Member postings for Dr_GMJN

Almost a year later, and I was back in Hamburg. I had another look at the ship engine, and noticed this plate:



Looks like it took him about 6 1/2 years to build. His “Titanic” engine is displayed next to it, and while not as complex, is also very impressive.

Got the taper pins and reamer. Then, while figuring out how to hold the forks and shaft for drilling, found an issue: For some reason years ago I changed the four hole offsets for the slide bars to be further out. I think I might have done this becasue as drawn, the round mounting pillars overhang the inner base walls a bit, and moving the holes makes them look much better.

The result of this is that the overall width of the fork and brass block assemblies needed adjusting by the same amount (about 0.9mm per side). This, I didn't do:





I don't want to offest the sliders, becasue the mounting nuts wouldn't be central.

I could make spacers to pack out the brass sliders, 0.9 mm wide. Since I can't find any images of a real engine having shims or spacers, I'm not really happy to do that.

Seems the only remaining options are:

1) Add (solder or screw) 1mm thick face plates to the outer faces of the brass blocks and re-machine them to match the existing block thicknesses (difficult to set up to make everything square again I guess). Would also require significantly wider slide bars.

2) Solder bosses to the forks (probably look rubbish due to the imperfect concentricity of the turned bosses to the end radii).

3) Make 4 new brass blocks.

4) Make 2 new forks.

I'm erring towards re-making the forks, since as I mentioned before, more substantial bosses would look much better, and I could mill them at the same time as the end radii using the R/T.

All this is a direct result of the fragmented timeline of building this model; I'd forgotten to note it on the slider drawings when I modified the base drawings.

I've got a day off on Monday, so hopefully I can get the new parts made.

OK this is the best compromise I can make for a symmetrical fish-bellied rod. No blend filing shown. It's a 3 degree overall taper at each end (topslide set to 1.5 degrees).



It doesn't look terrible, but overall think I'll abandon that and stick with what's in the plan. It's just that the plan version seemed such a subtle shape that it didn't suggest any real strength benefit over a straight rod.

Sorry Jason I don’t fully understand:

If I start at a shoulder and feed in with a button tool, I’m simultaneously reducing diameter and shortening the rectangular bit. Aren’t the chances of hitting the line, and the correct diameter at the same time pretty slim?

Ive CADed up a fish bellied design, and made the lengths to the blend centres equal. Why would the diameters be different at each end? After all, I’m defining them as the same. The blocks are different sizes, but the blends run into and out of them however they need to.

Yes I guess so. TBH I’m still puzzling over how to get length and diameter both correct and equal on both rods. The tapers have no straight line definition of where the radius runs out.

If I turn to the right small diameter, but the length is wrong, I’d then have to move along into the ends (potentially giving the concave geometry, then out sideways to get rid of that, but that would then change the radius run-out length on the blocks.

Im thinking find the centre of the rod by measuring from one end, then turn the whole circular length to the maximum central O/D, then mark the beginning of the taper onto an area of felt-tipped pen, set the topslide to the correct angle and turn up to the marked lines, then set topslide extension (hoping that by the ends, everything is right and runs out to the blocks.

All that would rely on setting lengths to the drawing, and hoping I can accurately set the topslide to a very specific angle.

Hmm it looks like a 4mm radius at the ends is a minimum in order to get a nice blend without the corners of the bosses being slightly concave with pointy corners (I want the blends to run out over all four faces of each end rather the being a small fillet against rectangular faces.

Thanks Jason. The PR drawings call for a 5/32" radius at each end (about 3.97mm).

Yes, the drawings show a straight-taper rod, but I would like to change this to a fish bellied type, as per Ramon's model.

Thanks Jason, yes I saw the links now.

So as far as I can see the procedure would be:

1) Mill my square stock to the rectangular section of the largest end (the stock I have is oversized).

2) Cut to overall length + c.10mm on each end.

3) Put in 4-jaw, centre drill one end, and extend it out of the chuck to be supported by the tailstock.

4) Mark out the ends of the radii at each end of the round section.

Not sure from here, because I can't figure out how to simultaneously turn the end blend radii to be the right diameter and to the right run-out length at the rectangular bosses. I can't turn to diameter first, because if it ends up being too far away from the end, I'll have a parallel section rather than a taper blending to a radius.

I'm going to get an 8mm diameter button tool for the radii, because I like the look of a larger radius there.

Thanks.

I like the idea of fish-bellied rods rather than straight-tapered, so hopefully I’ll end up with something like Ramon’s engine.

