Joinery question for benchwork

[carl425]

The recent benchwork discussions got me thinking about how to construct a joint I need.

I plan to support my n-scale 18" radius helix with 8 joists that radiate out from the center of the circle with 45 degrees between them.  Think of an 8-spoked wheel.  The joists will rest on a square of L-girders.  I'm hoping the real carpenters can tell me the best way to connect them all together in the center with sufficient strength to be supported only by the L-girders.  Like Sheldon, I like to be able to lean on my benchwork so overkill is welcome.

[ROBERT PETRICK]

Here's a rough rendering showing how I constructed the 12-sided base for my helix.

And a sketch showing the layout and dimensions for something similar with eight sides. The only tricky part involves the half-lap dado joints, but they're not all that tricky.

I used all-thread rods for the risers. I'm thinking you might use 1x4s.

Robert

[hon30critter]

I'm not a professional wood worker but that has never stopped me from designing and building solid structures. How about just using some 3/4" plywood as a plate to screw and glue all the joists to? It doesn't have to be eight sided or round as long as you have enough width to get a couple of screws into each joist a few inches apart.

If you really want it to be strong you could put plates both above and below the joists but that seems like overkill to me.

Dave

[Medina1128]

Have you considered using 1x4s for the framework as opposed to 2x4s?

[doctorwayne]

carl425

...I plan to support my n-scale 18" radius helix with 8 joists that radiate out from the center of the circle with 45 degrees between them. Think of an 8-spoked wheel....

Well I've never built a helix, but it seems to me you're over-engineering it when it could be done much more simply, with less material and likely be stronger, too.

If the helix is built using segments, cut from plywood and spliced together, you could use 1"x2" lumber vertically within the helix (narrow edge against the inner edge of the helix) and simply drive screws through the edges of the plywood and into the 1"x2"s.  I don't think that you'd need too many verticals with that small radius, but you might want to join a couple of them, at their tops, across the interior of the helix.
Rather than L-girder for support, I'd use a circle, cut from 3/4" plywood, with cut-outs into which the bottom ends of the verticals could be inserted, secured with screws.

Wayne

[carl425]

hon30critter

How about just using some 3/4" plywood as a plate to screw and glue all the joists to?

Thanks, Dave.

Funny you should mention that.  That is what I came up with, but rather than just running with it, I thought I'd solicit opinions and see if anybody had a better idea.

Another idea I had was putting plates on top and botton and connecting them with 4 carriage bolts to clamp everything in place.

[carl425]

doctorwayne

If the helix is built using segments, cut from plywood and spliced together, you could use 1"x2" lumber vertically within the helix (narrow edge against the inner edge of the helix) and simply drive screws through the edges of the plywood and into the 1"x2"s.

Thanks Wayne,

The first layer, where I don't have to worry about clearance underneath, will be of 3/4" plywood, which will be supported by risers attached to the wagon wheel of joists.  Subsequent layers will be a double layer of 1/8" ply (with the joints staggered) supported by 2" blocks of 1x2's as you describe.  This is how I built my last helix and it worked well.  I'm just looking for the best way to secure the joists.

[hon30critter]

carl425

Another idea I had was putting plates on top and botton and connecting them with 4 carriage bolts to clamp everything in place.

I think the carriage bolts are unneccessary. You're going to have to screw the joists to the plywood anyhow just to hold them in place while you assemble the wheel. Add some glue into the equation and you could probably bolt the 'wheel' to your truck axle and drive down the road with it!

Dave

[carl425]

hon30critter

bolt the 'wheel' to your truck axle and drive down the road with it!

So you're saying instead of carriage bolts I should use lug nuts? 

[hon30critter]

carl425

So you're saying instead of carriage bolts I should use lug nuts? 

Pardon my exhuberance. I just wanted to imply that you might be overbuilding the support structure IMHO.

However you build it, I'm sure that it won't be flimsy.

Just so you understand, I'm not being critical of your construction methods. I have overbuilt everything I have ever touched! As I have proudly claimed before, I built a $4000 deck for $7000!! It hasn't so much as squeaked in 23 years. Last summer I had to have the 20' wide steps rebuilt, not because they were rotting, but because I screwed up on the rise (too high) and it was getting more and more uncomfortable to go up and down the stairs. It took the contractors two days to get the old steps apart and figure out how to replace them. I had put in no less than eight concrete posts to support just the stairs alone!

Dave

[carl425]

hon30critter

Just so you understand, I'm not being critical of your construction methods

But that's what I want.  I am not a snowflake.  If I rejected critical thinking I'd never learn anything.

Of course I still reserve the right to reject your suggestions in favor of my own pet ideas. 

[hon30critter]

carl425

hon30critter Just so you understand, I'm not being critical of your construction methods But that's what I want.  I am not a snowflake.  If I rejected critical thinking I'd never learn anything.

