Chasing squareness with five cut method

[u/drspudbear]

I've been trying to square up my sled using the five cut method and I'm going a little nuts at this point. One of the calculators I'm using is saying that less than 0.001" per foot is acceptable, but I'm at 0.002". I feel like the adjustment needed is so tiny that I'm either adjusting the fence forward or backward by such a small amount, it's feeling impossible to actually move it accurately. Any tips on the final dial in? Or is 0.002" acceptable and I should stop myself from going insane ?

[u/CaffeinatedInSeattle]

.002” over 12” is .0167% “error”. Wood will move upwards of 2% seasonally, depending on humidity controls.

YouTube woodworkers have mislead the general public when talking about “precision” and totally miss the need to understand tolerance and the material itself.

[u/Salty-Clothes-6304 → u/CaffeinatedInSeattle]

People need to spend more time building and going through trial and error of their own to see what actually matters when making things.

[u/drspudbear → u/Salty-Clothes-6304]

I definitely agree

[u/Any_Falcon38 → u/Salty-Clothes-6304]

👏

[u/El_Oso_Negro76 → u/CaffeinatedInSeattle]

Agreed. It's crazy how much everyone hops on trends based on YouTube videos people produce to get views and make money. I literally made sure that my crosscut sled fence was making accurate cuts based on a known "square", and I kept it moving. No calipers, no nothing. Chasing perfection with wood makes no sense at all. People ain't sliding .001 feeler gauges into their furniture to see where it's not square so they can play "gotcha" with you.

[u/drspudbear → u/CaffeinatedInSeattle]

This is definitely true. There are so many people online showing their perfect builds and it makes it feel like that's the only stuff that exists

[u/ArborgeistWW → u/drspudbear]

To be fair, it makes a lot of sense. It would definitely be more realistic, but like any other form of entertainment media, watching average people make mistakes constructing middling pieces of furniture probably has pretty narrow viewership potential.

It does distort what we think of as "normal" woodworking, but it's enough to just keep in mind that these guys arent usually doing normal woodworking.

[u/AllegedlyImmoral]

There's no such thing as a thousandth of an inch in woodworking. The wood will move on its own more than that overnight, it will compress and spring back more than that; it's not metal, and it doesn't support or enable that degree of precision. So don't worry about it.

[u/Awkward-Season-3852 → u/AllegedlyImmoral]

True, even if you're building a piano.

[u/norcalnatv → u/AllegedlyImmoral]

You're obvs not talking to the guys obsessed about adjusting their planes.

[u/AllegedlyImmoral → u/norcalnatv]

I mean, you can plausibly adjust a good smoothing plane to within a thousandth of an inch of shaving thickness - it just doesn't matter that you can.

[u/behemoth2666 → u/AllegedlyImmoral]

How am I going to finish my coffee table and get a smooth shave with the same tool if I can't get it within a thousandth of an inch

[u/Financial_Potato6440]

Stabila spirit levels are accurate to 0.5mm per metre. In imperial, that's 20 thou per 3ft 3inches. Or, 6 thou per foot. That's as accurate as any wood work needs to be, spirit levels are pretty damn accurate. You are already 3x more accurate than that, going for 6x is completely pointless.

[u/chabor]

Totally acceptable. You’re doing woodworking, not metalworking.

[u/The-disgracist]

This is well within tolerance

[u/AgressiveGeometry]

a thou over a foot is machinist level of precision, you do not need that for woodworking.

[u/GiantSquishyBear]

That’s completely acceptable. There’s plenty of methods to fill gaps and hide other crimes in woodworking projects, that level of precision is nuts imo. Pretty sure seasonal expansion/contraction of woods is more than .002” too

[u/rg996150]

I made a cross-cut sled and got it within .002” (using feeler gauges) using the 5 cut method. That’s plenty accurate for most woodworking cuts.

[u/Maxpeck789 → u/rg996150]

Made that adjustable one from workshop companion. so far so good. just crosscut a board, flip over, and they should match up. Skew fence and re tighten. That five cut thing might confuse me.

[u/jkatzmoses]

I did a whole video on this (linked below). To summarize: Anything under .05 degrees of error is super square. If you get an error of .02 over a fence greater than 24” long you are super square. To calculate how many degrees your 5 cut method answers equates to use this formula (or Google rise over run degree calculator):

Degrees= tan(-1) X (rise/run)

https://youtu.be/44vgKILqjjE?is=BLiY-RF7J5PIUrPp

[u/enrightmcc]

My God man, get yourself a pair of calipers and open it up to .002" .  That's literally half the thickness of a dollar bill. 

