This year I decided to build one for real. This involves a whole level of commitment higher than I put into my prototype, both in terms of money and time.
I spent a few months looking at how to go about this, reading articles and blogs from all over the place. If you boil it down an oven really had 3 key ingredients: the base, the skin and the insulation. There is lots of discussion about the shape but I think the dome shape really wins and the math is pretty well understood (there is a mathematical relationship between the height of the door and height of the oven).
The decisions are largely technical and there is great advice all over the place. I made my decisions based on what I could get hold of locally and my budget. The key decision was about the actual dome and I opted for one made in clay.
I chose clay because I had a pottery supplier nearby who sold clay that was premixed with sand specifically for pizza ovens - the thought of having to mix and muddle what would be about 75 kgs of clay did not appeal. I had previously purchased a bag of the clay in question so I knew what it was like to work with and decided that it would be more pleasant that working with a refractory cement, which was the other option.
The building of the base went well as did the dome and I stood back and looked at my creation with a bit of pride. Everything had gone according to plan and actually within my time estimates too. A for execution.
Then it all went wrong.
This was the first time I had worked with clay and everyone talked about leaving it for a few days before firing it for the first time. I waited for 2 but very quickly realised this was no way near long enough. I came to this conclusion when I saw some cracks forming. Frantic searching about this revealed it was nothing out of the ordinary and to be expected in some cases.
I slowed the fire but the damage was done. The cracks continued growing and once it was all cooled I realised the scale of the problem was pretty big.
Time to find a happy place.
So my sprint went well but what my team had put together did not meet expectations. The team had done all they could to know just enough to get started - we ask teams to have courage as well as be transparent when problems arise. We need a retro to find out what happened.
"What went well this sprint?"
The techniques we used worked well. The clay dome came together quickly and was structurally sound. The base retained heat well too.
"What didn't go so well?"
When we fired the oven, cracks started to appear. By the time we cooled the oven down the cracks had grown significantly, one of which is very wide. We did not factor shrinkage into our design either, so the dome is smaller than we thought it would be.
"What caused the problems we experienced?"
The big problem was that we did not wait long enough before firing oven. The guides were very loosely worded which we never questioned - our clay needs a lot longer to dry before being fired! By firing too early, the water in the clay formed too much steam which had to escape forcing its way out by creating cracks. There is a good chance we created too big a fire, too quickly. In conjunction with being too eager to complete the dome, these combined are probably the root cause. The sand mould we used should have been bigger to take account of shrinkage, which was not something we considered.
"What could we have done to stop this happening?"
If we had done some black hat thinking we would have found out about what happens if you fire to early. Searching for cracking and repairs would have given us the information we needed. We could have talked to someone about what a "series of small fires" actually is, which is very subjective! We should have talked to the pottery people more, who suggested that we should not be too eager to fire the dome. We could have quantified this with them - I thought a couple of days WAS enough! The shrinkage could have also been quantified with the pottery people.
Now thinking like the PO, I still need to realise the value in work we have done. What are our options?
The engineers view is that the dome is bust. There is a stonking great big crack in it. We can patch it but it will never be 'right'. We know how to do it better, we should kill it and start again. If we don't fix it then doing the insulation layer would be a waste of money - if the dome fails then we will have to destroy the insulation layer to get to the dome, wasting more money.
The shrinkage is not a large problem but there is a gap between the dome and the arch which will need to be addressed.
The insulation is definitely a problem, well described by the engineers.
Thinking like the SM, we need to generate some options. If we are unsure about the dome, is there an alternative to the insulation that requires less investment? Is there a way we can return some value from our oven without investing more into it?
If we did the bare minimum and made 10 pizza's this weekend before the dome failed would that be better than investing more but delivering a 1000 pizza's over a much longer period of time? Would we loose anything by patching what we have? What could we learn by doing this and how long would it take?
A more interesting question: What happen's if don't do anything? Do we know the dome will fail or suspect it will? Could we add more insulation at a later point if we find out what we have is actually OK?
We are often divorced from the money when we do this for a living but if you behave like it's your money then maybe your thinking is different. Seeing the sprint as an investment and asking what gives the best return is often a great way of getting people to think about it differently. I often use this with teams in retro's instead of using dot voting.
In this case I am the engineer, the PO and SM. And it's my money on the table. An I still don't have yummy pizza! As much as I hate the mistake I made, I can also see a half way house that allows me to get some value from what I have along with some more learning without additional investment. I might have less options in the future but I get some value now, which is a compromise I am happy to accept.
If I have to make another one, you can bet it will be awesome.