VansAirForceForums  
Home > VansAirForceForums

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

- Today's Posts | Insert Pics

  #1  
Old 01-18-2018, 11:55 AM
Mlidzct Mlidzct is offline
 
Join Date: Nov 2016
Location: Southington, Ct
Posts: 78
Default Hole size after dimpling

I understand it's a given that the hole will stretch after the dimpling operation. The amount it will stretch can be influenced by the die used, starting hole size, and hole prep (over deburring/chamfering too deep).

What I'm having trouble with is understanding how the hole specs come into play here. I would assume the hole tolerance applies regardless if the hole is dimpled or not. Mil-std-403 table I specifically has limits for the hole before and after dimpling. I found some builders calling it good as long as the starting hole was in spec. Other builders apply the limits to the dimpled hole.

I recently dimpled some holes for AD4 rivets in .032 material and the holes came out .140-.143 (checked with gage pins). The starting holes were reamed #30 and measure .129. The deburring/edge breaks were anywhere from clean/sharp to .003 max chamfer.

So I freaked a little and emailed Vans since this was over the high limit of .135 given in MIL-R-47196 which is the spec Vans references. The response was as long as the starting hole was good there is no problem, which is in line with what I found some other builders saying.

I kind of don't like that answer because how should we evaluate if there is a problem. If my holes came out .160 would it still be considered good since the starting hole was good??
__________________
RV-7A QB under construction
Reply With Quote
  #2  
Old 01-18-2018, 01:04 PM
RV6_flyer's Avatar
RV6_flyer RV6_flyer is offline
 
Join Date: Jan 2005
Location: NC25
Posts: 3,005
Default

I did the measurements you are doing 30-years ago. Yes the numbers are a very large hole that you would not think is ok.

Bottom line, DO NOT measure the hole after it is dimpled. Only the size of the drilled hole is what matters.

If you want to run more tests, measure what a rivet expands to after it is set but DO NOT set it in any metal. Just squeeze it with nothing around it. It expands to fill a hole a lot larger than what the spec calls for.

Years ago, others have done pull tests of what it would take to break a rivet joint using poorly set rivets. Ones that most builders would remove and redo if it were on their airplane. IF you find the data, it shows that many of the poorly set rivets still hold a lot more than one would think.
__________________
Gary A. Sobek
NC25 RV-6
Flying
3,300+ hours
Where is N157GS
Building RV-8 S/N: 80012

To most people, the sky is the limit.
To those who love aviation, the sky is home.
Reply With Quote
  #3  
Old 01-18-2018, 03:26 PM
bpattonsoa bpattonsoa is offline
 
Join Date: Apr 2005
Location: Indepenence, Oregon
Posts: 279
Default

A whole bunch of years ago, I asked myself the same question, especially after doing some double dimple practice rivets. Do some and then section a rivet by cutting away the skins one the edge of the riven and then use a fine file to trim it back to the center of the rivet.

What you should see is that all the crevices have been filled with expanded rivet material.

Then do it about 20K more times and fly away.
__________________
Bruce Patton
Building Rans S-20 Raven 796S reserved
Going to the light side!
RV-6A 596S flying since '99 (Sold)
HP-18 5596S flying since '89
RV-10 996S tail, quick build wing and slow build fues., - dual Skyviews with complete system, two radio and not much else. Interior completely finished with Zolatone. CF plenum, interior complete. 1624 lbs, FLYING after a 21.5 month build.
Reply With Quote
  #4  
Old 04-06-2018, 09:26 AM
rsr3 rsr3 is offline
 
Join Date: Feb 2018
Location: UK
Posts: 8
Default

Please bear with me while I ask what seems a silly question - I am very early on in my riveting days, having received my tail kit but only yet dared to practice on scrap sheet!

I have just been setting AD3 and AD4 rivets into some practice sheet. The AD3 flush rivets set very nicely in dimpled sheet. However, when I moved onto the AD4s I have been getting a very inconsistent finish. It seemed to me like the holes (drilled with #30) were too big for the rivet by the time they'd been deburred and dimpled. So I did a few tests to see at which stage the enlarged holes were appearing, and as you all say - it appears to be at the dimpling stage.

Ok, so you all say the hole is fine as long as it was the right size to start off with, but when I set the rivets they sometimes twist off centre in the hole and the head isn't square and entirely flush with the surface.

Can anyone offer any advice on how to correct for this, please?

Thanks in advance!
Reply With Quote
  #5  
Old 04-06-2018, 10:05 AM
ppilotmike's Avatar
ppilotmike ppilotmike is offline
 
Join Date: Jan 2010
Location: Denver, CO
Posts: 1,793
Default

Quote:
Originally Posted by rsr3 View Post
Please bear with me while I ask what seems a silly question - I am very early on in my riveting days, having received my tail kit but only yet dared to practice on scrap sheet!

I have just been setting AD3 and AD4 rivets into some practice sheet. The AD3 flush rivets set very nicely in dimpled sheet. However, when I moved onto the AD4s I have been getting a very inconsistent finish. It seemed to me like the holes (drilled with #30) were too big for the rivet by the time they'd been deburred and dimpled. So I did a few tests to see at which stage the enlarged holes were appearing, and as you all say - it appears to be at the dimpling stage.

