Tandem Tom

As I get down to final braze-ons here is my quandary. I want to install threaded boss in the seatstay for a rear rack. But not sure what rack I will eventually use. I might even like to try making my own.
So a suggestion on how to locate the bosses would be appreciated.
Thanks!

unterhausen

There is no standard. Most racks adjust as a result of that. I think somewhere around the same height as the top of the tire makes sense. Or you could just make yourself a constructeur style rack that mounts to the brake bosses

Andrew R Stewart 

Tom- I like to have the rack stay struts attach to a boss that stands off the stay a tad. Quite different then the common "hour glass" braze on bits. The reason is to not have the paint get scratched from a wrench slipping, to have a through hole (not a blind one) and since I make fairly small bikes to make leveling off the rack need slightly less strut length. I strongly suggest having the rack in hand during this Andy

JohnDThompson 

I agree with Andrew; it's best to have the rack in hand so you can be sure you're putting the mount points where they need to be.

Doug Fattic 

Tom, lets' review. Like others have said you want to have not only the fender in place but also the brakes attached and possibly any cables to make sure nothing gets in the way of the rack's arms. Now you have to pick a rack so you can locate your bosses. Some racks have adjustability up and down and, if so, you want to place the rack as low as possible and still miss the top of the fender. This is for center of gravity control. If you have some choices like at a bike shop, you will choose one that can meet your objective of the bottom of the rack being just above the fender. And have adjustable arms that will miss stuff and look normal when attached. If you will eventually be making your own rack you want the bottom of the rack to have a boss as an additional attachment point for the fender. The top of the rack of course should be level. There is no rule of thumb rack boss distance that I know about because any custom geometry variable can change a rack's attachment position. As can what brakes are chosen.

Actually before you put the rack on you want to scribe a line along the side of seat stays to make it easier to place your drill mark. This is done with a machinist square touching the tops of both stays and the angle piece dragging along the side leaving a mark right on the side center.

I like the arms to be parallel to the top of the rack but sometimes that isn't possible. If they angle down you still want them to look normal. Awkward arm placement distracts from the aesthetics of a custom frame. After positioning the arm so it misses everything and isn't at a stupid angle, make a mark on the centerline of the seat stay where the center of the water bottle boss should be located at the hole in the end of the arm. Do the same on the other side and measure both to see if they are exactly the same distance from the dropout eyelet. If not figure out how to make the distance the same.

Andy's idea of how to do rack mount braze-ons is a solid one but I prefer the looks of a water bottle boss on the side of the seat stay. This is especially true if the rack is sometimes removed when not needed.

Tandem Tom

Thanks Doug! I found a rack in the corner of my shop this afternoon to use as a "sample". I will mount the fenders and brakes tomorrow and play around with it.
Picked up a short 1/4" but at McMaster Carr so I can get the bottle bosses installed. Cable stops are on.

bulgie 

With many sidepull or dual-pivot brakes, the best location is blocked on one side, especially if the seatstays are narrow, like with a fastback seat cluster. So I made this lightweight rack for my wife's '79 Erickson with a strut on one side only.


Only pic I have of it on the bike is from before it was plated. We tried it for a while before committing to chrome.


Weighs about 6 ounces, and strong enough for me to sit on it, so it holds well over 200 lb static loads. Maybe not recommended for riding with that much, but probably still OK! Not that I'm against redundancy, but two struts to the seatstays is not necessary.

Flickr album with more beauty shots and in-progress shots here.

Mark B in Seattle

bulgie 

Is "but" a typo for bit, as in drill bit?
Just asking in case your bosses are really 6 mm. That's what they were back in my day.
Are H2O "top hats" 1/4" nowadays? If so I'm mildly disappointed. No measurements on a bike should be based on the length of three barleycorns. I thought we'd evolved past that.

