Great Idea

The Biscuit Joiner is a great Idea and will also work with spline Road bed when you have a squared off end but personally the gorilla glue isn't what I would use because of the Foaming action as it dries and it expands as it foams. I would use weldwood Glue or Elmers Carpenters Glue, It eliminates the need to scrape the foam off the top surface 20 minutes after gluing when you use Gorilla glue. I do reccomend Gorilla Glue for assembling the base structure of your railroad as once the gorilla glue dries you don't have to ever worry about joints comming loose.

The Down side of Bisquit Joinery is you need the more costly 5/8 to 3/4 inch plywood because there isn't enough thickness to the plywood on 1/2 inch and 3/8 plywood to leave any strength at the joints unless you add a support layer across the under side of each joint. Then again you need the support layer on !/2" & 3/8" ply no mater how to connect the sections.

Dan

Blue Foam and Biscuit Joints.

I have used biscuit joiners on 2" blue foam quite successfully.  The plate jointer cuts the foam beautifully, and Liquid Nails for Projects (the latex formula) makes for great stable joints.

Jeff Fry

Re: Great Idea

Rio Grande Dan sez:

"...but personally the gorilla glue isn't what I would use because of the Foaming action as it dries and it expands as it foams."

The foaming action isn't really too much of an issue.  A single-edge razor blade in a scraper tool removes the excess in a few seconds.  Clamping the joint also eliminates any problems with the glue expansion throwing alignment off.  Again, regular wood glue is what I also prefer unless the strength of the polyurethane glue will make a significant difference.  The extra strength comes in handy at such locations as the vertical curve near the crest of a grade where yellow glue can fail.

"The Down side of Bisquit Joinery is you need the more costly 5/8 to 3/4 inch plywood because there isn't enough thickness to the plywood on 1/2 inch..."

I've used biscuits on 1/2" plywood all over the layout.  The plywood in the photos is 5/8", but I've achieved good results with the 1/2", including a helix or two where the thinner material was needed to keep the vertical separation under control.  I'm not using "good" 1/2" ply either, the cheap sheathing grade is all I use.  I got a killer deal on the 5/8" from a modeler who was moving and clearing out his layout stash, or I would probably be using 1/2" for the area under construction in the photos too.  Did I mention I'm cheap?

Question Is it a Model RR or a Furniture Project

Biscuits cost money and you have to have special tools to use them.  I alway have plenty of scraps. Just plante the seam.  Why 3/4 playwood not necessary.  If you are not going to have sceney and leave the bench work open I would be impressed.  Other wiise who is going to see it. 

Furniture?

Art Houston sez:

"If you are not going to have sceney and leave the bench work open I would be impressed.  Other wiise who is going to see it."

Not rying to impress anybody here, Art.  Just trying to build strong roadbed, eliminate misalignment that affects the track, and make efficient use of scrap by joining roadbed materials of varying thickness.  Since it's all buried under scenery, I want it solid so it won't cause trouble in the future.  But then again, splices are the way "we've always done it."  Reminds me of an editorial I read a while back...

Biscuit Joinery on 1/2 inch Helix roadbed

Well, I have been using biscuit joinery on my helix roadbed for the same reason everyone else has -- it makes a strong joint in a place where deck thickness is critical. Now, I had the tool kicking around from cabinet construction, so it just seemed reasonable. And the arcs of the helix were fabricated using a pivot plate on the bandsaw -- rather than tracing it on the plywood and jigsawing it. Nice pictures of the process -- the trick I found was pulling the ends together so the joint was really tight. I fabricated major segments of the helix using an approach I have seen used laying solid surface countertops. A block is attached to each end close to the joint with screws (on the counter top they use hot glue). This provides an anchor point for clamps to pull the joint together while the glue sets. I use Lee Valley high solids cabinet glue. It is gap-filling and slightly brittle -- so if one really has to take a joint apart a sharp blow will fracture the glue line (not a light tap, by the way). Spacing on the helix was initially set with blocks glued in place between the layers -- these were easily removed by giving a quick twist with a pipe wrench. Bottom line is that a lot of the underpinnings of railroading is woodworking -- and if one has the tools and experience there are a lot of ways of building this stuff. And having fun along the way.

Biscuits

The biscuits are a great idea if you already have the tool.  Versatile, strong and easy to do regardless of material thickness etc. and no screws!  Nice.

Handy Tool

Biscuit cutters are relatively inexpensive tools and downright handy to have.

Re: Biscuit Joinery on 1/2 inch Helix roadbed

Thanks for the suggestion on the Lee Valley high solids cabinet glue.  I think I'll give that a try.  Your suggestion on the anchor points and clamps as in countertop construction is a good one too, and one I've used on the layout.  Sometimes I clamp the anchor point in place so it can be removed with no fuss at all.