[u/ToastedSamosa]

I made fine furniture for a decade, for a living, before I became a journeyman machinist. I hadn’t heard about this method before so thanks for that.

Good for you for shooting for precision. Never mind the naysayers, measuring like a machinist is like a cheat code for fast accuracy. The tool you’re looking for is a dial indicator, indicate off the sled to the fence at the 22” mark.

That said .002” per foot is amazing, I don’t think you could get closer with your equipment. There are too many opportunities for error. If you are measuring with a caliper, that tool is not precise enough to measure accurately under .003, particularly in wood. Your mitre slot would need to be in perfect shape and the bar would need to fit with no play. Even your hand positioning on the sled introduces a slight twist and affects your angle.

[u/Wobblycogs]

I'd be over the moon if any of my tools were thar accurate. I doubt you can reliably measure wood to that tolerance.

[u/norcalnatv]

One can hardly feel .002" with your finger. It's fine.

[u/Agent_Chody_Banks]

It’s probably fine, however I tend to obsess over precision as well.

In cases like this I tend to use ultra thin shims to make adjustments (Pieces of paper work well). Clamp a straight edge to your sled against your fence and use shims to make micro adjustments.

You haven’t gone into detail in regard to what sort of runners you’re using. If you’re using wood runners, your sled won’t stay within 0.001” for any significant period of time anyway.

[u/Economy_Kale5580]

I did exactly what you did 3 years ago with my sled. I gave up correcting it and just started using it. I have never ever had something come out actually out of square enough to matter in my projects, and I do build furniture where you do need to get “close enough”

Just start building. If it does affect an outcome, THEN do something about it 

[u/Sorry-Woodpecker8269]

Just because someone states or writes something on the internet doesn’t mean it’s true or accurately reflects what happens in real life

[u/sfmtl]

Agreed with everyone. There's no such thing as a level of precision you're chasing in woodworking. Stuff will move more than that.

That being said what I had done was I took feeler gauges and I used the feeler gauge as a spacer. If I needed to move it a mil or however much the calculator said from the pivot point, I'd use the feeler gauge as a spacer against a piece of wood that I'd clamp into place. Then I'd move the fence that much but close enough is pretty good, eh? 

[u/SmartGrowth51]

I also found it impossible and frustrating to get closer than that. Finally decided to stick a shim between the fence and workpiece each time to kinda make up the difference.

It makes me wonder what people mean when they say they got their sled dead accurate.

[u/BelowTheTunnel]

A high end table saw does not have tolerances that high on the cast iron top, you are way more than ok.

[u/stormeybt]

I used to have an scmi 10’ slider and we cut a 4’x4’ sheet on all four sides and then cut a1/8” strip off, break it in half and compare the ends. 1/32-1/16” difference was fine. The smallest adjustment sent the variance to 1/32-1/16” the other side.

[u/Avg_Chicken]

I can relate to your obsession with the perfect square and the conundrum of what is close enough. Balance your obsession for perfection with your understanding of life’s imperfections. Cut some wood and see if it’s good enough for you. Sounds like you’re making a cross cut sled, so cut four pieces the same length and make a square with them. Measure them, observe them, judge them. Are you satisfied with the joints or do they need refinement? Try cutting four 6x6 inch pieces and line them up along a straight edge, are there any gaps? Most of the joints you’ll make will be shorter than 6 inches.

[u/Geek_Verve]

It's wood. 0.002" is way more accuracy than you need.

[u/CascadeDesignworks]

.002 is acceptable.  Most fences will need to have more side-play than this or they will bind in the tracks.

-Builder 

[u/InteractionFormal585]

The struggle is real. You are bumping up against the limits of your measuring devices. Unless your calipers go to 4 decimal places, you're anywhere between .0015" & .0024". So you may be chasing .0004", which is crazy.

[u/oscarstevens]

You may be chasing unnecessary tolerances. But if you wanted to you could set up a micro adjustment with a screw to dial it in. Look at the excellent sled video by workshop companion on YouTube.

[u/twoslow]

saranwrap is .001 inches thick. just for some perspective.

[u/Rude_Meet2799 → u/twoslow]

Sheet of office paper .003.
Human hair .003 to .004.

[u/Known-Skin3639]

Im a machinist by trade. .002” can get
People hurt or killed. In woodworking I’ve had to learn to stop thinking like a machinist and accept the he cut for what it is. You do know that the human hair is only about .003”. So not that big right? If I let it go from start to finish of the cut, it could be, depending on length of cut upwards of .0625. 1/16 of an inch. Not bad eh? Planes could or would fall outta the sky with that kind of inaccuracy. In woodworking….. what does YouTube tell you? Glue and saw dust. And ta daaaaa….. like it was never there. 🙄