What I meant was that I wasn't trying to be nasty or condescending. Obviously you take criticism very well. That is not always the case so I try to make sure that people understand that I am not trying to offend.

Dave

[gregc]

how are you planning to attach the helix roadbed to the joists?

[carl425]

gregc

how are you planning to attach the helix roadbed to the joists?

The first level roadbed will be screwed to risers as done in any L-girder or open grid construction.  The upper levels will rest on 2" spacers cut from 1x2.

[davidmurray]

I would secure the 1x2's and plywood with 1" number 6 wood working screws.

I would also strongly suggest securing each circle of track before adding the next layer of plywood.

Dave

 

[rrebell]

I would build a 1x4 rectangle ans add a smaller 1x4 rectangle to each of the long sides, basically ending up with a cross. Then I would add peices so it end up as an octigon. This should suport your weight, even before what you put on it. If you use ply, it will proubly suport two people.

[gregc]

carl425

gregc

how are you planning to attach the helix roadbed to the joists?

The first level roadbed will be screwed to risers as done in any L-girder or open grid construction.  The upper levels will rest on 2" spacers cut from 1x2.

 

have you considered using corner braces attached to the underside of the helix and to posts just inside the helix.  The posts would require some cross bracing, but the helix would provide additional structural strength.

 

[carl425]

gregc

have you considered using corner braces attached to the underside of the helix and to posts just inside the helix.

Yes, I have.  I came up with 2 issues that I couldn't find a good fix for.

1. Because the width of the roadbed is more than double the clearance between the levels, and the the 2 sides of the brace are the same length, the vertical parts of the braces would overlap with each other.
2. The fact that the roadbed is a curve on a grade, some degree of twisting of the roadbed is required to keep it level across the rails.  With clearance vs grade as an issue, I need to keep the roadbed as thin as possible.  This makes the roadbed too thin to use screws through the braces to enforce that twist.

[gregc]

carl425

1. Because the width of the roadbed is more than double the clearance between the levels, and the the 2 sides of the brace are the same length, the vertical parts of the braces would overlap with each other.

couldn't they be offset?   even if the posts were just 1x2s, there is enough room for two braces side-by-side

and do the braces need to be the width of the helix roadbed?   if that amount of support is necessary, could you add addition 1x2" posts on the outside of the helix

if  there are (1x2") posts both on the inside and outside of the helix, straight brackets could support the helix and rest on short angle braces on the side of the posts.   height could be adjust by putting washers under the straight brackets on the angle braces.

carl425

1. The fact that the roadbed is a curve on a grade, some degree of twisting of the roadbed is required to keep it level across the rails.  With clearance vs grade as an issue, I need to keep the roadbed as thin as possible.  This makes the roadbed too thin to use screws through the braces to enforce that twist.

you mention building the helix sub-roadbed from 2 layers of 1/8" plywood.   aren't there screws that short?   could you use machine screws threaded into the wood?   all they need to do is hold the roadbed in position, not support any weight.   short dowels?   Maybe having the ability to lift the level above the one you want to reach into would be helpful.

 

 

please take my comments as food for thought requiring no explanation.  maybe they will help you be most comfortable with the approach you choose.

[carl425]

Here's how it came out:

The joist parallel to the wall and the one perpendicular to it are half-lapped.  The others are 45 degree mitered on both sides to a point and glued into the corner created by the first two..

[rrinker]

 I am planning to have a helix in my layout, but I thinkt he LAST thing I want to do with a helix is put something filling up the center of the base level - what sort of access will you have to each level? I want to keep the center of mine open so I can duck under and pop up inside the helix if it becomes necessary to retrieve something.

                     --Randy

 

[carl425]

rrinker

the LAST thing I want to do with a helix is put something filling up the center of the base level

I have a disability which makes it physically impossible for me to pop up in the center of the helix so that wasn't a consideration.  I chose this configuration instead to keep the footprint as small as possible.  The whole layout will be at swivel chair height (33" for staging, 40" for the visible track), and since I can stand for short periods of time if I have something to lean on, access will be from the top and outside via a removable hilltop and fascia.  Since the layout is much closer to the floor than usual, in an emergency, I can get an assistant to sit on the floor and reach up between the joists.

This helix is also only 2.5 laps to get me down to staging under the sceniced portion of the layout and 2/3 of the top lap will be visible.

[SeeYou190]

carl425

Here's how it came out:

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That looks great. Very well built.

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I hope you continue to share progress.

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-Kevin

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[carl425]

SeeYou190

That looks great. Very well built. . I hope you continue to share progress.

Thanks Kevin,

I've been thinking about a layout build thread, but I'm not sure my pace would be swift enough to keep readers interest.