finger joints - wisconsin knife works, inc. joints 71 reversible by far the most common joint....

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REVERSIBLEBy far the most common joint. Requires two heads; onewith thick cutter at top of stack and one with thickcutter at bottom of stack. This joint may also beachieved on a single head shaper by reversing alternatepieces of stock machined.

MALE-FEMALE OR END MATCHLess common joint than reversible. Always requires twoheads; one with all thin cutters and one with a thickcutter at both top and at bottom of stack.

RE-SAWSpecial joint with thick cutter at center of stack to allowfor finger jointed stock to be split or re-sawn into twopieces.

SCARF OR FEATHER JOINTUsually requires no thick cutters. Used when dimensionsof stock will vary significantly.

TYPES OF FINGER JOINTS

1-800-225-5959 FAX 1-800-336-1254 www.wkwinc.com

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LENGTHS OF FINGER JOINTS72

order online at www.wkwinc.com

Finger joints are used in a wide variety of applications. The reasons for fingerjointing may be varied. One goal is to remove knots and defects and then to produce usable long pieces of wood by finger jointing the short pieces. Anotherreason for finger jointing is to produce a finished component that has a greaterstrength than ordinary wood. A properly finger jointed length of wood will have a strength factor greater than the same piece of wood that has not been finger jointed.

LENGTHS OF JOINTSJoint length will vary with the application. Increasing wood costshave necessitated the development of shorter joints. 4 and 5 mmjoints are becoming more common in non-structural applications.Keep in mind that with very small joints, the finger joint machineand assembly components must be in top operating condition tofacilitate the assembly of the joint.

NON-STRUCTURAL JOINTSMillwork, mouldings, trim, door, and window components aresome of the main uses for these joints. Typically 1/4" or 3/8" jointshave been used, however, many users are finding that 4 or 5 mmjoints will save enough material to pay for the cost of toolingconversion in a short time. See formulas for calculating potentialdollar savings in section entitled “Technical Information andFormulas”.

STRUCTURAL JOINTSLaminated beam and I-beams utilize the strength of the fingerjoint to produce load bearing components for an industry wherejoint strength is closely monitored and tested. Typically a 1-1/8" or7/8" joint is used.

For sub-structural joints such as finger jointed 2X4 studs, a 5/8"joint is used.

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PARTNUMBER

JOINTLENGTH

CUTTERRADIUS

TIPTHICKNESS TIP INDEX

THIN ORTHICK

BG 1394 .177(4.5mm) 1-1/2 .044 .121 THIN T684BG 1395 .177(4.5mm) 1-1/2 .250 .327 THICK T684BG 1258 .197(5mm) 1-1/2 .040 .118 THIN T684BG 1259 .197(5mm) 1-1/2 .250 .328 THICK T684BG 1392 .197(5mm) 1-1/2 .044 .125 THIN T684BG 1393 .197(5mm) 1-1/2 .250 .331 THICK T684BG 1411 .197(5mm) 1-1/2 .044 .125 THIN T684BG 1412 .197(5mm) 1-1/2 .250 .331 THICK T684BG 1137 .250 1-1/2 .045 .138 THIN T684BG 1138 .250 1-1/2 .250 .343 THICK T684BG 1316 .250 1-1/2 .047 .139 THIN T684BG 1317 .250 1-1/2 .252 .344 THICK T684BG 1515 .250 1-1/2 .047 .139 THIN T1462BG 1516 .250 1-1/2 .252 .344 THICK T1462BG 896 .300 1-7/8 .045 .153 THIN T683BG 897 .300 1-7/8 .250 .358 THICK T683BG 899 .300 1-1/2 .045 .153 THIN T684BG 900 .300 1-1/2 .250 .358 THICK T684BG 903 .300 1-7/8 .049 .152 THIN T683BG 904 .300 1-7/8 .254 .357 THICK T683BG 919 .375 1-1/2 .045 .169 THIN T684BG 920 .375 1-1/2 .250 .374 THICK T684BG 1420 .375 1-1/2 .046 .1685 THIN T684BG 1421 .375 1-1/2 .251 .3735 THICK T684BG 1079 .375 1-7/8 .049 .168 THIN T683BG 1080 .375 1-7/8 .254 .373 THICK T683BG 1305 .406 1-1/4 .045 .169 THIN T981BG 1306 .406 1-1/4 .250 .374 THICK T981BG 1315 .375 1-1/4 .394 .518 THICK T981BG 564 .500 1-7/8 .093 .2655 THIN T683BG 565 .500 1-7/8 .343 .5156 THICK T683BG 854 .500 1-7/8 .030 .152 THIN T683BG 855 .500 1-7/8 .343 .465 THICK T683BG 1434 .610 1-1/2 .046 .2085 THIN T684BG 1435 .610 1-1/2 .2124 .375 THICK T684BG 1204 .625 1-1/2 .044 .1685 THIN T684BG 1205 .625 1-1/2 .250 .3746 THICK T684BG 737 .625 1-7/8 .062 .214 THIN T683BG 738 .625 1-7/8 .343 .495 THICK T683BG 1244 .656 1-7/8 .029 .185 THIN T683BG 1245 .656 1-7/8 .160 .316 THICK T685BG 741* 1.113 2-1/8 .030 .248 THIN T685BG 742* 1.113 2-1/8 .343 .561 THICK T685BG 1101 1.113 2-1/8 .030 .264 THIN T685BG 1102 1.113 2-1/8 .343 .577 THICK T685BG 751* 1.113 2-3/8 .031 .243 THIN T686BG 752* 1.113 2-3/8 .283 .495 THICK T686

