Building a Large Curved Trestle on a Grade – Part 5

Part 5 – Building the Beam Assemblies

The Beam Assemblies

There are two beam assemblies each made of eight 3/8” x 1½” beams spaced equally with angled braces as shown in Figure 1. These rest on short bents attached to a full-height bent. Bents #8 and #12 rest on these beams. Two additional beams run between the main assemblies, running through bent #10.

Figure 1 Beam Assembly

Figure 1 Beam Assembly

As there are only two of these I will not build a jig. Each beam has a 7.5-degree angle at each end, matching the bent angle. A full-size paper plan was glued to acrylic with a washable glue stick to keep it flat. The cuts are measured directly from the plan by putting a beam in place and marking the location. I also used some ½” square stock cut at the same angle for blocks to reinforce the beams and provide attachment points to the support bents. Photo 1 shows beams and blocks on the plan.

Photo 1 Beams and Blocks

Photo 1 Beams and Blocks

The beams and blocks are first glued in pairs, then the pairs are glued and finally the two halves are joined as shown in Photo 2.

The beam assemblies were then glued and nailed to the support bents. Note that the beams are NOT square to the bents – the bents are square to the workbench. Finally, the bent resting on the beams (also not square to the beams) is glued.

Photo 2 Beam Assembly

Photo 2 Beam Assembly

Adding Girts

Photo 3 Bent 7, 8 and 9 Assembly

Photo 3 Bent 7, 8 and 9 Assembly

Following RGS practice (on this bridge), there is 1 girt in the center and 1 near each end of every sill except the mud sills. So there will be 3 girts per story between each pair of bents. Because this bridge is curved, every girt will have angled ends (3.75 degrees), and mostly different lengths. The ends of each girt is notched a bit to better hold the bent in position. To accurately measure the length, a 3/8” square girt is positioned completely covering one sill, and marked where it crosses the other sill. I used a mini-hacksaw to cut a slit 5/16” from each end and a hobby knife to make a vertical cut. A quick pass with sandpaper finishes the notch. In theory, I should be able to mass-produce each size I need, but in practice I’ll not be surprised if each one is unique.

Figure 2 Beam Detail

Figure 2 Beam Detail

This assembly is fairly rigid. The bent 7, 8 and 9 assembly is shown in Photo 3.

Cement Board Base

Figure 3 Base Layout

Figure 3 Base Layout

Transfer plan Figure 3 to 2’ x 3’ cement boards. Use rip

ped Trex 2×6 for footings glued down with Gorilla Glue. Before gluing footings, use the lines to locate and drill holes from the top for screws driven from the bottom to secure the footings. Drill holes in the mud sill and the Trex for brass pins. Photo 4 shows the base after gluing and screwing the Trex footings.

Beam Assemblies

Photo 5 shows the two complete beam sections ready for assembly in the railway. Photo 6 shows the prototype bridge beam sections.

Photo 5 Beam Sections

Photo 5 Beam Sections

Photo 6 Prototype

Photo 6 Prototype

Weekend Project

This Memorial Day weekend, I did a small, non-train project. I made a planter box plus an old bed headboard that we had on hand. It went pretty well, in spite of the fact I had no plan. (I should have had a plan.) Here is the basic box-planter. This was built with less than $25 of materials; all cheap cedar fence boards.

Planter before adding plastic liner and soil.

Top trim detail

My first attempt at angled corner trim. It went well.

Finished and planted!

Here it is with soil and plants. My wife loves it. ‘Nuff said?

Cedar Planter Instructions

Materials:

  • (10) 5/8″x5 1/2″ x 5-foot Cedar Fence Pickets (not dog-eared)
  • (1) 5/8″x5 1/2″ x 6-foot Cedar Fence Picket (good quality)
  • Box of 1 1/4″ Finishing Nails
  • Exterior wood glue (Tite Bond 3 recommended)

Tools:

  • Table Saw
  • Speed Square
  • Hammer

Directions:

If the material is of poor quality, get an extra 5-foot board or two to account for huge knots and/or damaged boards. The 5-foot pickets were less than 2$ at Lowe’s and the 6-foot picket was just over $2.

