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Saturday 20 June 2015

SketchUp to Blender

I have not spent enough time learning SketchUp to be able to create detailed models. I like the idea, it has a free version (for non-commercial use), people can produce some excellent models in it but as I am already familiar with Blender, I tend to want to work in that.

I can produce some basic shapes very quickly in SketchUp but I start to struggle when trying to add very detailed shapes and manipulate existing models.

SketchUp has a huge following that create some excellent models and make them available, many of them licence free, on the SketchUp 3D Warehouse. Once I exhaust what I can do quickly in SketchUp I usually convert them to Blender.

I export them from SketchUp as a Collada (.dae) file which usually Blender can import.

I have had a few problems importing SketchUp files and if necessary I'll install the OBJ exporter available from the Extensions Warehouse. Click on the icon in SketchUp to open the Extension Warehouse and search for OBJ.

It is intended to work with SketchUp 2014 but I found it also worked with SketchUp 2015. A bit clunky but it worked to get the tricky models in to Blender in OBJ format.

At the Blender end it may be necessary to adjust the rotation to get the model upright. Usually +Z Up is the correct selection.

Wednesday 17 June 2015

Road bridge railings

I have now used the 3D printer to create a scenery component for my Scalextric layout :-)

Where the Scalextric track crosses a bridge I wanted to have as much visibility as possible.

A stone wall would have looked nice but it would block out the view.  It would also be impractical in the real world because there would not be enough height to have a stone arch to support the span. Although the layout does not have to be realistic the scenery always looks better to me if it could exist and support itself in the full size world.

I decided to opt for a modern bridge style with an implied concrete and steel support structure and the thin metal railings being the only thing on show.

The railings are very easy to look through, which is what I wanted. The drivers can still see the curve of the lower level road just before the cars go under the bridge.

I could have made them from odds and ends but I now have a 3D printer so this was a chance to try something out.

The design was fairly easy to work out. Created in Blender, as usual.

I made minor changes to the design to suit 3D printing. The fronts of all the rails are level with each other. This allowed them all to lay flat on the bed for printing.

The first attempt at printing was a failure because, even though I had positioned the barrier on its front, the posts still overhung in mid-air.

I re-imported the model and selected the option to print support structures, for the second attempt. These are finely printed extra bits automatically added by the Cura software to support overhangs.

This worked very well but obviously requires a little bit more cleaning up afterwards.

Some of the details are a bit fine for the normal print quality. This took just under 2 hours. If I wanted to fix that I could either thicken up the fine edges or print using the fine or ultra fine modes but that would take a lot longer to print.

TIP: A thickness of 1mm is too fine to guarantee to print using the normal detail level. 2mm thickness prints out perfectly on the normal quality level so somewhere between 1mm and 2mm is the smallest detail for this setting.

I was very impressed by how easy the automatic support structures were to remove from the finished print.

In place on the track, the railings look exactly as I intended.

Another success.


Blend file
STL file
Licence share alike


Monday 15 June 2015

Vacuum forming machine

Between other jobs, over the last few weeks, I have been putting together a vacuum forming machine.

When looking at 3D printers I noticed that they cannot do proper transparent areas because they extrude in layers. The vacuum forming machine is to create windows.

I used one at college over 30 years ago, that one was made from a timber frame, some board and an industrial vacuum cleaner. I wanted something smaller so I knew it was fairly easy to make one from bits in my shed and the Internet confirmed that a normal home vacuum cleaner had enough power. All I needed was a box with holes in, some frames to hold the plastic and a heat source.

The design and photos show it all.  Instead of glue I used silicone sealant and screws to hold the joints of the box together. The better the seal the more the suction works where you want it.

By luck I had a 32mm cutter which is the exact size of the vacuum hose end.

In practice the vacuum pulls the hose end in to the hole to make a better seal so I did not need any gasket or other cover for the hose hole. There was plenty of suck to pull down the plastic. The grid of holes in the top of the box are all 4mm diameter in rows and columns 10mm apart and staggered.

I tried to use an old sandwich maker as the heat source but that didn't get hot enough so I resorted to the kitchen oven which I had already identified as suitable.  It was but I had to pay attention. Once the grill was hot it only took a minute for the plastic to droop and a few more seconds for it to run all over the oven shelf! I'll use a lower setting next time.

The grill in our oven only works when the door is closed so I had to remove the handles I had added to the frames to get the frame to fit. I had a very simple bent wire support from a disposable BBQ that was the ideal height to raise the frames, holding the plastic sheet, above the oven shelf.

By experimentation I established that the optimum time to take the plastic out of the oven was as the droop was about half an inch down. I must get round to cleaning the glass on the oven door to make it easier to see that stage.

My first experiments confirmed that the machine worked however my choice of mold was too ambitious. I could not get rid of the webbing on the tall section and the plastic, pulled in to the lowest thin slots, was too thin. That was disappointing but it confirmed in my mind that simpler, lower shapes would work.

Having the vacuum already on before putting the plastic on the mold worked best for me.

Sunday 14 June 2015

Walls and more walls

I've been decorating the track in reverse order. Top down.

The overview of the track has looked odd to my eye up until now. At last there is something solid supporting the roads.

The walls are either made from floral foam, that I have mentioned before, or plaster filler on a hardboard backing.

The floral foam is easy to carve but has no strength. The plaster filler is too sticky and difficult to sculpt but is strong so can be used on very thin surfaces.

This time I used a bit more PVA glue on the foam. The first coat was a 50:50 mix but this time, once dry, I added a second coat of 75% PVA to 25% water. That plus the paint made the finished walls a bit stronger. Still easy to crush but it is less likely to be accidentally damaged.

