Squaring a trailer frame - having problems

[con_fuse9]

I'm building a small 5x10 trailer.

I don't have the most level/flat driveway so I built up two beams (6ft wide) leveled them, and used them to lay the main rails.

All the measurements are perfect (within 1/16 of an inch) including both diagonals.
However, when I go with a simple carpenter's square, the two corners are out of square. Not a lot, but one corner is greater than 90 and the other is about the same amount less than 90.

I think the only way this makes sense is if I have a twist in the frame.
So I measured with a digital, 6ft level and all sides are less than .1 degree off (they all measure the same just the display is limited to =or - .1 degree). according to my math that's .1" over 60" - or 5ft.

Its just a stupid utility trailer, I'm inclined to just put some heavy tacks on the corners and fit up the rest of the pieces. However, the perfectionist in me is bothered.

By eye balling the steel, it all looks straight. All measurements are done on the top edge. Its all C channel (C3x5). I was trying to miter the corners etc.

Inside the frame rails from side to side is 60 and 0/16 and 62 and 15/16 outside to outside
Front to back (outside measurement) is 121 and 7/16 (should have been 8/16 but.... cut a bit short).
Corner to corner I get 136 and 12/16. My engineering calculator says 136.778 is expected...

Any ideas?

Shoot the engineer and get on with production?

A friend suggest that as long as I get the axle square to the hitch, who cares?

Thanks

[zapster]

Measure from corner to corner in a "X" pattern and report back.

...zap!

[DSW]

If you want to be dead level, use a water level. Some clear tubing, a 5 gallon bucket and some water with food coloring will tell you if any part of that trailer is not level ( assuming you set up the level in such a way that it's easy to take measurements. A standard level may not tell you if all corners are even and level, but a water level will ( assuming you don't move the level.)

As far as straight, A string line will tell you if there is a bow in the steel. I usually space out the string with something like a piece of 1/2" plywood so you can easily tell if the piece bows out or in.

You've already pulled diagonals and that's usually the best way to determine square accurately.


I've seen plenty of carpenters squares that are anything but square. The easiest way to check this is to set the square against a straight edge. Draw a perpendicular line with one side of the square. Flip the square over and using the same edge against the straight edge, draw a 2nd perpendicular line starting at the same base point on the straight edge. If the square is true, the lines will match. If the square is out, the lines will not match, but will either trail in or out depending on whether the square is over or under 90 deg.

[newbury]

If you want to be dead level, use a water level. Some clear tubing,

Like they sell in pet shops for aquarium air hose. Get a piece long enough to go from one corner to another plus say 5 foot.

a 5 gallon bucket and some water with food coloring will tell you if any part of that trailer is not level ( assuming you set up the level in such a way that it's easy to take measurements. A standard level may not tell you if all corners are even and level, but a water level will ( assuming you don't move the level.)

and check level across diagonals. What I do is put the colored water in a 1 gallon milk jug (handy handle and you should not need 5 gallons of water), put the hose in and siphon til the hose is about full. Then I hold the hose against the milk jug and mark the water level on the jug AND tube with a sharpie.

As far as straight, A string line will tell you if there is a bow in the steel. I usually space out the string with something like a piece of 1/2" plywood so you can easily tell if the piece bows out or in.

and be sure you are not stretching the string.

[DSW]

and be sure you are not stretching the string.

Actually we stretch the string as tight as possible. Many times I'm using the string not only to check bow in and out, but up and down to set height for example. A string that isn't super tight will sag in the center over a distance and give you a false reading of a straight line as far as up and down is concerned.

Where you can get messed up is if you are trying to pull that line tight to the item, say a beam, and the beam pushes out on the line. That's why it's often a good idea to space the line off the material. If you do keep the line in tight, you have to make sure you don't push the line out as you set the material to the line.

[CEP]

If you want to be dead level, use a water level.

When we built the Budweiser brewery in Fairfield California in the early 1970s, all the conveyors were set with water levels.

[newbury]

Actually we stretch the string as tight as possible. Many times I'm using the string not only to check bow in and out, but up and down to set height for example. A string that isn't super tight will sag in the center over a distance and give you a false reading of a straight line as far as up and down is concerned.

Where you can get messed up is if you are trying to pull that line tight to the item, say a beam, and the beam pushes out on the line. That's why it's often a good idea to space the line off the material. If you do keep the line in tight, you have to make sure you don't push the line out as you set the material to the line.

Yeah, I should have phrased that differently. If I can't measure corners with a steel tape because they are too far apart I like to use heavy duty fishing monofilament and a sharpie. I like sharpies

[DSW]

Yes THEN you do have to worry about stretching the line. Same goes with nylon tapes over long distances, especially in hot weather. It's easy to gain a foot or more over 100 feet if you pull the tape super tight. That's why surveyors always use a steel tape, as it will not stretch.

[M J D]

Your end rails or side rails maybe both pulled from the heat so there is probably a bow somewhere. If there is twist it will probably rock where it sits on the beam. Check your square with a 3-4-5 or multiples of that to see how you sit. Its common for a square to be off and the frame good or vice versa.

[duaneb55]

If you're getting less than 90 on one end, more than 90 on the other with the same framing square and the diagonals are the same then you've got one end narrower/wider than the other.

