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Ok to sand before router?

I’d like to drum sand some stock flat before putting it under the router.

I remember from 7th grade shop class we were told never ever do that. So I’ve been faithful many years carefully planning order of operations around the principle.
I think the reason was that abrasive from the belt could get embedded in the wood, then the router bit could hit it and a poorly brazed tungsten carbide cutter would go flying through someones eyeball. One tends to remember safety lessons from a guy with less than the recommended number of fingers.
Then I realized most finish plywood is factory sanded on at least 1 side and I’ve only ever had 1 carbide come off a router bit in wood, and that was after using it on aluminum.

I know sand paper, carbides, and brazing methods have improved since the 80s, so is this still a thing?

Now, looking back, I guess its silly to be reckless enough to chamfer aluminum with wood bits and still be nervous about maybe a piece of sand. I’d still like to hear if anyone has adverse experience with sanding before routing.

I wouldn’t worry about it. sanding, staining and varnish are done last for the simple reason that you get tool and working marks on the plywood or boards as you are working on them. Same reason painting is the last step when working with metal.

Thanks for the green light.

Because that shop teacher was experienced and trusted at a time when I wasn’t, I substituted his judgement (rule) for my own critical thinking. Now that I have more experience, I trust myself on anything new that I learn, but require an added push to break old habits. That is probably why I am so much more comfortable with radial arm saws than table saws. It is what I learned on.

Does anyone have shop “rules” that shouldn’t be rules any longer?

Forgive the ‘blunt’ question please.

Belt seems to indicate rubber. Any information about the particle size? Rubber could be a breaker on the sled, but wouldn’t a quick brush solve this?
From the regular sandstorms we have here (the big dust stays outside and the micro dust makes it anywhere), I noticed that this dust has a beneficial effect for the sliding of the sled.
Warps in the sheet do have significant impact on the Z-depth.
Do you have a sanding machine to run a complete sheet of ply through?

No, belt was not rubber. It was a misnomer on my part. I was referring to the paper/cloth backed sandpaper strip that is wrapped around the sanding drum.

I get mine by cutting refills for my 6" belt sander. That way I just order 1 part number for both machines and stick it to the drum with a spray contact adhesive. I did have a 52" wide homemade drum sander, but the bearings were not as concentric to the surface as I would like, so it is in the que for a machinist to whack off the welded HAZ and press fit some lathe turned endplates when he gets time. Hopefully the remainder is still over 48". I got the chrome plated hydraulic rod used for the drum free when a pit hydraulic elevator was being converted to cable. Note: in general, a new hydraulic rod works great, but used free ones are usually terrible because they only get replaced when they are bent. Because leaky pit hydraulic elevators are an ecological hazard, some public buildings replace perfectly functional straight rods.

Flattening warps is the reason I want to use the drum sander, but not for plywood. I have some diagonal cut, natural edge “tree cookies” done with an Alaskan chain saw mill. They make nice oval shaped coffee/cribbage table tops. If Maslow had good enough Z control, I would use depth maps of local lakes, or topographical maps to make coffee table models. The lake depth models are really nice because covering it with glass looks like the water surface. Topo models usually require inserting a raised perimeter which is a bit harder to add to the digital file than just truncating the beach elevation.