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Frame design decisions - your opinions?

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Frame design decisions - your opinions?

Old 01-24-18, 04:56 PM
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mikeread
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Frame design decisions - your opinions?

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.

1 I will be using an off the shelf carbon Fork (At the moment I am looking at the Columbus Minimal) 1 1/8 inch as there is a lot more choice and the larger HT will help handling.

2 I will stick with .8 .5 .8 tubes but use a 35 mm DT, to reduce flex.

3 ST and TT to be 28.3 to retain some comfort. Reynolds do a ST that tapers from 31.7 at the BB to 28.3 at the top - might consider this. The frame will be sloping top tube so I can use a relatively long 27.2 seatpost which I believe helps comfort.

4 631 or 853 ?? Reynolds have a minimum order so I could get 2 sets of 631 tubes or 1 set in 853. I believe they will both feel the same so am leaning toward the 631 with spare tubes for a second frame or in case of errors.

5 Seat stays and chain stays - not sure yet maybe lightweight seat stays and some beefier chain stays.

6 I have considered going fully oversize with 31.7 TT and ST I am not sure if this will make the bike too stiff, also, seat posts for this size seem to be few and far between.

7 Geometry. I am looking at 73 degree HT 72.5 seat tube. 57mm trail 75mm BB drop and 419mm chain stays

8 BB will be approx 260 to 265mm off the ground depending on tyres. Possibly lower as I dont race and am OK with a low BB

Does this all seem logical and practical ?
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Old 01-24-18, 06:15 PM
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Everything makes sense there. From what I have read there is no different in rigidity between different chromoly steels. Dent resistance and durability of higher grade steels should be better though.

As for the partial double over size design it seems like a decent idea to me, but if stiffness is indeed your main concern than going 31.7mm TT would be better as would larger seat stays. The seat stay diameter will effect the lateral stiffness of the rear triangle. How much stiffness the seat stays add is something I've been wondering about lately as tiny seat stays are quite popular, but then as a counter point to the possible benefits of small seat stays you see a Pegoretti and it has HUGE tubes in the rear triangle and read Silca's blog post analyzing where comfort comes from on a bike and the frame is the least important part of the equation relative to wheels and tires. So, maybe large seat stays would be great on a bike that is built to ridden hard and fast.

Are you building with lugs?
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Old 01-24-18, 10:04 PM
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If you want a stiffer frame with minimal weight penalty, use a heavier gauge down tube and chain stays. That's what we did BITD, using Columbus SP down tube and chain stays, and SL elsewhere.
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Old 01-25-18, 12:06 AM
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We all like somewhat different frame design/bike handling manors. I have moved away from trail amounts of less then 60mm for the most part. If this were my bike I'd reduce the head angle to 72*. I'd also consider extending the stays a tad. Do you know how much seat set back you run? Do you know what your front center will be? What size tires will you typically use?


I see nothing wrong with your tentative design. But there's so much that one can take into account when designing a frame and I'd want a lot more info before I would feel that I had a handle on the givens, from which the resultants come from.


A few odd comments:


I think that the fork's contribution to the overall frame flex is greater then many talk about. I have felt a major increase in preserved frame stiffness between very similar self made steel bikes where one had a 1" steerer and the other a 1.125" steerer.


I think that "working" the TT has more impact on rear triangle stiffness then that of "working" the seat stays. One structural aspect that often get's left out of discussions is that most bikes rear ends are a three dimensional form made up of triangles, the rear axle is one of the edges and ties the two large side facets together. That results in a pretty stiff structure for the amount of material. OTOH the top tube is a simple beam with far less cross sectional area then any facet of the rear end. Stiffening up that helps to better tie the front and rear together, especially when seated or with a rear load IMO.


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.


Last thing I'll mention is that this is much of what I've gone through recently. I want to make a couple of frames for the wife and I which will be our weekend warrior rides. I made a couple of S&S coupled bikes for us a few years ago that, geometry wise, have been about perfect. So I have a wish to mimic their fit and handling traits and lighten them up. To best do so means a fork on her bike that no one makes as a stock production model. Now this isn't a problem if I were wanting (and this is all about wants) a steel fork. But I was really hoping for carbon. Weight is a major part of a pound less and the road feel can be pretty good, lastly not having to make and paint a "mini frame" twice is a plus. After going through many designs (I use BikeCad) I've come back to the need for a fit and a ride being more important then weight or effort. So a couple of days ago I ordered fork materials and will set the carbon forks aside. I guess I should see this as meaning that my painter has more canvas to work on... Andy
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Old 01-25-18, 10:47 AM
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stiffness goes up with the diameter, too , add an 8th in OD..
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Old 01-25-18, 12:52 PM
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Originally Posted by WheelNut2 View Post
Everything makes sense there. From what I have read there is no different in rigidity between different chromoly steels. Dent resistance and durability of higher grade steels should be better though.

