# Creating Negative/Complementary templates from existing shapes



## CascadeBoxer (3 mo ago)

I have a question about using a template/shape to make a reverse template/shape. For example, if I take the baseplate off of my trim router and use double-sided tape to stick it to a piece of wood, I can use my router table and a flush trim bit to make an exact duplicate of my baseplate. But my desire is to make a template from my baseplate that will let me route out a hole exactly the size of my baseplate.

I watched James Hamilton/Stumpy Nubs' video on complimentary curves: 



. This looks like it will do exactly my goal for simple faces that align with each other. But I'm looking to take an existing shape (whether a simple square/circle or more complex) and then create an exact reverse outline that will enable me to route a hole to contain the shape. Kind of - starting with Wile-E-Coyote and creating a template for making Wile-E-Coyote shaped holes.

The brute force solution is to scribe the outline of the shape in hard board and then use a band saw or scroll saw to cut out the inside, with sanding and trimming to perfect the tolerances. Unfortunately I don't have either tool. So I'm looking for a formula or process to start with one shape X, and with one or two steps, a router and some bits and/or bushings. and some double-sided tape, end up with a template that I can use to create shape X holes.

My immediate project is a router table that I can drop my existing trim router - with its current base plate - straight into. But there are possibilities with inlay projects, tool storage outlines, etc that would call for this technique as well. So far my web searches for router/flush trim/template/reverse/complimentary are not producing the fruit that someone on this forum might know. Thanks!


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## jw2170 (Jan 24, 2008)

Welcome to the forum.

Sounds like what you need is an inlay kit.









Whiteside Router Bits 9500 Solid Brass Inlay Kit


Whiteside Router Bits are made with Premium Carbide Precision ground for proper balance at high RPM Industrial Quality




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## jw2170 (Jan 24, 2008)

Router Workshop: Making an inlay with your router


Introduction: Many simple projects can be made fancy with an inlay design applied in a contrasting wood or other materials. The snack tray we have illustrated in this project is made of ash wood with walnut hearts inlaid in the corners. The Router Workshop Series 100 Episode #112...




www.routerworkshop.com


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## old55 (Aug 11, 2013)

Welcome to the forum.


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## bfblack (May 2, 2012)

I am familiar with the techniques in the Stumpy Nubs technique/video; see attached photo of a tissue box. I might be able to help you but first I want to understand precisely what you are trying to accomplish. My reading of your description did not give me a firm idea of what you want to do. Are you wanting to make exact copies of your router base but not use a flush trim bit? Some sketches would be helpful and hand drawn sketches are more than adequate.


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## CascadeBoxer (3 mo ago)

bfblack said:


> I am familiar with the techniques in the Stumpy Nubs technique/video; see attached photo of a tissue box. I might be able to help you but first I want to understand precisely what you are trying to accomplish. My reading of your description did not give me a firm idea of what you want to do. Are you wanting to make exact copies of your router base but not use a flush trim bit? Some sketches would be helpful and hand drawn sketches are more than adequate.


Hi BFBlack!

I have used a flush trim bit to make an exact copy of some templates, and I think that I understand the mechanism there. It wasn't a router base, but it was a hook for attaching yard tools to french cleat bases - I used the template to repeat a batch of them with a flush trim bit.

I think that the advice I've received so far about using an inlay kit is the most relevant. JW2170 made a post on this thread with a link to RouterWorkshop, which was helpful and clear. If I describe the inlay process, and then contrast it with my imagined project, it might be the clearest description. 

The steps on RouterWorkshop appear to be *Template / Cavity / Plug*.

Begin with a *template *- a flat piece of material with a hole in the shape of the desired inlay. (The hole is a little bigger than the exact inlay shape, because of bushing tolerances.)
Cavity - Equip with larger bushing and a spiral bit. Use the pattern to cut the inlay *hole/cavity* in a board. Either cut all the way through the board for a hole, or remove the material at depth for a smooth bottom cavity.
Plug - Equip with smaller bushing and a spiral bit. Mount the template to a piece of plug material. Use the pattern to cut the perimeter of the *plug *piece.
Do the Inlay - place the plug into the cavity, some tweaking may be required for corners and small radii curves but it should be a match.
For my project, I am starting with a specific Router base, and I want to recess it into a workbench. So the order of operation here seems to be *Plug / Template / Cavity*.

