Member postings for Dr_GMJN

I need to sort out the turning before I can progress.

Do you think a left-had turning tool would be ok - no radius and the flats would be easier to grind? A bit like the boring tool geometry on the round off-cuts Ramon sent me. They seemed fairly easy to get right, although it was on cast iron.

Thanks.

This is the centre drill I’ve got:



Not sure if there are smaller ones, but by the time it gets half way up the cone it looked too big to me. The end is 1.6mm diameter.

The centering bar I made is spring loaded - works fine. Yes, I hold the end from rotating during measurements.

Thanks.

Thanks Jason. I’ll re-draw for 1/2” and treat it as a machining trial.

Im not really sure what you mean by ‘honing’. I’ve got a large ‘oil stone’ for chisels, and some ARC diamond laps, but it seems like whenever I try to clean up a cutting edge, I actually get the angle slightly wrong and end up - probably - dulling the edge. I find it difficult to judge whether the abrasives are actually doing anything, often feels like they’re just skimming across the surface without touching it. The only way I can do it is by trial and error - usually error, and…it just brings me one step closer to packing up the tools and doing something else, when I really want to make progress.

Hmmm bit of a rubbish day on this, with little to show for a lot of effort. Same old story when turning steel - poor surface finish, plus it’s inconsistent. Also, for the lengths and step sizes I need, my HSS tool is too big and clunky - undercut lengths are huge. It didn’t give a very good finish on the actual shaft material either:



I tried re-grinding it, touching it up on the sander to sharpen it, but I don’t really know what I’m doing. There’s no way I can get an accurate tip radii either, and every modification means re-setting the tool height. I’ve reverted to a GT insert, with finishing with wet and dry paper. It gave the same finish, and also gives much neater undercuts.

I’ve concluded that inserts are the way forward for me since I don’t have the experience to consistently grind HSS, and it’s a difficult skill to learn from a book.

I have at least decided to not have centre holes left in the shaft ends - I’ll face them off in the chuck. On a 9.5mm diameter shaft, centre drillings look far too big to me.

Also realised my drawing is no good, since stepping the shaft has given me a middle section bigger than the stock 1/2” material I got. I could use the 7/16” stock, but as discussed before, it’s slightly undersized, and gives 0.002” runout after centering. It looks pretty thin before skimming it to give no runout. The step sizes also become very small. I’ll probably re-draw it for the 1/2” stuff, but ending at 12.5mm or something.

Currently going to cut a new shaft length, and start again. Any advice on getting a good finish obviously appreciated.

Thanks Jason, yes that what I meant. I’m not sure what you mean by back end wants to be free though?

Didn't have much workshop time today, so prepared material for the split main bearings.

Hacksawed the square section brass bar into radius sized pieces (the only size I could get was too small to cut in half and re-solder, so I had to offset the cuts:



Milled them flat, with identical thicknesses:



Tinned and sweated them together:





Them milled the assembly to clean-up the sides:



Centre drilled ready for fitting in the 4-jaw chuck. I did this knowing that the offset from each side to the join was identical, and after checking everything was correct with the edge finder. I thought it would serve as a method of double-checking my centralising of the piece in the 4-jaw; I can centre using the telescopic pointed shaft thing, and also using the dti on opposite faces. Pretty confident it's spot-on though:

One question regarding this: I assume that if this single bar is for both bearings, then I bore all the way through (in order to be able to get the journal lengths fully engaged beyond the crank spigot), periodically checking fit on the shaft? Once parted-off for the first bearing, I'd double-check for fit on the other journal? I assume that the bore will taper slightly, so, assuming both journals are identical diameter, the second bore might need a spring pass or perhaps a few?

Re-worked the shaft drawing slightly, to revise the step lengths to give about 0.25mm float for bearing adjustment. I've also removed the undercut from the first steps adjacent to the eccentrics, since they're no longer needed (nothing abutts them). *ETA I guess I could also eliminate the undercuts at the inner ends of the bearing steps, since they no longer abutt the bearing faces. Would just need a decent chamfer or radius on the inside of the bearing bore?

Just thinking, the exposed shaft each side of the flywheel boss - will it look a bit crappy just seeing a thin gap next to the keys on the left? On the right side my intention is to move the pulley over to contact the eccentric, eliminating the gap at that side. Difficult to visualise how it will look in reality. The left end of the keyway extending into the step also looks a bit bodged, but will ultimately be invisible. Just seems it might look like something wasn't machined quite right (see lower image, basically the area between the left end of the key and the eccentric)...any comments on this area?





Ramon, I pinned the fabricated crankshaft on the 10V without much issue. Pins ended up barely visible:

Edited By Dr_GMJN on 26/08/2022 10:02:24

Yes, bosses on both sides of the eccentric with blend radii to the disc. Drawing just represents the overall width of the part to get the shaft dimensions about right.

Understood about the need for a bit of end float on the bearings. I've modified the cylindrical lengths to give about 0.25mm float, which can be adjusted to zero by snugging the eccentric against the bearing face, the eccentric subsequently being secured with grub screws (the fitting of which has been previously covered by one of Ramon's posts):



(upper geometry new, lower original).

I think we covered securing the crank webs previously, but my intention is to make them a snug fit on the shaft ends and loctite them on during final assembly. I've seen an axial pin put into the interface of the boss/shaft in some applications, maybe this would be a good mechanical solution to prevent rotation, or maybe there's a better method?

Also increases the bearing annulus area by moving the bearing face from the shaft shoulder to the eccentric:



I'm assuming this is what you meant?

Thanks all.

What about using an HSS parting tool, ground with a radius, then do the undercuts to final depth (after roughing to the largest o/d?

