Throwing out half of the material you purchase (as waste) is obviously not a good practice.
It is already common practice to use optimizing software to nest the parts and minimize waste on board material. On the solid wood side there is similar sophistication available. However, I find that companies accept the solid wood waste more than they accept particleboard waste. It shouldn’t be that way.
Managing the yield on solid wood is much more complex than on sheet goods. With solid wood, in addition to the wood size (length and width), the quality (grade), and the required quality (product specification) play an important role. Additionally, material loss is occurring all along the process chain.
Before starting into any improvement project, I always like to find a way to establish the baseline in order to prove that sustainable and measurable change has occurred.
The basic yield formula is simple: The higher the output, or the smaller the input, the better the yield. Most companies I know measure their yield (or their waste factor) in the break-out department. This means kiln-dried lumber is the input and cut-to-rough-size is the output. This is not wrong. It measures how well you optimize in the breakout area. But it does not measure how well you manage the overall yield of the solid wood material.
Before we settle on the measurement, let’s look at a theoretical maximum supply chain. It starts with the tree in the forest (input) and ends with the final product at the customer’s home (output). In every step along the way, wood is taken away and used for a less valuable use and/or is waste.
You need to establish where you start. If you always purchase kiln dried lumber, you start there. On the other end of the chain, you would go the practical end - i.e. shipping department.
The next is the unit of measure. The classic measure is BF (board feet), but you can use anything that suits you. For example, if you manufacture furniture you can have the exact amount of wood in the BOM (Bill of Material). With that number as the output and the purchase/consumption volume as the input you have the overall yield.
The consumption data have to be collected daily; however you calculate the yield % over a longer period of time. Again, it depends on the specifics of your operation, the minimum of one week and a maximum of one month. If it is shorter you have too many distortions and if it is longer the time between the results is too long and loses its meaning.
What influences the yield?
Product design and product specification
During the design and specification process you determined a huge portion of your waste factor. If the specification asks for big parts of clear material, but has no use for shorter pieces, your waste goes up. If your colour/stain selection focuses on light colours only (maple), then the brown maple cannot be used. Designing the product with the most abundant material available in mind, cuts down on waste and subsequently on cost
This has a big impact on what grade you are purchasing. The BF-price should not be the only decision factor. The overall cost needs to be considered as well. If you buy one quality level and need to sort and select the best for your product, the question remains; what to do with the pick over product? If you have use for it – great!
However, if you are starting to accumulate this material, returning it to the supplier with restocking charges or using it in place of lower grade (less expensive) material it is waste. If you have all the facts, you can calculate whether starting with a more expensive grade selection would have been more cost effective.
Depending on your variables, the result may be completely different in your situation. You need your facts.
It is a common practice to cut pieces slightly larger than required. The extra varies from one company to another. Obviously, the smaller the final piece, the more the extra size impacts the overall wood consumption. A 1/2" oversize on an 18" piece represents 2.7% waste; a 2" oversize represents 10% waste. Reviewing your minimum requirement and reducing your length oversize will reduce your wood consumption. On the down side, if you go too far, your rejects will go up and you will lose more than you gain.
The same applies for the oversize in width. An oversize of 1/4" on a 5" board is almost 5%. Any millimeter of sustained saving will add up to an overall saving.
During the time of mass and big batch production, adding a few extra pieces to the batch had minimal impact. One piece per hundred is one percent only. Now the batches are small. One extra for a quantity of 20 pieces is 5%; one extra when you only need one would represent 50% waste. To mitigate this problem we keep them in stock and use them the next time. Sounds good - but the chance that these parts become obsolete, get damaged, or have discoloured by the time we need them again is high. Extra quantity adds substantially to the waste. Reviewing your manufacturing model and applying lean manufacturing principals will bring results.
Too often, I see that glued-up panels are rejected because one strip was out of spec. One 3" strip in a 24' panel was bad and has been discovered after it has been planed down. A big portion of this bigger panel is now waste. Having a system in place to prevent this will save wood and labour. Setting standards and training the operators on these expectations can maintain a higher yield level.
When cutting wood, the width of the saw kerf has an impact on your yield. If you have not talked with your tool supplier for a while you might lose out on some improvements.
Equipment and Technology
There is a wide range of equipment available. The most suitable for you will depend on the available budget and scale of operation you have. Scanning and optimizing has advanced significantly over the last decade. An in-depth discussion with machine suppliers will open the range of opportunities. These discussions would be the preparation for trade show visits and plant visits. The subject of solid wood optimizing technology can be a subject of an article at a later stage.
Yield improvement is a complex subject. There are very few quick solutions. It takes focus and determinations to find sustainable results. The first step towards improvement is establishing where you are by establishing a baseline.
Sepp Gmeiner is a partner with Lignum Consulting. For feedback, questions and/or suggestions he can be contacted at s.gmeiner@lignum-consulting