Eurofighter Build Using Needle Cutter

[Colin]

For those who have been following the thread on building a needle cutter for foam parts we are now at the stage where we need to actually produce something and I thought it best to do a new thread in the build section.

What to build?
Originally i was thinking of doing something very simple to demonstrate the process, but then I realised that while this would show the techniques it most likely would not show all the problems that could occur so I decided on something I had been thinking of building for a while and that is the Eurofighter from RCPowers.
Many of you will have seen the Su-27s that Mick, Dave and myself have and I can vouch that these are great fun and the Eurofighter is from the same stable.
Why this? Well the other RCPowers plans I have tried have all worked out well, plus this model results in something that looks good without the complications of curved surfaces etc.
You can see a version of it flying here -


I intend to cover the full build here, not only the needle cutter process but also the actual build, finishing and maiden flight so here we go...

[Colin]

On the final post of the needle cutter thread I gave a list of links for plans so there should be one out there ideal for your build - ideally make sure it is a PDF or DXF plan as a bitmap can be a bit vague.
As I said I am going for the RCPowers Eurofighter and it has 2 pages of PDF plans...

Eurofighter Plans.jpg (522.06 KiB) Viewed 283 times

Normally with these sort of plans you would be printing them out fullsize by sticking together loads of A4 sheets and then cutting out the individual pieces, sticking them on the foam and cutting out manually.
Since we are using CNC we need to convert these plans by...

• Removing all elements of the plans that should not be processed for the CNC, e.g. text, logos etc
• Adjust the parts to fit within the cutting area

For the first part almost any graphics program that can handle vector graphics can be used but I prefer Inkscape here.
For the second part whilst it could be done within Inkscape I find Fusion 360 preferable but this is a personal preferance.

The use of Fusion is another reason for using Inkscape as it is easy to convert the PDF into the DXF format the Fusion understands.

We will start the process in the next post but let me finish by explaining my comment about vector graphics.

Normal PC graphics are bitmaps, i.e. the picture is made up by identifying every pixel, line by line, in terms of its colour, brightness etc. If you look at a vertical black line it is simply a connection of black dots on a screen and the fact it is line shaped is just co-incidental. This is often referred to as 'raster graphics' from the old analogue days when TV pictures were made of horizontal scans, or rasters, of the screen where varying levels of brightness were applied to give the required picture.

Vector graphics, on the other hand, don't give a damn about pixels. All they know about are the drawing objects, so a line is something with a start, finish, width, colour etc

So what's the difference so long as we have a line to work with. Well there are two key issues with bitmaps...

1. The CNC programs cannot work with bitmaps - they need vectors
2. Even if not using CNC bitmaps can cause errors

Let's have a look at this second point. Here I have a bitmap of one of my early favourites and flew this for many years in my early teens - the KK Caprice. I have opened it in Inkscape...

1.jpg (1.31 MiB) Viewed 283 times

Now let's zoom in to the gussets...

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Notice how jagged the lines are - this is because the lines are not defined, just a lot of dots that make up a picture of a line. Not so critical here for a gusset, but imagine was for a part that had to fit exactly to another, e.g. the tabs and holes in formers and fuselage sides. Where is the actual cutting line?
Now look at this - I have converted the bitmap to a vector image within Inkscape and now the line is clear...

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And even if I zoom in really tight I still have the lines...

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Unlike the bitmap...

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Doing this sort of conversion is great when you want to do your own scale model and all you have is a 3-view. You can convert it to a vector and then then scale it to whatever size you want.

[Colin]

OK so now we will start the nitty gritty stuff. Let me recap the main stages -

1. Import PDF (Inkscape)
2. Remove unnecessary elements (Inkscape)
3. Arrange onto sheet (Inkscape)
4. Split parts as required (Fusion)
5. Convert to gcode (dxf2gcode)

As I have said before all steps could be done in just Inkscape or just Fusion, but this is what works for me.

1. Setup Inkscape
So I open up Inkscape to see this screen...

Inkscape opening screen

Untitled.jpg (479.64 KiB) Viewed 267 times

The white area is the document area and I need to change this to reflect my document size. To do this I click File/Document properties or use the shortcut Ctrl-Shift-d. Once the properties screen opens I can enter in my cutting area size of 860mm x 340mm. (When measuring this don't forget you are measuring the limits of the needle, not the travel limits.)

Document properties

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Now I see the document size matching my cutting area.

Resized document

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To save having to do this every time you can save this as a template by clicking on File/Document templates... and then use File/Load template when it is required.
To make the template the default click the 'Set as default template' check box before saving.

