VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #11  
Old 09-15-2018, 01:02 PM
StressedOut StressedOut is offline
 
Join Date: Jun 2017
Location: Fullerton, CA
Posts: 113
Default

Quote:
Originally Posted by TASEsq View Post
Turner - GREAT idea using the centre punch dots to mark your parts L/R and their alignment. I have tried many things - like marking with a sharpie (acid etch took it off), wires / tags (time consuming and acid took the pen off the tags anyway!), keeping track of them (way too easy to forget or mix it up), so I finally went ahead and purchased a little vibrating pencil - figuring I would just make a little mark somewhere on the part for L/R or alignment etc - but this idea is even simpler. Thank you!
Two things here caught my attention: "vibrating" and "pencil". I'm not entirely sure what this is, but it doesn't sound like it should be used on aluminum.

Is a vibrating pencil something that will scratch into the surface and does it actually use a lead pencil? Both of these are things that are detrimental to the longevity of aluminum aircraft structure.

The carbon in a lead pencil will work its way in between the grains of the aluminum and react with it to form intergranular corrosion. It's difficult if not impossible to remove lead pencil marks completely once you've applied them. If this pencil actually scratches the surface as it's laying down carbon that's even worse. Alodine or primer afterwards won't help as the carbon is already between the grains.

Also, I'm wary of marking the part with a center punch. This causes a stress riser at the punch site and it's more likely to start a crack over time. I'd stay away from doing this. Use the punch for marking the location of drilled holes as it's intended.

I assume you're priming or applying Alodine since you mention an acid etch. You can reapply a sharpie mark after you finish the priming or Alodine and avoid all of these issues.

I'm sensitive to these issues since my day job is aircraft stress/DaDT analysis and design of structural repairs.

Edit: After I wrote this I went to Turner's blog to see exactly where the punch marks were. It looks like you've got two marks close to the blind fastener. The fastener hole and the marks each have their own stress concentration factor (SCF). By being in close proximity to each other they multiply. However given this is a control pushrod that won't see much load (and therefore significant stress), you won't have an issue with potential cracks. This might be a good area to include on the annual condition inspection though.
__________________
Art Jackson
RV-14A Kit#140433
Completed: Vertical Stab/Horizontal Stab
Scrapped: Rudder
Working on: Empennage (Elevator)
Construction log - mykitlog.com/ajackson
Dues paid on 10 October 2018
Member of EAA Chapter 92 (KCNO)
Pet peeve: "Lose" is the opposite of "find". "Loose" means "not tight".

Last edited by StressedOut : 09-15-2018 at 01:17 PM.
Reply With Quote
  #12  
Old 09-15-2018, 01:41 PM
mturnerb mturnerb is offline
 
Join Date: Apr 2015
Location: Ponte Vedra, FL
Posts: 722
Default

Quote:
Originally Posted by StressedOut View Post
Two things here caught my attention: "vibrating" and "pencil". I'm not entirely sure what this is, but it doesn't sound like it should be used on aluminum.

Is a vibrating pencil something that will scratch into the surface and does it actually use a lead pencil? Both of these are things that are detrimental to the longevity of aluminum aircraft structure.

The carbon in a lead pencil will work its way in between the grains of the aluminum and react with it to form intergranular corrosion. It's difficult if not impossible to remove lead pencil marks completely once you've applied them. If this pencil actually scratches the surface as it's laying down carbon that's even worse. Alodine or primer afterwards won't help as the carbon is already between the grains.

Also, I'm wary of marking the part with a center punch. This causes a stress riser at the punch site and it's more likely to start a crack over time. I'd stay away from doing this. Use the punch for marking the location of drilled holes as it's intended.

I assume you're priming or applying Alodine since you mention an acid etch. You can reapply a sharpie mark after you finish the priming or Alodine and avoid all of these issues.

I'm sensitive to these issues since my day job is aircraft stress/DaDT analysis and design of structural repairs.

Edit: After I wrote this I went to Turner's blog to see exactly where the punch marks were. It looks like you've got two marks close to the blind fastener. The fastener hole and the marks each have their own stress concentration factor (SCF). By being in close proximity to each other they multiply. However given this is a control pushrod that won't see much load (and therefore significant stress), you won't have an issue with potential cracks. This might be a good area to include on the annual condition inspection though.
Good points Art - as you might expect control pushrods and associated rod ends and jam nuts will be high on the list for condition inspections. I've used the "dot" method rarely and I think judiciously. Never in what I would think to be high stress or highly loaded areas.

