Swaging, crimping and peening

Thanks to everyone for all the advice and ideas so far, this website https://www.orbitform.com/assembly-processes-services/orbital-riveting-and-forming/ gives a really good description of the orbital rivetting process, although it may not be the way Meccano did things at Binns Road. The attraction is the 80% reduction in the pressure needed over a simple press but I think trying to use a mill drill might be a bit ambitious. I think the shape of the hole described by Dave would help to lock the part onto the brass boss in terms of resisting rotation and maybe the "rivet" part is instrumental in maintaining the alignment perpendiculat to the boss axis. I think some experimentation is needed!

Me too!

I turned a 3/8" diameter brass boss with a 4.1mm through hole and a 1.5mm deep step to form the swage. The diameter of the step was cut to be slightly larger than the boss hole's minimum diameter, ie an interference fit with the inner side of the lobes.

I used an odd bit of junk box steel to support the rear of the pulley and eased the boss into the hole with a 4" vice:

Then I made a 1/2" diameter mild steel die with a 4.1mm pin to fit inside the brass boss:

And squeezed the whole lot in my vice as hard as I could by hand:

Results not very exciting. Although the boss is firmly fixed, and the pulley is at a right angle to the boss, it's not obvious that any swaging has taken place. Actually the diameter of boss is 0.1mm bigger, so the brass has deformed slightly. Hitting the die with a 2lb lump hammer increases the diameter by about 0.1mm per whack BUT the rear face of the boss got damaged and the pulley moved off axis. Not good.

I conclude that the brass would have to be softened before this approach might work, and that using a hammer is likely to distort the gear. At least in my unskilled hands it does!

Now I'm off to investigate annealing.

Please let me know if you find a way of doing this Chris - I'm interested in making non-standard Meccano parts too.

Dave

Edited By SillyOldDuffer on 05/09/2017 15:59:36

Dave, just another thought or two. Looking at the boss you tuned, if it had been a bit longer to protude more and then undercut so that the section you pressed was thinner, would it not deform more easily in a straight press or with a profiled die, or even better with a rotating die that folded over the brass as it was pressed. This brings me back to the orbital rivetting process - I can see how this would produce the finish required.

Many years ago when I worked for a large American controls firm many cam packs for timing various switches had cam plates sandwiched around a central brass or die cast hub. These were staked in place to hold everything together. Many cam plates had a central hole with 4 semicircles cut around it just like the Meccano pulley shown.

The stake tool for these ops was not a plain punch / brute force. Sometimes one stake op was done, with a punch having chisel-like angled features and sometimes an angled ring which displaced metal sideways into the 4 semicircles. Sometimes after this op a second stake would be done with a punch having a rounded groove, to displace the flange out and down to grab the cam plates better. Another type of stake tool had 4 round punches to hit the outer rim of a bushing in a plate to push the metal down and outward to hold the plate over the bush. In this type of stake tool the centreline of the punches was on the joint circle of the two parts. The punches' ends were angled down and out to direct the metal flow.

We also staked bushings into 3 mm plates for water valves, before soft soldering to seal them. These stakes were radial chisel marks around the bush OD, displacing metal sideways into the plate.

Almost all staking involved angled faces in the punches and dies to move the metal sideways and down with a vertical punching action, or tools to do a rolled flange action. We had a fleet of literally hundreds of Denison electric pump / hydraulic cylinder one and two ton presses to do these ops. These were clean, accurate, quiet presses that people could use for a full shift without fatigue.

Staking was once a very common assembly method for metal parts but has fallen by the wayside in the last number of years due to alternate materials like injection moulded plastics, and alternate processes such as snap fits, glues and heat staking being used for the type of assys that used to be staked metal work.

I'd bet that Meccano did most of their hubs exactly the way my old firm did, with staking tools in some sort of press, displacing metal with angled features / rings on the punches. JD

I tried again yesterday with an annealed boss. Slightly more successful but still a failure. Also, the whole softened brass boss deformed under pressure, not just the flange. I will try lengthening and undercutting the 'to be swaged' part of the boss though I doubt it will make enough difference.

As Jeff reveals in his educated post, this job isn't as easy as I thought. My plain punch and brute force approach didn't work! However, I was able to move the metal enough to suggest that a combination of angled punch as per Jeff plus a thinner swage section might work. (In the hope the job can be done in an ordinary home-workshop.)

The boss might be counter-sunk like this:

And the starting punch shaped like this:

The tapered punch would be used to start the swage, and a plain punch used to crimp it down to finish. Pesky domestic commitments mean I won't be able to try until tomorrow.

Dave

That latest boss looks a bit more realistic. You should make the thin section as thin as possible, consistent with being strong enough (it's only a toy? Sorry!). If using a manual process, rather than a 2 stage tool starting with that conical punch, I'd expect a single tool with more of an annular section (semi circular in section), so that the thin section is bent back onto the flat surface of the gear, rather like a hollow rivet.

