A Riveting Question

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Donrecardo

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No, not a question you cant leave alone, but a question about riveting

I am about to try riveting for the first time and I will be using 3/64" brass
round head rivets
I looked online at rivet data and it tells me several formula
for the sizes of rivets like for eg the head diameter of the rivet is 1.75 the diameter of the rivets shaft , It also tells the height of the rivets head compared
to the shafts diameter but what I cant find is what length should the shaft be

I appreciate it will differ depending on the thickness of the metal it has to go
through , but how much in relation to the diameter of its shaft should stick
through the other side to allow me to form a full round head with a rivet snap on the other side , so it looks the same at the back as at the front

Cheers

Don
 

BaronJ

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Hi Don,

I think you gave the answer in your post ! Head diameter = 1.75 X the shaft Dia. So if you add that to the material thickness you have your answer.
 

Donrecardo

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Hi Don,

I think you gave the answer in your post ! Head diameter = 1.75 X the shaft Dia. So if you add that to the material thickness you have your answer.
Hi Thanks for replying.
Forgive me for being thick, but I dont see how that gives me the answer

To make a full round head I need to have enough shaft sticking out to be
deformed by the rivet snap to shape the head.
Now the shaft is of course much narrower than the head so its obviously
not a case of the shaft being the thickness of the metal to be joined plus
the thickness of the head , thats not enough metal to fill the dimple in the
rivet snap and give me a full head but then I dont see how using the metal
thickness plus the diameter of the head as you sugest will work either

Don
 

BaronJ

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Hello Don,

Lets do some sums. You said that the head diameter is 1.75 times the shaft diameter, which you gave as 3/64th " (1.2 mm)

1.2 / 100 X 175 = 2.1 mm or just over 5.25/64th " plus material thickness under rivet head.

Though the Saphire table suggests slightly less allowance at 5/64th " Based on 1.5 times head diameter. But I suspect that would be for a hand press rather than a hammer and snap punch.

Converting to mm makes the sums easier.

Does it make sense now.
 

Donrecardo

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Hello Don,

Lets do some sums. You said that the head diameter is 1.75 times the shaft diameter, which you gave as 3/64th " (1.2 mm)

1.2 / 100 X 175 = 2.1 mm or just over 5.25/64th " plus material thickness under rivet head.

Though the Saphire table suggests slightly less allowance at 5/64th " Based on 1.5 times head diameter. But I suspect that would be for a hand press rather than a hammer and snap punch.

Converting to mm makes the sums easier.

Does it make sense now.
Hi Baron
Well I'm not trying to be difficult but no , not really.
Yes I can follow your numbers but I just dont see why you use the head diameter?
I accept the difference between your result and the list on the Saphire site may only be 0.4mm which doesnt sound a lot but 0.4mm when you are using a rivet whose shank is only 1.19mm suddenly looks more of an error than if maybe you were using a 1/8" rivet . infact if you work out the numbers using
Saphires formula of 1.43 X diameter of shank then your result is closer to the size Saphires site says to use for a 1/16" rivet which is 30% bigger than the
rivet I am using
In my naive way I had imagined that the amount of shank sticking out would have to contain the same volume of metal as in the head I am trying to duplicate so to me it made more sense to think that as its the amount of shank we need to know that it would make sense for it to be a percentage of the shank diameter that we need to calculate rather than a percentage of the head diameter?
Having said that I am not an engineer so my thoughts are probably not worth a row of beans . but regardless ,Thank you anyway for trying to help me . I did appreciate that you took the time to try and explain

Don
 

goldstar31

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I'm not an engineer or a whatever but I own a Universal Pillar Tool which does most tasks including riveting but on the other hand, I was brought up in a blacksmith's shop when I was tall enough to see over Dad's anvil- and noted what went on in the real world of people who make things rather than go into the niceties of riveting so that left to then Noah would have still been building the ark.
All that is required is using a gauge the same diameter as the rivet's and a pair of front cutting pliers. It's brass, it's little and one guesses it is about one and a half times the diameter. The need to re-exam the Great Eastern story with the dead skeletons of the riveter and his boy is happily history.

So like Paddy, the bit sticking up is about one and a half times the diameter. Time then for a Bob and Aunty.

If one doesn't know what went on between Bob and Aunty----------------------- you've missed a lot.

