Production Tips, part two
by Nicholas C. Weidhaas
"Production Tips" courtesy of Woodworking International
Consider installing a lumber yield improvement program.
One of the nice things about lumber yield improvement programs is that they are "90%-99% successful". The reason for this is that with today’s cost of lumber, even very small percent savings in lumber can represent very meaningful cost reduction benefits. Naturally the amount of money which can potentially be saved is influenced by the level of waste at the beginning of the program. Potential savings in the range of 8-12%, however, are typical. And these savings can often be achieved with a minimum of new capital expenditure.
Formalize the yield improvement program.
To be successful and lasting, the program must be formalized. Someone must be appointed to head up the effort, a yield tracking or reporting system must be established, and a mechanism must be established to maintain interest in "yield improvement". This can involve scheduled meetings or discussion groups on yield; the establishment of a system whereby workers and/or supervisors receive a pay bonus which is based on "yield performance"; and the establishment of a checklist system for monitoring "yield practices".
Establish a checklist system for monitoring "yield practices".
Once each day, the department supervisor takes his checklist of proper lumber cutting procedures and observes his cutting operations. He observes and notes on his checklist such things as the average size of the first end trim on the board at the cut-off saw operation, and the average size of the edging strip at the ripsaw operation. He also notes whether the defecting decisions which are being made are proper, and whether or not correct sawblades are being used at the ripsaws, and whether or not the moisture content of the lumber is within established tolerances.
In short, all of the items which the supervisor checks are items which he should be checking anyway, but the checklist system is formalized. (Similar to an airplane pilot’s). At the end of the day, the completed checklist is turned into the "office" and is reviewed by the plant manager. Once each week the plant manager goes with the departmental supervisor and together they complete the checklist. Once each month, the vice president of manufacturing goes with the plant manager and the departmental supervisor on the inspection trip and participates in filling out the checklist.
In this way, the focus on the need for constant yield improvement is maintained, and communication between the different levels of management is enhanced.
Calculate what each "one percent" yield gain would save your company each year.
Now, calculate what would be the percentage increase of your company’s profitability if lumber yield were to increase ten percent … If you take the time to make this calculation I’ll bet you will be impressed. It would not be unusual, for instance, to find out that an increase in lumber yield of ten percent could translate into an increase in profitability of 30-50 percent for the manufacturer of furniture parts or dimension stock.
Reduce the saw kerf losses in ripping lumber and increase lumber yield.
Reduce moulder allowances.
In the furniture industry this allowance is typically ¼ inch. Thus, if a moulded width of 2 inches is desired, the rough size of the part, or the width to which it is ripped prior to moulding would be 2-1/4 inches. This represents a 11% loss in yield. In the kitchen cabinet industry the moulder allowances are usually less than in the industry. Typically, only 1/8 inch is added to the finished part width. Thus, 2-1/8 inches would be the rough size for a part to be moulded to 2 inches. This represents approximately a 6% loss in yield. In the millwork industry typically only 1/16 inch would be added to the finished parts width, and the part would be ripped prior to moulding to 2-1/16 inches. This represents only a 3% loss in yield.
We should ask ourselves why the millwork industry can operate with a 1/16 inch moulder allowance, the cabinet industry with a 1/8 inch allowance, but most companies in the furniture industry utilize a ¼ inch allowance. Actually some companies (but not many) in the furniture industry do operate with a 1/8" moulder allowance. Many others could benefit by trying hard to reduce these very significant, though seemingly small, allowances.
One factor which has helped the millwork industry reduce allowances is that this industry generally runs much more expensive and precision moulders than the furniture industry. Also most of the production of the millwork industry is cut on "multiple saw" or gang ripsaws, in contrast to the furniture industry which usually employs single-cut, straight line ripsaws. The "multi-rips" product rippings are typically more uniform in dimension from one end of the part to the other. Thus, minimum moulder allowances are easier to attain than when the straight line ripsaws are employed. However it is worthwhile for companies which utilize straight line single-cut saws to still work hard to minimize losses which are due to the moulder allowances. It is often one of the quickest ways that companies can improve their lumber yield. Sometimes all that is required is to change the cutting instructions on the route sheets or "shop travelers". And if you decide that you cannot reduce your moulder allowances a full 1/8 inch (some furniture manufacturers do utilize a 1/8 inch moulder allowance), then try to reduce them 1/16 inch. It is still usually very worthwhile… and fast.
Run stock in multiple widths through the moulder.
- Only one moulder allowance per "multiple" is needed rather than one allowance per single moulding.
