Tutorial: Foundation Library Dowel & Screw Patterns

Tutorial: Foundation Library Dowel & Screw Patterns


The most recent releases of the Microvellum Foundation Library (library version 23.0609 onward) have made a few noteworthy changes to the available settings of dowels and screw patterns. This article and video were created to document those changes, as well as offer Microvellum clients a brief overview of the settings for dowels and screws within Toolbox.

Available Settings


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Figure 1: Default Dado & Screw setting.
By default, the library is opened with the Dado & Screw method selected. To change this, open the "Project Specification Group" setting under "Toolbox Setup", then hover over the "Default Construction Method" option, and select Dowel to start, then scroll down to Dowel/Screw. 
All machining types with a pattern (dowels, screws, cams, invisible fasteners) have two styles to choose from, Auto Spacing and Custom Spacing. Users can change this setting either at the cabinet level or in the global. 

Figure 2: Dowel distance using auto spacing.
Auto Spacing is the default and is intended to be the simpler option with less setup. It uses a special MV spreadsheet function called CONSTHOLESPACING that calculates the delimited list of hole locations. This spacing will always place the first and last hole at a designated space and equal out the remaining holes in-between. It uses a “target spacing” value to approximate the distance between those center holes. Since it will always equal out the spacing, the distance between the middle holes will never be the exact target spacing value, unless the size of the part happens to match up exactly. This method works well for patterns that need to remain symmetrical for parts that need to be flipped and still align.
Figure 3: Dowel distance using custom spacing.
Custom Spacing is the second option and intended to be used when Auto Spacing cannot achieve one's desired pattern. Instead of a local function at the part level, it utilizes a LookUpTable inside the global variable workbook. This table lists out each part size, hole location, target spacing, and finish- allowing users to set nearly any pattern desired in terms of measurement. While users are able to input any custom measurement into the table this way, the general default formula within the LookUpTable is 16mm of spacing (32mm in versions prior to 23.0609). 

Dowel & Screw Variables 


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Figure 4: Dowel and Screw Formula Attributes.
The variables listed in this section may vary from what users currently possess in their own libraries, due to:
  1. The vast majority of these being rooted in updates to the Foundation Library from version 23.0609 onward, as well as the software being set to preserve custom user settings when updating. A fresh library would be required, in this instance. 
  2. Users currently utilizing one setting over the other (some of the listed variables are unique to one setting, either auto spacing or custom spacing.)
  3. Some variables pertaining to doweling not being listed, as this article focuses on what affects the pattern of Dowels & Screws. Variables unmentioned may appear in user libraries as red and dimmed out cells. 
  1. Distance to Front Edge, Back Edge, Top Edge, Bottom Edge, Left, Right, pretty straightforward. The UCN function simply accommodates imperial or metric as a shipping default. Once the library is installed, one's desired units can be hard locked. Personal settings are not subject to change by library updates.
  1. Dowel Distance to Edge Small Parts is for specific edge-measurement the system will enact if the part qualifies as “Small” such as nailers, rails, etc.
  1. Dowel Small Part Threshold Is the variable used to determine what is “small”.
  1. Dowel Offset - If users are using dual patterns such as dowel/screw or Cam/Screw, this setting is where one goes to offset one pattern to prevent them from hitting each other. 
  1. Dowel Target Spacing – In between the first and last holes, a target spacing variable will place holes at this distance apart. The default value is 128mm. Very important to remember that with Auto Spacing the value set here may not necessarily be the value used on the cabinet parts. It’s an approximate target value and could be greater than what is set.
  1. Dowel Do Not Exceed Target Spacing. Since the size of the part isn’t necessarily going to follow the exact 128mm (or whatever custom value is put in), there is going to be a fluctuation in the distance between holes.  Selecting this will force the workbook function to add an additional hole, preventing the distance between holes from exceeding the 128mm target spacing (128 in the default example). The spacing could be less than 128, but not more. Additional holes will be added with this option.
  1. Dowel Min Distance To Last Hole Custom Spacing – This is a new variable recently added to better accommodate the Custom Spacing option. Enter the minimum distance from the edge to add the last dowel.
  2. Dowel Use Last Hole Custom Spacing - Tick to add an additional dowel which will be placed at the end of the row of dowels divisible by the "Dowel Last Hole Divisible By Custom Spacing" prompt.
  3. Dowel Finished End Target Spacing – Also a new variable. With this, users can now specify a different dowel spacing at cabinet Finished Ends. (For example, say, 96). 
Figure 6: Dowel and Screw collision.
The settings for Screws and Dowels are best left on a single setting across the board: either autospace or customspace. If using both, users run the risk of causing overlap and collisions within the machining if both are turned on simultaneously, because if the total distance (absolute value of the end offset minus the start offset->rounded to the 5th decimal place) is less than the target spacing times two, but greater than the target spacing times one, a single midpoint is placed that is equal to the start offset plus the difference of the total distance divided by two. Based on the function parameters, two tokens can end up having the same midpoint. 

The recommendation in this circumstance would be to keep the dowel offset at zero and set the screw offset at something like 32mm.

The Custom Spacing Formula


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Figure 7: Spacing formula within the lookup table.
  1. The initial section of formula calculates the spacing. It examines the part size, the spacing, how many dowels can be fit, and then the very last hole that can be fit into the part. The leftover space would be the remainder. Remainder could be 100mm, 120mm, could be anything. Plus, could be a little more to wiggle with because this isn’t the exact panel size. Old tables went every 32mm, new one goes every 16mm.
Figure 8: Remainder formula within the lookup table.
  1. The second part of the formula determines the remainder. It calculates the unoccupied space based on the exact measurements entered in terms of part size vs dowel spacing + dowel number, then estimates whether or not another dowel or screw can fit within that remaining space. With the most recent update, new global variables are available for users to decide what to do with their remaining space. The “Dowel Use Last Hole Custom Space” allows one to add in an additional hole by a divisible number. If one opts not to have this in the formula, no additional holes will be added. 
  1. With the remainder calculated, a new variable called “Dowel Min Distance to Last hole Custom Spacing” determines the minimum distance from the last hole to the edge. 
  1. The final formula would be “Dowel Last Hole Divisible By Custom Spacing”. The custom spacing value will be used to find the last location of a hole available, based on division. For example, say one has a remainder of 64mm. With this portion of the formula, the system will determine that the final hole available would be at 32mm, because another 32mm would either fall off the panel or be too close to the edge. The value is going to measure the spacing based on the divisible value of the number entered (32, 64, etc.)

Full Video Tutorial


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