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Planning my first attempt at a homebuilt lugged frame - material questions

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Planning my first attempt at a homebuilt lugged frame - material questions

Old 09-23-19, 10:18 AM
  #26  
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Originally Posted by Andrew R Stewart View Post
If the frame is taken as a seperate from the rest of the bike device then I agree that the DT is the member which most determines torsional (pedaling loads) stiffness. But the frame is not ridden without other elements that add their flex. I've learned that the fork's steerer contributes a lot to the overall feel of a bikes stiffness. Also the more the load is over the rear wheel (like panniers or rack top stuff) the more the top tube comes into play. Andy
Agreed. As I say, there are many factors that affect the flex characteristics of a bike. I limited my answer to an analysis of the DT just as an example. I built 2 identical framesets other than the TT (*and wheels/components). The 25.4mm 858 top tube allowed the HT/steering to waggle and there was shimmy at high speed. The one with a 28.6 - 858 TT was fine so I am convinced that the TT has a lot of influence on HT stability and steering. As you mention I would assume on rear carring capacity as well.

My general point was that the tubing he has selected is too thin for someone of his size and strength (if he's really doing 30mph on the flats) and will produce a frame that I would consider too flexible and therefore unsafe.

I agree with you on the steerer and would extend it to the fork crown as well. I used an aero crown with 1'' steerer on one bike and was amazed at the vertical movement I got out of that fork - even just standing over it and pushing down on the bars. That bike is decommissioned and hanging in the rafters as a reminder to not chase weight.
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Old 09-24-19, 11:39 PM
  #27  
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Once again, thank you all for the helpful advice!

If I sum up everything so far, these are the answears to the questions I had:
The frame tubing I have looked at is a bit on the thin side for my size and weight, even for OS tubing.
The downtube is the one I should beef up if I insist on using super light tubing
The main problem with the tubing I have looked at is that it will be hard, next to impossible, to get a good, straight, frame as a rookie. That is due to the fact that heat control gets more difficult with thinner walls and thinner walls often also means heat treated tubing wich in combination (bad heat control + heat treated) is the reason for the difficulty level.

The advice is:
Use non heat treated tubing for more ease of after brazing alignment, this generally also means that the tubing will be thicker walled wich in turn also helps the frame stiffness.

I took another look at tubing. This time at Nova's CRMO range wich I assume is non heat treated? (Same with Columbus Zona?)
Top tube: Nova has an 8-5-8, Columbus Zona has a 7-5-7. The difference here is 7 grams (I have a spread sheet in excel that calculate the weight from the actual dimensions instead of the weights given by websites to get a fair comparison. Here I take the taper sections and add all but 10mm of each taper to the butt length, the rest (total 20mm) goes to the center section. Chain and seat stays are harder to get to grips with thou..)
So top tube isn't any real weight saving to be had. From the advice here the Nova tube should be better suited for me?
Seat tube: Due to shorter butt length the 9-6 ST from Nova is actually lighter than the 8-6 one from Zona. A whopping 13 grams!
Seat stays: Here I think my calculations might be a bit off, but 14mm Nova stays vs 16mm Zona end up to 34 grams lighter each for the Nova stays. Novas 17mm (0,5 wall) are according to my spreadsheet 11g heavier each than Columbus Life so not much of a difference there either. Nova claims however that the 14mm ones weigh 567g a pair, I get ~270g a pair (before length adjustment)
Headtubes are the same (1.1 wall, 36mm OD)

Chain and downtube then..
Chainstays: Nova's 30x16mm stays have 8-6-1mm wall thickness. Earlier I calculated that the Life and Zona stays were the same wall all the way. So my numbers might be a bit off. But the Life stays weigh 108g, the Zona ones 129 and the Nova ones 174!
Downtube: Nova has both an 8-5-8 and a 9-6-9 tube. These end up at 307 vs 359g. The Zona one is 8-5-8 and ends up at 305g.

