Keeping the Accuracy of a Combination Square

Is it possible to use wax or some other lubricant to prevent the slots where the ruler interfaces the head of a cast iron combination square from wearing down over time?

Keep the slot for the blade clean, free of crud, and lube with Starrett M-1. You should get a life time of use out of a combination square set. I have one of my dad's I've had since I was about 12 years old, still good as new. Of course, I have several sets that I float around in the shop, and my use is not that much, just a occasional use, meantime, they are stored in my machinist chest until needed. Your mileage my vary. Ken

Don't loan it to anyone no matter what. If you have issues with humidity put your tools in the tool chest when tot in use. Wax might help but it will wear off.

I like rem oil (a brand of gun oil) for tool lubrication it doesn't get sticky.

4GSR said:

Keep the slot for the blade clean, free of crud, and lube with Starrett M-1. You should get a life time of use out of a combination square set. I have one of my dad's I've had since I was about 12 years old, still good as new. Of course, I have several sets that I float around in the shop, and my use is not that much, just a occasional use, meantime, they are stored in my machinist chest until needed. Your mileage my vary. Ken

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Thanks! Someone told me to expect only 1-2 years of regular use before it looses accuracy. Didn't sound right to me, but maybe they were referring to an aluminum square. Does the lubricant actually stop wear?

carlherrnstein said:

Don't loan it to anyone no matter what. If you have issues with humidity put your tools in the tool chest when tot in use. Wax might help but it will wear off.

I like rem oil (a brand of gun oil) for tool lubrication it doesn't get sticky.

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Thanks! I've got plenty of Rem Oil here.

That's one more item in your annual service of your personal tools - check your squares. You can fine tune your combination square head if it absolutely positively has to be done. The slot for the scale is not merely square bottomed: it's raised in a convex like a bullnose on a the edge of a table top or stair tread. You can dress the crest of the convex with a thin slip stone to correct square error, maybe doctor up a cheap import square to usability.

Here's a video showing a general method for quantifying squareness by the doubling method using a surface gage, DTI, and surface plate. It works for combination squares too but you have to build a bridge of 1-2-3 blocks to pass the square head under the surface gage. This method, if carefully executed and the head (or stock) and beam are validated straight and parallel, will certify squareness to half the resolution of the DTI/span.

YouTube

In the third year of my apprenticeship, my layout and inspection mentor was Tommy Thompson. He told me the purpose of the slot bottom's convexity was to facilitate adjusting my brand new Starrett combination square set (bought with my first overtime check.) He suggested I get a Norton 1/16" x 3/4" x 4" slip stone in case of need. That stone has sat, unused, in the center left drawer of my toolbox with my other small stones for 56 years. I used that square my whole career and it's still within 0.0015" in 12", about the same as when new. Maybe someday.

The cheap ones with die cast alloy heads will wear, but if they are used properly they can remain square. If you loosen the screw enough before sliding and push against the side away from the screw while sliding the head any resulting wear shouldn't affect accuracy. IMO too many people apply pressure while sliding that wears the slot unevenly resulting in an out of square condition.

Imo a combo square is NOT used for checking square, except rough. If you want to check square, get a solid square set. Nothing to wear out unless you drop it or abuse it

MG88 said:

Thanks! Someone told me to expect only 1-2 years of regular use before it looses accuracy. Didn't sound right to me, but maybe they were referring to an aluminum square. Does the lubricant actually stop wear?

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I'm curious where that 1-2 year claim came from. First, it doesn't sound like it came from someone with 30 years experience since as several have attested, they don't actually wear much. Second, I'm wondering about what kind of use would actually make them wear and become inaccurate. By the law of averages, it ought to wear fairly evenly and accuracy wouldn't be going off the the Jones's in one direction or the other. And lastly, I'd wonder if this is another version of sending the new apprentice out for the left handed monkey wrench, the board stretcher, the bucket of prop wash or whatever. It almost seems designed to be fed to someone who wouldn't know the difference.

In any case, I'll second the "oil it and don't worry" advice. My Brown and Sharpe was new in 1975, lives in my toolbox, and still works exactly as advertised.

TGTool said:

I'm curious where that 1-2 year claim came from.

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A carpenter friend who is always buying new tools. It seemed odd to me, too, but I'm still learning. I didn't want to do anything to damage this tool I just purchased.

Carpenters aren't known for tender loving care toward tools.

MG88 said:

A carpenter friend who is always buying new tools. It seemed odd to me, too, but I'm still learning. I didn't want to do anything to damage this tool I just purchased.

