XKY Framing · Technical Resource Center
Knowledge Base
Professional troubleshooting guides, maintenance protocols, and technical specifications for underpinners, cutting saws, and pneumatic framing systems.
8
Technical Modules
90%
Faults from FRL Neglect
5K
Nails per Distributor Clean
24H
Emergency Support
01
Underpinner / V-Nailer Faults
Core Terminology
| Term (EN) | 中文 | Definition & Function |
|---|---|---|
| V-Nail / Wedge | 角钉 / V钉 | Mechanical fastener joining frame corners. Provides clamping force while adhesive cures. Available in Hardwood (HW) and Softwood (SW) grades. |
| Driver Blade / Hammer | 撞针 / 冲头 | Core component driving nails into the wood. High-frequency wear part — even 0.5 mm tip wear causes proud nails. |
| Distributor Block / Head | 分钉器 / 枪头组件 | Final channel the nail travels through before entering wood. Prone to glue residue build-up (60%+ of jamming faults). |
| Plunger / Vertical Clamp | 垂直压杆 / 压块 | Holds the frame surface during firing. Pressure calibrated via the "Business Card Test". |
| Rebate / Rabbet | 框槽 / 槽口 | Inner groove holding glass and backing board. British: Rebate; American: Rabbet. |
| Pneumatic Cylinder | 气缸 | Air-powered driver for the hammer or clamp. Aged piston seals cause blow-by (internal gas bypass). |
| Miter Joint | 45度拼角 | End-grain to end-grain joint — structurally the weakest wood glue joint due to wicking. |
| Stacking | 叠钉 | Two nails at the same point for deeper penetration. Used on high-profile (thick) mouldings. |
| FRL Unit | 三联件 | Filter + Regulator + Lubricator. Eliminating 90% of pneumatic failures when correctly installed. |
Fault 1 — Driver Blade Jamming
Driver Blade Jamming / Stuck Hammer
Symptoms: Machine fires but nail does not fully seat · Blade stuck in distributor · Requires manual reset
Root Causes
- Glue Residue Build-up (60%+ of cases): Hardened frame adhesive mixed with sawdust forms sludge inside the Distributor Block, increasing friction on the driver blade.
- Driver Blade Deformation: Tip burr or bend of 0.5 mm disrupts guide rail travel. Accelerated by cutting hardwoods (Oak, Maple).
- Consumable Tolerance Mismatch: Mixing V-nail brands (e.g., AMP vs. Alfamacchine) causes stacking in the feed channel due to differing glue coating thicknesses.
- Return Spring Fatigue: On older models (Cassese CS series), the return spring weakens, causing slow or failed blade retraction.
Solutions
- Deep Clean: Disassemble Distributor Block. Dissolve glue residue with isopropyl alcohol (IPA) or specialist cleaner. Inspect all rubber seals for hardening.
- Honing the Blade: Use a fine oil stone to remove burrs from the blade tip. Do not alter blade length — this changes drive depth.
- Dry PTFE Lubricant Only: Apply Dry PTFE / Dry Silicone Spray to the nail channel. Never use WD-40 or machine oil — oil attracts sawdust and worsens sludge.
- Single-Brand Nails: Do not mix V-nail brands. For hardwood, use 7 mm + 7 mm stacking instead of a single 15 mm nail.
⚠ Critical Warning
If the driver blade shows visible bending or a chipped tip, replace it — do not attempt to repair. A damaged blade will damage the more expensive cylinder assembly.
Fault 2 — Misfire / Dry Firing
Misfire / Dry Firing — No Nail Ejected
Symptoms: Cylinder fires normally · Audible action · No nail driven · Or nail exits without penetrating
Root Causes
- Pusher Mechanism Failure: The constant-force spring feeding nails forward is broken or detached. Debris ahead of the pusher (claw) also causes under-feed.
- Wrong Nail Size: Using 10 mm nails with a 7 mm machine setting — the thicker glue coat creates a jam before the nail reaches the blade.
