Mistake-Proofing Cabinet Jobs

Deep thoughts on office, shop, and job-site standard operating procedures that can reduce the human-error factor in cabinet production and installation. April 29, 2010

While I'm more of a Theory of Constraints theorist, I've been trying to digest more Lean/Six Sigma concepts lately. One that struck a chord with me was Poke Yoke, or the concept of mistake-proofing a task.

As an engineer, I've seen and been a part of more than my share of mistakes/disasters - things that aren't difficult to fix while on our desks, but are brutal on the bottom line of a project if they make it to the shop. This can be as simple as some extra machining that should have been included in the office for those custom drawer slides, to anything that needs to be reworked or remade. I know of a fellow who ordered an entire truckload of postform countertops the wrong color because a change order wasn't followed up on. Another I heard of recently was a fellow who built 400 or so cabinets the wrong height. I myself released a run of 4 cabinets the other day that were 1" short. One room had a 30" high ctr height and the other 29". I was working on both at the same time...

What processes have you put into place in your office to help ensure these mistakes don't happen? As an engineer I'd love to create a process that allows me to deliver the correct product, predictably and reliably.

Forum Responses
(Business and Management Forum)
From contributor S:
Properly engineered and detailed drawings! If there is a mistake on the drawing, most likely there will be error on the floor.

1) Draftspersons spend more time elaborating and have all necessary info reflected on the drawings.
2) Draftsperson field dimensions (not the Project Manager).
3) CNC programmer/cut biller (if any) checks for accuracy while generating parts/nesting.
3) Engineering Manager checks all the drawings for accuracy and possible errors before they leave office.
3) Project Manager overlooks entire process.

4) Shop Foreman double checks cut list or CNC part/nest reports against the drawings.
5) If significant mistake happens after all these, you should fire all of those dudes.

From the original questioner:
Contributor S, thank you. I've admired your work for some time now, so let me rephrase the question. How do you draw/engineer the very complicated jobs you undertake to ensure that there are no issues with your drawings?

From contributor S:
Thank you, I appreciate your opinion about my work

With a large or very complicated project, I follow these steps:

1) Draftsperson goes to field (sometimes long trips with overnight stay) with laptop computer, laser level, and all kind of other equipment required for accurate field dimensions.

2) Draftsperson draws the 3D model of the space/room or building that undertakes the renovation right there, on the site, and makes sure nothing is missed. Bench and datum marks are used to properly locate the windows, doors, soffits and other elements of the room.

3) Once we have an actual 3D model of the work area in hand, we create a 3D model of the millwork and cabinets. This means we will actually build it in our computers. Sometimes, more than one draftsperson works on the project. When parts are drawn, all the machining information, such as boring, grooves, notches, and anything else is actually drawn in 3D model. Cabinet by cabinet, part by part, and if something isnít right, you see it right there, on your model.

4) 2D submittal/fabrication drawings are generated from the 3D model. Accuracy is guaranteed because all three elements of the flats (that is what we call 2D drawings) - plan sections, elevations and vertical sections - are generated from one 3D model and cannot possibly deviate from each other.

5) We put in lots of dimensions, so people on the floor do not scale anything and do not spend time with their calculators.

6) Every person involved in this process must absolutely follow our company standards, layers hutches, dimensions - the entire CAD staff. Drawings must look readable to the average person, who may not be able to elaborate him/herself.

7) During the engineering/drafting process, progress drawings are posted on FTP and in our case, the customer (cabinet/woodworking shop) is asked to download and evaluate for possible errors or changes. It is easier and safer to do it before drafting is done. Also, if there is an architect or designer involved, they are asked to evaluate the drawings in progress and make necessary changes, if any. This way we can avoid extra work and we can expedite approval. When the architect receives hard copies, he/she already knows what it looks like. This is not always the case due to different computer and technical skills, but we try to involve as many parties as we can.

8) When we get to CNC programming, we simply take our 3D model apart (explode the view)... we lay it flat on the router bed. We program and nest actual parts that are modeled and assembled together and the possibility of mistake is minimal.

9) If large quantities of the same item have to be machined, we suggest that only one set has to be cut first, assembled and checked for possible mistakes. If everything is good, it is go ahead.

When the human factor is involved, mistakes happen. That is why we do not completely rely on the human factor, but instead have a complicated system in place. This may seem like it consumes lots of time and is a very expensive engineering procedure, but it is not. When the system works and competent and experienced people are involved, it is fast and effective and saves tremendous amounts of work - projects are manufactured and installed once and quickly.

From contributor Q:
Great post, contrbitutor S. As an installer I have to battle with things that never seem to quite fit in the field, and rework and have panels re-made, especially on large institutional panel systems. Your approach is what I have been trying to pump at the shops and don't ever understand why, when we spend so much time shimming, lasering in, and benchmarking a woodwork system, the project manager from the shop just shows up with a tape. Then I have to go the change order route. I really don't like to start down this road, but it is unavoidable to stay in business and on budget.