Ok, so you all say the hole is fine as long as it was the right size to start off with, but when I set the rivets they sometimes twist off centre in the hole and the head isn't square and entirely flush with the surface.

Can anyone offer any advice on how to correct for this, please?

Thanks in advance!
Chances are:
1) You're deburring too much and opening up the hole even more. Be careful just to take the burrs off, not countersinking or beveling the edge.
2) Your flush rivet die (for rivet gun) is not in flush contact with the sheet metal (i.e. the rubber around the die is keeping the face from being in contact, allowing the rivet to rise up and twist.
3) You're pushing too hard with the bucking bar, forcing the flush head up, as it sets. You should always have more force on the rivet gun side than the bucking bar side while setting.
4) Air pressure on the gun is too low, taking longer to set and allowing you more time to botch your pressure on the bucking bar (see #3) or twist the bucking bar out of square, pushing the back of the rivet off center.

All in all, practice makes perfect. Eventually, you'll get to where you drive perfect rivets, most of the time.
__________________
Mike Rettig
EAA Chapter 301, President www.eaa301.org
VAF Dues Current: as of 01/15/18
RV-10 (41PX Reserved) Fuselage
F-14 (Pedal Plane - Daughter's Project) "Flying"
http://www.mykitlog.com/mikrettig
Reply With Quote
  #6  
Old 04-06-2018, 10:31 AM
Larco Larco is offline
 
Join Date: Mar 2005
Location: DVT Phoenix
Posts: 1,061
Default

Sometimes if a rivet is just a bit too long it will have a tendency to lay over instead of squeezing nice and straight. Practice using the rivet gauge with longer and shorter rivets then are called out for and you will see some differences I'm sure.
__________________
Larry
Reply With Quote
  #7  
Old 04-06-2018, 10:43 AM
az_gila's Avatar
az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 9,607
Smile Drill #41

I preferred drilling with a #41 drill bit if the sheet is going to be dimpled as long as your dimple die will fit - all of mine did.

#41 is 0.096 and does fall within the Mil-spec hole size of 0.093 to 0.103

The couple of thousands less on the hole size seems to help the rivets fit a bit better in a dimpled hole and be slightly less likely to tip over during riveting.

Note that the above was used on a not pre-punched -6A kit. I'm not sure how the pre-punched holes will work with a #41 drill bit.
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
Reply With Quote
  #8  
Old 04-06-2018, 01:09 PM
Mlidzct Mlidzct is offline
 
Join Date: Nov 2016
Location: Southington, Ct
Posts: 78
Default

Quote:
Originally Posted by az_gila View Post
I preferred drilling with a #41 drill bit if the sheet is going to be dimpled as long as your dimple die will fit - all of mine did.

#41 is 0.096 and does fall within the Mil-spec hole size of 0.093 to 0.103

The couple of thousands less on the hole size seems to help the rivets fit a bit better in a dimpled hole and be slightly less likely to tip over during riveting.

Note that the above was used on a not pre-punched -6A kit. I'm not sure how the pre-punched holes will work with a #41 drill bit.

That's what I've been doing after my original findings. Drilling or reaming holes near the low limit for the starting hole seems to always keep it in spec after dimpling.
__________________
RV-7A QB under construction
Reply With Quote
  #9  
Old 04-06-2018, 03:11 PM
Marc Bourget Marc Bourget is offline
 
Join Date: Apr 2009
Location: Stockton, California
Posts: 180
Default

Lot's of good points, above. I think I spent an average of 15 minutes or so just on riveting in my Sun'nFun and Air Venture sheet metal forums. So many points popped into my mind reading this thread.

From Memory! About .110" is the smallest recommended or th -4 rivets. The smaller you go on the initial, pre-dimple, hole, the greater the chance of radial splitting. You can reduce that by adding a reaming step, with a custom sized reamer then deburring, again lightly.

The larger the hole, after dimpling, leads to more work hardening of the rivet shaft as it swells to first fill the hole, then form the shop head. It's battling for room with the dimpled skin and you can experience splitting (worst case) or skin distortion (also not desirable) as the shaft swells and hardens.

Get the freshest, softest rivets possible, or consider heat treating to anneal condition or "W" temper treatments, then, if possible, drive with the fewest hits possible.

My first set of wings, using annealed rivets, was done at 30 PSI on the #3 rivet gun and took about 4 hits, ( plop, plop, plop, plop).
Reply With Quote
  #10  
Old 04-06-2018, 04:00 PM
rsr3 rsr3 is offline
 
Join Date: Feb 2018
Location: UK
Posts: 8
Default

Thanks everyone - food for thought. Certainly my pressure is too low I think, and I suspect that I am pushing too hard with the bucking bar. On the odd occasion where I’ve just held the bucking bar steady and let it almost “rattle” against the shop head, it’s actually done a neat job.

Many thanks everyone for taking the time to reply. Much appreciated!
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 08:58 AM.


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.