Fabricate a Mortise & Tenon Template on a CNC Router

What Was Made for This Instructable

For this Instructable I designed and fabricated a 3/4" x 5 1/2" x 11" Mortise and Tenon Template from 3/4" PVC Trim Boards using a NextWave Piranha FX CNC router.

What Will The Template Do For The Woodworker

The Template, along with the recommended bits and tools, allows the woodworker to:

• Use the "pencil peeps" to align the C/L of the Template with pencil marks on the boards
• Repeatedly align and hold the Template to boards for mortising and tenoning
• Rout multiple mortises on various width board surfaces. Mortises will be:
• Rectangular shaped with 1/8" radius rounded corners
• 3/4" wide by 2 3/4" long
• 1/4" to 1/2" deep or depth TBD by woodworker via Plunge Depth Stops
• Rout the outer shape for deeper mortises (See "Forstener Bit Mortises below)
• Punch or Hinge Bit 5 dimples to guide the tip of Forstener bit to:
• Bore 5 overlapping, shallow or deep mortises
• Eliminate "jumping", a common occurrence when overlapping Forstner bit holes
• Rout a very clean, perfectly located 3/4" x 2 3/4" outer edge on the bored mortises
• Punch or Hinge Bit 5 pilot holes on the end-grain of the boards for:
• Mounting threaded steel tenons
• Mounting threaded metal inserts
• Drilling pilot holes to guide conventional fasteners
• Drilling pilot holes for thread tapping using a wood taps
• Punch or Hinge Bit precise center-points for other in-wood cavities including:
• Counterbores for recessed washers and bolts
• Rectangular mortises for 3/4" x 2 3/4" DIY washers of wood or metal
• Rout tenons on the end-grain of boards
• For as-is shallow tenons
• Or as guides to create precision deep tenons

About "Shallow" Mortise and Tenon Joinery

My "woodworking" projects tend to be of a larger scale (beds, bunks, stair railings, table bases and small structures). Because of this they need to be built in components that that can be fully assembled in a small shop but then disassembled for transport and/or to squeeze through narrow door openings. Because of this the joinery of those components must be "knockdown". The framing style is "Post and Rail" (AKA "Post and Beam" AKA "Timber Frame") and the joinery method "Mortise and Tenon". Since traditional wood tenons and mortises are not conducive to repeated knockdown I have tenons custom laser cut from 1/4" thick steel including several holes, one of which is thread-tapped to accept a machine bolt. Since the tenons are only 1/4" thick the mortises only need to be 1/4" deep. This shallow depth means the mortises can be routed with a small upcut spiral bit (1/4") mounted in a hand-held router. On some projects there are 20, 30 or more mortises. There is no better method for routing this quantity and type of mortise than with a "Router Template" and no better way to create that Template than with a CNC Router.

Topics and Methods Demonstrated in this Instructable

1. Why and how a Template was created for quick and precise routing/tenoning
2. Why PVC Trim Boards were used as the material for that Template
3. How the Template was digitally tested on digital boards
4. How a 3rd party 3D design file was imported into Vcarve, the CNC software
5. How the Tool Paths were created in Vcarve
6. How a custom CNC bed was used to align and hold the PVC board on the CNC table
7. How the CNC router carved cavities in the PVC Trim Board to create the Template
8. How the Template was used to rout mortises on various width boards
9. How the Template was used to "dimple" various width boards for Forstener Bit mortising
10. How the Template was used to dimple pilot holes to mount metal tenons on boards
11. How the Template was used to shape shallow tenons on the end-grain of boards

Software, Tools and Bits

• A 3D Design Software to design sample projects and digitally "test fit" components
• A CNC ToolPath Software (I use Vcarve Desktop Pro)
• A CNC Router with at least a 5 1/2" X 11" workpiece capacity
• Two 1/4" Up-cut Spiral Router Bits (one in CNC router/other in hand-held router)
• One Guide Bushing for 1/4" bit. (The Template assumes a 1/16" add-on for the bushing)
• One hand-held router w/Plunge Base and Vac Port (I use a Milwaukee 18v combo)
• One shop vac with hose matching router port

About Template Material Options

Before finally deciding that PVC Trim Boards would be my go-to material for router and dimpling templates I tested MDF, Baltic Birch, conventional plywood, clear hardwoods and even several synthetic materials:

• MDF: The lowest cost but absolutely hated the fine powder that filled the room when routing on the CNC. The MDF also absorbs moisture that will warp the Template and change the precise size of the cavities. The only way to avoid these issues was to spray several coats of varnish which offset the cost saving of MDF and added several steps to spray, sand, spray again...
• Baltic Birch: Modest cost and clean cuts but the router and bit on the CNC seemed to always be pushing too hard. To avoid breaking or burning the bit I had to manually slow the speed down on the CNC or reduce the depth of each pass in the Vcarve software. Another issue was the insides of the router cavities tended to grab the guide bushing so it was always jerky. Again the only way to solve this was to spray varnish the insides of the cavities.
• Conventional Plywood: Modest cost but chipouts everywhere plus all of the same issues as with the Baltic Birch above! Simply not worth it!