Begin with a *plug *(the router base).
Equip with smaller bushing and spiral bit. Secure the router base to a large flat piece of hardboard, and make a plunge cut with the bushing against the edge and a spiral bit to trace the exact perimeter of the router base. This creates the *template *for making router base-sized cavities. It should be oversized compared to both cavity and router base.
Equip with larger bushing and spiral bit. Secure the template to the workbench, and make a *cavity *only to the depth of the router base. This allows the router base to rest in the cavity like an inlay. Then route out the full hole that just fits the router chassis through the workbench surface, while leaving a supporting rabbet around the cavity perimeter.
I now think I have the order correct, and the sequence of using the different sizes of bushings. The mental geometry of lining up bushing and bit sizes and aligning them with the exact same vertical line (the plug/cavity edge) is the part that I'm slowly getting. Inlay kits appear to include Bits, Large Bushings, and Small Bushings that ratio correctly to one vertical line. (The Whiteside Inlay kit is 1/8" bit with 1/4" shank, 5/16" OD Bushing, and 9/16" OD collar. The Router Workshop post describes a 1/4" bit, a 7/16" OD guide bushing, and a 1/4" inlay bushing for an OD of 15/16".) This tells me that the difference in Large/Small OD of the bushing sizes should be double the diameter of the bit. The Stumpy Nubs video about complimentary curves supports the math, as he works with a 1/4" flush trim bit and then adds a 3/4" bearing for offset. 

I think I can follow this formula to start with any object (my Pinewood Derby gold medal, a ceramic coaster, a powerstrip surge protector) and end up with a template that I can use to make a hole to recess the object into.

Thanks, everyone!


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## jw2170 (Jan 24, 2008)

Hi @CascadeBoxer ,

There is a video on Youtube that shows the method you are talking about.

I will see if I can find it. It may be in my favourites...


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## jw2170 (Jan 24, 2008)

Bump.

I found the video that I was referring to.






Keep in mind: 
1 Read the comments to see how to size your template.
2 In your case, the base plate will be the plug, and you will need to cut the template from that....One size for the plug and the other size for the template,,,


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## DesertRatTom (Jul 3, 2012)

Interesting. Welcome, BTW.


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## bfblack (May 2, 2012)

CascadeBoxer said:


> Hi BFBlack!
> 
> I have used a flush trim bit to make an exact copy of some templates, and I think that I understand the mechanism there. It wasn't a router base, but it was a hook for attaching yard tools to french cleat bases - I used the template to repeat a batch of them with a flush trim bit.
> 
> ...


It looks like you are on the right track. It took me longer to put my thoughts on paper than I thought. You probably had the job finished before I got started with my document. Here are my thoughts on why the router inlay kits work.


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## CascadeBoxer (3 mo ago)

Hi Ben!

That article is very informative - thank you for putting it together. I share your feeling of wanting to know "why it works". In my case, I am sometimes working with a smaller set of tools, and knowing "why it works" enables me to adapt to a different size bit, saw blade, etc. You have worked through the math and also have the visual diagrams to satisfy both the left and right-brain sides of my mind. 

Sometimes a larger router bit is good for heat management, cutting surface, smoothness of finish, etc. Sometimes a smaller-diameter bit is good for tearout reduction, slower bit speed, handling tighter curves. Understanding the formula for router inlay with multiple bit/bushing sizes allows us to choose the right tool for the job, or adapt a different process for the tool we have in our possession.

In truth, I haven't completed my project yet. I have a Rockler trim router table that I clamp to my workbench when I need to template something. Using it requires me to swap the acrylic bases on my little cordless trim router. So the long term plan is to make something like a Folding Router Table that I can directly drop the trim router into - without swapping the base. Right now I'm procrastinating on choosing an inlay kit that will fit the Dewalt DCW600B.


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## bfblack (May 2, 2012)

CascadeBoxer: Thanks for your comments. Based on comments from some of my local woodworking buddies, I have rewritten the document. The first part now is aimed at those that are uninterested in the (math) details but will now see how to "roll their own" Router Inlay Kit.

The math stuff is put in an appendix for those that are interested. If you have any suggestions on improvements, please let me know. I want to eventually start a new thread with the document so that others will find it.


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