*NOTE: These cutters are used for producing joints for structural applications, and are used with spacer platesbetween the individual cutters. Please contact a Wisconsin Knife Works engineer for more informationregarding these cutters.

GRINDINGTEMPLATE

FINGER JOINT CUTTERS

CUTTER SIZES AND TYPES


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FINGER JOINTS74


PRECISION TOLERANCESDue to the demanding nature of the finger joint and the scrutiny that the finishedjoint is often subjected to, there is no room for either a sloppy or poor fitting joint.Some joints are required to be of a paint grade, meaning that the joint itself mustbe invisible when the finished product is painted. Other joints are used in structural products that must be certified to demanding strength and pull-testspecifications.

For these reasons, WKW cutters are produced to incredibly tight tolerances. Cutterthickness, tip centrality, tip thickness, flatness, cutter angles, and other criticaldimensions for each cutter are unsurpassed in the industry. As the industry hasevolved over the years, we have incorporated the best technologies available tocontinually improve the geometric specifications of our cutters.

You can rest assured that you will never have a tolerance problem with WKW cutters. Most cutters are held to an amazing thickness tolerance of plus or minus.0001, or one tenth of one thousandth of an inch. Whether your cutter stack is fivecutters high or fifty cutters high, WKW cutters are held to exacting specificationsthat ensure you of an accurate joint with no significant accumulated dimensionalvariations.

HIGH SPEED STEEL FINGER JOINT CUTTERSMost solid wood finger jointing is accomplished using Molybdenum HSS (HighSpeed Steel) tool steels such as A.I.S.I. M-2. This tool steel is especially well suitedfor natural woods, and has been the standard choice at WKW for years. With theexception of a few custom applications, 95% of the steel cutters furnished byWKW are A.I.S.I. M-2.

A.I.S.I. M-2 is a very specific blend of tool steel that uses the alloying elementsMolybdenum, Chromium, Vanadium, Tungsten, and Cobalt to produce a cuttingtool that exhibits excellent wear resistance, ease of grinding and superior cuttingedge retention. Other alloys are available and may be necessary in certain applications, however, M-2 remains the best choice of tool steels for natural woodfinger jointing.

ALTERNATE CUTTER MATERIALS


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OPTI® AND CARBIDE FINGER JOINT CUTTERSThe normal cutting material for finger joint cutters is HSS (High Speed Steel). Usually a highMolybdenum tool steel such as M-2 is used. In some applications a different cutting material isrequired.

WKW pioneered the finger jointing of engineered lumber products such as LVL (laminated veneerlumber), and other man-made wood products. Exotic hardwoods and very abrasive woods havealso been successfully finger jointed using WKW tooling. WKW’s OPTI® and Carbide cutters oftenare the solution.

OPTI® FINGER JOINT CUTTERS OPTI® finger joint cutters are specially-treated and designedprimarily for natural woods. The extremely hard cutting surfaceof OPTI® cutters generally produces run times that are up tothree times longer between sharpenings, as compared toconventional High Speed Steel cutters. OPTI® cutters have beenused at several of the largest finger jointing facilities in theUnited States.

The OPTI® process is a patented process that produces an ultra-hard surface on the cutter. Unlike the coatings used by othermanufacturers, OPTI® will not chip, peel, or flake off. Extremelylong run times may be obtained under certain circumstances.Check with WKW for specifics as to whether these cutters arecorrect for you. The grinding process with OPTI® cutters isslightly different than the grinding of HSS M-2 cutters. The sameabrasives are used, however, the grinding procedure is a littlemore demanding.

SOLID CARBIDE/CARBIDE TIPPED CUTTERS WKW Carbide finger joint cutters are often the solution to finger jointing very abrasive naturalwoods, as well as man-made and engineered lumber products containing glues. Plywoods andother laminated materials that were once impossible to finger joint are now being successfullyfinger jointed. WKW was the innovator of these types of cutters.

