Gresp15C

Andy asked me to start a new thread. I'd like to know how hard it would be to change the dropouts from vertical to horizontal dropouts or track ends on a steel frame. I'm good at silver brazing, but have never held a torch to a bike. Is a basic mapp gas torch sufficient for this work? One thought is that if I'm sacrificing the existing dropouts, I don't mind cutting them in half so I'm only working on one joint at a time.

CliffordK

I've heard of it being frequently done switching between road and track dropouts.

I think I have heard of the trick of cutting the dropouts in half, and perhaps pulling the old dropouts with heat and weights.

I have an old Trek that I acquired with a broken dropout, so I was going to try putting on a pair of vertical dropouts (Zeus?). When I got the parts next to each other, I discovered that the vertical dropouts were much smaller/shorter than the originals, perhaps having to do with where the seatstay lines up with the vertical vs horizontal slot.

At the same time, the wheel pops up vertically into the chainstays, and so much less clearance is needed. So, perhaps I simply need to reorient the seatstays.

Anyway, I probably would only do the change if your original dropouts are damaged.

obrentharris 

I'm not a framebuilder but I will throw an observation your way. On your typical horizontal dropout the axle sits below the chain stay. On track and vertical dropouts the axle is closer to level with the chainstay. I would think that some serious manipulation of the chainstay/bottom bracket joint would be required to switch dropout styles between horizontal and either of the others.
Brent

Andrew R Stewart 

Thanks for the fresh thread.

A Clifford says drop out replacement is done often enough. If done well there's little concerns. But besides the blacksmithy stuff (more later) the geometry stuff needs attention.

One assumes that maintaining the frame's handling/steering is wanted. So keeping the rear axle in the same horizontal relationship is the goal to not cause a shifting of the head angle and Bb drop. Placing the hoped for track drops next to the OEM road ones can suggest some of the changes needed for this goal. Stay bending, end repositioning and perhaps trimming is a common method to locate the new slot so it overlays with the OEM axle's location. Of course any goal to shorten the chain stay length also comes into to play, however miss guided

As to the blacksmithy- As I mentioned much is driven by the OEM axle location and the shape of the new drops. To this Henry James has made track drops in a few different tab extensions for varying OEM stay arrangements. Pulling the OEM drops is usually done by slotting through the drop out in a slice that allows for no interference for one stay/drop out joint being heater to melt out of the filler and easy pulling while that hot. Placing the drop out lowest and clamping a vice grip as a weight is a good method. Know that the heat level will have to be higher then the brazing level and enough all across the joint (which can run up in the stay a bit) to have all the filler liquid. Any wiggling of the drop out half can result in cracking of the stay's end. This is why a clear exit path (determined by the cut slice path) is important. Repeate for the second stay/drop joint. If chrome is present then it needs to be ground off first.

Once the stays are free of the old drop then the manipulation of the stays to fit the new drop to duplicate the axle location is next. The stay's insides will need to be cleaned out enough for both good brazing and drop out plate fit. The stays likely need some bending to align with the drop's tabs. Sometimes trimming the stay end down is needed. Slotting is the usual way to fit a drop tab to the stay. Not as easy when the stay is absent of the rest of the frame...

Let's say that all this has gone well enough. The OEM drop is gone. The stay ends are clean and prepped for the new drops. The new drops are in the correct spatial relationship to reproduce the same head angle. Their width matches the rear wheel. There's no tension in the stays as they fit to the drops and all is lined up. (and that says a lot). Now comes the brazing. Since the fit and gaps are usually a compromise with other issues gaps and slop exist. So no silver (56%) can be used. Brass/bronze is the order of the day. This is where your practice will be the difference. Does your MAPP torch get hot enough and in a way that works for brass/bronze? Some can do it some not so well. (and this is where making the move to OA makes things easier as one move through the project paths we try. OP is trendy but it too has flame challenges with brass/bronze).

Assuming one is good with brazing then tacking three of the tabs is a good idea. Both chainstays can actually they can be fully done as any slight misalignment will be absorbed by the horizontal slot's freedom. One seat stay could be fully brazed too. But the second seat stay is best left for after a final alignment confirmation can be done. There's no "slop" in seat stay length. Tack it and again check alignment then complete it. It's typical that some after brazing completion manipulation will be needed. Drops made parallel and rear triangle alignment too. Andy

Gresp15C

Wow, thanks. It does sound a bit daunting, especially if I have to up my brazing game. Amusingly, I've done oxy-hydrogen with silver solder, which is a strange beast, but works for stainless steel high-vacuum joints. I studied physics in grad school, and we pretty much built our own experimental apparatus. How is brazing different? Is it just that you can make a heavier fillet with it because it doesn't flow as much?

