Tilted Sanding Block

[Jmk89]

No not the Earl of Norton but a device to help sanding strip into trailing edge stock because one is much more likely to  have some sheet the right thickness, grain and density than to find a commercial piece of TE that suits!

Today I started making another rubber powered plane. I'll tell you more about it when I am more advanced in the build (still waiting for a package of balsa from Balsa Central in Adelaide to get here so that I can start cutting ribs).

However, my balsa stock did have some suitable timber for the trailing and leading edges for the wing and I bent the bamboo wingtips using my usual heating-soaked-bamboo-around-a-template method.

However, I realised that I had not shown you guys my trailing edge sanding tool. I think I stole the idea (and improved it a bit) from something I read in Aeromodeller (it may even have been John Stroud's Golden Wings column in the mid-70s.

Here are a couple of photos.

Basically, as you can see, the heart of the device is a piece of 50 mm x 25 mm aluminium rectangular tube 150 mm long  (I think it's 3 or 4 mm wall thickness).

To each side. I have created two sliding "legs" which have 3 mm wide slots cut in them. 150 mm long. The slots are about 35 mm from each end. Then in the middle of both sides of the centre section at the 35mm point I so that a 3 mm cheesehead  screw can hold the legs solidly to the side.

In fact, one leg of the device could be just a piece of aluminium strip glued to the side with 1.0 or 1.5 mm projecting since normally the rear of the trailing edge edges that I use come down to about 1.5 or 1 mm. The other side, however, does need to move so that the block is angled to create a nice triangular piece of trailing edge stock.

If the trailing edge is 12.5 mm wide, the long leg needs to be set four times the thickness of the trailing edge because the block is 50 mm wide and 12.5/50 = 4.

Of course, I forgot to mention that a piece of 120 grit sandpaper is stuck to the wide side of one face of the centre piece.

I tend to take off 70% or so of the balsa using a razor plane and then use the tilted sanding block to take it down closer to finished dimensions.

Maybe sometime soon I will do a 3D printed version of this

[Piecost]

Thanks for sharing your setuo. I tend to break many wing ribs when sanding trailing edges after assembly. So, I am a big fan of sanding prior to assembly.

[Jmk89]

Yes, that happens to me too.
Have you tried putting a strip of masking tape across the rib ends ( one strip along the whole wing with about 1mm sticking to the front of the TE? It helps to protect the rib ends.
I still preshape the TE because even when using masking tape after construction because I find it easier to handle and there are fewer sanding strokes required at the end

[lincoln]

Excellent idea. My guess is that you could do the same thing with a razor plane or other small plane.

Earl of Norton? I think I'm on the wrong end of the Earth to get that one.

[Jmk89]

Earl of Norton? I think I'm on the wrong end of the Earth to get that one.

When I typed the word "tilted" in the Subject line, the 'puter changed it to "titled".  So I gave some sandpaper a title.

[Jmk89]

I have designed a 3D printable version of the sanding block in FreeCAD.  However, the 3D printer is on the blink and I am waiting for the required spare parts.

Once they arrive and I have resussitated the printer, I will do a print as proof of concept.  After making any changes that the printed prototype sjhows are needed, I will do a quick tutorial on putting the thing together and using it to go with the STL files and put the lot in the Plans Gallery, so others can use it.

[lincoln]

Earl of Norton? I think I'm on the wrong end of the Earth to get that one.

When I typed the word "tilted" in the Subject line, the 'puter changed it to "titled".  So I gave some sandpaper a title.

Norton as in Norton abrasives? I'm pretty sure that the title said "tilted" when I read it.

[Jmk89]

Earl of Norton? I think I'm on the wrong end of the Earth to get that one.

Yes I caught it before I posted, but still liked the joke
When I typed the word "tilted" in the Subject line, the 'puter changed it to "titled".  So I gave some sandpaper a title.

Norton as in Norton abrasives? I'm pretty sure that the title said "tilted" when I read it.

[Jmk89]

The 3D printer is up and running again and here are some photos of the Tilted Sanding Block in 3D printed form.

I will be uploading the STL files for this to the Plans Gallery in a zip package over the next day or so. Instead of putting a PDF of the information about the printing and assembly of the device in a separate document as part of that package, this time I'm going to just include a link to this post in the description of it in the Plans Gallery.

Some 3D printing information.  These parts were printed using 1.75 mm PLA with support on a Neptune 4 printer.  The hardware required to complete it are:
4 M3 x12mm cap head screws plus washers
4 M3 brass threaded inserts.

Here are the three pieces as they come off the printer plus the hardware.



You will see that the centre block has supports on the inside. I thought there was no reason not to support the inside a little bit as there is no particular use for the tube element except to provide space for the screws. I decided not to print the device as a solid block, however, since I didn't want it to weigh too much.  The best compromise was a tube with interior support.

These are the brass threaded inserts that I have put into the sides for the M3 screws to run in.


The design has holes for the inserts to to go in.  The holes are a little bit smaller than the diameter of the insert. The trick here is to use the tip of an electric soldering iron to heat the brass insert at so that it gently melts the plastic and can be carefully pushed into place. Unless you have asbestos fingertips, it's wise to hold the threaded insert with tweezers or forceps while doing this. This also helps to keep the insert centred in the printed hole and makes it easier to insert the device squarely.

Finally, here's the device assembled.



As you can see, these screws have a can be tightened using an Allen key. However, I think that an improvement would be to use M3 thumbscrews.

Both threaded inserts and suitable thumbscrews can be obtained on eBay or Temu.

This is, of course, still in the nature of a prototype, so I may improve it over time and will post the improvements here. Similarly, if you have any suggestions or make any improvements yourselves, please share them with me or the group generally.