|Restoration & Preservation specializes in making
precisely machined re-creations of mouldings and
âA minimum of three custom knives and two CNC router bits are needed for every project,â says Drazen. âHowever we have needed over 12 sets of knives for some projects due to moulding variations from floor to floor in the buildings we work on. By having the ability to grind our own knives it not only produces a better end product â because we can sharpen periodically over the course of a run â but it allows us a quicker turnaround time on our product. The more we can do, or rather the more self-sufficient we are, aids us in controlling the end product and lead times.â
Using the digital approach improves the precision of the process, develops more exact knives and reduces labor cost as well, he adds.
âIf it is an existing wood frame, we start by removing an 1/8-inch slice of the moulding profile, which we then scan into the computer,â says Drazen. âWith the image imported into the computer, we refine it until it matches the profile exactly.â Alternatively, he says he can sketch the profile by hand and scan that image in or take it from architectâs drawings.
Drazen uses a Tem Tech to cut a template based on the scanned slice of wood, sketch or drawing of the profile. Template Cut Shop software allows the image to be rastered, which outlines the profile of the moulding. (It can also import files directly from a CAD drawings.) This file will be converted to G-code to drive the CNC moulder after the drawing is trued up to the profile, Drazen says.
The next step is to establish the offset of the cut and create the template. The template will guide the tool-cutting system or grinder as it cuts the tool from the knife stock blank, similar to cutting a house key from a blank.
âIf it is a 5-inch profile, I go with 5.5-inch template, which gives us the ability to adjust the knife in and out.â
From the template, Drazen uses an SCM profile grinder to cut the tools, starting from various sized blanks. âIn choosing a knife stock, Iâll select from 1.75-inch to 2.25-inch, depending on the depth of profile and width of the board weâre cutting in the moulder,â he says. âWhen you are choosing the knife stock, you should also make sure it is thick enough so you can get several sharpenings on it.â
After cutting the knife stock to the width of the template, Drazen says, âthen I put them on a tip scale to balance the knife stock and ensure the knives are equal in weight.â He then makes small cuts in the backside of the tooling steel of the knives as he adjusts them.
âThe closer and more balanced the knives are, the better the finish. You avoid getting hop, chatter and knife marks from being out of balance as the blades rotate in the moulder,â Drazen says.
The blanks or knife stock are ground within 0.015 thousandth of an inch of the template during the roughing cut on the profile grinder. The roughing cut, Drazen explains, is where you remove most of the steel from the knife stock as you follow the template of the profile.
âYou are just ahead of where you need to be,â Drazen adds. He cuts that in three steps â dressing the cutting wheel and cutting away 0.007 thousandth of an inch, then regrinds it at a slower feed to remove another 0.007 thousandth of an inch.
âWhen you are doing finish cuts, you use a constant fluid movement,â he explains. At this point there is 0.001 thousandth of an inch remaining to be cut away from the blade.
âWhen we go to get our final cut, the coolant on the machine is shut off and the grinding wheel is dressed. That finish cut is called your âsparkingâ â that is when the actual sharpening occurs. The sparking is what really polishes the knife and gives it a sharp, clean surface.â
As a last step, Drazen says he lays the knife on the original piece of moulding to see if they match.
âIn our case, if you can see any light between the knife and the original moulding, we do it all over again until itâs perfect. Before we begin grinding the knife, we also do the same check with the template to the moulding. There is no reason to waste the grinding time and labor if the template is not perfect first.â
Bill Esler is Associate Publisher of the Interiors Division of Vance Publishing and Editor-in-Chief of CWB magazine.
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