Does brass distort when heated up to silver solder?

Hi,

I'm making a hand pump for my locomotive and have run into a problem.

I have fabricated the body from brass. The cylinder is 3/4" OD with 1/2" bore. I reamed the bore.I silver soldered the the parts together which included the cylinder to the rest of the pump. After soldering I went to put the piston in and it did not fit. I measured the ID and it was 0.3mm out of round.

i tried to squash it back into shape and I could for the 15mm or so but I could n't true up the bit furthest in.

I'm going to replace the cylinder and have made a new one. I didn't want to end up with the same problem after I've soldered it.

So I was wondering if brass normally distorts like this?

If so is there something I should have done in the set up to stop it distorting e.g. put a piece of 1/2" bar in the cylinder when soldering?

Regards,

Greg

Why don't you solder first then ream?

Any joining process that involves molten metal cooling to room temperature will cause residual stress in the area of the joint. This is because the metal solidifies at a high temperature then shrinks as it cools down to room temperature. This shrinkage is similar to the effects seen with bi-metalic strips and the forces can cause distortion in the assembly. If you machine something with large stresses after it has cooled the stresses can equalise out in a new distorted position, stainless steel has a large coefficient of expansion so suffers from this if too much heat is used when welding. Stress relieving can help in some cases. All you can do with your assembly is leave material to be removed after the joint is made and do the final work when it is cold. You may find some movement occurs in the material as some is removed. For instance if you were turning a diameter you may find that the amount removed does not result in the expected diameter.

Martin

Hi John,

Good idea but it's a blind hole and I only have a hand ream which is tapered at the end and so the part furthest in would under size.

Hi Martin, that makes sense. The amount of distortion surprised me.

Here's what the pump looks like. I'm not sure how I could finish the machining off after soldering. What do others do when fabricating such a thing?

Apologies for the upside down photo. It's from photobucket for some reason it flips it when posted in here.

Greg

Edited By Greg H on 11/12/2016 09:14:41

Half inch machine reamers are cheap cheap these days. You can also buy a good British brand name used reamer on eBay even cheaper and usually they are still plenty good enough for home use. Will ream pretty much right up to the end of a blind hole.

Silver solder first, ream later is the only way I can think you will get the job done.

Or make yourself a D bit from silver steel.

I've never made anything so small, but when I worked in engineering pretty much any fabrications that required accuracy would be welded first, heat treated then machined. On large pressure vessels the amount of movement post heat treatment, was sometimes staggering.

Could you not have soldered first and then bored out on the lathe or mill ? I realise it would be a bit awkward to hold the part, but that flat base should give a good start.

i guess you might be able to clean up the existing bore by boring out slightly larger and making a new piston, or sacrificing your existing reamer and chopping the tapered portion off.

Did you have the parts clamped together when you soldered them?

The metal will be a lot softer at read head and the pressure from a clamp will be enough to distort the part.

Hi Jason, no I just had it sitting in place.

If I buy a machine reamer how will I know how far from the end it will be 1/2" diameter?

Edited By Greg H on 11/12/2016 10:12:17

Greg

Total flute length will be at marked diameter except for the small bevel at the end to provide the lead in required.

Emgee

Or a D bit - will cut right to the end. A fiver from Tracy Tools.

Or make you own....

That sounds ok.

Ok then sounds like they only way is to assemble and then ream after. So I'll have to buy myself a new reamer.

Thanks all for your advice,

Greg

A bit of a side issue but, I notice there isn't any link arrangement to prevent the piston twisting in the bore as the pump is operated. Isn't the piston more often a longer parallel ram connected to the lever by a link?

I went with a different design to how most are done. This design allows the cut out in the loco tank to be made smaller. It is similar to a car engine with gudgeon pins.

Got a reamer on ebay. $9.20 AUD with delivery included. So about a fiver Can't work out how they make it and also post it for that.

**LINK**

Unfortunately delivery is estimated at between 3 Jan and 23 Jan

Edited By Greg H on 11/12/2016 11:13:01

Edited By Greg H on 11/12/2016 11:13:38

Edited By Greg H on 11/12/2016 11:14:12

Hi Greg,

An interesting design of handpump.

I think you just had bad luck with the pump cylinder.

The cylinder is a bit on the thin side which probably hasnt helped.

Note that after silver soldering, brass will be annealed, and not the best material to use.

A gunmetal casting is available. If you dont want a double acting pump you can use the casting provided for your County Carlow loco.

Cheers,

Julian

Hi Julian,

I thought a smaller hole in the tank would be nice, but there's a bit more in the design and I do feel it may be a bit more fragile than a standard pump.

I knew brass was not a great choice but didn't have anything else at the time and had my doubts as to how successful the pump would be and so was keen to try it out.. I might use a bit of gunmetal for the new cylinder.

I also perused all the hand pumps castings on reeves looking for something suitable, but thought by the time it got here I could have made one, and I did, it just wasn't that successful.

Hopefully mark II is more successful.

Edited By Greg H on 11/12/2016 11:41:12

Hi Greg,

I would take a skim off the inside of your fabricated body with a boring bar, then lap the bore and make a slightly bigger piston.

Peter.

Hi Greg

This is a problem I too have encountered. Here is how I solved it. First plan for a thick wall, 1/8 minimum after reaming. Lay barrel flat and put in place the joining web (hold it any which way you can), apply heat evenly and solder in place. Be sure not to use higher temp silver solder or the whole thing might just melt! Now put in 3 jaw and drill/bore to the desired undersize for reaming. Next solder the base plate in place - the previously added web will help stop things distorting - apply heat to the outside of the base but dont clamp anything as if you do it will surely distort. You can then add the end section and hand ream as described by others. When I make mine I tap the end and screw on the ball valve section to do away with the risk of any distortion after fitting the base. If you go down this route you can solder it all together and then bore and ream in the lathe. I also always add several O rings and find that they are 100% reliable. Hope this helps.

Slightly unrelated but on the opposite scale of problems with brass, I happened to be reading an excerpt from my home machine shop book I bought from the states which talks about ball pein hammers being used to physically harden brass and copper by beating it with the domed side. Hence why you have to keep reannealing shaped material out of brass and copper.

Michael W