While I was making the walls I also decorated some of the cut down barriers that I have been using. Little mounds of concrete and earth round the posts.


Edit: 16 June 2015

This is in reply to a question on the SlotForum asking to know more about how the walls were created.

There are three separate areas:
- The walls made from filler
- The walls made from floral foam
- Painting


Walls Made from Filler

In a couple of areas of the layout there was not enough depth to use floral foam. Thinking about what I had in my shed I decided to make them by spreading a thin layer of filler on to hardboard.

The filler was Ronseal Smooth Finish. It's very strong but has the disadvantage that it dries so hard it is virtually impossible to sand. I used a farrier's rasp to finish it off.

- Cut the board to size
- Spread a thin layer of filler using a pallet knife
- Wait a few minutes for it to get less runny (not long because I have no patience.)
- Use a length of 9mm MDF as a ruler and spacer for the row height of the bricks
- Drag the pallet knife along the edge to form the horizontal mortar joints

The MDF would stick to the filler so this sometimes needed to be repaired after the line was drawn.

- Repeat for each row
- Hand draw the vertical joints with the pallet knife

This resulted in curled edges and corners, which bricks don't have. I had to go back over nearly every brick to sort out the corners!

I could not get a flat surface to the face of the bricks while the filler was wet. The pallet knife would pull the filler off the board! It had to be left for a day to go off.

As I said, the filler cannot be sanded once dry! I have a rasp given to me by a farrier. It was too blunt for his use on horses hooves but ideal for MDF and this filler.

- Rasp over the top of the filler to take off all the bits that stick up and give a level'ish surface.
- Further carve out some mortar joints with a knife where the rasping has removed the joint detail or where the curl was still too apparent.

Did someone mention the amount of work? :-)

That's it for the shape of the brickwork.
I then primed it ready for painting.

The decorative painting is the same for this and the floral foam walls, so I'll cover that at the end.


Floral Foam Walls

I have posted about using the floral foam before.

The foam is so easy to work with.
It is cut with a kitchen knife and the brickwork is simply drawn with a pencil.

This time, I glued the foam to a backing of MDF. This had two benefits. I could have long lengths and get the whole length the same depth, plus I could get the exact size to fit the terrain by cutting the MDF to fit tightly. Trying to do that with the foam always damaged the foam!

I used lots and lots and a bit more PVA wood glue on the back to attach it to the MDF. The foam soaks it up very easily but that gives the foam some strength.

The cat paw prints in the photo show how fragile the untreated foam is.

Do not get any PVA on the top surface of the foam yet. The PVA is nearly impossible to carve so ruins the result.

Cutting Tip:
- I used two equal height lengths of wood either side of the foam to get the same thickness over the whole length.
- Run the kitchen knife along the foam resting on the top of the lengths of wood

Brickwork Technique:
- I used layers of MDF as a ruler for the horizontal joints and drew with a normal pencil.
- I hand drew the vertical joints.

The arch was fun. I pushed a round plastic pot in to the foam to the depth I wanted then cut out the infill with the kitchen knife. I then drew the edge brick shapes round that arch, by hand.

So easy but you have to be very gentle to avoid crushing your own work!

- Clean out the joints with a small paint brush. Even the paint brush can carve the foam!
- Seal and strengthen with diluted PVA glue. Now you want the glue everywhere in every crevice.

PVA glue mixtures:
One layer of 50:50 PVA to water.
Let that dry for a day
Another thicker layer of 75:25 PVA to water.
It's now much safer to handle the walls and the PVA acts as a paint primer.

Let it all dry for a day then paint.



I don't claim anything special for the painting.  These are techniques I have learnt, mainly during my teenage years, by looking at others work and asking how they did it. Then a lot of trial and error.

In all cases my paint is water based. I don't get on with oil based paints!

- Base coat of mat dark grey house paint.  Get in to all the mortar joints with a thin brush.
- Dry brush with a mat light grey house paint.

Dry Brushing:
Dry brushing takes practice but is exactly what it implies.
- For the brick faces I used a wide thin artists brush. Dip that in the paint to fill the bristles then wipe virtually all of it off on a cloth or I use a paper towel.
- The first stroke usually has too much paint, so go gently, hardly touching the work and drag it over the surface.
- As the paint is used you can drag a bit harder until eventually the brush is clean.

The aim is to get a non-uniform finish which is more natural.
I found only one layer of dry brushing was sufficient for this brickwork.

I now add the grub effect where the wall touches the ground:

- I'm using a small round artists brush
- Raw Umber (dark brown) artists acrylic paint
- A few bricks at a time
- Paint the lowest 5mm'ish of the mortar joints
- Dry brush the surface of the lowest part of the lowest bricks.
Don't be afraid to ruin the brush. The fluffier and fainter the effect the better.
I use a low cost brush but oddly, despite the mistreatment, it has survived and returned to normal afterwards for many uses.

This is the final treatment. The aim to is to add even more variation to the surface colour and get rid of that just painted clean look. It is not dramatic but that barely visible change is the finishing touch.

- Make sure the previous layers of paint are fully dry.
- Mix up some very watery black paint. Again I'm using mat house paint but any water based paint would do.
It's more like water with a bit of colour, it must not have any thickness.
- Soak a sponge in the dirty watery mix.
- Hold the wall at about a 45 degree angle over something that will not be ruined.
- Squeeze out the grubby water in random blobs and make sure it covers the whole thing. Dab in some places where the dribbles miss.
- Do it a couple of times and make sure plenty gets in the mortar joints.
It will probably be too subtle to notice and does not show the full effect until it is dry. You can see the difference if you compare an untreated section to a weathered length.
- Lay it flat, face up, to dry. The best effect is if some of the muddy water has pooled in some of the mortar joints.

Once dry the job is done.