So if I mix and match a bit and end up with:
Nova DT .9-.6-.9
Nova HT 1,1
Nova ST .9-.6
Nova SS 14mm .7
Nova TT .8-.5-.8
Zona CS .7

The total would be: 1500g roughly for the tubes, + 340g roughly for the lugs.

Does this sound like a better suited list for a rookie? Or have I missed something about the Nova tubing?

Further savings could give 50g on the DT and 40g on the chainstays, but then I'd have tempered stays and a downtube that might give the frame some flex. The discussions here have mainly been regarding the main triangle, but I assume the same principles go for the rear? For example heat treated thin walled = very very hard to get straight for a rookie?

I also have some questions regarding the actual brazing. Getting the filler to flow, different heat patterns and so on is one thing. Before I give it a go I'll have to read up on that and take a look at some youtube videos to give me an idea of how to do it. But brazing material... Brass/bronze or silver from what I understand. Silver has a lower temp threshold to flow, but how low can you go temperature wise while still getting atleast a decent brazing? I know that there is a diffuse temp line that separates "brazing" from "soldering" and that I should be above this line but that's about it. Brazing rods with silver are available with liquid temps ranging from 400C to 900+C. I imagie that using a rod that works with an as low as "possible" temp would be better suited for a rookie, but I might be wrong?
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Old 09-25-19, 09:24 AM
  #28  
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Lot's in the above so here's some, incomplete, feedback-

Brazing VS soldering- Soldering is generally considered to be using a lead containing alloy, brazing brass/bronze or silver alloys. Yes the brazing family does require higher temps. What's the boarder? I don't remember. Does the boarder mater? Only when it gets close to the critical temp that the steel will go through a transition change. This is why Rey 753 was "limited" to silver, no brass/bronze. But some of the current "air hardening" steels need temps at or over a certain amount to attain full strength and silver doesn't do that.

Weight- As I tried to mention. The frame weight isn't the big deal that people make it. Just because you can weigh a frame and have a number to publish doesn't make that aspect the important one.

Brazing- Watch the flux. When the flux and filler are well suited for each other the flux will go through it's transition and indicate the steel's temp, which can be hard for some to monitor under the flux and through dark glasses. ( Story- When I moved to Raleigh NC the lack of real basement had me do my torch work outside under a white event tent. Way too bright to see the fine color shifts that the steel was having. Another, long gone, forum gave me the advice to watch the flux. While it is what I was first taught I needed reminding). As to heating patterns I try to apply the flame the same on each side of the joint, the same duration, distance and angle. Starting along the frame centerline then move to the sides, alternating side to side and flow a bit of filler each time. The more even the overall temp is the faster this flowing will go. With lugs I generally focus far more on the lug shells then the tubes in the beginning. BTW having a bunch of flux a couple of inches up the tube will act as a reservoir to draw more flux from. I will first brush the flame over the flux, all about the joint, to solidify it and minimize the dripping off during the heat up.

I think your new tubing choices are far better then the initial ones. The only quibble is the TT wall. If the bike will see transportation use or be handled by gorillas (baggage loaders, tour companies) consider the dent resistance of a thicker wall on the center section. Andy
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Old 09-30-19, 05:03 AM
  #29  
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Weight and stiffness affect eachother, so while weight might not be the most important factor, it certainly is a factor. 50g here or there might not make a difference in real use, but a quality custom frame is from what I have understood both stiff enough to suite the rider's type (spinner/masher/strength level etc) and intended use (Road/CX/MTB etc) while still being "as light as possible".

Or am I wrong here?

Back to brazing. Lower silver content = lower melting temperature. Lower temperature gives a bit more room for rookie mistakes (uneven heating pattern). What would be the lowest silver % you would recommend for brazing?

