Sunday, 20 October 2013

VG Construction Tips


Removal of Support Structure


The VG van is printed on end, which results in the optimum surface finish on the roof, sides and one end. Removal of the supports will leave small attachment points on the other end which require cleaning up.

In general, it is best to first cut away the supports from the areas which have small details, and the areas which will be visible on the the finished model with a sharp hobby knife.  (An X-Acto style knife with a #11 fine blade can be useful for the fiddly bits.) Take particular care removing the supports from the brake handles, shunters' steps, and underfloor brake gear.  On the end, take care around the vacuum hose and the vertical and horizontal strengthening angles.  The van is symmetrical so the visible end can be used as a guide to where these items are located on the end with the supports.  On delicate areas, such as the inside the vacuum hoses, it helps to lightly score the supports using several strokes of the knife, rather than trying to cut through in one go.

The brake handles and shunters' steps have "sacrificial" guards around them to provide some protection against breakage during production and shipping of the 3D printed model.  It is suggested to leave these in place until most of the other work has been done to minimise the risk of breakage to these delicate parts.

Once the supports have been cut away from the delicate areas, the remaining supports can be broken away by wiggling them or applying pressure to break the small attachment points.  It is not necessary to remove all the supports from inside the van body as these will not be visible on the finished model.

On the end to which the supports were attached, carefully clean up the remaining small attachment points using various knife blades (A scraping action can help.), fine files and/or sanding sticks.  There is some "bolt head" detail on the lamp irons and near the bottom of the vertical angles, so refer to the other end to determine which of the little "bumps" should be left alone and which should be removed.

Once the supports structure has been removed, the hardest part is completed!

Tapping Holes


The mounting holes for the couplers and bogies should be tapped 2-56 (or 8BA).  As printed, the holes are 1.8 mm dia.  Clear out the holes with a 1.8 mm drill in a pin vice.

Note:  Tapping the holes is preferable to using self-tapping screws which may fracture the material.  Although fairly robust, the material is more brittle than styrene or polyurethane.  

Bogies


Railwest Models sell suitable bogies.

An alternative is American Models S Scale standard gauge Bettendorf bogies which can be regauged to Sn3½ as described on the Sn3½ Blog.

If necessary, adjust the height of the van on the bogies so that the coupler mounting surface is 11.5 mm above rail level.

Couplers


The VG is designed for Kadee "whisker" couplers.  Either the #158 (scale size) or #148 (normal size) couplers can be used, with #262 draft gear boxes.

The draft gear boxes supplied with the #148 and #158 couplers do not fit as they have a different mounting hole position.  The #262 draft gear boxes are narrower and have been used because they allow details such as the brake hoses to be positioned the scale distance from the van centre line.  Also, the #262 draft gear boxes are easier to use as the lid snaps into position.

Note that the height from rail level to the coupler mounting surface should be 11.5 mm, the standard for Kadee couplers.

Handrails


Handrails can be formed from 0.4 mm brass wire.  Starter holes are provided on the side and ends, which should be opened out with a 0.45 mm or 0.5 mm drill bit.

The lengths of the handrails (centre to centre) are as follows:
  • doors (2 per side): 9.25 mm
  • sides (above brake handle): 10.75 mm
  • ends (above brake handle): 11.75 mm

Brake Pull Rods and Hangers



On each side, there is a brake pull rod which can be formed from 0.4 mm brass wire.  Starter holes are provided which should be opened out with a 0.45 mm or 0.5 mm drill bit.  On the brake gear hanger nearest the vacuum cylinder, support the underside of the small lever from the inside when drilling to avoid braking the small lever.  The distance (centre to centre) between the holes is 44.5 mm.

The hangers for the brake pull rods can be formed from brass ministrip 0.8 mm x 0.25 mm (made by North Yard NZ and available from Railwest Models).  Small slots have been provided in the underside of the door track for attaching the top end of the brake hangers.  The brass ministrip should be cut to lengths of 11 mm and 13.5 mm, with 2 mm at the bottom bent over to form a loop to support the brake pull rod.  (Refer to prototype photos for arrangement.)

Floor and Weighting


To allow the van to be 3D-printed in one piece, the underframe is a skeleton only, with no floor.  If desired, rectangles of styrene (approx 1 mm thick) can be cut and glued between the underframe cross members to represent the floor.  Optionally, some or all of these pieces can be cut from sheet lead to add weight to the van.  

With no additional weight, the finished VG with American Models (plastic) bogies weight approx. 78 grams.  The suggested weight for a van of this length is approx. 110 grams (See Sn3½ Blog.).

Moving from the centre of the van towards the end, the dimensions of the "floor" pieces are as follows:
  • Centre: 20.25 x 14.5 mm (2 required)
  • Centre + 1: 20.25 x 14.5 mm (2 required)
  • Centre + 2: 22 x 14.5 mm (4 required)
  • End: 25 mm x 14.5 mm (4 required)
Some of the pieces may require slight trimming around small details.