Straight Building Board

[wingsnapper]

I am about to begin a 100" Bird from skybench and noticed that my work surface is warped. I have been building planes for 5 years and to date this this the single worst frustration. I go the the local Lowes and after hours of serching with a strait edge deem every piece of wood in the building to be worthless. Every door was warped, every overpriced piece of "high grade" hardwood was warped.
Trying to get this bird in the air before first summer semester, does anyone have suggestions for a good surface? JS

[charlie tasto]

You might try building on a piece of glass. I build all my planes on a sheet of glass that sits on a drafting table. I ensure that the glass is flat by using a 5' straight edge to find low or high spots and then small shims (1/32, 1/64 balsa) to make it perfectly flat. Plans, wax paper and finally the parts are held in place using 3M Repositionable Adhesive (I always hated pushing pins through a piece of balsa that I'd spent more time than I'd like to admit selecting). Very little residue left on the parts although the plans arent good for more than two or three models...they get too tacky.

[Ollie]

Amplifying on Charlies recommendation: I use a piece of float glass about 1/2 inch by 12 inches by 36 inches. I got it from a local plate glass supplier at a discounted price because it had a few cosmetic scratches. I backed it up with rug padding so that unevenness in the bench top would not even slightly bend the glass. Lightly spray the glass with 3M75 and let dry. Lay down the plans on the slightly tacky glass. Lightly spray the back of waxed paper or plastic film and let dry. Lay the slightly tacky paper or film over the plans. Spray the waxed paper of film with 3M77 and let dry. The tacky surface will hold parts in place over the film without pins. After the plane is framed out, the wax paper or film can be peeled off leaving the plans clean. The plans can also be peeled off the glass leaving the 3M75 behind. A single edged razor blade can then be used to shave the glass clean.

Before laying the plans down, the trailing edge pieces can be beveled by coating the glass with 3M75 and letting it dry. The sheet balsa is laid along the edge of the glass and the tackiness keeps the sheet flat and in place while the bevel is planed and sanded to a feather edge.

Satelite City (the CA supplier) had an instructional video of this pinless method a number of years ago.

[2milehighguy]

Wingsnapper, I use two Guillows balsa building boards, 1" thick X12"X48". The ones seen advertised in the model mags. I have had them for 5 years and they work great,stay straight, and are easy to put pins in,cost about $30.

[wingsnapper]

Thanks guys, I have often kicked around the idea of using glass. Didn't really think anyone used it. I don't have much money to spend so maybe I could find some scrap somewhere. I just don't want my first large bird to be a disappointment. That 100" span will be a trick to keep perfectly staight even under the best of circumstances.
Also Ollie, how much does a Bubble Dancer cost? I have read a lot of praises about this model. Can one set it up as a simple RE? I have limited building time so can one purchase an ARF? Thanks JS

[Ollie]

The Ava is an ARF version of the Bubble Dancer and goes for something in the ball park of $600. The BD has to be scratch built. Materials for the composite version will run about $200. I built both my composite BD's without spoilers. Mine handled so well that I hand caught it on the first flight. To build a scratch BD requires that you pull together material and information from a lot of sources. You even make your own hardware for control linkages.

[wingsnapper]

Sounds like I should just make the best bird I can and be happy. There is always better looking grass on the other side of the fence. My neck is not that long. JS

[MTT]

Another good choice for a straight building board is MDF, 1/2" or 3/4" thick.
I just made mine, 8ft long, out of 2 layers of 1/2" MDF, and it is STRAIGHT !
Total cost was around $ 20.-

I made it that long, because I am just getting started on a 152" span Ka6, so every panel is 76 " long.

Later on, I plan to glue a layer of thin plywood onto to it, to have a surface into which I will be able to push pins.
BTW, this is the drawback of a glass building board, you can't pin anything onto it.

Michael

[Ollie]

Every type of building board has advantages and disadvantages. MDF will sag over time under its own weight if it isn't supported closely to remain flat. If one side is covered with plywood and the other side isn't, it will warp eventually. Glass is stable and a thick piece stays flat and, isn't warped by temperature and humidity like wood is. Glass won't take pins but pins aren't needed to hold the work to the glass surface. I used celotex and cork faced plywood boards and pins for 20 years. For me, glass is far superior and I wouldn't think of going back.

[MTT]

Posted by Ollie :
Glass won't take pins but pins aren't needed to hold the work to the glass surface

I don't quite agree on that one.

