H-Frame Hydraulic Press

Copyright © 2007 Dave Propst. All rights reserved.

Revised 8/22/2007

Introduction

This article describes a shop-built, multi-purpose, H-frame press.

Much more than just a tool to 'press' parts together, most any press can be used for a multitude of purposes. This particular press is used virtually every day for a variety of tasks from doing mechanical work to straightening or intentionally bending structural components. It is also used to take force related measurements such as spring rates of coil and leaf springs, and, deflection or yield strength testing of structural materials or assemblies.

Design

Consider what occurs in a press as the ram moves toward the workpiece during the task of straightening a bent beam, tube or shaft of some sort. First the ram closes the gap and contacts the workpiece. It might be assumed that the ram then applies a progressively greater amount of force to the workpiece until it yields and bends. That is true. That is what occurs, but, that certainly is not all that occurs. It is more complex than that. In a press of typical construction, as the ram contacts the work, ram force and travel is 'lost' to other things. The connections (usually by pins-in-holes) between the frame's cross-beams and its upright members have clearances or slack that must be taken up. Some ram force and travel is required to lift the upper cross-beams until its connections, whatever they may be, are well seated. As that is occurring, the ram-to-cross-beam mounting may consume even more ram travel. This can be caused by two factors-- clearance from either wear or design issues and deflection caused by mounting components that are too light relative to ram capacity. Also some amount of ram force and travel is required to push the lower cross beams down until pins are well seated into their respective holes to a degree greater than what gravity alone acting on the weight of the lower cross-beams can provide. Finally, as play in the frame is taken up, the ram force begins to cause deflection of the cross-beams themselves. The motion that occurs in taking up play causes wear. As more wear occurs, even more motion occurs. It is an endless cycle.

Depending on how much use the press has seen, other frame motions can occur as well. For example, as some press frames wear from motion, they don't wear evenly or symmetrically. They develop a tendency to parallelogram or even to twist or 'wind up' while being loaded by the ram. This tends to cause lateral motion at the ram-to-workpiece interface. The starting location of the ram on the workpiece is not where the ram ends up on the workpiece as the push or stroke occurs. This is all compounded if the frame is not bolted to the shop floor in such a way as to help resist motion.

In a loose-framed press, all of this above mentioned frame motion, and the ram force used in producing it, is counterproductive to many tasks done in a press. To explain... the term 'lost' as used above is just a figure of speech. Technically ram force applied to a workpiece is never actually lost in any press. It all gets applied to the workpiece eventually one way or another. However, the problem is that in a loose press it is difficult to tell what is deflection or clearance take-up in the framework of the press and what is actually a desired change occurring to the workpiece during a straightening or pressing task. Returning to the example of what occurs as the ram moves into the workpiece during the task of straightening a bent beam, tube or shaft of some sort... Working with a press frame that has a lot of motion in addition to beam deflection, it is very difficult to develop a feel for when or if the workpiece is beginning to deflect and when or if that deflection proceeds into actual plastic deformation of the workpiece. In fact if the workpiece is of relatively low yield strength in comparison to the press structure itself, the workpiece may well yield before all of the slack in the frame is taken up. This condition can make for a very touchy and frustrating task of straightening an object. The tendency is to go too far, bend the workpiece past 'center' and bow it in the opposite direction.

Many features that are normally of fixed position on commercially available presses of this size are, on this press, adjustable. When first set up, this adjustability was a way to allow extensive experimentation with different settings in order to arrive at a basic configuration that suits the majority of tasks the press is used for. Then once the press was 'in service', having all aspects of the press adjustable allows it to be used for specialized tasks that are more typically performed on the floor, workbench, or frame machine with the assistance of jigs, jacks, Porta Power, etc.

This adjustability is not achieved at the expense of rigidity or with the addition of 'play' in connections however. Quite the contrary, this frame is very solid because of the heavy bolted connections. Most adjustable components are held together by heavy duty reinforced mating surfaces, heavy threaded fasteners, and very precise diameter holes. This instead of the slip-fit pin connections found in a typical press. The reason for threaded versus slip fit connections is obvious-- less undesired movement of the frame and no need for supplemental bracing of the frame structure. To explain these two points of movement and bracing:

1) If the crossbeam-to-upright connections are of precise enough clearances and clamped together with enough force, no motion will occur in those connecting joints. That in turn means much less ram travel is consumed in taking up clearance. And... if little or no motion can occur in connecting joints, no wear will occur in those components-- wear that would result in even greater ram travel as the press ages. Thus the only motion of any consequence to contend with is deflection of the cross-beams. That cross-beam deflection, at the loads this press sees, is minimal in comparison to the motion of loose connecting joints in many press frames. Consequently, a very rapid and linear ramp-up of force against the workpiece occurs in this press, and, that will not change over time. The frame will not 'wear out'.

