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Tip: A New Take On De Burring

mike newall

Well Known Member
Sponsor
OK,

We all know that part of the 51% we have to do is the labor intensive, time consuming stuff.

Well, this came via a very experienced Engineer who has worked all sorts of metal for years.

To quickly de burr sheet you have drilled, consider this.

400 grit wrapped round a small tungsten bucking bar - light passes, putting pressure on just rips the paper.

Up and down the line of holes and feel afterwards.

Tried it on my empennage and was impressed. Compared it under a 10x lupe to a standard 3 flute twizzle de burring tool and quite frankly it was a lot better and cleaner !

Discuss :D

DSC01804.JPG
 
It's only 400 paper - pretty much what you would use for edge prep.

Also, with the backing of the tungsten bar it really only cuts the edges of the holes.

As I say - only light pressure is needed.

You get very slight scruffing at the edges but no more than you would with - say red Scotchbrite.

Having seen the difference under a 10x glass, I am happy this leaves a cleaner edge much quicker.

Mike
 
deburring 101

If that technique is faster than conventional, go for it....but. For me; I would like to see all of the swirl marks removed from the surface of the Alclad with a
maroon scotch-brite pad. As you say, these marks are light so five or six passes with the pad should clean these up nicely. We want to leave the surface as "satin" a finish
as possible..stress risers are not our friend!:)
Regards
 
I'm worried that too much deburring is going on around here; :eek:
My 'Standard Aircraft Handbook' 5th edition, page 54:
...deburring..must be performed if the burrs tend to cause a separation between the parts being riveted. Burrs under either head of a rivet do not, in general, result in unacceptable riveting. The burrs do not have to be removed if the material is to used immediately; however, sharp burrs must be removed if the material is to be stored or stacked, to prevent scratching adjacent parts or injury to personnel.
Care must be taken to limit the amount of metal removed when burrs are removed. Removal of any appreciable amount of material from the edge of the rivet hole will result in a rivet joint of lowered strength. Deburring shall not be performed on predrilled holes that are to be subsequently form countersunk
For myself, I deburr lightly, or wipe off burrs with leather gloved hand or scotchbrite etc.
The 400 grit - on - bar looks like a safe way, but might not be acceptable if a polished surface is required later?
 
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I would agree there !

If I let my Bro loose with the de burring tool, we had countersinks !

The old, single hole tool was OK, the 3 flute tends to be a bit harsh.

If you are contemplating polishing - this would be a no no, however I am pleased it is generating some discussion.
 
I started with Avery's 3-flute tool, but now I mostly find myself using a scotch brite pad. Much faster and better holes. There is probably little difference between the scotch brite and 400 paper for this application.
 
Couldn't agree more, deburring is WAY overdone in the RV world.

I'm worried that too much deburring is going on around here; :eek:
My 'Standard Aircraft Handbook' 5th edition, page 54:
...deburring..must be performed if the burrs tend to cause a separation between the parts being riveted. Burrs under either head of a rivet do not, in general, result in unacceptable riveting. The burrs do not have to be removed if the material is to used immediately; however, sharp burrs must be removed if the material is to be stored or stacked, to prevent scratching adjacent parts or injury to personnel.
Care must be taken to limit the amount of metal removed when burrs are removed. Removal of any appreciable amount of material from the edge of the rivet hole will result in a rivet joint of lowered strength. Deburring shall not be performed on predrilled holes that are to be subsequently form countersunk
For myself, I deburr lightly, or wipe off burrs with leather gloved hand or scotchbrite etc.
The 400 grit - on - bar looks like a safe way, but might not be acceptable if a polished surface is required later?
 
Folks,

Vans Kit builders have the convenience of rivet holes punched by a Trumpmatic CNC machine. AC43-13 references deburring rivet holes with a deburring tool or oversized drill. I believe simply sanding the skin will not achieve the desired results because a perfectly square hole edge still constitutes a stress concentration.

