What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Substituting 4's for3.5's

N355DW

N355DW

Well Known Member
I tried researching this but found nothing so I apologize if it has been covered.

After bucking several 3.5 rivets as called for in the plans in the HS skin to ribs and spars, I decided I did not like the look of the finished shop head. As near as I can tell, they barely meet the minimums for diameter and height, so they are okay I guess, but I just want a little more metal visible. Maybe my dimples are too much. I did use the tank dimples on the ribs and spars after reading some other posts, perhaps that is the problem.

Anyway, I tried some 4's, and I like them much better. They buck straight with no problem, and easily have both good diameter and height.

Has anyone else done this? Is there something I am unaware of that may not make this such a good idea?

Thanks, Damon
 
Sure did

N355DW said:
I tried researching this but found nothing so I apologize if it has been covered.

After bucking several 3.5 rivets as called for in the plans in the HS skin to ribs and spars, I decided I did not like the look of the finished shop head. As near as I can tell, they barely meet the minimums for diameter and height, so they are okay I guess, but I just want a little more metal visible. Maybe my dimples are too much. I did use the tank dimples on the ribs and spars after reading some other posts, perhaps that is the problem.

Anyway, I tried some 4's, and I like them much better. They buck straight with no problem, and easily have both good diameter and height.

Has anyone else done this? Is there something I am unaware of that may not make this such a good idea?

Thanks, Damon
Click to expand...

Damon,
Only on about 60 % of the rivets on my 8A. If you prime the parts before riveting, the "short rivet" situation is even worse!
Charlie
 
That is not completely unusual or unexpected

There are tolerence buildups on every part of the assembly and on drawings for building the airplanes at McDonnell Aircraft in the lower right corner of the drawing (I think it was in the Bill of Material. There was a substitution allowance for all fasteners allowing something like three size substitution each way from the callout. I must say most of my rivets were OK but if something doesn't look right you have to question it and don't hesitate to use the length that does the job right. As I got into the build of our RV-6A, I stopped buying short rivets. I just bought a 1/4 LB or 1/2 LB of #10 or #12 length if I ran into what you are facing I just cut them to the length I needed as I went.

Bob Axsom
 
Either is fine. The call out is computer generated I'm pretty sure, but if you feel better with the 4's so be it.

Larry
 
N355DW said:
......After bucking several 3.5 rivets as called for in the plans in the HS skin to ribs and spars, I decided I did not like the look of the finished shop head. As near as I can tell, they barely meet the minimums for diameter and height...
Click to expand...
Damon,

I always felt some of the rivet callouts are questionable and I can assure you as Bob Axsom pointed out, the same thing existed at McDonnell so it was no surprise when I encountered the same thing with the 2000 vintage RV-6A kit I built some years back. Whether it is building a combat aircraft to exacting standards or a homebuilt with no formal oversight, the builder always retains the option of installing longer length rivets as required. As far as my experience goes assembling the -6A and -8, the plans callout often indicates a 3.5 length rivet. In my view that length just barely meets minimums for diameter and height so more often than not, I chose to install -4's instead.

As an aside, Van's includes (or once did include) a bag of -3 rivets as part of the hardware inventory. For the life of me, I never understood why because I never encountered a single instance in which a -3 rivet length was appropriate.
 
I do this...

in many situations where I felt the shop head was too short. Rivet on with the longer lengths if they produce a better result.
 
Thanks to all! I just ordered a half pound of 4's. Back ordered on Spruce, so I have to wait on shipping from Oregon to FL, but I have enough left over from a previous project to finish the HS.

I knew that folks often question the callout in other situations, and was ready for that. I was just surprised since the skin rivets are so numerous, and the 4's just seem so much a better fit, at least in my situation.


Thanks again,
Damon
 
fehdxl said:
That's a *lot* of rivets...you sure you need that many? Just trying to help you save a few $$.

-Jim
Click to expand...


Hahaha! Yes, I probably overdid it, but I was going by a bag I had that said it was .1 of a pound. I'd rather have more than not enough, and I think it would saved me like 7$ to order just .25 of a pound.
 
N355DW said:
Thanks to all! I just ordered a half pound of 4's. Back ordered on Spruce, so I have to wait on shipping from Oregon to FL, but I have enough left over from a previous project to finish the HS.

snipped
Damon
Click to expand...

Damon,
I would suggest that you also order some 4.5s and 5.5s, while you are ordering from Vans. The extra rivets won't cost much, and you will save on shipping, if you order them later. You will need at least 0.2 pounds of each, later.
Like Rick, I never found a use for the 3-3 rivets, either.
Charlie
 
Thanks Charlie, I did just that today after I found I was replacing the call out for 4's with the 4.5's! So far I have replaced most of the flush rivets with one size larger, all the universal heads work as called for. I just finished the HS today!
 
As already mentioned.... final decision is always the builders responsibility because of a number of variabilities that can come into play.

I will say though, that "just barely meets spec" is still meeting the spec. Correct?
The other issue is related to what spec. you are talking about. If you are talking about the 1.5 Diam. X .5 thickness rule of thumb (this is actually not a spec, just a guide line), then you will often fined rivet call outs that you think are too short,
The actual Mil. Spec, for minimum rivet shop head sizes is less that the rule of thumb guide line.
Another basis for selecting rivet sizes that "just meet spec", is that if a particular size is just long enough, going to the next longer size will often be more difficult to set properly.
If you can consistently get good shop heads when using the next longer size, do what makes you feel good, but keep an eye on the rivet quality. Often times doing something like this to make things better can actually make things worse.
 
rvbuilder2002 said:
As already mentioned.... final decision is always the builders responsibility because of a number of variabilities that can come into play.

I will say though, that "just barely meets spec" is still meeting the spec. Correct?
The other issue is related to what spec. you are talking about. If you are talking about the 1.5 Diam. X .5 thickness rule of thumb (this is actually not a spec, just a guide line), then you will often fined rivet call outs that you think are too short,
The actual Mil. Spec, for minimum rivet shop head sizes is less that the rule of thumb guide line.
Another basis for selecting rivet sizes that "just meet spec", is that if a particular size is just long enough, going to the next longer size will often be more difficult to set properly.
If you can consistently get good shop heads when using the next longer size, do what makes you feel good, but keep an eye on the rivet quality. Often times doing something like this to make things better can actually make things worse.
Click to expand...


Yes, I am referring to the minimum height and diameter measurements for the shop head, for a 3/32 rivet taken from the spec table, measured with my micrometer, not a rivet gauge.

Except for about a dozen rivets out of all in the HS that cocked off a little, all the longer rivets I used set very well. I found it much easier to use a gun to keep the rivet straight than the squeezer. I did not have to fight the rivets, most set very easily. Except for a very few, the shop heads all had better than the median values from the table. Unless I am very careful, I have found it's much easier to overdrive a shorter rivet than use a longer one and keep it straight, so I think there is more danger of inferior shop heads using the shorter ones, at least in my case.
 
Last edited:
You must log in or register to reply here.
Back
Top