2) If the crossbeam-to-upright connections are strong enough and rigid enough, no supplemental bracing between uprights (as seen on most all commercial presses) will be required. If there is no bracing, there is nothing to interfere with end loading.

This rigidity, strength and lack of play in the framework as supplied by the bolted construction is the single greatest priority of design given the tasks this press is used for. This press is not meant to take the place of a rapidly adjustable commercially available press with its own brand of tradeoffs and attendant shortcomings. The two styles are designed to entirely different priorities.

So, to apply the above two points to real-world tasks the press is used for:

1) Ram travel should result in changes to the workpiece, not the press frame! As explained above, this type of press design provides high rigidity and no need for clearance take-up in its connecting joints. This is extremely important in testing the deflection or yield characteristics of various materials or car parts, straightening axle housings and other vehicle parts, measuring various suspension-related items, installing bearings in fragile castings, and on and on.

2) In the pictures below, notice there are no braces or brackets of any kind between the upright members as viewed from either end of the press. This is extremely important in that it allows unrestricted end-loading of long, large objects. Straightening car bumpers and straightening, bending or fabricating frame rails are two primary tasks. To have the ability to work (effectively) with frame rails in a press as opposed to spending large numbers of man-hours fixturing or jigging them on a frame machine is an enormous time-saver. The ample end-load capability and the six-foot long cross-beams at times are nothing less than the difference between being able to do a task at a price the customer can afford and not being able to do it within his budget because too many man-hours would be required by other means.

For the uses this press sees, the above two characteristics are of much more value than any of the advantages a slip-fit pin connection provides. But in fact this adjustability with rigidity and strength does come at a price. Changing the lower cross-beam height to new positions it is not performed as rapidly as is the case with a slip-fit pin design. However, when a cross-beam height change is needed, a portable hydraulic lift table actually does the lifting and repositioning. This lift table is used instead of an integral cable winch system because that would interfere with end-load access and ram trolley motion. All that is required of the operator is to run the lift table up to the cross-beams, remove nuts from one end of each of the four shafts and pull the shafts, change the lift table height, then replace the shafts. The heavy work plate and even any workpieces, etc  are left in place on the crossbeams  The operation can be done by one person in five minutes versus about one minute or slightly less for changing beam height of a well-designed pinned frame with integral cable winch.

To suggest this particular press should have 'rattle-fit' pin connections and be fitted with a cable winch is to misunderstand its intended usage. It is to misunderstand the forces involved at the connections given the open-ended design. It is to be unaware of the other elaborate equipment in the shop and the type of work done with it as presented at the rest of this website. It is to attempt to find a solution to a problem that simply does not exist. This press design causes no disadvantage in our shop since this is not the only press available. This press is not a 'stand-alone' piece of equipment. Rather it is only one tool among many in a commercial fabrication operation. Therefore, when a job is more appropriately performed by a traditional, rapidly adjustable, pinned-frame press, that job is done in just such a press! On those very rare occasions when the job is more appropriately done in a large, high-tonnage press, that job is taken to just such a press at a nearby heavy fabrication shop. This press is not meant to be a one-size fits all, be-all, end-all device. No claim is made to that effect. On the contrary, this press was designed to very efficiently perform tasks that are specific to custom car fabrication as explained at Shop Overview . This press is but one small part of a larger group of tools that work together.

Presses are like most any other mechanical device in that one style does not suit all tasks. For example, even though they are both motor vehicles, one would no more run a tandem axle dump truck in a drag race than he would attempt to use a Pro Stock drag car to move several yards of gravel. This does not mean tandem axle dump trucks are somehow 'no good'. What it means is-- tandem axle dump trucks are designed to a set of performance goals that do not include traveling a quarter mile in only a few seconds.

Frame Structure

Some notes about the images in this article: These pictures of the press frame are somewhat deceptive in that there is no common, everyday object in view to provide a meaningful reference for size. That is to say, objects in the pictures are larger than the perception one gets from the images. Therefore, while viewing the pictures, consider that the press is well over seven feet tall and well over six feet in length. Also, the press appears to be new and unused in many of the pictures. That is because, in fact, it was new at the time those photo's were taken circa 1997. 

Overall Dimensions:
Length - 6 ft. 6 in.
Height - 7 ft. 6 in.
Width - 20 in.