I suspect the material may be a ductile flavour of brass. Often you will select a specific alloy to suit the production process for a particular part. Having said that I have very little experience of brass myself.

We use those loads of those orbital riveters to rivet push rods onto pistons used in automotive pneumatic actuators in very high volumes. They are very quick, consistent and reliable but obviously quite expensive. Been around for decades or longer.

Murray

My posting title should have been "swaging, crimping, peening, staking and orbital rivetting"! I'm on holiday at the moment just thinking about my next project, little did I expect the extent of the knowledgable response, Meccano may only be a toy, but it gave many of us our first taste of engineering principles, Alec Issigonis famously asked for an Outfit No 10 as a retirement present. The larger rotating parts may not need to transmit heavy loads but they need to be rigid and concentric and fixed firmly to the boss. I am hoping that there is a way of making this type of fixing in a home workshop, and the way things are going, the problem will be solved for me before I even get home...

I would be more inclined to try and get some, 'Cartridge' brass as it is more ductile and would not need annealing. My thoughts are that Meccano actually rolled the edge of the boss over to sandwich the pulley.

Clive

Chris,

I'm not really bothered ... just curious:

Did you try Laurie Penman's rotary-swaging-in-the-lathe idea ?

MichaelG.

Michael, apologies if I'm being dense, where would I find that? (I am fairly new to this forum) Chris

Got home early despite the road to the village being closed and had a quick play.

Made these:

Didn't bother annealing the brass before giving them a squeeze:

I'm using 3/8" brass rod and have no idea what the specification is. It's quite hard. Bit blurred but the brass has started to split. I knew Clive and Muzzer's advice about ductile brass would be good, and now I've proved it! After more squeezing a vice, bits start falling off:

Despite the brittle failure I think the result is promising. Next I shall try annealing the thin cup end of the boss and see if I can get an undamaged swage from softened brass.

Dave

If you make the punch similar to that used for setting tubular rivets I think you will have better luck. Tubular rivets were used to attach brake linings. If you can find someone who had one of the rivet setting tools you could examine you could copy the contour. Reducing the wall thickness as you have done is an excellent idea. Ductile material is also a necessity.

I have a tool for setting brake rivets. I will try to measure the contour and make a sketch for you.

If you make the punch similar to that used for setting tubular rivets I think you will have better luck. Tubular rivets were used to attach brake linings. If you can find someone who had one of the rivet setting tools you could examine you could copy the contour. Reducing the wall thickness as you have done is an excellent idea. Ductile material is also a necessity.

I have a tool for setting brake rivets. I will try to measure the contour and make a sketch for you. You can scale it up for your application.

.

Chris,

I posted this on 05-Sept.

___________________

Chris,

If you want to reproduce the visual detail of the Meccano fixing, without the specialist machinery that Tim mentioned ... have a look at Figure 9 in Laurie Penman's article here: **LINK**

http://www.awci.com/wp-content/uploads/ht/March2012.pdf

___________________

.

I think It's worth a look ... Using the jaws of the drill-chuck is perhaps questionable, but the principle is sound.

MichaelG.

I have not been able to get to my shop to measure up the rivet set for tubular rivets. Here are some images that might help.

http://www.bing.com/images/search?q=setting+tools+for+tubular+rivets&qpvt=setting+tools+for+tubulr+rivets

This seems to be the clearest image of the bunch.

It first spreads the end of the tube. Then it turns the flared end outward. Finally it turns the edge down.

Thanks John for the tubular rivet picture, that shape makes a lot of sense. I'll have a go, but don't bet the farm on me making a good facsimile. It will be another first for me.

Michael, I read Laurie Penman's article and intend trying his approach too. (How on earth did you find the article? Talk about buried treasure, you must be the Indiana Jones of web research.) I'm not sure about using the end of a drill chuck directly as a swage and will probably turn something to protect the chuck. I know chuck jaws are hardened but even so. Perhaps horologists use a particularly ductile brass for that sort of work?

A quick internet search for Cartridge Brass was disappointing. I could only find it as used ammunition. I suppose it could be melted down but not in my workshop.

Ta,

Dave

Use CZ131 Brass for making rivets. Free machining brass with some ductility.

Somewhere I have a drawing with the dimensions for the correct form of the tool for swaging tubular rivets of

various sizes. If I can find it I'll scan it and try and post it on here.

Keith.

Cartridge brass as follows, CZ106 and CuZn 30. Cold forming excellent

Clive

I think brass is similar to copper(being a copper alloy ofc) in that it work hardens so you may get even better results by annealing after each successive stage of working, rather than just annealing once.

But the best stuff will probably be the cartridge brass, provided you can get it, but theres a little tip if you can't.

Might be worth looking into what hot brass pressings are, as well. 

Michael W

Edited By Michael-w on 07/09/2017 11:48:07