Clamp racks are an easy project with the CNC router. They are a good way to use up the ever increasing pile of plywood scraps.

I had an old and very simple rack for F clamps above the bench by the radial arm saws. However, it is not very convenient requiring a long reach to pull the clamps and some of the import clamps do not fit over the bar very well.

 

Another problem is that the pipe clamps are just piled in a corner by the patio door. THey were hard to get to and I was afraid of cracking the glass.

So, with some downtime from larger projects required due to recent Cubital Tunnel release surgery and a pile of plywood scraps left over from Olivia’s bed, I decided to make new clamp racks. The idea was triggered by the new Lee Valley catalog which has single row racks for sale.

The design goals were to:

• Allow for hanging from the walls or overhead floor joists maximizing flexibility of location.
• Provide space for multiple (4-6) clamps per row for either F clamps or pipe clamps
• Use up the existing plywood scraps without creating more.

This meant that the dimensions had to be flexible to adapt to the scraps on hand  without cutting into a new sheet and the “back boards” needed to be a bit tall to allow for hanging from the upstairs floor joists.

Layout for the backs was done in V-Carve Pro. The slots are 3″ high by 0.47″ wide. The mortises are then squared up with a chisel. This ended up being faster and easier than rounding the bracket tenons. You could do this with a regular router and fence as well, but remember to use 1/4 or 3/8″ bit as the slots need to be less than 1/2″ wide for a good grip on the brackets.

The brackets are 3.25″ tall. This was the width of several strips of baltic birch plywood that I had left over from making dresser drawers. The lengths were 7 to 8 ” depending on the rack.  The bottom edge is sloped at about 12 degrees – I thought it looked better than simply leaving them square. The notches at the ends are 0.7″ tall by 1/8″ wide.  This gives just enough shoulder so that the brackets are self aligning when driven home and the tenon is very slightly recessed when viewed from the back.

Apply glue to the slots and drive the brackets in with a large mallet.   They are basically self clamping.

1″ screws and fender washers are added to the back for added clamping pressure and to ensure the brackets cannot pull out under load. The screws and washers had been waiting for this occasion. I had not used them previously due to bits of epoxy and the washers being stuck on the screws. They were left over from doing the deck strips of the boat.

Now the clamp racks are hung and the clamps are much neater and more accessible. Next I will need to rearrange the various jigs and other items on the back wall since they are easier to get to with the new racks.

Finish is a couple of coats of shellac. This  was another left over and I need to mix up a fresh batch for the bed.

If I were doing it again I would make both racks with the jaws facing the back wall as this provides more clearance in front of the peg board.

Finish, then Assemble design

This design is based on the technique of: finish, then assemble. This will sound backwards to most people, but is a very logical and efficient way to do certain kinds of projects – especially those with lots of small parts.  It works well with many Craftsman designs or adaptations of them.

The primary key to making this succeed is to have joints where every surface has a reveal or offset.  This begs for mortise and tenon joinery as well as flat recessed or raised panels. This project was designed for reveals and recessed flat panels.

When designing a piece for this technique it is easy to go overboard with large reveals. This has 1/16″ to 1/8″ reveals. The key point is to not have any adjacent surfaces that when assembled must be flush (and then require sanding, planing or scraping).

The beauty of this technique is that the surface preparation is easy.  I really hate sanding and scraping into corners and to do this between spindles is a special kind of hell. It is so easy to create a divot while attempting to clean up that last little bit of “something”.  With the  all flat surfaces and you can spray the finish on all horizontal pieces ( no runs).  This works well if you don’t spray finish on a daily weekly or even monthly basis.

Sanding and scraping

I sand all of the pieces to 120 grit and definitely hand sand or scrape again after the drum sander to avoid nasty longitudinal scratches.   With well figured wood I will then hand scrape as well to better “pop” the figure once finish is employed.    Note that scraping after sanding requires more sharpening but this is a small price to pay.  For any large flat surface, scraping really is a must. It is not only faster than a good sanding job but also gives a better more transparent finish in the end (more chatoyance).  The random orbit sander no longer has a place here, as I am tired of cleaning up swirliques that show up once the stain is applied.

