Another mess

My incompetence strikes again . . .

Just spent a few happy hours marking out and drilling the frames for a "Henley" 0-4-0T in 3.5" gauge. I was very happy to have pilot drilled all of the various frame holes using the DRO on my nice Chinese mini mill. With that done I thought I'd mill out the space for the horns.

It was all going well and I was feeling quite content until, with characteristic stupidity, I obviously added when I should have subtracted with the result that the rear, driven slot is a beautiful 1" by 1.375" as per the drawing but the leading one is 3mm too wide (I know - metric and imperial).

Is there a way to fill the gap? The raw casting is only a slightly sloppy fit in the oversized gap so I could get away with JB Weld and a bit of luck plus a few ill spaced rivets.

Or I could essentially scarf/tenon in a filler piece that would allow the rivets to 'trap' the insert between the frame in a reduced gap. Not impossible but presumably integrity is reduced???

Or split the casting at the top to allow each side to be rivetted in and then employ a wider axle block to make up the space?? That would marginally shorten the wheelbase but everything else would fit in.

Will the driving forces from the cylinder just mangle any bodging in short order or is there a fix for this?

It should be clear now that I don't want to spend another £20 on frame steel and let's assume mig welding will cause too much distortion primarily because I am very bad at welding. Silver soldering is out. Insufficient kit and trying to avoid buying any new toys.

The right thing to do is to start again. Please don't make me do that. It was all going so well.

As ever any advice (that is within my skill set) gratefully received.

Sometimes I enjoy this hobby BTW. Not now though.

Andrew

I'm assuming this is one piece hornblocks? Quite a lot of designs have separate horncheeks, Emma Victoria and Sweet Pea come to mind. You could just saw your horns in half and fit them to the overwide slots, or make some out of bar, which gives you the chance to keep the wheelbase the same. If you want drawings of Emma Vic horns send me your email via pm

Andrew,

I would go along with Duncan's suggestion as being the simplest solution and avoid the wider axlebox idea like the plague. It will interfere with axle centres and possibly umpteen other measurements.

I made a big error once but it was more easily solved. Not trusting the worn/damaged end of the rule, I marked out my frames starting from the 1" position. Ended up with large hole in frames for exhaust pipe, 1" adrift from correct position. Cure, drill out new hole in correct position and patch plate over original hole. If it was good enough for the GWR to bodge their frames with riveted on plates then it's good enough for me and realistic!

John

Sleeve the casting to the larger diameter?

Bush the over-sized hole and remachine?

I dunno how much ‘meat’ there is available, but it should be a fairly simple choice.?

If it's the slot in the steel frame that is oversize for the casting, which I would guess is probably bronze:

First establish which side - front or rear of the axle - of the slot is the over-cut one. Or if both equally, which will make the next bit easier by making the error symmetrical about the axle centre.

Then sweat a brass shim to the horn-cheek side(s) as appropriate. Since it is only a spacer to fill an unintentional gap between two static parts, and takes no tensile or shear lead, soft-solder would be fine.

I would just make a wider pair to fit your slot from a piece of bar from the material of your choice, they don't take that much work to make, and the photo below shows a pair for a five inch gauge loco, and a pair of L.B.S.C.'s Molly type blocks, that I made from good quality cast iron, but bronze shouldn't be much harder to use.

Regards Nick.

I know how you must be feeling, I have recently spent the best part of two nights machining a universally jointed drive shaft for a device that I am making. I know the device works because it was demonstrated to me by the designer who personally sent me the drawings before he left us a few years ago, but I had my doubts about the proportions given by the dimensions as I proceeded. It didn't seem to me to be robust enough for the amount of power it was going to transmit etc. but I worked on the principle that those who have had designs published must have forgotten more about engineering than I could possibly ever know so I plodded on regardless. And guess what? I was right and the drawing was wrong, the errors must have crept in when the design was published because when I eventually tracked down a copy of the magazine where it appeared the accompanying photographs confirmed the shaft on the prototype device was much more substantial. So I will have to do it my way guided by the photographs I now have, with another doubt and IMO pointless complexity being removed along the way. I don't mind the time and the lessons learnt so much as the waste of material and the expense of acquiring some more. Good job the MMEX is coming up soon to replenish my stock.

Many thanks for your advice guys. Always a privilege to draw on the learnings of better minds than mine.

It looks as though I will attempt to split the blocks as a first attempt and rivet them in as separate cheeks. That is likely to more of a test of skill than the one piece option. Await more questions!

Just to be clear I have effectively created a front slot skewed backwards by 3mm. The knock on effect of using a wider bearing with the hole 'centred' is to reduce the wheelbase by 1.5mm. I think the design will take it.

Or

Fit a wider bearing block but bias the axle hole forwards to where it ought to be. Would such an asymmetrical bearing cause any problems on a small 0-4-0? I think I recall someone on here once describing Henley as effectively a 4 wheeled Rob Roy. 'Proper' wheelbase is 5.75" so losing a 1/16th or so seems preferable to the asymmetric bearing idea but, as ever, I am guessing.

Thanks again guys. I didn't want to buy any more metal.

No - Do Not try to correct the mistake in a way that alters the wheelbase!

That is compounding the error and will lead you into all sorts of troubles.

Even a 1/16" is a serious error you'd need compensate for elsewhere: coupling and connecting-rod centres, piston-rod lengths, say. If the driving-axle is in the wrong place then you start putting the valve-gear in the wrong places.

However you correct the horn-plates, do keep the axle-centres to design.

A pair of asymmetric bearings is not quite Gold Medal winning but as long as the axles are where they should be, the locomotive should still work.

I've only done locos in CAD but I wouldn't mess with the geometrics

Change one dimension and it's usually a nightmare domino effect

If you can MIG then put a small piece into the error zone and tack weld it in

15 or 16 volts

35 Amps

In and out, don't hang about, about one to two seconds per tack weld

A bit of practice on some scrap first, you can hold the workpiece with a gloved finger

The weld will be quite hard compared to the mild steel so tack sparingly, don't lump them in

Good Luck

Do you know anyone with a TIG, or maybe a local fabrication shop that would build it back up for you for a few quid?

Martin.