This has kept me out of mischief for a day or two

[Timleech]

The tug I've been working on, off & on, for a few weeks needed new bronze shells in one of the shaft bearings. It was an obvious move to say that I could do the job, there's nothing exceptional about it, but I hadn't quite realised how much it would stretch the capacity of my kit. It really was right at the limit at what I could have done unless I got involved in making special steadies etc.

Finished size is 5.5" bore, 11" long, it sits in 'saddles' in its iron housing of 6.5" dia with flanges at either end.
I'd ordered a piece of bronze 1" over length to give me something to get hold of, plus I could only get 5" bore without a wait of a few days, so it was a heavy lump of metal to hang off a chuck and I needed to get some weight off it ASAP especially as it was too big for my steady. Faced & skimmed out both ends & then supported the outer end with a rotating tailstock chuck:-



Then decided the extra inch could be managed without, so parted it off, & then rough bored from either end & then set up the 'blank' in the mill & sliced in two:-



Next soldered the two halves back together & started the finish machining. My 17" DSG lathe is not in its first flush of youth & wouldn't give a very good result on an 11" long bore (I can improve it when I get a chance to dedicate a bit of time to it!), so I decided to do this in the CVA.



Trouble was, I wanted to do inside and outside in one setup but the dia was too great to go over the saddle of the smaller lathe, so I managed to do the OD at one end & then it was back to a careful setup in the DSG to finish the OD, then a couple of minutes with a spring hone to smooth the bore:-


http://home.btconnect.com/duttondock...lowblock-4.jpg

Finally, split the two halves, & put the top half in the mill to slot it out for the oiling rings:-




The final pic shows the bottom half in its final destination, waiting for the shaft. Unfortunately the block casting had been mounted on resin blocks cast in situ, this must have been done with a worn bearing so now it's a few thou too high, we've had to turn the block over and grind a bit off the resin and the next stage will be to shim it back to height.

Tim

Re-edited so that four images now show (the limit!) and the fifth can be seen by clicking on the link.
Tim

[wierdscience]

The pics look good as does the work!

Always fun working to the limits of a machine,chuck jaws clearing the ways by a film of air while generating a breeze make one feel alive

[quadrod]

great job, pic's worth a thousand words. hate to ask but what did the bronze cost?

[Mcgyver]

Nice work Tim, little different than building a stuart turner enginer eh?

[Timleech]

great job, pic's worth a thousand words. hate to ask but what did the bronze cost?

About £300 stg, a bit over $500.

I did get a better quote back after I'd given up waiting and confirmed the order, but that would have involved a couple of days' wait and this was local, off the shelf.

Tim

[mark61]

Now and then I/we end up using a boring bar to do outside work when part is too big for machine. It works but you can go hogging off with it.

mark61

[Timewarp]

Tim, love to hear about big boat stuff! This tug has the inboard end of the shaft directly in contact with the bronze bushing? What is shaft material?
Can you describe the whole driveline, how a tug deals with thrust loads from the prop etc??
Thanks - just installing the driveline (universal shaft) for my own boat project!
Paul L

[Timleech]

Now and then I/we end up using a boring bar to do outside work when part is too big for machine. It works but you can go hogging off with it.

mark61

I'd considered using the boring bar on the outside, but on balance reckoned the best bet was to reset the job in the bigger lathe where I could whizz off the surplus in no time.

Tim, love to hear about big boat stuff! This tug has the inboard end of the shaft directly in contact with the bronze bushing? What is shaft material?
Can you describe the whole driveline, how a tug deals with thrust loads from the prop etc??
Thanks - just installing the driveline (universal shaft) for my own boat project!
Paul L

The driveline is a bit over-complex, as it's adapted from when the tug was steam powered.

The shaft has been turned down (from ~6" to 5.5") for the bearing.
There is one other similar bearing just ahead of the stern tube, and between the two is the original Michell thrust block which carried the prop thrust in steam days. This still acts as a support bearing, but the forward thrust collar has been removed. The aft collar has been retained apparently as an insurance policy, as there's evidence that the gearbox half-coupling has a history of coming loose on its taper, and if it broke free the consequences could be very serious.
The prop thrust is now carried in the gearbox by a big double-race spherical roller bearing.



Edited to add that what we know as EN8 or 080M40 (1040 to you??) is commonly used for shafting, but I don't know for certain what this is.
Tim