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drilled drums #778401 07/11/19 7:26 pm
Joined: Jul 2019
Posts: 1
betty plava Offline OP
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"nothing lighter than a hole" apparently, so bought a 1 1/2" HSS carbide tipped hole cutter especially for the job. but on centre punching the first indent (of 6) on the inside of the SLS drum on my BSA A65, a cap just popped out - so i guess the easy provision for some extra fresh air was already built in??? weighing the 6 caps = 10.4 grams so not much of a diet there.
added some budgie mesh to keep critters out.
on to the rear
the area available on the rear is smaller so i was planing on smaller holes. no indents on the rear so i made a template with 6 holes marked equidistant between the spline bolts. again, bought a brand new drill, fully expecting to burn it out on the cast iron. centre punched, then starting with a 4mm drill as a guide hole, i was surprised to have it bore straight through with little effort. jumping to the next size(s) up i noticed the metal wasn't producing the expected pasta curls of swarf but odd chips. the depth of the hole/thickness of the vertical face of the drum is only 5mm (the front is 7mm) but i expected a tougher material. it almost feels/looks like bakelite with a few iron filings thrown it just to make it metallic.

so finally my question: what is the rear drum of a 1966 BSA A65 made of?
i'm not confident to drill the now 14mm holes any bigger for fear of weakening the structure.

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Re: drilled drums [Re: betty plava] #778416 07/11/19 9:46 pm
Joined: Dec 2004
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kommando Offline
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Could be cast steel, Norton Commandos rear brake hubs are cast steel. You can use a grind test on a piece to tell you if it's iron or steel.

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