A very slight bevel, even if a few thousanth's is preferable. Having experienced crack formation upon dimpling (guess where my opinion on the necessity of deburring with a drill was reinforced?) with holes I forgot to debur, (and never experienced with holes I did debur), I'm an advocate of deburring with a drill. I use a dedicated, new drill, that I installed in a file handle. No weight, simply the weight of the drill, lightly spun by hand - about 1-1/2 turns.

For holes added by the builder, careful drilling technique is required. Make sure you're "normal" (90 deg) to the skin, Consider using a "spotter" to insure your vertical. Slow down when you're about to "punch through" so as to minimize burr size.

I'll be repeating my Aircraft sheet metal seminars at Sun'nFun and I am scheduled for Airventure if any novices or inexperienced are interested. I won't presume that I can aid, or change the minds of the experienced!

Onward and upward
Marc Bourget
TC#5436
 
Might work for some, but I will continue to debur the old fashioned way. I like my skins looking clean on the outside surfaces, and then scotch-brite pads before prep and priming on the inside..

I like building and don't mind the extra time involved with a simple single twist of the debur bit in every hole. Tried and true, and looks good.

After two years into this project I don't know what I am going to do with myself when it is finished.. Build another I guess. ;-)

Thx
 
. . .After two years into this project I don't know what I am going to do with myself when it is finished.. Build another I guess. ;-)
My predicament exactly. My first flight was July 2010. Since then I have gone home at night after work (my real job) and "twiddled my thumbs" while watching boring TV. I am going stir crazy this winter after 5 years of building. :(
 
A Vans rep told me at Arlington one year that the factory uses a maroon scotchbrite pad to deburr holes in wing skins. One or two passes along the rivet line, and you have an adequately deburred surface in almost zero time.
 
It would be interesting to get some information on Bonanza as to just how they edge prep and de-bur holes prior to assembly.

I recall there was a video about them some time ago - anyone got a link, or a current video ?
 
Folks,
I believe simply sanding the skin will not achieve the desired results because a perfectly square hole edge still constitutes a stress concentration.

Ok, now I am lost as to the reason to de burr. drilling can leave an lip on he edge of the hole that can be felt when you run a finger over the hole. I assumed deburring was to round over the edges of the hole, both sides, to eliminate a stress facture point.

spinning a drill bit in a hole would smooth the inner wall. Running 400 grit over the hole would trin the lip but leave a sharp edge. Which I understand is bad..

so why do we deburr?

Len
:confused:
 
....

spinning a drill bit in a hole would smooth the inner wall. Running 400 grit over the hole would trin the lip but leave a sharp edge. Which I understand is bad..

so why do we deburr?

Len
:confused:

The bit that is spun over the hole is larger than the hole so it removes any protruding burrs. It is not spun in the inner wall...

We deburr so that the sheets will sit flat on each other and that the rivets will sit tightly against the sheets...

Section 3.3.1 here http://www.vansaircraft.com/public/Specs.htm

Most builders do seem to over deburr. The spec call for a 10% of the thickness countersink only. A mere 0.0025 inch on 0.025 sheet....:)
 
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I agree

To me a slight twist with an oversize sharp drill bit, applied with very little pressure, gives a better and quicker debur. Maybe its because the included angle is 118 degrees instead of 100 for standard countersink tool??

I was taught to debur slightly before coin dimpling so as to eliminate any cracking from the dimpling procedure.

For tight spots with 4 rivets I use these:

http://www.ezburr.com/index.php

Haven't tried the 3/32 size. They debur both sides at once, but you have to be very careful or they will easily take away too much material.