(Not saying that an even heating pattern isn't important, but the more heat you use, the more important a good heating pattern becomes since the difference between highest and lowest temp of the heated area with the same heating pattern will probably be a percentage and not a fixed number. Therefor less heat should make the heat differences smaller in the heated area giving the molecules a closer to equal increased ease of movement and thereby distortion of the tubes should be less than if a higher total temp was used)
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Old 09-30-19, 06:13 AM
  #30  
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I use 56% for lugs and 45% for areas that need a fillet. There aren't many people that vary from that. Lower percentage builds more, so it's a little harder to get it to flow into a lug.
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Old 09-30-19, 08:38 AM
  #31  
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"as light as possible" is only a factor for me when it's a factor for the rider. Since I am that rider for many of my frames and I don't race but want a frame to reflect my mechanical and accessory tastes many of my frames are not as light as possible. But I don't make them any heavier then needed

Two major reasons why I have moved away from using silver as a filler for joints (and a number of braze ons) are, one, the joint geometries I tend to use (and the tube sizes) are not readily done in a lugged manor. Lug options are lacking and modding lugs, while not very hard, takes time and one still ends up with issues with internal gaps and such. The other is that some joinings (like rack braze ons, binder bosses) have a better track record if done with brass/bronze. The small contact surface having the gaps for silver can be problem as silvers (especially 56%) drop off in strength quickly as the gap grows. Thus most of my recent frames are filleted (with the latest shown below an exception).

So any one frame will have both fillers used in various areas. Examples: When I was making Terry type bikes for my late wife (and they were lugged) I would brass the lower head lug because at an angle of about 66* even a well modded lug will have huge interior gaps. Other joints I use brass on are the seat lug, due to the later attachment of the stays, and the ST/shell, again due to later adjacent joints.

After a while I decided that brassing the whole frame (less some braze ons) seemed to be as easy and less costly. Flowing brass isn't much different then silver if your heat control is practiced. I do prep the lug fit ups with greater gaps for brass.

Here's a shot showing how both fillers are in play on the same area. The lug is self made with brass as the binder and stay end "caps" are too. The TT and ST are silvered inside that lug with the stays also silvered to the sides. (note the vent hole sealing with silver too). Andy
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Old 09-30-19, 09:00 AM
  #32  
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There are some very good points being made by Andrew and uterhausen that are easy to miss (so I'll reiterate...):

- Watch the flux. When the flux is coming up to temp it will turn liquid and try to slide off the joint. Different fluxes are more prone to this than others so some research is useful before purchase (I learned this the hard way.) It's absolutely critical to have good flux coverage when brazing if you want the filler to flow well.

- 56% and 45% are the standard silver fillers. 56% is very liquid and will flow into tight lug joints. The joint can't be too tight though (it should be a light slip fit.)

- The lugs should not have large gaps or overly tight. Bend the lug as needed to achieve the proper fit.

- Thin wall tubes are more prone to denting than thicker. This is particularly important on the top tube where people often lean the bike against something.

- In my opinion silver is more newbie friendly than brass because the temperature to flow is lower. If you use too much heat the flux will start to char (not a good thing) before you get a chance to overheat the tube and damage it from heat. Obviously, you need to pay attention to everything but at least with silver the risk of damaging the tubes is pretty low.

As far as this "lightness" thing is concerned, I'm one that always pays attention to such things even though I realize it's just a minor consideration in the end. My main concern for Cassus is to simply caution him against going too thin on his first frame. Save that for later after your skills improve. .8/.5 is a good mix for a lugged frame, and go for light stays since even light stays are not very light anyway.

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Old 10-01-19, 12:37 AM
  #33  
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Thank you once more for all the tips and recommendations! Now I feel I have a good base of knowledge to further dive into details (such as flux type/brand, heatng paterns/techniques etc).

