H: Hubs, Wheels and Tyres Brake drum skimming

overdale

Forum User
VOC Member
Having got the wheels rebuilt for my 1951 Black Shadow, I'm now preparing to fit the drums. However closer inspection of the drums shows some areas of corrosion an the braking faces (previously hidden by masking tape) as I think the bike stood outside for some time before I bought it in 1971.
Set up in my lathe jig, the run out on the undamaged faces of the drums are all less than 0.1mm but the rough areas of corrosion need to be removed. They are the standard ribbed cast iron drums and I'm all set up to skim them, but would like to know what is the maximum diameter I can safely take them out to.
 

overdale

Forum User
VOC Member
Hi Martyn, thanks for your quick reply. The problem is that the corrosion of the surface is quite deep and concentrated, indicating water standing in the drums for some time when is was left outside motionless. Just to be safe, I wonder if anyone knows if there is a maximum safe diameter for skimming the drums.
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Hi Martyn, thanks for your quick reply. The problem is that the corrosion of the surface is quite deep and concentrated, indicating water standing in the drums for some time when is was left outside motionless. Just to be safe, I wonder if anyone knows if there is a maximum safe diameter for skimming the drums.
Problem is if you skim the drums then you will need to regrind the linings to match the new diameter - and if you are not careful you can end up with pretty thin linings.

New drums and shoes are available from the likes of V3 (see mph advert) of rom Timetraveller on this forum - but Oh $$$$$$
 

BigEd

Well Known and Active Forum User
VOC Member
VOC Forum Moderator
Hi Martyn, thanks for your quick reply. The problem is that the corrosion of the surface is quite deep and concentrated, indicating water standing in the drums for some time when is was left outside motionless. Just to be safe, I wonder if anyone knows if there is a maximum safe diameter for skimming the drums.
Without seeing a photograph of the extent of the corrosion you mentioned it is a little difficult to comment. (Send a photograph if you can. A picture is worth a thousand words.:)) My personal view is that if the corrosion is pitting then a rub with some emery would clean up any upstanding areas of the surface and the pitting would have little effect on braking. If the corrosion is deep then there may be a safety aspect so new drums should be considered. Skimming disadvantages have already been mentioned if you have to remove much material.
 

vibrac

Well Known and Active Forum User
VOC Member
Its just a question of the proportion of the hub surface that is affected after all the hub surface is about a third bigger than the shoe area any small loss of braking area will be insignificant and would soon get filled with compacted dust what constitutes 'a small area' is for you to decide consider the area taken up by rivet heads before we used bonding or lost by tapering of leading edges.Structural integrity as Ed says is a different matter.
 

Vincent Brake

Well Known and Active Forum User
VOC Member
I have plenty strd ribbed drums.
Think 60pcs.
Than we went 30 mm wide.....

But skimming a drum takes rubber hard wind arround outside, to avoid vibrations.
Dont take it out any furtheer as 179 mm that is
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Having never adjusted brakes that soon as they contact the drum they touch continuously for a full revolution. Indication is that all braking surfaces are not true even with the very nicely made Vincent Speet TLS arrangement. Have all ways thought of being able to turn wheels on their own bearings and machine the drums true. It is well worth consideration.
bananaman.
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Having never adjusted brakes that soon as they contact the drum they touch continuously for a full revolution. Indication is that all braking surfaces are not true even with the very nicely made Vincent Speet TLS arrangement. Have all ways thought of being able to turn wheels on their own bearings and machine the drums true. It is well worth consideration.
bananaman.
Yes Marcus,I have seen a devise sold in the USA that does exactly that BUT then there remains the problem of radiusing the shoes to match
 

overdale

Forum User
VOC Member
Thanks for all your replies with some very good points - it's good to get different opinions.
I had already taken onboard that skimming the drum would possibly require thicker linings to compensate and have already organised thicker linings so that the shoes can be machined to suit the drum diameter if necessary. Fortunately, the procedure is well described in previous members posts! Obviously I want to avoid the cost of new drums if possible and will assess whether some skimming within safe tolerances can improve the braking surface without compromising the strength/safety of the drum. Will check things out tomorrow.
 
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