# Making an eccentric strap



## tel (Aug 25, 2009)

This topic came up not so long ago, and as I am up to making the strap for the Ridley half beam, I though it might be timely to post a few 'how I do it' pics

First cut a big-enough piece from the parent stock, in this case 5mm brass, 20 mm wide





Then mill the long edges straight and square.





.... and do likewise on a small section of one end, for indicating purposes


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## tel (Aug 25, 2009)

Perhaps before we go any further, a look at the drawing would be in order.


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## tel (Aug 25, 2009)

the piece of material - big enough for the two halves, plus a bit for luck





Indicate the edge and pick up the centre of the piece, then do likewise to the end





then step along and drill the four holes - the first two are clearing size for 8BA, the other two are tapping size. At this point there is a broken no.49 drill firmly wedged in the rightmost hole.


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## tel (Aug 25, 2009)

20 annoying minutes later the broken drill has been cleared and the two holes tapped





The two pieces roughed out on the bandsaw





.... and screwed together


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## tel (Aug 25, 2009)

The profile is marked out - sorry about the quality of this one - I was using natural light, of which there wasn't much




After a bit more roughing out on the saw, the piece(s) mounted in the 4 jaw





... and the boss for the eccentric rod turned, drilled and tapped





That's all for now - I'm tied up the rest of this week, so it'll be a few days before we move forward


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## ozzie46 (Aug 25, 2009)

Would really be interested in how you cleared the broken bit? Puuulllleeeeese??    


 Ron


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## tel (Aug 25, 2009)

No biggy Ron - if you look at the pic you will see that I roughed out the bolting tab on the bandsaw, then a bit of nifty file work allowed my to get at the pointy end of the broken bit and drive it out with a small pin (actually a small allen key)


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## arnoldb (Aug 25, 2009)

Very interesting and informative Tel Thm:
Thanks for the step-by-step!

Regards, Arnold


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## ozzie46 (Aug 25, 2009)

Thanks Tel.


 Ron


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## abby (Aug 25, 2009)

Nice piece of work Tel , or for 2 quid you could buy one of my castings


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## tel (Aug 25, 2009)

And a nice looking casting it is mate, you go from strength to strength. 

Trouble is, the bit of brass was _here_, the casting _there_!


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## Philjoe5 (Aug 25, 2009)

Nice work Tel. Thanks for the pics and explanation.  :bow:

Cheers,
Phil


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## CrewCab (Aug 25, 2009)

Nice one Tel 8)

Cheers

CC


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## tel (Aug 29, 2009)

OK, moving right along.

Some years back, on an idle afternoon in what must have been a particularly lucid period I made a little 3" faceplace from an offcut of CI, this plate is just the duck's guts for little boring jobs, so it's what I used here.

The embryo strap is mounted on the faceplate with the centre dot running true, centre drill.





Then the hole is opened out to 1/2" or so with progressively larger drills, and bored to fit a previously made plug gauge





The strap is then hand fitted to the eccentric - this required a little scraping and lapping of the sides. BTW, for scraping in little bores like this, I use the corner of a piece of square HHS tool bit (if it's good enough to ream .303 barrels with, it's good enough for me) Then the eccentric was mounted on a stub of crankshaft material, put in the 3 jaw in the lathe, and run in with a little oil for a short while.




More later - watch this space


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## tel (Aug 29, 2009)

OK, we're on the home straight now.

Next step is to turn up a couple of filing buttons - the small diameter is a good fit to the bore in the strap, the larger is equal to the required finished size of the strap. The holes are in 'em purely to make the parting off (from 1" bar) easier





Now back to the bandsaw (you should know the way _there_ by now) for a final roughing out.





Now insert the buttons, bung the whole package in the vise, and have at it with a file





The end result should look something like this





Seen here with the previously made eccentric. Not the only way to do 'em, probably not the best way to do 'em, but it's the way I'm comfortable with. Still need a little cosmetic work, but for the purposes of this exercise ....





Hope it's been of help to someone.


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## zeeprogrammer (Aug 29, 2009)

Helped this someone.
No need yet...but very glad to learn for future.
Thanks tel.


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## 4156df (Aug 29, 2009)

Tel,
Terrific post. Very informative. I've tucked it away for future reference.
Dennis


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## arnoldb (Aug 30, 2009)

Tel, Thank you very much. I will need this for one of my planned future projects 

Regards, Arnold


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## bearcar1 (Aug 30, 2009)

Nicely done mate. And thanks for your efforts in sharing with us. A fine example of one of the methods used to make such pieces. This method can apply to many other sorts of parts that require concentricity and the need to be separated.

BC1
Jim


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## mklotz (Aug 30, 2009)

Very nice work, Tel.

When I was first starting out, I "invented" filing buttons. I was proud as punch of my discovery until I started reading ME regularly and realized that model engineers have been using them since the late Jurassic.

Newbies should pay close attention to the technique and practice it at the first opportunity they encounter. For most newbies the file is the most underrated and underused tool in the shop. The reality is that it's one of the most useful and developing some skill with it is essential to the craft.

Note too that buttons need not necessarily be round. I've used flat "buttons" to achieve straight and angled contours in locations where conventional milling would have been difficult or impossible.


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## tel (Aug 30, 2009)

I couldn't agree more Marv - some mastery of the file is almost essential in this game. Quite often a part can be produced with files in the time it takes to even start thinking about setting up a machine.

You are right about button shapes as well - the scope for shapes is limited only by your imagination. One further word on buttons - a lot of folk advocate hardening them, they must have a far larger file budget that wot I have, in most cases the buttons are only required for a limited number of pieces and with care unhardened mild steel is fine.


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## mklotz (Aug 30, 2009)

Like you, Tel, I prefer them unhardened. Not only does it save the file, but the file marks on the buttons when you reach the right dimension are a very good visual cue to tell you to stop. (Those of us who become entranced while beavering away with a file need such clues.)


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