3D printed leading edge sanding block

[Winston]

I was reminded of this idea in another recent thread here. Since I don't typically contour leading edges of LPR rocket fins since my balsa fin paper laminating technique almost requires square fin edges, I'll leave it to someone else to try this or some better variation of it if they think it's a good idea and choose to do so. And since it's a kinda' obvious idea anyway, maybe someone has already tried it.

Below is a photo of the 3D printed sanding block I tried on 1/4" birch plywood some time ago before I decided that it was just easier to 3D print the leading edges. A 2:1 aspect (fineness) ratio ellipse cutout was designed with the packing tape reinforced sandpaper thickness taken into account in its dimension. If I'd have further pursued this method, I'd have made a set of sanding blocks for progressively deeper/steeper sanding and knocked off the edges of the plywood leading/trailing edge with a Dremel or belt/disk sander first.

Anyway, I think this method might be much more appropriate for use with, for instance, MPR fin thicknesses of light plywood and LPR balsa fin leading edges. Perhaps rather that using sandpaper over the sanding block due the possible difficulties with that caused by the much smaller groove width, diluted epoxy could be painted onto the block, sprinkled with an abrasive, and the excess abrasive shaken/knocked off. Such a block would probably last a very long time when used on balsa.

 

[dhbarr]

I've been hoping someone would make a several-sided 6:1 VK profile sanding block for 1/16" through 1/4" by 32nds.

Would essentially be a cylinder with small size-marked channels in it. Was thinking of having it machined out of alumina, but that's way overkill.

Does a fraction of a percent efficiency make it worth it? Probably not, but I don't "need" thus fancy fin jig either 😂

 

[neil_w]

Since I don't typically contour leading edges of LPR rocket fins since my balsa fin paper laminating technique almost requires square fin edges

This statement was a little curious to me, since papering rounded edges is not difficult (if I can do it, then it is definitely not too hard; here's my latest go at it). Not that rounding edges on LPR rockets is a big deal, and everyone has their own papering technique, and by all means you should build however you prefer, but it seems that if you really *wanted* to round the edges then papering should not get in the way.

I feel like for LPR balsa fins, rounding the edges is so easy that it's not worth a jig (and all my various curvy fins wouldn't work in there anyway), but I can imagine for the harder stuff in larger models something like that could be useful if it worked well.

 

[Winston]

This statement was a little curious to me, since papering rounded edges is not difficult (if I can do it, then it is definitely not too hard; here's my latest go at it). Not that rounding edges on LPR rockets is a big deal, and everyone has their own papering technique, and by all means you should build however you prefer, but it seems that if you really *wanted* to round the edges then papering should not get in the way.

I feel like for LPR balsa fins, rounding the edges is so easy that it's not worth a jig (and all my various curvy fins wouldn't work in there anyway), but I can imagine for the harder stuff in larger models something like that could be useful if it worked well.

My papering technique described in that other thread I mentioned in my initial post in this thread along with the reason I usually don't care about square edges in LPR:

https://www.rocketryforum.com/showthread.php?134806-Estes-Star-Orbiter-9716&p=1666972#post1666972

EDIT: In the rare occasions when I need rounded LPR edges, I modify that technique with a more time consuming one where I pre-cut smaller pieces of label material that are set back from the edges of the fin by the radius of the rounded edges. I then round the edges and apply the water thin CA. An aerodynamic test model I will launch soon uses that technique.

 

[Winston]

I've been hoping someone would make a several-sided 6:1 VK profile sanding block for 1/16" through 1/4" by 32nds.

Would essentially be a cylinder with small size-marked channels in it. Was thinking of having it machined out of alumina, but that's way overkill.

Does a fraction of a percent efficiency make it worth it? Probably not, but I don't "need" thus fancy fin jig either ��

If you plan to use it on plywood, I'd strongly recommend a stepped/progressive stepped grooved design. Also, I believe I read in a fin/nosecone design document I've posted a link to elsewhere here that anything over 5:1 VK is not productive. Also, for 1/4" its much easier just to 3D print the leading edge although I've never subjected mine to extreme velocities.

As I said, I think the sanding block idea would be easiest to implement successfully for balsa fin LPR use and light ply MPR use. If an elliptical shape is not required, I've used a router bit on a scrap piece of hardwood, too. LPR altitude competitors might want elliptical. 2:1 elliptical is the best subsonic shape.

On the fraction of a percent difference mentioned, if one is bothering to make a 3D printed sanding block in the first place, the "3D printed" part being the most important benefit, why not make it a more efficient shape when that is just as easy to do so as it is for a rounded shape? The primary goal in this is not necessarily to achieve the most efficient shape, it is in creating a cheap 3D printed tool to make uniform shaping of a leading edge easier.

EDIT: Once someone comes up with one or more STLs for these they can make them available on-line and either a friend who has a 3D printer if you don't have one can print one or more for you, a lot of 3D printer groups will do this for the low cost of the filament as many hobbyist 3D printers site idle most of time, many libraries are opening maker spaces with 3D printers as part of STEM, or someone could even make and sell these.