Id like to stick with machined from solid, but where do you fit the carrier if machining between centres? Do you clamp the carrier around the faceplate end, and constantly swap the workpiece as you turn the tapers, hopefully not damaging anything?

Presumably the tapers are done by re-setting the topslide rather than offsetting the tailstock?

Is it a question of marking the start and end of the tapers with a marker and working to scribed lines, then swapping the ends and repeating the cuts?

I think I’ll use the parallel middle and two angled cut method (5 facets in total per rod) then smooth them. I will have to do a drawing to get the marking out right.

Thanks.

Thanks Ramon. Glad to see you posting here again.

The end radii of the circular section rods, where then run out into the rectangular ends.

I might have a go at the connecting rods next. I guess I have no choice but to make a tool for turning the end radii.

I seem to remember some talk about fish bellied rods being more accurate than the plan versions, but can’t find it in the thread. There was some mention about the machining method bring wrong (which I did find), but no mention of the profile.

Maybe the plan is ok after all?

OK thanks, I’ll re-calculate and amend my drawing. I’d assumed the 1:48 taper was along one side only (in plan/elevation view).

I did leave my in-hardened buttons loose, but the jammed occasionally during flatting, hence the damage. I think the forks look ok overall though.

Thanks Jason, that worked ok, although they might need a bit more hand rounding to get them spot-on. The bosses aren’t too pronounced, but they have equalised the thicknesses of the three bits of fork. I won’t bother increasing the side chamfers, because I think they look ok as they are:

Still got to ream them, and I need to get some taper pins and taper reamer ordered. I think now they look much more refined and match the rest of the engine a bit better.

Edited By Dr_GMJN on 09/07/2023 19:02:34

Double- checking, I put 4.6 on the brass block drawing, 4.7 on the forks. I must have looked it up twice and rounded up on one, down on the other, or something daft. Anyway, I assume if I run through them all with a 5mm reamer I can do it by hand? Presumably it will self-centre, or should I setup in the mill?

Re. The face bosses - seems like there’s about 0.3mm excess on the faces compared with the cross-piece, so to make them equal I could machine them leaving the bosses raised. Question is, having filed the rounded ends, I guess I might end up with a step on the radiussed end. Less chance of the if I mill them on the R/T, but easier to setup in the 4-jaw and turn them. Also I’ve not got a milling cutter with a 0.3 tip radius, but I’ve got plenty of turning inserts with 0.2mm radii, which would make a nice fillet.

Any thoughts?

Drilled the counterbores on the fork bosses:



Also chamfered the bosses.

Then drilled the pin holes:



Turns out the pre-ream drill I used was too big, so the reamer didn’t cut anything. I measured the drill at 4.7 (same as I used for the brass sliders), but…anyway.

Made some filing buttons:



And filed the rounded ends:



Then chamfered the sides:



Progress so far:





I suppose I could hand ream the holes and brass blocks at 5mm, (which is about 0.009” more than 3/16&rdquo. I’ve already got a reamer and some 5mm stainless rod. Seems par for the course for me these days to end up correcting something, so no big deal.

Thanks both. Presumably the 1:48 taper angle is per side rather than overall?

Should each end of the pin protrude slightly above the part?

I drew out a 1/16” pin on the fork, and it looks like it would need quite a few diameters and depths drilling to minimise material removal. Should be OK though.

Hmmm autocorrect!

* taper pin and reamer.

Thanks both, I think I’ll get a pin a screamer and do it that way then. I don’t have the plans to hand, but I’m wondering if I can use the same reamer for the crank pin bearing.

Thanks both.

The tool didn’t move in the collet, nor the workpiece in the vice. After it grabbed, and damaged the vice, I was able to continue with much smaller cut depths. The thing is, if you look carefully at the witness mark (which leads to the cut in the vice) it’s a significant depth and distance that the tool dragged itself along. Seems like a load of deflection must have occurred if that was the case.

Re. the forked ends: I think I’ll go with rounding them, and some small chamfers on the boss and shoulders. I can’t make the raised cheek plates without thinning the forks, and I’d rather not do that.

I understand if rounded, the locking bolt hole would be right on the tangent line and wouldn’t look great. Do the taper pins fit in parallel drilled or reamed holes? If I do this, are they drilled with the rods in place? My intention was to drill and ream the forks to 3/16” (as I did with the brass sliders). If this is the case, what’s the best way of holding the rod in place while doing these operations? Do the taper pins have nuts to draw them in (like on the connecting rod crank end adjustment)? If you just tap them in with a hammer and drift, is there a risk of damaging something on assembly (e.g. the slide bars), and how do you disassemble them?

Thanks.