D95 banana van

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Guy Rixon
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Joined: Sun Mar 27, 2011 6:40 pm

Re: D95 banana van

Postby Guy Rixon » Fri Jan 08, 2021 5:18 pm

While thinking about how to fix the body, I drew and printed the brake assemblies.

IMG_8067.JPG

I was not expecting these to print well, planning to have them done at Shapeways, but took a test-print at home anyway to check clearances. In fact, the home print has worked very well. It seems the Mars Pro is better at spindly things than chunky bits.

The pull-rod in the centre of each assembly seems to have come out thinner than expected relative to the parts with rectangular section. This seems to be a feature of the printer (or the slicing software), that the round parts shrink in on themselves. In a production print, I will thicken that part to compensate.

The strategy, as with the SECR coaches I'm building, is to cut a gap in the cross-member such that the assemblies fit over the axles with the printed pull-rod passing beneath its axle. The rods to the centre crank will be added from wire when the brake assemblies are fixed.
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CornCrake
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Re: D95 banana van

Postby CornCrake » Fri Jan 08, 2021 5:34 pm

Which Bill Bedford W Irons are required for this model?
Steve

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Guy Rixon
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Joined: Sun Mar 27, 2011 6:40 pm

Re: D95 banana van

Postby Guy Rixon » Fri Jan 08, 2021 6:33 pm

CornCrake wrote:Which Bill Bedford W Irons are required for this model?
Steve

I'm using the "1907 RCH" kind, which are my standard fitting for pre-group wagons with 3'1.5" wheels.

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Guy Rixon
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Re: D95 banana van

Postby Guy Rixon » Sun Jan 17, 2021 9:07 pm

IMG_8109.JPG

The brakes needed several tweaks in their supports to get them close enough to the middle bearers, but they are now sorted.
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Guy Rixon
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Re: D95 banana van

Postby Guy Rixon » Mon Mar 15, 2021 5:13 pm

A quantum of progress after a long pause: I got the basic body-shape to print without distortion. This is actually a big step forward.
IMG_8179.JPG

Previously, it was warped in various ways. Now, everything seems to be straight, and the interface to the chassis has come out cleanly. The support line where the roof fits is going to need some sanding, but that's OK.

The difference between this and the failed body-prints is that the walls are half the previous thickness (now 1.5 mm) so the weight of the thing is not pulling it out of shape. I've also supported it better, and print rotated 10 degrees about both x and y (i.e. with one corner uppermost).

It's still not quite perfect, being a scale inch over length. I need to adjust the shrinkage allowance.

The photo reveals that the chassis isn't quite there yet either.
    - The vertical alignment with the headstocks is right, but the buffer height isn't, so I need to move the bearing pads for the axleguards down a bit. Suggests serious brain-fade when working out the initial numbers.
    - There are gaps at the ends of the solebars, so they need to be longer and sanded to exact fit if need be. (Shouldn't be necessary, but.)
    - Why's it warped in the centre? Didn't use to be warped when first printed and cured. Possibly I need to add support brackets across the middle of the body and then force the chassis straight when gluing to the body. Or weight each new chassis down flat for a month while it finishes curing. Or something.
Anyway, onward and sideways.

PS: after posting the above, I realised that I'd tested with the v3 chassis. The v4 chassis already fixed the warping problem, but still has wrong buffer-height by ~0.5mm and some slight gaps at the solebar. Further, I think the axleboxes are keeping the bearings from moving to their lowest position, and this will be reducing the buffer height. Therefore, v5 chassis to be made with a little less deflection in the cosmetic springs and that may be it for the underframe.

PPS (also d'oh): the shrinkage correction only applies after full curing and I'd measured the body before curing. After two minutes under the sunbed it's smaller already, so will probably come out right in the end.
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Winander
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Re: D95 banana van

Postby Winander » Sat Apr 24, 2021 12:30 pm

Found this on the LNWR Society forum. Nothing of major significance but some of interest.

http://www.lnwrs.info/viewtopic.php?f=9&t=330
Richard Hodgson
Organiser Scalefour Virtual Group. Our meeting invitation is here.


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