Spraying

Once the parts are sanded I lay them out on left over strips of wood for efficient spraying. The goal is to have them close enough to minimize wasted finish but far enough apart to get good edge coverage.  When gang spraying pieces like this  I spray at approximately a 30 degree angle so that the edges get good coverage. The rack of pieces gets 2 passes so that I can hit both sides. This means that as you walk down the row the first pass will not have full coverage on the face, but as you reverse direction for the second pass it will.  The edges achieve full coverage as the get hit when each face is sprayed.

When I first started doing spindles like this, I placed them close together and sprayed per normal directions and still had uneven sides. Using the current technique the sides turn out great and it only takes half the time as I only flip once per coat instead of four times .

Mortises and dadoes when finishing

For proper glue adhesion, you really do not want to have the finish layers inside of the joints.  Having finish inside of the joints is a recipe for glue bond failure.  The tenons are easy – tape them.

However the mortises and dadoes are more difficult. There are two major types: those that meet with a shoulder and those that do not. The top and bottom rails are good examples of those that meet with a shoulder. The mortise is hidden well within the end of the stock with the tenon that fits into it. These well hidden mortises can be covered with masking tape. The mortises and dadoes that will not have broad shoulders covering their edges are more difficult as masking tape will easily protrude on to what will be exposed areas.  Rolled up paper towels , newspaper and even wooden scraps can work, but the easiest by far is using foam “backer rod” that is used for weatherstripping and to fill the big gaps in your house that you can then caulk over.   Here we have 1/2″ backer rod filling some of the mortises.  The pieces can easily be re-used for future projects.

 

Finish schedule – all sprayed except for the gel stain:

Behlen solarlux dye – Golden fruitwood

2 light coats 1 lb cut garnet shellac

General FInishes gel stain – mix of 2 parts Georgian Cherry, 1 part Candle lite   – rub on, rub off and let dry 5-7 days. The long dry time is due to it  (oil based stain) being followed up with a water based finish

1 coat General Finishes Endurovar gloss precat water based urethane

2 coats General Finishes Endurovar Satin precat water based urethane . The precatelyzed polyurethane is exceptionally durable and UV resistant.  It is very brushable as well . I also enjoy the opportunity to promote a local business which really does have a superior product.  Their factory is <20 miles from my home.

If you are wondering; “Why gloss then satin?”. The reason is that the first coat of finish is often much heavier than the later ones,  and each coat of satin will drop the clarity of the finish. So the rationale is to build up the finish coats with gloss for depth and  sandability. Then switch to satin for the last 2 coats to provide the desired lustre.  While I would prefer to have just one coat of satin for best clarity, my technique is imperfect and I need 2 coats of satin to make sure there are not glossy patches showing through in the final finish.   I do the same with most other finishes where I want a non-gloss lustre.  The exception is Sherwin Williams pre cat rubbed effect lacquer.  This stuff is glorious, but must be used outside due to toxicity and not wanting to risk the house going BOOM.

Final assembly

Once the pieces have been finished, it is time for assembly.  This is where the epoxy comes in. This is not just the fast hardening hardware store syringes but rather the slower setting high strength epoxies from: Gougeon Brothers / West System, System 3 and Glen-L Marine Designs.  Beware of those selling “penetrating epoxies” which are basically the same base components with thinners / diluants but then lack in mechanical strength.

For the final assembly we do one last dry fit-up.  This verifies that we have all of the right pieces in place and there are no finish issues (blobs) impeding assembly.

The epoxy is thickened with silica. The colloidal silica keeps it from running or sagging during assembly. The high strength silica adds bulk. Think of adding sand and stone aggregate to concrete as the logical equivalents.   This mix is then tinted to match the darker colors in the wood.  The dark colors blend in well to the grain and look natural in the crevices of the joints if your clean up is imperfect. However if it is lighter than the background wood color it will stick out like a sore thumb.

We are also careful to clean up any squeeze out or fingerprints with plenty of paper towels and denatured alcohol. The epoxy will discolor in sunlight due to the UV rays and what may not be noticeable now may very well be in 5-10 years.

Rails and Slats

Today we were mortising the crib side rails and slats. The lower rail mortises were done on the CNC  router.  Overall, there are 50 mortises to cut for the slats.

