Making cycle cotters in Stainless Steel

[Tim StevensParticipant @timstevens64731]

Hello from Wales

I need to make about a dozen cotters to fit the brakes on my 1928 Lea Francis car. I have the necessary taps and die (9/32″ BSF – an odd size I believe is only used for cotters – ?). As the cotters (two per brake) need to be removed when working on the hubs, brakes, axle etc, I need to ensure long life and resistance to damage, so I am thinking of stainless steel, but I need advice on which grade, treatment etc.

As a reminder, each cotter is made from 3/8 round bar, with an angled flat about an inch long to fit snug against the groove on each shaft, and at the narrow end, a (smaller) male thread about 3/4″ long. Removing a cotter means driving it out by knocking on the end of the thread, so to avoid future damage I intend to add an extractor thread on the other (cylindrical) end, made extra long – 5/16 BSF (as 3/8 would be too big to leave room for the spanner). The nuts will be made from 1/4 BSF plain stainless nuts, bored to 6mm clearance, and tapped 9/32 x 26 tpi. The plain washers will be stainless, too.

So, will ‘ordinary’ 3/8 stainless bar serve, or should I seek hard-drawn, or some high-test material? So far as I can tell, the cotters currently on the market are mild steel, and (in case anyone is interested) many of them have a 6mm thread and 10mm nuts, which tend to pull the washer into a cone. Proper sized cotters do exist, but some dealers don’t know what they are selling.

I look forward to suggestions – many thanks in advance.

Tim

PS for those with an interest in WORDS, a cotter-pin was originally named from this type of cotter, used in larger sizes than bicycle versions to hold proper man-sized machinery together when Victoria was a mere twinkle.

[bernard towersParticipant @bernardtowers37738]

I personally would use 304 as its easier on your precious 9/32 taps and dies. its a pity the thread is offset otherwise you could screwcut them unless you fancy offset turning and threadig them then having the problem of set up for the angled cut. the extractor thread is a good idea.

[martin haysomParticipant @martinhaysom48469]

with all that stainless on stainless make shaw you use plenty of your favorite anti seize paste.

[duncan webster 1Participant @duncanwebster1]

If you’re worried about seizing, the North Sea guys sometimes use aluminium bronze nuts on stainless bolts. Warning, aluminium bronze is a pig to drill, never tried tapping it

 

[John ATTLEEParticipant @johnattlee20632]

I would agree not to use stainless nuts because stainless bolts and nut tend to seize.  Stainless is far tougher than MS so any grade will do provided that you can cut the threads.

I think that it is a nice touch to improve something by using a better material and with an extractor facility.

John

[Tim StevensParticipant @timstevens64731]

Reasons for using 1/4 BSF stainless nuts:

1. The toolkit includes a spanner this size;

2. It avoids cutting the flats;

3. It was the traditional ‘standard’ size for these parts;

4. I know I can tap them;

5. I have them in stock.

But thanks for the reminder about lubrication for stainless fasteners.

Cheers, Tim

[Anonymous]

303 is the go to stainless for ease of machining, threading etc, it doesn’t work/heat harden easily. 304 is a pig, wouldn’t entertain it for anything other than its weldability.

[Andy_GParticipant @andy_g]

I would also avoid 304 stainless for that application – it is softer than a decent grade of carbon steel, and very given to galling in sliding contact. I certainly wouldn’t put stainless nuts on a stainless thread, even with goop.

I would suggest something like EN16T for the pins.

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