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Big Blue Saw Blog General Updates

Converting PNG and Other Raster Files to DXF Format

You might want to read the first two articles in this series on working with files to prepare them for waterjet or laser cutting: The Difference Between Vectors and Bitmaps and EPS, PDF, and SVG files.
We’ve covered all of the major file types except PNG, JPG, GIF and other raster format files. Raster files can be converted to vector/DXF format, but they take some fussing to get to the vector stage. In this article we'll see how to take raster and bitmap images and convert them to vectors. We'll take a look at a PNG file as an example, but the techniques should apply to any raster format file.
You’ll need 3 programs downloaded to convert a PNG. Luckily they are all free: Inkscape, Gimp, and LibreCAD.
PNG files can be converted to DXF using the tracing tool in Inkscape. That said, this works best on simple designs like rectangular plates with holes in them with low tolerances and organic designs for decorative objects. If you are working on a specialized plate that needs holes in precise places, PNG isn’t going to help you. If you are working on a crest for the chest plate in your cosplay armor, then PNG can be an avenue to a DXF of the part.
The Big Blue Saw online quoting and ordering tool supports raster files in the PNG and GIF format, but for maximum control over the finished part, including exact sizing of features and distances between holes, you will want to convert to DXF before uploading the design to Big Blue Saw.
At this point we have a crest and it is saved as a PNG.
First thing we need to do is open it in Gimp and set the color and edges.
We open our image in Gimp and from the menu bar choose Colors, and click on Brightness/Contrast.
Set the contrast as high as it will go (red arrow). Don’t adjust the brightness. Click OK.
This sharpens the edges of the part.
Next we need to index the colors to just black and white.
Go to Image, Mode, Indexed. Click the radio button for black and white 1 bit palette and click Convert.
Now we have a file we can trace in Inkscape. Export it or do a Save As a PNG file and open the file in Inkscape.
Now if you look at the edges closely, they look a little rough. This is normal on a converted file. When Inkscape traces the outlines, they will smooth out a bit. That way we will have really sharp edges and an all black image. 
Here's a closeup of the image so you can see the individual pixels:
Now open your new PNG file in Inkscape and click on the image.
See how the resizing arrows are around the document edges and not around the crest itself? That is one hint that we aren’t dealing with a vector image.
So go to Path in the menu bar and select Trace Bitmap.
Make sure your image is still selected. In the pop up window, you’ll change a few settings to get a nicer trace.
The brightness cutoff is usually pretty good for tracing black images, so you can leave that radio button selected. Check the Live Preview button so you can see if the settings are warping your design really crazily. 
I usually bump the threshold up above 0.550 but below 0.999. With live preview checked you can see if your design is starting to look clunky. Then click OK and Inkscape will trace your design.
Now you have a vector image from a bitmap/raster. We can see this by changing the View to Outline Mode.
 There are now two versions of my crest in this file. The bitmap that was in the PNG, and sitting on top of it is a vector. I usually select the bitmap and delete it at this point.
Then File and Save As. From the file extensions list, choose DXF.
For simple shapes, you can likely upload the resulting DXF straight to the front of our website and check out. But sharp corners like the ones in my crest have a tendency to get a few extra lines when you save as a DXF in Inkscape. They can be cleaned up easily in LibreCAD though, so a quick clean and a save and then this will be ready for the big leagues.
Open the DXF file in LibreCAD:
See the extra lines? They're highlighted with red arrows in the zoomed in image below.
Click on all of them one at a time to select them.
Then go to Modify in the menu bar and select Explode at the bottom of the menu.
Now click on all of the extra lines to select them. Then hit the delete key to delete them from the file.
Now I resave as a R12 DXF file using the same name.
At this point, you can make any other adjustments to the scale, sizing, or outline path to make sure that your design is exactly how you'd like it to turn out when it's made into a real part. Now that it is cleaned up and good to go, time to upload to the website for a quote.
If I don’t have any errors, it will upload cleanly. If there are errors, then the website will give me an error message. If you get that message on your drawing, there is usually an orange link that will take you to a diagnostic view of the part. Click the diagnostic view and use it as a way to troubleshoot your way through whatever is hanging up the quoting software. If the quoting software can’t read it, the laser and the waterjet can’t cut it.
Yay! It worked. Now take a quick look at the size under the rendering of the part.
When I designed this crest, it was a little smaller than what is showing up on the website. This is common with traced files. The line width of the ellipse tool I was using added to the crest’s size. This can also go the other way in a traced file, where the part is showing up larger than drawn due to line weight. Be sure to carefully check your part’s size at this stage. 
If the sizing would make a difference in my costume, I would click the Resize button, and enter a new width or length. The resizing button on the website proportionally scales parts up or down using the measurement you enter first. In this case, it isn’t an issue, so we move on to the materials list.
And choose a material.
From this screen I can get pricing for cutting multiples of my crest, see renderings of my part, and check the Part Details at the bottom of the screen.
Always check the Part Details to make sure the measurements look good, the renders look like the part you want to cut, and that the correct number of holes are listed. Then enter the quantity of parts you want in the quantity box, and click Order Custom Parts to checkout through the website.
And that is how you turn a PNG into a DXF vector file. A bit fiddly and not great for precision parts, but good for parts that have a little wiggle room on the tolerances. It also makes a good introduction to Inkscape and LibreCAD as programs, which can help you skip tracing PNGs for future projects.
Happy designing!

