Jointing Carbide Knives 101

      Technical tips on selecting and preparing stones for jointing your carbide cutters. February 14, 2007

This article was reprinted with permission from Wood Tech Tooling,

There is more than one way to properly joint carbide knives. All techniques described below are assuming either carbide inlay knives or BAK-PAKŪ type knives are being jointed.

Selection of Jointing Stone
As in grinding, individual operator techniques will greatly influence which stone will work. Here are some parameters for proper stone selection. In general, silicon carbide stones work better on machines with 3,600 RPM spindle speed. On 6,000 RPM machines, depending upon your application, either silicon carbide or a specialized aluminum oxide stone can be used. Since each application is slightly different, a few different stones may have to be used to determine the best stone for your application.

Preparation of the Jointing Stone
First, layout the stone using the pattern knife to be jointed. It is most important to maintain as accurate a mirror image fit as possible to the profile being jointed, as the jointing stone will in effect re-profile the knife if not properly formed. Now pre-shape the stone as accurate a fit as is possible.

Taper the stone on both sides at a 45° angle. This angle allows faster chipping-in of the stone. Insert the stone into the holder on the machine, and chip the stone in for exact fit. The use of only one knife in the chipping-in process results in a better fit. After the stone is chipped-in to fit, start the spindle and bring the stone into the knife at a slow to moderate speed. One technique is to bring the stone in and out in 1 second intervals, making minor adjustments at each interval. Another technique is to bring the stone in and hold it in slight contact with the knives. Depth control adjustments are made while contact is being made. This technique is tricky as extended time of contact can cause the stone to glaze or the carbide to overheat and crack.

Please remember the following:
* Different grades of carbide joint differently.
* Proper fit of stone to knife is mandatory.
* Jointing of carbide is tricky; please allow time for trial and error to learn the technique which works best for you.
* As in any joint stone forming process, use ONLY a wheel to form the stone that has not been used to grind ANY knives. Using a grinding wheel that has been in contact with knives will result in small metal particles being impregnated into the jointing stone. This foreign matter will adversely affect the stone performance by nicking the knives.

This article was reprinted with permission from Wood Tech Tooling,

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