- Fully Blocked Distributor: Glue residue or broken nail fragments completely obstruct the exit channel.
Solutions
- Blow Out Pusher: Weekly — use compressed air to clear the pusher channel. Check that the constant-force spring is hooked correctly and not fractured.
- Verify Nail Size: Always match nail size exactly to machine setting. Confirm brand compatibility before switching suppliers.
- Full Deep Clean: Follow the distributor cleaning protocol (Module 1, Fault 1). Check for broken nail fragments inside the block.
02
Pneumatic System Failures
Fault 1 — Air Leaks
Air Leaks — Hissing Sound / Pressure Loss
Symptoms: Hissing at rest or under operation · Drive force progressively weakens · Compressor cycles frequently
Diagnosis by Location
- Foot Pedal Valve: Hissing worsens when pedal is depressed. Cause: worn O-ring on valve spool (NBR material).
- Main Cylinder Seal: Continuous hiss unrelated to operation, from inside lower machine. Cause: piston seal blow-by.
- Fittings / Quick-connects: Hissing at air line joints. Test: apply soapy water — bubbles confirm the leak point.
- Regulator Bleed (Normal): Short, intermittent hiss from the pressure regulator is normal pressure-stabilization — not a fault.
Solutions
- Pedal Valve: Replace O-ring on valve spool (standard NBR size). If valve body is degraded, replace complete pedal assembly.
- Cylinder Seal: Replace Piston Seal Kit. Inspect cylinder bore for rust or scoring — damaged bore requires full cylinder replacement.
- Fittings: Use ISO standard pneumatic fittings. Apply PTFE tape or liquid sealant. Ensure correct torque.
- Prevention: Install a refrigerated air dryer or automatic water trap. 90% of pneumatic failures originate from moisture in the air line.
Fault 2 — Insufficient Driving Force
Weak Drive — Proud Nails / Incomplete Penetration
Symptoms: Nail won't seat in hardwood · Works on softwood only · Gauge reads normal but drive is weak
Root Causes
- Incorrect PSI Setting: Hardwood requires 6–7 bar (85–100 PSI). Softwood uses 4–5 bar. MDF: 5–6 bar.
- Internal Cylinder Leakage: Worn piston rings prevent peak pressure build-up. Machine "moves but is weak."
- Insufficient Air Supply: Compressor tank too small (<50 L), pipe diameter under 6 mm, or shared air line with pressure drop.
- Bottom-Up Resistance: Common in some Chinese-made machines — lower cylinder force is less than upper clamp force, preventing full nail travel.
Solutions
- Adjust Regulator by Material: See PSI Reference Chart below.
- Air Leak Test: Charge to working pressure, shut off compressor, wait 15 minutes. Drop >10% = serious leak requiring immediate repair.
- Upgrade Air Supply: Ensure compressor tank ≥50 L and pipe bore ≥6 mm. Avoid multiple tools sharing one circuit.
- Balance Cylinders: Use "Business Card Test" to verify clamping vs. drive pressure. Reduce upper clamp or increase lower drive as needed.
PSI / Bar Reference Chart by Material
Hardwood (Oak, Maple, Walnut)
6–7
bar · 85–100 PSI
Softwood (Pine, Cedar)
4–5
bar · 60–70 PSI
MDF / Composite
5–6
bar · 72–87 PSI
Business Card Test
Place a business card between the frame and clamp pad. After clamping: can withdraw with effort but not easily = correct pressure. Falls out freely = too low. Cannot withdraw = too high.