Man-made materials such as LVL (laminated veneer lumber), plywoods, particle board, M.D.F., andother products containing glues or other non-wood products are much too abrasive for tool steelor OPTI® cutters. Solid carbide and carbide tipped cutters are often the answer to these problems.In some cases, carbide cutters may be used to produce extremely long run times in solid woods,but generally speaking, the high cost of these cutters suits them for only the most extremeapplications.

Solid carbide, as well as carbide tipped cutters, are available in a variety of joint configurations.Please contact WKW for assistance in determining the correct solution to your unique finger jointing application.


CUSTOM FINGER JOINT CUTTERS76

CUSTOM PROFILESIn addition to the stock cutters listed previously, WKW has designed andmanufactured scores of other finger joint configurations. Our Engineering filescontain hundreds of profiles. Many of these profiles were developed as the resultof close work between a user and our engineers. From micro joints to largestructural joints, if a standard profile is not suitable for your application, WKWengineers will assist in the development of a finger joint profile to get the job done.

CUSTOM CUTTER MATERIALSM-2, Carbide, and OPTI® are used in the majority of applications, however, difficultand unusual applications are welcomed at WKW. D-2 tool steel, high cobalt alloys,and other materials may be the answer for you. As always, WKW engineers areyour best source of information here.

Whether your needs are for a specific finger joint profile, a custom designedcutterhead to fit your machine, or a cutter material to machine a particularly hardor abrasive wood product, WKW has the technical support that you need.

See the following chart for information on OPTI®, carbide, and other alternatecutting materials.

COATED FINGER JOINT CUTTERSVarious coatings are available for enhanced performance. Please contact WKW formore details.

MATERIAL APPLICATIONS COMMENTSHSS M-2 Normal woods Very good run times and clean cut

OPTI® Normal woods* Extra long life

CARBIDE Man-made materials* Excellent life and performance

D-2 Karbo Krome® Very wet woods* Only used in difficult applications

*Contact WKW’s engineers for assistance in these applications.

ORDERING INFORMATION


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ORDERING INFORMATIONMachine make and model number

Head Number* (if re-ordering same heads, use number engraved on head)

Swing Circle or maximum diameter

Bore diameter and type (i.e. Hydro-Loc™, Quick-Loc™, collet style, etc)

Number of bolts or wings

Bolt length (if known) or number of thick and thin cutters per bolt

Joint length or cutter number desired

Type of joint (i.e. reversible, end match, etc) and species of wood.

Wood Thickness

If assembled, number of cutters per bolt, and assembly configuration

*Note: Always provide the part number engraved on head or cutters when re-ordering the same items.

TERMINOLOGY

HOOK ANGLECUTTING ANGLESWING CIRCLE

CUTTER FACE

BOLT CIRCLE

GULLET

HUB DIAMETER

HEAD BORE

GREASE ZERK

HEAD DIAMETER

LOCK RING HOLES

PRESSURE RELEASEVALVE


CUTTERHEAD TYPES78

HYDRO-LOC™ BOREWKW Hydro-Loc™ cutterheads are affixed to the machine spindleby means of a pressurized inner sleeve. The inner sleeve iscompressed onto the spindle by charging or pressurizing thesleeve with a special high pressure grease gun. Locking collarsare always recommended as an additional measure of safety. SeeAccessories and Set Up sections for more information.

QUICK-LOC™ BOREThese heads are similar to the Hydro-Loc™ heads above exceptthat they do not require the use of a grease gun to pressurizethem. The head is pressurized by merely tightening a screw withan allen wrench.

STRAIGHT BORE COLLET HEADSAlthough not as common as they once were, these heads rely onself-centering tapered collets (or cones) to center the head on thespindle when the spindle nut is tightened.

LAMINATED BEAM CUTTERHEADSThe production of structural joints, as used in laminated beams,(see pg. 69) requires very sophisticated tooling. Cutter stacks ofup to twelve inches demand that the cutter thickness and tipcentrality on each individual cutter be held to a very high degreeof accuracy and consistency. WKW has produced the toolingused by the major producers of structural beam products. Threeand four wing heads are used to produce joints 1 inch or longer.In most cases, these applications require special spacer plates(shown) between each cutter. For information on spacers, seeAccessories section.

ACCESSORIES


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SWINGCIRCLE

CUTTERRADIUS BORE

SINGLEPOST 6 POST 8 POST 10 POST

9" 1-1/2 1-1/2 36442 TF1818-B TF1834-B ———9" 1-1/2 1-13/16 36446 TF1818-A TF1834-A ———9" 1-7/8 1-1/2 TF1344-B TF1963-B ——— ———9" 1-7/8 1-13/16 TF1344-A TF1963-A ——— ———9" 2-1/8 1-1/2 TF1598-B ——— ——— ———9" 2-1/8 1-13/16 TF1598-A ——— ——— ———

10-1/2" 1-1/2 1-1/2 TF1964-B TF1965-B TF1966-B TF1967-B10-1/2" 1-1/2 1-13/16 36444 TF1965-A 36448 3645010-1/2" 1-7/8 1-1/2 TF1968-B TF1969-B TF1886-B ———10-1/2" 1-7/8 1-13/16 TF1968-A TF1969-A TF1886-A ———10-1/2" 2-1/8 1-1/2 TF1970-B TF1971-B ——— ———10-1/2" 2-1/8 1-13/16 TF1970-A TF1971-A ——— ———

Accessories.

