Getting A Disc Tab Welded On Frame

[arw_86]

recently ive gone front disc and although its not perfect the modulation you have with it is incredible. Combined with rear vee not having hardly any modulation its made me ponder about getting a disc tab welded on to my marino.

my frame is already raw (apart from laquer i can get off easily) and i have a new rear hope pro 2 with disc mount ready to go.

So how easy would it be to get one welded on? I need answers to the following questions i guess;

- where do i get a disc tab from?

-how do i know what size i need?

-how do i know where it needs to be welded? (positionally speaking)

-how much would it roughly cost to be welded?

-do i need to add frame support in the general area?

-recommended rotor size?

-IS IT ALL WORTH THE HASSLE?

any info would be appreciated.

thanks dudes

Edited December 3, 2011 by arw_86

[Revolver]

If you're in Birmingham, you're fairly close to Loughborough, where Josh is.

I'm sure he could answer all your questions and do the welding for you.

He's Rob Leech on here. Send him a PM!

[davidbarr]

Pretty sure Jake Hickey tried it as well. You might want to speak to him.

[monkeyseemonkeydo]

- where do i get a disc tab from?

-how do i know what size i need?

-how do i know where it needs to be welded? (positionally speaking)

-how much would it roughly cost to be welded?

-do i need to add frame support in the general area?

-recommended rotor size?

-IS IT ALL WORTH THE HASSLE?

If you're serious, your best bet would be to get a brake so you can offer up the caliper and make a mount to suit. Mock something up in cardboard to start with to get the dimensions and placement right, transfer to a bit of sheet steel (5mm thick would be a rough guestimate to thickness). Adding a diagonal support from opposite the front mount hole to the chainstay wouldn't hurt. Use a hole saw on a pillar drill with the tube held at the right angle to get the mating surface pretty good prior to welding.

The biggest problem will be getting it aligned for welding. If it were me I'd bodge together some kind of bracket which would sit on a simple 'axle' inside the dropouts, with the mount bolted to it (in the correct place) to ensure that the mount remains perpendicular to the axle. It may also be worth tracking down someone with a disc mount facing tool too just to make it all good.

What size wheels are you running? 24" or 26" I'd go for 180mm, 20" you'd get away with a 160mm.

If you can get it sorted easily enough via mates etc then yeah, go for it.

[winchman]

In the bike factorys they have a jig that holds the frame in position and holds the bits you need to weld on, its easy if you have the stuff, I would try a few local frame builders as they should be able to do it.

The main thing is it has to be in the correct place, if you can get a man on the moon tjis should be simple, measure twice, once more for look and weld

Some US links here

http://www.sheldonbrown.com/rinard/framebuild.htm

[Azarathal]

So everyone claims that welding a crack will weaken the frame further and thus render the effort put in pointless and yet you're trying to help and condone this guy welding a disc tab on?

[Luke Rainbird]

Fortunately this frame's steel, so it's a different matter

Adam, knock up whatever it is you need out of a bit of spare wood (I'm assuming you should have some 6mm MDF offcuts or something lying around?) and make sure it's bang on. Mark up precisely where it needs to be and get in touch with a local engineering place or a mate who's handy with a welder and you're set.

For a frame brace, a bit of 20mm steel tube should do it, just cut/file/whatever depending on available tools 'til it's as good a fit as you can and you're onto a winner

[winchman]

So everyone claims that welding a crack will weaken the frame further

Which engineering principal is this?? Its common practice in engineering to weld cracks up.

Technically the crack would be ground along its length to make it wider then a run of weld put in the larger crack you now have. The weld will be stronger than the metal around it so it could move the stress concentrations by a few milimeters, but in the real world this dosnt make any difference.

Correct me if you think I am wrong but I see no harm in welding any bike frame.

The thing to consider is you need a competent welder, I can weld to a good standard and have the paper to prove this, but I get our coded welder to weld bike frames as he is much better than me and has his work tested on a regular basis to prove he is as good as he should be.

