105mm (4-1/8″) M42 Cobalt Bi-Metal Hole Saw – Large Duct Openings, Tank Ports & Electrical Enclosures

Product Overview:

The 105mm (4-1/8″) diameter is a critical size for commercial HVAC, water tank fabrication, and large electrical conduit entries.

Standard hole saws at this diameter suffer from excessive vibration, slug jamming, and backplate bending. Our 105mm M42 Cobalt saw solves these problems with 8% Cobalt teeth for heat resistance, a 4mm reinforced backplate, and 5 wide ejection slots.

What it delivers: A round, accurate, burr-reduced 105mm hole in steel up to 5mm, PVC up to 12mm, and fiberglass up to 15mm.

Cause – Why 105mm Hole Saws Fail:

Problem 1: Slug weight causes jamming

A 105mm steel slug weighs over 250 grams. Standard 2-slot saws cannot eject it easily. Users waste 2–3 minutes hammering or drilling out stuck cores.

Problem 2: Backplate bends under torque

Standard 2.5mm backplates flex at 105mm diameter. A bent backplate cuts conical holes – wider at entry than exit – which ruins seal integrity for cable glands and bulkhead fittings.

Problem 3: Chip packing stops progress

Large-diameter cuts produce long, continuous chips. Without sufficient chip evacuation paths, chips pack between the saw and material, causing stalling in metal or melting in plastic.

Solution – How Our 105mm Saw Fixes These Issues:

Solution 1: 5 ejection slots for instant slug removal

Five slots at 72° spacing. Insert a screwdriver into any slot and lever. Slug pops free in under 3 seconds.

Solution 2: 4mm reinforced backplate

40% thicker than standard. No flex. The saw cuts straight-walled holes every time.

Solution 3: Deep gullet geometry + 5-slot chip evacuation

Each tooth has a deep chip pocket. Chips exit through the 5 slots. No packing. No melting. No stalling.

Solution 4: 8% Cobalt maintains hardness above 600°C

Standard M3 saws soften at 400°C. M42 stays hard. In stainless steel and abrasive fiberglass, you get 3–4× longer life.

Solution 5: 4/6 variable TPI reduces breakthrough kickback

Alternating 4 and 6 teeth per inch means only 40% of teeth engage at breakthrough. Sudden torque release is cut by more than half.

Specifications:

Application – Where to Use 105mm:

Commercial HVAC Systems

Create 105mm openings for large duct collars, fresh air intakes, and exhaust ports through metal cladding and insulated panels. Recommended RPM: 130–180 for mild steel, 250–350 for aluminum.

Water Tank & Vessel Fabrication

Drill 105mm ports for level sensors, inspection windows, and bulkhead fittings in polyethylene, polypropylene, and fiberglass tanks. The 5 slots prevent chip packing in plastics. RPM: 250–350 dry.

Large Electrical Conduit Entries

105mm matches common cable gland sizes for main building power entries. The burr-reduced finish preserves IP65/66 seals without secondary deburring. RPM: 65–95 with cutting oil, magnetic drill recommended.

Marine Through-Hull Fittings

Deck fills, tank vents, and transducer mounts through GRP hulls. The 8% Cobalt resists abrasive fiberglass wear. RPM: 130–200 dry with dust extraction.

How It Works:

Step 1 – Pilot centering: The pilot bit establishes the exact center. At 105mm, this prevents wandering.

Step 2 – Variable tooth engagement: 4/6 TPI creates interrupted cutting. Coarse 4 TPI removes bulk material. Fine 6 TPI shears remaining ridges.

Step 3 – Chip evacuation: Chips curl into deep gullets and exit through 5 slots. No packing.

Step 4 – Heat management: 8% Cobalt maintains hardness above 600°C. Teeth stay sharp longer.

Step 5 – Breakthrough control: Variable pitch smooths torque release. Reduced kickback risk.

Step 6 – Slug removal: Lever screwdriver through any slot. Slug drops out in 3 seconds.

How To Choose:

Equipment recommendation: For steel at 105mm, use a magnetic drill press or right-angle drill (10+ amps). Standard hand drills lack sufficient torque.

 FAQ :

Q1: What RPM should I use for 105mm in stainless steel?

A: 65–95 RPM with heavy cutting oil. The large diameter creates high tooth tip speed even at low RPM. Never exceed 120 RPM – heat will work-harden the stainless steel and destroy teeth.

Q2: Why 5 ejection slots instead of 2?

A: A 105mm steel slug weighs over 250 grams. Two slots provide only two leverage points, often on opposite sides of a stuck slug. Five slots at 72° spacing mean you can always reach the slug with a screwdriver tip from any angle. Ejection takes under 3 seconds.

Q3: Can I use this on a standard hand drill?

A: For PVC, wood, or thin aluminum – yes, with an 8+ amp drill with side handle. For steel or thick fiberglass – no. Use a magnetic drill or right-angle drill. A standard hand drill will stall or grab dangerously.

Q4: Will this cut through a fiberglass boat hull?

A: Yes. The 8% Cobalt resists the abrasive glass fibers that quickly dull standard saws. Cut dry at 130–200 RPM with dust extraction. The variable TPI prevents gelcoat cracking on the exit side.

Q5: My 105mm hole is coming out oversized. What's wrong?

A: Check three things: (1) Pilot bit worn – replace it. (2) Arbor connection loose – tighten fully. (3) Material flexing – back with a wood block. If all three are correct and the problem remains, contact us for a replacement under TIR <0.2mm guarantee.