Ten post set up fixture.

SET UP FIXTURES


ACCESSORIES80

Use of a grinding template will prevent incorrect bevels(above) that lead to poor-fitting joint.

See troubleshooting section for correct grinding.

PARTNUMBER CUTTER RADIUS

T683 1-7/8T684 1-1/2T685 2-1/8T686 2-3/8T981 1-1/4

GRINDING TEMPLATES (HOOK GAUGES)

PARTNUMBER BORE & TAPER

SB 536 1-1/2 X 5/16-20°SB 755 1-13/16 X 5/16-20°

COLLETS (OR CONES)

CLOSE TOLERANCE SPACING WASHERSAvailable in various thicknesses. Used for replacing cutters or forstacking between cutters. Call for info.

PARTNUMBER Bore Pin Spacing

SE 1624-A 1-1/2 2.56SE 1590 1-13/16 3.14SE 1646 1-13/16 2.56

LOCK RINGS

Length RH Thread LH Thread

4-3/4 DC503-J DC591-C4-1/2 DC503-H DC5914-1/4 DC503-G DC591-G

4 DC503-F DC591-A3-3/4 DC503-E DC591-F3-1/2 DC503-D DC591-BNUT NB207 NB207-C

1/8 Washer W4051/4 Washer W405B3/8 Washer W405C1/2 Washer W405DC Washer W329-A

*Please refer to drawing at left to determine length of bolt.

FINGER JOINT BOLTS, NUTS & WASHERS

SET UP AND ASSEMBLY


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HOW MANY CUTTERS?Which type of joint you should use (see page 71 for joint types) depends on severalfactors. The vast majority of finger jointing for mouldings, door and window parts,and general recovery of short pieces is done using a reversible joint. A single headwith one thick cutter per bolt could be used to cut both sides of a reversible joint,however, production finger jointing usually requires both a left and a right head.

The end match, or male-female joint, is a less common joint that is used in caseswhere the finger jointed stock will be moulded or shaped on both sides, as in thecase of finger jointed chair backs. Two separate heads would be required for an endmatch joint, since one head would have thick cutters on both the bottom and thetop of the stack, and the other head would have all thin cutters.

The re-saw joint utilizes a thick center cutter to leave a thick shoulder to allow forsplitting the stock into two thinner pieces.

The number of cutters that will be required to cut a particular thickness of materialcan usually be calculated in the following manner. Please refer to the chart on page73 for cutter specifications such as thickness and index.

EXAMPLEHow many cutters (per bolt) will I need using BG 919 and BG 920cutters to cut a reversible joint on 1-1/2 inch thick stock?

SOLUTION (Stock thickness) minus (tip thickness of thick cutter)then, divided by tip index. Round to the next number.

OR 1.500 minus .250 equals 1.250. Then, divide 1.250 by.169. = 7.4

The answer obtained using the formula above is 7.4, and must berounded up, giving you the answer of 8. This means that the number of thin cuttersneeded per bolt would be 8. In other words, when cutting a reversible joint in 1-1/2inch stock, using BG 919 and BG 920 cutters, you would need 8 thin and 1 thick cutter per bolt.

Depending on your actual stock thickness, in many cases, a smaller shoulder will beacceptable, and an extra thin cutter can be added. This will increase the lineallength of glue surface area, and could lead to a stronger joint, but this also meansthat the shoulder cut by the thick cutter will be correspondingly smaller. The aboveformula may be used in most cases, however when in doubt, please call WKW for

an exact computer generated pattern layout for your specific application.

CORRECT BOLT LENGTHWhen an order is placed for a complete head assembly, WKW willprovide bolts of the correct length to accommodate the cutter stackthat you will require. For re-ordering purposes, the bolt length youwould require can be calculated by using the drawing to the right. Besure to verify the thickness of your head body. The combinedthickness of the body and bolt will either be 1.000 or 1.250,depending on the head you have. The part number for the bolts youwould need to order may be found on page 80.


SET UP AND ASSEMBLY82

CUTTER AND BOLT BALANCEBalance of the finger joint head is extremely critical to a good finger joint. Even avery slight amount of imbalance or improper setup may produce a joint that willfail. All cutter stacks should be assembled so that they will keep the head indynamic balance during operation.

The best way to ensure cutterhead balance is to weigh each stack of cutters,and then install stacks that weigh the same in a configuration 180 degreesacross from each other in the head. If there is more than one tenth of a gramdifference between stacks that will be installed across from each other, theheavier stack should be lightened by grinding material off the flat area on theback of the cutter.

