Sunday, 20 October 2013

CXB Construction Tips

This page is applicable to CXB's produced from October 2013.  For the "original" CXB design available in limited numbers prior to October 2013, refer to earlier Construction Tips.

Removing Support Structures

Carefully remove the support structure from both parts of the wagon.  It is suggested to use a sharp knife  carefully cut the supports away from the roof, ends, and the underframe.  Take particular care around the brake handle, brake hoses, W-irons, brake shoes and remainder of brake rigging, and the shunters steps.  The end of the brake handle and the shunters' step have a "sacrificial" guard to reduce the risk of breakage during production and shipping.  You may wish to leave the guards in place until the majority of the assembly work has been complete to minimise the risk of breakage.

Because of the fine ribbing on the brake hoses, the 3D printer's automatic software has generated many support points, which have merged into one.  Carefully cut between the brake hose and the support structure, using repeated cuts with a sharp knife (e.g. Olfa snap-off blade type or X-Acto knife with #11 blade), to separate the support structure, then carefully trim the remnants from the hose.

Interlocking Parts
Note that on the underside of the roof, alternating ribs extend a short distance beyond the edge of the roof to interlock the two parts when it is time for final assembly.  

The support structure extends inside the upper and lower decks of the wagon to support the inside of the wagon sides.  From the outside, cut through supports attached to the small circular brackets for the horizontal wires above the side planking on each deck, on the underside of the roof, and the underside of the middle floor.  When you have cut as many of these supports as possible from the outside of the wagon, gently wiggling the supports structure (e.g. with needle nose pliers) from the open side, will break the remaining supports and allow pieces of the structure to be torn away. Be careful not to apply excessive force to avoid damaging the side planks and door areas.

Once the majority of the support structure has been removed, carefully go over both parts and cut away the small supports which typically extend from one part to another, for example, around the brake rigging and between the frame members of the underframe.  An X-acto type hobby knife with a sharp pointed blade (Exacto #11 or similar) is quite useful for getting into the nooks and crannies.

Go around the surfaces of each part where they will join together, and smooth off any remnants of the fine supports, on the roof, ends, middle and lower floors, etc.  A sanding stick or small file can be useful for this, but be careful not to damage the projecting parts which are designed to interlock.  Also remove any remnants from the very ends of the projecting parts.  When you think you have finished, test fit the two halves together.  Interlock the roof ribs first, then gently bring the underside of the wagon together to see how it fits.  There are four frame members in the underframe which have retangular pins which fit into oval holes in their opposite number (a variation on the square peg in the round hole concept). 

If the two halves don't close completely, dismantle again and check for and remove any tiny bumps from the support structure attachments.

Near each end of the wagon, there are small tabs designed for 1 mm x 3 mm long pan-head self tapping screws, to secure the two halves of the wagon together.

In the long term, you have the option of gluing the body together, e.g. with superglue, or continuing to use the screw fixings.  A half-way option is to just glue the roof area together, which would allow the join in the roof to be smoothed off, but would probably allow the underframe to be separated enough to change wheelsets, should that be necessary in the future.

As part of the clean-up stage, remove the four W-iron/axlebox assemblies which are attached to the rest of the wagon by four cylindrical supports (and probably some smaller supports).  It is suggested to "nibble" through the supports with fine sidecutters rather than trying to cut through in one go.  Once freed, the remnants of the supports should be cleaned up from both the W-iron/axlebox assemblies and the wagon sideframes.

Tapping Holes


Tap the coupler mounting holes 2-56 (or 8BA).  As printed, the holes are 1.8 mm dia.  As you tap the holes, sight through the gap between the lower double floor layers and stop when the end of the tap hits the upper floor.

Note:  Tapping the coupler mounting 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.  

Adding Wire Detailing


Several lengths of 0.4 mm brass wire are required as follows:
  • A - 59.5 mm, above timber side rails, 4 pieces per side
  • B - 13.5 mm, above timber side rails, upper deck only, 2 pieces per side
  • C - 12 mm, upper doors, 2 pieces per side
  • D - 24 mm, lower doors, 2 pieces per side
  • E - 28.5 mm, upper door top guide, 1 piece per side
  • F - 25 mm not including 90 degree bend on one end, brake pull rod, 1 piece per wagon
The holes for the above have all been incorporated in the 3D-printed model.  The holes for the horizontal rods above the side planks have a nominal diameter of 0.6 mm.  If a wire does not go in easily, do not force it.  Clean out the hole(s) with a 0.45 mm or 0.5 mm drill bit in a pin vice.  The holes for the wires in the doors and the upper door top guide are smaller, and will definitely need cleaning out with a 0.45 mm or 0.5 mm drill bit.

Also using 0.4 mm wire, form the handrails which are located vertically on the ends of the wagon, above the brake lever and shunter's step.  The spacing between the holes is 6.5 mm.

W-Irons and Compensation Options


Either of the readily available etched brass W-irons can be used, i.e. the "closed" or "open" style.  These are available from Railwest Models.

