Thread: Grinding very small curve

Hello - Sorry if this is super basic for this group but i'm a woodworker mostly and i'm restoring a lot of 100+ year old wood windows. Some of the profiles of these windows are in bad shape and i need to make myself a metal card scraper so i can use it to revive the profiles. Basically i want to take a normal wood "card scraper" which is just a .8m piece of steel and cut the moulding profile that is used on the rails, stiles, and muntins of the window.

I was able to transfer the pattern onto my steel stock and then i used my 6" grinder to remove most of the metal. I then used some files and my dremel with a small drum to grind to most of my lines. Problem is the curve in the profile is a bit elongated and when i grind with the dremel it creates part of a perfect circle. I tried to use some small rounded files but it makes it a little jagged and that shows up when i scrape the wood.

Not sure if this picture does it justice but i guess how do i grind to a elongated curved line so its a smooth curve end to end? I have a feeling this is a stupid question that metal workers do all the time...

scraper.jpg

Draw filing.

Instead of working the file across the material, you go along it. Produces a very smooth edge.

EDIT: Draw filing is generally used as a final clean up, you still need to get the shape right to start with. Try wrapping some sandpaper around your files, it might be less aggressive and give you more control.

Welcome Dave. Not a silly question at all.

I ground similar profiles into a card scraper for removing mouldy varnish from my windows. I freehanded it on my bench grinder and tidied it up with a round chainsaw sharpening file. I found it wasn't critical to get an exact copy of the profile as you can tilt the scraper in two axes to get contact with the wood. If you're getting jagged edges, use a smoother file or some 400 grit sandpaper on an appropriate diameter rod to smooth it.

I ground two profiles into the one card scraper. As they differ slightly I find one might work better on one window where the other will work better on a different window. Often I'll use both to get full coverage.

Yep that is exactly what i'm doing - removing 100 year old varnish from the windows...

I've got lots of different rods i can wrap sandpaper around and make that work - didn't think of that and was working whatever files i had around. Don't have different rounded files so this is a good solution.

Thanks!

Originally Posted by DaveInPA

I then used some files and my dremel with a small drum to grind to most of my lines. Problem is the curve in the profile is a bit elongated and when i grind with the dremel it creates part of a perfect circle.

If you constantly move the dremel drum sander side to side you can create elongated or oval type profile, just don't stop in one place.

I also ground up some scrapers from HSS blanks. Very handy for getting into tight spots in the moulding. They stay sharp forever.

I've also had to cut some strange curves, I managed to do this by angling the metal to the abrasive, ie. at 45 degrees gives a shallower curve than at parallel.
HTH
Kryn

G'day Dave,
Another way to get a fine finish is to get the profile as close as possible with your file then wrap the file in some 180 grit emery cloth and work your way up through the grits to get the quality of finish you require.
Cheers,
Greg.