Clear opening between uprights for front loading - 4 ft. 1 in.
Clear opening between uprights for end loading - 13.5 in.
Clear opening between inside of cross-beams - 8.5 in.

Comparing the picture below with the picture above illustrates that the ram mounting assembly can move to a position anywhere along the length of the upper cross-beams. It can even be moved past the left-side upright members and into the overhang area (for three-sided loading access) without the need to disassemble or unbolt anything.

If any one dimension of the workpiece will fit into the 13.5 inch upright spacing, it will fit into the press no matter what its length is.

In the photo below:
Again a view of the clear opening between uprights for front loading of 4 ft.1 in. but....
Upright on left can be moved and bolted to extreme left end of cross-beams for front loading up to 5 ft. 9 in.
Lower cross-beam height adjustable (via bolt holes) down to floor level.
Upper cross-beam height adjustable (three positions) from top of frame to 7.0 inches below top of frame.

The press frame is almost always used in the configuration seen above because that setup provides maximum usefulness. Since the ram can be moved end-to-end without unbolting anything, jobs requiring front-loading, jobs requiring end-loading and jobs that demand the three-sided access of the overhang on the left can all be done without reconfiguring any of the press frame members unless a cross-beam height change is needed-- which is a very rare circumstance indeed. This since ram travel is 10.0 inches, and, as explained later, ram height is adjustable 6.0 inches independently of cross-beam adjustment thereby providing a total of 16.0 inches of travel before any cross-beam change is actually required.

Overhang end total overhang length is 19 in.
Overhang end loading depth 12-1/2 in. (With ram at max left outboard position the distance between center of ram and frame uprights is 12-1/2 in.)

Vertical uprights are 3/4 x 4 in. flat bar with 1/2 x 3 in. flat bar bolted at 90 deg.
 
Adjustment holes machined in a mill with hole centers all referenced to single point (upper cross-beam top mounting hole center) for consistent alignment with cross-beam holes at all heights.

In photo above note that the extreme end of the lower cross-beams is not yet finished-- or more accurately was unfinished as of the time the photo was taken. The large diameter holes are for the optional end mounting of the uprights. A combination upright reinforcement/mating pad and work-block stop is not present in the above photos. 

Cross shafts are 1-1/4 inch OD, 4140 chromium-molybdenum ground and polished shaft with ends tapered down to 1 x 8 thread. The taper serves to help align holes and the reduced thread diameter serves to protect threads for more rapid re-assembly when changing cross-beam height.

Outer sleeves (1-5/8 inch diameter) on the shafts are in compression between cross-beams when nuts and uprights are torqued against reinforcement/mating pads welded into cross-beam channels. These reinforcement/mating pads on the cross-beams have a machined mating surface that meets the back face of the uprights. Since the large outer sleeves on the shafts, the upright members and the cross-beams are all held in compression and are quite rigid, these joints exhibit some traits of a double-shear joint-- at least more so than does the typical frame with pinned connections. Again, less deflection than as seen in a simple pinned joint.

Nuts are torqued to a level that provides 20,000+ lbs clamping force per shaft to prevent any potential elongation of any mounting holes as the press is used. But, beyond that, the unthreaded 1-1/4 OD portion of the shafts is what is in contact with the ID of the holes in the uprights. The 1-1/4 OD is a precise fit in the holes. So even if a load exceeded the combined effect of the 20,000 lb clamping force 'friction joint' offered by each of the four shafts on the ends of the press-- a substantially higher load yet that was repeated often would need to be present before holes or shafts began to wear, bend or distort.  

Upright members at bottom are bolted to 4 x 4 x 1/4 in. square tube cross-members with 1/2 thick end plates via four 7/16 bolts per upright.

Press assembly is bolted to floor with six 1/2 in bolt 'drop in' anchors set 4 inches into reinforced floor.

Ram Mounting

Ram travels full length of cross-beams unobstructed by left-side uprights.

Ram trolley assembly weighs several hundred pounds. However it easily rolls with one-handed push on four 2-5/8 in. diameter sealed ball bearings acting as wheels. By turning the three-handled spinners seen below, the assembly is either clamped (top and bottom) to the crossbeams or released to ride on the trolley wheels for movement to a new position.

Unlike many other traveling ram mount designs, the clamping mechanism captures cross-beam channels' upper and lower flanges on both inside and outside edges to prevent any non-vertical bowing or twisting, which in turn lessens vertical deflection of cross-beams as they are loaded by ram motion. In other words the cross-beams are (mostly) only free to move in a vertical plane.

Looking up from under ram and upper beam:

Ram is Enerpac 25 ton x 10 in. travel (30 or 50 ton can be fitted)

Gauge is Enerpac 10,000 psi glycerine filled unit.

