Dear Claudio,
Can you share your sanding technique to get this kind of smooth and relular profile? Well, maybe my question is too hard to answer in words. I do understand that the multiply gives you some indication along the way. But how do you tackle the task? Like, do you move your sanding bloc mostly in the length or in the width direction? Any pointer would be usefull.
Hi Sylvain,
nothing more simple, just good eyes and elbow control.
I make myself various size and grain rasps using plywood as support. Sometimes the abrasive paper is glued onto some times just free - see pics.
The guide is the color change of the balsa or any other wood. The secret is only the multiply that provide a clear indication when one layer is reached also because of the epoxy resin contrast.
Cheers
ClaudioD
Excellent! This is exactly what I was hoping for. Thank you for your time.
Hi Sylvain,
Another trick for better tracing the sanding work is to alternate balsa sheets with colored paper, preferably black, or 1/64 veneer wood like mahogany, while little heavier. see : http://www.wood-veneers.com/beauty/beauty.html
Once I was brutally criticized because I used carbon tissue as a tracer believing that was used to increase the strength against flexibility.
Some narrow minded peoples when indicating the moon they look at the finger !!! eheh !!
Since I need to make a second rudder with different size and form, I will employ this method again !
See below some samples of a Class M fin made some ten years ago.
This time I will use colored paper to avoid costs and critics !!! btw, the next rudder recall the Spitfire wing !
Cheers
ClaudioD
PS : I did not find at home black paper only reddish !
Hi Claudio,
I read the threads about the NZL-20, the OneTwoTwo, the foaming techniques (Azur, Fluxia 65 and American Eagle) and your book about VRC. But, I’ve some (basic) questions on the bulding techniques for the hull. Please correct me if I’m wrong.
You build a positive mould of the hull in hout and try to have it as smooth as possible with epoxy primer, filler and a lot of sanding dry and wet. Than you wrap the hulll with packing tape for lamination.
–> Do you laminate directly on the packing tape or do you still use wax or latex to facilitate the extraction of the hull ?
After this there is still sanding work to come to a smooth hull.
–> What are the finishing steps ? Is it sanding and painting or do you use gelcoat ?
moulding the hull directly on the master offers the advantage of being more easy, but the thickness of the hull come on top of hull design as defined by the frames so that the shape of the finished hull is not corresponding to the original plan. furthermore, in your book, you mention the gelcoat has the lowest roughnes (0.2µ against 5µ for painting).
–> Why using this technique and not building a negative hull with gecoat if performance is the final goal ?
I guess there are already answers to those questions in the forums, but I haven’t found them yet.
Thanks,
Frédéric.
See above
ClaudioD
Some progress about fin and rudders
To note on the new rudder the use of reddish colored paper is very useful to trace the sanding work. Increasing the number of thinner layers ,the work obtained is more precise.
ClaudioD
PS : Counter shadows made, ready to start work with the hull.
Claudio,
Is the red paper bonded to the balsa with epoxy?
Also, I would have thought that using carbon as the trace layers for the fin was an excellent idea - a uni carbon could be laid at varying angles between the balsa sheets which would surely improve ridgidity. I guess it may create problems when sanding owing to the relative hardness against the balsa, but nothing that can’t be overcome.
Regards,
Row
Hi Row, is not valid your assumption.
In mechanics the beam resistance is coming from the external skin layers. Every reinforced layers closed to the neutral fiber do not contribute to the bending strength.
Almost he same strength can be reached with air replacing the balsa. Unfortunately the external skin may risk to collapse if not sustained by more solid element. Balsa can be substituted by foam with the advantage of weight gain.
It is a pity to use expensive carbon tissue when colored paper acts perfectly.
When I did used some carbon tissue, some years ago, was simply due to the non availability of colored papers to get the contrast when sanding. It is true that the relative hardness is another reason to avoid it.
In the pictures above there is a the demonstration on how it is useful.
Cheers
ClaudioD
PS : e.g. : according to my calculations memory, a plain rod of 20.5mm has the same resistance to bending than a tube of 24mm OD and 20mm ID
I can certainly see the advantages of using the coloured paper - I’ve made a ‘mk 1’ rudder for Enterprise using thin mahogany faced ply (it’s far too heavy) but the colour differential made shaping the required section for each side very straight forward.
