Do-it-yourself cutting machine from a grinder

Recommendation points

• What to take angle grinder
• General design description
• Machine base
• Swivel-broaching mechanism
• Clamping device
• Electrical connection
• Customization and revision

Angle grinders can be used in combination with additional equipment, including homemade ones. By following this instruction, you can build a small frame that will allow you to turn an ordinary grinder into a real pendulum saw.

What to take angle grinder

No matter how high the temptation is to use an existing tool, it is still better to purchase a new grinder for a homemade machine tool. This is due to the fact that even with a carefully thought-out design of the cutting saw, the removal and installation of angle grinders takes quite a lot of time, especially taking into account the adjustment of the power tool to maintain the accuracy of the cut. In addition, a number of additional requirements are imposed on the grinder used in the design of the cutting saw:

1. Speed ​​control. Not every craftsman will be satisfied with the maximum cutting depth that a standard angle grinder with a 230 mm disc can provide. It may be tempting to use larger diameter cut-off wheels, for which it will be necessary to reduce the speed to achieve the correct radial speed.
2. Minimum body length. Too long a stick or an increased length of the engine forces the designer to construct the main arm of the pivot joint with a long overhang, which increases the material consumption and the load on the pivot unit, and this also negatively affects the accuracy of alignment.
3. Minimum overall dimensions of the gearbox. With these, everything is clear: the larger the “clean” diameter of the circle, the greater the depth of cut. For Bulgarians of comparable cost and power, this indicator may differ significantly.
4. The presence of standard holes for attaching the front handle is the most important indicator. Usually in grinders there is a thread with a diameter of 12 mm with a pitch of 2.5 mm, this is a non-standard size, usually artisans have to use a threaded pin sealed into the handle to fix it. However, in many angle grinders, the holes are two-stage, the usual M10 thread is hidden in the depth – this is ideal.

Otherwise, the requirements for the tool are low. Of course, it is better not to give preference to grinders of “one-day” brands of Chinese origin, a relatively reliable Intertool or Fiolent with a capacity of at least 2 kW will be enough.

General design description

On the Internet, you can find a huge number of variations on the topic of making a homemade pendulum saw. Most of them are completely unsuitable for everyday use, although there are some really interesting technical solutions. We offer a generalized frame with a lever joint that meets the basic requirements for reliability and ease of use. We warn you that such a performance requires careful and diligent attitude during assembly, but the result is definitely worth it..

At the base there is a frame made of rolled steel, which can be additionally covered with hot-rolled sheet. The most important requirement for this part of the machine is high rigidity and weight for sufficient stability, or the presence of fasteners for stationary installation on a solid base.

Ideally, a homemade saw should have a mechanism for both lever-rotary and broaching feed. In the factory version, a conventional hinge on the rolling units and rail guides are used for this. We offer a variant with two joints, in which the correctness of the stroke is ensured by the selection of the force of the compensator springs.

Machine base

First you need to weld a corner steel frame with a cross section of at least 40X40 mm. The specific size of the table depends on the massiveness of the workpieces and the dimensions of the tool, but on average, a width of 40-45 cm and a length of at least 65 cm will be sufficient.

Spacers and corner gussets must be added to ensure sufficient rigidity. At least one additional tie made of steel strip should be installed in the center of the table, another one – with an offset of 60–80 mm from the rear edge where the base of the hinge will be attached. The whole structure is made on welded joints with double-sided welding of seams. The upper plane of the frame must be sanded for a snug fit of the sheet.

The table frame can be sheathed from above with sheet steel with a thickness of 2 to 3 mm. Optimally, if the sheet is removable, for this you need to weld the threaded parts of 6 mm bolts in the amount of 12-14 pieces to the wrong side, evenly distributing them over the table area. The sheet should cover at least 2/3 of the base starting from the front edge. No more needed, the base of the hinge must still be fixed directly to the supporting structure.

Swivel-broaching mechanism

We come to the most difficult part of the machine – the lever feed mechanism. Its main unit will be a connecting rod of an automobile engine; in order to reduce costs, it is recommended to purchase spare parts for cars of such brands as Daewoo or Chery. You can also use used components, but without neck deformation and without traces of strong wear.

To attach the connecting rod to the table, it is necessary to make a fork from a steel strip with a thickness of about 6–7 mm; it can be either hot bent on a mandrel, or welded from three rectangular fragments. The distance between the inner walls should be equal to the width of the upper connecting rod head. In the side walls of the bracket, two coaxial holes must be drilled, the diameter of which corresponds to the size of the connecting rod sleeve. The connecting rod is fastened in the bracket by means of a standard piston pin, while the protrusions along the edges are selected with distance washers, and then tightened with a bolt and nut.