PVC Trim Boards To the Rescue

After testing each of the above I kept returning to PVC Trim Boards. This is a material used by carpenters to trim the exterior of homes and commercial structures. There are soooooo many benefits:

1. Available off-the-shelf at all of the big-box stores (Menards, Home Depot, Lowes...)
2. At about $26 for an 8' board a template costs about $3.00
3. Consistent thickness at perfect 3/4". No need to tweak depth stops on router bases
4. Consistent width (I mostly use the 1 x 6 which is actual 3/4" x 5 1/2")
5. Due to widths there is no transporting or ripping of large sheets as with plywood
6. Amazingly easy to saw, drill, router or whatever
7. Equally gentle on the router and bit mounted in the CNC
8. No "Dust" during CNC routing. Only the goofy plastic shavings
9. Allows for highest CNC routing speeds and fewest passes
10. It's PVC so can be stored outdoors if need be
11. It's PVC so no varnishing or painting
12. Accepts any PVC-friendly (silicone, wax...) lubricant for friction-free routing

For all of the above reasons I used PVC Trim Boards for most of my router and dimpling templates. For this Template I used the 1 x 6 (actual 3/4" x 5 1/2").

About the Software Used to Design the Template

I am well aware that Instructables is part of AutoDesk and therefore Fusion 360 would have been the preferred application for designing the template. Hopefully, at age 70 with grandkids, I qualify for some sort of "grandfather clause" to have used the software I grew up with, SketchUp, to design and illustrate the digital template design and functions. That said, and from what I can see on the web about the hand-shake between Fusion 360 and Vcarve, it seems like the process of designing the template and then importing that file into Vcarve might be identical. If it helps I did an Export of my .skp file to create the .stl file attached below. If there is a better way to make the .skp file compatible and editable with Fusion 360 please place a Comment below or PM me.

The Anatomy of a Mortise and Tenon Template

On large projects there may be 40+ mortises that need to be routed on various-width surfaces and the same number of tenons to mount or shape on the end-grain of boards. These are ideal applications for a router template like the one created for this demo. In this case a small structure had been designed earlier including a digital CutList that included dimensions to all mortises and tenons. An initial draft of the template to rout those mortises was also drawn. The video below is a narrated "tour" of that template explaining the shapes and the color scheme.

Video: Tour of CNC Fabricated Template for Routing Mortises and Tenons

Digital Dimensions With Digital Pencil on Digital Boards

When carpenters layout a stud wall for framing they typically measure from one end of the top and bottom plate then place a pencil mark where the "edge" of each stud will be placed. Using this Template for mortising is done differently. The boards will still be laid out from one end (left in this case) but the pencil marks are placed at the CenterLine (C/L) for each mortise. In the video for this Step I demonstrate on a sampling of boards for a small structure project how those boards are dimensioned digitally in a similar format.

Video: Digital Dimensions With Digital Pencil on Digital Boards

Digital Alignment of Digital Template on Digital Boards

Now that the boards are dimensioned it was time to "digitally" test fit the Template on typical locational scenarios including:

• Routing a mortise with C/L located at pencil marked locations along the board
• Routing a mortise on 2" thick and 4" wide surfaces
• Punching dimples for Forstener method mortises on above scenarios
• Punching dimples on the end-grains to mount fabricated tenons
• Punching dimples on the end-grain to pilot for manual fasteners
• Routing portions of a tenon shape on the end-grains

2D Transparent Vs 3/4" Real Template

Although the actual template will be 3/4" thick I find it easier to draw the template in a transparent 2D. The transparency helps with alignment to the digital pencil marks on the digital boards and to see through the template to confirm such alignment. This 2D also comes into play later when preparing the 3rd party design application file for import to the Vcarve Toolpathing software. With the above in mind the video for this step starts with a completed design for the Template and then shows how that Template is digitally placed over each location on every board to confirm it will do what it needs to do.

