The eastern street of the warehouse district had a different noise from a week ago. The loading rhythms were still there, carts, voices calling counts, bay doors swinging on their hinges.

But underneath all of that was something new.

The hollow thud of shelving being broken apart, the tap of stone being fitted into stone.

On the roof of one of the eastern buildings, a crew was adding a chimney stack, and the mortar smell reached the street before the building itself came into view.

Beorn walked the length of it on his way in, ledger under his arm. Charcoal was already moving across the margin with the absentminded habit of a hand that worked while the mind was elsewhere.

The two buildings on the eastern stretch had been cleared of their contents, the first with its loading bay doors removed and a timber frame braced in the opening.

Two men were inside the hole, arguing about where to put a second support beam.

"It wants to be closer to the left side," one of them was saying. "That’s where the load’s going to come from, and you want it to-"

"It wants to be in the middle, Ead. That’s how a beam actually works."

"That’s not my name."

"Not the point."

The second building was farther along. The chimney addition was nearly done, with two men on the roof and the rest of the crew below passing up the last course of stone.

The man at the bottom kept count in a patient voice of who had been keeping count for three hours.

"Last one!" he called up. 𝒻𝘳𝘦𝘦𝘸ℯ𝒷𝘯𝘰𝑣ℯ𝑙.𝘤𝑜𝘮

A man on the roof looked down and answered, "You said that two hours ago."

The man below did not stop stacking. "I meant it both times."

Beorn marked a note in the margin and kept walking.

The district’s existing warehouse workers and the new construction crew had been into the coexistence of people thrown together in the same space for different reasons. They stayed politely separate, occasionally joining up when something needed two pairs of hands, otherwise giving each other room.

The old workers moved around the construction materials the way water moves around stone. nobody needed to be told.

The new foundry was in the second cleared building.

The furnace stood against the far wall with the draft ports Beorn had specified, and the ceiling above the casting floor had already turned darker from the test fires. The original color of the beams was gone.

The smell was iron, heat and char, the smell that had come to mean something was being worked out.

Wynn was at the workbench, arms crossed over the day’s output. He looked up when Beorn came in and did not bother to greet him.

"Crossbow heads are fine, we are within range on those. Quarrel tips are good."

He moved along the bench to the next set of pieces. "The flintlock barrels stock are bad, four in ten are passing check. The rest are coming out oval, or the bore wanders off center before it finishes."

"And cylinders," Beorn said.

Wynn shook his head once. "We haven’t started cylinders. No point running the pour when I already know what I’m going to get."

Beorn did not argue with his opinion. "What have you tried on the barrels?"

Wynn answered simply.

Slower pours gave a marginal improvement, but not enough to make up the production difference against the time cost, and longer cooling did not change bore shape. He had started checking every mold before the pour instead of spot-checking every third.

That helped more than anything else, but it still did not help across a full shift, because by the end of the day the molds were being packed faster, the crew’s hands were tired, and the packing showed it.

Beorn set the ledger on the bench and opened it to the working page. The charcoal moved while he listened.

"The mold casting is the first thing to fix," he said when Wynn finished.

He tapped the page once with the charcoal. "The molten metal is taking the right shape in the sand, that part is working. What isn’t consistent is how firmly the sand is packed around it. We’ll standardize the process, then every mold will be the same, and the casting will start right."

Wynn picked up one of the molds from the bench. He looked at it as if it was a piece of a puzzle.

"Some of my guys press harder than the others. I reckon that’s the problem then."

"Indeed," Beorn said.

Wynn set it down and picked up the second. The surface was flat and even.

"I packed this one myself this morning."

"That’s what four in ten looks like," Beorn shrugged.

Wynn stopped to think over the mold for a moment without performing. There would have to be a new step that checked the first pack of every shift rather than the finished output.

Two additional checks per shift. Roughly thirty minutes each.

Wynn was noting the cost, not objecting to it.

He would do it.

Beorn marked it in the margin.

Then he moved to the far end of the workbench where the boring tools were laid out. The bar, the cutter, the housing without a way to advance it at a steady rate.

He had been looking at it since the problem first showed itself, with five crossed-out theories in the ledger.

Every one of them had failed for the same reason. The tool went where the iron let it, not where it was told to go.

After Aestrith woke up, he was finally able to concentrate on the problem, the knowledge was there before he pushed for it. He had written the thought down without examining why it had come so easily. He had not pushed to find out.

He picked up a bolt from the workbench.

One of the ordinary ones scattered around any working foundry, used to fasten the bench frames.

He held it out to Wynn. "What makes this go through a nut at a fixed distance every turn."

Wynn looked at the bolt. Then he picked up a spare nut from the bin at the end of the bench and threaded it on.

He turned the bolt. The nut traveled. He turned it again. The nut traveled the same distance.

Wynn looked at Beorn.

"The grooves on the screw."

Beorn explained. "Each full turn moves the nut forward the same amount every time. It doesn’t matter whether the nut turns easily or with resistance, it doesn’t matter what’s around it. One turn equals one fixed distance because the grooves never change."

Wynn turned the bolt slowly, one full rotation, watching the nut arrive at exactly where it had to.

"The cutting tool sits inside a frame."

Beorn continued. "Now imagine a long rod carved with the same kind of spiral grooves. The frame grips those grooves from the inside, and when the rod turns, the frame is forced to move forward. One turn moves it the same distance every time."

Beorn picked up the bolt and turned it slowly between his fingers. "You choose that distance when you carve the grooves, and after that the rod does the movement for you automatically. It doesn’t matter whether the tool is cutting soft iron or hard iron, the movement stays the same."

Wynn set the bolt and nut down. He was quiet for a moment, the practical quiet working out how to build something rather than whether to build it.

"The rod needs to be long enough to run the full bore," he said.

"Correct."

Beorn gave him the dimension for the V3 engine cylinder. He already had it in the margin.

Wynn asked three more questions in sequence.

What material for the rod. How the frame would attach to the bar. Whether the spiral grooves needed to be cut before or after the rod was hardened.

Beorn answered the first two and said the third was Wynn’s call. He had more practice than Beorn with how iron behaved in a foundry.

Wynn turned to the man working the rear section of the bench. "Hobb."

Hobb looked up from the piece he was fitting.

"I need a rod, length of my arm, iron stock. Bring it over."

Hobb set down what he was doing and went to the stock bin without asking why. That was how Wynn’s crew worked.

By the time Beorn left, the rod was on the bench. A chalk line was wrapped around it at the spacing they had discussed, and Wynn was explaining the process to Hobb in the stern tone he used for all instruction.

The first pass on the project was scheduled for the next morning. If it came out close enough, they would run the frame along it. If not, they would adjust the spacing and start the next rod.

He walked out into the afternoon.

The district was visible from the doorway in its half-made state. The chimney crew on the roof was packing up their tools. The two men who had been arguing about the beam had resolved it in favor of the left side, and the beam was up.

The mortar scent had spread over the block.

He was turning to leave when motion caught him at the foundry’s back corner. A figure came out of the side door quickly, taking the southern street, small build, apron tied at the waist.

He watched Tam disappear around the corner without seeing him.

He looked at the district for a moment more, at the half-built chimneys and the new street cobblestones stopping two-thirds down the block where the paving crew had left off when the conversion work began.

Then he told his guard it was time to go, and started walking toward the citadel.