KK Radian +

Great looking plane.
Are the hollow ribs cut from a single piece of balsa or is the top part cut separately from the bottom? In the former case I would be worried about grain runout.

dirk gently wrote:Great looking plane.
Are the hollow ribs cut from a single piece of balsa or is the top part cut separately from the bottom? In the former case I would be worried about grain runout.

Hi Dirk,

Yes they are cut from one piece and your worry about grain run out is an extremely valid comment for anyone trying to emulate this. I am always "experimenting" with builds mainly by copying other chaps ideas and modifying them.

It would be easy for me to dismiss this comment but there are other factors in play that I haven't explained.

Producing these ribs wasn't as easy as I thought. Setting up the laser to produce clean cuts started off more than a little hit and miss - trialling cutting speed, laser power and the number of passes. I quickly found out that balsa selection played an important part in setting up.

After trial runs with some of my "grotty"balsa  wood offcuts - I thought I had reached perfection. Mapped out all the ribs on a sheet of 1/16th and started the run,

Disaster - I thought I had selected a medium balsa sheet by weight but this sheet had very soft and very hard spots in it. Clean cuts - no! Charred mess in places and bare penetration in others, Even after careful removal, some ribs were just too delicate - mainly because of grain runout particulary in the soft areas.

I looked at each rib and noted the grain on the successful cuts and then was more careful with sheet selection.

The next run was perfect and I checked each rib before using it.

Here is one from my test runs,



Takes quite a twist!

The weak spot is the centre and the front strut but my wing picture doesn't show the final D front centre section and the cross grain rib supports further out.

The cap strips add more strength and the final wing is well strong but light.

It is also one of the very few planes I have built where I haven't broken a rib during construction but I think that was down to me taking more care.

The other thing to take into account is that this is a small plane.

Ummm, help me out please. What is "grain run-out?"

944_Jim wrote:Ummm, help me out please. What is "grain run-out?"

When you have a thin piece of wood like that on the rear slope of the rib - the grain doesn't follow the entire length or shape of the curve of the piece. It cuts across in many places - a bit like cutting a spar cross grain rather than with the grain.

944_Jim wrote:Ummm, help me out please. What is "grain run-out?"

I haven't been able to find a video that discusses grain runout in aeromodelling context, so instead here's luthier Dan Erlewine doing a great job explaining it (the interesting part starts at 1:20):


In case anyone cares, he's the one that made Albert King's custom Flying Vs that Joe Bonamassa now plays.

ian1954 wrote:
The cap strips add more strength and the final wing is well strong but light.

I now realise I failed to comprehend there were cap strips, which make grain runout a lot less of an issue.

Great looking build and plane , got me looking at Lazers again , the Stepcraft over here is about 400 usd bucks . Have you had good success with it ? Those ribs are thin !

getback wrote:Great looking build and plane , got me looking at Lazers again , the Stepcraft over here is about 400 usd bucks . Have you had good success with it ? Those ribs are thin !

If you are looking for a laser cutter - peruse the Banggood site

https://www.banggood.com/search/laser-cutter-machine.html

The "starting price?" for the smallest Stepcraft machine is $1799 to $4999. I bought mine years ago but it has cost a fortune to upgrade and I have to wait months for parts and accessories. It is made and packaged in China now. While it is a good all rounder - it is cheaper to buy dedicated machines.

The laser is not very powerful only 3W and now costs Euro 605 as an add on. Most complete 10W laser cutters are under that price. I also don't think they sell it in the USA.

https://www.stepcraft.us/

My Stepcraft is the first version and there are no dedicated spares for it now. When they bring out a new model - the Stepcraft 2 and now the Q series - support for the older systems disappears. When I first got it - I was very pleased - now, it is one of my legacy tools and merely OK.

Well with that said at 2K i don't know if i need one that bad LOL But after reading about the D420 and the surface area is very good at 16?X11?" and will do all i would ever need , with just the thought of dropping that much in it for me i would have to figure a way to help pay for itself !? And the learning curve / even though i have a friend that is computer savvy But don't want something i have to Keep upgrading to do what i want Thank for your input Ian !