Pick your best two 5-foot pickets to be the front and the next-best three for the back and ends. Use the poorest quality three to make the bottom. The remaining pickets will be ripped into 2 ½” stock for the braces and legs. The 6-foot pickets will be ripped into 1 ½” widths for the top trim.

Rip 3 Boards for the bottom, two 5″ wide and one 4″ wide all cut to 58 3/4″ length. Cut four 2 ½” x 14″ braces, assemble the center T-brace with nails and glue, and nail and glue the braces in place onto the bottom boards. Definitely use a square to make sure this is an accurate rectangle!

For the sides and ends, rip 5 pickets to 5” width. (I did this because 1 edge is typically not in good shape and about 9” deep is fine for planting.) Cut one into four 14” pieces. Use the 2 ½” stock to make the ten 16” leg pieces. Glue and nail the legs to make two end assemblies and two side assemblies.

Put the base on its side, and attach the end pieces with glue and nails. (Use some scraps to prop the bottom up 5/8”.) Then attach one side piece in place, flip the structure and attach the second.

I cut more 2 ½” stock to make three layers of additional support for the bottom, glued behind the legs, essentially making a laminated post at the corners and center.

Rip the 6-foot picket into three 1 ½” strips for the trim. Position each piece on the box with the edge flush with the box inner edge and mark where the angle cuts are to be made. Work carefully and fit each piece.

You may wish to finish this with a colored or clear stain, or leave it to weather to a gray shade. I left my planter natural.

Construction Drawing (PDF): Cedar Planter

 

Building a Large Curved Trestle on a Grade – Part 4

Odd-sized Stories and Bent Assemblies

After a break for the Holidays and the generally unpleasant freezing weather, I’m back at it. In this installment, I’ll be building the odd-sized stories, adding the mud sills and assembling complete bents.

A spreadsheet was used to calculate the height of the bottom story for each bent, as I’m building the terrain to fit the bridge. If you are fitting a bridge into existing terrain, you would measure the total height and use that to calculate the required stories.

Bent Calculation

To calculate the required heights, I’ll use a bent that is 26 13/32” tall as an example. The top story is 9 11/16” tall not including the bottom sill, the second story is 9 5/8” tall, so the third story height is:

Height = 26 13/32 – 9 11/16 – 9 58 = 7 3/32”

Allowing for the bottom sill, the third story post assembly should be cut to the bent height less the mud sill height:

Cut Length = 7 3/32 – 5/8 = 6 15/32”

(Note that the calculations are to the nearest 1/32”, but I doubt that level of precision can be achieved in practice. Shims and/or sanding will be used to adjust heights if needed.)

Odd-sized Stories

All of the third stories, and many of the top and second stories, are not full height. The posts will be glued in place before cutting. Then a rubberized push block will be used for sawing the odd-sized stories to even the posts. The friction will help prevent the posts from flexing when run through the saw. I made a brace using scraps to hold the posts in place, but that didn’t seem necessary. I had no trouble running a story assembly through the saw without any braces.

The only jig needed is for post gluing. Figure 1 shows the Third Story plan that will be attached to a plywood base. (The Top and Second story plans were in a previous post.) Note that on the Butterfly trestle, no additional inner angled posts (shown as dashed lines) are used. The extra angled posts between the normal pair of outer angled posts are used only on the beam support bents (7a, 9a, 11a and 13a). Gluing these odd-sized stories may require some creative use of blocks as shown in Photo 1.

Figure 1 Third Story

Figure 1 – Third Story Drawing

Photo 1 Creative Clamping

Photo 1 Creative Clamping

 

To attach the full-size drawings to the wood base, I made a wheat paste from 1 Tbs of flour plus 5 Tbs water, heated in a small pan, stirring constantly until thickened. Spread a very thin layer on the surface of the wood, apply and smooth the paper plan and let it dry overnight.

Really Odd-sized Stories

The second story of bent 10 has the center posts resting on the heavy longitudinal beams, with a separate short sill as shown in Figure 2.  The third stories of bents 11 and 13 are on split-level footings, so there are two separate cut lengths as shown in Figure 3. For these stories glue and trim the short ones first, then glue and trim the longer ones.