It is good practice to check and rebalance cutter stacks every 4 to 8 weeks, orafter approximately ten sharpenings. If the stacks are significantly out ofbalance, you may need to increase the frequency of rebalancing. Again, aproperly balanced stack will be within one tenth of a gram from the stacklocated 180 degrees across in the head.

Balance of cutter bolts is just as important as the cutter balance. If you arereplacing bolts or re-assembling a cutterhead, bolts that are straight across fromeach other must be balanced within one tenth of a gram. Be certain to use carewhen pressing bolts in or removing them from the head. Always use an arborpress, and be sure that both the bolts and the head are completely free from dirtor debris. Bolts that are worn or scored must be replaced as they can significantlydeteriorate the quality of the finger joint.

HEAD BALANCEAll WKW cutterheads are factory balanced to extremely tight dynamic balancespecifications before they are shipped. This balance is critical to a precision fingerjoint. It is counterproductive to install perfectly balanced cutter stacks in a headthat is of questionable balance. If the cutter stacks and the head are not bothbalanced properly, it will be difficult to obtain a good finger joint. Poor balancingpractices will contribute to vibration, runout, and a poor joint.

If there is any reason to suspect that your head is out of balance, or if it has beendropped, or if it has hit any foreign object, please contact the plant forauthorization to return it for possible rebalancing.

Cutter stacks must balance with stacks 180° across in the head.

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THE SET UP FIXTURE (SINGLE POST)WKW finger joint tooling is manufactured to the highest of tolerances and is capableof producing a perfectly machined, strong finger joint. However, care must be takento be sure that the tooling progresses into the wood at the correct angles. A perfectstack of cutters will cut a distorted, poorly fitting profile if the head is not set up tothe correct geometry. The set up fixture is an extremely accurate tool, and it is yourassurance that the precision tolerances on your tooling are perfectly machined intothe wood.

The set up fixture must always be used any time the head hasbeen disassembled or any time the cutters have been sharpenedto the point that there is .015 to. 020 gap between the face of thecutters and the set up post.

Once the fixture is mounted securely in a vise, carefully slide thecutterhead onto the arbor. Note that there are three locatingholes for the “L” pin. To loosen or tighten the bolts, position the“L” pin into one of the side holes that will hold the cutters awayfrom the locating post. (The center hole is to be used for set uponly, and you should never loosen or tighten the bolts with the“L” pin in the center hole.) Only apply torque to the bolts whenthe “L” pin is in one of the side holes. At this point, check to besure that there is a spacing washer between the nut and thehead flange. This washer ensures that the torque will be moreevenly distributed and that the nut will not cut into the flange ofthe head. A 1/8th inch spacing washer is supplied with all heads,however, close tolerance spacing washers of different thicknessescan be used when the cutter stack size is decreased. See page 80.

Next, loosen the nut, and relocate the “L” pin to the center hole.Rotate each cutter in that stack up to the locating post so thatall cutters are flush with the post. You may want to check with afeeler gauge, no more than .002 thick, to be sure that all cuttersare rotated completely to the post. Snug the nut up by hand, andcontinue the same procedure until all stacks have been reset tothe post and hand tightened. Be certain that cutters have notmoved away from the post during this hand tightening. You maywish to use left hand threaded bolts as they will minimize thecutters rotating away from the post on counter-clockwise heads.Left hand bolts are listed on page 80. Never use a wrench toloosen or tighten the nuts with the “L” pin in the center hole asthis hole is for locating only and torque applied to it coulddisturb its accuracy.

See section titled “Torquing the Head” on page 84.

Note three holes on set up fixture.

SET UP AND ASSEMBLY


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THE MULTI POST FIXTUREA single post fixture is a precise instrument, and it offers a very high degree of accuracy.However, there is also a fair amount of time involved in repositioning the head for eachcutter stack. The setup time involved can become substantial when the toolroom is servicing more than one finger joint machine. For this reason, a multi post set up fixture

can pay for itself in a short time.

The multi post fixture allows all the cutter stacks on the head to be loosenedat once, without repositioning the head for each stack. After all the stacks areloosened, the locating pin is positioned to the center (setup) hole and all thestacks are rotated up to their own post. Again, there is no need to repositionthe head for each stack. Finally, once the cutter stacks have been reset andhand tightened, the locating pin is moved back to the torquing location andthe bolts are properly torqued.

TORQUING THE HEADPrior to torquing, double check to see there is a spacing washer betweeneach nut and the head flange to prevent the nut from cutting into the head

flange. This will also increase the surface area of the torque for a better assembly.

