The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: Duncan R on 11.09. 2010 18:31
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Hi ,
In order to try and sort out my woeful front brake I think I need to have it skimmed and oversize shoes fitted. Can it be done with out dismantaling the wheel?
Thanks
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I think this depends on if the lathe used has a big enough clearance to take the whole wheel in it.
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The brake drum gets out of round by irregular spoke tension, so skimming it when mounted in the wheel with all spokes tighened is the only thing that makes sense.
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MG's comment is logical--if you have access to a wheel jig for lacing, set up the wheel and check the inside of the drum with a dial indicator. See if adjusting the spoke tension makes a difference in the indicator reading.
As far as turning the drum with wheel intact, at one time lathes with special headstock risers were made specifically for the purpose and gave sufficient swing to turn car and truck drums with wheels assembled. I dont know how many of these exist any more.
Tom B.
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Just had a look on the SRM site , they do it but I should imagine the postal charges would be quite high
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I have that problem on the cafe after re-spoking. Originally the rim was close to true (about 1mm) and the brakes were great. Now I have the rim with 0.25mm side ways and 0.3mm vertically the front brake is s**t. The thick Akront rims take a lot of spoke tension to true.
I was thinking of making a jig to skim the drum with the wheel in the forks. Might be a while before I get around to it, but will post if successful.
Cheers
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Just checked with Bob, you need to find someone with a gap bed lathe, as this will take the whole wheel. Do you know any jobbing engineers. Bob has an old lathe in the garage that will do this and he can't be the only one. He's not an engineer by trade but I know some of the engineers at work have set up's at home. There must be other similar engineering companies about where you could enquire.
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if you know any lorry drivers or owners ask them, had my wheel skimmed local and they apparently skim lorry brake drums
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Thanks for your help everyone.
The mechanic at the shop where I had my MOT done is getting a hairline crack in my brake plate welded for me, I will check with him as he owns a Triumph to see if he knows anyone in the local area. I might drop SRM a mail and get an idea of postal costs as well.
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First of all and extremely important.
BSA used an alloy called "nickasil" for their drums
It is very, very, very hard and even harder to machine.
It needs to be ground, not machined with any thing that vaguely resembles a lathe tool.
here is the trick.
knock out the wheel bearings and mount the wheel on a spindle.
the spindle needs to go all the way through the chuck and you can use a live center on the other end to add extra support.
Use a centerless grinder mounted on a pedistal behind the lathe
Method 2
Use a mill with a powered rotary feed.
Very few mills will spin quick enough to use a grinding wheel but if yours dose not then use a strait cutter.
It is very important to cut the full face of the drum as point cutting tools will flex & skip giving you a durm that resembles a corrigated iron tank.
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Trevor,
Please don't take offense, but unless Nikasil is something completely different in English language use than in German, this can't be right.
"Nikasil" is a trademark owned by Mahle and was first used in the late 60s (afaik). It is a silicone-carbide coating (nickel matrix, hence the name) deposited in thin layers, mainly used as coating for alloy cylinders (with direct contact to the piston, thus cast iron liners can be omitted). So Nikasil (again, in German!) is a coating material, but definitely no casting alloy.
Maybe you meant Dural or Silumin?
The Ariel hubs I have simply have a steel ring cast in.
Cheers, Markus
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Thanks Trevor
I think its cast iron ,would it still have the Nikasil coating? My BMW has Nikasil coated bores and there is hardly any wear on them after 90,000 miles so it must be good stuff.But would it be useful in a situation where you need friction?
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I know it's very amateur and Heath Robinson and you can all chuckle, but faced with the same problem, not having a lathe big enough nor a deep enough table on my modest miller, and not wanting to be sending wheels away for ages, I made the attached to rectify the drum on the front of one BSA.
All it is is a fly-cutter bit held in a bit of round mild steel bar with a milled flat one side for locking it by means of the smaller tommy bar, mounted on a piece of thick steel bar in which the tool can slide (and be locked for and aft and side to side by the screws and the ugly 6mm rod with nuts on). The big piece of flat bar is drilled to go exactly over the wheel spindle and be done up fast with the nut that holds the backplate.
