Power wet sanding with mineral spirits?

[Roger Bull]

I'm going to resurface the tables on my jointer. The previous owner left the surfaces 'inconsistent' at best. I was thinking I would use a quarter sheet sander and mineral spirits as a lubricant. Am I risking fire started by the sander motor?
Or is this an elbow grease only task?

[Jim Becker]

The few times I've sanded a machine top like this...I just sanded it and cleaned it afterward with the MS. That said, I don't believe you're at risk by wet sanding the cast iron with mineral spirits.

[Roger Bull]

Thanks Jim. Thats what I thought but I knew if there were any unfortunate tales you guys would have heard them. I'll give it a try.

[Wayne Lomman]

You will get a much better and more accurate result using a stone if you table finish is inconsistent. Any form of soft pad follows inconsistencies. As for fire danger, I wouldn't do this in a blue fit but on the other hand I spray solvent finishes all the time in my shop which many here don't risk. Cheers

[Bill Dufour]

Or you could do like a real machinist would and scrape it flat. You do not need anything close to what a machinist does.
Bill D

[Nick Shattuck]

I wouldn't use mineral spirits because it will flash rust. You need to use mineral spirits + oil, aka WD-40. It'll keep the cast-iron from rusting while you work. I've found the best way to refinish the surface is to attach a scour pad to the bottom of my sander and go over the table after coating it with WD-40.

[Bill Dufour]

A carbide blade in a paint scraper will probably work well enough if you only need to remove a few high spots. I do not really want frosting on my wood working tables because I do not like the look on wood tools. Of course many folks like the look of frosting. To really get it flat you will need a third flat reference surface. Either a surface plate or another table.
Bill D.

https://video.search.yahoo.com/yhs/search;_ylt=AwrTceDHQHZaUEsA1mcPxQt.?p=hand+scrapi ng+metal&fr=yhs-pty-pty_maps&fr2=piv-web&hspart=pty&hsimp=yhs-pty_maps&type=ma_appfocus1_ff#id=2&vid=b6082f2223333a719fe698ce6673d59d&action=view

[Roger Bull]

A carbide blade in a paint scraper will probably work well enough if you only need to remove a few high spots. I do not really want frosting on my wood working tables because I do not like the look on wood tools. Of course many folks like the look of frosting. To really get it flat you will need a third flat reference surface. Either a surface plate or another table.
Bill D.

https://video.search.yahoo.com/yhs/search;_ylt=AwrTceDHQHZaUEsA1mcPxQt.?p=hand+scrapi ng+metal&fr=yhs-pty-pty_maps&fr2=piv-web&hspart=pty&hsimp=yhs-pty_maps&type=ma_appfocus1_ff#id=2&vid=b6082f2223333a719fe698ce6673d59d&action=view

Wow. That is pretty impressive how they scrape the surfaces. Personally I would be looking for a tall building before I would spend that effort on 7' of jointer tables. Good thing it is way more than I need.

I ended up sanding with mineral spirits and keeping it wet. I didn't see the post about WD-40 until I was done. That would have helped. I started at 150 grit because there were a lot of issues from the previous owner. I finished with 600 grit and it looks pretty good. Rust and stains are gone. There were some scratches that didn't go away but they are now smooth enough. I'll just consider them to be extra spots to hold the wax. ;)
I'm happy with how it turned out. I should have taken before and after pics. It's a pretty dramatic difference.
Back to making sawdust tomorrow.

[Prashun Patel]

Respectfully, I disagree with this statement. Mineral spirits contains no water and cannot cause rust. I use it all the time on iron tops and blades and have never seen this happen.

[Bill Dufour]

Respectfully, I disagree with this statement. Mineral spirits contains no water and cannot cause rust. I use it all the time on iron tops and blades and have never seen this happen.

I agree that it does not cause rusting but you do need to coat it as soon as possible with oil or wax to stop flash rusting. I have even used water based cleaners to remove grease. Then quickly set the part in the sun to dry or even wave a propane torch over it and watch it dry.
For some reason in my shop the woodworking stuff does not rust, too thin of castings I guess but the metal lathe and milling machine can get condensation. The lathe weighs about 3/4 ton the mill/drill half that. I have to add some heat to them in winter to keep them above the dew point which is about 45 F. When I had a wood lathe there was no problem. I just added a goldenrod heater in the base and threw a blanket over the machine.
Bill D
Bill D

[Prashun Patel]

I have had flash rusting with Water, Water based cleaners and citric acid solutions for removing rust, but never with mineral spirits.