03
Join Quality / Corner Issues
The Physics of the Miter Joint
| Layman Term | Professional Term | Technical Explanation |
|---|---|---|
| 45° cut face | Miter Interface | End-grain to end-grain contact — the weakest glue joint in woodworking. End-grain wicks adhesive away (Starved Joint) before it can bond. |
| Glue sucked in | Starved Joint / End-grain Wicking | End grain acts like a straw. Solution: "Sizing" — apply a thin coat, let absorb, apply full coat. |
| Gap in corner | Gapped Miter (Heel or Toe Gap) | Heel Gap = outer corner open. Toe Gap = inner corner open. Diagnosing which type determines whether it's a saw angle or clamping problem. |
| Wood warping later | Wood Movement / Seasonal Expansion | Humidity changes expand wood across the grain. Cross-grain expansion tears the miter joint — not a glue failure. |
Fault 1 — Top Open (Gap at Face / Glass Side)
Top Open — Face Side Has Visible Gap
Back side tight · Front (glass face) has a V-gap · Fingertip detects raised step
Root Causes
- Insufficient Vertical Clamping: V-nail recoil lifts the moulding. Top Pad pressure too low to counteract.
- Pad Positioning Error: Top Pad not directly above the nail insertion point — lever effect tips the corner up.
- Saw Angle <45°: Even 0.1° × 8 corners = visible accumulative gap.
- Moulding Warp / Twist: Pad cannot achieve even contact across a bowed profile.
Solutions
- Increase vertical cylinder pressure; validate with Business Card Test.
- Reposition pad directly over the V-nail entry point. Closer to Rebate = better leverage.
- Switch to L-shaped pad or triangular felt pad for irregular profiles.
- Recalibrate saw angle using precision machinist square. Detent adjustment required if deviation >0.1°.
Fault 2 — Bottom Open (Gap at Back Side)
Bottom Open — Gap on Back / Wall Side
Front tight · Back has gap · Opposite of Top Open
Root Causes
- Saw Angle >45°: Obtuse inner angle — primary cause of bottom-open gaps.
- Fence Not Square: Left/right fences not at precisely 90° to each other causes angled seating.
- V-Nail Position Too High: Nail near Rebate causes moulding to pivot outward ("kicking foot").
- Debris Build-up at Fence Corner: Sawdust prevents moulding from seating fully against the fence.
Solutions
- Re-calibrate miter saw detent. Verify with digital angle gauge.
- Check fence perpendicularity with precision square. Adjust cam bearings or lock nuts.
- Move first nail toward outer edge of frame (away from Rebate). Outer nail acts as pivot, pulls inner seam closed.
- Clean fence corner with brush or compressed air before every session.
Fault 3 — Corner Misalignment / Step
Corner Misalignment — Surface Step / Height Difference
Two moulding surfaces not flush · Tactile step at seam · Visible offset line
Root Causes
- Moulding Warp / Twist (most common): Profile itself has bow or cupping. Batch-to-batch thickness variation also contributes.
- Hard Pad Material: Rigid rubber pad cannot conform to slightly curved profiles — creates uneven pressure.
- Hold-down Pressure Imbalance: Top Clamp and Front Clamp pressure not matched, causing drift.
- Thickness Variation Between Batches: Tolerance >0.2 mm between lengths in the same frame set.
Solutions
- Visually inspect moulding for straightness before cutting. Reject severely warped lengths.
- Replace hard rubber pad with triangular felt pad or adaptive silicone pad.
- Validate both Top and Front clamp pressures independently with Business Card Test.
- Use moulding from the same production batch per frame. Target thickness tolerance ≤±0.2 mm.
04
Precision Cutting Systems
Fault 1 — Blade Runout & Deflection
Blade Runout / Wobble — Wavy Cut Surface
Rippled cut face · Inconsistent kerf width · Vibration on hardwood cuts
Root Causes
- Flange Planarity (primary cause): Mid-range saws use stamped flanges (not machined). Face runout >0.05 mm causes visible wobble.
- Arbor Bearing Play: Worn bearings reduce radial stiffness. Irregular chatter marks on cut surface.
- Blade Plate Quality: Uneven blade plate or loose arbor hole fit.
- Mounting Debris: Sawdust or glue residue on flange face adds eccentric thickness.
Solutions
- Measure flange face runout with a Dial Indicator. If >0.05 mm, grind or replace flange. Best: machined stainless steel stabilizers.
- Test bearing play: rock the blade by hand. Detectable slop = end-of-life. Replace with hydraulic press and FAG/SKF industrial bearing.
