Further to the post of Matty Leahy, I would like to know how you guys are doing it.
This is a very important top safety issue and should be considered carefully.
Over here in Israel, it is common to run the drum on a lathe and machine the inner face accordingly to the fresh friction faced shoes. They should be aligned and match one to each other.
An expert is doing this job, of course, and he's relying on years of experience regarding drum wall thickness.
He once invalidated my front BMW R51/3 drum and rejected the job, saying the wall was too thin. This old gentleman passed away unfortunately.
How is it in the NL? The UK? Other countries?
Have a nice weekend!
Hi Michael
I think in the UK we can count ourselves quite lucky in that many of us 'fettlers' seem to have a lathe ir access to one. But if not, then there are many small engineering firms who would undertake the work. The judgement call on wall thickness is one I would make myself, but others may need dimensions to check and decide.
My lathe helps me out all the time and saves a small fortune too 😀
Darren.
The M20 standards book (if my memory serves correctly) gives the limits for machining the drums...The machining should be done after the wheel is built and fully 'tensioned and trued'....
The wheel is built in the wheel building jig using the bearings as the 'datum' and the rim is then trued to those..The drum must also run true to the bearings so I used those to mount off for machining the drum.....
With the spindle fitted I fully tightened the bearing adjustment nuts to lock the bearings, held one end of the spindle in the lathe chuck and supported the other end using a 'running' centre...(front wheel)
The problem here is that you need a lathe with a removable 'gap' and of sufficient size to have a large enough 'swing' to accommodate the wheels diameter..So a 20" 'swing'...
In other words it isn't going to happen on any of the smaller lathes...My own 48" bed Harrison 300 won't do it for example...That has a 13" swing with the 'gap' removed...
When I earned my living as a Toolmaker I had access to lathes of this sort of size but I think most (including me now) would have to find an engineering shop to do the work....
The wheel can also be held on the rim to do the work but careful consideration should be given to feed, speed and cutting depth to avoid vibration...In that case I would go particularly gently to assess the situation and again it would require a large lathe to have the chucking capacity...Ian
I used to get mine machined by a chap who fitted a mandrel through the hollow chuck spindle to hold the wheel behind the lathe.
He had a rotary grinder set up on a pedistal .
I used to wonder about flex, but the ones he did for me were fine.