Sometimes you need to pin your stuff to the building board. For example, when you build a long wing like the ones I am building right now, you want the spar not to be able to move around, until you have everything together.
Ans sometimes the wood for spars or other things is a bit warped, and you have to force it a little to its correct position, how would you do that on glass ?

Michael

[Ollie]

The tack of the 3M75 is enough to hold the wood to the surface. If the tack of the 3M75 isn't enough to pull a slight warp out of the wood, then the wood needs to be replaced so that internal stresses aren't built into the structure. I usually build from scratch but, if I'm building from a kit and a bad piece of wood shows up, I replace it. Some designs call for bent wood. In those cases I laminate several thinner pieces over a form first. I've built lots of planes on a glass surface and have yet to run into a problem holding the work to the surface. Some structures don't have a flat that can be stuck temporarily to the working surface. In those cases a custom building jig is called for. Even in the case of a custom building jig, it is helpful to have the perfect flatness of the glass as a reference plane to support the jig. Admittedly it requires slightly different techniques but most people that have tried glass stick with it (pun intended).

I don't even use pins on the top D-tube sheeting. I use masking tape instead. Pin holes weaken the structure a bit and in the worst case they split the wood.

[charlie tasto]

Well I've got to agree with Ollie. If the adhesive wont hold the bend in a bad piece of wood, it's time to replace the wood. If I need to bend a piece of wood, for an eliptical wing for example, I'll either steam the curve into it or else I'll use thinner strips and laminate a curved tip.

[culiv]

Seems to me that everyone is overlooking the obvious. You can pin to the available building boards, but they don't stay flat. The building boards seem to be pretty consistent. The bends and sags are a result of the work bench or table the building board is placed on. That piece of glass is going to stay flat forever, but as noted you can't pin to it.

If you gotta pin instead of gluing it down, why not put a good quality building board on top of the glass? Best of both worlds.

[Ollie]

Pins are a choice, not a necessity.

Before I started using glass and the pinless method, I built an adjustable work surface. It was a piece of 3/4 inch plywood covered with a couple of layers of dense cork sheet to a depth of 1/2 inch for accepting pins. The plywood was supported to a 2 x 10 plank with 1/4 - 20 threaded rods on a 6 inch grid spacing. Before each building session I would spend about a half hour with straight edge and level flattening the work surface by adjusting the individual supporting rods. It worked but was expensive, complicated and time consuming just to accomodate pins.

[schrederman]

I am in the process of building a new workbench. I am using 4 - 8 foot pieces of engineered floor joists that are basically 16" I-beams and another to make some intermediate and end braces. This method builds a straight, rigid table and with 12" spacing the 3/4 plywood will not sag. A bit expensive but worth it if you build lots of long wings. I'll be duplicating it 28 feet long if I decide to build another full scale sailplane...a possibility...I'm getting bored standing on the ground... and miss the rush of the the 30 mile final glide at near redline...oooooohhh!!

Jack Womack

[green66]

A bit pricey but (as a one-time investment) you won't go wrong with an 8-foot folding utility table having a beefy 3/4"-thick pressure-laminated top ==> NOT the flimsy veneered platform of cheaper standard folding tables.

Got tired of rummaging among all the warped boards, hollow doors, and ply sheets at local hardware store, so I got this Table #BVSFTD3096QQ (enter p/n in search box if link doesn't work) (http://www.staples.com/Catalog/Browse/Sku.asp?PageType=1&Sku=BVSFTD3096QQ) almost 2 years ago and, upon eyeing along the edges and laying a 4-foot metal straightedge across the diagonals, can now see that it is still DEAD FLAT in all directions - a condition that's nonexistent in wooden boards of comparable size at the hardware store. Goodbye bows, warps and twists! Not only flat, but stiff as all get-out.

The 96" length nicely accommodates glider and giant-scale wings.

[huntermax3030]

Nice idea...also nice of you to post the part number. Question: What store or web site is that?

[green66]

What store or web site is that? Staples. Can probably get comparable tables at other big-chain office supply stores, e.g. Office Depot, Officemax, etc.

[asennad]

I just noticed this post and thought I’d add my two cents.

If you have a Home Depot nearby with a panel saw you can get them to cut 5/8 MDF shelf material 12x96 inch into strips 3 or 4 inches wide. Make a grid, 12 inches square, from the strips and sandwich them perpendicularly between two layers of MDF. Attach the faces using yellow carpenters glue making a box structure that will be perfectly straight and will never sag. I build tables tops this way. Cost of materials under $8.

You’ll end up with a building surface that only cost pennies and will retain its shape.