The front rails are 5″ tall and the end rails are and 6″ tall. So these had to be clamped upright to the  left pf the main work area on the router top. A new fence was made on the left edge of the work area to support the rails in the vertical position.  The fence was made from some 2×2 scrap stock. Once drilled and bolted in place, the router was used to cut the left face so that it was perfectly aligned with the router Y axis and exactly plumb.

As you can see clamping the ends is quite easy.  This is adequate for the crib end rails but not enough for the long front rail.

The front rail is about 53″ long and needs some support in the middle.  There is no good way to add a conventional clamp  as  are used on the ends.  At this time, the router does not have enough vertical travel to clear clamps placed over the top of the boards and there is always the fear of a crash with a misplaced clamp. So this was solved by taking a scrap of 3/4″ plywood and sawing it into a pair of wedges. These are placed between the stock and the side rail. A few taps with a hammer, and the wood is secured.

Here you can see the front rail clamped in place ready for the cuts.

Top end rail mortises

The top end rails need to be done conventionally with a plunge router and fence. However the start and stop points for each mortise need to be transferred to the parts.  However they are curved and there is a 6.5″ rise from the front edge to the back. Armed with a dimensioned drawing and a cutting mat, the parts were aligned to the grid of the cutting mat and a 1-2-3 block was then used as the vertical guide. A block of wood would work as well, but the mass of the metal block made things easier.  Here the leading edges of each mortise are being transferred.

The mortises now need the trailing edge marked. This is easily done by aligning one of the slats with the leading edge mark and then bringing the 1-2-3 block up to it and then making the mark.

The slats are 0.5×1.75″ and the corners are rounded over with a 3/16″ radius. This is done at the router table, which is an extension of my table saw.  Feather boards are placed to guide the cut (fewer ripples) and protect Teal’s fingers. After the photo Teal tucked the ties of her sweatshirt in.

Top Rails

The front and back top rails are curved as can be seen in the end view below. The rails start as a rectangular piece of stock 1.5×3″. 

The first task is to cut the tenons on each end. This is done at the radial arm saw with a dado blade.  An end stop is set for the length of the tenon and they are cut in 2 passes as you can see below where I am cutting the second pass.   Having the digital readout on the height adjustment greatly  speeds  up the setup.  The next step is cutting the bottom bevel which is at 38.5 degrees.

The bottom piece of the rail is 3/8 x 1 1/4″ and the mortises are again cut on the CNC router. However at that point the stock was left thick for added stability and rigidity and then after they were cut the stock was ripped to the 3/8″ final thickness.

Here the bottom piece is being glued to the rail. Note the off cut form the angle is being used to provide a grip for the clamps. It is lightly tacked in place with super glue (and some slipped).    This is another case where using many clamps with light to medium pressure works better than a few clamps with high pressure.

 

 

Return to the shop

The last few weeks were taken up with vacation and conferences. So there has been no progress on the crib. Teal and I had brought in the last of the wood from the shed, but it was not thick enough for this project and has to wait for another project.  This was the last of the Wisconsin Woodworker’s Guild Logfest hauls that I had set up to air dry. At its peak, it was over 1300 board foot of lumber,  which has now been reconstituted into many pieces of furniture for the family and friends.

Saturday

So yesterday we set off for Kettle Moraine Hardwoods which is our local lumber mill.  They had a nice selection of thick Red Oak (5/4 and 8/4 – 1.25-2″ thick) and we picked up some Hard Maple and an Elm slab for future projects, as well.

Once home, it was time to surface the boards on the jointer and planer and then cut them to rough length in preparation for sending them to the CNC router. At this point, there was a minor design change as the thick stock for the legs was completely cleaned up at 1.86″ vs the 1.5″ I had in the design. So we decided to go with thicker legs.  However, this leads to more work as I did not have a router bit that would cut deep enough, which will be detailed later below.

I fired up the computer for the CNC router and some problems arose. I had not used it for ~2 months and only had the windows 10 logo showing for 45 min. At this point, I rebooted again and it came up in a few minutes. However, Mach 4 which is the CNC controller software for the router had a whole series of errors when starting, and was unusable. Most of the plugins would not work. So I restored it from the backup copy, restarted the PC again and it started to work. However, in testing, many of the configuration parameters were missing including “little things” like the home switches and control for the spindle. Digging through my notes for the configuration values, I got it running again. Now, thoroughly annoyed, it was time for a reward of our home brew Imperial Stout which is now ready for consumption.

