Question
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.
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 isn’t 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.
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.
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.
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.
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.
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.