From contributor B:
One of the best and most sensible options is to cross check work with another engineer that is in the same company. It can seem like a great waste of time, but I have seen hundreds of thousands of dollars saved by doing this. It is difficult to see your own mistakes or misunderstood data presented by the customer.

From contributor P:
I agree with the above. Drawing in 3D is a lot of work, but... The old saying of an hour spent on engineering saves 3 on the shop floor - the corollary is also true. The more eyes on it, the better; it's easy to get into the ivory tower syndrome.

From contributor T:
There's a limit to how much you can process something and still have a profit left. Obviously it makes sense to vet the information enough to keep the mistakes at bay, but what is appropriate or even possible varies depending on the scale of the project and the players involved.

I don't really know who I would go to in my niche to get that second set of eyes. But something I can do is apply some 5S thinking to how I approach projects, with an emphasis on standardizing how we collect information. The attached PDF helps us remember to get every dimension while we are on the jobsite. It also standardizes where to find the information once we collect it. (Storage without a retrieval system is just landfill.)

The PDF at the link below shows an approach that would work for any wall you have to measure on any type of job.

Jobsite Measurements PDF

(Download the latest Acrobat Reader if required.)

From contributor M:
Nice worksheet. Can you explain the side to side and front to back? I assume this is where you are getting your square out/in from? Is this a plan or elevation view? I am working on creating one for our shop and like the layout.

From contributor T:
The trick on a form like this is to make sure it includes everything but to also have the boxes big enough that when you write something in them you can read it later. The reason for boxes is that every box must be filled out. This is how you ensure that you have checked for each possibility.

Side to Side and Front to Back roughly equate to north-south-east-west. The building can lean in or out, or from the left to right. The square box is big enough to indicate the discrepancy and the check box just indicates which direction the discrepancy occurs. A zero (0) value indicates plumb. The value "level" in the middle of the page is a departure from a red laser level line. Shear wall is important because it at least reminds you to ask the contractor if they anticipate adding any shear wall plywood. Forgetting to ask this question has been expensive for me in the past.

From contributor J:
After all you can do, you will still screw up sometimes. Just ask the team of rocket scientists over at NASA about O-rings or fried Martian space craft due to metric vs. standard measurements and other junk like that.

There will be days when you wind up using the claw-end of the hammer (all day long). I've never met a carpenter or cabinetmaker who couldn't curse up a real storm when faced with some fiasco of his own making. After all, no one's perfect.

From contributor U:
Contributor T, loved your worksheet. It is now a part of our site measurement package. It is clean, simple, and complete. Thanks for sharing!

From contributor I:
You just have to have the entire crew engaged. Everyone checks everyone. Everyone picks up after everyone, everyone has their brain engaged. If you are making all of the cut sheets in the office, all of the material ordering, etc., then you have put the burden to be perfect on the team members that work in the office. Everyone needs to be on the hook for their work. For example, the person on the shop floor needs to own the cut sheet. They either need to produce it themselves or double check it. Check and double check until, at every step, the person performing the work owns it.

As I understand it, lean manufacturing involves ways to check the work for accuracy. Go/no jigs, built in accuracy checks, visual references and more. Of course the challenge is to set up these processes, especially in a custom shop. By no means do I have it figured out. We constantly work on what information is needed at each step. Do you download or make available all the information at every stage? Seems a little cumbersome to me. There is just no substitute for plain old competent. But how do you systemize it? I am just now exploring lean manufacturing so I have a lot to learn, but it seems it is focused on systems that help people be successful. In that effort I applaud it.

From contributor S:
1) Everyone should do their work properly (you can call this perfect if you want).
2) Cut sheets are done automatically; they are computerized and integrated into the drawing files. There is no person doing it manually on a piece of paper.
3) To be perfect is not a burden, but a privilege.

From contributor N:
Ideas from a small 3 person shop. Old school skills. Rarely have an issue.

1. Have the customer sign off on anything built in. Appliances, TVs, anything. Packet them with model numbers and a signature line. Ask for a copy of the invoice when the appliances are ordered. If the appliances don't fit, you have proof.

2. One field measure, one secondary measure with approved drawings.

3. We lay out the drawing full scale on 16' poplar stock. This catches 99.9% of any drafting errors, misprints, hinge spacing to pullouts, door sizes, etc.

4. Full scale to full scale leaves no room for error. Lay face frames directly on layout, be sure all rails and stiles match.

This is a very old school method, but we've been here over 100 years. No CNC, each mortise and tenon milled one at a time. We have long time employees that can fly through this stuff. I (the draftsman) also do the layout, door sizes, hardware lists pre-made, so I can better understand the building processes. We can have a full kitchen from paper, layout, to frames, boxes, dovetail drawers, and doors made and assembled, ready for finish, in 10 business days. It works for us but I understand it won't for 95% of you out there. Biggest thing for us is laying out full scale. It catches 99.9% of any mistakes on paper.