So dont be put off, jsut check all alignments and weld it on if you are really paranoid inspect it everyday after you have done it to prove its ok, but I feel it will be fine, just copy the way it would be done on a new frame

[monkeyseemonkeydo]

Fortunately this frame's steel, so it's a different matter

And as far as I'm aware Marino's are still put together in the guy's garage so there's no initial heat treatment process used s nothing to need to renew post-disc mount adding.

Winchman- the issues usually arise with any ally frame where you get pre-treated tubes made of stuff with wall thicknesses not far off those of coke cans. Welding is difficult to begin with and it's thought (never tried it myself) that if the frame isn't heat treated afterwards, the alloy properties will mean that it will fail faster in the area which has been welded. Can't remember enough of my materials lecture materials to tell you the process behind it but I'm sure someone will!

[winchman]

And as far as I'm aware Marino's are still put together in the guy's garage so there's no initial heat treatment process used s nothing to need to renew post-disc mount adding.

Winchman- the issues usually arise with any ally frame where you get pre-treated tubes made of stuff with wall thicknesses not far off those of coke cans. Welding is difficult to begin with and it's thought (never tried it myself) that if the frame isn't heat treated afterwards, the alloy properties will mean that it will fail faster in the area which has been welded. Can't remember enough of my materials lecture materials to tell you the process behind it but I'm sure someone will!

Now if its Coke Can thin ally then you are in the brown stuff.

I dont remember the ally failing when its been welded bit either?

I will ask at work tonight if one of the coded lads is in as its an interesting point

[Rob Leech]

Which engineering principal is this?? Its common practice in engineering to weld cracks up.

Technically the crack would be ground along its length to make it wider then a run of weld put in the larger crack you now have. The weld will be stronger than the metal around it so it could move the stress concentrations by a few milimeters, but in the real world this dosnt make any difference.

Correct me if you think I am wrong but I see no harm in welding any bike frame.

The thing to consider is you need a competent welder, I can weld to a good standard and have the paper to prove this, but I get our coded welder to weld bike frames as he is much better than me and has his work tested on a regular basis to prove he is as good as he should be.

So dont be put off, jsut check all alignments and weld it on if you are really paranoid inspect it everyday after you have done it to prove its ok, but I feel it will be fine, just copy the way it would be done on a new frame

With ally frames, the problem arises with the localised heating of the weld area.

Because of the heat treatment processes that go into a frame post fabrication, any sort of introduction of heat will pretty much undo this process, leaving the area soft, which inturn may or may not lead to it cracking again, it's something that you can't really predict to a time scale.

I've repaired frames that have lasted up to 3 months, yet i've also repaired frames that have only lasted 3 days, a sound repair is very much more to do with looking where it is on the frame, why it has cracked there and trying to cancel out the movement that has caused it to crack there.

However, if this is a steel frame your wanting doing, go ahead, aslong as you gusset the area and use a competant welder, you wont have any problem with it cracking .

Cheers,

Josh.

[winchman]

With ally frames, the problem arises with the localised heating of the weld area.

Because of the heat treatment processes that go into a frame post fabrication, any sort of introduction of heat will pretty much undo this process, leaving the area soft, which inturn may or may not lead to it cracking again, it's something that you can't really predict to a time scale.

I've repaired frames that have lasted up to 3 months, yet i've also repaired frames that have only lasted 3 days, a sound repair is very much more to do with looking where it is on the frame, why it has cracked there and trying to cancel out the movement that has caused it to crack there.

However, if this is a steel frame your wanting doing, go ahead, aslong as you gusset the area and use a competant welder, you wont have any problem with it cracking .

Cheers,

Josh.

Sorry I am assuming its steel

[Rob Leech]

And as far as I'm aware Marino's are still put together in the guy's garage so there's no initial heat treatment process used s nothing to need to renew post-disc mount adding.

Winchman- the issues usually arise with any ally frame where you get pre-treated tubes made of stuff with wall thicknesses not far off those of coke cans. Welding is difficult to begin with and it's thought (never tried it myself) that if the frame isn't heat treated afterwards, the alloy properties will mean that it will fail faster in the area which has been welded. Can't remember enough of my materials lecture materials to tell you the process behind it but I'm sure someone will!