Then work on the diameters knowing that the tool will run into the groove and the lengths are already correct?

Ramon - I made a saddle stop a while ago, but probably don’t use it as much as I should. My saddle hand wheel is a bit sloppy, and if using power feed it’s easy to strain the drive when it hits the stop if I do t release the feed at precisely the right time.

Jason - so for the long central length, how do you get an accurate length? Not sure my top slide has the range (will have to check). Do you check for top slide x-alignment with a dti? Mine can turn and just had an angle scale on it with two clamp bolts. So potentially all the careful setup of the tailstock to turn parallel could be negated by using the top slide unless it’s set perfectly parallel.

Edited By Dr_GMJN on 25/08/2022 07:38:45

So regarding the crankshaft. Following Ramon's advice, I had a go at grinding an HSS tool. It's not pretty:





But somehow it did give a very good finish, at least until the 'step', when it chattered like mad. I tried increasing the relief at the sides, but to no avail. Also tried slowing the speed a bit, but again no luck:



Something I've never been totally comfortable with was turning to dimension in the Z-axis. Diameters aren't much problem, but specific lengths I've always struggled with in the absence of a DRO.

This is the basic geometry of the shaft, not checked the dimensions, but they're about right:



So, what's the procedure for getting accurate lengths, and the undercut bits?

Do I somehow angle the tool so that the left edge is perpendicular to the Z-axis, turn to diameter, move along to a scribed mark, the feed inwards and hope for the best?

Also, it was mentioned previously to work at the tailstock end, and turn the shaft to enable both ends to be finished. Presumably this is after the central portion is initially turned to size?

When swapping the ends, is it OK to put the carrier on finish machined diameters (maybe with a thin aluminium packing piece), or should the bar be significantly over-long so that the carrier tightens onto a bit that's cut off later, when finishing to final length? I want to face off the centre drillings to leave clean faces for this one anyway.

Thanks.

Thanks both.

Andy - the sight glass on mine would purely be a visual feature - it would immediately get full of oil, but I’m not too concerned about that so long as oil gets to the bearings.

The wick idea might be good for the big ends, but I guess the plain Stuart type with a cap would suffice (without an actual wick)?

Thanks all, very helpful.

I'll stick with the parallel tube, and the spigot location method because it gives a good shear area for the Araldite to grip. I tried Araldite last night, and this morning the assembly is rock solid.

I'll turn down the centre portion of the 'glass' slightly and polish it back clear, to give the impression of lipped caps (the O/D is currently a bit oval anyway, plus the wall thickness is a bit thick, so all good).

I'll reduce the glass length to 6mm, flatten the upper cap a bit, and add fill and vent holes.

I'll also re-design the necked part at the bottom slightly, cross-drill it, push a tight fitting drill smeared with vaseline down the oil hole, and fill the cross-holes with optically clear Araldite to form the sight glasses.

What is the best way to form the knurled adjuster tops? Do I need a special knurling tool? I've got a crosshatch tool, but it's a bit dodgy.

Thanks all.

All, I'm building a Princess Royal mill engine:

**LINK**

And as a change from machining the larger parts, I am looking at designing a set of oilers for it. The Stuart Turner oilers I used on the 10V are neat, but I guess not realistic since they're open at the top:



So I'm looking at the 'glass' type oilers. In previous posts, Ramon suggested using cut-down acrylic model rod storage tubes, so I found some, and drew one up on CAD:



Before making a set of them, I'm wondering if I'm on the right lines with the design? I've spigoted the ends of the acrylic so that it fits snugly into the brass cups at the top and bottom. I've made a test piece, and although it fits together nicely, presumably it needs Aralditing together, which seems a bit "non-model engineering practice":







Obviously, it needs its lid, and a hole in the base, which itself would be profiled correctly, and a threaded boss added. Intention is to use a small BA screw in the lid for filling, and also, if I turned the threads off and tapered the end, it could actually work in terms of being adjustable. Alternatively I could drill out the screw and use a needle in the centre.

I would design a set of them at different sizes for other parts of the engine such as the crosshead and crank pin, but perhaps accept that on the eccentric, an open type would have to do due to space constraints.

Am I over-thinking this?

Should it just be a cap with a screw rather than a needle valve?

Are oilers at this small scale usually "dummies" and you just fill them with oil?

Is assembling with Araldite acceptable, or should the acrylic be threaded somehow (would be tricky!).

Any suggestions welcome as always (as would be sources of commercially available items of this size.

Thanks.

Continued with the housings, a repeat of the previous process with a few minor tweaks for the additional radii:



I made a spigot to do the O/D, which worked well enough:





I also left the 1mm oil hole until after boring, because last time it caused a flaw when boring the hole:



Milled a pocket for the oiler bosses:



JB welded in place:



And a Milliput “rolling ball” fillet - far more satisfying than in CAD:



Currently awaiting primer:



Next, the crankshaft I guess.

I found my old Museum guidebook, it doesn’t give much more info. The builder is Karl-Friedrich Pohlmann. he also built a model of the Titanic’s engines, but must admit I didn’t notice them in the museum last week:

**LINK**

I can’t find out anything about the builder online. Certainly seems to know what he’s doing though!

Yes I’ve seen the washer stack thing on other marine engines. I expect the axial forces when going from full ahead to full astern are pretty monumental.

Some more general info here:

**LINK**

Yes, a lot of the models at the museum were made by or for shipyards or shipping lines. IIRC Basset Lowke used to build a lot of one-off models like this?

That’s how I understand it. Not much online about the engines, but the German Wikipedia seems to say they were 6 cylinder engines. The UK Wikipedia doesn’t mention them.

Is the additional small cylinder above the 10V the main cylinder, and the lower one a compound?