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Frame design decisions - your opinions?

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Frame design decisions - your opinions?

Old 11-20-18, 03:31 PM
  #26  
Andrew R Stewart 
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TH- where are you measuring the out of alignment? 3mm of twist measured at one end of the head tube, WRT the seat tube, equals about a half inch at the ground (of the ft tire being off line with the rear). That's a lot of offness.

The first few frames I did were off a full scale drawing (taped to the floor), tacked only and held up to a back light for main frame alignment. We used good wheels, a bench vice and c clamps for the forks and rear triangles. All were quite rideable. None would I say were straight though. Andy
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Old 11-20-18, 05:22 PM
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Thanks Doug for that very useful post. Interesting that the jig restricts expansion and causes distortion, makes perfect sense but it never occurred to me before. I am wondering if some clever jig design might prevent or reduce this, for example, replacing cones with sliding inserts or holding the tubes in the middle but not too tight to prevent them moving.

I do like you tacking/checking sequence and will likely try that method, I dont have a flat surface to check alignment on, but if my jig is accurate enough, can I just check things are straight by putting the frame back in the jig and seeing if it fits?

TH Did you use brass lugs/silvered lugs or fillets? I was hoping that using silver would reduce or even eliminate distortion. On my first frame I fillet brazed, (which I guess uses more heat than other methods) and the head tube developed a curve, you could only see it with a straight edge and it was in the fore - aft plane so not a real problem, but for such a hefty tube I was quite surprised. The bottom bracket was slightly off but not noticeable when riding, I measures a custom frame I have from a well respected builder and it was further out than mine. They both ride fine :-)
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Old 11-20-18, 05:25 PM
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I am still a bit unsure about this tacking business.

I assume you prepare, clean and flux the joint then do the tacks. Some time later when you come to braze the joint fully, will the re-heated flux still do its job properly? Is there some sort of time limit to this, is any re-fluxing required?
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Old 11-20-18, 07:12 PM
  #29  
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I don't tack until I'm ready to braze the whole thing. So anything that isn't going to see the light of day again, inside of lugs, parts of tubes inside lugs, gets its final coat of flux. I reapply flux to the outside after tacking. As far as the flux that is on during tacking, if you don't burn the flux, it will still do its job
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Old 11-20-18, 10:08 PM
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What Eric said. I plan to do the tacking, aligning and complete brazing in one day. Everything is prepped before that day completely. Like Eric I'll add fresh flux after things cool off and before I finish the brazing. I've never had an issue with this delay between tacking an brazing. I have seen and read of frames hangng around for many days between these steps, but I haven't done that myself. I have noted that flux will absorb moisture from the air after a while. Also if the flux was left wet the moisture can cause rust. When tacking I'll brush over the flux with the flame to dry it all out. Andy
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Old 11-21-18, 06:53 AM
  #31  
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I made a fork in '81 where I felt like I hadn't gotten full penetration at the crown, so I set it aside with the flux still on it. I carried that fork around with me for years, until sometime recently I decided that it was ridiculous to carry it around and cut it up. But the flux was still protecting the metal. I'm pretty sure that if I had heated it up, it would have still worked.

Of course, once I cut the thing up I found that it had a nice fillet of filler around the inside of the fork blades, so it was perfectly fine. Once that fillet forms, it's really difficult to get any more filler to flow into the joint.
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Old 11-21-18, 01:59 PM
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Excellent, I now have the brazing sorted in my head, just need to build a jig, order tubes, order lugs, buy an oxy-propane set, learn to braze, assemble and braze frame, get it painted, source parts and build up bike.