Regards

Norm
 

BaronJ

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Hi Don,

The reason the head diameter is used is because it allows you to calculate (rough guess) at the amount of rivet that needs to protrude to produce a similar size head on the other side of the work. So a thinner rivet would need to have more metal to compress in order to create the head. Conversly a thicker rivet would need less.

Don't dorget that you are reforming and compressing the metal in order to produce that head on the other side. If you have too much metal, then a ring is created around the formed head where it contacts the work. Too little metal and you dont get a fully formed head. Too much is prefered to not enough. 1.75 errs on the generous side so that you can adjust to suit.
Run a test and see what works for you.

As far as you being difficult ! No I don't see it that way. I would want my work to be right, and I hate having to do something twice.
 

goldstar31

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To put it another way- sliderules and log tables out, is to calculate the amount of metal contained in the head and then calculate how much metal- in the round needs to left to fashion a new head- as my old science master said 'Matter cannot be destroyed or created- merely moved.

Norm
 

bazmak

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Baron is right, 1.75 x the dia gives the right amount (volume of matl) to compress down to head dia and height. With my limited computer drafting skills
I would draw it out 10x size,when compressed down the 1.75 height of the rivet will compress down to the shape and size of the head.Approx 1/3 of a sphere if I remember
 

Donrecardo

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Firstly , Thanks everyone that replied

I just found a site http://www.had2know.com/academics/spherical-cap-volume-surface-area-calculator.html

Using that I calculated the volume of the head on the rivet
I divided that by the cross sectional area of the rivets shaft
and that gave me the length it needs to stick out from the metal to equal the same volume as the head of the rivet
I divided this " stick out length by the diameter of the rivets shaft to see what ratio it was and infact it came out at 1.702 times the rivets shaft diameter which is pretty close to Barons original answer of 1.75
so I think thats the value I will go with

Don
 

Jasonb

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Don't see how you got that from using the calculator in your link.

Height of the head is 0.75D (they are not half spheres)which = 0.9mm

You have said head dia is 1.75D so that is 2.1mm giving a radius of 1.05

Put those two figures into the calculator and you get 1.94 cu mm

If you work out the area of the shank and multipy that by 1.43D

0.6 x 0.6 x 3.142 x (1.2 x 1.43) low and behold you get 1.94 cu mm
 

tornitore45

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A bit of geometry tells that if you want to get a hemispheric head 1.75 times the shaft diameter you need a shaft length of ~1.78D or 343 x D / (3 x 64) to be exact.

That can be a starting value to fiddle around if you want a less domed head.
 

Jasonb

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As I said snap head rivits are not hemispheres that is why you need less that 1.75D and why 1.43D works
 

bazmak

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What you don't seem to realize is that when riveting we don't machine and mike up the rivet projection to close tolerances before hitting it with
a hammer.The calcs give a rule of thumb, experience and skill tell us whats
right and the finished head gives the proof.Whether its a hemisphere or 1/3
or 0.9 dia hemisphere.For small below 1/8 dia I had a pair of pincer/cutting
pliers which thru trial and error were ground to leave the correct projection
I never measured it but when the head came out correct it proved me right
!.43 might be theoretically correct but 1.75 is more correct .the extra material
being used as the rivet is expanded in the material.A good rivet should be watertight
 

Jasonb

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I did say that it will vary slightly depending on rivit clearance in the hole ons the shape of teh snap.

But if 1.75 is right I best drill out these couple of thousand rivits and start again. These were all cut with side cutters to approx 1.5D

 

dennisa49

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Hello Jason, Don,
Jason you are spot on.

Start with 1.5D rivet tail extended through the materials to be joined.
Tighten the material up to the rivet head.
Hammer the tail down.
Finish at 0.5D finished height.

Lot of rivets into a lot of flying aluminium.
Regards,
Dennis
 

bazmak

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Of course you are right Jason,very nice work.But you said approx. 1.5 high
What did you measure it with and was it 1.5 or 1.75,and 1000s of rivits
At the end of the day the final form of the rivet is whats important
not this extended discussion on the length of the rivet 1.5 or 1.75mm
who cares ,only the man making the finished product.As previously stated
1.75 is British standards with a lot of thought and many minds behind it
but at the end of the day its only a rule of thumb. Regards barry
 

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