Sunday

After re-zeroing the CNC router it was time to set up the first part and make a test run.   The crib end top rails were chosen as they are the smallest parts and least costly in case of problems.  The 8/4 stock for the leg pieces was over $150. Making wach leg approximately $35-50, so I was not going to try those first.

So the stock is clamped on the CNC router and you can see my “cheat sheet” where I have printed out the outline and marked the distances from the near end for the various clamps.

Next you can see the cut under way. At this point I have left off the dust shoe, so there are chips EVERYWHERE.

Now the top rail is completed and vacuumed off.

Another shot in progress, looking down with the dust shoe in place.

With the top rails successfully completed, now I move on to making the legs.  One of the front legs being cut.  In order to prevent the part moving I used not only the 5 clamps shown but also some small strips of double stick tape which help reduce the part sliding under load immensely. With this CNC router, the limitation on cutting speed is not the machine, but the ability to clamp the work and avoid it slipping under the cutting forces. Cutting speed was 100 inches per minute, 18,000 RPM at 1/4″ depth of cut with a 1/2″ 2 flute carbide end mill.

Set up for one of the rear legs – 43″, 110 cm long. Not your ordinary tabletop CNC router. . Note the beautiful curl figure in the stock. Later, you will see how I make this “pop” when finishing.

The other back leg ready to cut

This is why I use wooden clamps. Just a minor nick this time.   These are shop made on the CNC router.

Another look at the scale of these cuts and the finish off the CNC router. This was without a reverse last pass as I don’t (yet) have a router bit long enough to do so and that would look even better.

Here are the legs off the CNC router. As you can see I was not able to cut all of the way through. The depth of cut was limited to 1.5″ based on my largest end mill / router bit. So now they need to be run through the band saws and then flush trim routed.  The end curves are too tight for my big band saw (24″ with 1/2″ resaw blade ) and need to be run through my small one (12″ with 1/4″ skip tooth blade).

Bandsawing the excess off the legs on the 24″ band saw.

Flush trimming off the excess. The holdfast works great to clamp irregular stock like this. Teal also assisted in taming the work. The Oak is a bit unruly.  I often had to reverse directions to minimize tear out.  This means taking climb cuts which try to throw the work and router around.

 

First dry fit test. Not bad.  The cross pieces will be flush with the upper / inside edges of the legs in the final assembly.

The CNC router made this work feasible in a few hours. Otherwise I would have had to make templates, band saw to size and flush trim through several steps. I had done a similar project with curved legs – Elyse’s Sleigh Bed.  This is MUCH easier and with less chip out to fix.

Movies of the CNC router at work

The first part  is without the dust shoe (chips Everywhere) and the second part is with the dust shoe in place (much neater) .

Completed renderings

Today was Jessie’s baby shower. So I had a lot of opportunities to show off the design and gain some consensus on undecided points by 3 generations of mothers.

This image hides the front of the crib, so you can have a clear view of the back panels. 

The are 2 back panels each 1/2 ” thick. They are simple flat panel and frame construction.  The stiles are 3/4 ” thick.  The flat back panels were a hit especially by those such as Kelly who have had to clean up after the ejection of “processed formula”.

The slats are 1.75″ x 1/2″ wide with 3/16″ radiused corners. I need to remember to order some new router bits for the roundovers and the mortises…

The front and back lower rail bottom edges were lowered 1″ to allow for greater overlap with the mattress sides when it is in the bottom position (on the floor.

The inside of side rails will now be flush with the inside of the legs. This will mean there will be one screw per leg visible in the end. I am still not sure if they will be inserted from the top or sides. That will have to wait until I have the parts in hand.

Inside dimensions were double checked against the standards. I want the mattress to fit properly and not have too much of a gap.

Having the riser under the top horizontal rails will also allow it to have the mortises cut accurately without having to worry about how to jig up the curved front and back top rails.

The idea of doing some inlay work was rejected.  So much for Isla’s palm trees.

Assembly preview

As you can see above, all of the joints have a reveal. So this can be a “finish first and glue up later” process for the finishing and assembly as I have done on the craftsman style beds. This saves a LOT of time sanding, cleaning up glue squeeze out and removes worries about glue blotches. I use pigmented and thickened epoxy for the glue up. Additionally the longer set up time with a slow curing hardener allows for the alignment of the many parts that are in each assembly.

