Member postings for Dr_GMJN

So we go again. I did a drawing, and bought some new steel bar (£3.50!)



And turned the O/Ds to profile, and this time with the correct offsets:







Centered them in the mill:



And centre drilled them offset by 1/8”



Set up in the 4-jaw chuck:



Drilled:



Then bored to a location fit on the crankshaft:





Then fitted into the expanding mandrel and machined the bosses. I used a 0.8mm radius tool, which worked well. The steel gave a much better finish than I got with the 10V eccentric. That steel seemed to tear rather than cut:



Then back over to the mill and set up in the R/T for drilling the 90 degree spaced 7BA grub screw holes:

So tonight I spent 6 hours on the new eccentric, only to realise that I’ve made another mistake. I left some excess on the smaller raised eccentric boss length, but then sawed it off and faced it without adding the excess. So I’ve ended up with the right overall width, but the eccentric ring is too far over.

I only realised after setting it up in the R/T to drill the 90 degree grub screw holes:



It was turned, drilled and bored, and was pretty much spot-on. I’ve now used all my mild steel stock, so will have to get some more.

I don’t know whether my concentration is going, or whether there’s something up with me, but I can’t seem to make any progress with anything these days. I seem to be making mistakes at every stage. If I’m honest I’m quite demoralised.

I can only think that because I’m working from both the Stuart Drawing and the Article Drawing, I’ve confused myself. For all other parts, I’ve re-drawn them and converted to metric. I think perhaps doing this lessens the chance of mistakes (for me) because I tend to calculate dimensions I know I’ll need for machining, rather than overall dimensions that need things like offsets calculating.

Thanks Jason. What I did there was, once everything was to the correct diameter and width, I put the point of the tool in the corner, and fed in and along very slightly to form a tiny undercut, to get rid of any radius.

by the way - I re-read your method, using a parting tool to form the diameters. I tried this, but couldn’t get the edge of the tool to cut along its length simultaneously. Moving side-to-side would help, but right next to the raised ring would have been slightly tapered. In the end I used r/h & l/h turning tools, which seemed to work ok.

Edited By Dr_GMJN on 14/06/2023 08:45:24

Started on the eccentric sheaves. Turned down some mild steel to the locating ring diameter:



Marked out:



Then once machined to a perfect fit on the straps, cut it off and put in the chuck for facing and marking out for the eccentric offset. Padded the chuck jaws with paper to protect the bearing surfaces, and it immediately moved in the chuck, snapping the tool and trashing the part. Strange thing is I almost knew it was going to do that, but did it anyway. Very odd:



Second attempt:



Test fit:



The strap halves just lock onto the eccentric when tight, they need a slight gap between the joint faces:



I think this is right, so they can be adjusted for wear, and that’s why the strap caps have lock-nuts.



I’ll leave the sawing and chucking until tomorrow I think. I need to figure out a method of securely holding in the chuck without damaging them. Maybe an aluminium ring.

I wasn’t 100% happy with one of the eccentric strap profiles back in March, and I lost a bit of motivation to make another - they had taken a great deal of time and effort (even to get one slightly wrong!). Anyway, three months later I’ve finally made another, which is spot-on. Also added chamfers to the edges to neaten the bosses up. Just need spot-facing and drilling for the oilers, and they will both be done.

Strange how this one took less than a day, the previous ones took a week or more of messing about. Even considering not having to re-make the r/t fixture, I guess that shows the time it takes me to try and figures things out, plus chasing mistakes.



BTW - what oilers you folks put on these? I’m m thinking the plain brass oilers I put on the 10V main bearings might be OK, although presumably on a real engine e they’d be capped? Thanks.

Thanks Jason,

We ended up making it smooth because the grooves were tiny, and no reasonably sized band would fit. So I turned the grooves off on a mandrel, and formed a recess which both trued the wheel a bit, and made it more suitable for the drive belts that we had..

It’s finished!