- Choose blades with laser-cut stabilizer vents and polymer-filled plates to reduce resonance.
- Clean flange surface every blade change. Use torque wrench for lock nut — not hand-tight.
Fault 2 — Chip-out / Tear-out
Chip-out / Tear-out — Splintered Cut Ends
Wood fibers blow out at cut end · Top or bottom surface shows splintering · Moulding cannot be used directly
Root Causes
- No Zero Clearance Support (primary): Factory throat plate opening is too wide — fibers have no back support at the cut point.
- Positive Hook Angle Blade: Forward-raking teeth pull fibers upward rather than shearing them cleanly.
- Feed Rate Error: Too fast = tearing; too slow = burning from friction.
- Dull Carbide: Worn teeth tear instead of cut — chipping signature changes from clean to ragged.
Solutions
- Zero Clearance Insert (ZCI): Make a custom insert from phenolic or quality plywood. Gap between insert and blade: <0.5 mm. 100% fiber support.
- Sacrificial Fence: Attach MDF strip to fence back face. Provides zero-clearance rear support and captures small offcuts from the dust port.
- Switch to Hi-ATB, -5° to -7° negative hook angle blade for fine cross-cutting.
- Have carbide re-sharpened by specialist every 500–1000 m of cutting. Maximum 5–8 resharpen cycles per blade.
Blade Geometry Selection Guide
| Grind | Full Name | Best Use | Chip-out Risk |
|---|---|---|---|
| Hi-ATB | High Alt. Top Bevel | Ultra-fine wood cross-cut. Standard for professional framing. | Lowest |
| TCG | Triple Chip Grind | Aluminium, plastics, hard composites. Only choice for double miter saws on metal. | None (designed for it) |
| ATB | Alternate Top Bevel | General purpose. Less precision than Hi-ATB but longer-lasting. | Low–Medium |
| FTG | Flat Top Grind | Ripping with the grain. Not suitable for cross-cutting frames. | High |
Fault 3 — Dust Management & Extraction
Factory dust bags on all miter saws are widely regarded as ineffective. A systematic retrofit is required for professional workshop air quality.
- Shroud Aerodynamic Flaws: Passive 2.5" collection ports cannot capture high-velocity ejected particles.
- CFM vs. Static Pressure Mismatch: Adequate volume but insufficient static pressure to draw dust through long or bent ducting runs.
- Single-Point Limitation: One port cannot cover the full cutting zone — blade top and sides eject freely.
Retrofit Solutions
- Big Gulp Hood: Funnel-shaped collector mounted behind the saw, connected to ≥100 mm (4") duct. Captures escaping particles at low air velocity.
- Dual-Point Extraction: (1) High-static-pressure extractor directly at blade guard (Festool CT or equivalent). (2) High-CFM rear downdraft unit behind the saw for escaped dust.
- Rigid Duct Only: Avoid flexible hose — each 90° bend = equivalent friction loss of 2 m straight duct. Minimum duct diameter: 100 mm.
- Air Curtain (Advanced): Compressed air nozzle creates an air curtain directing fine dust toward the collection port. Requires precise directional tuning.
Double Miter Saw — Industrial Specific Faults
| Fault | Root Cause | Solution |
|---|---|---|
| Open Miters | Insufficient pneumatic clamping pressure or timing mismatch — workpiece moves at the moment of blade contact before clamping is complete. | Set cylinders to 6–7 bar. Verify solenoid valve timing: clamping must complete before blade engagement (Stage 1 = Clamp, Stage 2 = Cut). |
| Chatter Marks on Aluminium | Feed rate instability from oil dashpot (hydraulic damper) — low fluid level or trapped air causes irregular blade advance. | Check hydraulic oil level in dashpot. Bleed air from hydraulic system. Adjust damper valve to achieve smooth, consistent feed. |
| Length Deviation | Thermal expansion of scale bar. Parallax reading error. Mechanical wear in stop positioning. | Install Digital Readout (DRO). Calibrate at stable ambient temperature. Note: aluminium expands ~0.024 mm/m per 10°C — factor into production planning. |
05
Maintenance SOP
Every Day Before Operation
- Air tools (no auto-oiler): 2–3 drops ISO VG 32 / SAE 10W non-detergent oil into inlet port.
