[Shiny]

What tools do you use to shape/sand small radii like these 90-degree bends?

Things I tried left variation in the radius and/or waves that would look like caca when painted.

Are there scrapers, fixed-radius sanding blocks, or contour blocks for these small radii? I'm guessing OD on the lower edge of the bumper cutout is about 3/32" and on the more "vertical" edges, maybe 1/8"?

[SRGN]

Block sand, use a diagonal pattern, on the primer you should be using 400 grit, wet. Durablock makes some soft blocks that should make it a little easier. Never sand straight patterns, sanding on a diagonal allows you to keep your lines and curves consistent.

[ID67goat]

I use flexible durablock as mentioned or cut different diameter wooden dowels..

[Shiny]

Thanks for the replies.

I will try to clarify. The edges of the bumper cutout have sharp 90-degree bends with small outer diameters. When undamaged, these edges are straight with very uniform radii. They are not sharp corners.

I blocked the primer and filler on the panels as you describe using both flat and convex rigid long blocks. That went OK.

My question is how to get those sharp bends on the edges looking right? Basically, where two planes come together, there is a sharp radius along the fold. A big block or just folding paper around a foam block isn't consistent for me.

Are there sanding blocks or similar tools with a controlled radius that can make these edges look "crisp" instead of like I chamfered them with a dremel tool? If it was wood, a router bit might make sense. ???

Lots of newer cars have sharp edges like these that are highly visible. I figure there must be some "standard practice" or tools to keep them accurate ???

[Cammer-6]

My sand paper bucket has bits of fuel line,radiator hose,heater hose etc
stickyback sandpaper works good for this

[SRGN]

You have to kind of roll the block over the edge while moving diagonally, if that makes any sense. Put minimum pressure on the block, let the paper do the work. I'm not good at putting this into typed words, so feel free to ask questions. This is one of those times where seeing it done would be better than a thousand words.

[Shiny]

Thank you!

I think the tubing idea is what I was hoping for... something with a fixed concave radius like splitting a tube lengthwise.

I understand the concept of rolling a block around the edge while maintaining the crosshatch. I just don't have the skill to repeat that, let alone follow a contour or curved fold.

I did find a lot of concave foam blocks like those attached but nothing below 1/4".

I don't know if I'll ever spend what it takes to get the car painted so prep beyond epoxy primer is hot a current priority. But I still might try making some smaller versions of these. I could easily glue some small diameter brass or aluminum tubing to something like a paint stick and give it a try.

I'm honestly surprised they don't make something like this with bonded grit.. like a sanding sponge or emery board. Rolling paper inside a 1/8" or smaller tube may be a barrier. Something like 320 or 400 wet-sand paper might be the best option.

Mike

[400 4spd.]

My technique on rounded edges is to leave them alone until all of my flat blocking is over with. By then you will probably have a sharper edge than desired. Before final priming, simply take a piece of 220 or 320 paper and using your fingers, roll the paper over the sharp edge and lightly sand following the direction of the peak. You will be removing material and should end up with a softened edge. You can’t achieve this with a block, just use a light touch and read the surface as it sands away.

[Shiny]

Thanks for sharing your method.

That's what I tried after the filler/glaze which did leave a too-sharp edge. The underside of my bumper cutout fold is not flat, which added difficulty.

I just don't have the touch to make it uniform.

No biggy for now. If I get it painted a pro will have to prime and sand it again.

But I am entertaining making a tool just for fun. 3M and others sell abrasives on film substrates that will bend sharper than paper so just need small diameter concave mandrels.