As for the partial double over size design it seems like a decent idea to me, but if stiffness is indeed your main concern than going 31.7mm TT would be better as would larger seat stays. The seat stay diameter will effect the lateral stiffness of the rear triangle. How much stiffness the seat stays add is something I've been wondering about lately as tiny seat stays are quite popular, but then as a counter point to the possible benefits of small seat stays you see a Pegoretti and it has HUGE tubes in the rear triangle and read Silca's blog post analyzing where comfort comes from on a bike and the frame is the least important part of the equation relative to wheels and tires. So, maybe large seat stays would be great on a bike that is built to ridden hard and fast.

Are you building with lugs?

I plan to build with Lugs. My Audax frame was fillet brazed but I no longer have access to Oxy/Acetylene gear so I will probably get a Oxy Propane set and stick to lugs.

Will look up Silcas blog and have a read. Tyres make the biggest difference in my opinion but I do have an Aluminium bike with a huge carbon straight blade (disc brake) fork and it is painfull to ride, even with 28mm tyres at 60 psi. So the frame and fork deffo contribute. The bike handles great though which is the reason I started down the frame building road again.

Last edited by mikeread; 01-25-18 at 12:55 PM.
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Old 01-25-18, 01:06 PM
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Originally Posted by JohnDThompson View Post
If you want a stiffer frame with minimal weight penalty, use a heavier gauge down tube and chain stays. That's what we did BITD, using Columbus SP down tube and chain stays, and SL elsewhere.
BITD ? Back in the Day ?

I would prefer to go bigger than thicker - purely for cosmetic reasons though I do usually put function before form - having an engineering background
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Old 01-25-18, 01:10 PM
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This is the blog post here: https://silca.cc/blogs/journal/part-...re-and-comfort

All five parts are worth a read for sure. I mis-remembered the frame, wheel, tire compliance hierarchy. The tire has the most effect (obvious to all of us I think), the frame is second and the third is the wheel compliance. The tests referenced in this blog were just done at the seat post I believe, not at the head tube or bars.
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Old 01-25-18, 01:33 PM
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Originally Posted by Andrew R Stewart View Post
We all like somewhat different frame design/bike handling manors. I have moved away from trail amounts of less then 60mm for the most part. If this were my bike I'd reduce the head angle to 72*. I'd also consider extending the stays a tad. Do you know how much seat set back you run? Do you know what your front center will be? What size tires will you typically use?


I see nothing wrong with your tentative design. But there's so much that one can take into account when designing a frame and I'd want a lot more info before I would feel that I had a handle on the givens, from which the resultants come from.


A few odd comments:


I think that the fork's contribution to the overall frame flex is greater then many talk about. I have felt a major increase in preserved frame stiffness between very similar self made steel bikes where one had a 1" steerer and the other a 1.125" steerer.


I think that "working" the TT has more impact on rear triangle stiffness then that of "working" the seat stays. One structural aspect that often get's left out of discussions is that most bikes rear ends are a three dimensional form made up of triangles, the rear axle is one of the edges and ties the two large side facets together. That results in a pretty stiff structure for the amount of material. OTOH the top tube is a simple beam with far less cross sectional area then any facet of the rear end. Stiffening up that helps to better tie the front and rear together, especially when seated or with a rear load IMO.


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.


Last thing I'll mention is that this is much of what I've gone through recently. I want to make a couple of frames for the wife and I which will be our weekend warrior rides. I made a couple of S&S coupled bikes for us a few years ago that, geometry wise, have been about perfect. So I have a wish to mimic their fit and handling traits and lighten them up. To best do so means a fork on her bike that no one makes as a stock production model. Now this isn't a problem if I were wanting (and this is all about wants) a steel fork. But I was really hoping for carbon. Weight is a major part of a pound less and the road feel can be pretty good, lastly not having to make and paint a "mini frame" twice is a plus. After going through many designs (I use BikeCad) I've come back to the need for a fit and a ride being more important then weight or effort. So a couple of days ago I ordered fork materials and will set the carbon forks aside. I guess I should see this as meaning that my painter has more canvas to work on... Andy
A lot to think about there thankyou.

