[ali059]

As I do my build I was wondering why the rear INSIDE top cover rivets are rounded and not flat? Would it be easier to hold them in place for riveting if they are flat? I know you grind one side to fit closer to the top of the top cover, but the end is rounded.

Thanks!

 

[L999here]

...I'll take a guess..

My guess as to why they are rounded is for stregnth. If they were beveled into the plate,might not take the pounding well.

 

[jmann]

since they are not countersunk the rivet head would look like a nail head and that is not as strong.
Little bit of trivia. All the rivets I have seen on original colt 28's and mg38's were domed. On the commercial 28 the only rivet that was ground flush on the outside of the gun was the top large trunion rivet on the right side and that was to allow the leaf spring on the top cover pin to slide into its slot on the waterjacket. All other rivets, even the big ones had nice dome heads on them.

 

[Poverty Ridge]

02 worth

I question the strength part-- rivets are used in shear applications only not tensile. According to Cessna (414 Maint Man) the heads only keep the rivets in place and not much head is really needed.

 

[jmann]

I question the strength part-- rivets are used in shear applications only not tensile. According to Cessna (414 Maint Man) the heads only keep the rivets in place and not much head is really needed.

Wow, you have obviously never had an out of battery detonation in a browning. I promise you the forces are not shear forces on the rivet. While I understand what you are saying about rivets you cant tell me the rivets, espacially the large trunion rivets needed to be that big to keep everything in alignment. There was some size factoring done by JMB when he put rivets as large as he did in the trunion and I dont feel it was to keep the sideplates from slipping on the trunion as would be considered shear application. Technically the pintle pin would have done that.

 

[montytim]

Browning was an engineer

he knew rivets were not a tension member. JMHO.

 

[MSG]

I come up with two things:

1) I don’t think it’s about rivet strength, but rather the Top plate. The rivet hole is very close to two edges of the material, and cutting a chamfer means even less material to take the load.

2) As someone mentioned earlier, most rivets on earlier weapons have round heads. It was probably common practice to use round head rivets whenever possible; no need for cutting the countersink or grinding the head after peening. Cutting a chamfer in the inside of the Top plate will require a milling operation and a custom cutter. Is it really worth all that trouble when a pan head will work. The profit motive tends to eliminate unnecessary machining operations.

MSG

 

[stanamale1]

file a flat on it

When i build mine, i put a flat on the heads just to keep my bucking bar from moving. Just enough for a nice flat area but not enough to weaken the rivet. stan

 

[alcova]

You all are missing something...no way to get into that top piece to cut a countersink because of the edges that hang down

Walt

 

[Dan @ Angola Armory]

MSG has it correct:
1) I don’t think it’s about rivet strength, but rather the Top plate. The rivet hole is very close to two edges of the material, and cutting a chamfer means even less material to take the load.
Dan

 

[Lucky#13]

Lots of good points here. I have no engineering experience so I can't talk shear vs tensile applications. But I can add a bit to the military side of the history. jmann correctly points out the use of domes on the Colt commercial stuff. I have the remnants of the Colt rivets, including the large trunnion ones, on my 1928 kit. What I am hoping to figure out is how to accurately press a big dome like that when I build the bugger. Probably going to need some good heat on that one!

As for military production, all the rivets were chamfered and ground flush on the WWI 1917 production, including the cams on the LSP. As guns were rebuilt into 1917A1s, and 1919A4s were produced, there is some variety. The cams all have domed heads on new production. I have examples of 1917 LSPs where a cam has been replaced, so one is flush and one is domed, on conversion to 1919A4. Saginaw tended to use domes of about the standard size on the top plate at both ends, but I have seen a pic of one (appears original) where the rear is domed and the front flat. RIA uses a pretty large diameter, but short dome on the rear, and a smaller dome at the front. I have not seen conclusive images on BA guns, but my guess is they tended to domes like SG.

No question that the pan head with the ground flat, for inside the rear top plate, was the standard on every version of the series. I think the points by msg and alcova explain the most likely reasons. And at Dan to that, who slipped in while I was typing!

 

[Poverty Ridge]

Lets put this in a another perspective-- these brownings were made in a time of war.
It takes more labor,material, and skill to properly chamfer and shoot a typical AN425 (flush) style rivet versus the AN430 (round head) type of rivet.Besides the flush rivet really wasn't the NORM back then.

Fortunately I have not had my 1919 blow-up but the forces exerted when I examined them (at the attached pieces) are in shear forces.

As for the size of the trunion rivets--- most of the common steel back in the day was probably 1015 up to 1050 tops (SAE) so it was neccessary to use a larger fastener to increase the bearing strength for reliability or use more smaller fasteners to distribute the load.

As for the different angles of countersinking, it also is part of the factor of additional strength of the rivet by increasing the bearing strength on the rivet.

More surface area on the chamfer/countersink the more bearing strength in the riveted joint.

info: FAA Ac43.13 1A

Mr Browning really took a lot of factors into consideration time, availability, and reliability.

 

[Lucky#13]

The material thing gets interesting. No doubt the steels in WWI were somewhat primitive compared to even WWII. I can tell you that early drawings call for some interesting stuff, much of it hard to make sense of today.

On original 1917 side plates, the material called for was cold rolled steel. Yes, that is documented. Other things are just referred to as "gun steel" or "A" grade steel, "as rolled", later on. In revisions it is the "A" grade that is called for the side plates. "Drill rod" is another favorite. It is fascinating stuff.

I don't know if the 60 degree rivet thing was from an engineering spec JMB called for or just that this may have been the standard then, as 90 degrees is today. Certainly I think the size of the rivets did have something to do with the available area in the components that were being assembled, as well as for strength. Lots of room for big rivets through the trunnion, for example. Only three rivets holding the top plate, so slightly larger makes sense than for the bottom plate, where a longer area is being secured with several times the number of smaller rivets. Just some backyard engineering thoughts here, lol!