Boiler part 3 - brew reservoir weldup

Everything seems slower in August. The weather is good, the city has a relaxed atmosphere and somehow, sitting indoors in front of the computer is less attractive than it is in February. I do have some progress to report however. First, the brew reservoir is pretty close to completion. I tack welded on a couple of pretty hefty lugs that will carry the whole load of the boiler when it is attached to the frame. Then I brazed the G1/4" fitting in place. The fitting, by the way, was cut and tapped on the lathe from lead-free Ecobrass hex stock - which, though a little more difficult to machine than leaded brass, turns out to be pretty good. I have done quite a bit of soldering in the past but never any silver brazing - so I was exited to see how this would work. The white gunk in the before shot is flux which prevents atmospheric oxygen reaching the metals in the joint and oxidizing them as they are heated. Using an oxy-acetylene torch, the base part is heated evenly until the assembly reaches the melting point of the brazing metal (~1145 to 1650°F (618 to 899°C) depending on the brazing alloy). Just like with soldering, once the right temperature is reached, the liquified braze is drawn into the joint by capillary action. The hard part is actually to not overheat the joint - the oxy torch is a powerful beast - that and the cleanup afterwards which is a royal pita. This part just needs the final structural welds on the lugs and then it can be welded to the boiler tube.

Boiler part 2 - boiler tube

So, on to the boiler tube!

This is a piece of 6" schedule 40 316 stainless pipe. It looks quite innocent and happy on the lathe in the picture. Cutting it, however, was not so easy! It is held at one end nicely by the six-jaw chuck from the inside. The other end, however, is completely unsupported. As it isn't even sort of round, it can't be clamped externally, so the only way to hold it is with an elaborate internal expanding plug - which would take a day or so to make. As this is a part which will likely be laser cut when I need more of them, I didn't want to go there. So, with the lathe on dead-slow and taking extremely light cuts (0.001" per revolution) with a carbide parting tool I cut it unsupported. As the setup is not even sort of rigid, the tool tends to chatter a bit, which has the effect of resonating and ringing the tube like a bell. REALLY LOUD! Even with heavy ear protection, I could feel my back teeth buzzing. Still, it did a good job and the end result is a very clean edge about as perpendicular to the walls as you can get.

Boiler part 1 - brew reservoir

Over the last few weeks, along with spinning a few other plates, I sent out for some stainless parts for the boiler. I decided to go with an all stainless construction because, even though it is more expensive than copper alloys, it is far simpler to get the parts made. A copper and brass assembly would have required at least one, possible as many as three separate castings, plus a whole lot of hand fabrication; expensive and time consuming. The laser-cut stainless parts were delivered in seven days after I placed the order.

Clockwise from the top right - the flange to connect the group to the boiler, the boiler flange, bolt circle flange and the fixed end flange.

First the group flange has to be drilled out to the correct minor diameter and then tapped. Starting with the tap held in the drill press to make sure it goes in straight and then finishing by hand. 

The brew reservoir that sits behind the group flange to provide preheated water for the chamber is made from a small section of schedule 40 stainless pipe. The square end is cleaned up on the mill and then a radius is added to the opposite end which is rough cut at a 30 degree angle.

Then we fire up the tig welder to put a structural fillet on the outside of the joint and surface butt-weld to seal the inside. Welding, I am convinced, is good for the soul. A little buffing with a wire brush and the part is ready to receive the lugs than will hold it to the frame. Then the assembly can be welded onto the boiler tube. I also realize, while writing this, that I am missing a hole in the wall of the reservoir tube to provide an inlet for the water from the HX. 😶   It wont be terribly useful without that.

Test of the group body prototype

At the end of last week I received the prototype of the group body from the foundry. There was a little confusion with the shipping and the package got left on the doorstep of my office overnight! Very fortunately, despite spending the night on a busy street, it was still there the next morning. I have taken quite a few measurements and, although there are a couple of small problems, I am very pleased with the result. I put the new body into my stripped-down machine with the rest of the original group parts to limit the scope of the testing. The first results were a little worrying: even after a good warm-up, there was a constant flow of water past the lower piston seal. I took a closer look at the piston and decided to replace both seals, which, though they were working fine in the old group, are a couple of years old. Success - no more water past the seal. My suspicion, though I haven't tried to measure this yet, is that there is a certain amount of error in the alignment of the cylinder bore with respect to the top of the group. If the axis of the bore isn't perpendicular to the surface that the rest of the group parts are bolted to it will mean that the axis of the piston wont be parallel with the axis of cylinder. It also makes sense that a pair of cylinder and piston parts that have lived together for decades would generate a unique wear pattern on the seals. I may also add a PTFE (Teflon) guide ring to the piston which will greatly increase the concentricity of the piston with respect to the cylinder.

Finding a good fit for the portafilter seal was another small adventure. The groove for the seal has a couple of out-of-tolerance dimensions which will have to be addressed in the next production run. This means that there is less space (both axially and radially) than is needed for the generic 73mm x 57mm x 9mm Viton seal. To solve the problem for now I found an 8mm silicon seal for another machine (rancilio silvia i think) which is considerably softer and fits quite nicely. 

To make a a long story short: I made coffee on Friday. With old beans and without re-calibrating the grinder the results were actually pretty good. Now that the body has been tested, I can start on the rest of the group parts.

Handle blind nut

The last part of the day is the blind nut that holds the handle onto the lever. I would much prefer to purchase this part, but the closest equivalent I have found thus far is an internal Allen drive nut from McMaster, but because they are esoteric, they are expensive. However, the machining operations requiring different setups don't have to be done sequentially, so knocking out a bunch of these would be pretty quick.

I couldn't resist putting the three parts together.

Lever handle

The retainer plate took a long time to setup - nearly four days, most of which was getting up to speed with the cam software. Now that it is done, I decided to do something easy and rewarding.

Compared to brass alloys, of which there are quite a few, the array of engineering plastics out there is eye-watering. I presume that the lever, portafilter and valve handles are injection molded thermoplastic, but what kind I do not know. As designed, the valve handles cannot be turned on a lathe. The other two can be cut from stock quite efficiently however. My intention is to use black Acetal resin for the lever handle, but I only have white on hand - and they ain't gonna be white. I did have a rather nice piece of mahogany which has been waiting for a purpose for quite some time. It wasn't quite big enough in one dimension, so I split in two and laminated it with some birch plywood. 

You're not supposed to cut wood on a metal lathe because the dust quickly contaminates the oil film on the moving parts, but with a cover over the ways and a vacuum nozzle close to the cutter, I can contain the dust almost completely.

Profiling complete.

After the cutoff operation, the work piece is now unsupported at one end, so enlarging the bore is done with tiny cuts.

With a little sanding, some tung oil and about an hour and a half from start to finish including cam programming its all done! The new handle next to the original.

Retainer plate part 2

The foam test completed, I can move on to cutting the actual part.

With a small production run in mind, I made a jig to hold the stock which is then prepared with six holes, two for alignment with 1/4" dowel pins so the stock can be removed and replaced if necessary, and four threaded holes for the M8 screws that are required in the finished part and will do double-duty holding the stock to the jig.

The part after the program has run. The jig is intended to be semi-ablative - so the tool can cut past the part into the jig and I can skip the step of flipping it over and removing the base that would normally be held directly in the vice. However, there is another small offset error that left 2mm on the bottom of the part that had to be removed. 

A little clean up with a file and we are done.  :D  There are still a few small refinements to be made in the cam programming, but next time I should get it all right! For now, this one is close enough.