Most of the dimensions/geometry of the frame I have taken from another bike that I have and like. I know the relationship between seat, bars and cranks that give me a comfortable position. the big unknowns are the ride quality and handling. Having said that I am open to all suggestions and would certainly consider dropping the head tube angle to 72.5 or even 72. I guess this would give a more stable ride which is not necessarily what I want. It would certainly make it easier to get lugs to fit.

Front centres (BB to Front axle?) 610mm
Seat setback (BB to centre where seat tube meets saddle top?) 244mm
25mm tyres

Sorry I am not sure of the terminology.

I get what you are saying about the rear triangle, the stays do seem pretty spindly for the forces they are subjected to..

I find wider tyres are essential on our bad roads (UK) I suspect they are possibly faster on rough surfaces too.
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Old 01-25-18, 01:33 PM
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Originally Posted by mikeread View Post
BITD ? Back in the Day ?

I would prefer to go bigger than thicker - purely for cosmetic reasons though I do usually put function before form - having an engineering background
Well, Back In The Day, tubing diameters were constrained by available lug and bottom bracket shell dimensions, and dimensions of clamp-on components like front derailleurs.
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Old 01-25-18, 01:54 PM
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Originally Posted by JohnDThompson View Post
Well, Back In The Day, tubing diameters were constrained by available lug and bottom bracket shell dimensions, and dimensions of clamp-on components like front derailleurs.
Things have moved on, even in the years since my last build. I fillet brazed purely that time because the lack of suitable lugs. This doesnt seem to be a problem now
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Old 01-25-18, 08:05 PM
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Originally Posted by mikeread View Post
A lot to think about there thankyou.

Most of the dimensions/geometry of the frame I have taken from another bike that I have and like. I know the relationship between seat, bars and cranks that give me a comfortable position. the big unknowns are the ride quality and handling. Having said that I am open to all suggestions and would certainly consider dropping the head tube angle to 72.5 or even 72. I guess this would give a more stable ride which is not necessarily what I want. It would certainly make it easier to get lugs to fit.

Front centres (BB to Front axle?) 610mm
Seat setback (BB to centre where seat tube meets saddle top?) 244mm
25mm tyres

Sorry I am not sure of the terminology.

I get what you are saying about the rear triangle, the stays do seem pretty spindly for the forces they are subjected to..

I find wider tyres are essential on our bad roads (UK) I suspect they are possibly faster on rough surfaces too.

I don't want to tell you what your frame design should be, more to see how others do things.


The front center is getting long, some feel that this should be balanced by a rear center (chain stay) length. As the frame size grows so does the seat's set back from the BB center. So tall size with short stays and long front center means more rearward weight center.


Seat set back is generally thought as the horizontal dimension from the tip of the seat to a vertical that bisects the BB. 3-8cm is a range that many find right.


I agree about wide tires being better often. And
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Old 01-26-18, 06:02 AM
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Originally Posted by Andrew R Stewart View Post
I don't want to tell you what your frame design should be, more to see how others do things.


The front center is getting long, some feel that this should be balanced by a rear center (chain stay) length. As the frame size grows so does the seat's set back from the BB center. So tall size with short stays and long front center means more rearward weight center.


Seat set back is generally thought as the horizontal dimension from the tip of the seat to a vertical that bisects the BB. 3-8cm is a range that many find right.


I agree about wide tires being better often. And
What you say about the rear triangle makes sense. Looking at some manufacturers figures, they often use exactly the same chainstay length for all but the smallest frame sizes - I guess that is for production/cost reasons.

The chainstay length on the bike I am working from is 410mm and it handles real nice,. I have increased that to 418mm for clearence rather than balance. I am making quite a big frame so maybe I will increase it a bit further still.

The set back is 95mm on my drawing, I will check my other bikes as this seems a biy high going by your figures.

Thanks Andy, - these are the sorts of things I need to think about.
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Old 01-27-18, 12:45 PM
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seems now the big contract manufacturers like Maxway Ltd TW, generates all the lugs and other frame fittings for their client company ,

to make the finished product look like the customer-importer wants ..

Japan did same in the past.. My 85 Specialized expedition had a 1.25" Down tube

and a 1.125" seat and top tube ..




...

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Old 11-18-18, 06:14 PM
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My build is getting close to starting now - I don't work fast..
Frame design is pretty much sorted and I have also designed a jig based on the Arctos one but simpler to make.
I have ordered materials to build the jig and am finalising what parts and tubes I need to order to build the frame.