If you're getting less than 90 on one side, more than 90 on the other with the same framing square and the diagonals are the same then you've got one side shorter/longer than the other.

Sounds like you built a trapezoid. Double, triple check your outside (inside are irrelevant) dims.

[CEP]

String works good for short distance. If you want to be real accurate for long distance, use piano wire weighted at each end.

[wb4rt]

I just re-read your initial post. You are within 1/16" on the diagonals and less than 1 degree off in the corners.

Nail it and move on.

[CDad]

1/16" is close for that type of work. I'd weld it and move onto the next step.

[farmersamm]

Easiest way to make sure you're flat is to use your eyes.

I accurately set the plane on a 45' foot float using my eyes, and two pieces of tubing. Sight the air gap as you look from afar, and shim to make the gap equal clear across the plane. This is one of the easiest ways to do it, and it's very very accurate. Been doing it for years with excellent results.

Level is ok when you're working on a relatively level surface. My shop floor () slopes about 2 feet in 40 feet, so all I'm concerned with is whether something is planar (flat). Doesn't matter in what orientation you weld as long as it's flat.

If all measurements (L & W) are the same, then the diagonals should be the same. 1/16" over 20' is about as square as you're gonna get, and have good results. I always build to 1/16, and consider it good. Only time I go tighter is when pivots are involved. When I built my front end loader it was built to a .010 tolerance (the tolerance of the DOM pivot points), and it was also eye sighted for flatness/alignment, showing just how accurate the human eye can be.

Just a little side note..............You can get all anal with your measurements, then find that the spring bushings/eyes have about 2 miles of slop in them Trailer parts are just about as cheap, and sloppy, as you can get. Nature of the business. You only get into better quality when you get up into the Class 8 parts.

[BD1]

Are the corners racked ? Out of square a little ? Get 3/4'' pipe clamp and set it corner to corner '' X'' and tighten to square. If you don't have pipe long enough, you could use a ''C'' clamp as a stop for the pipe clamp. Are you using a 2' framing square ?

You could use the 3', 4' , 5' method too. 3' one side, 4' one end and should be 5' diagonal.

[Tcounty1]

Being out a 1/16 won't matter. Even having the axel out an 1" won't matter. It'll just look like a bulldog going down the road.


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[farmersamm]

Guys The key word in the OP's initial post was "carpenters square"

A square is definitely not the standard by which anything large is squared, they're notoriously off. They're a good beginning to set stuff up, but by no means a accurate check of measurements. Diagonal are the only way to go

[zapster]

I just re-read your initial post. You are within 1/16" on the diagonals and less than 1 degree off in the corners.

Nail it and move on.

Correct!
He asked about SQUARENESS...... not how level it is...

...zap!

[irish fixit]

There's always levels of precision for every job. My old boss used to say that a former employee tried to use aircraft precision for a plow.

Anyway there's ways to be off with any method used to measure the angle. Diagonals are ok but IMHO not the most precise way to do it. There's lots of ways for them to be off, from a rounded corner or burr on one side, slightly different joint fitup, slightly different lengths of sides and the list goes on.

As for squares you should check them and adjust them. I have perfectly good carpenters squares that I rely on. But I know they're right because I've adjusted them to be right.

If done properly probably the best method to check for square is the 3,4,5 method. Measure a multiple of 3 down one side (of any measurement that fits the job at hand), then a multiple of 4 down the other side, the diagonal should be a multiple of 5.

But as with all the other methods it requires the sides to be perfectly straight, the measurements to be precise, and proper care taken.

[Mikel_24]

I just re-read your initial post. You are within 1/16" on the diagonals and less than 1 degree off in the corners.

Nail it and move on.

Agreed. It is likely going to turn worse by the time you start burning unless you do a great job compensating/minimizing distortion. I think you should be ok.

[con_fuse9]

Thanks for all the responses.

The carpenter square I used was accurate. I had a bad one years ago and since then I have checked and double checked this one often. Sucks when you cut a 2x12 and the end isn't square.

So I also have this Bosch angle finder. I use if for custom cabinet/wood working where things have to fit. Keep in mind that when I do finish carpentry, I shoot for 1/32...

Uhm. Lets just say the corners are .2 degrees out..... yeah .2 Front right corner measured 89.8, Front left 90.2.

Still not 100% sure how, but I finished tack welding everything last night.

Finish welding tonight. Thankfully its been dry and hasn't rusted over where I sanded/cleaned.

[Old Skool]

To be square all pieces have to be the exact same length, not "within a 1/16"

[wb4rt]

Ok, now that's settled, con_fuse9 - let's see the pictures!

I love trailer build threads. I always learn a lot from the guy building and the guys watching.

[wb4rt]

Ok, now that's settled, con_fuse9 - let's see the pictures!

I love trailer build threads. I always learn a lot from the guy building and the guys watching.

[Bistineau]

Corner to corner I get 136 and 12/16. My engineering calculator says 136.778 is expected...

Any ideas?

Shoot the engineer and get on with production?

A friend suggest that as long as I get the axle square to the hitch, who cares?

Thanks

If the corner to corner measurements are 136 3/4" each way, then what's the problem? It's as square as it needs to be. Not really gonna get any closer. So yes, Shoot the engineer and get on with production. While your at it, tell the perfectionist in you to go take a break and while you move forward with the build or your gonna do him like the engineer.