With the wheel spindle mounted in clamps in a big vice, tool locked on and held rock steady (with an extra arm attached to stop it budging under any circs), I then rotated the wheel slowly by hand while introducing the tool very gently by means of the long screw, having set the depth of cut on the sliding block to take a thou or two at a time at the narrowest points of the drum. It got rid of 35 thou of ovality in many stages and didn't leave me with a bit of corrugated iron either. I just kept running the tool down (which is spring-loaded in the bit of blue tube to get it to come back up again) at the same settings time after time. Finish not per factory obviously, but smooth to the touch, and more importantly, a round drum, concentric with the spindle, which works a million times better.
With a slight mod (collars and spacers made up to suit), it finish-cut a home-made drum liner for an AMC front end after shrink-fitting it, with another OK (to me) result. Not something to do on a perfect and beautiful machine perhaps, but on my old clunkers it's worked fine and no-one's said to me 'wot, no brakes!'.
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Hi Duncan
Most wheel building firms carry out his service, last time I was quoted £75 / £85 for a skim and new lining, but ended up new rim etc.
Its important that the new oversize lining are machined to the new drum size.
Regards
Nick
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groily,
that's a brilliant tool, no need to hide your light under a bushel!
It might take a bit longer, but I can imagine you will get as good a result than with large machinery, the basic principle being the same.
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Groily,
I agree with Markus, that is very clever tool, also works well as a clamp for your wallet. I have a few questions:
1. Apparently, you did not run into any extreme issues with alloy hardness. The cutter looks like it could even be common tool steel, but I am guessing it is probably carbide. I that correct?
2. I couldn't quite follow the "milled flat" issue. I assume that is to keep the round tool holder from turning, but if it's locked up, how does the tool bar push out with the feed screw?
3. Would you like to copy this post over to the "Home Made Tools" topic so it appears under your name, rather than mine, if I were to do it (crediting you, of course)?
4. Is it for loan or for rent?
5. How's that patent working out for you?
Richard L.
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You're far too kind Richard, as ever (and you too MG) - it's just that old 'Necessity Mother and Invention' thing plus I've plenty of time on my hands. The cutter is just a fly-cutter bit in HSS bought with a few others for a few pounds - but it's done a bit of work and I only sharpened it once I think.
The 'milled flat' description was a bit of short-hand really - there's a brass pad between the end of the screw with the (small) tommy bar and the flat side of the toolholder. It's there for the reason you give - to keep things square. What I did was part-tighten the pad against the holder to keep a bit of friction on when using it - not really a proper approach, as an adjustable D-shaped gib strip of some sort the whole length would have been better. And then some micrometer dials would have been nice, and and and! But hey, it did what I wanted on the day and it was only for private consumption.
By all means stick it in the tools section, hadn't thought of that - thanks.
I wasn't thinking of making any others, and I don't have a drawing - euphemism for 'actually, I can't draw' (I just did a rough sketch and then poked about for bits of scrap and took it from there). If anyone was really keen I could probably convince a mate who's truly competent to draw something up and maybe incorporate some of the improvements it needs. Be nice to think there was novelty in the thing, but think probably not (from the patents angle).
The problem with all these things is that the time taken to make them (by somebody properly-skilled using good materials rather than by optimistic lunatics out of farmyard scrap) makes them a worse financial proposition than the 75 pounds odd mentioned above for a perfect job + the right to complain afterwards! I have a whole box of things that took me a day or so to make and which work well for me, because I'm too mean to buy them, even if they exist. Clutch centre removers, bearing pullers, fork stanchion pullers and pushers, mag pinion and camshaft pinion extractors etc. I know many of us have the same or similar.
I was looking seriously the other day, guided by two better-informed others of our number, at those 'chuck pullers' for removing small bearing inner races that go tight up against stuff. . . they exist, but boy, at over 100 Euros and then needing some extra bits for the sorts of applications I had in kind (mag bearings in that case), I reckon it was better to have made my own ugly things to do the same job. And then there are things that just aren't really feasible at home for the want of tough enough materials - flywheel pullers for magnetic flywheels come straight to mind as I bust a newly-made mild steel item only yesterday trying to get the 'volant' off a (- very sorry -) classic Vespa scooter. Same story trying to make a tappet-guide puller for my Enfield twin - just not a sensible option. Sometimes you have to pay, or do without.
