Can I get away with not soft soldering a saddle tank?

[ngfan]

I'm making the saddle tank for my Don Young 5" NG Hunslet, using laser cut parts from Model Engineers Laser.  These parts are cut from 2mm brass sheet, apart from the end plates which are cut from 3mm plate.  Included are two baffles/strengthening plates for inside the tank.  I am not putting a pump inside the tank, as per Don's design.

In truth I'm not a great solderer (my soldered Simplex side tanks were not particularly pretty).  To help my soldering I used 36 internal brass angles held by 6 and 8BA csk brass screws, and also a few long 8BA csk brass screws to pull the bottoms of the inner and outer plates together.  What I have now got is a very rigid tank, with just a few gaps between plates, and no gaps greater than 25 thou.  It looks pretty neat (by my standards), and I'm now wondering whether I can just seal it all internally with one of the petrol tank sealants that have been recommended, and then level the external countersunk screw heads with filler.

The 2 problems I potentially foresee are (1) The petrol tank sealant won't cope with a 25 thou gap, and (2) Any slight flexing (and I don't think it will be that great) may break the seal.

I know that the use of these sealants in our water tanks is quite common, but I'm interested to know whether anyone has done without soldering.

Any thoughts would be welcome.
John

[flyingfox]

Greetings John, have you considered using epoxy resin, as a sealant. You could make a little epoxy paste to fill your small gaps then resin coat the joints. Epoxy used in the boat/yacht world works well, and a local yacht chandlers could advise you. Make sure the brass is cleaned with emery paper, and remember to use a slow setting resin, because the brass will act as a catalyst.
Regards
Brian B

[ettingtonliam]

Saddle tanks can get quite warm, unlike petrol tanks, so make sure what you use will withstand 60 or 70 degress C

[rrmrd66]

Hi John

Is page 11 of my thread on the Don Young 5" Hunslet build of any use?

I used two different grades of solder to silver solder the joints (see CuP Alloys).

Followed by a tank sealant which appears to have worked well.

Good Luck

Malcolm

[ngfan]

Hi Malcolm,

Yes, I have read your description.  It was your experience that encouraged me to use so many angle brackets.  I was then surprised what a rigid job it was - my Simplex side tanks with their flat sides seem much more "flopppy".  I guess that the curvature of the top and bottom of the tank enhances the rigidity.

The truth is I'm trying to be a bit of a coward, and avoid soldering altogether.  I will do it if necessary, but if my past experience is anything to go by, I'll still have to bung up the remaining pinholes with a filler.

Cheers, John

[JonL]

If I can solder anyone can; my early failures tended to be because it either wasn't clean enough (I wash it with soap, then brake cleaner now), or I thought I knew better and used any old flux. These days I follow guidance better and my results are much more palatable, and water tight.

I think the frost fuel tank sealer is supposed to be very good with quite a good tolerance of larger gaps, but if the gaps are a problem you would fill them from the outside with body filler, then sand them back after? I think its got quite a bit of give. As said before, I don't know what the temperature tolerance is however.

[92220]

Hi Jon.

Never use soap to degrease before either painting, using adhesive or soldering. Washing up liquid, and soap, both leave a residue when drying, that is quite difficult to remove. You would need to use a very strong solvent, like cellulose thinner, and scrub the joint well.

Hi John.

Brian B suggests possibly using epoxy adhesive. If you use one of the epoxys they use for fixing car bodies to chassis, with no other fixings, it will work well I would guess. If you do go down that route, I have used Araldite 2021-1 adhesive, which drys quite quickly, compared with others I've tried, and it has a massively strong adhesion when fully cured (after 24 hours).

Bob

Edit:  I forgot to say, structural epoxys, like Araldite 2021-1, are quite expensive compared with the 'everyday' epoxys, and you need to buy a few extra nozzles. These epoxys use pre-mixing nozzles so they are one time only use. I just let the adhesive harden in the nozzle when I have finished a job, and put the adhesive to one side till next time. Next time I want to use it, I unscrew the nozzle and fit a new one. They can only be fitted one way so getting hardener and epoxy muddled up is not a problem.


