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Thread: Machining motorcycle brake drums using a mill and rotary table

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    opscimc is online now Hot Rolled
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    Default Machining motorcycle brake drums using a mill and rotary table

    I would like to be able to turn the drums of several old motorcycle wheels after the stresses from the rim and all the spokes have equalized themselves. Although this would be very easy to do on a lathe, unfortunately my lathe can handle 16", whereas the OD of the rims to which the brakes drums are mounted range from 18" to 21". However, it would be easy enough to mount these wheels horizontally on the rotary table of my Millrite vertical mill using a false axle in the bearings to accurately center and align them. But, what should I use as a cutter to skim the drums? The surfaces that will be cut will be around 7" or 8" ID and 2" (max.) deep, and I'm guessing that no more than 0.02" would need to be removed.

    There are no obstructions at the bottom of any of these drums so if there were simply a, say, 1/2" dia. end mill with cutting edges that were a bit longer than than "normal" (i.e. they would need to be 2" long) it could be used. However, is there a cutter better suited for such a job? Or, is there a better way to do this?

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    Boring it would be best by far. Big boring head and beefy enough tool to not chatter running out the side. use quill feed. Think of it as an inverted vertical lathe, such that you are spinning the tool and workpiece is stationary rather normal for a lathe. Then, if you can do lathe work, it can be similar. I would not use and end mill and rotary table.

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    lbhsbz is offline Cast Iron
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    Quote Originally Posted by annoying View Post
    Boring it would be best by far. Big boring head and beefy enough tool to not chatter running out the side. use quill feed. Think of it as an inverted vertical lathe, such that you are spinning the tool and workpiece is stationary rather normal for a lathe. Then, if you can do lathe work, it can be similar. I would not use and end mill and rotary table.
    That's no fun.

    Mount a stub axle in a collet and chuck up the whole wheel in the mill spindle, put a boring bar in the vise.

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    The fun part will be trying to keep the wheel bearings from spinning on the axle. What do you do, apply the brake?

    Quote Originally Posted by lbhsbz View Post
    That's no fun.

    Mount a stub axle in a collet and chuck up the whole wheel in the mill spindle, put a boring bar in the vise.

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    Quote Originally Posted by lbhsbz View Post
    That's no fun.

    Mount a stub axle in a collet and chuck up the whole wheel in the mill spindle, put a boring bar in the vise.
    21" in the spindle of a Millrite? "Neighbors claim UFO lands in yard after loud noise". News at 11:00...

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    Either way, it's going to sing to high heaven. You might look in to getting some Duck Seal, putting it on the outside and wrapping it with duck tape to keep the harmonics down.

    Duct Seal Compound Plugs (10-Pack)-DS-110 at The Home Depot

    Tom

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    opscimc is online now Hot Rolled
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    Quote Originally Posted by annoying View Post
    Boring it would be best by far. Big boring head and beefy enough tool to not chatter running out the side. use quill feed. Think of it as an inverted vertical lathe, such that you are spinning the tool and workpiece is stationary rather normal for a lathe. Then, if you can do lathe work, it can be similar. I would not use and end mill and rotary table.
    I wouldn't have thought of using a boring head for this, but I will look into it to see if there would be a practical way to implement it. Simply running the bar out the side of a Criterion head wouldn't work, because the bearing housing protrudes and would keep the head from getting low enough. It would require a boring bar whose cutting edge was ~2" below the bottom of the boring bar.

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    autofrite is offline Hot Rolled
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    the - swarf is going to build up and cause issues-maybe.
    a toolpost grinder may be something to consider.
    i doubt it will ring as it has the spokes and rim installed.
    spinning the drum and a cutter in the vise seems like a better idea,two cones and an arbor is the typical brake lathe setup.
    you dont need to see whats happening,as long as you have the depth set,the cutting will be easy to hear,especially if its out of round.
    i dont think you need a lot of rpm's
    why not take it to a garage and have it turned? most of the garages in my area still have brake lathes,and usually charge a small price to cut them
    oldbikerdude37 likes this.

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    opscimc is online now Hot Rolled
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    Quote Originally Posted by autofrite View Post
    why not take it to a garage and have it turned? most of the garages in my area still have brake lathes,and usually charge a small price to cut them
    Other than the necessary chrome and cad plating, my intent is to do 100% of the restoration myself. Even where it might be more rational to farm some of the specialized work out.

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    I don't see why you couldn't use your rotab like you originally wanted to.