Well, this 3D printed version is - it's approximately OO scale:



Jason B kindly gave me the CAD model he's done for his single-cylinder version, and I mirrored it and moved the crankshaft and linkages slightly to form a twin. Then printed a base and wrapped some brick paper around it for a bit of scale.

It's now in place inside a mill building on a work colleague's OO railway (with the flywheel powered by a geared motor and rubber belt).

Edited By Dr_GMJN on 18/04/2023 22:17:19

Set the fixture in the R/T:



And milled the outer profiles:



I used my EBay slip gauges, hot-glued together, to support the tail:



They seem ok - one is a bit off around the oiler pad for some reason. I think the pads are too small for an oil pot, so I guess I will need to spot-face them anyway:



I’ll also put chamfers along the square bolt boss edges.

These are a real pain. I’ve been playing catch-up and chasing my tail with various dimensions ever since the first hole went wrong.

Made the fixture for milling the outside profile:





The central hole is for a 10mm end mill so I can centre it inthe R/T a bit more easily.

Hopefully the clamp load will be enough to hold it together without bolts.

Continued with the straps this morning, marking out for setting up in the 4-jaw chuck:









Zeroed in the chuck:



Bored:



Internal groove turned:



Now for the external milling:



Too cold for comfort in the workshop today, so I’ll start again tomorrow.

I’ll hopefully get to making the eccentrics this weekend. I’ll give the parting tool method a go, although judging the right diameter I think I’ll find tricky.

I’m thinking I might turn the outer side of the ridge first, checking fit with half the strap overhanging, then when it’s spot-on, measure and machine the chuck side to the same measurement.

I’ll hopefully get to making the eccentrics this weekend. I’ll give the parting tool method a go, although judging the right diameter I think I’ll find tricky.

I’m thinking I might turn the outer side of the ridge first, checking fit with half the strap overhanging, then when it’s spot-on, measure and machine the chuck side to the same measurement.

I guess the reason for the separate central ring is to make machining to a good fit easier, since the eccentric boss can be turned in one pass rather from each side?

Presumably though because of the fitted bolts and lock-nuts, a tight fit can to some extent be compensated for?

Thanks guys,

I couldn't find much online, but if's in the OED with a description that matches what I was talking about, then as far as I'm concerned "Fash" is a valid term to use for a rough edge. And "Flash" is reserved for excess material outside a mould or die.

So the first teacher (and my Dad) were right, the second teacher was wrong.

Sorted!

The big dilemma during his engineering revision was sometimes whether to accept what was written in his exam revision notes, or to go with the correct answer.

I think you would be shocked at the incorrect answers which are marked as correct, and vice-versa. Also some of the dodgy things…

For example, in my experience, the hole centre distance of a car engine’s connecting rod doesn’t equal the stroke length. Of course, I’m mistaken.

It’s strange that “Fash” was used by both the teacher (2023) and my Dad (197x), both for engineering type things.

I always understood “Flash” only applied to processes that used a split mould.

Bit of a random one…

I’m helping my son with his GCSE Engineering. He’s been told by one teacher to use the word “Fash” for what I would call a “burr”. Another teacher told him it was wrong, and to use the word “Flash” for the same thing. I’m not so sure that’s right?

I remember my Dad used to use the word “Fash”, IIRC for excess thin plastic on model kits (presumably he meant “Flash&rdquo. He was a very good intuitive engineer, so I wonder if “Fash” is indeed an established term for a burr or other thin piece of excess material? Can it be used for I.M., Casting and general engineering, or…what?

Thoughts? Thanks.

Jason, yes, once I’ve found something that works, I’ll stick with it. As you know I find HSS tool grinding a massive pain in the arse, and will only do it as a last, last resort.

I don’t use the GT inserts for fly cutting, but for most other things they seem to give a good finish and I find them nice to use so…why not? I know the experts might disagree on where and when they should be used, but there we go.

Correct.