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Trimming Stiffeners

skelrad

Well Known Member
Friend
Just working on my practice kit, but figured I'd ask the dumb question before getting to the empennage...

The plans say to trim the stiffeners by cutting to the middle of the holes punched in the angle. That leaves kind of a sharp and awkward hook on the stiffeners though. Is there a reason not to just trim so that you take out the hole completely so it's a perfectly smooth edge?
 
Trim

Just working on my practice kit, but figured I'd ask the dumb question before getting to the empennage...

The plans say to trim the stiffeners by cutting to the middle of the holes punched in the angle. That leaves kind of a sharp and awkward hook on the stiffeners though. Is there a reason not to just trim so that you take out the hole completely so it's a perfectly smooth edge?

I hope it's ok cuz that's how I trimmed mine. :D
Technically I cut per instructions then filed till the sharp corners of the hole were gone.
 
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I hope it's ok cuz that's how I trimmed mine. :D
Technically I cut per instructions then filed till the sharp corners of the hole were gone.

For something like stiffeners I kind of figure it’s no big deal either way, but I like to push the envelope of “there are no stupid questions.” :D
 
Make a go-no go wedge gauge.

I tried to make them perfect- - - - lesson learned is perfect is what fits not what my interpretation of the instructions say.

So - make a wedge the same angle as the internal rudder/elevator cavity and test the stiffeners in there. My stiffeners touched the opposite skin, so some rework was needed.
 
After you do two or three you will get it. Cut them per the plans then grind them to shape. I have a grinder with a metal grinder on one side and a scotchbright wheel on the other. You will use both.
 
After you do two or three you will get it. Cut them per the plans then grind them to shape. I have a grinder with a metal grinder on one side and a scotchbright wheel on the other. You will use both.

Cautionary here - Not advisable to use a stone ‘metal grinder’ with aluminum. The grinding wheel tends to melt aluminum & if that buildup on the wheel gets too hot, has the potential of exploding off in your face.
Better to do your cuts & use a bench belt sander (or sanding disc) to shape your part, than clean it up on a scotchbright wheel or deburring tool.

This & many more safety topics are the first items we cover in our Sportair courses.

Lots of Best Practices discussion on this forum lately...
 
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I believe the reason they tell you to cut in the middle is so you don't accidentally remove material from the meat of a piece. I cut them then filed the left over tab even with the main piece and then deburred. The "remove" areas usually show you completely removing the tabs if you zoom in on the pictures. See enclosed.
 

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Grinder

After you do two or three you will get it. Cut them per the plans then grind them to shape. I have a grinder with a metal grinder on one side and a scotchbright wheel on the other. You will use both.

Only took one hit on my steel grinding wheel to take that off! I put a polishing wheel in it's place. Not saying it's wrong, just that I forgot it was there and caught a part on it. Had to buy a replacement. When I need to grind steel, I swap it.
 
....Better to do your cuts & use a bench belt sander (or sanding disc) to shape your part, than clean it up on a scotchbright wheel or deburring tool....

I use these tools in this order -

Bandsaw,
Sanding disk,
Vixen file if needed,
Mill files if needed.

To do these things -

Cut,
Trim to line,
Polish edge if the sander didn't,
Finish the corners and deburr.

Don't have a grinder or 3M wheel and have never seen the need for them.

Dave

Dave
 
I use these tools in this order -

Bandsaw,
Sanding disk,
Vixen file if needed,
Mill files if needed.

To do these things -

Cut,
Trim to line,
Polish edge if the sander didn't,
Finish the corners and deburr.

Don't have a grinder or 3M wheel and have never seen the need for them.

Dave

Dave

If you haven’t used the 3M wheel on a grinder yet, then you don’t know what you’re missing! BIG time saver, nice finish. Sure you can get by without it, but don’t knock it until you try it!
 
After you do two or three you will get it. Cut them per the plans then grind them to shape. I have a grinder with a metal grinder on one side and a scotchbright wheel on the other. You will use both.

Yes...the 3M wheel on aluminum, but NEVER the stone wheel on Aluminum, as noted.

Our shops have big-*** signs that say "NO ALUMINUM ON GRINDING WHEELS" or the like. And it's a serious offense to ignore that warning, not to mention dangerous and dumb. Use the right tool for the right job, or don't do it.

ETA: https://www.youtube.com/watch?v=iaoVqUpOrPs

Gory pictures, like most safety videos, but if this doesn't convince you, I don't know what will.
 
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My Tool list in order - makes shaping stiffeners a breeze!

Gulliotone (paper cutter works fine)
Belt sander - 240 grits
3 M wheel (mounted on the drill press).
 
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