- What and how to assemble a frame for the press
- Which jack to use and how to modify it
- Presser shoe making
- Adjustable support beam
- Return mechanism
For some operations, a DIYer may need a press with a significant compression force, but the purchase of equipment of this class will be completely unjustified. Today we will tell you how to assemble a reliable press based on a hydraulic car jack in a few hours..
What and how to assemble a frame for the press
The material for the bed, its structural strength and the method of assembly must be determined by the pressure that the jack is capable of delivering. For an accurate calculation, it is important to understand in which direction the loads act during operation.
The basis of the press is a rectangular U-shaped frame made of a channel or twin steel angle. The main acting force is the resistance to compression, expressed as a concentrated load. The main effort is concentrated in the centers of the horizontal bars. The forces stretching the vertical press racks and the phenomena of deformation in the compressed parts can be completely neglected..
1 – upper thrust beam; 2 – bolts; 3 – jack 20 t; 4 – returnable springs; 5 – movable beam; 6 – locking pin; 7 – adjustable support beam; 8 – cross beam; 9 – legs from the corners
For installation with a compressive force of up to 5 tons for the manufacture of a frame, you can safely use:
- Channel in accordance with GOST 8240–89, standard size 8P.
- A pair of hot-rolled corners in accordance with GOST 8509-93, size 50×5 mm, connected by 10 mm rods every 20-25 cm, or with a solid welded seam.
Sizes of channel 8P
Let’s make a reservation right away that we provide approximate data on rolled metal for a frame with an inner window no wider than 100 cm.Like, when using a jack with a force of up to 10 tons, the frame should be made of:
- Channel of standard size 10P.
- Twin angle steel 63×7 mm, one-piece joint with internal inserts of nominal cross-section.
Sizes of channel 10P
If the required compression force reaches 15 tons or more, then the frame should be made of:
- Channel of standard size 14P.
- Twin corner 75×8 mm, connection similar to the previous one.
Sizes of channel 14P
The above proposal for rolled metal implies a tenfold safety factor, which completely excludes the excess of the elastic deformation limit and is normal for installations of this kind. All frame joints shall be welded with one-piece double-sided seams and butt trimming. If the connection is not made by welding, assembly on bolts or cotter pins is allowed. In this case, it is imperative to take into account the maximum permissible shear load.
When bolted, the main load becomes dispersed and the compression force of the press must be divided by the number of bolts or pins. The destructive shear force of bolts made of the most common ST-3 steel is:
- M10 – about 2500-3000 kg.
- M12 – 4000-4500 kg.
- М14 – 5500-6000 kg.
To ensure the required safety margin, each fastening element must experience a load five times less than the destructive one. For steel fingers, the force can be taken 10-15% higher than the indicated values. If the required number of fasteners cannot be placed in the corner unit, the strength should be increased with gussets, for which it is preferable to use angle steel instead of sheet steel. The same applies to the welded frame structure, which also helps to avoid the use of unnecessarily massive rolled steel..
In addition to the loaded upper part of the bed, the bed includes two legs with legs that provide the press with sufficient stability, and a transverse beam, which can be adjustable for processing parts of different sizes. The section of the upper and lower beams must be equivalent, as well as the section of their fastening elements. Everyone is free to implement the legs and support according to their own considerations, they do not experience workloads in addition to the press’s own weight. The only requirement is the presence of a lower crossbar, which gives the structure additional rigidity.
Which jack to use and how to modify it
The most affordable and suitable for making a home press will be a glass-type hydraulic car jack. As mentioned above, you have the right to choose the working force for your tasks, there are relatively inexpensive devices on sale that can squeeze up to 20 tons and even more..
The main problem with these jacks is their inability to work upside down. It seems most logical to fix the jack permanently on the upper beam and use the lower one as a support for the part. However, this will require refinement of the hydraulic mechanism..
