What should be used to cut and machine paper and fabric based phenolics?

Phenolic machines without difficulty. As a rule, it is machined more readily than metals on standard tools such as those used for wood or metal fabrication
For most machining operations, ordinary high-speed steel tools are satisfactory. However, where production quantity, production speed, or finish are important factors, carbide tipped tools often prove more economical. Cutting tools must be kept extremely sharp to achieve accuracy and fine finish.

Phenolic is machined dry – cutting compounds and lubricants are not necessary. Cooling by air is preferable to the use of liquid coolants which are difficult to remove from finished parts. Machine operators should be cautioned to keep the temperature of the work below 150° C since temperatures above 150° C may distort the material. Cuttings are readily removed by suction.

 

Circular Sawing 

Circular saws may be used for straight or angular sawing. When smooth edges are required or close tolerances are important, a hollow-ground circular saw without set should be used. For rough cutting saw with set are satisfactory. Best results are obtained when the saw blade projects a minimum distance above the saw table.

12” saws are recommended for phenolic up to 1” thick, and 16” saws should be used for thicknesses up to 2-1/2” thick. It is important that all teeth be square, of the same height and free of burrs. The cutting edge should run wither directly toward or just back of the center hole. In both circular sawing and band sawing, the work should be fed as rapidly as possible without forcing.

 

Band Sawing 

The standard band saw is satisfactory where close tolerances or smooth edges are not important. It is most effective in sawing blanks from plate stock.

Saw blades should have between 4 and 7 teeth per inch with some set, the number of teeth depending on the thickness of the material being sawed. For heavy material, 3” thick and over, a blade with three teeth per inch is recommended. Operating speeds should be approximately 3000 feet per minute and blades should be tempered to permit frequent sharpening.

Width of the blade will vary depending on the radius to be cut. For circular cuts, the widths should be narrow. For straight cuts, the blade may be up to 1” in width.

 

Shearing 

Standard shears suitable for sheet metal are recommended in shearing phenolic. The knife blade should be kept sharp and the material held rigid with a hold down bar. Most paper laminates up to 1/16” thickness and canvas laminates up to 1/8 thickness may be sheared at room temperature (70° F min).

 

Turning

Ordinary high-speed tool steel can be use in finishing operations for all phenolic grades. However, carbide-tipped tools may prove more economical and will hold sizes more accurately from piece to piece. About .010 stock should be left for finishing. Laminated phenolic can be turned at 400 surface feet per minute with high-speed tools and about twice that with carbides. Tools should be kept sharp, ground with and included angle of 80-100 degrees, and with a 10–16 degree side clearance. Cutting should be done dry.

 

Milling 

Standard high-speed drill with lips backing off to provide plenty of clearance is satisfactory for all phenolic grades. However, for long production runs and deep holes, carbide-tipped drills give the best performance.

Drills should be lifted from the work frequently to prevent binding and excessive heating. The feed should be light and uniform and the speed of the drill should be considerably in excess of that used for soft steel. With tungsten-carbide tips, speeds may be as high as 16,000 rpm. Where possible, the material being drilled should be backed up with scrap phenolic or other soft material to prevent shipping out.

In drilling phenolic parallel to the laminations, extra care must be taken to prevent splitting. The material should be clamped in a vise or between plates and the drill should be lifted more frequently to remove chips.

Holes ¾” and over may be drilled in the conventional manner using radial drill presses or the counterbore method in which a pilot hole is drilled first.

Drill size – because of the nature of plastic material, the diameter of holes drilled is laminates are usually .002” under the drill size. Therefore, the drill selected should be at least .002” larger than the specified diameter of the hole. If the drill being used is dull, the hole size may be an additional .002” undersized, or a total of .004” less than the diameter of the drill.

The recommendations for drilling also apply to tapping; Taps used for metal are also suitable for phenolic. Tapping heads or tapping machines may be used, and for production work, collapsible taps are available in sizes over 1-1/4”.

 

Tap Size 

In tapping phenolic, high-speed taps .002” oversize should be used. The tap drill should be changed to .002” oversized to counter the tendency of the drill to cut undersize. If the thread is to be used frequently, metal inserts should be used.

For threaded holes over ½”, it is often more desirable to chase the thread on a lathe using a motor driven cutter mounted on the tool post.

 

Threading 

When cutting a 60 degree thread, it is always advisable to swing the compound reset on the lathe to a 30 degree angle. The tool is ground to cut on one side only.

For all other thread, standard methods are used with satisfactory results: the speed and feeds are similar to those used in threading soft steel.

 

Buffing 

Standard polishing rouge on a rag wheel gives satisfactory results for phenolic requiring a polished surface.

Grinding and sanding may be done by belt, disc, or centerless methods. No lubrication is necessary.

 

Stamping and Engraving 

Phenolic surfaces to be stamped should be smooth. Sanding may be necessary to obtain satisfactory results. Compression presses employing heated dies give best results.

Engraving can be done with any standard engraving machine. Tools should be sharp to produce clean cut edges.

Article Title:
What should be used to cut and machine paper and fabric based phenolics?
Article Summary:
Machining information for paper and fabric grade phenolics.
Article Date:
3/21/2008
Article ID:
816
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