Dave A.
6A build
 
I felt de-burring is a little overdone in most cases. The purpose of de-burring is to avoid sheet metal separation during riveting, not to create a rounded or chamferred hole edge. Actually, a square edge is preferred. Also, de-burring is only necessary on the exit end of the hole. with this in mind, and use whatever method you see appropriate for de-burring purpose, time spent on de-burring can be much less.
 
scrap carpet is best help for deburring

Save yourself a lot of time with deburring by using a piece of scrap carpet placed on your bench and a battery screwdriver with Avery adapter for a spigoted countersink bit in the end, lay your part on the carpet, a quick light wizz with the battery screwdriver and the countersink bit nicely centered in the hole with the spigot of the countersink bit nestling through in the carpet. Perfect deburring every time and 5 minutes to do a whole wing panel. Flip it over and do the other side. With practice you can also use a battery drill but keep the weight light and do not over do the deburring.
I save my hole deburring for evening when I try to be quiet for the neighbours.
I have spent a lot of time as an A & P mechanic fixing cracks from rivet holes that were not deburred in customer aircraft that I am determined to not have cracks in my RV7.
A deburred hole has a much higher tolerance to stress and cracking than a square hole that has been deburred by rubbing a piece of scothbrite over it. You do not find square fishing rods as they would would break very quickly when flexed and the same applies by putting a small radius on rivet holes achiving the same increased crack tolerance. cheers Morris.
 
<snip>

Having experienced crack formation upon dimpling (guess where my opinion on the necessity of deburring with a drill was reinforced?) with holes I forgot to debur, (and never experienced with holes I did debur), I'm an advocate of deburring with a drill. I use a dedicated, new drill, that I installed in a file handle. No weight, simply the weight of the drill, lightly spun by hand - about 1-1/2 turns.

<snip>

Onward and upward
Marc Bourget
TC#5436

I also experienced dimples which cracked during riveting on a friend's airplane due to the fact that he forgot to debut some holes.
 
....
A deburred hole has a much higher tolerance to stress and cracking than a square hole that has been deburred by rubbing a piece of scothbrite over it. You do not find square fishing rods as they would would break very quickly when flexed and the same applies by putting a small radius on rivet holes achiving the same increased crack tolerance. cheers Morris.

Not really correct.

The Mil-Spec a couple of posts above just references "burr removal" not chamfering or radiusing the edges of rivet holes.

The Cherry-Max specifications (approved aircraft rivets) specifically show a diagram that says radiused edges are bad.

Page 19 here - http://www.cherryaerospace.com/files/pdf/catalog/CA-1015.pdf

Remove the burrs, sharp edges meet all of the process specifications.
 
Seems the b787 is devolving cracks because holes did not receive A ?demurring chamfer?...

SUMMARY:
We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 787-8 airplanes. This AD requires revising the maintenance or inspection program, as applicable, to include an airworthiness limitation for repetitive inspections of the web fastener holes in the overwing flex-tees. This AD was prompted by a report that certain web fastener holes in the overwing flex-tees at the wing-to-body interface might not have been deburred properly when manufactured. Fastener holes without the deburr chamfer applied can develop fatigue cracking. We are issuing this AD to detect and correct cracking in the web fastener holes in the overwing flex-tees, which can weaken the primary wing structure so it cannot sustain limit load.


https://www.federalregister.gov/doc...iness-directives-the-boeing-company-airplanes
 
radius vs. square, rivet

It does seem to make sense that a hole edge that has been perfectly radiused would be less likely to have a stress fracture. The tools we use to deburr help create a more radiused hole edge - although not perfectly radiused - if used correctly.

It's not clear to me if the rivet that's put into the hole and then compressed, expanding to fill the hole and more, is happier with a more square hole edge or a radiused edge, and would this in any way affect the likelihood of a stress fracture?

Which-rivet-is-happier.png
 
Seems the b787 is devolving cracks because holes did not receive A ?demurring chamfer?...