Biscuit Joinery

Hey guys     For any one who is interested in trying this method you can pick up a bisciut joiner at Harbor

                    Freight for about $29.00  Just thtink I have one and never thought about using it for my road

                    bed.                ron netti

Helix road bed

I've been considering biscuit joinery for the segments in my coming-real-soon-now helix. Not having the extra thickness of a splice plate under the roadbed reducing overhead clearance is appealing. And I've had the same problem with sheets of plywood not having quite the same thickness (sometimes I use .010" styrene shims).

But I'm a bit concerned that the butt (with biscuit reinforcement) joints might be weaker than I'd like - especially given the flexing that a the road bed gets subjected to while installing and adjusting the laps. I've been thinking of cutting the roadbed ends at a 30 degree angled V increasing the glued surface and putting the two biscuits on a different axis. Sort of a crude finger-joint.

Has anyone tried this?

Charlie

Glues and joints

Fine Woodworking did an interesting scientific test on glue joints last year. You can see the video here:

http://www.finewoodworking.com/Materials/MaterialsArticle.aspx?id=28853

The upshot was that the worst glue of the lot was Polyurethanes (they used Gorilla Glue) and standard PVA was the best in a loose joint PVA was 3x stronger than polyu). You need to be a member to read the PDF, but there was nothing earth-shattering in there to me. The only other thing was that they confirmed that the tighter the joint, the better.

The keys to a glue joint are:

1. Maximise the surface area of glued joint.
2. End grain will not glue with any strength.
3. Don't starve the joint (ie, make sure there is plenty of glue on the joint).

When gluing the cut edge of plywood, 50% of the joint is end grain. Biscuits are a great solution as they are mainly long grain joints (the surface of the biscuits to the surface of the slots). If you use biscuits, remember that they are designed to swell up - they need a lot of glue to do that.

Cutting the joint on an angle to increase surface area of the plywood part of a joint will not do anything. If it lets you use an extra biscuit because of the greater length of the edge to be joined, that's a different matter.

Risers are a place to come unstuck. The end of a riser is all end-grain (if solid wood) of 50% end grain if plywood. The best way to glue that to the roadbed is to use a stick of solid wood at right-angles to the riser ("across" it and the plywood). That way all the joints are long grain.

I've tested plywood joints myself, and I can testify that PVA glue will join plywood to plywood in such a way that if you force it to break, it will be the wood you break, not the glue. If you don't believe me, try it - join two pieces of ply face to face and after 24 hours break them apart and look closely at the break.

30 or 90 degree

I certainly am not a mechanical engineer or an expert wood craftsman. Rest assured of that. With that said, I think the strength of a biscuit joint is in the fact the biscuit holds the two pieces tightly together so they cannot deviate from plane because of each other, not because of the biscuit. If this is true then a 90 degree joint is preferred. It offers the greatest angle of attack between boards when they attempt to move from plane. It would make for an interesting test. Cut and glue one so we know Charlie.

Quality biscuit joiner

I think this is a great Idea,

I think this is a great Idea, One thing about the type of glue though. The biscuits are made of compressed beech wood and are intended to be used with a glue that will swell them to fit abslotely tight. Don't know if Gorilla glue will due that. Another drawback may be the swelling biscuits may make a bump in the joint. Has the OP noticed any of that? Otherwise I really like this idea. I'm in the process of bringing my scenery together now and so have no immediate use here. Dang! maybe I'll go out to the shop and glue a test joint or two. BILL

Re: reklein

"One thing about the type of glue though. The biscuits are made of compressed beech wood and are intended to be used with a glue that will swell them to fit abslotely tight. Don't know if Gorilla glue will due that."

Remember, polyurethane glue is moisture activated, and the moisture alone will start swelling the biscuits.  It makes a VERY tight biscuit joint.

"Another drawback may be the swelling biscuits may make a bump in the joint. Has the OP noticed any of that?"

Nope.  I haven't seen anything like this on the layout.

Re: Charlie

"But I'm a bit concerned that the butt (with biscuit reinforcement) joints might be weaker than I'd like - especially given the flexing that a the road bed gets subjected to while installing and adjusting the laps."

I've built two helixes using 1/2" plywood and biscuits.  Note that I'm using six-inch wide trapezoidal segments with angled joints at 22.5 degrees, and two #20 biscuits per joint.  I assemble half a helix turn at a time (in my case four segments) with polyurethane (Gorilla Glue or equivalent).