Valentine's Day Sale on Custom Waterjet Cut Parts

We love our customers, and starting Monday, February 13, you'll be able to save with sweetheart deals on custom aluminum parts. During our Valentine's Day sale, Big Blue Saw is offering savings on waterjet cutting your designs from 0.125 inch (1/8 inch) thick aluminum 6061. 

Gather your loved ones together and place your orders online to automatically receive quantity discounts.

Here are some examples of how you can save:

This lovable 21 x 21 inch robot baseplate design is normally $114.40 when ordered in quantity 1. That's with waterjet cut from aluminum 6061 1/8 inch thick. During  the sale, this same part would be just $56 in quantity 1. That's a savings of $58.40, a savings even the most emotionless robot couldn't ignore.


Normally, our cherished "Butterfly" example piece is $92.10 in quantity 1. During the sale, it will be only $9.20. That's a honeybunch of savings of $82.90 or 90%.

This nameplate design (perfect if your paramour happens to be named "Gavin Chan") when waterjet cut from aluminum 6061 alloy in  0.125" is typically $92.10 when you're getting just 1 piece. But during the sale, you can get it in quantity 1 for just $10.60, or $81.50 off!

Remember that the sale is only on custom waterjet cut aluminum 6061 parts in 0.125 inch thickness ordered through the website during the sale. And the sale ends on February 15. So upload your designs to our online quoting and ordering system now.



How Thick is a Steel Gauge? And Why is My Part 0.002 Inches Too Thin?

When you order custom waterjet cut cold rolled steel on the Big Blue Saw website, you've got a choice of several different thicknesses for your parts. We offer the following thicknesses, from 0.0239 inch all the way up to 0.135 inch:

0.0239, 0.0299, 0.0359, 0.048, 0.0598, 0.075, 0.09, 0.105, 0.12, 0.135

But why these sizes in particular? Why not nice round numbers like 0.04 inches or at least useful fractions like 1/16 (0.0625)? These values aren't round numbers when converted to metric, either.

The answer lies in the gauge system of standard sheet metal thicknesses. In the US, standards for sheet metal come from the American Iron and Steel Institute (AISI). AISI standards tell manufacturers how thick to make steel sheets (the gauge) as well as what tolerances are allowed.

Many of our customers are used to the gauge system when ordering parts cut from steel sheet. So a customer might e-mail us to ask about getting a set of parts waterjet cut from 14 gauge steel, rather than asking for parts 0.075 inches thick.

Confusingly, as the gauge gets higher, the thickness gets lower. So 10 gauge steel is a stout 0.135 inches thick (about as thick as a stack of 2 quarters), whereas 24 gauge is a puny 0.0239 inches thick (thinner than a credit card).

In the chart below, you can see the thickness we sell, its corresponding gauge, and its metric equivalent. In the chart, inch and millimeter measurements are only for cold rolled steel sheet, not aluminum, not stainless steel, nor any other material. Other materials have their own gauge system. That's an article for another time.

Big Blue Saw's Nominal 
Gauge Minimum
 0.135 10 0.1285 0.1405 3.429 3.264 3.569
 0.12 11 0.1136 0.1256 3.048 2.885 3.190
 0.105 12 0.0986 0.1106 2.667 2.504 2.809
 0.09 13 0.0847 0.0947 2.286 2.151 2.405
 0.075 14 0.0697 0.0797 1.905 1.770 2.024
 0.0589 16 0.0548 0.0648 1.524 1.392 1.646
 0.048 18 0.0438 0.0518 1.219 1.113 1.316
 0.0359 20 0.0329 0.0389 0.912 0.836 0.988
 0.0299 22 0.0269 0.0329 0.759 0.683 0.836
 0.0239 24 0.0209 0.0269 0.607 0.531 0.683


For example, when Big Blue Saw gets an order for a part from 0.12 inch thick Cold Rolled Steel A366/1008, we'll use the gauge size sheet provided to us by our suppliers. Based on the standard tolerances,  the parts the customer receives may be as thin as 0.1136 inches or as thick as 0.1256 inches. Be sure to design your assemblies to tolerate this kind of variation in thickness.