Given some more thought to your comments about the carbon/balsa lamination for the fin regarding the mechanics of beam resistance / skin layers and done a bit of reading around the subject, so it’s beginning to make sense. I still can’t help thinking that while a central carbon lamination will have no effect, any additional laminations between the balsa skins must have some benefit. Of course, it would be nothing like as effective as additional layers of carbon on the ‘outside skin’. I’m probably way off the mark with this - my bedtime reading was somewhat hazy last night owing to a rather nice ‘Chateau Mussar’ !!
I reckon I’ll be reading it all again, so that’s it for now…
Regards,
Row
Hi Row,
the efficiency vs weight is very low when inserted in between layers.
At the end you get an heavier fin but not stronger. Far better to use fraction of that tissue weight outside to get increased strength !
I found a page of an old civil construction manual, see below pic
Get well
Cheers
ClaudioD
Deck sheer line stripes 3x5 obeche/samba bonded for the price of 8 grams !
Bulb layers for 1mm lead sheets retraced and printed (original from Bulb Calculator).
ClaudioD
Just superposed the deck to get an idea about the final look !
ClaudioD
Dear Claudio,
If you recall the choosen NACA foil used in Bulb Calculator, please fell free to share it with us ;).
Hi Sylvain,
here the requested data
Cheers
ClaudioD
PS: 2 hours cutting and the first bulb half is ready for bonding with cyanolite glue
Bulb assembly process .
Each sheet is drilled on the dot as per drawing indicating the CG.
The paper is removed with water sponge.
The dry sheet is positioned on the “tool” composed of a wooden bloc and a 3mm pin is used for alignment.
The polyethylene film will prevent gluing to the wood support.
Cyanolite glue is deposited some 4mm inside the the peripheral edge.
Small pressure exercised for 5 sec.
Here below the first result
ClaudioD
PS : Bulb fully assembled, rasp and sanding paper needed !!
After 1 and 1/2 hour with rasp and paper sanding, the bulb is shaped for final finish. Hole drilling will drop the weight for about few grams.
Actual dimensions : 28.5cm long and 4.85 cm diameter against 28.78cm and 4.78cm as per Bulb Calculator based upon a specific weight of 10.5kg/dm3.
The CG is at 11.8cm from entrance against 11.1cm from Bulb Calculator
Well satisfied with the results !
ClaudioD
PS : finish with water paper grade 800
Hi Claudio, just found your thread and wow fantastic work - wish I had half your skills !!!
I really like the sharp and sleek lines of your design - what software do you use for your drawings and to calculates the volumes ?
never saw building a bulb that way, very innovative… we normally use a stainless steel rod and use the moulding method but this avoids having to melt lead which is very toxic and dangerous. I take it that you cut your layers in a sheet of lead but what thickness of sheet did you use and how did you cut each shape precisely ?
can’t wait to see your progress …
Hi Claudio,
Wow, serious progress!!
As CelticSpirit alluded to, I also wanted to ask what you use for cutting the lead profiles.
Also, from one of my earlier posts, surgery cancelled for the time being - a hospital pen-pusher ordered in the wrong bits, because they were cheaper!! Now waiting for a new date…
Back to the current build, when you join the hull & deck will there also be a layer of glass over the outside joint or will it just be filled and faired with epoxy filler?
Regards,
Row
Hi Celtic Spirit,
After having seen the burns on the hands of a friend, I was so scared that I decided to use this method.
Is not new, it was already presented in several occasions in this forum while presenting model constructions.
This technique was used in the past to make hull and it is called ‘bread and butter’ construction, e.g. see http://www.building-model-boats.com/bread-and-butter-hull.html
The lead sheet is generally used here in France for roofs water proof construction around chimney.
The one I use is 1mm thick, I have also available in 0.8mm .
Once retraced each layer from the bulb calculator drawing, each printed paper template is glued on the lead sheet and cut by hand with a pair of scissors. Generally I need one day to print and cut and half day to bond all the sheets and another half day for shaping and finishing the surface including the hole drill that is the most delicate operation .
All my drawings are made with and old version of “Coreldraw 5” and often stored as PDF or Jpeg files. I do not use any 3D software for design development since I’m much faster with my drawing technique, generally I need less then one day to draw the typical 3 views.
Some time I use the free version of Rhinoceros just to make some simple 3D views as depicted at the begin of this tread.
I will prepare a sketch to explain the displacement calculation that is quite the same as the ‘trapezoidal rule’.
Cheers
ClaudioD
Here the surface calculation method :
Once all immersed surfaces are calculated, the sum is multiplied by the distance between shadows.
The calculated surfaces are also reported to an X-Y diagram in order to trace the Curve of Areas as depicted :