The first option for altering the jack is to install an additional expansion tank with a capacity of about 300 ml. The reservoir is connected to the filler hole of the jack with a regular silicone tube. For its tight fit, you can use threaded fittings for an oxygen hose, which are available in the range in any auto parts store..
Another modification option will require disassembling the jack. It is necessary to completely drain the oil and pump the plunger, then twist the upper clamping nut, holding it in a vice. After that, the outer glass is loosened with a rubber mallet, it must come out of the landing ring at the base of the jack. Directly near the plunger lever there is an opening for the intake of working fluid. The whole problem lies here: the glass is not completely filled and therefore, in an inverted state, the hole does not come into contact with oil. To eliminate this, a tube must be pressed tightly into it, almost the entire height of the glass..
If you do not alter the jack, you will have to implement a more complex mechanism with an additional third beam. It should slide on the side rails and fit snugly enough to keep the jack from moving when pumping up pressure. In our case, the jack is simply attached in an inverted position to the center of the upper beam. There is no need for massive bolts, it is enough to make a couple of holes in the base plate of the jack and ensure fixation with M10 or M8 bolts that can withstand the weight of the jack itself and a slight shear force at the initial stage of compression.
Presser shoe making
The jack rod is not very convenient to use, usually an increased area of the compression headstock is required to use a wide range of molds and work with large-sized parts. In this case, the force should be distributed over the entire area of the compressed surfaces evenly, without causing deformation..
In the simplest case, short full-bodied ingots can act as pressure shoes. It is quite easy to make threaded blind holes in them for fixing to the main structure of the press. But such parts are not always available to the layman, therefore we offer the option of our own production of attendants, capable of withstanding a significant compression force without harm.
The headstock must be able to be assembled with the jack rod, excluding movement during operation. Simply put, a blind hole should be made in the headstock, into which the heel of the jack will enter with a minimum clearance. You will also need a couple of holes for attaching the return mechanism springs..
Both headstock can be made from two sections of the channel or four pieces of angle, forming a parallelepiped with open side faces. The seams on the planes through which the axis of the main working force passes should be welded with a continuous seam from the inside, the rest – from the outside. One of the faces is muffled with a square insert, after which the inner cavity is filled with sand concrete of grade 500. After solidification, the headstock is welded on the other side, so two incompressible pads are obtained.
For landing on a jack, it is enough to weld a piece of pipe of the corresponding diameter in the upper part of the headstock, which will act as a casing of the glass. For even greater reliability, a washer with a hole for the stem heel is attached to the bottom of the sleeve. The lower headstock can simply be placed on a movable beam, but it is better to weld on a couple of corners or steel rods that limit the shift.
Adjustable support beam
As you already know, the lower beam should have a cross section not less than that of the upper one, but it is different in design. The support table is made of two channels, ribs facing outward, which are applied on opposite sides of the posts and are welded in the central part by inserts from a corner or thick reinforcement. There is free space along the center of the beam, which explains the need to manufacture the lower support block. The latter should rest on at least half the width of each shelf, the shear stops are welded in the center of the lower part.
The best way to secure the beam to the uprights is with massive steel pins. To do this, in the vertical channels of the frame, a number of circular cuts should be made at different heights with a parallel arrangement. As you can imagine, the diameter of the pins cannot be less than the combined section of all the bolts used in fastening the upper part of the frame..
The last part of the homemade press design is the spring mechanism that will fold the jack when the bypass valve is open. For this purpose, ordinary door springs are suitable, which can be purchased in unlimited quantities at any hardware store..
The task is complicated by the use of an upper pressure head, the significant dead weight of which will not allow the springs to compress. Alternatively, you can increase the number of springs to four or six, or use more powerful tension springs for the gate.
If there is no upper block, it is necessary to fix the springs to the jack rod. To do this, you need a washer, the inner hole of which is larger than the stem adjusting screw, but smaller than the piston diameter. The spring is attached to it through two small holes at the edges and is fixed to the upper beam in the same way or on welded hooks. It is not necessary to position the spring strictly vertically, you can compensate for the excess length by an inclined position.