Scribe a perpendicular line around fillets on a square steel tube

[Probablygrigsby]

I have rough cut 3x2 rectangular structural steel tubes to slightly longer than my desired length.

I would like to scribe a line as a guide to grind, file and sand them down such that the ends are as near as 90 degrees to the length as I can manage.

Using a machinists t-square works fine for the first face, but obviously it can’t follow the fillet onto the next face. Of course, I can’t measure from the bottom of the next face because they aren’t square and that’s the whole reason I’m doing this

My solution was to 3D print a sleeve that I can use as a guide for the scribe. I’ve attached a screen snap of the CAD drawing for the curious.

My question is: Is there another (better?) way to do this? My machinist grandfather wouldn’t have had a 3D printer, though he - unlike me - had a Bridgeport which could do the job. What might he have done if he didn’t have a Bridgeport and only had hand tools?

Thanks!

 

[Ed ke6bnl]

Welders use a wide pipe measuring tool rap for pipe.
May be able to put a hose clamp around the tube

 

[Probablygrigsby]

Welders use a wide pipe measuring tool rap for pipe.
May be able to put a hose clamp around the tube

A hose clamp (I assume paired with a machinist’s t-square) is a great idea! Thank you!

 

[woodchucker]

I have rough cut 3x2 rectangular structural steel tubes to slightly longer than my desired length.

I would like to scribe a line as a guide to grind, file and sand them down such that the ends are as near as 90 degrees to the length as I can manage.

Using a machinists t-square works fine for the first face, but obviously it can’t follow the fillet onto the next face. Of course, I can’t measure from the bottom of the next face because they aren’t square and that’s the whole reason I’m doing this

My solution was to 3D print a sleeve that I can use as a guide for the scribe. I’ve attached a screen snap of the CAD drawing for the curious.

My question is: Is there another (better?) way to do this? My machinist grandfather wouldn’t have had a 3D printer, though he - unlike me - had a Bridgeport which could do the job. What might he have done if he didn’t have a Bridgeport and only had hand tools?

Thanks!

That's an easy one for me. I use the center finding attachment from a Starrett combo square. The head has 90 degrees and will sit flat on a tube. I use it in woodworking all the time to mark my cuts. I use a knife for those and sometimes a pencil. The same can be done for cutting tubing.
If you don't understand, I can take a picture.

 

[woodchucker]

Here's what I am talking about. Also used to use paper to mark it. You just wrap the paper around and align it back up on top of itself and it creates a sleeve. A little spray paint on your tube and you have a clear defined line.

 

[Probablygrigsby]

Here's what I am talking about. Also used to use paper to mark it. You just wrap the paper around and align it back up on top of itself and it creates a sleeve. A little spray paint on your tube and you have a clear defined line.

View attachment 462356View attachment 462357View attachment 462358

That’s the second time in a few weeks where I’ve thought “I need a center finding attachment”.

I like the paper idea too. I’d used tape, similarly, but painting it like you suggest would be nice because when you’ve removed the paint you know you’ve finished.

 

[RJSakowski]

It can be done with two machinist's squares. Scribe the first line but leave the square in place (clamp if necessary). Place the second square on the next face so it is touching the first face and scribe the second line. Move the first square to the second line and repeat for the third. Reverse the first square on the first line and repeat for the fourth line.

 

[Flyinfool]

I have been using the paper wrap method for decades. it works on any shape object.
I have also used CAD to layout the spline so that when I print it on the paper and then wrap it around to pipe or tube I can just follow the line to get a perfect complex end shape like compound miters on round pipe.

 

[sdelivery]

See how Pictures made that so clear and easy? Even I got it!
MORE PICTURES EVERYONE!

 

[Probablygrigsby]

It can be done with two machinist's squares. Scribe the first line but leave the square in place (clamp if necessary). Place the second square on the next face so it is touching the first face and scribe the second line. Move the first square to the second line and repeat for the third. Reverse the first square on the first line and repeat for the fourth line.

Is this what you mean?

If so, that works, but I don’t think it works for my particular application where I’m scribing the end of the tube. That said, I could have scribed it before rough cutting it if I am interpreting the method correctly.