The video linked below is a narrated tour of the digital placement of the Template in all common locations. One of the important considerations for each location is alignment:

• Are there the 1/4" MDF Guides to align and clamp in position for stable routing?
• Will the pencil marks on the boards be visible through the Pencil Peeps?

Video: Location Testing of Digital Template on Digital Boards

About Importing a 3rd Party Design File into Vcarve

When I purchased a NextWave Piranha FX CNC Router about 6 years ago it was bundled with Vcarve Desktop Pro. I knew nothing about Vcarve and, quite honestly, had no desire to deal with the learning curve of a new software. Since I do all of my digital modeling in another software all I wanted to do was to import those files into Vcarve for the sole purpose of creating the Toolpath file that would talk to the NextWave CNC out in my shop. Unfortunately, 6 years ago, such handshakes were just coming into vogue so there was almost no documentation by Vcarve and, believe it or not, NO YOUTUBE VIDEOS ON THE SUBJECT! This meant I was on my own. Over time I came up with a flow that worked and still works quite well. Some of those steps take place back in the 3rd party design software to prepare the file for import. The rest of the process takes place in Vcarve. In the video for this Step I demonstrate some of the following:

• In the Design Software
• Hide all other objects except the object to be imported later
• If the object is not already 2D convert it to 2D so only the top surface remains
• Rotate the object to match the orientation the physical board will be on the CNC bed
• Save the 3rd party file in a version that Vcarve will accept for import
• In my case I save the .skp file in "Version 2017" format
• In The Vcarve Software
• Create a "New File"
• Tweak the default setting to match the board Width, Height & Thickness
• Click on the "Import Vectors" icon then navigate to the file to be imported
• If the drawings are not aligned use method shown in video to center
• Tweak any of the import defaults as needed (see full demo video)

Video: Prepare and Import a 3rd Party Design File Into Vcarve

A Couple of Tips

• Design software is 3D. Vcarve is 2D. It's the Toolpaths that add the 3rd dimension
• Vcarve does not import dimensions or notes
• Vcarve does not import colors but I use colors to indicate depth settings in Vcarve
• Leaving the design file open in another window/tab on the computer helps
• I frequently click from Vcarve over to the design file to reference color coding

Video: Creating Toolpaths in Vcarve From 3rd Party Design Software

In this Step I demonstrate the step-by-step of creating the Toolpath for every cavity. I attempted to upload the Vcarve .crv file to this Step for download by viewers but the download attempt came back as a not allowed file type. If anyone would like the file please PM me and we can figure out a way to get it to you.

The video for this Step demonstrates the entire process of creating the Toolpaths. Other random thoughts on creating the Toolpaths include:

• Using The Board Center for XY Datum Position: Since Day 1 I have always used "Center" as the XY Datum Position. Doing this means I never have to worry about being aligned with an edge of the board, instead everything is "relative" from that center position. If the PVC board were not aligned on the CNC bed exactly parallel and perpendicular to the XY travel of the bit it is NOT an issue since the same slots that are used to align the Template to the workpiece board are perfectly aligned to the router ovals, holes and other cavities. (Hopefully that makes sense. Feel free to contact me if not).
• Some Toolpath operations need to take place AFTER another. The Example shown in the video creates a 3/4" x 2 3/4" mortise full-thru (.8"). The next action tells the router to shape the "Dust Rim", a 3/16" wide by 3/8" deep "rim" along the outer edge of that mortise. The number of passes to create that rim were reduced from a default of 6 down to only two since much of that material had already been removed for the full-thru mortise opening. If the sequence of these two steps were reversed the router bit would attempt to gouge too much material in those few passes.
• Regarding "Full-Thru" Cavities at .8" Vs .75" Board Thickness: The PVC boards are a very perfect 3/4" (.75) thickness. The depth of every cavity to be routed in that PVC board were set in the Vcarve Toolpath process. None of those is all that critical for this Template. For example: If the slots for the 1/4" MDF guides are .55 depth as opposed to the intended .50 that is a non-issue. Same with all other cavities. The one I do want to make sure of though is the "full-thru" cavities (those colored-coded with red in the above image). It IS an issue if the bit stops 1/1000 shy of making it all the way through the PVC for those. The router guide areas must go full thru; the "Pencil Peeps" do no good if there is a thin layer of PVC covering the pencil mark; etc, etc. For these reasons I used .8 as the depth when programming the Toolpath for a .75 thick board. In the video you will hear a "ding" when I hit "Calculate" and then a window pops up warning that a "depth of .8 was selected for a board thickness of only .75. This warning can be ignored knowing the spoil board on the CNC bed will take the excess.
• PVC Vs Plywood/MDF: The material used for this, and most of my router templates, was PVC. PVC offers very little resistance to the bit and has no "hidden" knots (like in plywood) to worry about. For those reasons I was comfortable with the number of passes and speeds used. If the material were anything else I would increase the number of passes and possibly decrease the speed either in Vcarve or manually using the Controller of the CNC during the run.
• Using a Vcarve "Profile Toolpath" VS a "Pocket Toolpath": There are three rather large cavities on this template (the full-thru router oval and the two that shape the tenons). It would have been more efficient, for the bit and router, to have used the "Profile Toolpath" method where only the outer edge of those openings would be routed then "Tabs" added to prevent the chunk in the middle from popping out uncontrolled. While it might be more efficient on the bit it would have been less efficient for the following reasons:
• The Profile Toolpath method requires "Tabs". Those need to be removed after the CNC run. Additional time would have been required on my part to manually remove those tabs. I'd rather be drinking coffee watching the CNC do my work for me!
• When tabs are used I remove those tabs, safely, using a "mini router bit". The bearing on such bits is so small it fits in the 1/4" slot left by the 1/4" CNC router bit. Although this works great and very quick it still leaves a little stub or dent along the outer edge. Those bumps will be discovered by the guide bushing on the router when using the template to mortise. Not a big deal for a mortise that will be hidden by the tenon end of a board but not so if that mortise is intended for a DIY decorative wood inset.
• Running "Preview Visible Toolpaths" is worth the time. It saves on trips to the workshop; router bit wear and burnout; and on raw materials.

