Re: Bell cap how to

[PhilusEstilius]

I have myself over the years made several thousands of these items however not all in great quantity at one time, for after the first hundred or so the task becomes so mundane that one could start making footprints over the workshop ceiling.

When commissioned to make the Vindolanda and Trimontium chamfrons there were indeed numbers in four figures required, therefore to do the job it was better to make a handfull use them up and go do another type of job before insanity took over.

With the experience of having done this kind of work I can very well understand the way some of the Roman slaves in Fabrica must have felt poor devils.

[Tarbicus]

Here's an idea:

Get a load of these: http://www.rutlands.co.uk/cabinet-hardw ... pped-brass

Turn one upside down.

Hammer the inner hard with a punch of some type so the inner starts out above the leather.

Use with rivet as previously directed.

[PhilusEstilius]

Jim.
These could not work with the same function as the bellcaps being shown by Jurjen in his How To, the reason being as I have mentioned earlier the lower level of their countersink is at the same level as their outer edge and therefore it is against the leather before any riveting poundage is applied.

There is also that the walls of their countersink are more of a concave nature where as the walls of the countersink in a bellcap are convex, infact they would function very much in the same way as a flat washer creating around 90% more riviting poundage than a bellcap would need.

This is the whole purpose of these caps where they reduce the riveting poundage compared to that of a flat washer and prevent unwanted damage to whatever they are used with, infact it realy does need only very gentle tapping with a hammer to lock them.

[Tarbicus]

Okay, Brian. You blew that one out of the water. Thanks :wink:

[PhilusEstilius]

Jim.

It was not done with malice a forethought believe me, for I was thinking only of the technological aspect of these things. Infact it's only when one makes and uses them that the true understanding of them shows itself, that is why I say that it can only have been invented by some craftsman of long ago who truely understood the art of riveting.

[Tarbicus]

No, there was no offence taken. I really meant thanks! I like being corrected when I get something wrong, seriously.

[Magnus]

Brian, you still haven't shown any evidence what so ever that the inner and outer diameter of these bell caps/finishing washers are at two different elevations.

And BTW, why not call it a bell-cap washer, since after all, it serves the same function as a washer in terms of a fastener, but has the added bonus of material protection.

[Gaius Julius Caesar]

Brian, you still haven't shown any evidence what so ever that the inner and outer diameter of these bell caps/finishing washers are at two different elevations.

And BTW, why not call it a bell-cap washer, since after all, it serves the same function as a washer in terms of a fastener, but has the added bonus of material protection.

Matt, that is what it is....bell-cap.....short for bell cap washer....just runs off the tounge

you know Bell-cap, indisputable bell-cap, irrefutable leader of the gang...... :mrgreen:

[PhilusEstilius]

Jim.

I was not being serious honest and do of course understand what your saying.

[PhilusEstilius]

Matt.

Where you say that I have shown no evidence of the inner countersink base line being above that of the base line of the dome, it becomes very clear that if this countersink as shown by Jurjen is punched out on a domed former it cannot be anything but above it.


Then where you say that a bellcap serves the same function as a washer in terms of a fastener, it becomes clear that you are ignoring or are not aware of the poundage difference between a bellcap and a flat washer which I have already explained, The bellcap of course does also have this added feature where it is less likely to snag a tunic or other material, however it is the engineering aspect of riveting pressure that both Jurjen and I have been trying to get across.

[M. Demetrius]

I wonder if a test of riveting could be set up, using both sorts of domed washers, and a flat square washer for a "control". Seems like something systematic and pragmatic would make the argument either proven or disproven. Do each of them in turn, and see which takes the more/less effort to peen.

Oh, well, what do I know?? :|

[PhilusEstilius]

David

That is very true what you are saying and it's like what I have said if those who know anything about riveting would have a go at making and using these things they would begin to understand just what an engineering innovation they are.

I have to to say it has only been an estimation on my part but I'm sure it would be agreed by Jurjen that the riveting effort is reduced to only around 10% of that required for a flat washer.

Infact when it comes to riveting many are unaware that as a rivet is pounded down at it's shank end the whole rivet tends to also pull upwards and the head begins to crush the thing being riveted ie beltplate however the bellcap reduces this crushing effect greatly.

[Tarbicus]

Infact when it comes to riveting many are unaware that as a rivet is pounded down at it's shank end the whole rivet tends to also pull upwards and the head begins to crush the thing being riveted ie beltplate...

Good point. I've had this happen.

[Magnus]

Matt.

Where you say that I have shown no evidence of the inner countersink base line being above that of the base line of the dome, it becomes very clear that if this countersink as shown by Jurjen is punched out on a domed former it cannot be anything but above it.

On the contrary, Jurjen's reconstruction shows that the innner diameter is essentially on the same plane as the outer. On any soft surface like leather where there is some downwards force (like from the peened rivet), both inner and outer edges will be in contact. I would also argue that since these are not being built by a machine, but rather a human, that each piece will have differences to it. Again, your evidence is not even remotely convincing! And I'm still waiting for it lol.

And I would not base my conclusions on how an ancient artifact worked on a modern reconstruction. C'mon now...

Then where you say that a bellcap serves the same function as a washer in terms of a fastener, it becomes clear that you are ignoring or are not aware of the poundage difference between a bellcap and a flat washer which I have already explained, The bellcap of course does also have this added feature where it is less likely to snag a tunic or other material, however it is the engineering aspect of riveting pressure that both Jurjen and I have been trying to get across.

Oh really? So what you're saying then, is that the reason the Romans used bell cap washers, vs regular ones, is due to some "engineering" feature, vs preservation of equipment. I would LOVE to see you show evidence for that! Especially given the fact that the bell cap washer and regular washer do in fact serve the same purpose, with the difference in material protection (ie lack of sharp corners) for a bell cap washer. If they were such an engineering marvel, why not as much widespread use?

So it's not that I'm ignorant of your "reasoning", I'm just aware enough of the fact that it is completely irrelevant to pay no heed to it. Please try not to be insulted by this, but nothing presented by you so far has been strong enough or even provocative enough to make me think...hmmm...he may have a point here.

[Magnus]

David

That is very true what you are saying and it's like what I have said if those who know anything about riveting would have a go at making and using these things they would begin to understand just what an engineering innovation they are.

I have to to say it has only been an estimation on my part but I'm sure it would be agreed by Jurjen that the riveting effort is reduced to only around 10% of that required for a flat washer.

Sure, it sounds great, but again, why no widespread evidence of their use if they are in fact that innovative and efficient? It may just be that you have a preference to using these, which is why you defend them so staunchly.

Infact when it comes to riveting many are unaware that as a rivet is pounded down at it's shank end the whole rivet tends to also pull upwards and the head begins to crush the thing being riveted ie beltplate however the bellcap reduces this crushing effect greatly.

This is usually due to a lack of skill in rivetting...it's happened to me before too. I call this "Hulk Hand", when a person hammers the shank-end too much. It's simply a case of too much force on the shank end...sometimes people over mushroom the end, causing an overload of stress on the materials being fastened.

So maybe bell-caps were for assistant artisans who were still learning the fine art of rivetting.