Guys, thanks.
The first test went smooth, I just moved the structure as a unit about 20 minutes into the setting process. I lost one post joint, repaired that, and will run another lineal tonight. Then I can test how the pieces handle being cut.
I remembered a better source for mylar, space blankets sold as camping gear are much thinner and easier to come by in quantity, but so far, gluing the assembly down to a wooden jig hasn't been the problem I expected it to be.
jeffers_mz wrote: A thin plastic sheet could work though, merits a three post section trial at the very least. Saran wrap for sure, now where'd I put that mylar? Ah yes, old PC component anti-static bags, check.
A thin plastic sheet could work though, merits a three post section trial at the very least. Saran wrap for sure, now where'd I put that mylar?
Ah yes, old PC component anti-static bags, check.
I'd test the mylar with the adhesive you plan to use . . . While it's nearly impervious to water and resistant to dimensional change, I don't know if solvent resistance is its strong point.
KL
FWIW, I gave up building a wooden trestle as just too fiddly but made the fixture by tranferring the pattern onto a piece of aluminum plate then milling with an end mill to the required depth and width. Fixture worked well and didn't stick to the wood glue unless I got really sloppy.J.R.
"By the way, you are actually talking about fixtures. Fixtures hold the parts, jigs guide the tools. " src="/trccs/emoticons/icon_smile.gif">"
One of those, eh?
Have we worked together before? Your tone sounds familiar.
:-)
Seriously, this is both a jig and a fixture. It holds the parts, and guides the saw blade down the cutline after assembly. Looks like Chicklets, two rows of 12. Lay the crossmembers (too long, surplus bridge ties), then one sill plate, cut off the excess crossmember length, add a second sill plate to the cut side, then cut down the middle of the chicklets, to make two 12 inch lineal sections of beam and post.
Cut them to length (just past a post, architect's discretion) and now instead of an endgrain L joint using a 1/8th by 1/8th cross section, you're actually gluing two posts together, 3 to 6 times the glue surface area, plus the butt joint, with the grain running parallel on the post joints.
You know, I was actually going to use teflon for this jixture, but I had all this wood sitting around, and now it's already built.
Saran wrap, eh?
Fess up, you just want to see me sand all those ties down one fraction of a whisker on each side, don't you? You already know this, though some might not, but wood often looks crooked, even when it's straight. Especially arrangements that are supposed to be square or parallel. Subtle variations in size, slight twists brought on by the ever present quest for H2O content stability, the only way to defend yourself against untutored observers is to show them the bubbles sitting center and the tape measure agrees.
Those who note that this arrangement is not usually long term rigid have a point, but this isn't supposed to be a 115 year old town, it is a brand spanking new town, a boom town, 115 years ago, with no stain on raw pine and sap bleeding down the sides of structures completed ten minutes ago. Sides, I used to fire guys for crooked work.
Thanks.
I'll let you know how the tests come out.
If I'm understanding you right, this might work: Assemble your sill frame first on a flat surface. That should be relatively easy to get flat and square. Then glue your posts on top of the sill frame. If you flip it over and press it into your soft groundwork (allowing the groundwork to account for variances in post length) it should be easy to get the top of the sill frame level, or level enough for a model.
Regarding "jigs", the secret is to use a material that is incompatible with the adhesive being used. For example, plastic solvent cement does not bond to wood, so a tool for assembling styrene elements can be made of wood. For wood glues, plastic might work, but I'd advise testing to make sure it doesn't bond (there are a lot of different glues used with wood). Depending on the accuracy desired, durability, and the adhesive in question, aluminum, polyethylene, or even teflon could be used for construction.
If you are building on a paper plan, airplane modelers long ago learned to cover the plans with wax paper first. I suppose you could also use saran (PVDC) or other cling wrap as a barrier to solvent rather than water-based adhesives. Again, testing is in order.
By the way, you are actually talking about fixtures. Fixtures hold the parts, jigs guide the tools.
I agree that keylocks between foundation and buildings are a good idea, but extending corner posts may weaken the structure considerably. That's the only glue joint holding one side to another and bringing the post through there makes one glue joint into two glue joints. One other way to lock the building in place is to extend the bandboard trim down over the beam perimeter, another would be a block of luan on the underside of the building that fits in between the beam perimeters.
Pictures from the area show rectangular cross sections on the beams and posts, and this matches personal observation. There was a lot of timber in the area, the structures were built from local timer, and they did move sawmills into place to shape the rough cut material, I'm sure there were some beam and post foundations made from round logs, but you don't see them in pictures, probably because fastening round to round is a big pain in the neck, and those buildings probably weren't very photogenic even when new.
I've built lots of jigs before, trim carpenters spend as much time making jigs as we do running crown or building cabinets. He who dies with the most jigs, wins. I have several home-built miter box devices, but with small pieces, even using a stop, it is difficult to hold the pieces being cut perfectly still and the resulting play in finished lengths will make the difference between a support post resting on bedrock (plywood) and floating in midair.
