March, 1999
I recently received a report from the U.S. Consumer Product Safety Commission under the Freedom of Information Act concerning rotational kickback hazard on chain saws. The 45 page briefing package was sent to the commission, Subject: Effect of Re-sharpening 3/8" Pitch "Low Kickback" Saw Chain, June 5, 1985.
The Briefing Package was developed to respond to a concern which was raised by the McCulloch Corporation in a letter to the commissioners dated June 8, 1984.
The commission staff received test data from three manufacturers (McCulloch Corp., Carlton Company, and the Oregon Saw Chain Division of Omark Industries) relating to the effects of re-sharpening of saw chain and rotational kickback. The industry was in agreement that normal use and re-sharpening of saw chain will cause the saw to kickback at higher levels towards the end of the chain's useful life. The letters sent to the commission from Carlton Company and Omark Industries both requested that the information be given confidential treatment.
McCulloch Corporation's study showed that the average derived kickback angle of the low kickback production chain increased 97% over its useful life when subjected to periodic hand sharpening performed within manufacturer's guidelines and 45% with "fixtured" sharpening. Guideline means maintaining "raker" or depth gauge height. During testing with a special machine, the depth gauge setting was held at .029"-.028". In a dull condition, the kickback energy potential will generally be less than the same chain in a sharp condition. The average loss of kickback energy potential was 20% from a sharp chain to a dull chain.
The letter from Omark Industries dated January 30, 1985 stated that kickback goes up toward the end of the chain's useful life and as the depth gauges are lowered. Also, most casual users do not lower the depth gauges so at the end of the chain's life they are using a chain with rather shallow depth gauge settings.
In an inter-office memorandum - Omark Industries (Oregon Saw Chain Division) - dated May 14, 1974 - Chain #91 kickback increases about 30% when the depth gauges are filed from a .008" level to a setting of .020" on low profile semi-chisel chain. We do not require that depth gauges be re-adjusted throughout the filing life of the chain for this type of service and can take advantage of that fact to minimize kickback magnitude. Thus, at the end of chain life, the average casual user will be cutting with a depth gauge setting somewhere around .008".
Here it is, April, 1999, and not much has changed over the years with saw chain except for more rules. Below is a copy of the letter from McCulloch Corp. that got the ball rolling about saw chain and its rotational kickback hazard.
Regards, Russell E. Mollberg, Jr.
June 8, 1984
Commissioner Stuart M. Statler U.S. Consumer Product Safety Commission Washington, D.C. 20207
Re: Proposed Voluntary Chain Saw Standard
Dear Commissioner Statler:
Our engineering department has recently completed extensive testing and a study of the effect of normal use and re-sharpening of "low kickback" chain. The clear conclusion of the study is that the normal use and re-sharpening of "low kickback" chain will cause the chain to kick the saw back at much higher levels the would be permitted under the proposed voluntary ANSI standard that is now being considered by the American National Standards Institute ("ANSI"). This conclusion is established and explained in the enclosed engineering report.
Saw chain becomes dull after normal use and it is customary for users to re-sharpen the chain many times (our data indicates an average of 10 to 20 times) before the chain is worn out, discarded, and replaced with a new chain. The fact is that even "low kickback" saw chain that meets the proposed ANSI standard when it is new will in all likelihood NOT meet the standard after a limited period of normal use, wear, and re-sharpening. This is true to an alarming degree when the chain is resharpened by hand, and it is also the case even when the chain is fixture sharpened. Kickback increases dramatically after normal use and re-sharpening. At about the 2/3 point of a chain's useful life, the derived angle of kickback of a re-sharpened chain will far exceed the derived angle of kickback of the same chain when it is new. Our data indicates that greater kickback occurs after the chain is re-sharpened several times because such re-sharpening increases the distance between the top plate/side plate of each cutter and its corresponding depth guage and guard link, and as a result with continued use and customary re-sharpening there is an increasing tendency for the moving chain to "grab" and "snag" and therefore kick back with increasing force.
We know of no practical way that any saw - even saws equipped with low kickback chain - can be maintained for the entire useful life of the chain in a condition in which the user will be assured the saw will be in compliance with the requirements of the proposed ANSI standards after continued use and customary re-sharpening, unless the saw is also equipped with a chain brake (or other devices) that will stop the chain in the event of kickback (or prevent kickback from occurring) or the chain is replaced well before the end of the normal life of the chain.
We think it essential that the CPSC, manufacturers, dealers, and users be made aware of this fact, so that they can take appropriate action to ensure that the products they make, sell, and use will continue to be as safe as possible throughout their useful life.
The enclosed report clearly demonstrates that the present draft of the proposed ANSI standard does not achieve the objective of protecting consumers from kickback hazards. In fact, because kickback increases significantly as chain is used and re-sharpened, the effect of the proposed ANSI standard is to lull consumers into a false sense of security while they are exposed to an increasing greater danger of personal injury as they use and re-sharpen low kickback chain. We believe the ANSI proposed standard must be revised to take this dangerous phenomenon into account. For this reason, we urge that the CPSC give immediate and most serious consideration to urging appropriate modifications of the proposed ANSI standard as to insure that users are 1) fully informed about their increased exposure to dangerous kickback levels after a period of normal use and maintenance and 2) users are made aware that they can protect themselves from the latent hazard of re-filed low kickback chain only through use of additional safety devices, including devices that will stop the chain when kickback occurs.
Because we think it essential that all manufacturers be aware of the problem, we are providing them a copy of this letter and the accompanying report.
We are confident that neither the Commission nor the American National Standards Institute, nor the chain saw manufacturers want to see a standard promulgated which, while it might be a useful endeavor to insulate some manufacturers from legal liability for the products they make and sell, will not adequately protect users from exposure to personal injury.
We are extremely concerned that this letter may be viewed an as effort by McCulloch to advance its own interests since McCulloch has always advocated chain saw brakes as the best known method to achieve chain saw safety and all McCulloch's saws sold in the U.S. are equipped with a chain brake. Our study took a considerable period of time to complete, and it was not completed until this month. We believe our study is the only comprehensive test that has been conducted on the use of low kickback chain over its normal useful life. Our study is thorough and it was conducted very objectively. All of McCulloch's extensive engineering resources were made available for the study. We earnestly want any standard that may ultimately be adopted to provide the greatest possible and practical amount of safety to chain saw users. To do less would not only generate avoidable user injury and suffering, but it would also work to the ultimate detriment of every member of the industry (manufacturers, suppliers, dealers and servicers). Because we do not want the standard to become a football to be pushed back and forth by opposing commercial interests, we are willing to make our study available to everyone who desires to review it, and we will arrange for you or other members of the ANSI Committee to review it with the McCulloch personnel who conducted it. Furthermore, if the Commission or the Committee will coordinate a further study, McCulloch is willing to share, with other members of the industry, the costs of a completely independent study of the behavior of low kickback chain, which can be conducted by an independent research laboratory or by a college or university or other suitable organization with appropriate qualifications.
Please let me know if you would like to discuss this letter or the enclosures, or if you have any questions or comments in connection with this letter or the enclosed report.
Yours very truly,
Signed by Donald V. Marchese
President and Chief Executive Officer, McCulloch Corp.