Below is a preview of this finish and assembly technique from prior projects.

Over one hundred spindles laid out and ready for finish coats. Racked out and ready for the spray, turn, spray, turn, repeat routine.Spraying on the final coats on an unseasonably  warm March day for Teal’s and my bed.Dry fit assembly and masking the joints on Elyse’s bed.

Glued up and inserting the tenons. Note the chocolate color of the epoxy.

Glue squeeze out prior to clean up with a plastic scraper and denatured alcohol.

Cleaned up after final paring of the last of the squeeze out 8 hours later. Most is wiped up early but there are some areas that it is better to wait and pare off later.  At this stage the epoxy is sort of the consistency of cheddar cheese and cleans up nicely. It is not yet rock hard as it will be at about 24-36 hours. Final joint appearance.

Now that we have a starting point for the design, it is time to start gathering dimensions from the photos.   Traditionally, I have done this by printing photos at half or full sheet and then scaling it manually.  My goal when borrowing from an existing design is not an exact replica but rather using the original as a model to start for overall proportions.  I am not into doing reproductions. Additionally, in this case I am making improvements in the design.

First, I will note the major known dimensions. In this case it is overall height width and depth. This is done on each photo. Do not assume (or forget) that the scaling will be different in each  image.  Next the actual size in the photo for these is measured and the scaling amount calculated. I will normally do the actual measurements in mm to make the math easier (avoiding fractions). You can use a caliper or ruler – I like using a caliper.

I double check that the X&Y dimensions yield similar results.  If all you have is an angled or isometric view then this gets more complicated. Now I take measurements of measured features and do the math in a spreadsheet so I have a listing of my measurements and can easily double check for errors in case of a conflict.    I will also do the actual photo measurements in one color and the final scaled in another to avoid mix-ups

I will typically start on paper and make sure that the dimensions make some sense before transferring to Sketchup.

You can also import a photo into sketchup and then start drawing your components on top of it.  For rectilinear pieces it is better to use it to set a few lines and then draw as you normally would. Trying to match the photo underneath will otherwise lead to errors and out of parallel edges.

Here I have started with the curved end pieces. With the rudimentary curve drawing tools in Sketchup (arcs, lines and bezier curves) it took a lot of tries to get something that looked decent. I wish I could have gotten the NURBS lines to work which offer much more control.  At this point I will lay down a couple of lines to mark the lower rails and then hide the photo. So now I can move into 3D space.  each of the parts show becomes a component so I can mirror them for the other end and all of the modifications transfer as I work back and forth.

The top and bottom rails are then fit to the end posts.  Now I mirror the ends, and set them approximately the right distance apart. I am still not sure if the end top and bottom rails will fully or partially overlap the legs.

Next come the bottom rails and I then draw guide lines up the leg posts to show where the top rail should line up vertically and the  offset for the spindles from the inside edge.  The inside spacing is an important dimension as you are only allowed 28 +-5/8″ by CPSC guidelines so you don’t have too big a gap around a standard crib mattress.

The front top rail is next. It took a few tries to get something that is not too thick.  I may still make it a bit taller. Lets see after the rear top rail is in place. 

Now with the the back rail placed, and the frame colorized you can see the shapes better. I think it looks better with the taller top rails, but lest see what the girls say tomorrow.

Baby Crib Project

My daughters, Jessie and Elyse, are both due at the end of March 2018. Jessie still needs a crib. So the question of: “What is the next project?” has been decided, and I have a rather short timeline. However, if push comes to shove, she can use the same cradle that she slept in as a baby that my dad made, while I finish the crib.    This is another project where I am following in my Father’s footsteps making things for the grandkids.

Basic requirements:

• Solid back – avoid little fingers finding outlets and easier cleanup after dinner gets launched. Flat panel rather than raised panel per Jessie’s preference.
• Adjustable mattress height
• Convertible to a bed.  This will make it last, rather than be a 2 year item.   Appearance as a bed will take precedence over appearance as a crib.
• Follow CPSC guidelines for safety.  This includes no cut outs – so much for Mackintosh style slats I had wanted to do on the CNC router (besides Teal and Jessie are not fans).
• Design needs to complement the other furniture I have made for Jessie which is of a craftsman style and have the same finish

So we have been digging through many Google Images, Pinterest, LumberJocks and many other websites looking for ideas as a launch point.  There are a lot of ugly cribs out there! Besides, many designs that look OK as a crib  do not look very good as a bed.  On top of it you have the predominance of MDF and particle board based junk that is on most of the web sites.