I would like to get this all done before the sun comes back next spring :-)
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Old 11-21-18, 02:45 PM
  #33  
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For what it's worth, given the choice of having an alignment plate or a jig I chose an alignment plate. It's slow to build without a jig but doable, and the plate is super handy to assure everything is properly aligned during the build.
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Old 11-21-18, 05:07 PM
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I have ordered the materials for a jig so I am committed now. Have also now ordered tubes and lugs etc and have already spent more than it would cost to buy a frame :-)

Just wondering if I could pop into the pub and use the pool table as an alignment plate.
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Old 11-21-18, 05:58 PM
  #35  
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Mike- Many have used other then intended surfaces as reference ones. Milling machine tables, table saw tops, well done welding tables, counter tops (make sure of the flame aspect!). As long as one isn't using the surface as a prying counter point the surface can be soft or lightweight. I've even read of special epoxies poured into large enough shallow trays becoming flat surfaces. (I read this both in bike building and race car building forums.)

But I completely agree with the choice of a surface plate of some form as the higher need, compared to a jig. Making a crooked frame at a faster clip is of no use. Andy
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Old 11-22-18, 10:37 AM
  #36  
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Originally Posted by mikeread View Post
I assume you prepare, clean and flux the joint then do the tacks. Some time later when you come to braze the joint fully, will the re-heated flux still do its job properly? Is there some sort of time limit to this, is any re-fluxing required?
I put a thin layer of flux on both surfaces and then assemble. When I am ready to spot braze I put a glob on the spot area and tack. Once all the alignments and tacking is done and Iím ready to braze, I flux the entire joint area. I encourage students to flux a medium thick layer up the tubes another couple of inches beyond where I normally stop. This serves as a reservoir that can be called upon in case they take longer to braze. Many brazing problems begin when the flux runs out. It is a beginners mistake to put too much right on the joint as most of it will end up on the floor as it melts.

Iím going to repeat for emphasis what others have already said. If I was to start over again without any tools but with my present knowledge, the 1st thing I would get is some kind of decent flat surface plate. Random stuff can somehow hold the main triangle tubes in place on this table so they can be spot brazed together. Then it can become an accurate reference for aligning the frame during the build sequence. Depending on my future ambitions, it could be a carpenterís table saw top, a chunk of granite kitchen counter top or epoxy made for this purpose poured on top of MDF board. Auto makers are using this epoxy method now to make specialized surface plates. This is where I would put all my resources before bothering with some kind of fixture. One of my alignment tables is 32Ē X 48Ē cast aluminum with ribs I bought from the Wolverine Bronze Company for around $1500 and weighs 170 lbs. Smaller ones that could work are less than $1000. This is the foundation tool for making frames on which almost everything is based.

As a reference I have several very expensive fixtures in my shop. I donít trust them to be the solution to make accurate frames Ė particularly the rear triangle. Their primary purpose is to speed up the process and are at their best when making multiple frames that are all the same.
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Old 11-22-18, 12:47 PM
  #37  
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As Doug says, you definitely need to figure out how you are going to check alignment. A fixture is not enough. The beam style alignment checkers aren't ideal, but they work. For a while, I was using the table of my milling machine. You also need a height gauge and a good square. Drafting triangles are very square, but you have to be careful with them.
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Old 11-22-18, 01:35 PM
  #38  
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We have quartz worktops in the kitchen that I can use for checking alignment, Wouldnt dare braze on it though.

It should be pretty flat as long as it has been well supported, will have to figure out how to check.

I was planning to fix a straight edge to the bottom bracket, rotate and measure to each tube but using the kitchen surface would be easier. A vernier height gauge is something I could have used many times over the years so it will be worth investing in one.

Once again, thanks for the excellent advice, I am lapping it up.
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Old 11-23-18, 03:03 PM
  #39  
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Andy, the 3mm measurement comes at the head tube end of the top tube and down tubes. Head tube twist is measured against the seat tube. This last frame I built was in a home made jig, and it was off 5mm from center line at the BB end of the seat tube and down tube. Head tube had zero twist. The whole frame "leaned" to the non drive side by 5mm. It was really hard to bend back just the 2 mm I wanted. Cannot imagine moving it another 3mm. I assume the jig I made is off, however I have measured, and re-measured it time and time again. I have also put a known good frame in it and checked to see how it lines up in the jig and it checks out OK. Not sure if the heat pulled the frame to one side, but I am guessing it did. Need to do the tacking method the pros use as described in previous posts.

mikeread, all brazed joints are done with silver filler. As for using the kitchen countertop as a flat plate, do it when the wife isn't home. Protect the surface with something, too.
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Old 12-25-18, 09:47 AM
  #40  
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Originally Posted by mikeread View Post
I built an Audax frame a few years back and have been riding it ever since.

