Ricardo Aurelio

Hi

Can anybody explain me how do I fix (hold) a block of foam with the wing profile templates on the the table, to be wire cut?

Thank you,

e=mc2

Double stick tape and some weight on top of the block Some peoplr use glue or bondo, but unless you plan to really yank and bank stratigically placed double stick tape should be sufficent and easy to remove.

e=mc2

KENB85

AT THE FACTORY THEY PROBABLY USE A LARGE VACUUM PLATE - AT HOME YOU CAN USE CARPET TAPE (DOUBLE SIDED TAPE)

Ricardo Aurelio

Thank you Ken85 and e=mc²

Another question: Do you use the real wing profile or ist's "outside" as a template?

Al Stein

First, you were origianlly asking about keeping the foam block in one place on the cutting table right? I have never needed to tape a block in place and using glue is totally out of the question in my book. You must put some weight on the top of the block to be sure it does not rise or bend while being cut... I use several pieces of steel scrap, but a few books would hold the block very well.

For the template, it should be the size of the finished wing minus the thiscness of any sheeting you may use. So, for an unsheeted wing, use the final wing size but for a sheeted wing (or for a sheeted part of a wing) the template is smaller to allow for the thickness of the sheeting.

Ricardo Aurelio

Hi Al

Thank you for your kind answer.

I understood your explanation about the way you keep the foam block on the cutting table.
As regarding templates, my question is due to some articles I've read showing people using 2 templates to each wing end. Two templates (one at each end) to the superior cut and two templates to the inferior templates

Al Stein

G'Day Ricardo --

I use two templates when I cut wing cores. Following advice I received on the Web, I make the bottom cut first. That way the width of the kerf (the thickness of the gap cut through the material) is filled by the core as it drops into the gap... so when the top is cut the thickness of the wing is very acurate and it is not affected by the thickness of the cut.

Because this removes nearly all of the size difference caused by kerf width, I make my templates to the size and shape I want the core to have.

I'm not sure if there was another different question you were asking that I haven't grasped properly -- about wing profile vs. outside... is there more info you're looking for there?

e=mc2

I am not sure what Ricardo is asking but my guess is that he wants to know if 2 templates per side are better than 1 template per side of the core. (or vice versa)

I am not sure if there is any difference other than the thickness of the template, which can be acheived by creating one think template in the first place

Personally, I think it does not matter in the final result but in thoery having a "thicker guide" for the wire will make the cut more accurate. On the other hand there are a lot more factors that go into accuracy when cutting a foam (like wire tension, heat generated, technique). I am always surprised how difficult all this sounds, but how easy it really is!

Cheers!
e=mc2

CrazyHerb

My Feedback: (1)

I agree,
If you need to hold down your core with something other than a couple books or wieghts, your pulling too hard.

I actually have a couple of old sealed lead-acid field batteries that I use....just set them on top and go....

I have seen some tables with a small lip on the edge that works as well...

Good Luck!
CrazyHerb

KevinSheen

You have to weigh the foam blank down to ensure it is flat anyway. I don't ever use anything to keep the foam on the table except for the weights on top. If your foam blank moves, how much tension are you pulling your wire with?

As far as the templates go, I drill 2 or 3 holes in the base of the template (the upper airfoil / lower airfoil pair stacked together) and push sharpened pop rivets into the holes and into the foam blank. After I cut the lower, I reuse the same holes in the foam to make sure my templates are aligned.

good luck, Kevin

Ricardo Aurelio

I guess my poor English aren't enough to explain my question...
I'll try in other words.
If I could understand there are basically two ways of cutting a wing profile:

1-you just cut one airfoil profile template for each side, according to the profile you need minus the sheeting thickness and then just glue it (or pin it) in the foam block. Then you can cut one side (bottom first) and then the other, without moving or touching the foam block any more.

