Profiling grinding inside curves

levernut

Well-Known Member
I'm continually frustrated with my inability to profile grind a smooth and continuous, inside curve. An example of an inside curve is the spine of a swept back skinner or the bottom of a curved handle. There are two instances where this causes me grief. The first is the initial profile grind when following the pattern scribe lines. I use the platen on my belt grinder and adjust the belt to wrap around the platen. The small radii are easy but the larger ones (curves) are not smooth and continuous and have high and low spots. I then attempt to use a 4" rubber grinding wheel which helps but it tends to follow the valleys and not smooth out the high spots. In addition, the 4" is too large to blending a finger groove with the rest of the handle. The second instance is after the handle has been shaped and sanded. I like to grind the profile so it is flush with the handle material and then progress to finer belts for a nice finish. I use a 3/4" wheel to finish the finger guard but have trouble blending it with the rest of the handle, especially when those bumps and valley's are heat treated steel. Sorry for the long explanation.
Any suggestions?
 
During the rough stages you can use a half-round file and draw file the ripples/ lumpy spots down. During finishing I use different sized rubber drums mounted on 1/2" dowel rod, with sandpaper wrapped around it, and chuck this in my cordless drill. For the really stubborn ones I just use a stick and sandpaper and rub them down by hand.
 
Like Justin said, you need a round surface to make a smooth inside curve. Rotary tools like Dremels and Foredoms work well, or you can adapt and improvise.
 
I recently ordered a sanding drum for my drill press, and have been using my dremel tool for the purpose. For finer grits than the dremel drums come with, I cut a slot in an aluminum rod and place sandpaper in the slot and wrap it around the rod and secure with tape. This goes in the drill press. It's cumbersome, but it gets the job done for the time being.
 
I use the same method you use by working with my platten and allowing my belt to hang off if the edge. It just takes practice to get it to work. Slow your belt down and work the curve slow. You'll get the hang of it before long.
 
If I remember rightly Beaumont Metal Works makes a horizontal grinder that can be set up for 2x72 belts. Looks to be the ultimate solution for small wheel handle and inside curve finishing, as while the handle material is still flat before being rounded the whole glued up knife assembly can be finished to a high level all around the profile without any rocking or unintentional digging into the square blade spine.
 
During the rough stages you can use a half-round file and draw file the ripples/ lumpy spots down. During finishing I use different sized rubber drums mounted on 1/2" dowel rod, with sandpaper wrapped around it, and chuck this in my cordless drill. For the really stubborn ones I just use a stick and sandpaper and rub them down by hand.

I rough out my profile with my 2x42. I get down to just outside my scribe lines and then I finish up the profile with files. Like Justin said, use a half round file for the curves. I have an 8" and a 12". I also use sandpaper or shop cloth around a dowel for a smooth finish.
 
Since I last posted in this topic, I bought a cheap rockwell spindle sander. I wind up using a new 3/4" sanding sleeve for each knife I build. It's way faster and easier than any other method I've used so far, but I hope one day to get a tilting horizontal/vertical grinder so I can get away from using the spindle sander.
 
I use a spindle sander for the curves. 3/4" for the finger grooves and 3" for the larger curves.
 
I have a piece of 1/2 dowel rod, about two inches long, slotted about 1 inch with a coping saw. Chuck it in the drill press. Put a piece of sandpaper in the slot. Voila! Drum sander with your regular sandpaper, and easy to change grits.
 
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