But I am tempted to make a nice valve guide remover having seen the brilliant torture chamber instrument posted on here recently! Personally, I enjoy playing in the shed, failures included, just as much as getting out there and breaking the toys on the road (just so they have to be mended). Funny thing is, BSAs don't seem to go wrong very often . . . I THINK that makes me happy.
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In the UK, Supreme Motorcycles in Leicestershire will skim and fit oversized linings, you can even leave the tyre on.
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Trevor,
Please don't take offense, but unless Nikasil is something completely different in English language use than in German, this can't be right.
"Nikasil" is a trademark owned by Mahle and was first used in the late 60s (afaik). It is a silicone-carbide coating (nickel matrix, hence the name) deposited in thin layers, mainly used as coating for alloy cylinders (with direct contact to the piston, thus cast iron liners can be omitted). So Nikasil (again, in German!) is a coating material, but definitely no casting alloy.
Maybe you meant Dural or Silumin?
The Ariel hubs I have simply have a steel ring cast in.
Cheers, Markus
Markus,
you are far too sensative.
I am never more happy than when I am proved to be wrong.
It is really the only way to be sure that you have the right information and a prime way of learning.
Never met a scientist nor engineer who was offended top be proven ( to their satisfaction ) wrong.
The Nickasil I am reffering to (& I might have the name wrong ) is a cast iron alloyed with Silicon & Nickel.
Some of the carbon ends up as a Silicon Nickel-carbide ( or is that a Nickel Silicon-carbide).
In any case it is as hard as hell but no more brittle than standard cast iron, the perfect stuff for a brake drum.
FWIW to those who do not understand what a brake dose.
As energy can neither be created nor destroyed a brakes job is to convert one form of energy ( kinetic ) into another form of energy ( heat) and in the case of my brakes a fair bit of sound energy as well.
As a by product of this the softer bit , the brake material, gets ground away while ( hopefully) the harder bit , the drum/ disc , remains intact.
This is why brakes fade, the drums get hot and can not generate enough heat from the friction with the pad.
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Never met a scientist nor engineer who was offended top be proven ( to their satisfaction ) wrong.
I did, glad you are not one of those! *smile*
The mentioning of "Nikasil" (or "Nickasil") led me in the wrong direction, thinking of aluminium as base material (i. e. brake hubs), but there are literally hundreds of trade names for nickel-silicone-carbide materials of all kinds and I don't know what that special cast iron you mentioned would have been called.
But since 1966 Nikasil definitely is Mahle's brand name for the aluminium coating (it comes from the German words Nickel, Aluminium, Silizium). It was first used for the Wankel rotary engines (I did a bit of reading, as it raised my interest).
However, as this was far later the brake hub material might have had a very similar or even identical trade name, who knows.
Sorry for sabotageing your good advice on that material's (whatever it is called) hardness and potential problems in machining with superfluous discussion about brand names. ;)
Cheers, Markus
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I contacted Hagon regarding a drum skim and they said they can do it without having to dismantle the wheel and possibly the same day for £50. They are only a 40 min drive from me.
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Markus,
From memory ( and I have no intention of checking it ) the name comes from BSA.
Either in some advertising , a press release or a factory news letter.
I really should index these things so I can find them when I need to.
The hard drums became standard fitment to just about every thing post WWII.
The only exception I know of was the Ariel full width hubs which were bought in and not made at the BSA .
My daily ride BSA was a B40 and as such the drums did end up a bit oval so I sent them to be machined.
Got them back with an appology with an interior surface much like an 78 rpm record.
By the time we had ground them flat again they were .060 under size and just about US but being a poor uni student I managed to get them to work but it wasn't easy
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Brake fade has a lot to do with the coefficient of friction, as the temperature goes up, friction reduces.
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FWIW, I gotta agree with Markus here on the Nikasil thing.
But that all seems to be woefully besides the point since it seems that every brake drum that BSA made used cast iron with the possible exception of the Ariel and 190mm hubs...dunno about those.
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Hi All,
Rob at Hagons called me yesterday and said the drum had skimmed up nicely and all the grooves and heavy glazing had been removed. He said he done two cuts totalling 10 thou. Wheel is being delived by courier on Monday for &9.50. I could have collected it today but by the time I pay the tunnel tolls and petrol and sit in traffic jams it was cheaper to have it sent. Hopefully now I will have a working brake.