It is built with a Reynolds 631 main triangle (all .8 .5 .8) 28.6 TT and ST 31.2 DT and 31.7 HT with 725 seat stays and Columbus chain stays (cannot remember the specs of these) My weight is 168lbs and I am 6 foot tall

The bike is supremely comfortable and perfect for winter rides, Audax rides etc. It is a little flexy however and not ideal for fast club rides. I did take it touring once with just rear paniers and fast down hills were interesting

I am now planning to build another frame, again with 631 (or possibly 853) but want to make a pure road bike for faster club rides. So I would like it to be less flexy to improve handling whilst sacrificing as little comfort as possible. and of course, not adding too much weight.

My initial thoughts are below, your comments, advice and criticism would be appreciated.

<<sorry, snipped a lot of good stuff ...>>

Does this all seem logical and practical ?
I'm not a designer or builder, so I have less to contribute than the others in the thread, to critique your work. But I want a frame I would call "Audax" and that is very comfortable to my ol' body. I have a first O/S frame in ELOS, and it is a great and comfortable ride (a Mondonico ELOS). But I also have a few standard diameter frames in conventional Columbus SL and Reynolds 531 DB, and I know the physics of tube flexibility. I'm using similar wheels and tires on all of these (28 mm clinchers on Mavic Open Pro, or 22 mm tubular on Mavic GP4, no fatties on these bikes), and am surprised that the oversize tubings do so well in comfort and (seemingly) suppleness. Why aren't the 531 and SL frames more comfortable than the ELOS frame with 28 mm TT and ST, and 31 mm DT? I haven't tried to evaluate them mathematically in terms of belly moment of inertia, but I don't think I could deal well with the full butting profile anyway.

I also wonder if the step to stiffer tubes for the Go-fast significantly improves speed in a group-ride scenario, and why?

Also Mike, what wheels and tires are you using on the Audax, and what do you plan to use on the Go-fast?

Finally, it strikes me 75 mm trail for a fast road bike is a LOT of trail, though I've seen it quoted on hybrid-style frames. My nice Eyetalians are all around 60 mm trail.
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Old 12-25-18, 10:13 AM
  #41  
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Originally Posted by Andrew R Stewart View Post
...


Bikes that "feel fast" can be so. But don't confuse human perception with actual measurement. The best example of this, and currently the new "thing", are tires. It's becoming more and more accepted that the narrowest tires are rarely the most efficient for a few reasons. Yet it's the wider tires' damping of the data transmission (from the road to the skin) that also seems to tone down the perceptions of what's going on, we think wider tires are slower. Some of us have been saying much the same but WRT frame geometry. The "sharpest/fastest/quickest" can often, for us mortals (and that's the rub, we dream we're gods), be slower and possibly less able then what we would have made.


... Andy
I think another factor here is how much you ride that "fast" bike. On weekends? Or every day as a committed racer riding hundreds of mile every week. I raced a Fuji pro BITD. 75 head angle. Very, very quick handling. Tight. Lots of road feel. It took weeks in the spring to get comfortable and smooth. Longer to get fully confident no-hands. By August it was part of me and could and would extract everything this body had and apply it to the road. And really rough roads? I rode "light" and used them as a freebie way to move up in the field.