Firstly, no need to heat treat a steel frame, it's properties are wildly different to aluminium and can easily withstand the forces trials puts through it.

Also, if its one of his bog standard mild steel frames, it cant be heat treated due to the low carbon content, only high carbon steels can be heat treated (tool steels, EN series, ect) .

I'll say this again, like i have many times on here, you cannot re-treat a heat treated frame, not on a very specific point like a welded joint anyway.

The fact is, if you were to put the frame through treatment after a repair, the welded area may well be hardened again, but what about the rest of the frame?

A very large area that has not had any heat introduction and is still at its stated temper will now have heat introduced into it, putting you back to where you were in the first place.

Also, to do this, the frame would have to undergo the whole process, so solution treatment-

(a process where the material is taken close enough to its melting point to allow certain constituents of the material to become a solid solution, then being quenched extremely quickly to hold these constituents in place (in most frames, these constituents are silicon and magnesium))

and age hardening-

( where the material is subjected to a relatively low temperature (usually around 180 degrees) for a long period of time, which produces particals of an impurity phase, helping to stop the movement of dislocations in the material)

So it's not a small job in reality, dont forget having to make a jig for the frame, due to the extremely high temperatures involved in the solution hardening, the material can buckle and twist just under its own weight, and also finding somewhere to do it for you, which is very difficult as most places that will have the facilities to heat treat aluminium will be very large and probably only take jobs on that are massive in quantity.

Anyways, ramble over, there you go .

Cheers,

Josh.

Edit- winchman, there will be no problem with welding it if it is steel ^^^^^^

Edited December 4, 2011 by Rob Leech

[Azarathal]

*snip*

I never claimed it was any "principle". I was going by the fact that the majority of the forum claim welding a frame is usually pointless for the reasons Josh stated.

[Pugson]

definately possible if you persevere, my old boy had a new rear disc spec droupout cut from a sheet of ti. and welded onto the back of his m-trax team titanium. he did cut off the eintire rear dropout on one side , leaving only the two open endos of the rear triangle, he didnt just try to weld to what was already there. this alowed the new dropout to be machined incorporating 2 "locating spigots" that slid down the inside of the open tubes to aid allignment. a jig is going to help, but it dosent need to be over engineered, it only needs to hold the tab in place whils a few strategic tack welds are aplied, then it can be removed for welding. a combination of the hub holding the new dropout square and spaced propereley, the disc rotor setting height and a series of strong-backs you could do it by eye if you were good enough. if you tack it in the right places you could defo get away withe giving the wheel a spin to check for square, then force it slightly against your tacks to adjust until correct. (id do it myself but im a welder/plater by trade). the guy who did my dads worked at BAE systems for 40 years.

the problems people are saying about the heat are mostly correct, the problems usually occur after welding in what some call the HAZ zone (heat affected zone), this sometims results in cracks apearing along the toe of the weld. my old mans has lasted 8 years with a hope xc 4pot on it, however it is an xc bike, and ti is nice and springy aswell so that'll help to alleviate the stress. the thickness of the tubing wont matter to the actual welding process at all, unless its coroaded. obviously the thicker the tube wall the easier it will be and stronger afterwards. But a good welder with a decent Tig set could practically weld two pieces of foil together.

[Luke Rainbird]

Seriously though, f**k the theory just grab yourself a grinder and a drill and set to work on a piece of 5/6mm steel plate. Bit of tube for the brace and get it on there!

[Rob Leech]

Seriously though, f**k the theory just grab yourself a grinder and a drill and set to work on a piece of 5/6mm steel plate. Bit of tube for the brace and get it on there!

Very much agree with this statement .

[Chris Borneo]

Just a word of warning, I have a friend that had about three or four Rocket frames back in the day and ripped the disc mount off all of them. They were pretty burly too. Problem was the disc mount pulling away from the frame. Might be worth mounting it between the seat and chain stay. Don't know if there are any down sides to doing it this way mind.

[Revolver]

Don't know if there are any down sides to doing it this way mind.

So long as there's space. It might be more difficult with certain callipers, BB7 is the main one I think you'd have an issue with.