After each cutter stack has been reset, hand tightened, and the cutters have beenrelocated away from the setup post (by placing the locating pin in one of the side holes),use a torque wrench and begin to tighten the bolts in a diagonal or alternating pattern. Itis important to gradually tighten the head in this criss-cross method to ensure that you donot bind the flange on the bolts, and to ensure that all cutter stacks are equally tightened.Refer to the drawing below for the correct pattern for torquing.

Torque each stack in 50 foot pound increments following the same criss-cross patternuntil you have attained 200 foot pounds. Your application may require 250 foot pounds,however, 200 is adequate for many conventional applications. You may want to try 200foot pounds first. (175 foot pounds may be used to prevent cutter breakage in extremelydifficult applications, as this will allow the cutters to rotate out of the cut if too muchcutting pressure is encountered.) On WKW laminated beam finger joint heads equippedwith 1-1/8" diameter bolts, torque to 450 foot pounds.

Cutter stack size, material being cut, and other factors, may require slightly differenttorque. When in doubt, or if you encounter cutters rolling back out of location in the head,contact the factory for technical assistance

Remember that after a head is reset to the fixture, it must be resharpened to ensure theaccuracy of the head. See the section titled Grinding Cutters on page 83.

Bolts must be torqued in proper sequence.

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GRINDING CUTTERS–THE GRINDING WHEELGrinding the cutters correctly is a very important factor in obtaining a good fingerjoint. (See section on TROUBLESHOOTING, page 88.) The actual angle on the cuttersis extremely important to ensure that a good fit is achieved on the finger jointitself, but equally important is the configuration of the cutter gullet.

A properly ground finger joint cutter will have a smooth radius at the gullet forseveral reasons. A radius in the gullet will act much the same way that achipbreaker or radius gib does in a moulder head or planer head. The chips thathave been removed from the material will be smoothly redirected out of the gulletrather than packing in between the fingers.

A smooth chip flow is also critical for cooler cutting. When chips and debrisbecome packed in the gullet area, they will allow excessive heat to build up in theactual cutters. In wood machining, the chips serve as the coolant. A good freshchip flow is actually similar to a coolant flow in a metalworking environment. Asthe chips contact the cutters and are directed away by a flow of more chips, theyactually remove heat from the cutters.

This is also the reason that, for good heatremoval, chip load cannot be allowed to gettoo small. When the chips are more likesawdust rather than like formed chips, this isjust as if the coolant flow has been restrictedand there is not enough volume of coolant toproperly cool the cutters.

Another, perhaps more important reason for agenerous radius in the gullet is that a cuttergullet that has a sharp corner, rough finish, ortoo small of a radius could allow a stress pointto develop. This area may allow for thedevelopment of minute cracks that couldeventually lead to breakage. By maintainingthe gullet at the proper radius, breakage can beminimized.

SET UP AND ASSEMBLY


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GRINDING CUTTERS–THE GRINDING TEMPLATEGrinding the cutters correctly is a very important factor in obtaining a good fingerjoint. The cutters must always be ground so that the face bevel of the cutter matches the grinding template as shown in the figure. If the cutters are ground tothe incorrect face bevel, the joint will not fit correctly. (See section on TROUBLESHOOTING, page 88.) If you are not certain that you are using the correctgrinding template, please call WKW for assistance.

It is imperative that the grinding template matches the face bevel on your cutters. If it does not match, or if there is any space between the face of the cutter and thetemplate, you must immediately adjust your grinder. If the angle or face bevel on

the cutters is allowed to change, there will be a correspondingchange in the profile that will be cut. It is good practice to frequently check the cutter bevel so that any deviation will becaught and corrected before there is a problem with the joint.

GRINDING CUTTERSGenerally, you may run 2 to 4 shifts between sharpenings,however, always be sure to wear eye protection as well as properbreathing apparatus whenever grinding any cutting tools. Thegrinding wheel you select will have a great influence on cutterperformance. An 80 grit wheel at 1700 RPM will usually giveexcellent results on HSS and OPTI cutters. Depending upon your

own grinding technique, you may have better success with a 120 to 150 gritwheel. Dress the wheel so that it will produce a smooth radius at the gullet ofthe cutter. CBN (Cubic Boron Nitride) wheels are available with the correctradius to match the gullet of your cutters.

Once the head is mounted on the tool grinder, mark the faces of the cutterswith a felt tip marker. This will indicate whether you are making full contactwith all cutters in a stack. Be sure to remove only .001 or less in each pass,and always be sure to grind enough to remove all of the wear and any chippedareas.

It is very important to grind until the top corners of the cutters show a cleansharp edge (see illustration on page 89). It is possible to have a cutter thatappears to be sharp, but upon closer inspection, shows wear at the topcorners. This condition will prevent a good clean cut, and may contribute totear out or a poor joint.

