Deep internal threads in big bronze parts - rough the bore first or turn the OD first?

On big bronze work I've had better luck boring the pilot hole first, then roughing the OD, then letting the whole thing sit overnight before any finish passes. I did a big C954 sleeve for a dredge customer last year and the difference between finishing same-day and finishing the next morning was enugh that I could actually hold size. Bronze holds heat longer than you'd think, and a paint-bucket sized chunk is still warm deep inside hours after you stop cutting.

My sequence now is pilot bore, rough OD, then bounce back and forth for the finishes. Doing the finish bore last also seems to help, since the ID is what the customer usally checks hardest on these parts.

On the chips, yes, you recoup real money. I keep a dedicated barrel just for bronze and aluminum chips and the local scrap yard takes them separately. It won't come close to covering what you paid for the stock, but on a job like yours it's a meaningful chunk of change back, expecially if you keep coolant out of the pile or drain it well. Wet chips get discounted hard at most yards. One habit I picked up from an old timer: rough everything with the same tool pressure pattern on both ends of the bore so any spring settles evenly. Seems superstitious but it's worked for me on three of these monsters now.

I'd push back a little on the overnight wait. On my old LeBlond I did a couple of big bronze bushings for a sawmill customer, maybe half the size of what you're describing, and I never got good results from letting stock sit. What actually worked for me was bouncing back and forth like you mentioned as an option. Rough the OD, rough the bore, then go back and do a light finish pass on each with the tailstock end supported while there's still meat in the bore. Bronze moves around less than aluminum but it still walks if you hog one side and leave the other for hours. The bore opening up toward the far end in your case sounds more like tool deflection and heat from the long boring bar than from the order of operations. I fought the same thing until I started taking three shallower passes instead of one heavy one, and backing off the last ten thou to a spring pass. Also kept a fan blowing across the part. Crude but it worked.

On the chips, around here a scrap yard pays decent money for clean brass segregated from steel. Last load I hauled in paid enough to cover a set of inserts. Worth a call before you write them off.

That growing-at-the-far-end thing got me once on a long bronze gland nut. Turned out it was the coolant warming up through the cut, not the stock. Ran the finish pass dry with a fresh honed tool and the bore stayed dead straight. Only takes a few minutes on a piece that size anyway. Also, on the chip money, don't let the shop hands toss bronze in with the steel bin. Seen that happen at a place I worked years back, guy just didn't look. That mistake costs more than any scrap payout covers.

The thing that finally tamed a similar job for me was the finish tool itself. I was chasing a long bronze nut bore for weeks with whatever insert was in the drawer, always getting a slight taper toward the back. Swapped to a fresh insert with a bigger nose radius and took three spring passes at the same setting instead of one heavier cut, and the bore came out the same at both ends for the first time. On a chunk that heavy I also snug a steady rest on the OD for the finish work so the part can't nod off center while the tool is way down in the hole.

One thing I learned doing long bores like that on the old Monarch: the bar itself is half the problem. Sag and deflection a foot deep into a paint-can sized chunk is way worse than anything the stock is doing. I used to slip a heavy junk bar or a sleeve over whatever I had and rig a follow rest if the machine would take it. Made more difference than anything else I tried.

Also, on the scrap side, keep the big solid drops seperate from the chips. The yard pays alot better for clean solid bronze than for turnings, so save your cutoffs and ends.

Update: tried the dry finish pass with a fresh honed tool like the coolant guy suggested, and the far end of the bore stayed straight for the first time on a job this size. That was the culprit all along. Still chasing the last bit of bellmouth right at the entrance though. Do you guys chamfer it off or just let the customer live with it?