Fabrication Straight Talking – CID 866 Rules

Fabrication Straights

Fabrication Straights sound like they should be simple, and they are until you try to get clever with them.

When using CAMduct and input straight duct you can choose CID1 for machine cut or CID35 for coil. Simple. Why the need for this blog?

For many reasons, mostly to do with using Design Line in CADmep or ESTmep, the run of items are automatically populated with items.

Why the complexity?

The Fabrication database specifications set out what are ‘standard’ lengths of duct and the length of each straight CID 866 is controlled by this when the length = ‘Auto’.

When you only have a profile cutter (plasma, laser, waterjet) then it is simple as everything will need nesting.

When a coil line is used, the many different features of the machine or machines need to be catered for. Some of these features are:

  • multiple coils with different widths
  • roll the flanges/connectors like TDC/TDF
  • make holes in the sides

Now the decisions need to be made about what the coil line can do and what has to be done on the profile cutter. This blog is focused on Length. There are other settings that will switch a Decoiled Straight to Plasma Cut.

Bring on CID 866 for Coil and Machine Cut

CID 866 is a clever straight as it can change its manufacturing process between Coil and Machine Cut but how are the decisions made? The Straight Pattern CID 866 help confused me for a long time.


That flow chart is special! Here are some tips for what is going on.

  • The Specification sets the Auto standard length but has no influence on the Cut Type.
  • The Service determines how the Design Line is populated.
  • You can assign different Services to different segments of a Design Line to have more than one different standard length set to Auto.
  • The settings that decide on the Cut Type for CID 866 are found here:

With Machine Cut setting Machine If Length < , CAMduct will decide on the Cut Type most of the time.

In the default Metric database, I’m using the DW-144LV Specification which has the standard straights at 1500mm. This is what happens to the Cut Type:

Database Setting Machine If Length<  Length set in Item Cut Type of Item
1000 less than 1000 Machine Cut
1000 1000 or more Decoiled Straight
1000 Auto Decoiled Straight
1500 less than 1500 Machine Cut
1500 1500 or more Decoiled Straight
1500 Auto Decoiled Straight
3000 less than 1500 Machine Cut
3000 1500 or more Machine Cut
3000 Auto Decoiled Straight

When Machine If Length <3000 and the length is Auto then the Cut Type is Decoiled Straight otherwise it will try to be Machine Cut. Incidentally, if the length is 3000 or more than it will also be Decoiled!

More than one Standard Length

There are settings and options all around the database that don’t quite work like you think they might.

Single Dimension + Length

For example, when creating a new Specification you have the option of creating one with Single Dimension + Length.

You can then add multiple length tables (TIP: The breakpoints are in metres) so it would look like this:

These work well with controlling everything but the Cut Type. For example, if you have 2 different standard straight lengths of 1200 and 1500 then Database Setting Machine If Length< will still control the Cut Type. The Design Line will populate the run with the first straight that fits the criteria and that will be the 1.2m table and the 1.5m will be ignored.

Multiple Specifications

The way to get the Design Line to use different Standard Lengths is to have a Specification for each length like this:

When you get to the Design Line, edit the Design Line and change the specification for the segments you want to use a different standard length.

As the lengths of these straights are all set to Auto, they will be decoiled.


But I’m given a MAJ or ESJ and they are wrong

What happens when you are given a MAJ or ESJ file and it is full of CID866 straights? Do they all look like they are for the decoiler and won’t nest?

This is where real collaboration kicks in as you want the supplier of the file to get as much right as possible and they may not understand your workshop and how you like to build duct. They are probably doing their best to get things like pricing right and without knowing what is decoiled or machine cut will get pricing wrong as well. If this is someone sitting next to you or in the same company, put your foot down and make everyone use the same database! No excuses.

If you are collaborating with other organisations, then don’t be afraid to share your database (you might want to obfuscate pricing). Making duct is a really, really well-known process and you are not giving up IP! I admit you have spent many days, weeks or years getting things set up for your own business but it is highly unlikely that this is of much use to any competitor, after all staff move around taking the good ideas with them anyway. Collaborate! Rant over.

You could sort out all the straights that are decoiled and delete them from the job to be nested then fix the odd length ones that need to be machine cut. Messy but commonly done.

You can override each item by editing and using the ‘Override Cut Type’ option:

This option is a pain for larger jobs as you can only do one at a time. I will write a script for automating Override Cut Type property. If you read this previously I said that I couldn’t find the property to set but I have been corrected by Andrea at Autodesk. Thank you, appreciate the information.

Better to have your own specification that works nicely without upsetting the design.


In the situation that you have a plasma table and a coil line that will only do one fixed duct length:

  • Set Machine If Length <a big number more than your table can do. e.g. 4000
  • Make sure your Specification has the Standard Lengths set so that they can be decoiled. e.g. 1400
  • Make sure to use Length = Auto for those ducts you want decoiled. If you type in the length it will change to Machine Cut.

If your decoil machine(s) can do more than one fixed length, set things up the same as above and:

  • Use a different Specification for each standard length so you can use Length = Auto
  • Use the correct Specification for each duct segment of the Design Line







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