Sanding cast iron table saw surface

[Michael Kellough]

My old Walker Turner saw has worn down a bit in front.

It’s not really a problem in terms of using the saw to cut stuff but I like to use the surface to assemble small stuff and it’s getting to the point that I need to add shim stock to the front area.

I wonder if I could sand the area around the blade to bring it down to match the front? I have straight edges to monitor the progress.

Any tips on what abrasives to use and what to avoid?

 

[TSO_Products]

Michael,
have you considered removing the cast iron top and having it (re-)ground flat?

Hans

 

[Cheese]

I'm with Hans on this one Michael...look for an automotive shop that blanchard grinds flywheels and clutch plates, it'll probably be pretty inexpensive.

 

[rvieceli]

Don’t even try to go it yourself. Find a machine shop that will regrind it for you.

Ron

 

[Scott in San Diego]

I wouldn't sand or grind.  Because the throat plate recess and miter slots may not be deep enough and could require further machining.  Also, consider any side wings that may not have enough adjustment to sit flush with the main table.

I would set a piece of MDF, or the like, on the saw table as a reasonable flat work surface.

 

[guybo]

Question? after grinding would not the miter slot also have to be cut? or accessories that use them be affected?

 

[Michael Kellough]

If the arbor hung from the cabinet instead of the table I'd do that (take the top off and get it ground).

On this saw the trunions key into slots in the underside of the table and it took days to get everything right which included fileing and shimming and every iteration included jacking the cast iron motor up and down precisely enough to align the trunions with those slots. Not to mention getting four bolts and washers into holes located as far away the hole your arm has to pass through as possible.

Now that it's just right and the table is level and rock solid (semi permanently anchored to the concrete floor) I'm never going to do the above again.

So, how to go about it?

What abrasive?

Does sanding cast iron make sparks? If so, do the sparks stop forming at lower speeds?
I'm thinking of zirconia belts on my belt sander with sanding frame.

 

[Michael Kellough]

Question? after grinding would not the miter slot also have to be cut? or accessories that use them be affected?

I only need to take the middle down about .01" or less. I could run a file in the slots if they got too shallow.

It came to mind to try to improve the flatness of the table after I modded a cast iron lathe extension to fit my lathe, for which no such accessory was made. It was remarkably easy to cut, drill, and file the cast iron so it got me thinking...

 

[guybo]

wet and dry silicon carbide ?

 

[Packard]

Glue large sheets of sandpaper paper to a sheet of 1/4" float glass, and work it across the entire surface.  We used to "mill" the heads of our go kart engines exactly that way.

Float glass is very flat.  You want at least 1/4" thick or more.  Glue on a couple of handles to make your work easier.

Apply Prussian blue to the surface to see the low points after sanding.  The alternative is to remove the top and send it out to be Blanchard ground.  An expensive option.

Blanchard grinding will flatten the surface to within ±0.001", but there is a height restriction so the top would have to be removed.

There are Blanchard grinding companies all over the place.  You should be able to find one locally.

 

[Svar]

Cosmas Bauer (youtube) milled his cast iron saw with wood router.
I flattened aluminum with router, but that wasn't pretty.
Have you considered filling the depression with epoxy?

 

[jeffinsgf]

I sanded my table saw top to remove rust, but not remove much material. If you use a random orbit, I don't think you'll get any sparking. It would take more friction and higher rpms to generate enough heat for sparks. If you really need to remove ten thousandths (0.010") you'll need to start with some pretty aggressive paper...maybe 80 grit. Once you get it approaching flat, start working toward finer grits in very small steps. After about 320 switch to wet dry paper and spray the top down with WD-40 as you sand. Makes a helluva mess, but the top will look and feel like new. Oh, yeah, I'd buy a bargain basement R.O. sander to do this, not one of your Festool ones.

I would not try to use a belt sander.

 

[tsmi243]

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. 

 

[Michael Kellough]

Thanks for the tips!

There isn’t a depression. The front is just worn down a little from 65 years of wood being started from there.

Looking more closely it’s only the first three inches that are worn down below the overall plane of the table. The worst is .01 low at the very front and it it’s back to within .001 by 3 inches in.

It only came to my attention while assembling a small table that occupied the whole saw top. Then the little gap between the wood and the iron was apparent.

I’ll probably just run Scotchbrite over the whole thing and wax it but if I do any more I’ll post it here.

 

[Michael Kellough]

Never considered wipe on poly. Doesn’t it scratch off?

 

[tsmi243]

Mine didn't.  I didn't let it sit on the surface, I wiped it off immediately, so there wasn't any real "film" to it.  Just what the iron absorbed.

 

[DeformedTree]

Not a sexy option, but you could always build it up with something like bondo. Scrape that back to flat with the rest of the table.  Paint the top while at it if you like

Sending the top out to be ground would be the correct option, miter slots could be milled while they are at it. But be warned, the top might deform afterwards.

If you are bored, you could work on your hand scraping skills. Videos on youtube on how to scrap down iron beds for mills and such.

 

[tallgrass]

How about scraping, then flaking? I bet it would be beautiful. You could also decide what level of "flatness" you would be ok
with.

 

[kevinculle]

I would not attempt to level the top if the issue is only near the leading edge, you are more likely to end up with a less functional tool in the end.  As long as the majority of the table surface is flat just make sure you avoid placing pressure on a workpiece over the dip at the front.

 

[Michael Kellough]

I would not attempt to level the top if the issue is only near the leading edge, you are more likely to end up with a less functional tool in the end.  As long as the majority of the table surface is flat just make sure you avoid placing pressure on a workpiece over the dip at the front.

That’s what I’ve been doing and will continue with that. I’ve refreshed my knowledge of the surface and can avoid registering anything on the low side.

So it’s going to stay the way it is. Working with it yesterday I realized that if it was bright and shiny clean I’d be blinded by the reflection of the overhead lights. It’s a scratchy dull grey and comfortable.