Allow the wheel to “spark out” after the wear line is removed, or after every.006 is removed from the cutters if you will be grinding more than .006. Be sureto feed at a slow steady rate, and only advance the wheel into the cutterswhile the wheel is in contact with the cutters. A micro finish of 50 RMS orbetter will give the best results. Although you may get several sharpeningsbefore you need to reset the cutters, best results will be obtained with morefrequent setups.

Both cutters shown above are incorrect and willprevent you from getting a good joint. Please seeTROUBLESHOOTING section on page 88.

A correctly ground cutter will fitthe template perfectly asshown. The face bevel of thecutter should contact the edgeof the template with no gap orspace.

Always grind to leave a smoothradius at gullet of cutter. Lackof smooth radius may allowcracking.

CORRECT

INCORRECT

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GRINDING CUTTERS (continued)Frequently, after sharpening, you will notice that there may be a very slight burr atthe cutting edges of the cutters. Never attempt to remove this edge with a stone orother device. Attempting to remove this slight burr will dull the cutters.

This burr is a common occurrence and your finger joint system will very easilyaccommodate it. As the freshly ground cutters progress through the dullingprocess, you may wish to maximize your run times between sharpening as follows.

Immediately after sharpening, the cutters will cut a slightly larger (wider) profile.This is because of the burr produced in the grinding process. Your machine shouldbe set up to take this into account by adjusting to a slightly shorter finger length.This is normally accomplished by an adjustment to the trim saw. Your goal is toensure that the finger thickness on the tips of the wood exactly match the width ofthe bottom of the joint.

After a length of running time, the burr will naturally begin to wear off, and thecutters will cut a slightly smaller (narrower) profile. The operator then may adjustto cut a slightly longer finger. Again, the goal is to match the tip of the wood to thetip width at the bottoms of the joint.

As the cutters wear, and the cutting edges begin to dull, they may produce aslightly smaller (narrower) profile. The operator then may be able to adjust againto cut a slightly longer finger, again matching the tip of the finger to the width ofthe bottom of the joint.

GRINDING OPTI® CUTTERS Opti cutters are ground exactly like high speed steel except that extra care shouldbe used when grinding OPTI finger joint cutters. The extra hard surface may chip iftoo much material is ground off per pass. Careful grinding will produce anextremely durable and sharp surface that will give very long tool life. Close inspection of the cutting edge with a magnifying lens may be necessary.

Side view of cutter. Face view of cutter. Close-up of tip. Be sure to grind to create sharp corners.

SET UP AND ASSEMBLY


87


TROUBLESHOOTING88

PROBLEMS FROM IMPROPER CUTTER BEVELAs shown on page 86 in the section on cutter grinding, the incorrect bevel on yourcutter face is indicated by the grinding template. Great care must be taken to besure that the correct cutter angle is maintained as the incorrect angle may producethe problems shown below.

CUTTERS GROUND TOO SHARPIf the bevel on the cutters is ground too sharp, asshown, the joint produced may be characterized byfingers that are concave. This situation will producea joint that will either not glue up correctly, or onethat will be visibly loose.

CUTTERS GROUND TOO BLUNTIf the bevel on the cutters is ground too blunt, asshown, the joint produced may be characterized by fingers that are convex. This situation will produce a joint that is very tight or difficult toassemble.

CUTTERS GROUND CORRECTLYIf the bevel on the cutters is ground correctly asshown, a good fitting joint will be the result, as longas the trim saws are correctly set up. See followingpage for trim saw set up.

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PROBLEMS FROM MIS-ALIGNMENT OF CUT OFF SAWCorrect setting of the cut off saw is crucial for a good fitting finger joint. The overalllength of the fingers is extremely critical as well as whether the saw is running trueand cutting a good square end. Following are some common problems and how thejoint will be affected.

FINGERS TRIMMED TOO SHORTWhen the trim saw removes toomuch material from the end of thestock, the joint will be tight at thesides of the fingers before thefingers are able to reach the bottom of the joint. This condition is shown at the rightand it is noted that there is visible space at the end of the fingers while the sides ofthe joint are in contact with each other. The saw must be adjusted so that theresulting fingers are longer.

FINGERS TRIMMED TOO LONGWhen the trim saw is set so that itleaves too much material, theresulting joint “bottoms out” beforethe sides of the fingers are incontact with each other. Remember that unless you are using a special headequipped with trim knives, the fingers themselves are not cut on the ends by theheads. The trim saw must be set accurately to ensure the perfect fit.

FINGERS TRIMMED CORRECTLYWhen the trim saw is set so that itleaves the correct length finger, agood fitting joint is possible. Alwaysbe sure that the cutters themselvesare correctly ground (see preceding page) or a poor joint will result.

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JOINT OPEN ON ONE SIDEThis problem is evidenced by a tapered opening on theface of the wood. In addition, there will be tip thicknessvariations from one side to the other. This is usuallycaused when the wood is allowed to move during thecut, or when the wood is not fed squarely.