I am going to build lugged in steel and use System 48 Silver Solder and flux.

Would it be problematic for a beginner like me to mix a few stainless parts into the frame. The bits where the paint always gets chipped and rust sets in. The rear drop outs, front mech hanger and cable stops, Everything else to be non stainless.
I will be using socket type rear drop outs with Columbus Life stays and if possible the System 48 Silver.
Thanks - Mike
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Old 11-18-18, 08:11 PM
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Mike- Classic over reaching with a first frame Really if you do a lot of practice with SS and steel joining sure, why not use some SS. But do know it has a rather different character under the flame and a far narrower time/temp window the steel has. I would say that if you're doing cosmetic stuff like a head badge or non structural things like a casing/cable tunnel there's little chance to have a problem if you have a problem. But I would be rather conservative with structural items and SS, unless you really do your homework well. Andy
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Old 11-18-18, 08:22 PM
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From what you say I'd recommend using Llewellyn XL Compact lugs. I just finished a frame using them and they are simply fantastic lugs. I've been riding frames with XL OS tubes for quite some time and love the ride; firm but not harsh, and the bottom bracket stiffness is excellent. My latest frame uses Life for the Top tube, Seat tube, and chain stays, Zona for the down tube, and Deda Zero seat stays. All up (pre paint) the frame weighs 3.8 lbs for a medium sized frame. I wouldn't fret regarding the frames contribution to ride quality: tires are the most important thing and the fork second. The frame itself can matter but it's not as important as those other things.

Enjoy your project!

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Old 11-19-18, 02:14 AM
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Anderw, I understand the over-reaching thing but I would rather fail to make something I want than succeed in making something I dont Having said that, the stainless bits are not that important and I won't use them unless absolutely sure I can do it.

With socket type stainless rear drop outs could I put a coil of silver inside the stay and just heat the drop out until it flows - job done? Would this work, how could it go wrong and how would I know if it was wrong?

Nessism I am planning to use the LLewellyn lugs. On my first frame I found the hardest part was mitering the top of the seat stays and they ended up a half inch or so lower than I intended. The seat stay sockets on the Llewellyn lugs look like a good idea to make the build a bit easier. I will enjoy it too, I love all this design and figuring things out.

Loads more questions to come ...........................

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Old 11-19-18, 02:31 AM
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I decided to build a proper jig for this frame. Last time I built one from mdf and it caught fire, more than once.

I am a bit confused about what work should and shouldn't be done in the jig. Obviously all the parts and tubes can be prepared and fitted together in the jig but I read that it should be tacked and removed from the jig for brazing.

If this is the case, how do you tack lugs? It makes sense for tig but do you do the same for lugs? Is the flux/surface prep inside the lug compromised by tacking then cooling then brazing fully. Do you tack the whole front triangle before completing any joints?

I know there are recommended sequences for brazing the joints but would this way work:

1 Braze the hockey stick
2 Braze all the tubes into the bbkt (including chainstays
You now have the 'spine' of the frame complete
3 Check alignment and cold set if necessary. (I assume it is not good to re-heat a lug and re-align a tube, for example the DT in the BBKT if the HT and ST are not parallel)
4 Braze in TT
5 Check alignment again.
6 Locate seat stays, check with a wheel in frame then braze.

Thanks

Mike
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Old 11-19-18, 07:19 AM
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I've got to defer to the pro builders on pros and cons of tacking vs. brazing in your jig, what I can say is that there are pros that do it both ways so there is no right and wrong answer. Some guys use pins (nails) and drill/drive them while in the jig too, then braze outside, so add that to your list of methods.
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Old 11-19-18, 09:16 AM
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Just tack the lugs at a couple of spots per socket. It isn't going to move even though it seems like it will. If in doubt, then pin. The last alignment that counts on the main triangle is after tacking/pinning and before fully brazing. Non heat-treated 4130 will cold set, but it's not a good idea. Anything better than that is likely to fold. When it's only pinned, you have a lot of freedom to realign

Alignment is really difficult to change once you have the seat stays on. So fully braze everything else first and add the seat stays after you check the alignment. The most significant problem is the coupling between the main triangle and the rear dropouts. Not having the seat stays keeps them independent.

I have often thought that a lot of alignment is actually done by bending the bb shell. Although most chainstays will bend a little.
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Old 11-19-18, 10:36 AM
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I'll tack the lug points and other sides along the frame's centerlines. Two tacks per lug. I'll pin usually only once per lug to maintain alignment (tube rotational and length, not geometry) so during the many times I take apart and reassemble tubes/lugs on a jig before tacking everything lines up the same each time.