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    Quote Originally Posted by opscimc View Post
    I wouldn't have thought of using a boring head for this, but I will look into it to see if there would be a practical way to implement it. Simply running the bar out the side of a Criterion head wouldn't work, because the bearing housing protrudes and would keep the head from getting low enough. It would require a boring bar whose cutting edge was ~2" below the bottom of the boring bar.
    You could always make an L shaped bar to hold a tool. If so, If I were planning to do very many, buy a large boring head to hold 3/4" daimeter. Make a bar of 3/4" diameter steel bent in L the correct length. Square notch in the end and 2 holes for set screws to hold 1/4" square shank carbide tipped lathe tools.

    But, the more I think about it, the more I like the suggestion to make a setup to put it in the spindle, if it is feasable. It doesn't need to spin fast. I don't like not being able to see... perhaps use a mirror. The benefit is, you don't have to fuss with indicating, if made right, it'll spin true to the axle centerline, and the turnings will fall out of the way. Tool in the vise. reverse the quill feed direction to retract, start cut at full depth, working it's way out. Whatever kind of arbor you make for it, bring the end to a point so you can use it to "eyeball" the tool "height" to center before starting. But, that all depends on whether or not it'll fit (enough spindle to column distance) in the spindle.

    Yes, I said "turnings" instead of swarf. I don't know If I like that word for that use. I always called them curly-Qs, and is something I first heard. To me, swarf sounds like when a hot curly-Q flings off, lands and your arm, and makes a nasty burn mark. But I have worked with some odd ducks that make up their own weird terms

    I'd call that burn mark a "swarf"

    Bump yourself and leave a red mark or bruise, it's a "biff" mark

    put a big dent in something, it's a "swoopnanny"

    An old foreman use to call a slide hammer a "whambam"

    He called is big ass deadblow a "slambam"

    If you really F'd something up, it was "hotdog" (a really messed up story behind that one)

    And the sick F'er would ask you if you wanted some "duckbutter" to put on your sandwich ..... if you don't know what is meant by that, don't ask

    everybody called him "boyman" cause he was short. and he sure like to piss you off the best he could
    John Welden and gregg-k like this.

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    77ironhead is offline Titanium
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    Quote Originally Posted by opscimc View Post
    However, it would be easy enough to mount these wheels horizontally on the rotary table of my Millrite vertical mill using a false axle in the bearings to accurately center and align them.
    You'd be better off pulling the inner race and bearings altogether and using the outer races to locate and indicate on. A small adapter from the center hole on the table to the lowermost race for location should be sufficient. it would eliminate any play present from the bearings' pre-load, and will also prevent chips and swarf from getting into the rollers.

    Is your rotab a crank table or a free-spinning one? I've used both, but the free-spinning ones are a lot harder to get a decent surface finish on.

    Quote Originally Posted by opscimc View Post
    But, what should I use as a cutter to skim the drums? The surfaces that will be cut will be around 7" or 8" ID and 2" (max.) deep, and I'm guessing that no more than 0.02" would need to be removed.

    There are no obstructions at the bottom of any of these drums so if there were simply a, say, 1/2" dia. end mill with cutting edges that were a bit longer than than "normal" (i.e. they would need to be 2" long) it could be used. However, is there a cutter better suited for such a job? Or, is there a better way to do this?
    Use the biggest diameter endmill you can reasonably put in your spindle- a 1/2" endmill with 2" of flutes will flex. I'd suggest minimum 3/4", but 7/8 or 1" in a Weldon holder would be better.

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    Quote Originally Posted by opscimc View Post
    Other than the necessary chrome and cad plating, my intent is to do 100% of the restoration myself. Even where it might be more rational to farm some of the specialized work out.

    Hmmm, you didn't mention in your original post what brands and years of motorcycles these wheels come from. Since you speak of restoration of motorcycles, a subject with which I have some familiarity, why not disassemble the wheels and do the hubs/drums on a lathe? That would be much more straightforward, especially since you are now talking about plating, a process which will require complete disassembly in any case.

    If we are talking about something really interesting like a 1953 Vincent Black Shadow (4 brake drums) or a 1937 Harley-Davidson EL, that would be the prescribed method.

    OTOH, if you just want some sort of functionality, then I guess you could try it on a mill, although it really sounds like a difficult process to maintain any sort of precision with the wheel rim in the way.....

    Could you perhaps elaborate?

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    Quote Originally Posted by 77ironhead View Post
    You'd be better off pulling the inner race and bearings altogether and using the outer races to locate and indicate on. A small adapter from the center hole on the table to the lowermost race for location should be sufficient. it would eliminate any play present from the bearings' pre-load, and will also prevent chips and swarf from getting into the rollers.
    Yes, I agree. I described it the way I did (false axle in the bearings) to make the description shorter and easier to understand, but I would use the outer races along with an adapter I would turn on my lathe.