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Well, that might be an alternate strategy. If your tools get beaten up and damaged a lot in the workplace, you might tend to buy disposable tools. And the cheap tools are also more likely to get damaged in the workplace. In tool rooms I've worked in, guys tend to have good tools, they take care of them, and borrowing tools around is a negotiation. If you don't return it in good time and in good condition, you won't get to use it again.

People working together in the shop learn who has what specialized tools, who are responsible users and so on. I recall working with a moldmaker who had a set of angle blocks he'd made years ago. Nice blocks, hardened and ground and reliable. Some were made with a toe, or block at the end so they could be stacked without sliding apart. He was good about offering knowledge and advice and you could borrow from him if you really needed. One of the other guys who started with me had borrowed the blocks to set up a workpiece on the mill vise. He was tapping the piece down to seat everything and must have been a heavy handed tapper because he popped the toe right off the end of an angle block. That's a hard one to recover from, because you can't offer to just buy the guy a replacement since it's not a commercial product. Making a replacement might be just possible if you can sneak the time in here and there and you'd damn well make certain that is was as accurate as the original. Dunno how the two of them made out after that.

I'm a retired carpenter who has used combination squares often. I inherited two Starrett combination squares, 12" and 6". I only took the 6" square to work and only if it was a trim job. Other jobs I kept a inexpensive square in the tool box. The tool box square got an occasional spray of WD-40. This square was prone to dirty conditions that could not be helped. The Starrett combination squares are at least 50+ years old and have never been waxed, sprayed etc.
In my home shop the only time I would use a combination square was for any work but machining.
mike

"Does the lubricant actually stop wear?" Well, no. Nothing will ever stop wear if the square is being actually used. Motor oil in an engine keeps the wear down to a bare minimum, but engines still wear out. So will squares. It is just a matter of how long that takes.

What type of lube or preventative and how well it works is a matter that depends on many factors. For instance, in a dusty environment, use of an oil could actually trap that abrasive dust between the surfaces and cause them to wear faster. Under more normal circumstances, that same lubrication or preventative could greatly decrease the wear. It just depends.

I have about a half dozen adjustable squares, some many decades old and have not seen any great problems with only occasional application of a very light coating with oil. I apply it with an oily rag and wipe it down after that so very little is left on the rule. And in most cases, these applications with oil are months apart.

However, I will suggest something that will probably result in a lot less wear than even keeping them immersed in a bath of oil could. Get a pair of Flat, Ground Stones and clean up the edges of the blades on an occasional basis with them. Flat, Ground Stones are abrasive stones that have been ground flat with a diamond wheel on a surface grinder. They are very flat. They are purchased in pairs so that they can be carefully rubbed together before each use. This rubbing is to eliminate any projection above their flat surface that could scratch the object being treated with them. When you rub them together on the first few strokes you will feel some resistance but then they quickly just glide over each other. That is when they are ready for use.

These Flat, Ground Stones are what is being talked about when a machinist says to stone a milling table. And they can be used on any flat surface, like the edge of the blade of a combination square. Lightly stoning those edges will eliminate anything that rises above a flat surface and greatly improve the edges of all but the most premium square blades. When used with normal pressure and for only a few strokes, they will not remove any metal from the flat edge of the metal blade, only raised areas that you do not want. Be sure to hold the blade square to the stone while doing this. You want to stone the full width of the edge and not just one corner.

I would suggest that before stoning a square's blade for the first time, that you lap it on a sheet of extra fine sandpaper (400 grit or higher) that is held down on a sheet of float glass. You should only need a few strokes on this sandpaper as you do not want to remove much, only any larger burrs that may scratch the Flat, Ground Stone. Do this lapping ONLY ONCE. Never on a repetitive or regular basis. That's what the Flat, Ground Stones are for.

This is a good treatment for other precision surfaces in your shop like 1-2-3 blocks, machinist's levels, etc.

MG88 said:

Thanks! Someone told me to expect only 1-2 years of regular use before it looses accuracy. Didn't sound right to me, but maybe they were referring to an aluminum square. Does the lubricant actually stop wear?

Click to expand...

MG88 said:

A carpenter friend who is always buying new tools. It seemed odd to me, too, but I'm still learning. I didn't want to do anything to damage this tool I just purchased.

Click to expand...

Not even very many carpenters nor cabinetmakers actually USE "combination" squares. "Framing", staircase, or "roofing" squares, and a few more types, rather.

Not all that different with metals fabricators.

Combo square is a minority-use tool for most because a fixed one JF works for most of what needs doin' and is lighter, more rugged, fast and cheap to replace when damaged.

