The prototype of the group body is done. Although there are a few minor surface blemishes, the overall finish looks to be on par or better than the two vintage groups that I have. Certainly, the lines are a little crisper. A closer inspection of the photos indicates that there may be an issue or two to address with the secondary machining processes. I've requested a few more photos and some QC measurements. The part may have to go back for a little more machining before it is shipped.
The goal of this project is to build an 'update' to the aurora, which is my favourite vintage single group machine.
There are several variants of the aurora, at least four that I know of, which were imported to in North America by various resellers. I am lucky enough to have two of them. The one in the picture in my first post was made in Milan and imported to Canada. The one below, with a different boiler and HX, was restored by Orphan Espresso. I believe that it was assembled and sold in the US by Termozona, a company from Connecticut, who added the "Europa" branding. I'm not sure how much of the case of the Europa is original, but the design and build quality on the European import are better.
Dividing the machine into its component assemblies, the plan at the moment is as follows:
Group - everything that I have read about this group is positive. The main casting contains over 7lbs of brass and consequently has plenty of thermal mass to maintain temperature stability. It makes a killer shot and I prefer its aesthetic qualities over other lever designs I have seen. Consequently, this, apart from a change in a few of the materials for reasons that I will go into later, will remain faithful to the original design. As this part of the project is the most difficult, this is where I am starting.
Boiler - after the group, the boiler is, imho, the most important part of the design as it determines how well the whole machine performs. Here again, I want to stay true to the original design while benefitting as much as possible from the performance improvements that are offered by contemporary control electronics. So, much as I like the project that EspressoForge is leading that pairs an Ascasa Thermoblock with a lever group, I am going with an old school boiler and heating element, with an HX.
Control - this is the area where there is the most room for improvement over the original design which, depending on whether it is an autofill variant or not, uses a Gicar and Sirai pressurestat. This last is a rather blunt instrument with a deadband, when it is new, of around 0.2bar (considerably wider when the diaphragm of the stat gets old). Although I may start with a pressurestat as it will work "off-the-shelf", ultimately the control will be handled with some flavour of micro-processor which will drive the element using an SSR. A starting point for this may well be EspressoForge's combination of the arduino + TC4.
Autofill - yes. Fairly straightforward with a solenoid valve.
Sight gauge - not currently planned. The sight gauge adds a lot of complexity to the plumbing and the case design which would be eliminated by providing feedback from the water-level sensor with an LED.
Case and chassis - with the goal of making a commercial quality machine that can live on the counter top in the kitchen, I am going to try to slim down the profile and footprint a little while remaining faithful to the styling. The drip tray and sump designs also have room for improvement.
One particularly cold February morning, I got up to discover that the auto-fill circuit on my Brugnetti Aurora had failed. As I opened up the Gicar controller a few days-without-proper-morning-coffee later to figure out what was wrong (an old and faded capacitor), I realized that I had now either fixed or maintained every system on the machine except the lever group. So I took that apart too and replaced the spring and the gaskets. As I was putting it back together I started wondering about what it would take, given that the original Brugnetti company no longer exists, to make more of these fantastic machines.
A few days ago, after nearly three months of research, drawing, discussion and negotiation, I received these photos:
... a wax positive of the group body which, over the next few days, is going to be encased in plaster and replaced with molten brass.
The photos are also a sign, at least to me, that this project is now well and truly underway and that it is time to share it with the generous people on this forum, whose advice I have greatly benefited from since my obsession with coffee began. I am a long, long way from a working machine, but you have to start somewhere.
So I decided to undertake a non-destructive conversion of my King 10x36 Gear head. Not replacing the acme screws with lead-screws means that the mechanical conversion is pretty easy. Backlash and precision are not going to be great, but they may be good enough for the application. Time will tell.
Here is the saddle with the compound and the cross slide removed.
The lead screw is 5/8 x 10tpi acme. This has always been the weak point of this machine. It seems impossible to torque the acme nut to the compound and have the acme nut correctly adjusted to eliminate unreasonable backlash. Fixing that would likely require replacing the bearing, mount and probably also the nut and screw. More trouble that I think it is worth going to at this stage.
A shot of the existing screw and fixed bearing assembly. The double nuts at the end of the journal bearing are a very poor solution as counter-tightening the second nut tends to dramatically alter the load on the bearing.
I'll be using 5mm HTD timing belts and pulleys from SDP/SI (who have a very useful pulley designer on their site) rather than direct drive for this build. The X axis is the tricky one as the pulley plus the belt and the cover have to fit under the cross-slide. I was trying for around 2:1 advantage, but couldn't quite get there on the X. The configuration for the X is 13 double flange : 22 no flange with a 60 tooth belt. The Z is 19 df : 38 nf with a 77 tooth belt. Three of the four hubs all had to be re-bored to the correct shaft size. The 13 tooth was a total pita.
A 6A25M022NF1508
A 6R25M060150
A 6A25M013DF1506
A 6A25M038NF1510
A 6R25M077150
A 6A25M019DF1508
The disassembled fixed bearing and, at the bottom of the shot, the journal extension with a 0.3745" stub, a section of M10 x 1.5 thread and a 0.5000" shaft to receive the drive pulley.
Here, the existing threads have been cut off the end of the lead screw journal and I'm just about to centre drill, drill out and ream a 0.3750" hole that will receive stub of the new journal extension.
A little loctite and a coffee break later and the new journal is done.
All finished except for a cover (which turned out to be a little hard than I thought and after a couple of false starts isn't done yet). Note the brass nut replacing the double M10 nuts. This can be tightened to put just the right load on the bearing and then locked in place with a set screw. I dropped a little brass slug into the set screw hole before torquing it down to avoid damaging the screws on the journal.
The stepper (an Oriental Motor PK296DAA I think) and the mounts just fit inside the splash guard. A couple of final thoughts... There is an alternative to this mounting position as the King has an excellent gear box on the saddle to power either the Z or the X axis. Mounting the motor on the drive shaft of the gear box instead of directly to the end of the X lead screw would be very easy. While taking the X axis fixed bearing apart and reassembling it a few times I realized that, in addition to it being the least well-built part of this machine, it also isn't really intended to handle radial loads. While the motor and timing belt aren't particularly large loads, they still shouldn't really be on this bearing. If this proves problematic, I can either attempt to replace the whole bearing assembly with something better off-the-shelf, make a housing for the existing bearing that will handle the load or move the whole shebang to the gear box drive shaft. I decided not to go this route at the start because the gear box will induce considerably more backlash.