    Quote Originally Posted by 77ironhead View Post
    Is your rotab a crank table or a free-spinning one? I've used both, but the free-spinning ones are a lot harder to get a decent surface finish on.

    Use the biggest diameter endmill you can reasonably put in your spindle- a 1/2" endmill with 2" of flutes will flex. I'd suggest minimum 3/4", but 7/8 or 1" in a Weldon holder would be better.
    My table is a 9" Troyke with a crank to turn it (which can be disengaged to make it free turning when I want).

    So far, three possibilities have been suggested: 1) wheel on rotating table with large endmill; 2) wheel static on mill table with large boring head; and 3) wheel spinning in the spindle with single-point tool in the vise.

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    Quote Originally Posted by Newman109 View Post
    Hmmm, you didn't mention in your original post what brands and years of motorcycles these wheels come from. Since you speak of restoration of motorcycles, a subject with which I have some familiarity, why not disassemble the wheels and do the hubs/drums on a lathe? That would be much more straightforward, especially since you are now talking about plating, a process which will require complete disassembly in any case.
    The "standard" way is to turn the drums while disassembled. However, that relieves any asymmetric stresses caused by the spokes and rims, which will be returned once it is relaced. So, the standard way, although easiest, is not designed to produce the best possible result.

    In the case of three bikes, the wheels will be apart for rechroming the rims, so I do intend to turn the drums on my lathe at that point. However, after reassembling them and letting them sit for a few months -- since you've restored motorcycles yourself, you know that "a few months" is always involved -- I would like a way to make them round again should they have distorted. For at least one other old bike I have, which I won't be restoring, I'd definitely like to be able to turn the drum without unlacing the wheel.

    I'll add an important caveat here. I will measure the out-of-roundness before unlacing the wheels, then again after they've been unlaced. If the change is negligible, the standard way of turning the drums will be fine. What I'm doing with this question is collecting information to be ready to solve a problem I think will arise, but which might not.

    Quote Originally Posted by Newman109 View Post
    If we are talking about something really interesting like a 1953 Vincent Black Shadow (4 brake drums) or a 1937 Harley-Davidson EL, that would be the prescribed method.
    The three bikes that prompted this post do satisfy your criterion of "really interesting." One is a 1950 Vincent Black Shadow.

    The two ends of the spectrum of "restoring a motorcycle" are to send it to someone else along with a huge pile of cash, or to do it entirely yourself. Most nicely restored bikes got that way by a path somewhere in the middle of this spectrum. My intention is to do these three bikes as close to the by-myself end of the spectrum as possible.

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    I'll assume that the problem for the solution is being sought has been quantified by measurement? I've done this on a vintage road race bike with some braking issues. I removed the backing plates and reinstalled the wheel in the fork with some spacers I made to compensate for the absent backing plates and indicated the faces of the drums. They were quite round as I recall - surprisingly so.

    I question the assertion that there are differential forces in play for which the removal of material is necessary. There are - or rather there were - a tremendous number of drum brake motorcycles in the world. Most scooters and many small bore motorcycles still have rear drums. In my decades of working on, restoring and racing motorcycles and years I spent on the technical side of the powersports industry - I can't recall an instance where the interior of a drum needed attention for any reason aside from having been ridden with no friction material remaining on the shoes. The drums by design machine themselves round and fairly cylindrical.

    And spoke tension is equal and uniform around the periphery of the hub - the differential in tension between the sides of a rear bicycle wheel caused by the necessity of "dish" to accommodate the gear cluster is not an issue of a front motorcycle wheel.

    My point is that I don't see it as a problem.

    If you'd like to get the opinion of the guys who are the undisputed experts on the topic:

    Welcome to Vintage Brake!

    ...They really know about this arcane topic.

    Also - http://www.thevincent.com/vinbrake.htm

    (I'm friends with a number of the local-ish Vincent guys - all of whom do their own work, and in most cases have pretty nice machine shops at home)
    starbolin likes this.

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    All joking aside (sorry, couldn't resist ), I think that it would do fine on your rotab. I would do as 77 Ironhead stated & use a Weldon holder with the largest diameter endmill you could get. The less flex you get in your setup, the less taper there will be in the drum, top to bottom. Also, after you get a full cleanup, keep the finish pass on the lighter size to minimize flex, also. Finally, some pics of the setup & finished drums would be top-notch, if possible. I Googled Vincent Black Shadow...pretty cool.