- Slides & rails: White Lithium Grease on all metal-to-metal sliding surfaces.
- Never use WD-40 on pneumatic parts — degrades O-rings over time.
- Do not over-oil — excess mist contaminates timber.
Every 5,000 V-Nails
- Disassemble Distributor Block completely.
- Dissolve glue residue with IPA or specialist cleaner. Soft brush + compressed air. No-lint cloth to dry.
- Inspect rubber seals for hardening or cracking.
- Check driver blade tip for burrs or chipping.
Daily (Filter) · Monthly (Full)
- Filter: Drain condensate daily. Replace element when discolored yellow. Clean monthly.
- Regulator: Verify pressure reading and exhaust port function. Check accuracy of gauge.
- Lubricator: Maintain 1/2–3/4 full. Verify drip rate: 1 drop per 10–20 cycles.
Monthly or on Fault
- Charge to working pressure. Shut compressor. Wait 15 min.
- Drop <5%: Normal wear — acceptable.
- Drop 5–10%: Inspect O-rings on pedal and fittings.
- Drop >10%: Serious leakage — stop production and repair immediately.
Before Every Use
- Visual: check for chipped teeth, cracks from arbor hole outward.
- Clean resin/adhesive with specialist blade cleaner or alkaline solution — soak 10–15 min, soft brush, rinse, dry fully.
- Never use steel wire brush on carbide teeth.
- Sharpen every 500–1000 m cut. Max 5–8 resharpens per blade life.
Quarterly or on Fault
- Saw 45° angle: Verify with machinist square. Adjust detent. Target deviation <0.1°.
- Fence 90°: Confirm fence-to-blade perpendicularity. Adjust lock nuts. Both fences must be precisely 90° relative to each other.
- Underpinner pressure: Business Card Test on all clamping axes independently.
- Underpinner fence: Precision square check. Adjust fence fixing screws.
Fault Diagnosis Decision Tree
Underpinner Sequence
Underpinner — Step-by-Step Fault Isolation
1
Audible hissing at rest or during operation?
Yes → Air leak fault. Check foot pedal valve, cylinder seals, and fittings (Module 2). No → Continue.
2
Does the cylinder actuate (mechanical action audible)?
No → Check air pressure, foot pedal, solenoid valve. Yes → Continue.
3
Does a nail eject?
No → Pusher mechanism failure or wrong nail size (Module 1, Fault 2). Yes → Continue.
4
Does the nail fully penetrate?
No → Insufficient pressure or worn driver blade. Increase PSI, check blade for burrs. Yes → Continue.
5
Does the corner have a visible gap?
Top open → Clamping pressure or pad position (Module 3). Bottom open → Saw angle or fence (Module 3). Step/offset → Moulding warp or pressure imbalance.
06
Brand-Specific Guide
Cassese
France · Precision Underpinner
Models: CS88 · CS299 · CS-299M XL
Smart Wedge Cartridge vs. Uni-wedge — consumables are NOT interchangeable between series. Confirm model before ordering.
Hammer Stuck Down = degraded Return Spring inside pneumatic cylinder or worn Bumper rubber. Disassemble cylinder to inspect.
Glue residue on Wedge Distributor is the most common fault. IPA cleaning every 5,000 nails.
CS88 O-rings: solenoid valve O-rings are universal NBR industrial components — source locally if OEM parts unavailable.
Pistorius
USA · Heavy Industrial
Models: MN-200 Double Miter · VN Series
Company defunct — but machines remain in service. Source electrical relays from Grainger / McMaster-Carr as universal replacements.
Arbor Runout on MN-200: first check is Arbor Bearing play. Replacement requires hydraulic press. Use FAG or SKF industrial-grade bearings.
