ronan
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Thats sad, but its the same as the "classic" track/road racing, brand new manx nortons at £40,000 a pop. Money spoils everything.
Thats sad, but its the same as the "classic" track/road racing, brand new manx nortons at £40,000 a pop. Money spoils everything.
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Chris Stevens
Guest
These are very thin sliders and all those I have done in the past have distorted. Forks are very difficult to get hold of so need to work out best possible way of doing them.
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Chris Stevens
Guest
So are the Marzocci folks we use. Tissue paper in fact. Still not had a problem.
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Chris Stevens
Guest
Have to give it a go then..........will make some sort of heat sink first though I think.
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Chris Stevens
Guest
I think a heatsink of some sort would be a good idea, but maybe filling with oil as suggested by someone earlier would be even better?
addjunkie
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- Northumberland. Reet oot in the sticks
Years ago when i raced power boats, there was a guy who used to repair ali props, if theyd been abused or blades broken off.
He would suspend it in oil to protect the center boss with just the bit that needed welding sticking out, and in he would go with the tig. It was some kind of transformer oil i think, non flamable. I watched him doing it a couple of times.
Cash job was cheaper than a new prop.
He would suspend it in oil to protect the center boss with just the bit that needed welding sticking out, and in he would go with the tig. It was some kind of transformer oil i think, non flamable. I watched him doing it a couple of times.
Cash job was cheaper than a new prop.
norlander
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Chris Stevens
Guest
Harris is sold
norlander
Member
- Messages
- 3,389
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- Europe, mocycling paradise
So? the blokes with the experience are still around.
Wedg1e
They call me Mr. Bodge-angles
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Just a small point but depending on the radius of the discs, the caliper might be mounted so far up the leg that any distortion in the bore would be irrelevant as the fork stanchion bush might not 'sweep' that area anyway... might get a bit of stiction putting the stanchion in first time, of course.
Edit: Hmmm, skim-reading the rest of the thread, maybe this has already been said
Double Edit: on the other hand a trials bike might just have the fork travel for it to be a problem...
Edit: Hmmm, skim-reading the rest of the thread, maybe this has already been said
Double Edit: on the other hand a trials bike might just have the fork travel for it to be a problem...
Preheat would be my approach. Heatsinks and the like are sometimes useful with materials like stainless or Ti but are kinda at odds with the properties of ally... something like 4 - 5 times the thermal conductivity of steels, ~ double the thermal expansion and about twice the solidification shrinkage too although the AlSi filler alloys reduce the latter
Putting a heatsink in the slider is mostly just gonna result in needing to throw more heat at the part to get a weldpool as whatever is in it is gonna help the ally conduct the heat away from where you want it
A steel mandrel is gonna expand less than the part so won't do much to keep the leg round* IMO but could be a right PITA to get out afterwoods depending how much the slider shrinks. An expanding mandrel similar to the expanding heatsinks some bicycle frame builders use would fix both of those potential issues but is obviously more work to make. While they reduce the amount of post welding machining needed they don't guarentee that head tubes/BB shells/seat tubes don't need reaming or chasing etc
Stainless is a potential bitch for severe local distortion because it has lower thermal conductivity than carbon steels coupled with a higher rate of thermal expansion. With ally distortion is typically less of an issue than steels due it's thermal conductivity i.e. the entire part quickly gets 'kin hot so you get less of a thermal gradient. Also because it's it's relatively weak (especially at high temps)... lots of restraint won't necessarily stop a stainless from pulling all over the place while with ally lots of restraint is more likely to result in a weld that's more prone to solidification cracking instead which brings back to AlSi filler and the reason they're less prone to solidification cracking...
* i'm assuming roundness is affected more than straightness if/when welding caliper tabs on results in problems?
