Bolster/Guard transition to scale/handle material

[kuraki]

Help me out here. When I have a flat surface that starts with a bolster or guard, and that meets a scale or handle with a flat surface in the same plane, I have no problem keeping them in the same plane as I sand. On the machine or hand sanding. I use a hard backer when hand sanding and keep my pressure towards the bolster since it's usually far more abrasion resistant than the scale.

My problem comes when I have a convex bolster surface meeting a convex scale surface. I inevitably wind up with a scale that has been sanded below the level of the bolster.

Part of this problem may be from my order of operations, which are typically as follows:

1. Finish blade, wrap and protect.
2. Install bolsters and rough grind to shape.
3. Install scales and rough grind to shape.
4. (maybe this is where my first mistake is) Rough grind final shape of bolster and scales, and bring them in line with each other.
5. Finish grind as above. At this point I have a pretty good looking knife shaped object, and since building a rotary platen, I can have everything plumb and even at this point
6. Finish hand sanding. Here's where everything really goes to hell on convex surfaces.

At #4 should I leave the scales higher than the bolster? If I finish ground the bolster before installing scales, then left them proud, maybe by time I finish hand sanding everything would be plumb?

I know why the hard backer on a flat surface makes this less of an issue, so do I just need to make up a bunch of concave hard sanding blocks? Because using a flat one isn't working the way I'd like either, I end up with multiple facets.

This is my experiment knife, a little EDC. This is currently plumb but not finished to my liking because every time the scales dipped below the bolster I went back to the rotary platen at 600 grit to line everything back up. Then just quit at 600 and hit it with the buffer for the time being. I would like to take it to 1200 grit to get the most out of these scales I made.

Same problem with my bowie experiment knife, just a guard and tang rather than bolsters. This knife is what drove me to make a rotary platen, and I can come off of there plumb, it's the hand finishing that kills me. I think in this picture you can even see that the guard is proud of the handle. I haven't taken one since regrinding on the rotary.

Then I'll see some of the really fantastic knives being posted where the handle is proud of any fittings, with a nice radiused edge, rather than completely plumb. They look astounding but just looking at them I understand how much more complicated that is to do and make it look correctly - the only reason I mention it is because by necessity to get that form factor one must leave the handle proud, which brings me back to maybe I'm shooting myself in the foot roughing everything together.

 

[HSC ///]

depending on the contours and definition of the features, you can use a flat disc sander to keep the mating surfaces even.
of course this flat disc sander won't work for all the variations.

curious to hear other solutions

 

[kuraki]

You know, I was hoping to do that for a lot of things, but my "flat" disc from True Grit isn't flat. They sell a flat and a 1 degree, I ordered the flat and it's definitely not 1 degree but it is noticeably not flat. I've just been finding ways around using it when I should just buy another disc.

 

[Shaw Blades]

Definitely more complicated with bolsters...especially with wood scales. I have to constantly go back and remove the scale material to flush it up with the bolster once it gets washed out. For me it works better with less time on the grinder and more time with files and sandpaper. And for sure not a lot of slack belting in that area.

 

[kuraki]

Files for sure helped before I had the rotary platen.

I think I'm going to try a thermoplastic backer. Something I can heat up and mold to the convex shape over and over. Kydex or something similar. If I get into a convex radius I want do duplicate repeatably I'll do something more permanent.

 

[john april]

never move the hard backed paper off the bolster while sanding, even at 1000 grit. the scale material usually sands away 10x faster compared to the guard. so one swipe will do damage. i usually end up with about 2 inches of the handle sanded when doing the guard/handle junction, when i sand the rest of the handle, always stay an inch or more from the guard and feather it in. you can ruin it from either direction. make sure the paper is tight around the block, and not floppy. also be aware if you have to buff some scratches out of the side of the guard, you will wear away the handle material. if the sides of the guard are well sanded to 1000 grit, 2 or 3 light swipes across the buffing wheel is all you need. i use this method, and i can close my eyes and run my fingernail over the joint and not be able to detect where it is.

 

[groy87]

John has it right. I use the half round file I used to shape the handle as a sanding backer for the transitions where your finger would go on the orange knife at the bolster scale junction. Just be sure to wrap the paper once or twice around the file. Else the ridges on the file will wear through the sandpaper and ruin your hard work with sanding.

 

[HSC ///]

John has it right. I use the half round file I used to shape the handle as a sanding backer for the transitions where your finger would go on the orange knife at the bolster scale junction. Just be sure to wrap the paper once or twice around the file. Else the ridges on the file will wear through the sandpaper and ruin your hard work with sanding.

U can also take an old file or any bar and glue on whatever hardness rubber u like as the backer. If you use a timing belt with grooves it acts like a serrated wheel.


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[kuraki]

What I'm getting from the discussion is what I thought - this is a problem for everyone and there's no magic bullet to deal with it, just careful work with hard backers.

I was hoping Larry would chime in as he seems to do many knives with bolsters and wood.