A few questions about splines

[misterW]

Since I plan on making an oversized (5x12) wall out of 3/4" plywood, I have been thinking about getting the 1/4" 3 wing slot cutter for the router. That would leave me with a 1/4" of space for a spline to fill. Here are my questions:

(1) Do I want a 1/4" thick spline or something that is slightly less to allow for glue?

(2) Is plywood readily available as a true 1/4" thickness?

(3) Along the lines of question #1, would 15/64" plywood be good because it leaves room for glue or bad because it would be too loose?

(4) How well would it work to cut out 1/4" splines on the table saw from, say, a standard 2x4 or other lumber that I have around? Would that be much weaker than using plywood?

Thanks in advance for any questions that you can answer!

[bobhenry]

Lost of good info here and a few hard and fast rules that are good to know.

http://www.newwoodworker.com/makeplines.html

[boomboomtulum]

Try this link for some useful info. from one of the members, Doug H.

http://tnttt.com/viewtopic.php?t=34381

[misterW]

^^ That thread was what sent me in this direction originally. I just wasn't sure where to get the splines from, since I haven't been able to find any true 1/8 or 1/4 ply locally.

However, I just came across this: http://kencraftstore.com/ply3.htm#baltic. Looks like I can just order some wood to cut splines out of.

I guess now I just need to order a slot cutter bit and practice on a bunch of scrap before I attempt the real deal.

[doug hodder]

I use baltic birch for the splines so it fits tightly and rip my own. Don't use a solid wood, it will split on you. Baltic birch is true dimensioned ply. PS.. I think you'll find that the 1/8" bit will work fine for you and maybe give you more options to using it in the future over the 1/4". Just my opinion. Doug

[Lou Park]

I know that I'm going to start a bit of trouble with this answer, but here it goes. Using a spline to connect two sheets of plywood together is possibly the worst way to extend the length of plywood for a project like this. Not only is it the weakest splice, but if done incorrectly will cause the ply to split. I know a few people highly support and believe in it, but in reality it should never be used for this type of project. In most projects that use splines, you may notice that these are stationary, when finished projects, such as tables, picture frames, paneling. Your trailer will be going 60-70mph down the road. This means constant 70mph winds, potholes, and attempts at flexing. With the spline system your sides are relying on the roof and floor structures, the exterior and interior coverings to support it, keep it together rather than the all of these being supported by the sides. Sooner or later it will, not may, but will separate. For those that will tell you they haven't had a problem yet, ask them what is covering the splice. Your best bet is the time proven method of half laps in the ply along with never allowing four corner connections. If I read your post right, you already have a router, so get yourself a straight bit, a dado bit with changeable bearings. You will not be sorry.
Lou

[afreegreek]

Since I plan on making an oversized (5x12) wall out of 3/4" plywood, I have been thinking about getting the 1/4" 3 wing slot cutter for the router. That would leave me with a 1/4" of space for a spline to fill. Here are my questions:

(1) Do I want a 1/4" thick spline or something that is slightly less to allow for glue?

(2) Is plywood readily available as a true 1/4" thickness?

(3) Along the lines of question #1, would 15/64" plywood be good because it leaves room for glue or bad because it would be too loose?

(4) How well would it work to cut out 1/4" splines on the table saw from, say, a standard 2x4 or other lumber that I have around? Would that be much weaker than using plywood?

Thanks in advance for any questions that you can answer!

you want enough room to allow the joint to come together without scraping all the glue to the bottom of the spline groove. the general rule with carpenter's glue (titebond etc) is to leave enough room so you can wrap a dollar bill over the spline and still be able to slide it in by hand. this will allow for the glue and a little swelling caused by water based glue

plywood is never exact sizes. it's usually under but sometimes it's over the stated size.

better option is to get a 3/16" cutter and cut a groove to match the 1/4ish stock you have for making splines in two passes.. or get the 5/32" size for lemello biscuits and use those instead.

cutting splines from solid wood is fine but a hard wood would be better. ply wood is stronger but solid wood is plenty strong enough. lemello biscuits are very strong and fast. they are the best option of the three.

[halfdome, Danny]

Any material (solid wood, Masonite, MDF etc) other than a quality plywood like Doug suggested for a spline will break under stress. I've seen some previous co workers make that mistake. I spine my 10' sides together at the galley end and sister on a piece of 1/2" plywood (glue & staple) over the spline to strengthen it at the unsupported portion of the galley wall just after the bulkhead. It can and does fool people who look at my galley walls & it's very strong. I spine the extra height of my profile towards the roof and glue 1/8" Red Oak plywood on the interior and contact cement my aluminum skins on the outside. My floor is also splined together since I only build 5'x10' teardrops and is covered with plam on both sides and bolted (24 bolts) to the chassis. I use the Dexter Torsion Axle for a very smooth ride and things stay together as built. Danny

The raised area covered in plam is the 1/2" sistered plywood over my spline.

Here it is finished. The walls are 3/4" but look like 1/2". The sistered portion looks like 3/4" but is 1/2". All because of a continuous 1/4" rabbet along the profile edge. Danny
Just plan where your splines will fall and you'll do okay.

[doug hodder]

There's lots of ways to skin a cat...I've done 5 this way, dragged a couple across the country and like mentioned, haven't had any problems yet. When and will it fail...I dunno, but I think the construction methods/glues that I've used are far superior to a lot of the furring strip and staples that many of the RV's past and present utilize. It's not uncommon to find a 30yr. old RV still on the road with much less into it. Hey...do whatcha want, this has worked for me. With care...I'd bet they outlast me. Doug