Modelling a cannon cypher in Fusion 360

[Kevin-the-lubber]

A bunch of us are creating STL's of a range of English cannons, a group project led by Allan. While the barrels are simple to model in CAD programmes, the cyphers take a bit more work and I agreed to share the way I did this one.

 

 

First, a bit of preamble: I work entirely in Fusion 360. The method I'm going to describe is undoubtedly not the only way even in F360 so feel free to chip in. I played around with the surfacing mode first but that way led to madness!  Extruding the shape from a 2D drawing is very straightforward in F360 but left me with two issues; it doesn't properly wrap to the cannon barrel i.e. the edges would be uniformly vertical when they should follow the curve, and it doesn't allow the interweaving of the letters. So what I did was use the 'sheetmetal' function, so that I could correctly wrap, and lofting to get the interweaving. It goes like this;

 

Step 1: create a dummy barrel section. It needed to be hollow in order to be 'sheetmetal'. I use a thickness of 20mm but any thickness will be okay. This dummy section gets 'discarded' later

Step 2: Cut away half vertically

Step 3: add a flat flange in order to unfold

step 4: convert to sheetmetal and unfold. this allows me to create the cypher in the flat, and wrap it at the end

step 5: create a centreline sketch. I form the cypher 90 degrees off it's correct position, so that it doesn't sit astride the split/flange. If it sat astride, I'd have to made it in two halves. The important thing here is that this centreline is not vertical, but is set to the correct angle in the flat

step 6a: position the cypher sketch on the centreline

step 6b: an explanation of the cypher sketch. I'm making this in two parts - the crown, and the lettering. For the crown I simply extrude aspects to different heights in order to create the 3D relief. For the lettering, I create section profiles at different points in each letter and then loft the sections. This creates the sweeping under and over effect. The placing of the section profiles is entirely subjective and a bit of trial and error is needed. The centrelines through each letter are essential; the outer lines are only a rough guide and don't really dictate the finished shape.

 

step 7: create planes at at angle (90 degrees) and section profiles

step 8: loft through these sections

step 9: extrude either side, and that's the first part done. 

step 10: repeat that process for all remaining parts of the lettering. A point of detail here is that lofting centrelines can't 'loop' so you have to break those sections into segments. This requires a lot of planes and section sketches, roughly 30 in this case. I worked to this photo to more or less replicate the interweaving (and have just noticed a little mistake on the 'R')

 

step 11: make the crown via straightforward extrusion

step 12: combine (join) the crown and lettering to the unfolded dummy cannon section

step 13: refold the section

step 14: cut away the flange and dummy cannon section

step 15: rotate the cypher parts through 90 degrees

step 16: combine with the cannon barrel and we're finished

I hope that helps, happy to discuss and learn a better way!

 

 

[allanyed]

Thanks Kevin, this is really well presented.

Now for some aspirin as my head hurts. 😁

Allan

[druxey]

Beautifully presented, but I find it looks a little too high or deep. Can this be adjusted (see photo of the real thing)?

[Kevin-the-lubber]

2 minutes ago, druxey said:

Beautifully presented, but I find it looks a little too high or deep. Can this be adjusted (see photo of the real thing)?

Yes, it can easily have the height reduced and the profiles made more true to casting reality - rounded edges, a curved top - but I fear at even 1:48 it would end up looking like a smudge, let alone any smaller scale. Right now we are having a very cold snap (or a slightly cold day for you north americans and canadians) but once the weather warms up and I can print, I'll do some sampling.

[PietFriet]

In the spirit of sharing alternative ways of doing the same thing.

You can use the Emboss tool to project a sketch directly on a curved surface.

 

 

[Kevin-the-lubber]

44 minutes ago, PietFriet said:

You can use the Emboss tool to project a sketch directly on a curved surface.

PietFriet, thanks, I never noticed that feature (note to self, to spend some more time on study). That would give a flat topped but properly wrapped cypher - is there another or better way to create the interwoven letters within F360?