SUMMARY:
We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 787-8 airplanes. This AD requires revising the maintenance or inspection program, as applicable, to include an airworthiness limitation for repetitive inspections of the web fastener holes in the overwing flex-tees. This AD was prompted by a report that certain web fastener holes in the overwing flex-tees at the wing-to-body interface might not have been deburred properly when manufactured. Fastener holes without the deburr chamfer applied can develop fatigue cracking. We are issuing this AD to detect and correct cracking in the web fastener holes in the overwing flex-tees, which can weaken the primary wing structure so it cannot sustain limit load.


https://www.federalregister.gov/doc...iness-directives-the-boeing-company-airplanes

If they are fasteners as opposed to rivets, as the AD seems to imply, then a burr at the hole edge could certainly stop any bolt or similar fastener from sitting flush and in full contact with the material surface. This would prevent the fastened joint from developing the design strength characteristics.
 
What I wanted to see, as an aerospace stress engineer, was square edges, round holes, joints in flat contact to each other with no debris between the pieces.

Especially for hole-filling fasteners like driven rivets, that let the rivets actually fill the hole. Over deburring would have the rivets see more bending moment than otherwise, which is bad for fatigue. Fatigue life was increased by the preload force that the rivets create between the parts, as that provides some shear to transfer through friction.

Dave
 
You're assuming that a rivet when driven will expand to fill the filleted edges. You're also overlooking the fact that this graphic only shows one sheet, when in fact you'll have two sheets stacked, with back-to-back fillets that would need to be filled in.

To fill in the fillet under the manufactured (round) head, the rivet shank would have to swell a lot starting right under the head. That's not going to happen, and because the rivet is unsupported by the skin at that point it's more likely to crack at the sharp corner where the shank meets the head.

On the shop head side, I could see the rivet expanding to fill the space. But nowhere else with any consistency.
 
2 sheets

You're assuming that a rivet when driven will expand to fill the filleted edges. You're also overlooking the fact that this graphic only shows one sheet, when in fact you'll have two sheets stacked, with back-to-back fillets that would need to be filled in....
Correct - I missed that critical detail, thanks Rob!

Here's the modified picture - I think you are right, the rivet will probably not expand properly to fill in the gaps.

2-sheets-happy-rivet.png
 
Correct - I missed that critical detail, thanks Rob!

Here's the modified picture - I think you are right, the rivet will probably not expand properly to fill in the gaps.

2-sheets-happy-rivet.png

I have done quite a bit of analysis of riveted joints by milling away 45% of the hole diameter, polishing, and then viewing under magnification.

A rivet actually does a very good job of swelling into the irregular areas caused by excessive deburring or the voids that result from nested dimples.

Where the rivet doesn't swell as well is directly below the manufactured head. All of the additional material in the larger diameter rivet head causes this

That is why the one with sharp corners will be stronger. The small amount of shank swelling that happens in this location is more likely to tighten up in this part of the hole.

The one with radiused corners will result in less baring area against the rivet, of the sheet directly under the manufactured head.

This issue gets worse as the stack-up gets thicker.

BTW, this is why some specialty rivets have a raised nub or dimple in the center of the manufactured head. When the rivet is squeezed or driven, the extra material is pushed down the center of the rivet shank helping the portion of the shank just below the manufactured head to swell more than it would have otherwise.
 
Edges

This is an extremely helpful conversation for a new builder such as myself.

Could one of you comment on the technique you use for deburring edges? You've convinced me I have done too much deburring the holes in the practice kits so I'll adjust my procedure.

Currently I vixen file, then edge tool, then single-cut ******* file, then scotch bright. I've got a feeling I'm spending way too much time on this.

Greg
 
simple

... Currently I vixen file, then edge tool, then single-cut ******* file, then scotch bright. I've got a feeling I'm spending way too much time on this. ...
Greg, I think you are right. The goal of deburring is to have a very very slightly rounded edge. The radius should be very small, just enough to take the corner off, which reduces the likelihood of a stress fracture.

https://www.eaa.org/en/eaa/aviation...l-working-tips-for-first-time-builders-part-1
 
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