The gauge is utilized extensively when doing straightening or bending operations. However, digital scales/load cells --placed on the one-inch plate on top of the lower cross-beams-- are generally used when more accuracy is needed for measuring springs, etc.

The photo below is not upside down. The gauge is intentionally mounted this way. By positioning the gauge upside down, it can be placed as close as possible to the bottom of the upper cross-beam without placing any of the hose or fittings in harm's way below the cross-beam. The gauge at this height is in a good line of sight for an operator 6' 0" to 6' 2" tall.  If the gauge was placed upright, the operator would need to move neck and head upward at an awkward angle, interrupting his concentration on the workpiece. Another choice would have been to use a center-mount gauge (a gauge with the fitting on the rear of the case) and mount the hose and fittings a little closer to the bottom of the cross-beam. That idea was discarded because a center-mount gauge on the front side of the gauge adapter would place the gauge outward several inches and into harm's way. The gauge, positioned as seen here, is tucked in and well protected by the clamp and the guage adaper itself. After more than ten years of use of the press, the gauge has never been hit, whereas the clamp and the gauge adapter block have been struck on occasion.

Also note that the gauge is placed laterally centered on the overall width of the press instead centered in the distance between the uprights. This gets the gauge close enough to the operator's position when using the ram at the overhang end of the press that it can still be seen. 

This talk of gauge height leads to the subject of why the upper cross-beam height is adjustable. Recall that there are sets of adjustment holes for three positions for the upper cross-beams. As the press is set up in these photos, the center set holes for upper cross-beam height is in use, and as stated this suits an operator 6' 0" to 6' 2" tall. Suits him, not just with regards to the gauge readability but in fact relative to overall ergonomics of the press-- reaching the ram trolley clamping spinners without standing on a step, having the work at a comfortable height, etc.  The lower set of adjustment holes would suit an operator somewhat shorter than the 'normal' 6' 0" to 6' 2" height, while the highest set of holes would be appropriate for those somewhat taller than 'normal'.

The builder was free to consider his own height as being 'normal' and therefore appropriate for the center of the three adjustment choices. Unfortunately no provision was made for the pro basketball players among us. 

Of course any change in the height of the upper cross-beams would be matched by an equal change to the height of the lower cross-beams so as to retain the well-optimized ergonomic relationship between the two.

The ram mounting assembly provides high rigidity in plane across cross beam channels with two 2 x 4 x 14 in. solid blocks. However the blocks can rotate some small amount in relation to each other because of the design of the components inside this assembly. This permits absolutely uniform loading of all four corners of ram assembly against cross-beams.

When the ram trolley is placed such that the ram is exactly in line with the left-side uprights of the press frame, so as to remove cross-beam deflection from being a factor, a 25 ton push of the ram causes only 0.035 inch total movement and deflection. In other words, with the ram hydraulic pressure at zero psi, a reference bar can be set up vertically via shims so that its ends just touch the upper and lower cross-beams. When a 25 ton load is applied by the ram, a gap of only 0.035 inch is measured between the bar and the upper cross-beam. Releasing ram hydraulic pressure back to zero returns the gap to 0.000 inch. So... when extreme precision is needed, the ram is placed near the uprights-- workpiece size permitting of course.

Below are two pictures of the ram mounting components before assembly. (With apologies for quality of images. These are low resolution images from VHS video capture.)

Picture below is the view from above the press looking down at the ram mounting and trolley system.

Trolley components before assembly. (Another low-resolution image.)

Close-up of ram mounting. Ram height is adjustable for 6 in. vertical range on threaded rod.

Threaded ram adjustment rods are B7- 1 x 8 with grade 5 nuts on bottom of plate and grade 5 'heavy' nuts on top of plate (as well as at bottom end of rods), providing up to 40,000 lbs load per rod, in theory allowing use of up to 80 ton ram.

Example Uses

Currently this section of the article contains only pictures of press brake die use but more photo's are to be added at later date.

Brake Dies:

In the next two pictures below, because of camera position the upper die appears to be merely placed under the ram with no secure attachment. That is not the case at all. In the photo above the upper die is removed from the ram internal ID and set down on the plate so the mounting method can be seen. The removed upper die is the part with the cylindrical end sitting just to the left of the lower die in the above photo. Just as is the case with the manufacturer's own ram accessories, the cylindrical mounting boss, which all upper dies have, protrudes about 1.5 inches up into the ram shaft's hollow ID with very close tolerance. This prevents upper dies from cocking sideways and being accidentally ejected from the press. 

End of Article