Figure 2 Bent 10

Figure 2 Bent 10

Figure 3 Bent 11-13

Figure 3 Bent 11-13

 

Cutting to Size

 

Photo 2 Cutting Supports

Photo 2 Cutting Supports

I built cutting supports for the stories to help position them and support the posts when they are run through the table saw to cut them to length. These differ from the gluing/cutting jigs because the cut length may vary quite a lot. Photo 2 shows the cutting supports for second and third stories.

 

 

 

Photo 3 Sawing Supports

Photo 3 Sawing Supports

One problem I had earlier was that the small post scraps cut off sometimes would travel back into the saw blade and get ejected in pieces, at high speed. The blade guard protected me, but the adjacent posts were sometimes not so lucky. Several were broken loose by ejected debris and had to be reglued. The solution that I found was to hot glue a scrap of rejected brace material to the ends past the cut line so as to make a single piece that travels through the saw intact. Photo 3 shows two stories with a support glued in place.

 

Mud Sills

Photo 4 Mud Sills

Photo 4 Mud Sills

These odd-sized stories are all at the bottom of the bent (except #10), so a mud sill (or two spliced together) will be glued and nailed on to each one. Photo 4 shows a few bents with mud sills being attached. I’m adding a blue tape label showing the bent number as I complete them. Note that an acrylic sheet was used to prevent excess glue from attaching the bents to the workbench!

Braces

Since the braces for these odd-sized stories are all different, measure the distance between the corners of the top and bottom sills, then cut a brace about ½” shorter than that. These will be glued without using a jig, speeding the process considerably.

Bent Assembly

Photo 5 Top-Second Assembly

Photo 5 Top-Second Assembly

Take a top story and second story, put glue on the bottoms of the top posts and on each brace as shown in Photo 5, then slide the second story top sill into place, angling both slightly so that the brace glue doesn’t smear until it is in position. Add brace material scraps to support the pieces then clamp in place and let cure. Nail the glued braces to the sill for added strength.

Photo 6 Complete Bent Assembly

Photo 6 Complete Bent Assembly

Repeat the glue and brace process for the third story. I’m improvising the braces as appropriate for the third story of each bent, roughly following the prototype. Photo 6 shows two complete bents being glued. Note that I numbered each with blue tape labels so I could keep them straight later.

Bents 7, 9, 11 and 13 have an adjacent support for the bent support beams. I added a very thin spacer between these before gluing the pairs to allow better drainage and drying. Note that bent 7 in the foreground of the photo has a doubled bottom story.

After repeating this process several times, Photo 7 shows many completed bents showing the height progression from end-to-end.

Photo 7 Complete Bents

Photo 7 Complete Bents

Next time: Building the Center Beam Assemblies

Building a Large Curved Trestle on a Grade – Part 3

Mass Production of Bent Stories

To efficiently build a large trestle such as this, I will take advantage of the many identical assemblies of bent stories. Of the 20 bents, four are less than full height. I’ll handle exceptions like those individually. In this article I will describe how I build the bent stories in batches. These will be 16 top stories (with 5/8” x 11/16” cap) and 6 second stories.

CAD Drawings

LibreCAD is used to draw the construction plans. It is a free open-source CAD program that is relatively full-featured for 2D drawing. The learning curve is a bit steep, but I find it invaluable to get a good, accurately measured drawing.

Link: http://librecad.org/cms/home.html

User Manual: http://wiki.librecad.org/index.php/LibreCAD_users_Manual

Figure 1 Bent Top

Figure 1 Bent Top

Figure 2 Bent Second

Figure 2 Bent Second

Figures 1 and 2 are (not to scale) plans for the top and second bent stories. There are many of these that are identical, so producing them in a batch makes sense. I had a few drawings printed full-size (18”x24”) through Staples to use during construction. (At the bottom of this post are links to the DXF and PDF files.)

Link: http://www.staples.com/sbd/content/copyandprint/engineering-prints.html

Assemble materials

Photo 1 Material

Photo 1 Material

I first ripped the materials needed so I could do a whole run of many bents without interruption. Photo 1 shows my supply during production, and the spreadsheet I used to track how much of each size and length I would need. I need a LOT more than what is shown, but I have enough to start producing bents.

