Monday, November 12, 2012

T2-21 Build-Series #1

The first article in the KEP's T2-21 build-series!


KEP's T2 .21 Presentation

KEP's T2 .21 Freebie

Note 1. Some of the pics in the build series is from me building the prototypes that are a little bit different to the T2 freebie. I will point out when that is something you need to know...

Note 2. Most of the pics are taken with the iPhone so do bare with me regarding lack of picture quality. ;)

Print the PDF's

You have downloaded the PDF's and had them printed out on A1 sized drawing paper by a print-shop in 1:1 scale / 100%, right? If so, here we go...

Make the templates

Cut the paper copy of the templates out with a pair of scissors - leave them a bit rough. Use spray glue and attach the paper templates on a 1 mm thin plywood and cut them out in a band-saw. Use a small plane or a flat bar-sander with 80 grit sandpaper and shape the template edges. You should shape it out so the outline is removed or just barely visible. If you can see the outline of the template the parts will be too big... When you are satisfied with the shaping use a drill press and a 1.5 mm drill bit and carefully drill holes exactly in the middle of the marked out holes.

Make the tub-side laminates

I strongly suggest that you make your own laminates for the T2-21 tub-sides. We have used 4 mm gaboon marine plywood on the prototypes but that is just too soft. You want the finished laminate to end up being 4 mm thick but some of the wood is not the thickness you think it is. Most are a little bit thicker then what the label says they are...

This is what I recommend using as glue when making the tub-sides laminate - Cascol Polyurethane. Or Gorilla Polyurethane glue if you are not in Sweden. Note, I earlier recommended Titebond-III to be used as a glue when doing the laminates. Even though you get a good glue joint with that it will be booth heavier and crate a softer laminate vs a PU glue.

Here is a couple of updated pics of my laminate making set-up. I use a couple of flat honeycomb cores covered with thin plastic food wrap. Leave under pressure over night...


Take the tub-side laminated sheet and cut that in half so you have two pieces that are about 50x700 mm. Use pieces of normal carpet-tape and stick the two laminates together.

Take the tub-side template and use a sharp pencil and carefully draw a line around the template. Be careful so you don't move the template! Take a sharp pointed item and make dimples where you should drill the engine mount holes, sponson tube holes and also the NAVIGA number plate holes if you intend to race over here. Remove the template.

Now you need a band-saw with a decent fresh and sharp blade. Adjust the band-saw so it will do straight cuts etc. Start sawing the tub-sides! Make the cuts AT the line - Not outside the line. When the tub-sides are done the complete pencil line should be just about gone...

After you have cut them out you need to shape the edges smooth and make sure that the edges are straight and true (90 deg). I highly recommend Great Planes Easy-Touch Bar sanders (GPMR6170) with the most course adhesive backed sandpaper (80 grit) for it (GPMR6180). That's in fact the only sand paper I personally use for the sanding bars.

Use a steel straight ruler and check that the edges are true and straight and a true-angle square to check that the edges are 90 deg.

When you are happy with the tub-side shape it's time to drill the engine mount holes and the sponson tube holes. For that you need wood spiral brad-point drill bits with 11 & 12 mm diameter.

Use a drill-press so you know the holes will be straight. Also use a wood base underneath the tub-sides while drilling. Use gentle force and go slow while drilling - especially when your just about going through as the drill-bit can make the lower/outer plywood split...

When that is done - take the tub-sides apart and drill the smaller holes for the threaded brass inserts in the left tub-side only. Glue/thread them in with epoxy glue. Leave to harden. Cut/sand the protuding part flush with the tub-sides. Use a suitable thread tap (M4 or 8-32) and clear the threads.

Glue small 10x10 mm cover pieces of 1 mm plywood on the inside of the threaded inserts to make the holes water-proof. Make sure that there is no glue that will drip down in the threads. This step can wait also until you have glued all the bulkheads that will be showed in the next build article. (The picture shows a tub side from one of the prototypes - that had a stepped deck and we used soft gaboon plywood.)

Mark the insides of the two tub-sides where the bulkheads will be located.

Done for now - next steps are bulkheads and setting up the simple glue-jig. :)

The second article in the build-series is HERE.

No comments: