circle is best. A circle form, when rotated about the vertical axis, will become a projected ellipse. But if you start with an ellipse shape, you can’t rotate it into a circle.

3. For edge scraping is the scraper edge sharpened at 90 degrees

Yes. And prep and use both edges, just like a card scraper.

Anything about making this sharpened edge different from a card scraper?

Well, it’s a lot more time-consuming. Convex edges can be squared with a file or on a stone. Concave surfaces can be worked with small round stones or with sandpaper wrapped around a dowel. Work the abrasive along the edge, not across the edge. It is important to get a fair curve – no bumps or lumps. Much of my curved scraping is accomplished with scrapers similar to those at the link below. If they are the wrong size/radius for your needs you can modify them or make something similar in a more convenient size. If you do make your own scraper, getting a fair curve in the steel will pay dividends in use.

In use, rotate the scraper around it's vertical axis (perpendicular to the wood surface) until its projected profile best fits the work at hand. You may need several scrapers, convex. concave, different radii, to work a complex molding. A round edge will probably require just one concave scraper. Work a small section of arc at a time along the entire length of the molding, then move to the adjacent arc and so on. Little or no flexing of the scraper is possible so a light cut (or thick scraper) is needed to avoid chatter.

I use scrapers on curved work to remove wood faster than I can with sandpaper. The scraped surface almost always will have to be sanded to obtain a surface suitable for finishing.

Ed


Scrapers

Re: I'll bite

Ed Mulligan, Cape Cod

>Maybe I bit too soon. My comments refer to a hand-held card scraper with a curved profile. Now in re-reading Bill's question, I wonder if you are talking about a scratch stock? If so, please ignore my previous post.

Very helpful, thanks

bill tindall

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