Setting template

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2. Import PDF
To import the PDF click on File/Import and select the file you want. It is possible to import all pages of a PDF but I prefer to work on one at a time by making sure the 'All' box is unchecked.

PDF import

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Straightaway we can see that we need to do a lot of work to get the parts to fit our cutting area...

Initial PDF load

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But the first job is to remove the unnecessary elements which we will do in the next post.

[Colin]

OK - so now we have the plan in Inkscape we need to get rid of the elements that are not part of the cutting plan.
To do this is straightforward but can be tedious depending on the original plan.
To give a bit of background, when a PDF is brought into Inkscape the various parts of the drawing can be separated into individual elements. We can then delete the elements we don't want. The problem is that some elements can actually be groups of elements, or worse could be groups of groups so we need to ungroup all the elements until there are no groups, just individual elements.
To do this we select the whole drawing, (Ctrl-A),then use either Object/Ungroup or Shift+Ctrl+G to ungroup.

Here is the Eurofighter after the first ungroup command...

1st ungroup

1st ungroup.jpg (367.82 KiB) Viewed 182 times

Note the line at the bottom of the screen reporting 283 objects. We need to repeat the ungrouping until that number stays the same and does not increase. Depending on how the original drawing was done you may need to do this just once or many times.

2nd ungroup

1st ungroup.jpg (366.37 KiB) Viewed 182 times

In this case we are lucky in that it only needed to be done twice and as you can see we finished up with 298 objects. Now we can go through and delete those not essential for the cutting process.

To do this we zoom into the area we want to work with and just select the unwanted object and press delete.

So I will start by removing the title text.
Zoom in and select it. In this case it is composed of several elements so I just click the left mouse button to draw a box round the whole thing...

Select title

Select title.jpg (269.32 KiB) Viewed 182 times

Now I just repeat for the whole drawing. (Note the scale underneath the title - I never delete that as it allows me to check the drawing as I move it between Inkscape and Fusion.

And now I press delete to get...

Delete title.jpg (197.49 KiB) Viewed 182 times

Note that sometimes drawing a delete box might include objects you want to keep. In this case use Shift-Left Click to select the individual elements to remove and then press delete.
If you inadvertently delete something you meant to keep, just press Ctrl-Z until it reappears and then re-delete the rest.

So here's my cleaned up plan...

Cleaned up plan.jpg (157.82 KiB) Viewed 182 times

So the next stage is to break the parts up to fit the cutter bed size. This is where Fusion comes in, and I'll cover this in the next post.

[Colin]

OK so now into Fusion. (Note this could be done within Inkscape but it's a lot easier with Fusion.

First thing is to save the Inkscape file as a DXF file by using the File/Save As option and then select the R14 DXF file type.

In Fusion start a new project. First right click the top line in the browser (Unsaved) and check the bottom menu option - if it says 'Capture design history' then click that option as we need to have this active in order to get some of the options we need.

Now select 'Insert' and choose 'Insert DXF' and select the file in the dialog that is presented to get...

forum pic.jpg (145.03 KiB) Viewed 114 times

Click OK.

First thing is to check that the drawing has come across in the correct scale. Click the 'Top' face on the orientation cube to get the overhead view and then zoom into the scale. Click the scale line and check the length reported in the bottom right hand corner to check it is correct.

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The process now is to create a number of components, one for each sheet that which we need to cut. Then we will project the shapes we have imported into each sheet as required and arrange them as required, splitting them as necessary.

First of all we need to extrude the shapes to bodies as we cannot project sketch objects. To do this go into the 'Sketch' part of the browser and select the sketch that has been created from your import.
For this process to work all the imported shapes must be closed profiles. To check this just hover in the profile - if the lines are black it is OK, if not then it is not closed. Here is an example. Note how the first shape has gone white with black outlines, but the second shape has not changed. This means that there is a gap between the lines somewhere.

forum pic3.jpg (362.77 KiB) Viewed 114 times

To fix this we need to find the gap which can be hard. Fortunately there is a ad-in you can install called 'SketchChecker'. Install this, open the sketch and run the add-in and it will highlight potential gaps with dots...

forum pic3.jpg (91.79 KiB) Viewed 114 times

Now its a case of extending the lines until they intersect and the profile closes. Remember to trim any excess line extensions. If you still have problems then one trick is to add lines cutting across the shape and if any of the smaller sections don't show as profiles you know where to concentrate the search...

forum pic4.jpg (24.21 KiB) Viewed 114 times

Here we can see that the top left section is OK, so we need to focus on the other parts.

Carry on until all the shapes are closed profiles and then in the next post I will describe the next stage.