Mark B in Seattle

Tandem Tom

Yep should have been bit! Yes 1/4" as I did a few practice ones on an old frame.
I like the rack! Tell me about the chrome process and $.
Thanks!

unterhausen

just about every steel tube made is in inches, it's just that they hide it by translating it to metric.

bulgie 

Yeah a lot don't even hide it -- one inch top tubes, steerers etc. Not to mention 1-3/8" BB threads, etc. I just hate to see us backsliding, on some things that were previously standardized on metric. But this is a very minor preference, and I know no one but me cares! My drilling jig has drill bushings for 6 mm, but I have a lifetime supply of 6 mm braze-ons, so I'm not put out by this in the slightest.

-mb

Doug Fattic 

Tom, just a couple suggestions since you aren't using a #3 center drill to drill your water bottle holes. Steel drill bits come in 118º angle and 135º angle. For thin tubing, 135º is best. A 135º bit will still drift off center (and not drill a perfectly round hole) but will do better than a 118º bit. Because of a drill bit's tendency to wander, it is better to use several drill bit sizes to get up to ø. Watch carefully with each increase in size. As you get off center (a very likely possibility), use a small round file to round the hole and keep it between your long and cross marks.

Whatever you do, DO NOT just center punch your mark and then drill a hole with a 1/4" bit and then look and see what happened. I can tell you now what will happen. The hole will not be round and not be on center and by the time you correct with a file your hole will be bigger than you want. Of course a bigger lip on the boss can allow the boss to be centered in a too big hole. You have to be extra extra careful with drilling holes in your 14mm seat stays. They are easier to get off center and more difficult to correct.

Tandem Tom

Yep, gradually working my way up in size. That my plan. Thanks!

unterhausen

Consider using a spotting drill. Sometimes McMaster calls them "short length drill" It's tough to drill a hole on center on an already-built frame, so I have a spotting drill that is about 4.5mm.

Doug Fattic 

Actually I know you know about using increasing diameter drill bits to stay on center but Andy and I like to use a specific illustration to explain to anybody else that might want to learn more about that subject. So my post included your name but it was really written to a general audience.

bulgie 

I generally try to drill the holes before the tubes are put into the tacking jig, but for repairs/mods, a right-angle drill is handy. Most home shops don't have much in the way of air power, but if you do, an air-powered drill is handy for how small/light they are. Also more durable than most electrics.


Here's a cheap electric (under $40!), probably not very good, just one of the first hits I got. I have used the Milwaukee that this is a clone of, probably worth the extra $$

Andrew R Stewart 

I acquired a right angle drill a few years ago. Like any tool is exactly what you need till then next stumble...

I like to drill my bottle bosses a tad undersize and increase to size with a file. Using a center drill and stopping at the piloting drilled hole then moving onto increasing larger hand drills Many of the commercially available bosses are not quite .025" in fit. Not that it really maters. Andy

Tandem Tom

The 1/4" short drill bit I picked up at McMaster Carr the other day still required a few file strokes to allow the boss to fit.

JohnDThompson 

I use a 1/4" piloted bit for bottle mount fittings. I marked the spot with a punch, and the pilot doesn't wander as readily as a larger bit:

bulgie 

Filing is OK, but I prefer to use tapered abrasives called cartridge rolls or spiral rolls. Skip the rest of this post if you already know all about 'em.

The ones I use taper from about 3/8" down to about 1/4", so a brand-new one will barely start in a 1/4" hole, but they get smaller as you use them and you'll always have a used one lying around. Enlarging a hole for a H2O boss takes like one second.
Here's a pic:

Don't use sea-shells though, they're too brittle and not abrasive enough.

The mandrel has a 1/4" shank, but the part that goes through the cartridge roll is 1/8"

Though the cartridge is not accurately round, when they spin they tend to make round holes. Being tapered, you just shove it in until it's grinding equally all the way around.

These little suckers are so handy that I like to keep one mounted in a die-grinder full time. Works fine in a small hand drill too though. The cartridges take about a second to swap by hand. Note you can also mount the cartridge backwards, handy sometimes when you want the big end to go into some tight space.