I used a spreadsheet to keep track of how many pieces of each size wood I needed. I’m going to do the 15 Top and 6 Second stories in a batch. The others are all unique sizes that I will leave for later. For the top story there are (15) 5/8” x 11/16” x 8 ½” Caps, (30) 5/8” x 5/8” x 9+” vertical posts (leave them just a bit long) and (30) 5/8” x 5/8” x 9 ½” angled posts (3-in-12 batter, or 14.0 degree angle). The second story will need (6) 5/8” x 5/8” x 11” sills (at the top), (24) 5/8” x 5/8” x 9” vertical posts and (48) 5/8” x 5/8” x 9 ½” angled posts.

Construction jigs

Photo 2 Gluing

Photo 2 Gluing

Post jig – This is used to glue the cap or top sill and attached posts. It is positioned with the bottom of the posts at the edge of the jig so a table saw can be used to even the bottom up for a perfect fit onto the next story assembly or the mud sill. Photo 2 is a saw jig being used for gluing posts.

Photo 3 Saw Jig

Photo 3 Saw Jig

 

 

 

Photo 3 shows a Saw Jig in place on the table saw. Note that the blade guard was raised for the photo, but was in place during cutting!

 

 

 

 

 

Photo 4 Brace Jig

Photo 4 Brace Jig

Brace jig –Braces as seen from behind are top-left to lower-right, so when they are viewed from the front of a bent are top-right to bottom-left. Photo 4 shows the Brace Jig in use. The brace being glued is placed on the jig, dots of glue applied and the bent is set on top of that and weighted.

Glue the paper plans to plywood, for example, one plan with the bottoms of the posts at the very bottom of the jig to use on the table saw to evenly trim the posts, and another to be used for brace gluing and bent assembly. I attached a strip of plastic using a glue stick where the posts meet the cap, so the glue won’t stick to the paper. (It is not visible in the photo because it is clear.) For the braces, I add brace scraps under the posts so the bent sits level during the gluing process.

Production

Photo 5 Stories

Photo 5 Stories

So working from saw jig to saw to brace jig, glue the posts to the cap or sill, then the brace on one side, then a brace on the second side. I let the glue set for about 1 hour before moving on to the next step, so the mass production process is a few small steps spaced apart by a bit of time. (20-20 hindsight made me realize that braces could have been glued twice as fast if I had positioned the saw jig guides so that it could also be used for braces.) Photo 5 shows the result of a few days of work.

Tip: You will need clamps for posts and gluing weights for sway braces. For weights, I use a combination of small snack-size bags filled with sand and a couple of old gallon pails about half full of sand.

To finish construction, drill a pilot hole through the cap or sill into each post and drive a 1 ¼” finishing nail into that for extra strength. Each brace should also be nailed to each post it crosses.

Next time: Odd-size Stories and Bent Assemblies.

What is Batter?

Batter is the amount of offset in the angled posts expressed as feet offset per 12 feet in height, so 3-in-12 would mean 3 feet horizontal offset for each 12 feet in height. The Rio Grande Southern typically used 2-in-12 batter for tangent (straight) trestles, 3-in-12 for curved and 2½-in-12 for combination trestles. Since this trestle is curved, it uses a 3-in-12 batter. The angle to use on a miter saw is 14.0 degrees.

Note: If you want a different angle, the conversion from batter to degrees is angle = tan-1 batter, where batter is expressed as a decimal, so 3-in-12 = 3/12 = 0.25. For example, a 2-in-12 batter would give an angle of tan-1 (2 / 12) = tan-1 0.16666 = 9.46 degrees. Or, here you go:

Batter to Angle
Batter (in 12) Angle (deg)
1 4.8
1.5 7.1
2 9.5
2.5 11.8
3 14.0
3.5 16.3
4 18.4

 

Drawings of bents, 3-in-12 batter, 1:20.3 scale. The PDF files are designed for printing on 18″x24″ paper.

Drawing DXF PDF
Top Story DXF PDF
Second Story DXF PDF
Third Story DXF PDF