Bob. 

[JonL]

Every day is a school day.... That being said I hadn't noticed an issue, perhaps my use of the brake cleaner was getting rid of the residue

[92220]

That could be. Actually, I've not tried brake cleaner, but probably it is solvent based, and formulated to take off most nasties!

Bob.

[ettingtonliam]

Thats interesting about the effects of soap. Many modern paints tel you to wash the brushes after use in warm soapy water.

[JonL]

Nov 2, 2021 12:58:02 GMT 92220 said:

That could be. Actually, I've not tried brake cleaner, but probably it is solvent based, and formulated to take off most nasties!

Bob.

Brake cleaner is fantastic stuff; gets all the grot off without damaging (most) paints. A very good degreaser, but very volatile and smelly. Obviously its worth reading the COSHH datasheet before you use it, and test it on an area you don't care about first.

[Gary L]

Nov 1, 2021 23:05:44 GMT 92220 said:

Hi Jon.

Never use soap to degrease before either painting, using adhesive or soldering. Washing up liquid, and soap, both leave a residue when drying, that is quite difficult to remove. You would need to use a very strong solvent, like cellulose thinner, and scrub the joint well.

Hi John.

Brian B suggests possibly using epoxy adhesive. If you use one of the epoxys they use for fixing car bodies to chassis, with no other fixings, it will work well I would guess. If you do go down that route, I have used Araldite 2021-1 adhesive, which drys quite quickly, compared with others I've tried, and it has a massively strong adhesion when fully cured (after 24 hours).

Bob

Edit:  I forgot to say, structural epoxys, like Araldite 2021-1, are quite expensive compared with the 'everyday' epoxys, and you need to buy a few extra nozzles. These epoxys use pre-mixing nozzles so they are one time only use. I just let the adhesive harden in the nozzle when I have finished a job, and put the adhesive to one side till next time. Next time I want to use it, I unscrew the nozzle and fit a new one. They can only be fitted one way so getting hardener and epoxy muddled up is not a problem.


Bob. 

I suggest you investigate polyurethane sealants. They stick very well, and can be used as adhesives. There are many different makes and recipes, but a builders’ merchants will have a selection in stock, applied from a cartridge gun. Advantages over epoxy are greater gap filling and flexibility, less sensitive to surface preparation, cheaper and don’t require mixing. Mostly they moisture-cure, so residual water or damp is not a major problem. Finally, they are a little less likely to give you dermatitis (though the moisture-curing means they stick to skin like -er- glue. White spirit will remove it if you catch it before it has cured.) They take paint well too, though most paints can’t match the flexibility of the polyurethane substrate, so avoid
painting large areas of it. (Do not confuse with silicone or acrylic sealers in similar packs, which are very inferior products)

Most epoxies do not like elevated temperatures, though this is not likely to be a problem with any water tank. Properly applied, epoxy makes a tough, strong joint, but it is a bit unyielding, and a heavy smack might break the bond. This wouldn’t happen with a polyurethane sealer, because as well as adhering well, they are extremely flexible.

HTH

Gary

[Gary L]

Nov 1, 2021 16:22:19 GMT flyingfox said:

Greetings John, have you considered using epoxy resin, as a sealant. You could make a little epoxy paste to fill your small gaps then resin coat the joints. Epoxy used in the boat/yacht world works well, and a local yacht chandlers could advise you. Make sure the brass is cleaned with emery paper, and remember to use a slow setting resin, because the brass will act as a catalyst.
Regards
Brian B

Genuinely curious about this comment re catalyst action of brass on epoxy. I've used a lot of epoxies over the years but never come across warnings about this or noticed the effect. On the other hand, brass and copper are known to retard the setting of Polyester resins, so when it is necessary to embed 'yellow metal' in GRP, the advice is to encapsulate it in epoxy first. Grateful for any further information.