"Closed" (left) and "Open" W-irons.  Photo courtesy of Railwest Models
Remove the W-irons from the fret, fold them up and fit brass bearings in the usual way.

The underframe of the wagon includes eight small holes at each end for mounting the W-irons, using 1 mm x 3 mm pan-head self tapping screws, although each W-iron requires only two screws.  (These are available from DCC Concepts part no. DCS-PH103.)  

(Of course, you can glue the W-irons in position if you prefer, in which case the holes and grooves included in the underframe help to locate the W-irons in the correct position.)

Different sets of holes are used at each end, depending on the type of W-iron used and whether compensation is desired.  Note that if using compensation, the rocking W-iron is positioned at the end of the wagon opposite the brake handle so that the rocking action does not interfere with the brake handle.  The various options are:

Open W-Irons, No Compensation

Use the pair of holes at each end which are closest together (7 mm spacing) on the wagon centreline.  Slide the W-irons (without wheels) sideways into position between the brake shoes, and fix them in position with screws.

Open W-Irons, Compensation with Screws as Pivot

Use the same holes as described above for no compensation, and fit the W-iron at the brake handle end without modification.  However, at the end opposite the brake handle, remove the small brass tabs which project from the top surface of the W-Iron which then allows the W-Iron to rock sideways slightly using the fulcrum strip built into the chassis.  After tightening the fixing screws on the rocking W-iron, back them off slightly to allow it to rock.  It may be necessary to open out the etched holes in the W-iron slightly with a 1.1 mm drill bit or fine round file to obtain free movement.  

Open W-Irons, Compensation with Wire Pivot

At the brake handle end of the wagon, use the 7 mm spaced holes on the wagon centreline and fit the W-iron without modification.

At the end opposite the brake handle, remove the separate pivot bracket from the centre of the W-iron and fold up the ends to match the etched holes in the W-iron.  It may be necessary to bend the ends slightly more than 90° to minimise slop in the rocking W-iron.  The plan is to use the holes in the pivot bracket to secure the rocking W-iron to the wagon, using the pair of holes on the axle centreline spaced 7 mm apart.  

As per the intended W-iron assembly procedure, pass a piece of brass wire (e.g. 1 mm diameter) through the pivot bracket and the corresponding holes in the side of the W-iron, and solder the wire on the outside only to the pivot bracket.  Check that the W-iron can move freely with respect to the pivot bracket.  Trim the excess wire from the outside of the W-iron, and file the wire and solder until it is almost flush with the sides of the W-irons to allow it to be slid sideways between the brake shoes, and fit two screws into the holes in the pivot bracket.

Closed W-Irons, No Compensation

Use the fixing holes which are located on the axle centre line to fix both W-irons into position.  One W-iron fits the holes which are 15 mm apart, while the other fits the holes which are 7 mm apart.

A styrene spacer approx. 0.75 mm thick will be necessary to achieve the correct height of the wagon above rail.  On the end of the wagon opposite the brake handle, the spacer will need to be in two pieces to fit either side of the raised fulcrum strip.

Closed W-Irons, Compensation

At the brake handle end of the wagon, use the fixing holes which are located on the axle centre line, 15 mm apart, to fix the W-iron into position.  A styrene spacer approx. 0.75 mm thick will be necessary to achieve the correct height of the wagon above rail.  

At the end opposite the brake handle, remove the separate pivot bracket from the centre of the W-iron and fold up the ends to match the etched holes in the W-iron.  It may be necessary to bend the ends slightly more than 90° to minimise slop in the rocking W-iron.  The plan is to use the holes in the pivot bracket to secure the rocking W-iron to the wagon, using the pair of holes on the wagon centre line spaced 10 mm apart.  To allow clearance for the screw heads, file or grind a hollow in the side of the W-iron.

As per the intended W-iron assembly procedure, pass a piece of brass wire (e.g. 1 mm diameter) through the pivot bracket and the corresponding holes in the side of the W-iron, and solder the wire on the outside only to the pivot bracket.  Check that the W-iron can move freely with respect to the pivot bracket.  Cut the centre of the brass wire out, to allow access for the fixing screws.  Cut the wire initially at a 45° angle to avoid forcing the sides of the W-iron apart, then cut the remaining section out leaving just enough to form the pivots for the rocking action.  Also trim the excess wire from the outside of the W-iron, and file the wire and solder until it is almost flush with the sides of the W-irons to allow it to be slid sideways between the brake shoes.

To allow the pivot bracket to sit flush against the bottom of the underframe, grind away the raised fulcrum strip.  Then, fix the W-iron in position with two screws.

For all W-Iron options:

Fit the wheels (26 mm axle length) and check that wagon sits at the correct height above the rails, i.e. the coupler mounting surfaces should be 11.5 mm above rail level, and adjust if necessary.