Two "ladders", one stacked on top of the other, will end up between a 32nd and a 16th higher than the jig blocks, so clamping a pair of long one-bys down on them, on either side of the cut, will lock them into place and prevent cutting forces from pulling them apart.
Still looking for answers as to how the trestle builders keep from gluing their bents down to the jig. If need be, I can free the assemblies with a sharp knife in under the edge, but I suspect there's an easy simple trick to avoid this in the first place. I just don't know what it is yet.
In the prototype world, this type of construction suffered greatly from settling problems. Any place the posts did not directly contact firm rock foundations, the posts would often settle unevenly over time causing the floors to be uneven and far from level. This was particularly true in the permafrost regions of Alaska and Yukon territories. Heat transmission that melted the permafrost layer would (and still does!) create wildly uneven settling rates that led to collapse of many buildings.
The settling probems were the likely cause of today's building codes for foundations and footings (no factual evidence, my speculation).
So when your building is less than perfectly square and level, remember there is a prototype for everything! :-)
Fred W
Jeffers,
Are you sure about the posts being 6x6 sawn timber? Where I came from many of the foundations were round log type. Why do all the work of sawing the timber? Stands the weather better if it has not been sawn too.
If you can live with round posts, I would drill holes right through the ply and push the "posts" through so that they can be level at the top. You can trim the excess under the base board after the glue dries. Drill the beam to take each post. Alternatively drill a few to give adequate strength, but leave the rest to be but joints to save work.
The posts material is up to you. Wood if you like. Wire if you like, then disguise it as wood. Even nails if you get the right size, but cut the heads off.
I just thought of another way out idea. If you want square posts, you could use wire or nails then coat them with some filler to give a square shape. Bit of a pain doing that. I really think you would find many posts were round. Except those that were made of brick .
The critical thing of course is to drill "square holes". Holes that go perpendicular into the ground that is.
I think that in the long run it would be easier to put the assemblies together one at a time. I think I'd draw out the outline of the foundation on cardstock as a guide, and then build the rectangular beam frame first. After that's glued together solidly, then I'd add the posts with CA glue, so that I could hold them in place for the few seconds it would take for the glue to harden.
I'd extend the posts up above the frame as well. This would let you slide the structure down on to the beams and have the posts in the corners to keep it centered.
It takes an iron man to play with a toy iron horse.
The last spot of bare plywood on our layout is about to be covered, it's time to spackle in the terrain around the town of Silverton. The town sits on a subtle grade, half an inch above plywood at the foot of the mountains, down to a sixteenth or eighth inch where it meets other scenery near the river banks.
Since we want to be able to swap similarly sized buildings in and out later on, the plan is to lay the foundations on bare plywood and spackle in around them for streets and terrain.
Checking pictures from southwest Colorado circa 1890, I see that few of the buildings had foundations of stone or concrete.
Instead, most appear to rest on beam and post foundations, 6" x 6" vertical posts every 4 feet under a 6" by 6" sill beam which then carries the joist system, flooring etc. Since we're working in HO, 1/8' by 1/8" wood stock seems to be the right size to use.
In a perfect world, I could spackle the whole area, then simply push the foundations, horizontal beams with vertical posts under them, arranged in a building sized rectangle, down into the wet spackle after the whole area is suitably graded.
The problem I foresee is building these beam and post systems square and even. If the average spackle depth is 1/4 inch, and I want about one scale foot of post above grade under the sill beams, then the uprights will be about 3/8" long.
Trying to get tiny little posts like this cut to the same lengths, and then trying to get them glued in square with the beam looks to be a challenge.
What I'm thinking of trying is to cut all the posts double length, and then make a jig to glue up "ladders", two beams, say a foot long, with "rungs" 3/4 inches tall between them. Once the glue dries, I could then cut right down the middle of the ladder with a Jap saw, and end up with two beam and post assemblies.
I have two questions about doing this.
One, how do I ensure that I don't glue the assembly down to the jig, which will be made out of wood? I envision a piece of plywood with rectangular blocks of luan glued on top for the jig, so wax paper won't lie flat, and I'd rather not foul the jig and the beam and post assemblies with some sort of non-stick spray like Pam, but I know from experience that glue will ooze out of the joints where I can't see it and stick the model to the jig. This has to be an issue in making trestle bents, how do you all glue them up without gluing them to the jig?
Two, will a finished "ladder" stand up to the stress of being cut in half lengthwise after the glue dries? The plan is to leave the assembly in the jig while cutting, and cut the jig blocks and the beam and post assemblies both at once.
I envision about two cut lines on the jig, since the heigth of the piers needs to change with the grade as it rises in elevation. Cutting 3/4" double length piers at 3/8" would leave me with two equal halves, and cutting at the 1/4" mark would leave one assembly with 1/4' legs and the other half with 1/2" legs. From lower to higher then, I'd have three different heigth foundations, 1/4", 3/8" and 1/2".
Am I way out in left field here? Is there some simple way to do this I've completely missed? Any insight on making these without gluing them to the jig or tearing them up with the saw later on?