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Soldering Minnie wheel hubs

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Dominic Bramley07/07/2020 09:18:09
8 forum posts

Hi all,

I have been using our enforced confinement to make some progress on the rear wheels for a Minnie Traction. I have the spokes and strakes on and am at the point of soldering on the hub inner and outer plates to the hubs.

I am using the 60/40 Tin Lead Solder Paint from Cupalloys and a mapp blow torch.

The first wheel seemed to go ok - all be it with a bit of run-off onto the side of the hub which needs cleaning.

However the second wheel the plates are refusing to stick. The solder is running and there is some tinning around the edges but the plates just pop off once the bolt clamping them together is removed. I have had two attempts now with the same result.

Any suggestions as to what could be going wrong?

Would too much heat cause problems? (clearly too little heat could also an issue). Would using an oven be better than a blow torch?

Is cleanliness as important with the paint as it is with silver solder? If so what should i use to clean it. I have some citric acid pickle but would worry this would cause corrosion on the spokes.

Do the surfaces need to be in contact or should there be a small gap as is the case for sliver solder? Currently they are touching when clamped together - but I guess i could use a couple of center pops to create a small gap.

Any suggestions would be appreciated - a ton of work has gone into the wheel thus far and I'm worried that I will make a mess of it if I don't get this right soon.

Cheers

Dom

Clive Brown 107/07/2020 09:52:27
453 forum posts
14 photos

Odd that one hub was successful. Cleanliness of the joint area is very important wth soldering. Another observation is that if your MAPP torch is like mine then the flame is quite small but intense, could be locally overheating and burning the flux. Keep it moving.

I don't think measures to create a joint gap should be necessary.

Hope that helps.

Edited By Clive Brown 1 on 07/07/2020 09:54:23

JasonB07/07/2020 10:04:10
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18318 forum posts
2024 photos
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Leaving a gap should not be as issue if you are painting the solder on first, it will if trying to apply to the edge of teh joint and hoping it will flow into it. Don't overtighten your bolt either, just enough to locate the parts

If you are still having problems then you can "tin" each surface first, that is apply a thin layer of the solder paint and then heat until the flux bubbles off and the solder flows at which point wipe it with a cotton rag to remove excess. Once all joints are tinned apply flux or a little more paint, assemble and heat which will allow the two layers of solder to flow into one.

Do clean off the wheel well afterwards as the flux in the paint is quite aggresive and will rust the spoke sin days and weeks to come.

Gently heat from a torch so that the whole thing heats through not just the thin covers leaving the hub cold.

Dave Halford07/07/2020 12:08:10
801 forum posts
8 photos

Dom,

If you tin the spoke ends first then wipe the excess off towards the palms with a cloth you get both a surface that solders to the hub easily and one that keeps the flux away from the steel and prevents rust bleed out from inside the hub/plate joint. You can use ordinary multicore solder like this with some extra flux.

Your issue is either the plate is not contacting the hub because the spokes are holding it off or the hub is not hot enough.

Is there any sign of solder tinning on the hub beneath the plate? If the spokes have blued under the plate they were too hot. Solder paint is not for gap filling, use a multicore (resin cored) solder. If the solder paint is lead based use a lead resin core solder.

Abrade the steel to remove any blue. Bring the hub up to multicore melting point then use an old flat blade screwdriver as a scratch to spread the solder along the spoke, wipe excess off. Tin the underneath of both plates fully and re-bolt the whole thing up with an M6. Don't clamp the bolt in a vise you don't need a bigger heatsink, open the vise up to support the rim and heat the hub whilst in mid air.

You can add extra multicore to the spoke/hub joint where the tinning is exposed to fill any gaps.

Check the bolt hasn't loosened (it will have), nipping up will any squeeze spare solder out.

This is obviously much simpler to do the tinning when the wheel is not riveted.

Dominic Bramley07/07/2020 13:31:08
8 forum posts

Hi,

Many thanks all for the advice. Seems to have gone OK on the third attempt.

I believe it was a combination of clamping the plates too hard together with the bolt and not getting the hub hot enough.

Dave - tinning the spokes to start with sounds like a great idea and I think i may well take that approach when I do the front wheels. (some time in 2034 judging by my rate of progress thus far!)

The solder paint is certainly merciless and am seeing corrosion already - so am mentally prepared for much cleaning over the coming days. Fortunately building these wheels has already been a masterclass in patience!

Regards

Dom

old mart07/07/2020 16:31:39
1829 forum posts
148 photos

Boiling the wheels after soldering would help to remove the corrosive flux.

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