After checking that the wagon runs happily, fit the cosmetic W-iron/axlebox assemblies to the outside of the brass W-irons.  It will probably be necessary to clean out the holes in the W-iron/axlebox assemblies with a 2 mm (or slightly larger) drill bit to fit over the brass bearings.

Weighting


With no additional weight, the completed wagon including wheels and couplers weighs around 38 grams.  The "desirable" weight for a 4-wheel wagon is around 65-70 grams to ensure optimum operation including operation of Kadee couplers.

Addition of a Marbelup Models sheep load in Aluminide material adds approximately 24 grams, bringing the total weight up to around 62 grams.

If modelling an empty wagon, the weight can be increased by gluing lead shot or sheet lead between the various frame members of the underframe, where it would not be seen in normal operation. 

Painting


Either enamel or acrylic hobby paints can be used to paint the finished model.  

If desired, the interior of the wagon can be painted (airbrushed) prior to assembly.  Experience to date suggests that this is probably not necessary as overspray from painting the outside tends to take away the "bare plastic" look on the inside surfaces.  

Obviously, if a sheep load is to be included, it should be added after spray painting the wagon itself. Tamiya XF-78 Wooden Deck Tan is a reasonable colour for the sheep load.

Once the wagon is completely assembled, the join line on the roof can be filled and smoothed off. The join lines on the ends are virtually invisible as they are aligned with the angle iron end braces.



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.



Saturday, 5 October 2013

WAGR WMD Hopper Wagon

First Test Print of WMD (no added detail)
Due to popular demand, Marbelup Models has created a WMD version of the WMC iron-ore wagon.

WMD's were used to carry coal, wheat and talc, and roamed widely over the rail network including the Metropolitan, South-West, Great Southern and MidWest regions.  The photo below from the Rail Heritage WA Archive shows one being shunted at Narrogin.


WMD's could often be found in general goods trains compared to WMC's which ran in dedicated block trains in iron-ore traffic.  WMD's were painted both in grey, the same as WMC's and later in Westrail yellow.  For more information on the prototype, see the WA Wagon Pages.

The expected price of the WMD (body only) will be about AU$95, subject to exchange rate variations.  The reason for the price difference compared to the WMC is simply the additional volume of resin used to print the hungry boards, as the costs for this particular 3D printing process is based on the amount of material in the finished item.  3D-printed bogies are available for $30 per pair, not including wheels.


Friday, 4 October 2013

CXB 4-wheel Sheep Wagon

CXB Sheep Wagon after added detailing and painting

CXB Sheep Wagon available to order Now!


Marbelup Models has revised the design for the CXB Sheep Wagon to comply with the changed i.Materialise print specifications, so the CXB is now available to order.  The price is approx. $105 each, subject to change due to exchange rate variations against the Euro.  3D-printed sheep loads are also available for $15 per wagon (90 sheep) or $30 for 2 wagon loads (180 sheep).

The revised model has slightly coarser details than the model shown here, due to the change in print specifications from 0.3 mm minimum detail size to 0.5 mm, although the difference in the finished model is barely noticeable.  The revised model has been designed to accommodate readily-available etched brass W-irons, but cosmetic axleguard/spring units will be included in the 3D print.



The 3D-printed model includes:
  • Floor detail include double floors on upper and lower decks
  • Roof including rain strips and downpipes
  • Detailed axleboxes and springs
  • Brake shoes and vacuum brake cylinder 
  • Vacuum brake hoses
  • Brake lever
  • Shunter's step
Most of the photos show the model after detailing, but prior to painting.  The grey parts are produced by the 3D printing process.  As always, click on any of the photos to zoom in.

To complete the model, the modeller will be required to add:
  • Wheels (12 mm diameter 4-hole or disc, 26 mm axle length)
  • Etched brass W-irons (available from Railwest models).
  • Brass bearings (e.g. North Yard 2 mm diameter, pinpoint)
  • Couplers and fixing screws (e.g. 2-56). Recommended couplers are Kadee #158 with #262 draft gear boxes.  Note that the #242 draft gear boxes, supplied with the #158 couplers, have a different mounting hole location and are also too wide to clear the brake pipe.  If preferred, Kadee #148 couplers can be used with the "full size" knuckle rather than the "scale" knuckle.  Both the #148 and #158 are "Whisker" couplers.
  • Self tapping screws for fixing body and W-irons - 1 mm x 3 mm pan head, 6 required per wagon. (DCC Concepts DCS-PH103).
  • Brass wire (0.4 mm) for horizontal rods in body sides and doors, upper door guide rods, end handrails, and brake rod.  3 lengths are required per wagon.
  • Glue, paint, decals, etc.
The model consists of two unequal "halves", with a vertical join running end to end.  This will allow access to the interior for painting and adding a load of sheep, if desired.

The two sections are 3D-printed on their sides, which results in a good surface finish on the roof and outside surfaces.

For help with assembly, see the CXB Construction Tips.  For information on the prototype CXB's, see the WA Wagon Pages.