Once the glue has set, I can pick up the helix arc by one end and shake it around without breaking any of the joints.  I had a visitor to the train room that was wondering about the strength of the joints while I was building a helix, so a picked up an assembled arc (68 inches across) and subjected it to stress from some vigorous shaking while holding only the exteme end, and the joints all remained rock solid.  I would have no concerns about yours holding up to the normal stresses encountered during installation.  The whole thing is MUCH stronger than the prvious helixes I built using splices.

As a test, I built the next helix with PVA glue and it wasn't as strong.  I could force a joint to fail more readily by holding an arc from the end, but it still required a good bit of effort to do that.  Scientific glue tests notwithstanding that was my experience - it was the glue that failed, not the plywood or biscuits.  The finished helix is still plenty strong enough to fulfill its role on the layout though.

Biscuit Joinery on 1/2 inch Helix roadbed

My experience using biscuits for a number of years is that because the compressed wood that makes up the biscuit swells as part of the joining process, the joint is often stronger than the rest of the material. So a simple, straight edge is quite adequate. Plywood does vary in thickness from lot to lot, so the one critical thing about using this technique is to be consistent as to which side is used as the reference surface for the cuts. Obviously it should be the top surface where the track is going to go. I try to do all my cutting in one go to minimize the possibility that the guide on the cutter might shift. Actually, my jointer has a thick enough sole plate that just clamping the parts on the surface of the bench is good enough. In my helix, there was the need to thin the plywood at one point to provide sufficient clearance for a reverse loop to exit -- and the rise was just not quite enough. So I peeled off a ply or so and built a reinforcing ridge along the top edges over this stretch to maintain rigidity.

Mini biscuit joiner

 Ryobi made a mini-biscuit-joiner, DBJ50, but apparently they've discontinued it.  This would be perfect for joining stuff in smaller scales.  You can find them on eBay and similar sources.  I have one but I have not used it for benchwork, etc.  

dave

Helix Photos

I uploaded a few helix photos this morning...

Here's a shot of the trapezoidal roadbed sections.  Note how the roadbed is a lot wider than the track at the joint, allowing for use of two of the large #20 biscuits.  Spacers are located on the inside of each section at the midpoint, and the outside at each joint (the latter are not visible from this angle but the screws attaching them can be seen).  All of the plywood is nominal 1/2" sheathing grade material, nothing fancy.

This is one of the spacers across a joint as noted above.  Thre are multiple tracks and roadbed chunks coming together in this spot, but nothing special was needed to keep it all aligned since the biscuits took care of that.  The roadbed at upper right is thinner than that at upper left, and is actually OSB sheathing left over from when our house was built.

Another two-turn helix shows how the biscuit joinery allows for minimal spacing between levels, and for the track to get very close to the inside edge of the joint since there are no splices in the way.

I'm a bit confused by the

I'm a bit confused by the dialog.  Here's what I have in mind for 'butt' joining helix sections...

(note: I showing a 45 degree angle (90 at the point) in this instead of the 30 I'd be thinking about)

Charlie

Charlie, I think the joints on your design would be weaker.

You don't show the width of your helix, but I think those "points" on the "female" connections would be weak due to a lack of plywood material, and I'm not sure that the "male" points would be any stronger once the slots for the two biscuits was cut into them.  I think you would have stronger joints with either a butt joint with a single biscuit or an angel cut butt joint with 2 biscuits.  This opinion is not based on wood working experience, the cabinet makers among us would know better than I do.  I'm looking at it as a mechanic, and thinking of the relative strength of plywood when cut into relatively narrow pieces.

Hmmm...

Charlie - I'd also be concerned with the strength of the plywood on the "female" side of the joint you illustrated.  Little pointed ends of plywood like that are prime candidates for delamination under stress. 

Another potential problem is clearance for the plate joiner tool.  The closest the centerline of mine can get to an inside corner is 2 5/8".  In the case of the design you posted, that would perhaps move the biscuit slots a bit close to the outside edges of the "V."   This could further weaken the joint by forcing the slots to be in a location where there isn't much plywood to start with. 

Your diagram shows roadbed that's 9" wide.  That's more than sufficent for two #20 biscuits on a typical 90-degree straight joint, and you'd have more strength than you'd ever need.  Then again I'm being pretty unscientific here, so you may be just fine...

Biscuit Joints

Hey guys .... Can I say something here?

No 1  Are you fogetting that we are talking about models here not the real thing?

No 2  As a former cabinet maker turned architect any biscuit joint is strong. Try using the new plastic type they dont swell. I use to make my own biscuits on a scoll saw with thin plywood for a supper strong joint.

No 3  IF there is any swelling just take a palm sander an touch up the joint you are most likely going to use cork roadbed.

No 4  For you scientific guys and engineers you are way over doing this ... like I said these are MODELS ... yes there is a little weight, but come on now!

Enough said!         
 

Ron Netti