Sanding cast iron table saw surface

[Spandex]

So, I've actually done this.  The advice you're getting isn't wrong, per se, but it's just not as hard as everybody's imagining.

Cast iron sands pretty easy.  Just go at it with a random orbit, and start around 120 grit to get a feel for it.  Cast iron isn't steel, so start off easy and dial up the aggression as you see fit.  If you like how it's going, and want to move down to 80g, go for it.  Just watch your progress, and don't overshoot your mark. 

Be careful with the iron dust.  If the motor is exposed, cover it with a bag.  The dust doesn't travel much, but it DOES stick to stuff.  The dust will stain, too, so if you have an old junker sander, now is the time to use it. 

I finished up with 320, and then one coat of wipe-on poly.  I REALLY liked the result.

I don’t think anyone is claiming that sanding cast iron is difficult. It’s a relatively soft metal and will sand easily enough with power tools. If the aim was to lightly refinish the surface cosmetically I think sanding would be absolutely fine.

What the OP is suggesting though, is sanding a surface flat. In this regard, it’s going to be no different to sanding a large piece of wood - as you move your relatively small sanding pad around the large surface, it’s virtually impossible to only remove material from the high spots. Your sander just rides up and down over the surface and often you just end up accentuating the imperfections that were already there.

 

[Michael Kellough]

So, I've actually done this.  The advice you're getting isn't wrong, per se, but it's just not as hard as everybody's imagining.

Cast iron sands pretty easy.  Just go at it with a random orbit, and start around 120 grit to get a feel for it.  Cast iron isn't steel, so start off easy and dial up the aggression as you see fit.  If you like how it's going, and want to move down to 80g, go for it.  Just watch your progress, and don't overshoot your mark. 

Be careful with the iron dust.  If the motor is exposed, cover it with a bag.  The dust doesn't travel much, but it DOES stick to stuff.  The dust will stain, too, so if you have an old junker sander, now is the time to use it. 

I finished up with 320, and then one coat of wipe-on poly.  I REALLY liked the result.

I don’t think anyone is claiming that sanding cast iron is difficult. It’s a relatively soft metal and will sand easily enough with power tools. If the aim was to lightly refinish the surface cosmetically I think sanding would be absolutely fine.

What the OP is suggesting though, is sanding a surface flat. In this regard, it’s going to be no different to sanding a large piece of wood - as you move your relatively small sanding pad around the large surface, it’s virtually impossible to only remove material from the high spots. Your sander just rides up and down over the surface and often you just end up accentuating the imperfections that were already there.

That’s why, if I were to attempt this, I would use my belt sander with sanding frame. With the sanding frame only the high spots are abraded.

 

[tsmi243]

Your sander just rides up and down over the surface and often you just end up accentuating the imperfections that were already there.

I didn't say "run the sander around randomly like a moron"...  :

If you actually try a little bit, the results will be just fine.

 

[Packard]

Paint the surface with Prussian blue first, then sand.  The blue will remain in the low spots.

Prussian blue is usually used for "layout" on steel.  This two minute video gives you an idea of how it is typically used.  It won't gum up your sandpaper. 

 

[Spandex]

That’s why, if I were to attempt this, I would use my belt sander with sanding frame. With the sanding frame only the high spots are abraded.

But your ‘high spot’ is the entire table (bar the front edge). Because the problem you described is a low area at the front edge, you need to remove material from the entire table to create a flat surface that meets the lowest point on that edge. The sanding frame may reduce the risk of removing too much material in one go, but it’s still going to be extremely difficult to remove that much material completely evenly with a handheld sander.

In woodworking, you sand something smooth, not flat. Flattening isn’t done with a hand held sander.

 

[Packard]

I was not familiar with this saw.  I see used examples for sale for $175.00. A non-working version would be cheaper.

I think I would look for one with a flat top and swap it out. I would save any possible useful components for future repairs.

 

[Bob D.]

"I’ve refreshed my knowledge of the surface and can avoid registering anything on the low side."

Maybe mark this low area in some way to jog your memory and avoid it when using the saw as an assembly surface which is I believe when this becomes a problem.