deburring - what I was taught vs. what's necessary

kritsher · #1 07-05-2007, 08:23 PM

Please forgive another newbie question... I'm just getting started on my -7 empannage.

A couple months ago, as I was contemplating the purchase of my tailkit, I took a great Intro to RV Building Techniques class. The teacher was great... A real stickler for detail on tasks like... deburring.

He taught me to use a vixen file to remove any and all tool marks and to round over the edges of all parts until they were smooth to the touch. Only then did he take the parts up to the ScothBrite wheel for just the lightest touch to take off the file marks.

I've been doing the same thing faithfully on my kit. Frankly, it's starting to get old. Today, I took a scrap part up to the ScotchBrite wheel without bothering with the vixen file or anything else first. After a few passes, the edge looked great. I had to do a couple extra passes becuase I could still see traces of the shear marks after the first couple of passes, but in the end I couldn't tell the difference between the parts I did the tedious way and the parts I took straight to the wheel.

So... my question is... what gives? Is Scotchbrite straight out of the parts box adequate? Or do I need to keep doing it the hard way? What other techniques are out there?

Thanks

lostpilot28 · #2 07-05-2007, 08:41 PM

I'm probably doing it wrong, so my advice is to not listen to me (so why am I replying? Who knows). Anyway, I take almost every part to the 3M wheel. First I smooth down the edge to remove any marks...then I do one or two passes on each side to remove a ridge, even if no ridge exists. Always comes out smooth.

The only hard part to me is getting in those little nooks & cranny's that can't be reached with the 3M wheel...if it's small, I use a cordless dremel with a scotchbrite wheel. If it's big I mix it up...sometimes use a vixen file then a scotchbrite pad...sometimes maybe just a scotchbrite pad.

That little "V" edge deburring tool sucks, by the way...in my opinion it doesn't work. Anyway, just my 2 cents.

L.Adamson · #3 07-05-2007, 08:49 PM

I debbured most parts with a 90 degree air die grinder and the 2" blue scotchbrite pads, or the large scotchbrite wheel. Would have given up a long time ago, if it was filing by hand.

Would be like using a arm powered hand saw and hammer to build a complete house. No way!

However, there are the few times to use the file, but IMO, it's just ancient craftsmanship to use it all the time.

L.Adamson

RV8Squaz · #4 07-05-2007, 10:09 PM

The pros (i.e. the production workers at Raytheon and the USAF sheet metal shops) don't even use a Scotchbrite wheel. They use a standard ******* double cut file or single cut. Sometimes they use that red emory cloth stuff that comes in a roll that Avery sells. Don't use regular sandpaper.
I found that with a file and then the wheel I was much quicker. It took too many passes on the wheel to get the marks off completely. Plus all those extra passes did a number on my wheel. I use the Vixen file to get the real heavy stuff off (i.e. bandsaw cut marks). Otherwise I use the the file I mentioned above. For gettting into nooks and crannies I have a set of 6 small files and a set of miniature files. Recently purchase chainsaw files (for making a nicer radius than a rat tail file) and a 6" single cut file quickly became my favorites. The single cut file leaves such a smooth finish it doesn't even require a scotchbrite pass.

Jerry
RV-8 N84JE flying since 4 Feb 07, 98 hrs.

Mark Burns · #5 07-05-2007, 10:27 PM

Quote:

Originally Posted by RV8Squaz

<cut> The single cut file leaves such a smooth finish it doesn't even require a scotchbrite pass.

Jerry
RV-8 N84JE flying since 4 Feb 07, 98 hrs.

Jerry mentions how smooth a finish can be from filing.
I'm sure Jerry is drawfiling.

I want to point out that drawfiling is what you need to do for a smooth finish.
I lot of folks don't know what drawfiling is...I didn't either before I was shown.

With a 6" file you can do it with one hand. See link below for an explanation.
I like a single cut mill smooth file.

http://www.btinternet.com/~hognosesa...drawfiling.htm

Bob Axsom · #6 07-06-2007, 01:32 AM

I deburred all accessible edges (including holes) with the deburring tool that worked best for the job. That's all.

Bob Axsom

Brantel · #7 07-06-2007, 06:15 AM

Medium and Fine Emory cloth, large 3m wheel for long easy to handle parts, and a 1" 3m wheel mounted on a die grinder for skins and hard to get to parts like lightning holes.

rv9aviator · #8 07-06-2007, 06:56 AM

I usually use a file first then clean things up with the emory and scotchbrite. I found a red 3-M scotchbrite paint removing pad mounted on a 1/4 inch stem for use in a hand drill that I put in the small drill press for deburring that works great in some areas too. I wore out two on the wing ribs. It is about 4-5 inches in dia and 3/8 inch thick. It is the same stuff as the red pads. They make one that has two pieces of scotchbrite that works the best because you can clean two side of a rib flange at the same time. Pictures are half way down the page showing the tools I use for deburring.
http://www.jimsairplanes.com/wing.htm

WSBuilder · #9 07-06-2007, 10:12 AM

The purpose for deburring and polishing, of course, is to eliminate stress risers. To really understand the load path, and thus the potential for cracks through any given part requires training, software and/or good intuition (and even then the experts get surprised). I think the latter serves most of us pretty well on these kits, so it's relatively easy to determine where you might be best served to use the purist craftsmanship you were taught and where you can relax a little bit. A big part of the success for most people in completing any big project is not burning yourself out by being too anal about every little thing, but judiciously applying THE BEST practises when it's needed. I haven't finished my plane yet, but I built and trimmed two houses, by myself.

Busy or thick structure, lots of big rivets or bolts, bent parts and sharp corners are all indicators of load paths and thus crack-potential places.

I'd like to hear experiences from builders with high-time airframes. Did cracks form in areas where you wished you had done a better job deburring/polishing? Did they appear where you were a perfectionist?

Jeff R · #10 07-06-2007, 11:01 AM

I have tried to be good about deburring and all, but in those long weary hours of mindless activity of deburring and smoothing, I have wondered if the folks at Cessna and Beach go through all of this. Is that one of the reasons spam cans cost so much -- all those union employees standing around Scotchbright wheels spending countless hours deburring all those cutouts and rivet holes and rounding and smoothing all the edges of the rib flanges and spars???

As Bill just asked, do we go too far here? Do the edges of the flanges in the middle of a rib really have to be baby-bottom smooth? There are really no forces there to initiate a crack to begin with, that I can see. Sure, near bends we need to be careful, but what about the circular rib cutouts? I mean, if we see a crack develop, we are told to do what? Drill a hole there to stop it. So, why do we smooth out the rib cutout holes when we use holes to stop cracks from propagating? Sure, we want to knock off and smooth out any nicks and chips, and we don't want to be overly worried about cutting ourselves on a too sharp edge, but do we sometimes go too far?

I don't really know....maybe these are mindless ramblings from a mind strung out on excessive deburring (maybe I can blame my botched riveting on being strung out from too much beburring?..). I guess we do because we simply don't want to take any chances, and a few extra minutes or hours now just might prevent some more serious problems later. But, if I were to learn that the C-152's and C-172's I flew were made with parts that were not deburred, where the ribs were riveted in fresh from the stamping machine, then I might have to wonder if should be worrying about something else.