They come in different grits, lengths and sizes, tapered or not, so pay attention when ordering. If you like big fillets then you may want to go for the one with a faster taper, 1/2" at the big end, but I like small fillets so I mostly use the 3/8". They're cheap enough you might want a couple boxes of different sizes. Get yourself a couple arbors too, because you will drop it on the floor, and Murphy's Law says it'll bend the skinny part of the mandrel. You can straighten them, but eventually the 1/8" part will break off.

Mark B in Seattle

Tandem Tom

Another neat tool I have not heard of! That's what happens when you do woodworking most of your life!

duanedr 

I found a tapered hand reamer that works really well for enlarging boss holes, cleaning up ends of fork blades other similar jobs.

Tdotbikes

Thanks for posting this! I have never seen these and have recently added a compressor with the capacity to run air tools.
What is the overall length of your preferred spiral roll? I am going to order a bunch of 3/8” 80 grit spiral rolls. Also what is the size of the mandrel?

unterhausen

He said 1/8" arbor hole. Mcmaster has some that size, I didn't keep looking after that. Amazon doesn't seem to have the 1/8" arbor hole variety, but search there can be hit or miss

bulgie 

Show some gumption son -- buy a few sizes and find out what you like! Just kidding, here's the link:
https://www.mscdirect.com/browse/tn/...navid=12100146
1-1/2" long, 3/8" diameter, "full" taper, 1/8" arbor hole.

I find as I use one up, the small end kinda goes away to nothing, then the 1/8" arbor is exposed. But you can continue using that cartridge if the arbor is shortened. For that reason I have an arbor that I've shortened a bit, maybe 1/4" shorter. You can use the shorter arbor with a full-length cartridge too, the little bit at the end that's unsupported still works pretty much normally.

I also made a mandrel with an adjustable, replaceable 1/8" part. Left that at a previous employer, so I can't show a picture, but easy to make:

1. Cut the 1/8" part off completely
2. Drill what's left, the 1/4" part and the spiral part, all the way down the center at 1/8" (must be done on a lathe, with decent precision)
3. Slit the back end of the 1/4" part with a hacksaw, where it gets clamped in the collet or chuck in use
4. Put a piece of 1/8" drill rod or piano wire down the middle.
5. Adjust the 1/8" part to length as you're tightening the collet or chuck, which will squeeze the part with the slit, clamping the 1/8" part in place.

That's worth it if you're using cartridge rolls a lot in production environment. I was making lugless frames all day every day for a while there -- mostly tandems, track sprint, and time-trial funny bikes. Later I stopped cleaning up the fillets -- just left them as-brazed. We still offered the fully filed and polished fillets as an upgrade, but once people saw the as-brazed, no one wanted to pay the extra for smoothed, because they couldn't tell the difference under paint. Then the cartridge rolls got used a bunch less.

Not filing/polishing the fillets also lets you use thinner tubes to some extent, because with the thin stuff, any filing/sanding at the edge of the fillet risks thinning the steel. Or put another way -- you will thin the steel tube a little when you clean up fillets, no matter how skilled you are -- it's just a question of how much. With very thin tubes, keep the cleanup to a minimum.

Getting your fillets to where they need zero cleanup is a good goal, but unless you make a lot of lugless bikes, it's hard to get that many hours 'in the saddle' so to speak. So zero cleanup might be an elusive goal, but any improvement you can make towards smoother, less lumpy fillets is worthwhile. Hint: this does not mean going back over and re-melting the fillet -- that's causing more heat damage to the tubes, and likely boiling the filler, causing porosity. Just lay 'em down as fast and smoothly as you can without looking back. Ironically, at some point in the learning curve, going faster makes them smoother. You'll find you like a bigger flame too -- but don't push it until you're ready. Beginners and intermediates should use a smallish flame.

But I am getting way off topic.

Mark B