Pneumatic Hold-down Diaphragm Rupture: source Parker or Festo equivalent diaphragm by dimension — not OEM part number.
Fence Scale Calibration drift after bearing replacement is normal — re-verify with machinist square after every major service.
Fletcher-Terry
USA · Manual Cutting
Models: 3000 · 3100 · Point Driver
Curved cutting line: inspect Plastic Bushings / Wear Pads inside cutter head — worn pads introduce Lateral Play and must be replaced.
Rocker Head wobble indicates worn bearings in the head pivot assembly.
Glazier Points vs. Framer Points: these are physically distinct — do not substitute one for the other.
Running Rail damage (scratches, glue) causes cutting line inconsistency. Clean rail surface monthly.
Alfamacchine / AMP
Italy / USA · Modern Standard
Models: U300 · U400 · Minigraf 4
Nail bending mid-insertion: Driver Blade alignment error or V-nail Block clogged. Confirm hammer strikes nail dead-center.
Vertical Clamp Pad Slippage: worn pad face or insufficient pressure. Replace pad and retest with Business Card Test.
V-Nail Driver Blade (L-type or flat) is a high-frequency wear part — stock spares on-site to avoid production downtime.
Joystick control (NN-series high-end): pneumatic logic fault — check solenoid valve sequence before assuming electronic failure.
Morso
Denmark · Foot Chopper
Models: Model F · Classic
Not suited for high-volume production or very hard woods (Maple, Oak) — sustained hardwood cutting wears Head Travel Guides rapidly.
Worn Head Travel Guides produce "Banana Cut" (curved miter face) — inner corner gap that no amount of clamping will correct.
Hollow Ground Blades produce glass-smooth cut faces — worth the premium for visible joinery. Scalloped Blades for shaped / ornate profiles.
Glue residue on blade degrades cut quality noticeably — clean blades after every session.
07
Professional Communication
Expert Communication Scripts
Scenario 1 — "My machine is jamming"
"Please check whether there is Glue Build-up inside the Distributor Block — specifically in the return channel of the Driver Blade. Sawdust mixed with hardened adhesive increases friction significantly. I recommend disassembling and cleaning with IPA solvent, then inspecting the blade tip for any Burr. Also confirm you haven't recently switched V-nail brands — mixing brands is the second most common jam cause."
Professional Response vs. "clean the gun head"Scenario 2 — Corner Gap Complaint
"To diagnose accurately I need to know: is it a Top Open (gap at the glass face) or a Bottom Open (gap at the back)? Top open usually indicates insufficient Vertical Clamping Pressure or Pad Positioning — run the Business Card Test to verify. Bottom open points to a saw angle greater than 45° or a Fence Square issue. These have completely different fixes."
Structured diagnosis vs. "check your saw"Scenario 3 — Evaluating a Used Underpinner
"Before purchasing, run these four checks: (1) Inspect the Hammer Driver tip for bending — this is the most expensive wear part. (2) Perform an Air Leak Test — charge to working pressure, isolate the compressor, wait 15 minutes. Pressure drop should be under 5%. (3) Check Pedal Response — there should be no detectable delay. (4) Bring a straightedge and verify Table Flatness — a warped table prevents square corners regardless of any other setting."
Systematic evaluation vs. "let's try it out"Scenario 4 — Addressing "Chinese machine" Concerns
"Our machines use Open Architecture with Universal Wedge Standard — you source V-nails locally without proprietary lock-in. The Driver Blade is a designed Sacrificial Part that protects the cylinder assembly — and replacing it takes under 5 minutes on our machines versus complex disassembly on some European models. All fittings are ISO standard, which means O-rings and connectors are available at any industrial supplier. We back every machine with complete technical documentation, video training, and 24-hour remote support."