Given that Jessie is expecting a girl, I was hoping for a sleigh crib / bed sort of design. However, many “sleigh cribs” have weird lumps for curves that seem to have been tacked onto an otherwise square leg. I want something that will be smooth and flowing.  Plus, this will give me another excuse to play with the CNC router. Although, a band saw and spokeshave or template and router would probably work well, too.  For Elyse’s queen size bed, the curves were laid out on a template and then pattern cut with a band saw and router.  Her bed (ca. 2009) is shown below.

Now, I want to do something that is more “organic and flowing” for the end posts rather than ending squarely at the floor.  This is a tall order for an engineering mind.

Safety

Much has been said about the changes in safety standards for cribs. The slat spacing requirements have changed, no more drop fronts (yeah!). However I was still worried about safety and started more research. The primary resources I used are:

• CPSC website: Full-Size Baby Cribs Business Guidance & Small Entity Compliance Guide which provides the inside dimensions but is silent on spindle spacing.

• International Association on Child Safety: iafcs.org/docs/Docs_Head_Entrapment_Presentation_Revised_2013.pdf    which does provide spindle spacing and other useful information.
• http://www.narts.org/files/pdf/SafeCribGuidelines_BW.pdf
• National Institutes of Health: Age, side height, and spindle shape of the crib in climbing over the side.

Where to start?

After several evenings of web searches and IM messages back and forth with Jessie, a leading candidate for the basis of the design emerged.   It is the “Franklin and Ben Mayfair Crib”.   For an example see:  Mayfair Crib  This was the first site that it popped up on. Others sites list it as discontinued.

This is just a starting point. As on many projects, I will look at multiple designs and then take the pieces I like and modify for more robust construction and the techniques that I prefer.

Things I like in the design:

• The outside sweep of the posts – especially the inward curving feet and no “lumps”
• Curved top rails (teething deterrent). These will end up looking more like Elyse’s sleigh bed
• Looks nice as a bed
• Nearly solid back
• Openings at the ends of the back panel

Things that must be improved:

• Flat panel in back looks like it was tacked on
• Lots of fasteners and holes showing
• Flat inside edges of the legs when viewed from the side
• Extra side and bottom parts hanging on when converted to a bed
• Front bottom rail – likely will be removed as this will not be a day bed  but rather converted to a full size directly (pending approval)

So now I need to gather basic dimensions and start the new design.

Lessons learned

With the first batch of the top drawers out of the way, it was now time to start on the rest of them.  These are bigger, and I had learned a few lessons from the first set of top drawers:

Consistency and repeatability are paramount.  This lead to fixture board end stop additions and minor redesign to remove most human error.    I had some sides on the first batch which did not line up perfectly and I was lucky to be able to fix the fit by sanding the backs of the drawer fronts.

After the first roughing pass, the new stop fingers had been “modified” due to the low Z axis clearance between cuts. 

Drawer and side thickness MUST be consistent.  This time all of the boards were drum sanded to the same thickness. It is surprising how much variation even a large well tuned planer has (mine is a 20″ Jet).  This made a big difference in the fit for the 18 drawers vs the earlier batch of 9. Planing single handedly does not help.

Scoring the faces of the sides to prevent tear-out is a must. The roughing cut sequencing of Joint Cam causes a lot of tear out. It would be better if the roughing cut was the same sequence as the finish / dovetail pass. However , scoring the face heavily with a marking gauge, largely mitigates the problem .

Fixture additions must account for bit profile differences between the roughing and finish passes. It would pay to run the finish pass air cutting to make sure the fixture fingers are not in the way or you could end up with a snapped bit or missed steps. I  had to trim back the corners by hand to allow room for the dovetail shaft.

The new LED light ring around the front of the motor nicely illuminates the work .

This shows the touch plate I use for setting the Z axis zero. There is something funky with the Mach4 CNC controller touch functions. I now repeat each zero touch to verify the value does not change. 

Now for cutting the dadoes and assembling the 18 drawers.