Gary

[92220]

Nov 2, 2021 13:19:41 GMT ettingtonliam said:

Thats interesting about the effects of soap. Many modern paints tel you to wash the brushes after use in warm soapy water.

I would guess that is for water based paints, which are not generally suitable for most model engineering projects. 

Bob.

[ettingtonliam]

OK,point noted.
Now how do you regard lighter fluid (for cigarette lighters) for degreasing. Its very good for cleaning clock mechanisms, but does it leave a residue?

[92220]

Nov 2, 2021 21:01:49 GMT ettingtonliam said:

OK,point noted.
Now how do you regard lighter fluid (for cigarette lighters) for degreasing. Its very good for cleaning clock mechanisms, but does it leave a residue?

Hi.
Lighter fuel can be made up of various different solvents and other chemicals. It is good at removing greasy surfaces, whatever it's chemical composition. However, depending on what it's formula is will have an effect on whether it leaves a deposit or not. Because it is not intended for use as a cleaning agent, I would be careful about using it as a degreaser before painting, and would recommend using cellulose thinners if on a metal surface, or white spirit or turps substitute for normal modelling plastics. Some other plastics can be quite safe when cleaned with cellulose, so it is important to check a hidden area before risking it's use on any plastics. If degreasing a pre painted surface, ALWAYS check a hidden area unless you know the paint is resistant to cellulose. Generally, domestic paints are either water based or white spirit based, so should only be degreased with white spirit. Isopropyl alcohol (IPA) can also be used on white spirit based paints, but a test should be made if being used on a waterbased paint. Some are resistant to alcohol when fully cured, but some are not.

Bob.

[miken]

For degreasing I would suggest using an actual proper degreaser like automotive panel wipe. This is what car body sprayers wipe down bare metal with before spraying a car. Obviously the metal must be perfectly contaminant free before they spray or all the preparation is wasted.
After using it for making your tank you can then use it for when you eventually come to paint it.
You can buy it from your local automotive paint supplier or, I bought a 5 litre can off ebay.

[JonL]

I've used that too, and a 5 litre can goes a long way. I used it when respraying my GT6 and even then barely used a litre for the whole car.

[92220]

Nov 3, 2021 17:28:48 GMT miken said:

For degreasing I would suggest using an actual proper degreaser like automotive panel wipe. This is what car body sprayers wipe down bare metal with before spraying a car. Obviously the metal must be perfectly contaminant free before they spray or all the preparation is wasted.
After using it for making your tank you can then use it for when you eventually come to paint it.
You can buy it from your local automotive paint supplier or, I bought a 5 litre can off ebay.

Hi. Actually panel wipe is not as good as cellulose thinners, at degreasing, and cellulose is generally cheaper. Panel wipe is basically a mixture of isopropyl alcohol (IPA) and distilled water. There are also some greases that IPA has a hard job cleaning. Cellulose thinner will clean all greases. Just one point...It doesn't matter what solvent is used for degreasing, or for any other job, for that matter, if you get it on your hands, wash them afterwards, and use a moisturising handcream.

Bob.

Edit:  The other reason IPA is the basis of Panel Wipe, is that it can be used on any kind of vehicle paint without doing any harm, where cellulose thinner would attack some vehicle paints. That is not a problem when using on bare metal, as for most model engineering degreasing jobs.

[ngfan]

I think I'm going to use a polyurethane sealant to fill the obvious gaps up to 25 thou, then use a petrol tank sealant to block the tiny holes. Finally I'll level the countersunk screw heads with a car body filler.

However, first I've set up a little test piece. I've held 3" by 1" pieces of 2mm and 3mm thick brass sheet at right angles 25 thou apart with brass angles, and filled the gap with polyurethane sealant. When the sealant is set I'll take the angles off, and see how the sealant is performing, particularly with regard to adhesion to the brass.

I'm about to go off for a week's holiday, so the bonding should definitely be at full strength when I return. I'll report the result.
John