Wood movement can be prevented by checking to seethat there is sufficient air pressure and that the air bag isnot restricted. Worn bed rails will also allow movement.If you are unable to resolve this problem, the machinemanufacturer should be contacted.

If the feed dogs are not square, or if they are damaged or loose, the wood may befed at an angle. This will also result in the incorrect joint shown.

FINGER ENDS VARY IN THICKNESSThere could be several reasons why you may experiencethis problem. The wood may be moving during thecutting process as outlined in the previous section. Also,your machine may not be feeding the material squarely,or it may be unable to hold the wood securely due toother factors. If you suspect that the machine is toblame, you may need to contact the manufacturer.

If your cutters are extremely dull, there will be excessivetool pressure that may contribute to movement of thewood. Please refer to the section on grinding (page 84)and be certain that the cutters have been sharpened

enough to remove all of the dullness. It is possible to grind the cutters only to findthat they are still dull if enough material is not removed to bring the face of thecutters to sharp edges and corners.

JOINT OPEN AT TOP OR BOTTOMThe trim saw adjustment is extremely important, and your finger jointmachine manual will offer a complete guide on alignment of the saw.However, the problem shown here could be a direct result of the mis-alignment of the trim saw. Another reason for this problem may bethat the material handling system on your machine may be allowingthe wood to miss all or part of the trimming operation.

It is extremely important that the wood be held securely and squaredperfectly before the wood comes to the finger joint head itself. Remember that thefinger joint cutters do not contact the ends of the fingers. The critical ends of thefingers are cut by the saw, and if the saw is out of alignment, it will be difficult orimpossible to achieve a good joint.

CLOSED

OPEN

THICKER

THIN

OPEN

CLOSED

USEFUL INFORMATION


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91

CHIP LOAD PER CUTTERIn order to get both a good finish on the wood and to prevent burning of the cutters,it is important to remove the correct amount of material with each cutter. Themeasurement that must be monitored is “chip load” per cutter.

Extremely high temperatures are generated at the cutting surface of the knife, and thewood serves as the coolant. Too small of a chip load will result in too much heat andwill either glaze the wood, burn the cutters, or both.

The target range to shoot for in finger jointing is approximately .020" for the actualchip.

The following formula will help you to determine the chip load you are getting.

Chip Load per cutter = Feed Rate ( in feet per minute) x 12

Number of wings in head x R.P.M.

When you insert your data into the above formula, you will be able to determine thechip load you are getting. Again, the ideal figure is about .020", however your datamay vary from that. The important factors are whether you are getting a good cut andif you are getting good life between sharpenings without blackening or burning thecutters.

The following table shows some recommended feed rates for different heads. You mayachieve good results at higher or lower rates depending on your application, but therates shown are in the typical operating range.

RECOMMENDED CHIP LOAD AT 3600 RPM

FEED RATEIN FEET PER

MINUTE2 4 6 8 10 12 14

10 .01720 .033 .01730 .025 .01740 .033 .022 .01750 .028 .021 .01760 .033 .025 .020 .01770 .029 .023 .019 .01780 .027 .022 .01990 .025 .021

100 .028 .024110 .031 .026120 .029

NUMBER OF CUTTER STACKS IN HEAD


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KNIFE MARKS PER INCHThe number of Knife Marks per Inch (KMPI) directly affects the quality of the finishedcut, however, the “chip load per cutter” (see previous page) is the figure more oftenreferred to when calculating the ideal feed rate. If you would like to calculate thenumber of knife marks per inch, the formula is simple. Also note that a comprehensiveKMPI chart is found in the moulder tooling section on page 68.

Knife Marks per Inch (KMPI) = RPM x Number of Bolts

(Feed Rate) in Feet per Minute x 12

For illustration purposes, figure a 10 bolt head at 3600 RPM and a feed rate of 60 feetper minute.

The answer is 50 KMPI. (3600 x 10) = 50

(60 x 12)

COST SAVINGS OF SHORTER JOINTSThe trend to shorter joints continues to push for the development of tooling capableof producing a good quality joint. Each inch of salvaged wood adds up quickly as thefollowing will illustrate.

For illustration purposes, let’s figure that you are considering changing from yourcurrent 3/8" long joint to a 1/4" joint. We will figure based on 40 joints per minute or2400 per hour.

Lineal feet of wood saved = Joints per hour x Savings per joint

12

OR

2400 x .125*

12

The answer is 25 feet of stock per hour or 200 feet per eight hour shift. These figuresare somewhat conservative, however, the amount of material savings adds up quickly.If you would like assistance in evaluating whether a shorter joint may be of benefit,please give us a call. In addition to the 1/4" joint discussed above, we also offer muchshorter joints for certain applications.

*.125 is the difference between 3/8" joint and 1/4" joint

finger joints - wisconsin knife works, inc. joints 71 reversible by far the most common joint....

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