COMPASS AH-3 / AH-3T Arch Hold Downs

A Woodworking Hold Down You’ve Never Seen Before!

Almost every woodshop has some Hold Downs (or Holdfasts) because they are essential to secure the workpieces in place for safe operation. Hold Downs have been around for centuries, but most of them still need to be satisfactory. One of the flaws of the regular hold downs is that they are designed in deformable Cantilever Structures. When holding force is applied, the clamping point will produce excessive tilting displacement due to the bending deformation of the structure, which obviously will undermine the holding security and damage the workpiece surface. In addition, because of the overturning bending moment under loading, the hold down pillar shaft continuously damages the workbench dog holes. So it has been Harvey’s aspiration to design a better hold down for woodworkers.

Zhaozhou Bridge - built from 595 to 605 AD

Pont du Gard - built in the first century BC

Rialto Bridge - built in 1591

Patent Notice: This product is protected by one or more patents in certain jurisdictions.

Famous Arch Structure Over the World

Inspired by the ancient wisdom of Arch Building Structures, Harvey team came up with a completely new structural design for hold downs, called AH-3 Arch Hold Down. With the unique “Arch” shaped frame, the AH-3 is able to firmly hold workpiece down with no tilting deformation.

And it features a balancing leg which provides adaptive full balance to the working leg to eliminate any overturning moment on the pillar shaft. Also its innovative “Quick-Release Pressure Knob” and “Toolless Workbench Installation Mechanism” allow you to clamp your workpiece ideally with joy!

Besides the AH-3 Arch Hold Down, Harvey also created the AH-3T model – the version for T-slots mounting application.

The Mechanical Benefits

of the Arch Structure

By nature, an ideal Arch Structure is a pure compression mechanical form. When a vertical force is applied on its Crown Point (the highest point), the Arch will resolve the load into compressive stresses, and thereby eliminate tensile stresses. This miraculous property gives the structure a great deal of mechanical advantage over a beam structure (especially cantilever structure) , because the Arch can minimize the deformation.

Stress Analysis of the Arch

Stress Analysis of the Arch

Owing to the unique Arch structure, the AH-3(T) hold downs are able to securely clamp the workpiece in place (with pure vertical pressure) without pressure deformation and overturning moment on the pillar shaft, thus achieving the highest stability.

Adaptive Balancing

Applicable for thin workpiece

Because of the balancing leg of the AH-3(T) and the mechanical nature of the Arch, clamping force on the working leg will be always automatically balanced without transferring any bending moment to the pillar shaft, no matter what the thickness of workpiece is.

Applicable for thin workpiece

Infinite Clamping Force

The pressure applied by the Arch Hold Down can be easily adjusted to the proper amount by simply rotating the pressure knob. The maximum downward force applied by the Arch Hold Down can be as great as 1100N (246 lb) which is sufficient in most cases.

Quick-Release Pressure Knob

The pressure knob of the AH-3(T) hold downs is equipped with a Quick-Release Button to allow you quickly releasing the clamping force.

By pressing the quick release button, you don’t have to take the time to unscrew the knob when you need to release the hold down force, and the knob will glide to anywhere you like along the pillar shaft.

Toolless Workbench Installation System

(AH-3 Version)

To eliminate the hassles of hold down installation on a workbench, Harvey developed a unique “Toolless Installation Mechanism” on the bottom of the Pillar Shaft. So when using the hold down, you simply insert the pillar shaft into a dog hole, the latch on the end of the shaft will automatically flip over (by off-center gravity) when it passes the bottom of bench top.

Insert the Toolless Installation Mechanism through the workbench hole.

Secure the Arch Hold Down while the mechanism is latched to the underside of the workbench.

By turning the installation knob, you can easily lock the pillar shaft firmly between the upper and bottom surfaces of the bench top without touching the dog hole, and the pillar shaft is perfectly perpendicular to the bench top surface.

When removing the hold down, what you need is to unscrew the installation knob, the shaft latch will automatically retract (under gravity), and you can easily pull out the pillar shaft to remove the hold down. This smart and tricky mechanism makes the AH-3 a lot of fun to use!

Applicable Workbenches

The AH-3 Arch Hold Down can be installed on any workbench with dog hole diameters of 3/4" to 13/16" (19mm – 20.6mm) and bench top thickness from 2" up to 6" (51mm – 152mm).

T-slot Installation

(AH-3T Version)

The AH-3T Arch Hold Down is designed to be installed on the surface of various equipment containing T-slots which are commonly found on sliding tables & sliding table saws. The AH-3T Hold Down comes with a T-slot Locking Block which has two sectional dimensions that can be used for different T-slot installation.

The AH-3T is compatible for installation of the following two T-slot section dimensions:

To ensure proper fitment, compatible T-slot dimensions are as follows:

T-Slot Top Width: 15.5mm (5/8” in.)

T-Slot Height: 13mm (1/2” in.)

T-Slot Bottom Width (Cross Section 1): 30mm (1-3/16” in.)

T-Slot Bottom Width (Cross Section 2): 20mm (25/32” in.)

NOTE: AH-3T Arch Hold Down will NOT fit standard 3/4” T-slots

Structure Design,

Materials and Workmanship

Like any other Harvey products, the AH-3(T) Arch Hold Downs are designed with deep considerations ofFunctionalities, Reliabilitiesand User-experiences.

The structure is made of CNC machined 6 series Aluminum Alloy with beautiful anodizing and Polished Stainless Steel.

The two supporting feet are fitted with polyurethane drum shaped protection for minimum surface pressure and optimized friction grip.

To enhance the working experience, Harvey team designed a polished egg shaped Palm Rest on top of the pillar shaft, so that your hands can rest on the silky smooth surface for pleasure.

All in all, the AH-3(T) Arch Hold Downs are dedicatedly crafted just to make sure you will like woodworking even more. Thanks for the interest!

Specifications