Check the accuracy of the ripped widths.
Measure some stock in your plant. Reduce length and other width-trim allowances.
"Re-examine" your defecting decisions in cutting up lumber.
Consider the following question as it applies to a "cut-to-length-first" furniture manufacturing operation: Should the boards be cut-up in such a way that the knots fall in short or long cuttings?
Many companies have the decision-rule that the cutters should try to cut in such a way that the knots fall into the shortest lengths.
However, when this is done, it is often possible after ripping cutback to the defective piece in a salvaging operation, since the lengths of the "salvaged" pieces would be too short to use.
It is often desirable to cut in such a way that the knots tend to fall into the longer lengths (medium lengths are best), so the salvaged pieces would be of sufficient length to use.
Usually, it is best to cut in such a way that the knots fall at the ends of the piece, thus minimizing the amount of unusable material.
Cut with the salvage or cut-back saw in mind.
Try to "match" the shape of the panel to the shape of the part.
For instance, when we produce a round table top from a square panel, we lose about 21% of the rectangle in "corner waste".
When we produce a "fiddle back" chair seat from a rectangular panel, a similar loss occurs.
When curved chair parts are cut from a panel, we lose the half-moon piece on the bottom of the panel and the corner pieces at the top.
Some companies have recognized these very significant losses and are doing something about them. To reduce the types of loss shown in figure 6, some companies are "step gluing" their panels in the production of such parts as chair seats, and dining room table half-tops, etc., so that the shape of the panel more closely resembles the shape of the ultimate part. This can be most easily done on a glue reel, but also can be accomplished on electronic batch gluers through the aid of some "filler blocks".
To overcome the type of loss shown in figure 8, some companies are performing the following operations:
- First they glue up a rectangular panel.
Are any of the parts in your production line good candidates for this type of treatment?
Tip 21 (continued)
Try to "match" the shape of the panel to the shape of the finished part.
Carefully evaluate your lumber grades.
Some ideas to consider in this analysis are:
- Very often use of lower grades can be very economical. The additional yield which you can get from the higher grades often simply is not worth the additional purchase cost.
- Be careful when you decide to use a lower grade of lumber. Lower grades take longer to process through your plant for a given output of product. Make sure that you have sufficient production capability to meet your plant’s output goals, or that you can supplement your in-plant production capability with the purchase of "outside" dimension stock. Consideration of all options can be "mind-boggling". This is why N.C. State University is working hard to develop some computer programs which can help in this evaluation. Write me (N. Weidhaas, N.C. State University, Box 8005, Raleigh, NC 27695-8005) if you are interested in finding out more about these programs.
- Do not assume that you are utilizing the optimum grade-mix today even if you went through a recent extensive evaluation of your lumber purchasing. Prices, output, goals and available productive capacities change.
Evaluate your company’s product specifications.
- What will "go" and "not go" at the ripsaw? What defects do the ripsaw operators really have to cut out? If we leave this question to be answered by the machine operators, generally more defects than are necessary will be cut out because the operators want to stay "out of trouble". It is management’s responsibility to establish these specifications.
- Can repair operations be expanded? A little extra effort to repair a defective seat, chair back, etc. can be much less expensive than replacing it.
- What is the maximum "width of strip" which will be allowed in an edge glued panel? Many companies put a width-limit of four inches or so for the size of the strips going into panels. (Some companies limit strip size to three inches). Their objective is to minimize the tendency for the individual strips to cup in the panel. The company’s objective is admirable, but this specification is very significant from a cost standpoint. It causes additional costs to be incurred in ripping, and reduced productivity and yield.
Originally, the concept was to reduce wide boards to narrow pieces, and then "flip" every other piece cut from the board so that the "grain directions" of the strips would alternate and minimize warpage. However, today often little effort is made on the factory floor to alternate the grain directions. Thus, when the strips are "reassembled" for gluing, the strips which had been cut are simply glued back to their original, non-alternated configuration. So, what has been accomplished by cutting the board into smaller pieces?... One thing for sure, labor, productivity, and yield have been lost!... Be aware that this specification is dangerous and costly! We are not saying that companies should allow twelve-inch wide strips to go into their edge-glued panels. Run a few tests in your plant to find out how wide the strips can be for your product line and still keep your company out of significant warpage trouble.
For more infomation, including videos, books, and training programs, visit the: The International Productivity Center Web site at http://www.woodvideo.com/. Their products are designed to assist manufacturers of lumber, furniture, cabinets and similar wood products in their machine operator and supervisory training efforts.