Video: Using A CNC Router to Create a Mortise and Tenon Router Template

Transferring The Toolpath Files to The CNC Router in Workshop

1. Copied the .tap (Vcarve Toolpath) file from the PC hard drive to a USB thumb drive
2. Sent myself an email with the digital files for backup and for viewing on a device in shop
3. Printed an image of the Template to view in the shop and for making notes as needed

Creating the PVC Blank

I keep an inventory of 3/4" thick PVC Trim boards typically in 5 1/2" widths. One of those was crosscut to 11" creating a blank PVC board 3/4" x 5 1/2" x 11". The PVC boards are "reversible" in that they are smooth on one surface with a wood-grain finish on the other. When using the Template to rout mortises I prefer to have the wood-grain surface facing up for less friction on the router base plate. When creating the Template on the CNC it is the underside (smooth surface) of the PVC board that faces "UP" because the 1/4" guide slots and Dust Rim cavities are not full-thru. Since the smooth surface will face UP during CNC this is the surface where the Center Crosshairs were measured and pencil marked.

Loading the .tap File and PVC Board on the CNC Router

Several years ago I made, via CNC, several custom CNC beds. As you will see in the video all that is needed is to slide the PVC Blank between a couple of sacrificial 1/4" dowels. These help align but also prevent any side movement imposed by the router bit pushing to the left or right.

In the back of the CNC bed there is a custom hold-down, again with sacrificial 1/4" dowels, that slides on the two aluminum tracks and is then snugged down to the PVC Blank using the two sacrificial pegs. This eliminates almost any possibility of the router bit hitting the main hardwood hold-down. This same method is used on the front. The PVC board is now in position; square to the travel of the CNC router bit; with pegs on both sides; held down by the sacrificial pegs; and prevented from moving forward or backward by the edges of the main hold-down cross boards. That PVC is going absolutely nowhere!

Setting The Z Zero Position and Resetting XYZ During Initialization

The PVC boards are a very perfect 3/4" (.75") thickness. As mentioned above the depth of every full-thru cavity to be routed in that PVC board were set in Vcarve at .8 for a .75 thick board so all cavities go the distance and then some and the "Z 0 Position" at "Material Surface". Keeping both of these in mind during initialization I use the "Down" on the digital keypad to move the bit just slightly into the surface of the PVC before clicking on the "Reset XYZ to Zero" phase. Again, the spoil board under the PVC will absorb the excess depth.

Keeping One Finger on the "Stop" Button

Clicking the "Start" button on the CNC Controller never ceases to amaze me! Just watching that bit follow my instructions is a form of entertainment that "only a mother can love". When I run the first board of a new Toolpath I stay nearby with one finger not far from the "Stop" button on the CNC Controller just in case I goofed up in the Toolpath programming. Anyone that uses a CNC router recognizes that "gunk, gunk, gunk..." sound when the Toolpath tells the router to go beyond its physical limits. If this happens all that can be done is to quickly hit "Stop", resolve the issue in Vcarve then come back to reset and start over. Sometimes the only issue is where the bit hits one of the sacrificial wood-dowel hold-down pegs which is a non-issue so long as there is remaining on that 1/4" dowel enough material to still hold down the PVC workpiece and that the impact was not enough for the "gunk, gunk, gunk" that would throw off all remaining coordinates. During this 1st run I also keep an eye on all of the cables hanging overhead to make sure none of those could get jammed.