Originally Posted by Andrew R Stewart View Post
"as light as possible" is only a factor for me when it's a factor for the rider. Since I am that rider for many of my frames and I don't race but want a frame to reflect my mechanical and accessory tastes many of my frames are not as light as possible. But I don't make them any heavier then needed
Isn't this really the same thing thou? If your building a frame "not heavier than needed", and it's tailored for the rider. And then you build a frame "as light as possible", but still tailored for the rider. It will also not be heavier than needed. Tomata - Tomáto? In my case a .65-.4-.65 DT would be too weak, so in order to get a stiff frame I need to use a heavier tube for exampla a .9-.6-.9. That is both not heavier than needed And as light as I can use to get the stiffness I believe I need.

In order to build an even lighter frame, while maintaining the same stiffness one would have to resort to other tube dimensions and/or other material.
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Old 10-01-19, 07:23 AM
  #34  
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Cassius- Sort of, kind of but not really.

An analogy- when you ride a route in one direction you experience the ride in a certain way. the hills, the scenery, the wind and such. When you reverse the way you have a different experience. The houses are seen from their other sides, the wind hits you differently and the hills come at you in another way. have you done the same ride? yes and no.

With my building I see this aspect in the details. How much filler to create how large a fillet. How large a bridge tube to use. making the braze ons to satisfy my personal mechanical analities. Use of a brazed on head badge. Which drop outs. Sure the basic tubes are the same but the little details will be different when I focus on minimal weight, which I almost never do. I do have various bikes with differing purposes and thus build but for the most part I let the frame weigh what it will to serve that purpose.

Perhaps this is more of a philosophy then a plan. Perhaps it's my playing with myself and thinking I am bucking the stupid marketing focus on a "measurable aspect that has so little real effect". But it's the way I like to go about this thing, building yourself a nice riding frame (that will have 4 or 5 times it's weight of components before the accessories are even added). Andy
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Old 10-01-19, 07:36 AM
  #35  
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True, one can always build one frame "not heavier than needed", then an other one with the same tubing/lugs/methods but use a brazing material with lower density, heat cycle the lugs in order to shrink them for a tighter fit and thereby use less brazing material, skip the paintjob etc and end up with a frame that's a couple of grams lighter.

But apart from that, you haven't convinced me it's not the same thing

I must say I'm looking forward to start this project, but I really should do the ECU wiring system for the car first.. Then I had planned to build a set of new wheels for the Aelle frame.. Then maybe I could atlest buy the material and notch/mitter the tubes.. After that I need a good heat source.. and a decent place to do the brazing.. Or maybe I'll just do everything simultaneously! But I can't neglect the Mrs and our 7 week old son.. Or work.. Dammit life! Why do you have to be so complicated all the time?
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Old 10-01-19, 08:57 AM
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Life is as full and challenging as one makes it. I know very few smart producers of stuff that don't feel somewhat over worked, especially raising kids. But I also believe that they love the involvement and would be bored if just sitting around on their behind while their silver spoon (because it takes money) or family does all the work for them.

I've not heard of using heat to shrink lugs before. Where did you pick this up? Andy
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Old 10-01-19, 10:26 PM
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Originally Posted by Andrew R Stewart View Post
Life is as full and challenging as one makes it. I know very few smart producers of stuff that don't feel somewhat over worked, especially raising kids. But I also believe that they love the involvement and would be bored if just sitting around on their behind while their silver spoon (because it takes money) or family does all the work for them.

I've not heard of using heat to shrink lugs before. Where did you pick this up? Andy
That's true. I work in construction (site management) which is also more or less full throttle all day, sitting still might be nice for a day or two then I get an itch and have to do "something"..

It's something I picked up from a car builder, I didn't research it more at the time but idea was the same as with bending a tube with heat. Heat one side of the tube and it will contract (root cause of a crocked frame due to overheating when brazing), heat the other side later and it will pull straight again but end up a notch shorter. This car builder wanted a tighter fit on a slip in coupling and used heat to eventually shrink the tubed section of the joint by a couple of thousands of an inch (0,05mm if I remember correctly). As I said, I never looked into details of how he did it, only read what he wrote..
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