Putting a heatsink in the slider is mostly just gonna result in needing to throw more heat at the part to get a weldpool as whatever is in it is gonna help the ally conduct the heat away from where you want it
A steel mandrel is gonna expand less than the part so won't do much to keep the leg round* IMO but could be a right PITA to get out afterwoods depending how much the slider shrinks. An expanding mandrel similar to the expanding heatsinks some bicycle frame builders use would fix both of those potential issues but is obviously more work to make. While they reduce the amount of post welding machining needed they don't guarentee that head tubes/BB shells/seat tubes don't need reaming or chasing etc
Stainless is a potential bitch for severe local distortion because it has lower thermal conductivity than carbon steels coupled with a higher rate of thermal expansion. With ally distortion is typically less of an issue than steels due it's thermal conductivity i.e. the entire part quickly gets 'kin hot so you get less of a thermal gradient. Also because it's it's relatively weak (especially at high temps)... lots of restraint won't necessarily stop a stainless from pulling all over the place while with ally lots of restraint is more likely to result in a weld that's more prone to solidification cracking instead which brings back to AlSi filler and the reason they're less prone to solidification cracking...
* i'm assuming roundness is affected more than straightness if/when welding caliper tabs on results in problems?
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Chris Stevens
Guest
Thanks................the sliders seem to go very slightly out of round when welded, and can see your points regarding heatsinks. Maybe honing or reaming is whats needed here, as its possible that some degree of distortion is impossible to avoid?
Pretty much. Heat a lump of metal up evenly and it expands in all directions before returning to its origional dimensions as it cools. Heat one spot up and the surrounding colder material restrains it in some directions so it expands more in the directions it can. As it cools it shrinks in all directions changing dimensions/shape which is how flame straightening/bending work
With a weld your adding extra metal which also shrinks as it solidifies and cools
I didn't bother mentioning it yesterday as it'd had already been brought up by Ronan and it seems to be a relatively popular modification that works but my first thought was that it wasn't the best idea due to the change in load paths... more than few people found out the hard way that adding disc brake mounts to a mountain bike designed around cantilevers often ended badly with cracked or broken seat stays as they weren't designed to be loaded that way. Don't remember any front forks snapping as a result but IIRC fitting bigger/better disc brakes to old forks often highlighted how flexy they were?
Only a guess but i'd have thought that if sliders are heat treated it's probably only to make them nicer to machine after casting in which case it'd make as much sense for them to be cast from an AlSiCu alloy that machines nicely in the 'as cast' condition. Weldability and/or HAZ properties is a bit of a craps shoot either way
An idea that might help reduce distortion/spread it out rather than concentrate it one area? Drawings a bit pants but hopefully it makes sense
Basically instead of welding the caliper tab directly to the slider shape a bit of ally to make a doubler of sorts... more surface area to spread the load and instead of having fillet welds very close to each other on the slider they're now smaller lap welds further apart. Usual gusset rules apply; radius all corners, no welding circumfrentially around the tube to make a giant stress riser etc
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Chris Stevens
Guest
That seems a good idea.........it would be possible to get caliper brackets made on a CNC, but cost is a major factor here and few if any would want to pay the extra for something like a CNC mounting bracket. Have been looking at floating reamers, and wonder if something along those lines with some sort of guide mandrel would get the slider back to round?
I was thinking more along the lines of a mallet and a suitable lump of barstock to bash some 3ish mm thick sheet over or maybe pressing the sheet to shape/cutting the doubler out of some suitable diameter ally tube if you want to be posh
Unless you were to get lucky and find a used example i'd have thought an adjustable floating reamer would make a batch of CNC'd caliper brackets look dirt cheap, and that's before a holder/guide mandrel for it has been machined to suit?
If forks are rare and you're paranoid about distortion i'd do a dummy run... machine some ally tube or barstock to the match the ID and OD of a slider and knock up a fake caliper bracket complete with doubler. Weld (with 4043 and without 'over welding' it) the two together and then mic the ID again and/or see if a stanchion with new bushes will slide in thing without excessive stiction.
Unless you were to get lucky and find a used example i'd have thought an adjustable floating reamer would make a batch of CNC'd caliper brackets look dirt cheap, and that's before a holder/guide mandrel for it has been machined to suit?
If forks are rare and you're paranoid about distortion i'd do a dummy run... machine some ally tube or barstock to the match the ID and OD of a slider and knock up a fake caliper bracket complete with doubler. Weld (with 4043 and without 'over welding' it) the two together and then mic the ID again and/or see if a stanchion with new bushes will slide in thing without excessive stiction.
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Chris Stevens
Guest
Thanks for your thoughts. Guy who makes pistons for me is a very clever engineer, and might give him a call today and see if he has any good ideas.