All that said, is there a bit too much focus on perfection and avoidance of any/all blemishes on our aircraft? I've owned and flown any number of 30-40 (or more) year old aircraft that have had their share of dings and less than perfect assembly without structural issues related to these - at the same time the structural failures/broken parts on those aircraft have typically occurred either from material defects or high-wear parts that reached a very reasonable service life. I guess my point is each of us as builders has to stop somewhere short of perfection in our building. Heaven knows I've obsessed excessively over any number of issues that my very level-headed EAA tech counselor has assured me were "just fine".
__________________
Turner Billingsley
RV-14A In Progress
N14VB Reserved
https://turnerb14a.blogspot.com/

Last edited by mturnerb : 09-15-2018 at 01:50 PM.
Reply With Quote
  #13  
Old 09-15-2018, 01:54 PM
TASEsq TASEsq is offline
 
Join Date: Aug 2017
Location: Melbourne, Australia
Posts: 108
Default

Hi,

This is a ďvibrating pencilĒ for want of a better description. Not a pencil and not lead.
https://www.amazon.com/General-Tools.../dp/B004YK66NM

Iíve tried marking after etching (Iím using Stewart systems clean, etch then prime) - but the sharpie marks really donít bleed through hardly at all. Havenít had much success with the other methods listed below.

Is a couple of dots here and there really the doom and gloom you predict? I figured a little scratch with the vibrating pencil to mark orientation would not be that bad - Iíve made much worse by accident with the male dimple die! (Albeit scotchbrited them out before priming).

As an example, the doubler plates for the rudder spar had to go on with one face to the spar. Would one dot on each face make a difference?

Donít get me wrong, I donít know either way!! I just thought I had found a good solution in Turnerís idea...
__________________
___________
Trent Stewart
Melbourne, Australia
http://www.tasrv14.blogspot.com.au/
Dues paid until April 2019
Reply With Quote
  #14  
Old 09-15-2018, 03:24 PM
Navy76 Navy76 is offline
 
Join Date: Apr 2018
Location: Corvallis, OR
Posts: 12
Default

Kevin, I too recently received my QB wings. I was having difficulty getting the fuel sender rod set just right and ended up calling Vanís for advice. They recommended removing the tanks , as doing so makes fitting the sender much easier. They also mentioned that it is nearly impossible to test the z-brackets for leaks with the tanks in the wings.

I elected to remove the tanks and the left one came off without any issues and setting the fuel sender was, indeed, much easier with the tank off of the wing. On the right side I found that two of the bolts through the spar into the z-brackets on the tank had been stripped. The were very difficult to reach and I finally had to drill them out. It wasnít fun but doable with the wing in the wing stand. It would have been nearly impossible with the wing in the plane, I think. So, given that our wings are of the same vintage, you might want to make sure you can remove each of the fasteners even if you elect not to remove the tank itself.

Lyn
Reply With Quote
  #15  
Old 09-15-2018, 06:15 PM
StressedOut StressedOut is offline
 
Join Date: Jun 2017
Location: Fullerton, CA
Posts: 113
Default

Quote:
Originally Posted by TASEsq View Post
Hi,

This is a “vibrating pencil” for want of a better description. Not a pencil and not lead.
https://www.amazon.com/General-Tools.../dp/B004YK66NM

I’ve tried marking after etching (I’m using Stewart systems clean, etch then prime) - but the sharpie marks really don’t bleed through hardly at all. Haven’t had much success with the other methods listed below.

Is a couple of dots here and there really the doom and gloom you predict? I figured a little scratch with the vibrating pencil to mark orientation would not be that bad - I’ve made much worse by accident with the male dimple die! (Albeit scotchbrited them out before priming).

As an example, the doubler plates for the rudder spar had to go on with one face to the spar. Would one dot on each face make a difference?

Don’t get me wrong, I don’t know either way!! I just thought I had found a good solution in Turner’s idea...
Trent,

That's an excellent question! The short answer to the "doom and gloom" query is of course, it depends. The longer answer is, well, longer.

Just like a fire requires three components (heat, fuel, oxygen) to burn, a crack requires three components. First you need some kind of initial flaw. This could be a tool mark, an imperfection in the material, poorly formed grains, etc. Secondly, there must be repeated loading on the part. The final component is sufficient stress in the area of the flaw to cause it to grow on a microscopic level. If any of these things are missing a crack will not form.

A scratch not only serves as your initial flaw, but it also bumps up the far field stress at the flaw by the stress concentration factor.

I'm not suggesting that you can't have small blemishes here and there still be safe. I know I've got a few on my build, but nothing that gives me concern. Just like in real estate, it's all about location, location, location. In high load areas like spar flanges I'll make sure to remove any and all defects. For control rods like those mentioned in Turner's blog I don't have a problem with dots especially if they're not near fastener holes.

Regarding the marking issue, I was suggesting you mark the parts after the primer is cured. You just have to take steps to remember which part is L/R/front/rear while there's no identifier. I use little notes and lay the parts on opposite sides of the table to keep track of them. As soon as they're cured I mark them.

I looked at the link for the tool and it's labeled as an engraving tool. I would avoid using that and find another alternative. I remember before I started my build I read a great many builder's logs online and found one builder who stumbled on what he thought was a great idea. He started engraving the part number on all his parts with an engraving tool. I shuddered when I saw that.
__________________
Art Jackson
RV-14A Kit#140433
Completed: Vertical Stab/Horizontal Stab
Scrapped: Rudder
Working on: Empennage (Elevator)
Construction log - mykitlog.com/ajackson
Dues paid on 10 October 2018
Member of EAA Chapter 92 (KCNO)
Pet peeve: "Lose" is the opposite of "find". "Loose" means "not tight".
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 02:51 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.