Ben
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Old 12-25-18, 01:26 PM
  #42  
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Ben- Your first sentence speaks directly to my point, perception. The more you ride one specific bike the more in tune you become with it. Additionally I have found the stiffer/quicker handling a bike is the more better I felt when riding it when I was in better condition. Andy
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Old 12-26-18, 09:22 AM
  #43  
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Originally Posted by Road Fan View Post
Why aren't the 531 and SL frames more comfortable than the ELOS frame with 28 mm TT and ST, and 31 mm DT? I haven't tried to evaluate them mathematically in terms of belly moment of inertia, but I don't think I could deal well with the full butting profile anyway.
The easy calculations of stiffness people always do don't really translate well to a space frame anyway. Although I suppose it mostly goes back to moment of inertia.

I am currently riding a 9/6/9 25.4/28/28 Reynolds 531 bike for audax which I like a lot. Prior to that, I was riding an OS 28/28/31 7/4/7 Columbus Spirit 4 Lugs bike that I liked a lot. I don't see how tubing contributes much to comfort because of the triangulation of the frame. However, those two tubing profiles have very similar bending properties. On most designs, there is very little vertical deflection except possibly in the fork. I have heard people complain about 2OS bikes feeling dead to pedaling force. One thing about current fork tubing is that it is generally thinner than the old stuff, so even a go fast bike can have more fork compliance over a similar fork from 35 years ago.
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Old 12-26-18, 01:19 PM
  #44  
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Originally Posted by unterhausen View Post
The easy calculations of stiffness people always do don't really translate well to a space frame anyway. Although I suppose it mostly goes back to moment of inertia.

I am currently riding a 9/6/9 25.4/28/28 Reynolds 531 bike for audax which I like a lot. Prior to that, I was riding an OS 28/28/31 7/4/7 Columbus Spirit 4 Lugs bike that I liked a lot. I don't see how tubing contributes much to comfort because of the triangulation of the frame. However, those two tubing profiles have very similar bending properties. On most designs, there is very little vertical deflection except possibly in the fork. I have heard people complain about 2OS bikes feeling dead to pedaling force. One thing about current fork tubing is that it is generally thinner than the old stuff, so even a go fast bike can have more fork compliance over a similar fork from 35 years ago.
I'm going to get pedantic again, because I value your opinion and I want to take advantage of any benefit it may hold for me.

Are you saying that, for example, if you compare two different frames, same dimensions, joinings, workmanship, configuration and construction, except that one is 1.0 mm straight gauge and the other is 0.4 mm butted (double on the TT and DT, single on the ST), that an instrumented torsion test could show that the one with the 1.0 walls is more elastically flexible than the one with 0.4 mm walls? That's what your comment suggests. If this is not what you mean, please bring your intention down to earth. I am leaving fork flexibiity out of it.

I accept that brazing, craftsmanship and lugwork may be unmodelled variables.

I assume that by your repeated use of "I like(d) it a lot," you mean both felt similarly comfortable and perhaps responsive. I'm not going to attempt to check your statement that "these two tubing profiles have very similar bending properties," and I assume you mean their moment of inertia values are similar. If so, your comparison says, "I think the comfort of my two frames was similar, and their MoI numbers are similar in value." To me, this implies that there IS value in comparing the MoI of different tubes to make at least a comparison of which frame might feel more or less comfortable. Remember, I am assuming your two frames are the same geometry and proportions.

You seem to be implying first that no quantitative engineering can yield insight into bike frame flexing, yet you seem to imply that two frames with aanlytically similar properties actually had similar performance. I see this situation as contradictory.

Bottom line: please clarify your post. I can't see what you are advocating or trying to assert.
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Old 12-26-18, 04:00 PM
  #45  
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It's very likely that stiffness (whatever that means regarding a frame) is going to be monotonically related to the moment of inertia of the tubing. All else being equal, e.g, frame design, geometry, etc. So, for example, if you measure the vertical deflection of the frame from a load applied vertically at the top of the seatpost and could change the tubing parameters, you would find that it varies smoothly with the 2nd moment of inertia. What I meant was that I often see people trying to extrapolate from a simply supported beam and that leads them to exaggerate the importance of moment of inertia. They should look at a fixed-fixed beam. But that's a lot more confusing, appropriately I would say
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Old 12-27-18, 03:59 PM
  #46  
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Road Fan - Not sure where you get the 75mm trail figure from, I think you might have it confused with bb drop !

