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Semi-Automatic Underpinner

 Product Number: 178650001CE

The U-300 is a bench-top, frame joining machine and the most popular model of custom frame shops. It is compact, well constructed, and built for many years of trouble free operation. The design of the U-300 allows the operator to set the front and back measuring stops for V-Nail insertion. The frame is then moved across the nail head and V-Nails are driven or stacked anywhere along the frame joint. The V-Nail insertion is actuated through the use of a pneumatic pedal.

Former Model Reference - Alfamacchine – M3

Purchase Package
  U-300 Purchase Package
(1) 7mm Nail Head
(1) 10mm Nail Head
(1) 12mm Nail Head
(1) Single Vertical Positive Placement Clamp
(1) Magnetic Base of Clamp Assembly
(1) Single Metal Pressure Plate
(1) Blue Rubber Pads (SW)
Yellow Rubber Pads (MW)
(1) Black Rubber Pads (HW)
(1) Round Pressure Pad (Felt)
(1) 4mm Allen Wrench
(1) 5mm Allen Wrench
(1) Front Horizontal Clamp
(1) Machine manual
Power Requirements

Compressed Air 4NI at 5 Bar

CE Compliant

Replacement Parts & Accessories


Replacement Clamping Pads


397100003 Blue Replacement Rubber Pad (recommended for SW)
397100002 Yellow Replacement Rubber Pad (recommended for MW)
397100001 Black Replacement Rubber Pad (recommended for HW)


Replacement Nail Heads

394950010 Nail Head – 3mm
394950060 Nail Head – 5mm
394950020 Nail Head – 7mm
394950030 Nail Head – 10mm
394950040 Nail Head – 12mm
394950050 Nail Head – 15mm


Extension Wings

291650010 Extension Wings Kit



P/N Description
240450030 Floor Stand Option
244120130 Magnetic Base for Clamp Assembly
298390370 Single Vertical Positive Placement Clamp
397100005 Magnetic - Single Metal Pressure Plate
242230010 Round Pressure Pad, Felt
242230040 Round Pressure Pad, Vulkolan
243160020 Adjustable Fence -2 Knobs
375600010 Fixed Fence - 120°
375400010 Fixed Fence - 135°
243180010 Fixed Fence - 90°
242170010 Frontal Clamp


Extension Wings accessory for large frame joining  U300-Sq-UpFrameinMachneFinal.png

Sales & Technical Documents
U300 1.png                                     U-300 AlfaA4 Sellsheet1-9-15.jpg 


- Italian Version

U-300 Literature

- Italian Version
- Spanish Version

- French Version
- German Version




Unique Performance Features

  • Features pneumatic loader to eliminate nail jams
  • “Soft Clamping” pneumatic feature for damage free joints
  • Quick-change, magnetic pad hold down feature fitting most moulding profiles
  • Small table-top footprint needed – 12” (305mm) wide x 19” (483mm) length x 14” (356mm) high
  • Operates only with pneumatic air, no electrical hook-up needed
  • Dual function foot pedal for separate control of mould clamping and V-Nail insertion
  • Designed with a unique, trouble free piston V-Nail driver block-blade system for years of dependable single and multi-stacking operations

Frame Joining Capabilities

Moulding Width
(min to max)

Moulding Height
(min to max)

Max Distance
Between V-Nails

¼” up to 3 3/4”
(6-60 mm)

¼” up to 3 ¼”
(6-80 mm)

3 1/4” (80 mm)

Pre-set V-Nail
Position Stops

V-Nail Sizes

V-Nail Channel


5, 7,10,12,15 mm

220 V-Nails/channel

Machine Dimensions & Weight

Width 300mm (11 ¾")
Length 485mm (19")
Height 456mm (18")

32kg. (70lbs.)

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