Multiple Copies

If all goes as planned I frequently run additional copies. Sometimes this might be to prepare for an upcoming workshop where each student can have their own Template. Otherwise having multiple Templates saves time later by allowing me to install the 1/4" Guide Plys for the most common scenarios (2" width, 4" width, 5-Hole dimpling Vs routing etc) and then leaving those all set up. In those cases I usually add a dab of PVC-friendly adhesive in the 1/4" slots so the Guides don't work their way out. One of the benefits of using PVC is there are no "hidden" knots (like in plywood) so running copies of the same, now-trusted, Toolpath means I can do other things in the shop still within hearing range for the "gunk, gunk, gunk" but without much concern.

Half-Size Templates

The 11" Template can be cut into two separate Templates at 5 1/2" each. This is the reason for that shallow oval included in the Toolpath. Placing the PVC template on a mitersaw then aligning the blade-shadow (laser on some miter saws) directly over the center of that oval then crosscutting creates two Templates at 5 1/2" x 5 1/2" each (minus minor saw kerf loss). (BTW this again is why I use the "Center" for the XY Datum position so the loss of saw kerf material does not affect alignment during use). These shorter Templates seem to sit better on the workpiece, especially when routing tenons or punching dimples on the end-grain yet there is still enough surface area to prevent the plunge base on the router from falling off the edge when routing mortises.

That's It! The PVC Blank is now a "PVC Mortise and Tenon Router Template" ready to be tested in real-time to rout mortises, tenons and to mount fabricated metal tenons.

Video: Testing The Router Template on Real Boards

Templates Require Accuracy in Board Thickness and Width

If there is a downside of Templates it's that a template designed to slide over a 2" thick board will NOT slide over a 2 1/6" thick board. Same with any other thicknesses or widths that are controlled by the 1/4" plywood guides. Especially for testing it was critical that the test beam was run through a planer for a perfect 2" x 4" shape. In real life if the boards are undersized, intentionally or accidentally, two thin shims, one placed on each side between the board and the Template 1/4" Guides, will keep the router ovals or dimple guides centered on the board.

Testing Multiple Applications for the Template

Test #1: Rout 3/8"d x 3/4"w x 2 3/4"L mortise with its C/L @ a pencil mark on a 2" edge

Test #2: Confirm the 4" spacing between 1/4" Ply Guides was accurate

Test #3: Punching 5 dimples on the end-grain for future mounting of tenons or fasteners

Test #4: Shaping portions of a tenon on the end-grain then using a miter saw to complete tenon

As the video shows, all of the above tests came out perfect with the exception of some instability of the Template when clamped to the end-grain. After a bit of analysis it became clear that the clamps were holding the 1/4" Ply Guides quite firm to the workpiece but the Template was slipping out of the Guide's grip. Going forward two changes will be made for end-grain applications (routing tenons or dimpling pilot holes):

1. The 11" Template will be cut in half so only the 5 1/2" portion remains. This will minimize the "cantilever" affect caused by the weight of the router or other pressures.
2. The two 1/4" Ply Guides will be glued permanently into the slots using a PVC-friendly adhesive
3. A 3rd option can also be to use a temporary screw, countersunk to stay below the surface, in one of the 5 holes. This will not only hold the Template in place but it will, in itself, create the pilot hole otherwise made by a metalworker's punch or by a Hinge Bit

The "testing" was complete! In fact it went so well that there does not appear to be any need for tweaks to the Template Design or the .crv or .tap Vcarve files. I can now run several copies on the CNC, cut some/all in half and then preload the 1/4" Ply Guides to be ready for action on my next project a "MikroCave" AKA "Super Selfish Sanctuary" TBA soon at an Instructable near you!

Hopefully this Instructable was helpful. Please feel free to Comment or to contact me directly via PM with any questions, corrections etc.. I also encourage you to check out my previous Instructables and to Subscribe/Follow to be automatically notified when I publish more woodworking Instructables. Better yet maybe plan a trip to Door County, Wisconsin to attend woodworking, metalworking or other workshops held at TheClearing.org, a non-profit where I teach woodworking.

Mike