I am more and more thinking that comfort -- ie vertical flex, has little to do with the frame:

As an experiment last week I changed the Deda 215 bars and stem on my very comfortable Audax bike for a modern oversize set up - Deda Newton/Deda Zero2

The ride is significantly harsher. Are the bars what makes the difference? I have always been aware that the 215 s have a lot of give, I have them on two bikes, both are very comfortable.

Since light weight, good quality, non oversize bars don't seem to be available any more what are the options for those who don't want 'stiffness' all the time?
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Old 12-27-18, 07:46 PM
  #47  
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The industry has a solution for you. It's bar tape padding This is somewhat tongue in cheek. I find it so interesting when the industry changes the standards and then has to follow up with a patch for the new design so the masses can use it comfortably. (Linear brakes with spring loaded cable noodles comes to mind). Andy
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Old 12-27-18, 08:08 PM
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Originally Posted by unterhausen View Post
It's very likely that stiffness (whatever that means regarding a frame) is going to be monotonically related to the moment of inertia of the tubing. All else being equal, e.g, frame design, geometry, etc. So, for example, if you measure the vertical deflection of the frame from a load applied vertically at the top of the seatpost and could change the tubing parameters, you would find that it varies smoothly with the 2nd moment of inertia. What I meant was that I often see people trying to extrapolate from a simply supported beam and that leads them to exaggerate the importance of moment of inertia. They should look at a fixed-fixed beam. But that's a lot more confusing, appropriately I would say
Ok, thanks.

I guess you could look at each tube as a fixed-fixed beam, or at the frame as a whole or a "black box" that is free-free, or as the assemlbly of tubes as a statically indeterminate complex object.

Oh, well. More fish than I can fry.
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Old 12-27-18, 08:32 PM
  #49  
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Originally Posted by mikeread View Post
Road Fan - Not sure where you get the 75mm trail figure from, I think you might have it confused with bb drop !

I am more and more thinking that comfort -- ie vertical flex, has little to do with the frame:

As an experiment last week I changed the Deda 215 bars and stem on my very comfortable Audax bike for a modern oversize set up - Deda Newton/Deda Zero2

The ride is significantly harsher. Are the bars what makes the difference? I have always been aware that the 215 s have a lot of give, I have them on two bikes, both are very comfortable.

Since light weight, good quality, non oversize bars don't seem to be available any more what are the options for those who don't want 'stiffness' all the time?
Mikeread: I see the problem - you wrote "57mm trail 75mm BB drop" and I read "trail 75mm." My bad, your 57 mm trail makes more sense, as does 75 mm BB drop.

Re the handlebar issue: Maybe your frame is too stiff, though it's hard to compare as Unter and I have been debating about. But here's my thought: My Mondonico ELOS has oversize compact-style bars that narrow down to accept standard Campagnolo Ergopower levers, on a Reynolds carbon fork. The Al is a high-strength alloy so the walls are probably kinda thin. I feel 28mm TT and ST, and 31 mm DT. The TT and DT have .4 mm walls and the ST has 0.6 mm. I rarely feel harshness through the bars, even with the 28 mm tires inflated to 100 psi. I'm guessing the frame gets significant compliance from the thin frame tube walls and from the carbon fork. My wheels are hand made 32 DB spokes with Mavic Open Pro rims, but while that is all good stuff it's really nothing special as far as ride comfort. Not sure if you were talking about the frame tubes on your Audax or the frame tubes planned for your go-fast, but I wonder if those tubes are making things harsher then they need to be.

Did you say what wheels, tires and pressure you usually run on your Audax? increasing tire width or reducing pressure are known ways to reduce harshness.
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Old 12-27-18, 08:38 PM
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Nessism
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ELOS has a magical ride quality to it. I remember my first ride on that tubeset coming from SLX and it was noticeably more cushy. One of the all time greats.
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