Jointing an Edge for Gluing Installing Knives

the experienced operator can usually tell whether jointer knives are sharp or dull by the sounding there are also other ways of telling the stock will be difficult to hold down on the table also dull cutters may burn marks on the stock if the cutters are nicked they will leave ridges you'll notice that this dull knife has a shiny blunt cutting edge and the back is dirty and blackened knives in this condition do a poor job they are juice and must be changed sharp knives will look like this to change the knives remove the fence and [Applause] guard to prevent the machine from being accidentally started place the safety guard over the switch then get the necessary cleaning fluid distillate and kerosene or any good solvent may be used wipe the knives and throat pieces with the fluid to loosen and remove the dirt and pitch that accumulates on the knives and cutter head use a straight edge to establish the height of the knives set the in-feed table slightly above the cutting height of the knives thus lining up both infeed and outfeed tables loosen the screws that hold the infeed table then move the table back to make room for the cutter head do the same with the outfeed table notice that the knives are held in place by a bar called a throat piece to keep the cutter head stationary drive a wedge between the cutter head and frame a special wrench is furnished with the machine to loosen the screws that hold the knives in place if the screw does not start easily loosen it by tapping the handle of the wrench use the wrench carefully to avoid injuring your hand on the cutter head knife when all the screws are loosened the knives are lifted carefully from the cutter head now put solvent in the recess to loosen the dirt and clean when new or sharpened knives are to be installed they must balance they are weighed and if necessary re-ground till they all weigh the same this is done to reduce vibration and wear when replacing knives set each one so that the heel of the knife is approximately 1 16 of an inch above the cutter head if the knife is perfectly straight tighten the end screws first just tight enough to hold the knife in place [Applause] then remove the wedge now using a straight edge set the knife so that the cutting edge will be exactly in line with the top of the tables if it is high enough to move the straight edge it is too high and must be lowered at this point be careful to tap only the heel of the blade never the cutting edge to make sure that the knife is the same height at all points lay the straight edge over the knife at several places and turn the cutter head back and forth the knife must barely touch the straight edge place the straight edge over the knife at various points along the cutter head to make sure it is uniformly set when the knife is correctly adjusted insert the wedge and proceed to tighten all screws in order [Music] [Music] take them up gradually until they are securely fastened repeat the same operation on the remaining knives knives are sometimes slightly sprung or bowed along their length they can be held to straightness however by tightening the center first and forcing the ends down if the curvature is concave or if convex the ends are lightly fastened first and the center is forced down until it becomes straight again when all the knives are set and the wedge is taken out then move the tables back in place [Applause] then revolve the cutter head to make sure there is clearance between the knives and the lips of the table approximately 1 8 of an inch and when clearance is established the tables should be locked into position with the holding screws put the fence and guard back into position with sharp knives replacing dull ones the jointer at work creates a pleasant sound for the woodworker [Applause] one of the routine jobs best done on the jointer is straightening lumber here is a board with the regular edges before this board can be used it must be straightened on crooked stock the concave edge is jointed first set the in-feed table for approximately 1 8 of an inch cut and joint to high points on both ends of the stock with several runs over the cutter head do this until a cut can be made the entire length in one run now the opposite edge must be straightened or sized by rip sawing to 9 and 5 8 inches which includes a 1 8 of an inch allowance for joining now the sawed edge is jointed the finished width of the board will be nine and one half inches the edges are now true and this piece of lumber can be used this job order calls for a table top to be made of glued up stock 30 inches by 5 feet the top will be made of boards glued edge to edge gluing up stock saves a great deal of lumber by using waste pieces and increases strength and prevents warpage glued edges are apt to pull away from each other because wood dries out quicker at the ends of a piece of stock than in the middle this tendency is overcome by using hollow joints which means hollowing or curving the edges to be glued when the boards are pulled together pressure is created at the ends which counteracts their pulling apart boards on the table to see if they are wide enough to make the tabletop which is called for on the details [Music] then face mark them so they can be identified when ready to be glued with the fence set at 90 degrees adjust the in-feed table for a 1 8 of an inch cut [Applause] lower the outfeed table slightly below the cutter head start the machine and with a trial piece about the same length as the stock make a short cut stop the machine and bring up the outfeed table till it exactly touches the trial piece and then raise it approximately one sixty fourth of an inch to make the first trial glue joint if the jointer is equipped with a tilting out feed table it may be adjusted to the desired angle by moving the lever toward the left sufficiently to make the desired glue joint now a trial hollow cut can be made use the left hand to exert pressure on the end of the board that rests on the outfeed table check the amount of curve of the hollow the degree of curvature should vary with the length and width of the sock with the jointer properly set run the stock with the grain and with the face of the stock firmly against the fence a perfect joint will not be possible unless the cut is made at exactly 90 degrees run the rest of the pieces checking the stock and fence to make certain it remains at 90 degrees see that the hollow is of the proper width to make a good joint then reassemble the boards according to the face mark since pressure applied by glue clamps on the edges in the process of gluing mars the edges sufficient stock is allowed for finish sizing of the table top blue joints of the hollow type are widely used in all kinds of furniture and cabinet construction remember that dull knives will not cut smoothly and are very dangerous change them in replacing knives be sure they balance set the knives so that they will be exactly in line with the top of the in-seed table be sure the knives clear the lip of the tables the straightened boards joint one edge true rip saw the opposite edge and then jointed [Applause] save lumber by using waste stock to glue up when possible always set the fence at exactly 90 degrees or the joints will not be true when making hollow joints keep the greatest pressure on the end of the piece on the outfeed table the jointer will do many important jobs but like all woodworking machines must be operated with care if you follow the rules and take every safety precaution the jointer may be operated with confidence and safety [Applause] you