If you're wondering how these sizes relate to various real world objects, read our article on deciding on a material thickness.


Early details on upcoming sale

It's time to start planning for the next sale on custom waterjet cut parts. The sale starts Monday, February 13 and runs through Wednesday, February 15, 2017. The sale material this time around will be aluminum 6061 in 0.125 inch thickness. Get your designs ready now and upload them to the online quoting and ordering system.

EPS, PDF, and SVG files

In our last article, we talked about two different branches of image files you may have for your parts. I said that you can also convert EPS, PDF, SVG and PNG files to DXF for cutting, with some caveats. Each file extension has its own quirks, so lets go through these one at a time.


Is a format most commonly used in graphic design. It converts over to DXF very nicely, but not every design software suite can open and alter them. I also haven’t found an online converter that is easy for a layperson to use. If you have an EPS that you can’t convert, send it to us by uploading it to our online quoting and ordering system, and we will get it converted for you.
Generally speaking, the vectors in EPS files are really clean and allow them to convert to DXF with relatively few issues. The trick is to make sure that you are starting with a black and white file that has defined outlines, and no grays or gradiated borders.


I can convert PDF files that have a vector image in them to DXFs. The difficulty here is that you can also get a PDF that is a bitmap image embedded in it. PDFs with embedded vectors do not do so well when I try to trace it. An easy way to test if your PDF has vector or bitmap is to open it in Inkscape and in the menu bar change the Display Mode to the Outline view.
If you see a box with a red X in it, you have a bitmap PDF. 
Using bitmap editor Gimp’s contrast and color indexing tools you can probably get a sharp enough black and white image for the Bitmap Tracing tool in Inkscape to trace this. But it is going to come out blobby, organic, and if there is any pixel resolution issues the edges will be all craggy and there may be tiny holes showing up in your part. If you get craggy edges, the quoting system is going to charge you for cutting out those plus all the tiny holes, which means your part will quote much more expensive than it would cost if we ran a clean version through the quoting software. We have cut some decorative parts that were organic in nature from a traced bitmap that came out nicely, but this process can be dodgy in getting you the parts you want. 
If you have a scanned copy of a mechanical drawing in your PDF the chances of it not working is extremely high. The resolution and amount of background digital noise on the average scanner is pretty high. Given the tolerances that usually need to be maintained with the parts in mechanical drawings, there are only one realistic way to resolve this. To have a designer (yours or mine) redraw the part completely in CAD software. 
If you see your part outlined in a thin black line, then you have a vector file. Yay! First thing you need to do is to check to see if it is the right size, so click on it with the pointer tool. Just below the title bar in Inkscape there is a toolbar that should show you the size of the part. You may need to change the unit of measurement to inches in the pull down box to the right of the height measurement.
Is that the size you intended? If not, select the part profile and any holes. Don’t select any measurements if this is a mechanical drawing, especially if they are laying on top of the part’s edges. Then click the little lock button between the Width and Height boxes so it is closed.
Now if you know the width of your part is supposed to be 3”, type 3 in the width window and hit the Enter key. Now your part is sized proportionally to the correct size. That said, this only works if your part is drawn to scale. So if your designer wasn’t paying attention to the measurements when he or she drew the part or if there are jogs in the part profile, then this isn’t going to fix the sizing. In that instance they need to get you a proportionally drawn part. (Also note that the line width affects the size.)
If it is a mechanical drawing and has a bunch of measurements and sheet notes in it, go ahead and select and delete those now. Their presence in the DXF is only going confuse the quoting software as to what is the inside and what is outside of the part profile.
Save As a DXF. Try uploading it to our main page. If there are errors in the part, click on the diagnostic link to see where they are. Use LibreCAD to connect any endpoints that came unglued and delete any extra lines. You can get LibreCAD for free from the LibreCAD website.
So that covers EPS, PDF, and SVG files. What about PNGs you say? PNGs can also be converted to DXF format, but they take a little doing. So in my next article we will be talking about how to convert PNGs and what that entails.

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Big Blue Saw
5.0 stars - based on 17 reviews
Waterjet and Laser Cut Custom Parts.
Address for correspondence only:
3522 Ashford Dunwoody Rd NE #145
Atlanta, GA 30319
Phone: (678) WAY-SAW4 (678) 929-7294