Initial testing

One of the goals when making the CNC router was to be able to do general woodworking joinery including dovetails, sliding dovetails and mortise and tenon joints. The mortise and tenon capability was proven out when I did the blanket ladders.  The dovetails needed another project and the dresser project with 27 drawers is a perfect fit.

The CNC router was set up with a special base for the dovetails and the horizontal fences were CNC routed to final spacing in place (20″ apart) to match the vertical fences.

Over the last week I had prototype the joints using JointCam and using scrap pieces of plywood that were of the approximate thicknesses of the drawer fronts and sides. I tested both equally spaced and equal spaced dovetails and both turned out well after a bit of initial tuning.  Teal liked the equal spaced better and these could be done with both pins and tails in one pass so this was chosen.

Wood for the drawers

The drawer faces are white or red oak depending on the dresser . At this point I am doing the top row of smaller drawers.  The 3 top drawers for each dresser are cut from a single board so that the grain runs across the face of the dresser. If one is botched then all 3 are scrap.  So there is a bit of tension here with some nice pieces of quarter sawn white oak (big flakes) and near quarter sawn red oak for the drawers.

The drawer faces are approximately 3/4″ thick.  The drawer sides are 1/2″ nominal (0.47″ actual) baltic birch. I like the baltic birch plywood for drawer components. The even coloring and lack of voids make for nice side pieces.

Now for the “production”

The off cuts were again tested and everything seemed to work although the joints were a bit looser than expected from the earlier testing . Jointcam has a setting for adjusting the fit and this was used. New pieces tested OK so on to the real stuff.

At this point things fell apart. The router bit was progressively creeping out of the collet during the cuts. This was apparently exacerbated by the oak drawer fronts. I reduced the feed rates and increased the spindle speed but it was still happening. I tried a new dovetail router bit with a longer shank and really cranked down on the collet but it was still creeping out and then the shank of the router bit snapped just past the collet. Time for a beer (or 3) and think through the alternatives.

Plan B

There is not a lot of info on the net about CNC cutting dovetails. There are bits on commercial work where you cut everything flat and add a false front, but little on the trials and tribulations of doing this properly.  The JointCam info mentions the use of roughing and dovetail bits and passes but no guidance on when to use this vs single pass.  So after the beers and sleeping on it I decide to be conservative and use a roughing pass (straight bit) and finish pass with the dovetail bit but switching to a 1/2 ” shank dovetail in the hope that it would grip better. I had one more of each on hand – 1/4″ straight and 1/2″ 14 degree dovetail with 1/2″ shank.  As you can see from the photo below, the pieces are cut 2 at a time as right / left pairs.

Testing

Testing went well. However it is tedious as you need to do a bit change for each test (straight and dovetail passes). So by late morning it was a go for this method. Now I just had to make a new set of drawer fronts for the dresser that had them ruined in the first try.

I also found that while JointCam makes a scoring pass for the dovetail / finish bit, one is needed for the roughing pass on the plywood sides. The side faces tend to splinter easily.  So I took a marking / cutting gauge and scribed a line across each of the sides before routing. This contained the  splintering.

Production part 2

I did the drawer fronts first. These were labeled as to sequence on the dresser, inner face and top edge. The top edges were placed against the fences on the CNC router.

First pass for the stack of pieces was with the straight bit.  After all were run, I changed the bit to the dovetail (and it is nice to have a soft mat under the edge of the CNC to catch the dropped bits vs. the concrete floor).

Now that the fronts were done (pins) and they fitted reasonably well against the test sides it was time to do the sides (tails).  These were cut and after the first pair I test fitted them to the fronts. They were close but there was still some variation form one front panel board (set of 3) to another. One small adjustment of the fit clearance (-.001 to +.004″) was made in JointCam for the sides to match the fronts. At this point the sides are labeled right and left (blue tape on the rights) and for each dresser set.

Video of the CNC router cutting the joints is here: Dovetail cutting

Final fitting

There was still some tweaking to do. One set was still tight even with the +0.004 correction. These pieces were tight and had a gap at the end of the tails. So I took this set of 3 to the drum sander. I took off about 1/64″ on the inside face and everything fit nicely.  So now I have the 9 drawer faces and sides fitted up and ready for the dadoes for the bottom and backs.