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    Quote Originally Posted by opscimc View Post
    The "standard" way is to turn the drums while disassembled. However, that relieves any asymmetric stresses caused by the spokes and rims, which will be returned once it is relaced. So, the standard way, although easiest, is not designed to produce the best possible result.

    In the case of three bikes, the wheels will be apart for rechroming the rims, so I do intend to turn the drums on my lathe at that point. However, after reassembling them and letting them sit for a few months -- since you've restored motorcycles yourself, you know that "a few months" is always involved -- I would like a way to make them round again should they have distorted. For at least one other old bike I have, which I won't be restoring, I'd definitely like to be able to turn the drum without unlacing the wheel.

    I'll add an important caveat here. I will measure the out-of-roundness before unlacing the wheels, then again after they've been unlaced. If the change is negligible, the standard way of turning the drums will be fine. What I'm doing with this question is collecting information to be ready to solve a problem I think will arise, but which might not.


    The three bikes that prompted this post do satisfy your criterion of "really interesting." One is a 1950 Vincent Black Shadow.

    The two ends of the spectrum of "restoring a motorcycle" are to send it to someone else along with a huge pile of cash, or to do it entirely yourself. Most nicely restored bikes got that way by a path somewhere in the middle of this spectrum. My intention is to do these three bikes as close to the by-myself end of the spectrum as possible.
    Well, that's fine whatever way you go. That said, if your theory that the installation of the spokes would somehow distort the brake drums after assembly were correct, that would mean that all motorcycles with brake drums would have had drums that are out of round since wheels are always assembled after the drums and hubs are machined.

    So, from what I can gather, you will machine the drums perfectly round, in situ, then disassemble the wheels for plating, reassemble them and expect them to be round. OK. Whatever you say.

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    Quote Originally Posted by Motomoron View Post
    I'll assume that the problem for the solution is being sought has been quantified by measurement?

    I question the assertion that there are differential forces in play for which the removal of material is necessary.

    The drums by design machine themselves round and fairly cylindrical.
    It's the "cylindrical" where there can be a problem, because there definitely are differential forces at work. For example, the spokes on my Gold Star pull only on the part of the drum closest to the center of the wheel, with the portion at the outer edge totally unsupported. This allows the drum to form itself into a cone under the repeated pressure of the shoes along with the heating they cause. It's true that the brake material also will wear to mimic any such "coning" that takes place, but until that happens the brake is at less than 100%. This is not a hypothetical problem, since this coning effect is present in one Triumph wheel on the shelf in my garage. Also, while the front drums on both of my Matchlesses are full width, with spokes symmetrically located, still, the inner portion of the drum is held in place by metal, while the outer portion is being tugged on by the spokes while being pushed on by the shoes.

    Quote Originally Posted by Motomoron View Post
    My point is that I don't see it as a problem.

    If you'd like to get the opinion of the guys who are the undisputed experts on the topic:

    Welcome to Vintage Brake!

    (I'm friends with a number of the local-ish Vincent guys - all of whom do their own work, and in most cases have pretty nice machine shops at home)
    The Triumph hub I referred to shows this can be more than a hypothetical problem, and is what prompted my question in the first place. I have not measured the hubs on the bikes I'm about to start restoring, so it well may not be an issue at all with them, but I want to be prepared. Since I, too, have a pretty nice machine shop at home, I'm able to do the necessary measurements to determine if it's a problem in a given case, and address it if it is.

    As for your recommendation of Vintage Brake, I've had Michael Moore do two of my bikes in the past, and definitely will use him again in the future. The John Tickle TLS brake in my Gold Star is not that much worse than a modern disk, which is saying a lot. Even the stock SLS brake in a BSA stops remarkably well with the shoes he installed.

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    opscimc is online now Hot Rolled
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    Quote Originally Posted by Newman109 View Post
    So, from what I can gather, you will machine the drums perfectly round, in situ, then disassemble the wheels for plating, reassemble them and expect them to be round. OK. Whatever you say.
    Not quite. I will measure the brake in situ to see if it is perfectly round and cylindrical. No matter what I find, I will then disassemble it and send the rim for rechroming. If it was *not* round, I will machine it on the lathe. If it was round, I won't. After the rim has been returned, relaced, and aged in the corner of the garage while I continue my slow pace of working on three bikes in parallel, I will remeasure it. If still round, I'm done. If not, then I'm at the point where I asked the question in the first place, of how to use my mill to make a drum round.

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