Well, if I don't end up doing this, I will still take away some good learning about soldering and brazing.

CliffordK

Thanks Andrew,

A comment about the issue that @obrentharris noted. Horizontal dropouts typically aren't quite horizontal, but rather slope up and back. The chainstays also have an up and back slope, but the horizontal dropouts typically have a little extra slope.

Track ends typically are set fairly parallel to the chainstays, or even parallel to the ground.

That means that if the the wheel is set towards the middle or rear of the horizontal dropout, the axle will end up towards the middle of the chainstay. And, there may not be that great of a difference between a track dropout and a horizontal dropout. 1/4" max? It might not have a huge effect on the overall frame geometry.

Theoretically it should be possible to cut replacement dropouts on a CNC, or even a regular mill. Track dropouts are often fairly crude, but one might be able to even cut vertical dropouts to one's specs, and thus make fitting easier.

CliffordK

So, if you have a damaged dropout, keep it long enough to document what you have, then chop it up and throw it away.

But, what if you wish to preserve the original dropout, perhaps for another project? Then how would you approach the problem?

I realize the issue of the stays coming down at an angle, and the dropout tabs extending up into the stays. I hadn't thought of the potential for tearing or damaging metal in one of the stays.

But, is it possible?

CliffordK

I've dealt with desoldering tools. The cheap ones work OK. The Radio Shack one I had, push in the plunger, get a molten puddle of solder, then push the button and vacuum the solder into the tool. Then pick the solder out of the the plastic nozzle and repeat. Actually, I think the plunger had a pin that pushed solder out of the nozzle.

Could something similar be done with brazing? I'm thinking of a small vacuum tank. Pull a vacuum. Get your brass molten, then suck it up into a ceramic tip. Release agent? i assume some bike brands use space filling between the stays and the dropout tabs.

Andrew R Stewart 

I have never heard of a Debrazing tool. I have heard of (and done a bit of) shaking out molten brass/silver from a stay while things are hot. Not to be counted on till one practices.

Space filling- Generally no. Since brass/bronze fills gaps so well and is so low cost and is so common (see the two previous points) why would one go to the effort to create a filling material? The exception that I know of was when Rey 753 was first used. For the stays/blades with their large gaps a filler "plug" was sometimes employed. These days far less often.

And the release agent- that pretty much considered as flux. You want the surfaces to be kept clean and agreeable with the next round of brazing. Andy

JohnDThompson 

At Trek we used solder wicks and wire brushes for that type of work. Melt the brass and suck up as much as possible with the wick, then use the wire brush to brush off more. Do it well and all that's left is a very thin layer of brass.

Andrew R Stewart 

I had forgotten about the braded wire trick to wick away excess filler, thanks for that.

To Clifford's question about both saving a drop out for recycling and maintaining the stays for a replacement drop out. I don't know, never tried to do that. I suppose one could just hack off one stay (seat?) a couple inches up from the drop out then do a drop out removal as usual. Then splice a new length of stay back on before attaching the new drop out.

I would never want to deal with a broken drop out until I had the replacement on hand and was ready to do the complete job. Andy

markwesti

Kind of a stale thread but anyhow , I have owned a few track bikes and I ride (not race) the Carson velodrome . Well I sold all that stuff but then I really missed it so I made one , sure it's not a real track bike . The main thing the BB shell should be about a inch more off the ground . To me it doesn't really matter because you are riding perpendicular to the track so a pedal strike is really not a concern . On my other track bikes the head tube was a few degrees steeper and made a super twitchy ride , this one not so much .

In the OP it was wondered if Map gas was OK , I have often thought about that , yes well too bad not gonna work at least if you are going to change a dropout to a track fork . IMO . Lucky me my O'l buddy has a shop and lets me use his OA rig but it's kind of a pain because he can't just stand there , ultimately he grabs the torch from me and wants braze . fine with me it's all good .

So I had to make a simple frame jig to get started . I sold my machine shop years ago , not to worry O'l buddy has a lathe that I needed to make the spacer for the track forks . Bonus , as I was turning the spacer on his Logan lathe 12" , I noticed this little Atlas 6" sitting there , he gave it to me .

Here is the jig I made . Before we started I cold set the frame , a 84' Centurion Comp TA , to 120 mm .



DSCF2336 by mark westi, on Flickr



DSCF2338 by mark westi, on Flickr



DSCF2469 by mark westi, on Flickr



DSCF2580 by mark westi, on Flickr

fietsbob

there .. as long as axle does not change location, keeping BB drop and wheelbase somewhat similar .. Boom..

another fixie for the velodrome?