Machinists? Hardly ever use 'em. Gots all sorts of OTHER options, small to large, including ground blocks, angle plates, cylindricals, etc.

For layout or vetting a setup, I have "good old" B&S solid squares for seldom-used heirlooms, far less expensive Polish ones bought NEW and even East German ones bought used, in far more sizes. Day to day use, those are "don't cry-if-damaged" compared to the scarce old B&S.

So a sixty year life for a decently made Cast Iron and NOT light-alloy combo square - so long as protected from corrosion - is no surprise.

Just not the whole story.

Even the Iron ones don't cost a great deal of money - not by the average of what we Chickn's have to invest in - and COULD be tossed in the bin periodically & replaced with new without breaking the bank.

Run what you got. But marry sumthin' ROUND.

Not square!

Even if "combo".

reminds me of old shutdown for years factory tool crib i went too. they had 10ea new looking precision combination squares in individual wood box case and squares was individually wrapped in plastic and sprayed with heavy thick rust preventative
.
they looked brand new until I saw the locking screw and nut rusted solid together on ALL of them. apparently the rust preservative didnt get on screw and nut. not many things stay in good shape over decades unless submerged in oil. as for wear most replace any worn tool as needed.

EPAIII said:

"Does the lubricant actually stop wear?" Well, no. Nothing will ever stop wear if the square is being actually used. Motor oil in an engine keeps the wear down to a bare minimum, but engines still wear out. So will squares. It is just a matter of how long that takes.

What type of lube or preventative and how well it works is a matter that depends on many factors. For instance, in a dusty environment, use of an oil could actually trap that abrasive dust between the surfaces and cause them to wear faster. Under more normal circumstances, that same lubrication or preventative could greatly decrease the wear. It just depends.

I have about a half dozen adjustable squares, some many decades old and have not seen any great problems with only occasional application of a very light coating with oil. I apply it with an oily rag and wipe it down after that so very little is left on the rule. And in most cases, these applications with oil are months apart.

However, I will suggest something that will probably result in a lot less wear than even keeping them immersed in a bath of oil could. Get a pair of Flat, Ground Stones and clean up the edges of the blades on an occasional basis with them. Flat, Ground Stones are abrasive stones that have been ground flat with a diamond wheel on a surface grinder. They are very flat. They are purchased in pairs so that they can be carefully rubbed together before each use. This rubbing is to eliminate any projection above their flat surface that could scratch the object being treated with them. When you rub them together on the first few strokes you will feel some resistance but then they quickly just glide over each other. That is when they are ready for use.

These Flat, Ground Stones are what is being talked about when a machinist says to stone a milling table. And they can be used on any flat surface, like the edge of the blade of a combination square. Lightly stoning those edges will eliminate anything that rises above a flat surface and greatly improve the edges of all but the most premium square blades. When used with normal pressure and for only a few strokes, they will not remove any metal from the flat edge of the metal blade, only raised areas that you do not want. Be sure to hold the blade square to the stone while doing this. You want to stone the full width of the edge and not just one corner.

I would suggest that before stoning a square's blade for the first time, that you lap it on a sheet of extra fine sandpaper (400 grit or higher) that is held down on a sheet of float glass. You should only need a few strokes on this sandpaper as you do not want to remove much, only any larger burrs that may scratch the Flat, Ground Stone. Do this lapping ONLY ONCE. Never on a repetitive or regular basis. That's what the Flat, Ground Stones are for.

This is a good treatment for other precision surfaces in your shop like 1-2-3 blocks, machinist's levels, etc.

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Thanks for all the helpful and informative posts!

The takeaway seems to be, don't abuse it and it won't change to a noticeable degree. Other than that, it can be filed. I wonder if a very thin shim could be inserted to correct as well?

Where is the best place to purchase flat ground stones?

MG88 said:

The takeaway seems to be, don't abuse it and it won't change to a noticeable degree. Other than that, it can be filed. I wonder if a very thin shim could be inserted to correct as well?

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I think you should just relax and use your square. And forget about shims, do the math and you'll see even the thinnest shim is a HUGE adjustment.

Accuracy for a carpenter is in 1/32's of an inch, not your best authority for this. I've used Starrett 12" combo square for precision woodworking, and they are great for that. I have an old one, bought used 50 yrs ago, and one I bought new, maybe 30 yrs ago, Both are about the same accuracy, as far as I could tell without inspection grade stuff.

What kind of work are you going to use these for?

richard newman said:

What kind of work are you going to use these for?

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Cabinetmaking, primarily.

MG88 said:

Cabinetmaking, primarily.

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If you have a Starrett, Mitutoyo, or similar, you're set for life, or until you drop it.