The forked end of the connecting rod is designed to hold a seamless pipe of the corresponding diameter in it, which can be replaced with a steel rod fitted in a rolling bearing of a suitable standard size. In the latter case, no inserts are required. The upper knot should remain movable; the best option is to grind the insert with a tolerance of about 0.02 mm. The best way to avoid insert misalignment is to groove the two snap ring grooves. On one side, the pipe or rod should have a protrusion for attaching a lever, which is a good choice for two wide steel strips or sections of a profile pipe. They need to be bent taking into account the shape of the grinder’s body and drilled two holes for bolting the gearbox.

The swing movement of the mechanism is provided by the upper connecting rod head. At the same time, the disc moves obliquely from the front of the workpiece to the rear bottom, which increases the maximum stroke length and cutting depth. The broaching is carried out at the expense of the lower head: when the turning reserve is exhausted, the entire joint tilts forward and allows the disc to move an additional 80–100 mm. To regulate the actuation force of both joints, the springs must be matched with the appropriate force. Alternatively, we can offer hydraulic racks for furniture fronts..

It is very simple to adjust the force of springs or struts – by varying their pre-tension and fastening height. In the thin part of the connecting rod neck, a row of 6 mm holes must be drilled with a pitch of 15-20 mm. Since the steel in the connecting rods is alloyed and heat-treated, for drilling, you should use a concrete drill with a victorious brazing, sharpened in the classical way with the formation of an apex angle of 120 °. By changing the attachment points of the springs to the hinge and the table, you can quickly achieve the desired ratio of tension and compression forces.

Clamping device

At the front of the machine is a clamping mechanism that fixes the workpiece during cutting. A simple transverse stop can be dispensed with, however, reliable and safe fastening, ensuring high cutting accuracy, can be achieved only by introducing a screw clamp into the structure. There are three versions of this node..

The first is to use the standard cut-off saw clamp removed from the donor. This option is good for its simplicity, but finding such components is very difficult. Nevertheless, if you purchase the entire assembly complete with a turntable and a graduated angular scale, the ease of use of a homemade machine will be one of the highest..

Another option is to use a locksmith vise. Thanks to the swivel base, you can even set the cutting angle, while the fixation of the workpiece will be the most reliable. The main disadvantage of this method is the absence of a reference horizontal plane; the part has to be verified with each installation or independently to build a stand. Also, when using a bench vise, the height of the workpiece is greatly increased. It can be compensated only by raising the bracket in which the pivot joint is attached to the appropriate height.

The third way is to make the clamp yourself. This requires a trapezoidal screw with a pitch of at least 2 mm and a nut of the same type that is welded in the front of the table. As a pressure stop, you can use a piece of ordinary angle steel, to which the screw is attached by means of a thrust bearing or on a sliding fit.

Electrical connection

When using a homemade cut-off saw, it is extremely inconvenient to constantly fix the standard power button for the power tool. Therefore, as a rule, it is excluded from the electrical circuit, either by blocking mechanically, or by short-circuiting the wires..

Safety rules for the use of stationary metalworking equipment require that the control elements are switched with a voltage of 12 or 24 V. Thus, an inexpensive pulse transformer and an intermediate contactor of a modular type are added to the electrical circuit. You can place electrical equipment in a regular shield with a DIN rail, fixed at the back of the table.

Of the switching methods, it is most preferable to use a pedal without locking, this is the safest type of switching device. You can also use the usual “Start-Stop” button with bypass, but in this case it is better to additionally install an emergency mushroom button.

Customization and revision

When the main saw units are assembled, it is necessary to adjust the machine. It consists in aligning the two reference planes and the cutting disc relative to each other.

When clamped, the part occupies a certain position in space, determined by the plane of the cross stop and the table. Also, for horizontal positioning, an additional add-on can be used, as in the case of the curved vice. Since this plane cannot be adjusted, the position of the cutting disc is set relative to it using a locksmith’s square. It is possible to tilt the cutting plane accordingly only by deforming that part of the lever mechanism by means of which the grinder is attached to the hinge.

As for the transverse stop, it is installed last, aligning the pressing plane with respect to the disk, previously installed perpendicular to the plane of the table. To do this, it is enough to fasten the stop on bolts to the base of the machine through holes of a larger diameter.