seanreit

My Feedback: (60)

In the attached pictures, you show the airfoils, and I get all that, my question is two fold.

You talk about a "pivot point" where the trailing and leading edge lines meet? Is this accurate?

How are you mounting the templates to the foam in the attached pictures? 1/4 20 screws? And if so, is your template a one piece top and bottom airfoil? Or are you taking the top template off and putting the bottom template on?

My experiance putting templates to foam is that they shift when you pin the template to the foam??

da Rock

It appears from his pictures that he places the templates for the top cut to the foam with what appear to be nails. Plain heads, no screwdriver slots. The picture of the template for the bottom cut isn't so clear, but the heads do not show slots there either.


The first and second pictures show his top cut templates in place. He would make that cut and then remove those two templates. He'd place the two bottom cut templates and probably also the top shuck and maybe a couple of weights. Then make that cut.

He'd have 4 templates. Two for the top cut as shown in the first two pictures, and two for the bottom cut. The 3rd picture shows the bottom cut templates in place on the bottom shcuk and the finished piece beside that shuck and the top shuck in the background.

BTW, if you stack the templates and drill the stack for the locating pins, the pins all wind up using the same holes in the foam. You get an automatic line up of the templates when you switch from one set of templates to the other.


"others"

Strat2003

My Feedback: (1)

I've used this method and it works very well. The templates are secured with ordinary galvanized roofing nails, about 3/4" long, but the actual vertical location of the templates is achieved by the base resting on the benchtop.
da Rock is right, you stack the top and bottom template for each end to drill them...that maintains your fore-aft location.

I cut the bottom profile first. That way the core drops down after it's cut and the "melt back" doesn't thin the section quite as much...your core ends up closer to the template thickness.

da Rock

Some people make the templates to allow for that thinning. You have to allow for the skin thickness for the template anyway if you're attempting to produce an exact profile copy. And the way some people allow for the thinning is to consider it as the allowance for the skins.

Keep in mind that when you cut the bottom first, you have to be careful to align the "loose" foam part you just cut with the bottom part before doing the top cut. If you don't, the second cut won't make your profile. It will make a core that is either too thin in the back or too thin in the front. And all your alignment of pin holes will be a waste of time.

We used to mark the ends of the blank before cutting. A couple of lines with a magic marker helped keep everything in alignment.

In our hobby, there are almost always a couple of ways to do something the best way. [sm=wink_smile.gif]

Strat2003

My Feedback: (1)

Yep, you're right about keeping the core aligned with the bed. I use the marker line trick, too. The weights on top keep everything in place once things are lined up.

Tony Hallo

Seanreit,
I believe all your questions are answered except for pivot point. When I referred to this, I was talking about cutting high tapered sections such as rudders. The pivot point is the imagionary point where the leading edge and trailing edge would intersect if projected beyond the surface, at this point I will loacate the pivot point for cutting high tapers, the cutting bow will pivot about this point.
I use 1 1/2" aluminium siding nails to hold the templates in place, never though about drilling both together, will try this in the future. I align the templates to the foam with a reference mark to the leading edge.