If you get flash rust it is because the surface has contacted Water. It could be that the mineral spirits removes any patina or protective oils that prevent rusting in theory but That has never happened to me.

I am only pushing this point because we use mineral spirits in some products precisely because any amount of water would be ruinous in the product. Mineral spirits is strictly hydrocarbon and will repel Water, not attract it from the air as alcohol based solvents will do.

Mineral spirits is in fact identical to mineral oil in its aversion to water. It is simply more volatile.

[Bill Adamsen]

I too use mineral spirits for cleaning tops ... even as a lubricant if using a small section of synthetic pad under a block of wood for deep cleaning. The waste cleans up easily and doesn't introduce risk of corrosion. Many of my tools have planed surfaces and the objective is simply to clean and wax to reduce friction, not remove much material. This approach with mineral spirits has served me well for many years, though I'm always open to improving.

[John C Cox]

Please do not power sand using mineral spirits.. That's asking to catch yourself and your shop on fire...

Instead - use mineral OIL... Much lower flash point.. Doesn't produce much in the way of vapor at normal room temperature ranges. Very unlikely to light on fire from a stray spark.... Another alternative is to just go buy some cheap 0w20 motor oil for use as a lubricant...

Barring that - use vegetable oil or canola oil... It's pretty cheap - and you probably already have enough in the house... But clean it all off with mineral spirits when you are done and then wax...

I would consider taking the table to a machine shop to have it reground... Especially if you want any sort of precision..
But.. If parts are still available - you may well find a new replacement table cheaper....

[Justin Meyer]

It could be that the mineral spirits removes any patina or protective oils that prevent rusting in theory but That has never happened to me.


In the scope of our shops and machinery (and efforts to protect surfaces), this is what happens.


If you get flash rust it is because the surface has contacted Water.


And even a non-visible layer adsorbed from the vapor in the air is sufficient. Even under non-extreme conditions, flash rust can form in under 5 minutes--generally, though we have much more time to put a first coat of wax on.

[Justin Meyer]

Instead - use mineral OIL... Much lower flash point..


John, you mis-typed "higher" (~355degF). :-)

[Rich Engelhardt]

We used to pump bulk mineral spirits out of a 55 gal drum where I worked.
I used to fill my Zippo lighter with what was always spilled on the top of the drum.


Use mineral spirits to sand with if you want, but, please don't do in around me or anything I own.

[Roger Bull]

Good advice. Clearly there are better lubricants to use. Had I seen more posts on this thread I would not have wet sanded with mineral spirits. If I have to do it again I'll use light mineral oil or something with a similarly high flash point.
I did move the jointer outside while sanding just in case. Plus it is warm and dry here so being outside in the sun helps prevent the possibility of flash rus

[John C Cox]

Mineral spirits works fine for wet sanding by hand with blocks... It's about the only way to "wet" sand shellac finishes. I have done this several times with very good results...

And if you are doing this by hand (no power sanding) - sand your cast iron table outside and let it dry out real good before putting it back into service....

100.000000% never around anything that can spark, anything electrical, or anything with a flame on it (gas water heater?)... And never ever ever do the sanding with power tools - or you will have a long stay in the burn unit (if you are lucky)....

[Joe Jensen]

Are you trying to re-level the surface or just remove rust? I have tried using a lubricant to power sand a finish and while the lubricant worked as intended, buy a lot because you will "lubricate" everything within 15 feet of where you are working. My orbital flung lubricant (in my case water) everywhere. If just removing rust I can't see the need for lubricant.

[Roger Bull]

Are you trying to re-level the surface or just remove rust? I have tried using a lubricant to power sand a finish and while the lubricant worked as intended, buy a lot because you will "lubricate" everything within 15 feet of where you are working. My orbital flung lubricant (in my case water) everywhere. If just removing rust I can't see the need for lubricant.

I was just trying to remove rust and and some scratches. You are correct about lubricant being flung everywhere. It was quite an effort to remain dry because in the chance it did ignite I didn't want to become a candle.
I did do this outside and started off dry. I didn't move to wet until 400 and 600 grit.
It worked out well for me but I would do it differently next time.

[Joe Spear]

...

Instead - use mineral OIL... Much lower flash point..


Don't you mean a much HIGHER flash point for mineral oil? It doesn't vaporize very fast at all and needs a higher temperature to ignite.