Help Needed from the Cabinet Pros

[Andy Sowers]

I'm building a cabinet base for a DIY CNC router. The size of the cabinet is roughly 5' x 5' x 3' and will be made from 3/4" ply (probably BB). Note: A welded steel base isn't in the budget right now, plus I need additional storage space that the cabinet base will provide.

I'm worried about the unit racking... then the thought occurred to me that this unit is basically similar to a kitchen island. So I'm putting this out there for the cabinet pros for your expert opinions. Here's two sketchup models of my preliminary design... the first is the overall unit, the second one I removed the top, doors, and drawers to highlight the internal structure. Are the "pink" cabinet partitions sufficient to prevent the unit from racking? If not, how can I improve the rigidity? Face-frames?

Thanks in advance...
Andy
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[Richard Wagner]

I am not a cabinet pro by any means but I do see one thing that I believe you need to change. The two end panels, I believe should rest on the base not attach to the end of the base. I would think a rabbet would be the appropriate joint.

Possibly the same goes for the horizontal members on top. I would think these members should each be one piece reaching the entire width.

If the center divider was one piece (maybe it is - can't tell) that would prevent racking.

I don't know if face frames add much to structural integrity or not but surely there will be face frames - right.

[johnny means]

Your basic plan is plenty stout. It wont rack, but I would revisit the base design. I would do a plynth that supports the entire thing.

[Moses Yoder]

How high is the table on the CNC router? I think our table was about 34" off the ground, so if you're building a 36" base and setting the router on top it may be uncomfortably high. I don't like frameless cabinets myself, although we have built a number of them. Yes, they always rack unless they are tied together and screwed to the wall on one end. I would suggest using a mortice & tenon face frame with 1-1/2" wide stiles & rails, 3/4" long tenons, although you could get by with pocket screws and properly glued joints.

[Homer Faucett]

I'm no expert, but have built cabinets almost exactly like you have drawn up, and have no problems with racking in my kitchen, even with a granite countertop and the occasional climbing on top of the counter. I used glue and screws (actually, pocket screws) with butt joints much like you have drawn up. I used the cheapest 3/4" plywood with 13 plys that I could find, and it worked out great. The only difference between mine and yours is I used solid plywood across the top instead of nailers, and I added top and bottom nailers across the backs (your pink area) that were glued and pocket screwed to both sides and the bottom or top (that really helped with drawing any slight bow or warp out of the plywood and really strengthens the whole box). This adds quite a bit of insurance against racking, but what really tied everything together was gluing and stapling just a simple 1/4" ply skin on the back. Fast, simple, effective. You could rabbet and/or screw in 3/4 or 1/2 ply there if you found it necessary, but I think it's overkill.

The only change I would probably make is to make the cabinet modular (build 6 small cabinets and screw them together), as that would make them slightly stronger and easier to build. However, that uses more plywood and adds weight. Additionally, I agree that I would make the base support the entire structure, and have the ends of the base directly under the plywood sides. I'd also use the heavy-duty leveling legs you can get at Rockler or Woodworker's Supply.

Sure, you could rabbet and/or mortise and tenon every joint, but this is a tool base for a tool that will be obsolete in 20 years (probably a lot sooner). Don't overthink it.

Good luck to you, and let us see how it turns out!

[Andy Sowers]

Thanks all...

Richard/Johnny: Yeah, I wasn't really happy with the way the base worked out... but I wanted to add a toe kick all the way around. One thought I had was to eliminate it alltogehter and just increase the overhang of the top by a few inches. I think I'll rework it along the lines you suggested...

The center divider/partition isn't a single peice, but certainly could be. I wasn't worried so much about he racking of the unit along that portion of the cabinet but moreso concerned about flexing along the less supported areas where the doors/drawers are located.

Moses, I intend for the final spoilboard height to match my TS height... right around 34" That way if I'm feeding long items through my TS it won't hit it...

Homer, there will be a solid ply top. I'll use the nailers to secure this ply top to the cabs, and then drill a series of holes in the ply top to bolt the CNC to it. I thought of making 6 individual cabinets. BUT, in this case, once its assembled in my shop. Its not going anywhere, so its not like its going to have to be transported and reassembled in a new location. I do plan on making use of several pocket holes to put this together in the event I want to tear it all apart, down the road.

Thanks!! Keep the ideas coming!! Really useful input!

[Peter Kelly]

I've built my workbenches more or less identical to this and haven't had any issues with racking. I would recommend inset 3/4" backs on each, held in place with pocket screws. You might also screw those shelves in place.

[scott vroom]

The plywood sides and 'pink' center panel are sufficient to prevent racking. Make sure that the pink center panel is a single plywood board and not 3 separate panels, and that it is dadoed/glued into the side panels. A mortise and tenon ff is unnecessary...pocket screws/glue are fine.

[Don Wacker]

Thanks all...

Richard/Johnny: Yeah, I wasn't really happy with the way the base worked out... but I wanted to add a toe kick all the way around.

You can basicly ignore your base when designing. Build your base cabinet, when its all done build a ladder frame for the base. Set the ladder frame in place, level it out then set the cabinet on the ladder frame. If you want it to be pretty this makes it easy to scribe the floor for the toe kick face. I do all base cabinets this way.

Don

[Jeff Monson]

I agree with Scott that the pink panel should be one piece. With a top securly attached this should be a solid piece.