Technical confidence vs. generic reassuranceLayman → Professional Terminology Swap
| Layman Term | Professional Terminology |
|---|---|
| Blade wobbles | Runout (Axial / Radial) / Deflection |
| Cuts crooked | Blade Walk / Alignment Deviation |
| Rough / splintered edge | Tear-out / Splintering / Chip-out |
| Dust everywhere | Poor Extraction Efficiency / Particulate Containment |
| Blade is dull | Carbide Degradation / Edge Retention Failure |
| Angle is off | Detent Slop / Miter Calibration Drift |
| Leaking air | Pneumatic Integrity Breach / Air Circuit Failure |
| Nail didn't go in | Driver Blade Jam / Misfire |
| Something loose / rattling | Mechanical Play / Backlash |
| Part discontinued | Obsolete Component / Legacy Part |
| Not enough pressure | Insufficient PSI / Regulator Drift |
| Corner has a gap | Gapped Miter / Heel Gap / Toe Gap |
| Corner is uneven | Step / Corner Misalignment / Offset |
08
Advanced Theory & Wood Science
Joint Reinforcement Methods
| Method | Key Terms | Best Application | Notes |
|---|---|---|---|
| V-Nail / Underpinning | Mechanical Fastener · Clamp-while-cure · Spring-back Prevention | Standard production framing — all profile types | Not just a nail — provides mechanical clamping while adhesive achieves full cure strength. Critical for warped mouldings. |
| Splines (Hidden) | Blind Spline · Kerf · Floating Tenon | Narrow or heavy solid wood frames requiring extra tensile strength | Spline thickness must match blade kerf exactly. Invisible from exterior. |
| Exposed Spline | Keyed Miter · Decorative Spline | High-end custom frames with decorative corner accent | Use contrasting species for visual effect. Requires table saw jig. |
| Biscuit / Domino | Floating Tenon · Shear Strength · Registration | Very wide frames, heavy mirrors, canvas floaters requiring alignment | Domino provides superior shear resistance. Biscuit primarily for surface registration. |
Adhesive Chemistry Guide
| Adhesive | Type / Grade | Best For | Key Property |
|---|---|---|---|
| PVA Type II (Yellow Glue) | Polyvinyl Acetate · Moisture Resistant | Standard timber frames — industry default | Must have visible squeeze-out (溢胶) along full joint line. No squeeze-out = Starved Joint. |
| PVA Type I | Waterproof grade | Bathroom mirrors, exterior frames | Higher water resistance. Longer open time than Type II. |
| CA Glue + Activator | Cyanoacrylate · Instant Bond | MDF mouldings, rapid production | MDF acts like a sponge — CA outperforms PVA on MDF by preventing wicking. Activator gives instant structural bond. |
| Epoxy | Two-part structural | Oily woods (Teak, Rosewood), maximum strength joints | PVA cannot bond oily grain — epoxy penetrates regardless. Use when frame must bear significant load. |
Master Craftsman Techniques
Burnishing — Closing Hairline Gaps Without Filler
When a corner shows a near-invisible gap, use the round shaft of a screwdriver to firmly burnish (rub) along the miter seam. The compression forces wood fibers into the gap and visually closes it without any filler material. Works best on softwoods and painted profiles.
Coloring the Cut — Hiding Glue Lines
On dark-stained or ebonized frames, raw end-grain on the miter face will show as a light line after gluing. Apply a matching paint or spirit marker to the raw miter cut surface before applying adhesive. This pre-colors the end-grain so any micro-gap reads as shadow rather than a white glue line.
Protecting the Rabbet — Glue Contamination Prevention
Squeeze-out adhesive flows directly into the Rabbet (glass channel) during V-nail firing. Hardened glue in the Rabbet prevents glass from seating correctly. Keep a damp cloth or purpose-made silicone chisel at the machine — wipe the Rabbet corner immediately after each firing, before the glue begins to skin over.
Sizing End-grain for Stronger Glue Joints
To overcome end-grain wicking, apply a thin "sizing" coat of diluted PVA (50% water: 50% glue) to both miter faces. Allow 60 seconds for absorption. Then apply full-strength glue and join immediately. The sizing coat seals the capillary pores, preventing the working glue from being absorbed before it can bond.
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