# How to measure straightness on a HEX Long Bar

1

#### 12kennedya

I am working to find a new way to measure the straightness of a hex bar 12' in length. Ive come across a couple different ideas but no really make since.

#### Miner

##### Forum Moderator
Staff member
One critical item will be adequate support for the entire length, so straightness is not affected by gravity on unsupported sections. That support will also have to be 'straight'. You will also have to measure in such a way that any parallelism issues between the opposite surfaces do not show up in straightness. Or does this have to be measured in a free state?

#### optomist1

##### A Sea of Statistics
Super Moderator
a drawing hopefully with GD&T might help...

1

#### 12kennedya

Miner, No it does not have to be in a free state. We have a table we sent out to have flattened 100% by a machining company.

#### John Predmore

Trusted Information Resource
If you could hang the bar vertically by one end, gravity would not cause deflection from straight. Not the most practical solution, but novel and cheap. A plumb bob made of string and a weight can show where a surface deviates away from a vertical line, as long as you check all six sides. Laser pointers are also very inexpensive, if you fashioned a holder to clamp on the end of the bar so the beam projects parallel to the bar surface at a offset equal to your straightness tolerance. A little more involved would be to design a metal tube with inside dimension that will pass freely a straight bar, but a bar slightly bent will bind in the tube. This Go/NoGo tube idea will be checking size as well as straightness, but if the bar is drawn the size tolerance is very tight, so you can almost ignore variation in size.

#### CreativeQC

##### I truly have no idea what I'm doing half the time.
If you have a table that is getting flattened you could also lay a grid on it to see if there is any bending in the bar. You could have two employees check which line on each end of the table it lines up with and roll it to check all sides of the hex. If you wanted to get fancy you could also mount an overhead camera to drop labor costs.

1

#### 12kennedya

All of these seem logical, I really like the GO/NoGo Tube Idea. If you guys come up with anything else let me know.

#### Project Man

##### Involved In Discussions
What is the straightness requirement? This will better direct the correct solution.

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