Planer Knives and Inserts: Types, Changing and Care

Makers do not share one name. Powermatic calls its insert heads helical, as does Grizzly for its G0958 and G0959; Grizzly's G0634 and its benchtop G0946 and G0947 have a 'spiral' head; JET describes its benchtop jointer's inserts as set 'in 2 spiral rows'. The words describe the same idea — small square carbide cutters set in staggered rows — and BenchRoot uses each maker's word for its own machine. When one insert is nicked, JET says to turn only the inserts affected; it advises turning all of them together for ordinary wear. Powermatic also notes a way round a small nick on its straight-knife 54A: shifting a knife 1/32 in sideways, a setting it gives for rabbeting.

An insert head is not something every machine accepts. DEWALT's DW735 manual says helical cutterheads have not been tested with it and are not recommended, so a 'helical wood planer' upgrade for that machine is outside what its maker allows.

• DEWALT DW735: knives sit on pins through oblong holes, the head locks while each is changed, and a magnetic wrench lifts them; DEWALT says never touch them with your fingers.
• Makita 2012NB: disposable blades go into a set plate with magnetic holders; standard blades are set in a blade gauge; bolts are tightened lightly from the centre out, then fully, with Makita's own wrench only.
• JET JJ-6HHBT: each insert is unscrewed with the star-point driver supplied, the seat cleaned, the thread lightly oiled and the screw torqued to about 50–55 in-lb; Powermatic gives 45–55 in-lb for its 15HH.
• Electric hand planers: both blades change together; Makita uses a gauge base, Milwaukee slides the blade into its clamp and pushes it against a step on the drum.

Some makers supply a tool for setting knives, a 'planer blade alignment tool' in effect: Makita's blade gauge, Powermatic's knife gauge on the 60C. Because each fits one machine, the manual's own method is the one to use. In a workplace, OSHA requires jointer knives to project no more than 1/8 in beyond the cutterhead's body.

• A fuzzy surface: dull knives tear the fibres rather than cut them (JET).
• Torn or raised grain, or a rounded, glossy surface (Powermatic's troubleshooting).
• The machine's breaker tripping: DEWALT says dull knives are the usual cause on the DW735.
• More snipe, or a rough finish and motor overload (Powermatic, Makita).

Fuzz also comes from wet wood, which Powermatic lists beside dull knives; a moisture meter tells the two apart. Gum and pitch on the edges add friction and heat; JET removes them with a strong solvent. Sharpening isn't covered here beyond what the makers say: disposable and carbide blades are never sharpened (Makita, Milwaukee). Sharpening a hand plane's blade is a different job, covered in the plane blade guide.

Electric hand planers take a matched pair of narrow blades. Milwaukee's 2623 takes only 3-1/4 in tungsten-carbide or carbide double-edged blades, reversed or changed in pairs; DEWALT's DW680K takes either resharpenable high-speed steel or reversible carbide. More on these tools is in the electric hand planer guide.

How cutterhead choice affects buying is covered in choosing a jointer and choosing a thickness planer; the machines themselves are in the planer guide, the jointer guide and jointer vs planer. Setting a jointer after a knife change is in how to use a jointer, and a combination machine's head in a jointer-planer vs a planer.