[Peter Quinn]

I recently built a similarly sized cabinet for my own shop. I chose to include two divisions per side and leave one end as open shelving. This in effect creates a shear wall on the end of each opening side which contributes greatly to stiffness. I could put doors rather than open shelving but chose not to for my application. Its a shallow opening, maybe 14". I chose to make the center partition continuous and make the dividers between drawer banks the loose partitions. I started with one large I formation and built out from there. Mine is not Frameless, but most of the frames are 1" white oak to maximize usable drawer space. Instead of a pedestal or toe kick I made a stout frame for each long end from laminated QSWO 3x3 material. One of these frames is glued to each long side. They act as stretchers to carry the weight of the entire cabinet and any load placed on its top. They have levelers in the leg bottoms. You can pretty much hit this cabinet with a fork lift and not get it to flex. But it's all built around a design similar to yours. IME frameless cabs need e support of a house to remain rigid. It's better to build a workbench frame from 4x4 material and hang cabs in it's opening than to rely on framless cabs for strength. How heavy is the CNC that will live on top, and does it have it's own support or does ot rely on the strength of the table below it for flatness?

[Peter Quinn]

Here are a few JPEGS of sketch up renderings of the cabinet/bench hybrid. Sorry but I just realized I have never taken a pic of it! TRy to imagine the frame pictured glued to the cabinet.

[Andy Sowers]

Thanks Peter! I was just about to ask for a sketch/photo and you beat me to the punch! I like your frame idea vs the toe-kick concept I was thinking about... If possible, can you PM me a sketch of the two pieces merged together (or a photo if its easier). I was wondering how the ends of the carcass meet up with the legs/stretchers.


The weight of my CNC itself is probably around 200pounds. The table of the machine itself will be a 3/4" sheet of MDF which is bolted to a "ladder" of Aluminum extrusions. This MDF table can/will be flattened by the router, so its not uber critical that my table base is perfectly flat (although that would help).

[Peter Quinn]

Will do as soon as the camera battery finishes charging! I tried merging the two sub assemblies but it wasn't particularly clear from that rendering what was happening. Basically there are cleats screwed to the bottom of the longer leg of the cabinet carcus from below flush to its edge. This increases the glue surface and provided a clamping aid during assembly. The lower rail on the FF and cleat together were slightly greater in width than the outer frames 3", so the bottom of the lower drawer in each bank starts just above the outer frame. From the book shelf open end the legs of the frame appear as a slightly over sized FF. The H parts of the frame were made with double 5"X1/2" loose tenons at each joint. I remember thinking when holding the loose tenon stock in my hand that they looked like Fred Flintstones version of a domino. Super sized! Putting a box at the end of the case rather than 3 openings in a row adds great shear strength to resist racking. Its sort of like the shear walls in modern garage construction. Those little walls to the left and right of a garage door opening are critical to the stability of that large opening for the same reason, as is the large header required for each door. In a sense the frame aspect of this cabinet acts just like the framing of a garage door opening. I call this bench cab hybrid "Oak Berg".

[Kevin Presutti]

What Don said.................:D

[Andy Sowers]

I liked Peter's bench so much, I decided to rework my base (along with some of the other suggestions)... Here's the latest incarnation:

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I'm not sure if these changes will make it any sturdier... but I like this look much better! Thanks Peter!

Andy

[Peter Quinn]

I liked Peter's bench so much, I decided to rework my base (along with some of the other suggestions)... Here's the latest incarnation:

213215213214

I'm not sure if these changes will make it any sturdier... but I like this look much better! Thanks Peter!

Andy

My pleasure Andy. I like the look of that! I find this set up to be pretty rigid in use. I needed a hand tool bench and a new TS outfeed, I needed a lot of cabinet storage for router bits and hand tool, I needed a place to put TS accessories and blades. This one bench pretty much does it all. I started off thinking Roubo type work bench with a cabinet underneath, and it evolved into that hybrid version with the best features of both.

Looking at your design I'm thinking if there was a rabbit or even a dado in the legs to accept the plywood that forms the end panels it would be a good way to strengthen that connection. Or perhaps a cleat behind the panel that drops into a dado in the legs that lets you screw that part of the from behind could make things easy.

Good luck with your project, I'm sure you will work al the ideas here into a fine bench for your CNC. i love to see pics of the final form!

[Andy Sowers]

Here's the final bench for the CNC build (well, I still may install doors/drawers in the base--I haven't made up my mind yet on that).

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It bears a striking resemblance to Peter's! I was initially concerned about racking, but this thing is absolutely STOUT. No worries anymore!

Andy

[Peter Quinn]

Andy, I like that bench! Nice work there. Looks pretty solid.

[Russell Sansom]

Your box looks pretty stiff and it's not going to be heavily loaded, so I doubt any small bit of racking is going to be an annoyance.

Ernest Joyce in "The Encyclopedia of Furniture Making" says a book case needs a cornice or a plinth to keep from racking. Sorry, I couldn't find the page. I've also always considered this advice to be axiomatic. I've also always taken that to mean "...or equivalent." Basically I try to put a box somewhere in the structure. Even a very thin torsion box works fine, so long as it can't distort around any of its three axes. A face frame won't prevent a carcase from racking, but naturally screwing it to the wall will. There's a nice big torsion box!
You can easily confirm for yourself how well an attached box works by looking at the successful and the unsuccessful 5-sided cases all around you. Give a bump to any loaded down bookcase that is built naively and watch it swing its shoulders.