2- you cut a pair of templates for each side, two to the upper airfoil and two to the lower airfoil as Kevin said (deducting the sheeting thickness), and then cut the bottom, remove the bottom template, install the upper airfoil template and then do the final cut.

I'm I right?

Al Stein

Right.

I think that e=mc2 is using a single template and both Kevin and I are using the two templates.

You can get very good results with one template or with two templates.

e=mc2

Seems like I misunderstood (again! ).

I am not sure what the "a pair per side" method is? I am sorry Ricardo, but I still didn't understand the # 2 method. Looks like Al knows what you are talking about maybe he can make me understand

I am going to take one more shot at it. Are we talking about wing skins cores here? I was assuming we were talking about full wing cores.

e=mc2

Ricardo Aurelio

Hi

I guess Al got it.
Anyway I have a image I could send you but I don't know how to do it via this forum...
How can I attach a JPG image here?

Thank you.

e=mc2

Look for a "Upload Images" link directly below the text box that you type your reply in and the instructions from there are pretty self explanatory. I am curious to see this image.

Thanks
e=mc2

heli001

My Feedback: (5)

I use the 2 template per side method for root and tip - upper and lower cuts. This way, the block of foam does not have to be moved or turned over, and anything reset.

As for weighting the block down, I fill 1 gallon Ziplok bags with sand (about 5 lb each), they come in handy for many task around the shop, also I use a 3 foot steel bar that is 4 inches by 1.5 inches thick ( also does a very nice job when it falls of of the table on your foot.....). With the sand bags and this bar, I can do just about anything that requires weight to hold it down.

Has anyone figured out why the Xacto knife ALWAYS falls point first...? It must be the aerodynamics of the handle, and NEVER, NEVER work barefooted....! Ask me how I know....

Ricardo Aurelio

Before anything I wish you all the very best for 2004!!!

I'll try to make my doubts more clear.
Please find below the two kinds of templates I understood can be used to cut foam wings.
Correct me if I'm wrong, but I guess with single template per each side you don't need to move the foam block to make the upper and lower cut, wright?

Ricardo Aurelio

Fisher
I did not understand how can you change the templates without moving the foam block, and how can you precisely replace the second template for the second (upper or lower) cut without changing the airfoil, not even a bit??

RAMFlyer

My Feedback: (65)

Ricardo,

The technique I use has two templates; one for the bottom airfoil and one for the top airfoil. The main thing to keep everything lined up is that the holes for the nails or rivets used to hold the templates in place are drilled at the same time.

I don't have any pictures of my set up so I "borrowed" a couple off the internet. First position the bottom template and cut the bottom airfoil.

Then, using the holes in the top template that match the holes in the bottom template, cut the top airfoil.

Some people use overlaping tabs at the front and rear ends of the templates and bolt them together. Flip the top one out of the way, cut the bottom airfoil; drop the top template back into place and cut the top airfoil.

Hope this helps and isn't too confusing!

heli001

My Feedback: (5)

RAM,

Thanks,

I could have not explained it better myself...............

Ricardo Aurelio

Yes, I got it!!

Thank you William and all of you that have helped me.
As a matter of fact my drawing for the templates should have to be as bellow, right?

Rc-Warehouse-USA

My Feedback: (28)

How do you install the root and tip templates on the foam block for a 33% extra 300. Do you draw a centerline on each end of the block and install each template on the center line?

RAMFlyer

My Feedback: (65)

Ricardo--You Got It!!! Make sure the holes line up (drill them at the same time) and you will get a great core.

Quicksand--Yes, draw a centerline on both ends of the foam block and line up the centerlines of the templates with the block lines.

Washout is programmed into the core by raising the trailing edge of the tip template the appropriate amount above the block's centerline, measured from the tip template trailing edge centerline. Keep the template leading edge centerline on the block centerline.

Rc-Warehouse-USA

My Feedback: (28)

How do you determine how much washout is needed on a 33 % extra 300 96" wing span