Was metal filler used on my cast iron top?

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Forum topic by knexster posted 01-19-2017 02:52 AM 1094 views 0 times favorited 10 replies Add to Favorites Watch
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43 posts in 1427 days

01-19-2017 02:52 AM

While refinishing my table saw top I came across several areas where there are small and pointy bumps in the top. I am wondering if metal filler was used to try and fix pitting in the top at one point. Anyone know what it could be? I am also worried that some of these small bumps are pointy enough to scratch my work piece, but I am not sure how to fix this without using a more abrasive solution that will possibly scratch up the surface and/or make things worse. Any suggestions?

While I am asking about the cast iron top, the wings are pretty rough and I doubt I can clean them smooth. Has anyone ever painted the cast iron wings, or used any other surface treatment in particular to smooth these out? Seems like all the tips out there apply to the main section of the top, but not the wings.

Pictures attached for clarity.

-- Don't think outside the box. The box was never there.

10 replies so far

View papadan's profile


3584 posts in 3512 days

#1 posted 01-19-2017 03:10 AM

You just got this saw? Someone was welding something on top of your saw. They probably connected the ground clamp to the table and just sat the metal pieces to be welded on it. You will have to “carefully” grind off the welding slag and smooth out the top with and orbital sander. Clean up the wings with the sander and paint everything but the top surfaces.

View MrUnix's profile


6928 posts in 2343 days

#2 posted 01-19-2017 03:17 AM

Looks like welding slag to me as well (notice the little ‘beads’). I’d first try using a grinding bit in a dremel, or perhaps a cutting disc, before trying more aggressive methods. As for getting the surface smooth – don’t worry about the blanchard grinding marks, as they are actually a good thing. You don’t want a mirror smooth table top or wings. Clean them up with a scotch brite pad and some solvent and then wax – they will be just fine. And any ‘tips’ for the table top equally apply to wings, or any flat cast iron table surface for that matter.


-- Brad in FL - In Dog I trust... everything else is questionable

View LittleShaver's profile


397 posts in 763 days

#3 posted 01-19-2017 01:55 PM

One way to find out if they’ll scratch your stock would be to wrap a piece of flat wood with a piece of fine wet/dry sandpaper (400 grit or better) run it over the area and see if the peaks shine up or leave tracks on your paper. Thinking about it, you could even use plain paper instead of sandpaper and look for tracks.

If you get track, then the dremel grind on the points would work to get them below the rest of the surface. The spots look small enough that they should not pose a problem if they become divets.

-- Sawdust Maker

View OSB's profile


147 posts in 670 days

#4 posted 01-19-2017 06:07 PM

I agree, it looks like weld spatter. Usually things like that are not completely fused with the underlying metal so when I clean up a welding table with spatter, I first get a chunk of steel bar stock with a nice sharp corner and slide it on the table top to try and shear off the spatter.

That can create some shallow scratches which are no big deal on a welding table.

If a few strokes of the bar stock doesn’t get it all, I get out a chisel or an angle grinder with a flap wheel disk.

I would try a method like that, hoping to shear off the spatter but all the welding tables I have cleaned were steel plate, not cast iron, I don’t know how it would react.

View Kelly's profile


2092 posts in 3088 days

#5 posted 01-19-2017 06:28 PM

I’d go the way Dan suggested – a sanding block. The longer, the better.

I’ve brought my top to a near mirror like finish using my variable speed angle grinder and diamond polishing pads with oil as a lubricant. I use my pads that are too worn for granite work. They still work fine on iron.

I’d start out with no more coarse than four hundred and a quick buff, just to see what I was dealing with.

If I had to, I could tape the ends of a file to knock down really high spots, before going to the block or taking the buff pad route.

View splatman's profile


586 posts in 1543 days

#6 posted 01-20-2017 12:04 AM

If I had to, I could tape the ends of a file to knock down really high spots

- Kelly

Exactly what I was gonna suggest. Give it a go.

View bigJohninvegas's profile


490 posts in 1606 days

#7 posted 01-20-2017 04:37 AM

At work today our welder was cleaning the slag up on his welding table. Looked just like that. He was using a angle die grinder with a flexible wheel that looked just like 40 grit paper that I have for my RO sander. He was pretty casual about it, and not being very aggressive at all. Table came out as smooth as our table saws.
A quick google search found this twist lock abrasive disk. I am sure it was this sort of disk he was using, except his was about a 4” disk.
I know the flexible disc will be less likely to gouge the surface, and I think I would try a finer grit like 220 or finer even. I bet it will make quick work of it, and if not you can always go more course. I think OSB is right too, its most likely not fused, but more of a drip that stuck to the surface. Some may come off with a sort of scraper.
All I have ever had to clean up was some minor surface rust. Some wd40, with 600 grit on my RO sander, followed by some paste wax or glide coat. That saw will look as good as new.

-- John

View OSB's profile


147 posts in 670 days

#8 posted 01-20-2017 05:15 AM

Yeah, those little disks would work, we used a flap wheel because they were more aggressive and if you use them enough you can develop quite a bit of finesse. We were not terribly concerned with scratching our welding tables, we wanted them flat and tried to avoid spatter but it happened.

A couple of our tables were Blanchard ground and drilled with a pattern of 1/2-13 holes so we could use milling machine style Teco clamps for work holding. They were also big, I think a hair larger than 4*8’ and needed 8 legs with screw adjustable feet so we could dial out the sag created by their weight.

Any way, we needed to clean them up every so often so we would shear off everything we could and then grind any remaining high spots. We didn’t want to create any dips in the surface so if we didn’t have to grind a spot, we didn’t.

View knexster's profile


43 posts in 1427 days

#9 posted 01-22-2017 03:23 AM

I don’t have a grinder, so it seemed like my best bet was the dremel. I bought a tiny dremel from harbor freight and managed to scrape it all off pretty well. Thanks everyone for all the great suggestions, and explaining that it was welding slag.

-- Don't think outside the box. The box was never there.

View OSB's profile


147 posts in 670 days

#10 posted 01-22-2017 08:39 AM

Sorry for being a terminology Nazi but you would have much bigger problems if you had slag on your table.

You had MIG weld spatter.

Slag is the residue from the flux coating of a stick weld or the burned steel left behind after a torch or plasma cut.

Spatter is little globs of metal that kind of shoot out of a MIG weld. If you have ever heard a MIG welder, it should sound like bacon frying at 3-4x speed. The sizzle and crackle is the MIG wire/electrode melting and the arc shorting and opening and like bacon grease some of it pops off which is why you wear a shirt when you cook bacon and why you don’t MIG weld close to your table saw.

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