Hydraulic Ledge Clamps

Hydraulic Ledge Clamps are separated into single clamps and double clamps with the single clamps taking up a single T-slot (Models 425 and 428) and double clamps taking up two slots (Models 126 and 128).   Double clamps provide for significant force at 22,000 lbf and 26,000 lbf respectively, however distance between slots is specifically 12 inches and cannot be changed.  For large retrofit applications and medium force applications is it typical to use multiples of the single T-slot clamps Model 425 at 8,000 lbf clamp force and Model 428 at 10,000 lbf clamp force.

The “Locked” designation (L) is added to the model number for the Locking screw that can be used to secure the clamp in position so Hydraulics can be removed during stamping.  Locking clamps are commonly referred to as Hydra-Mechanical Clamps (HM) as they are hydraulically clamped and mechanically locked.  Units are also available with a handle to make moving the clamps easy for operators.

After selecting the model and Locking/Handle options, the clamp part number is built up based on the model number and then the clamping plate height or clamp height (CLH) and T-slot size.  The clamping height is sized in ¼” increments for the small clamp heights and ½” increments above 2.00”.  Note that these types of clamps are designed to clamp on a plate height that is fairly consistent as the clamping stroke of the clamp is designed to accommodate variations in T-slot to T-Nut gap and some gap to slide the clamp into position.  Fundamentally these are not adjustable clamp height clamps.  See Nut Clamps or Adjustable Rocker Clamps for clamps designed to accommodate moderate variations in clamp plate thickness.

For selecting the appropriate components to achieve catalog clamping height (CLH), PFA assumes standard JIC T-Slot dimensions to fit the T-Slot and typically Neck height is assumed as .750” for 5/8” slot, .875” for 3/4” slot, 1.000” for 1” slot).  See the specific Rocker Clamp User Guideand/or Specification Drawing for details on recommended gaps and heights.

Standard Configurations

		Model 425	Model 425L	Model 428	Model 428L	Model 126	Model 126L	Model 128	Model 128L
Clamping Force at 5,000 PSI		8,000 lbs.		10,000 lbs.		22,000 lbs.		26,000 lbs.
T-Nut Spacing		N/A		N/A		6”		6”
A		4.25” no handle 4.50” with handle		4.25” no handle 4.50” with handle		12”		12”
B**	CLH* .50” .75” 1.00” 1.25” 1.50” 1.75” 2.00” 2.50” **	No Lock 2.75” 2.75” 2.75” 3.00” 3.25” 3.50” 3.75” 4.25” **	Lock (L) 4.25” 4.25” 4.25” 4.50” 4.75” 5.00” 5.25” 5.75” **	No Lock 3.75” 3.75” 3.75” 3.75” 4.00” 4.25” 4.50” 5.00” **	Lock (L) 4.25” 4.25” 4.25” 4.25” 4.50” 4.75” 5.00” 5.50” **	No Lock 2.75” 2.75” 2.75” 3.00” 3.25” 3.50” 3.75” 4.25” **	Lock (L) 4.25” 4.25” 4.25” 4.50” 4.75” 5.00” 5.25” 5.75” **	No Lock 3.75” 3.75” 3.75” 3.75” 4.00” 4.25” 4.50” 5.00” **	Lock (L) 4.25” 4.25” 4.25” 4.25” 4.50” 4.75” 5.00” 5.50” **
C		Jaw Opening to Match CLH* + .18” gap		Jaw Opening to Match CLH* + .18” gap		Jaw Opening to Match CLH* + .18” gap		Jaw Opening to Match CLH* + .18” gap
D		4.00” no handle 7.25” with handle		4.75” no handle 7.25” with handle		4.00” no handle 7.25” with handle		4.75” no handle 7.25” with handle
E		.88” Max.		1.14” Max.		.83” Max		1.12” Max.
Weight (approx.)		8 lbs.		12 lbs.		25 lbs.		35 lbs.

*CLH= Clamping height – Nominal Clamp Plate Thickness based on clamping plate being within 0.030” of nominal. Clamp plate may be thicker than CLH as desired but less than the 0.18” total gap available. Clamps are provided with “C” open dimension, which is the CLH + 0.18” gap to allow for an option of .090” die lifter rail clearance and .060”-.090” air clearance for moving clamp in and out of position – allows lifting and moving dies under open clamps if necessary. Difference between C dimension and Actual Clamping Height should not exceed 0.18” which is 1/2 of the 0.36” total stroke of the clamp. Clamping height is also based on standard JIC T-Slot dimensions for T-nut sizing. T-Slot dimensions are typically neck height .875” for 3/4” slot and 1.00” for 1” slot.

** B = Product Height Dimension is related to clamp height needed for clamp plate thickness. Stock sizes listed, but others are easily available. Allow 1/2” more for nominal variations.

***Handles (H) available on all models. Contact PFA for details.

Example: 8,000 lb. die. Use 8,000 clamp such as Model 425, clamp plate thickness (CLH) is 1.0” and has 3/4 T-Slot.
Locking (L) and Handle (H) are added directly after the main model number. Examples are 425, 425L, 425H and 425LH.

• RC-425 / RC-425L (Hydra-Mechanical, Locking)
• RC-428 / RC-428L (Hydra-Mechanical, Locking)
• RC-126 / RC-126L (Hydra-Mechanical, Locking)
• RC-128 / RC-128L (Hydra-Mechanical, Locking)

Rocker Clamp Installation and Gap Set Video

Ledge Clamps are moved into position with the lower body stop set against the die plate (gaps between clamp and die/slot allow movement) or may be permanently mounted on one side to act as a side stop. When hydraulic pressure is applied, the clamp nose moves downward onto the plate, clamping the die. Hydraulic pressure is maintained during operation, or the Locking Nut (L style) is engaged to allow removal of clamp hydraulic pressure during stamping. To unclamp, hydraulic pressure is removed and clamps open under internal spring force. (Note: Reapplication of hydraulics is required to unlock the Locking Clamps (L) prior to releasing pressure and unclamping).

Using a bench top setup and RC-425 Rocker Clamp, initial fit of rocker clamps to the press bolster is discussed, including T-nut interface, clamp bolting, running gap, and base plate and nose piece shims for proper clamping height.

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