[PietFriet]

Kevin,

The flat topped result worked for me because the height is only 0.25 mm, but I can see that if you want a variation in height your technique is more precise. I am actually thinking of reducing the height even further because 0.25 mm is too high for scale 1:48 (12 mm). But with a printer resolution of 0.05 mm (x-y) there is not much to play with.

Peter

[Kevin-the-lubber]

I set the height at 20mm full size, aimed at about 0.2mm at 1:96, for the same reason. To be honest I think the degree of detail I've added is probably a waste of time and effort, but, that said, I did some very, very fine detail scroll work on the HMS Victory stern and was surprised that it was both visible and, to my eye, looked worthwhile. I'm not certain now but think I was starting to work to 0.1mm level changes. Anyway, I'll review once I do a print session and, unless it really does show at scale, I'll shift to embossing, not least because that is such a quick and easy method. Lofting takes hours.

[Kevin-the-lubber]

So... I've run a test print, and indulged in a bit of colouring. These are 32lb-ers at 1:48 and 1:96. Druxey is right, the cypher stands too proud. It's lovely, but not right. At 1:48 you can clearly make out that it's George II, but if you didn't know the letters are interwoven I doubt you'd spot it. At 1:96, you can just see that it has a cypher but it could be for Genghis Khan as much as King George.

 

Consequently I'm reducing the height by 50% and embossing as per PietFriet. That should make it a little quicker to get through a set.

 

[thibaultron]

Unfortunately, my present camera, will not focus on these small prints, I did of my cannons for this project, but I can give some results from my first prints. Here are graphics of the two heights I tried. My cypher was shown on the drawings as the one I used, not the Royal Seal from the posts above. Please ignore the length shown in the taller cypher graphic. Due to limitations in SketchUp, I do all my drawings in feet (in equivalent to full size inches)  and inches, instead of full size inches. So the 166 foot 8+ inches, really scales to ~166 + inches, when I'm done. SketchUp does not like items that are smaller than about 1/32 inch when you draw directly in just inches, which makes small items like the cypher difficult to work with. I rescale the model in Netfab, when I create the STL files.

 

I printed one of each cannon in 1/48th, 1/64th, 1/72nd, and 1/96th. They were printed on an Anycubic Mono 4K with a 35um pixel size and at a 35um layer height.

 

In any case, the taller cypher scales out to 1/2" tall at the anchor ring, and 1" over all. The lower one scales to 1/8" and 1/4" respectively.

 

When I printed them the tall cypher stood up way too much, for the three larger scales, but was still clear, if still too tall at 1/96th. The lower cypher looked better with the shorter offset for 1/48 to 1/72nd, but was almost invisible at 1/96th. At all the scales even this lower resolution cypher is lacking in visible detail, but can still be recognized, due to printer limitations.

 

I had a couple of the cannons fail, but my FEP needs replacement, of the cannons that did print (and stayed on the base), these are the best pictures I was able to get.

 

The first is the cannon with the lower offset cypher at 1/64th scale. The second is the taller offset cypher at 1/64, 1/72, and 1/96. The lower offset cypher looks more reasonable for those on a real cannon.

 

 

 

 

 

[druxey]

I've seen examples of a physically flatter cypher that was given definition after the piece was blackened by a dusting of lighter grey powder to give just a little visual emphasis to it. Very effective.

[PietFriet]

On 3/13/2023 at 4:43 PM, Kevin-the-lubber said:

So... I've run a test print, and indulged in a bit of colouring. These are 32lb-ers at 1:48 and 1:96. Druxey is right, the cypher stands too proud. It's lovely, but not right. At 1:48 you can clearly make out that it's George II, but if you didn't know the letters are interwoven I doubt you'd spot it. At 1:96, you can just see that it has a cypher but it could be for Genghis Khan as much as King George.

 

Consequently I'm reducing the height by 50% and embossing as per PietFriet. That should make it a little quicker to get through a set.

 

 

They look fantastic !!! Your approach creating a 3D effect in the letters certainly pays off when viewed in close-up (I had not expected that).

It seems the only limitation now is our eye-sight 🙂.