I do the main frame as one complete assembly and after tacking on the jig will align on a flat surface then complete the brazing free hand. Then another alignment check and back into the jig for the chain stays, tack, remove, align, complete braze and back into the jig for the seat stays. Between each brazing and reinstalling in the jig I do as much filing/sanding finish work because access is easier with less frame in a bench vice. I've begun to leave one seat stay/drop out un tacked or brazed and then use a builder's wheel for that last joint to insure best alignment.

Much the same with the fork. Tack, remove, check alignment and free hand braze. I do the steerer crown (as well as the BB/seat tube) as initial complete brazings before the rest of the steps.

Some day I plan to try all tubes in the shell and a hockey stick. I use to do the main frame in two pieces before I had a jig or flat surface.

Mike- Where are you? It would be cool to get together. Do you ever travel to bike/frame shows? Andy
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Old 11-19-18, 04:55 PM
  #23  
mikeread
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Hi Andrew

I am in the UK so a meet up, which would be great, is going to be hard to arrange.
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Old 11-20-18, 11:25 AM
  #24  
Doug Fattic 
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Mike, there are multiple good ways to build a frame as well as poor ones. What method is used is probably based on the particulars of specific equipment and how someone was taught. Most likely a pro learned from a master that had already weeded out bad techniques. Like most professional builders I know (I had the great fortune of learning from a master in Yorkshire) I don’t braze a main joint in a fixture for several reasons. It restricts optimum brazing positions and doesn’t allow the frame to move freely when it expands with heat.

The goal for lug brazing is to get compete silver coverage and have all the tubes end up in the same plane. Since they can move a lot while brazing it can be challenging to finish with an aligned frame. My procedure is to braze the seat tube to the BB 1st. This serves as my alignment foundation for the rest of the frame. Then I assemble all the main tubes into one of my main triangle fixtures I have laser cut and etched in Ukraine ($1000) that lays on my alignment table. I put 2 spots on the centerline of each lug (one on each tube). After it cools I align the frame on the flat table and put 2 more spots on that down tube lug on the available centerline places still left and align again. Now I braze that joint free outside of the fixture. Because the rest of the lugs allow for a little movement I can easily realign the frame again and put 2 more spots on the next lug (making a total of 4 on one lug before brazing). I align again before fully brazing that 2nd top tube lug. This align, spot, align and braze sequence insures I end up with a frame well within a tight tolerance. I don’t pin because with my method I need the joint to have a little ability to move to compensate for brazing distortion. All of my frame building class students that have not yet developed exceptional brazing skills to reduce distortion have ended up with frames well under 1mm out of alignment with this method.

Many builders successfully pin but that requires a very accurate fixture and/or set up on an alignment table. The origins of pinning comes from the European technique of hearth brazing when the whole joint or joints got entirely up to temperature before adding the brass so of course any spots would not be able to hold the frame’s position. That is how I brazed my 1st frame at Ellis Briggs in Shipley in 1975.

My method avoids the issue of the hockey stick possibly changing angles just a little. The old method British builders usually had some kind of make shift fixture to hold the down and head tube angle when they were brazing the hockey stick to avoid that problem. The equipment I got from Johnny Berry’s shop in Manchester after he passed away had a fixture to do just that. At Raleigh’s custom shop in Ilkeston I have a picture of them brazing a 753 hockey stick with angle iron holding the tubes while the whole 3 piece assembly lays on a steel table.

One of the greatest challenges of building a frame is getting a rear wheel to exactly center. That is why I don’t braze the chain stays with the down or seat tube. Too much is happening all at once to guarantee success. I also want to be able to file the lugs 1st without the rear getting in the way. It is a bit problematic to give too much detailed instructions in a subject post on the web. For example my frame building class manual which outlines framebuilding steps is 150 pages long. And even then I provide a lot more personal instruction so everything is clear.

Doug Fattic
Niles, Michigan
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Old 11-20-18, 03:19 PM
  #25  
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Mike, you may find this interesting:

The first frame I built was without a jig and free hand in a bike stand. Pinned the main tubes and the triangle was only 3mm out of alignment. The second frame I did the same way, but much more careful and it was out by 2mm. Either one was not enough to affect the tracking of the bike when ridden. This last frame I did in a jig and it was 5mm out of alignment! Not sure what the heck happened, but I spent a lot of time getting 2mm of movement out of it to bring it back into compliance of plus or minus 3mm.
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