A tabletop belt grinder, or, in short, a belt grinder (although, if you really pronounce this English word, it’s a grinder) is a drive device designed for grinding and finishing flat surfaces, removing a layer of rust or paint, as well as eliminating sharp edges and burrs from steel and any non-metallic parts. But the price of industrial models, even domestic ones, starts from 16...18 thousand rubles. It’s worth thinking about a homemade grinder...
What is Sanding Belt?
Sanding belt ( sanding belt
) is a flexible material on a fabric or paper basis, onto which a thin layer of abrasive is applied.
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Homemade grinder. Important points.
There are many designs of homemade grinders. Some make them using an engine from an old washing machine, others make them from an old grinder or drill, but all these models share the same technical details. Let's look at them in more detail.
Dimensions and design
There are no specific sizes that are the same for all grinders; they can be purely individual in each specific case. When choosing the overall dimensions and design of a belt grinding machine, you need to be guided by the free space in your workshop and the rule that the longer the belt, the more resistant to abrasion it will be and, accordingly, the less often it will have to be changed. If you are going to purchase ready-made, already glued tapes for the grinder, then the machine needs to be designed taking into account the size of these tapes. If you are going to glue the tapes yourself, then the dimensions of the machine can be arbitrary, but it is best to stick to the standard sizes of the tapes.
Abrasive belts for grinders are available in two widths: 50 and 100 m. The length of such tapes can be 610, 915, 1230, 1600, 1800, 2000 millimeters.
It is best if you have an abrasive belt of the required length, then it will be easier to adjust the size of the grinder to it.
The main components of the grinder are a machine frame with a work table and a tape clamp, an electric motor with a drive roller, a tension roller, a barrel-shaped roller and, if necessary, additional driven rollers. The barrel roller can also be a tension roller.
The most compact grinder can be made with just two rollers, one driven on the electric motor shaft, and the second barrel-shaped tension roller.
Belt grinding machine with a washing machine motor.
The same machine with an engine from a washing machine. View from a different angle.
Drawing.
The machine is made with a plywood frame.
Grinder.
Grinder with furniture gas shock absorber.
This machine is made using rollers from the car's timing belt.
Another band saw with a plywood frame.
Grinder driven by an angle grinder.
Compact machine with furniture gas shock absorber.
Compact belt sanding machine on two rollers.
Machine with a plywood frame.
If the grinder will work with long abrasive belts, then it will not be possible to do without additional driven rollers.
Why do you need a barrel shaped roller? When assembling the machine, it is almost impossible to maintain perfect parallelism of the axes of all rollers. For this reason, the tape tends to come off the rollers. To eliminate this drawback, a barrel-shaped roller is used. By adjusting the tilt of its axis, you can “force” the abrasive belt to remain in place.
To adjust the axis of the barrel roller, you can use the principle of a regular door hinge. The roller axis is welded to the movable part of the hinge, and adjustment is made using a bolt. Which rests on the movable part of the loop.
The photo shows a barrel-shaped grinder roller.
Note the barrel roller and adjustment bolt.
Barrel roller with adjustment mechanism.
Barrel-shaped grinder roller.
The mechanism for tensioning the abrasive belt can be made in several ways. The most common is using a spring, the second is using a furniture gas shock absorber and the third is using regular rubber, for example from a bicycle inner tube. If you use a furniture gas shock absorber, you need to know that it does not work well at low temperatures.
It is recommended to make the tape support two-layer. Make the base of the stop from a metal sheet and glue smooth porcelain tiles onto it. Thus, the emphasis will practically not heat up during intensive work on the grinder. Also, porcelain tiles wear out much slower than metal. It can be conveniently replaced as it wears out; you just need to heat the connection with a hair dryer, and it will come off. You can glue it to a regular silicone sealant for marble, for example Silirub MA from Soudal.
The stop must be adjustable relative to the tape. It must be moved to the tape tangentially to it or with a slight overhang of up to 0.5 mm. This overhang does not cause excessive wear of the belt, but it allows you to grind long strips longitudinally without touching the convex parts of the rollers.
Porcelain tiles on a grinder.
How to calculate the diameter of the drive roller.
To calculate the diameter of the drive roller, you need to know the belt speed at which the grinder will operate and the number of engine revolutions.
Belt speed should be selected according to the belt manufacturer's recommendations. For example, for a 3M Cubitron tape on steel it should be 22-25 m/s; from the same manufacturer, a speed of 30-35 m/s is recommended for tapes with aluminum zirconate. Belt speed is highly dependent not only on the type of abrasive, but also on the grain size. And so on average it is recommended for carbon steel 32 - 38 m/sec, alloy and stainless steel 18-30 m/sec, Titanium -15 m/sec, non-ferrous metals 35-45 m/sec, plastics 10-30 m/sec, malleable cast iron 38-34 m/sec, gray cast iron 35-45. As for wood, it is recommended not to exceed 20 m/sec, and you also need to know that different wood will burn at different speeds.
Formula for calculating belt speed:
V tape (m/s) = (3.14* D * N) / 60000,
where D is the diameter of the drive wheel in mm, N is the engine revolutions per minute.
Formula for calculating drive roller diameter:
D(mm)=(V*19108) / N,
where V is the belt speed in m/s, N is the engine revolutions per minute.
Calculation example. It is necessary to calculate the diameter of the drive roller for processing steel (22-25 m/s). Electric motor 2800 rpm.
D=25*19108\2800=170.6mm
The speed of rotation of the belt for different materials can be adjusted by changing the diameter of the drive roller or adjusting the engine speed. It should also be understood that as the diameter of the drive roller increases, the load on the engine increases and if it is of low power, for example, from a washing machine, then it will often stop even from a slight load.
Which engine to choose for a grinder.
On the Internet you can find information about machines made using electric motors from old washing machines. Such electric motors are low-power and low-revving. Most often it is 180 watts and 1400 rpm. Such grinders, as a rule, do not have enough belt speed and engine power, so they can be used to perform light work, for example, sharpening knives or processing small pieces of wood. They are not designed for anything more serious.
Below is the formula for calculating engine power for a grinder.
Formula for calculating engine power:
P(W)=(D*N)\570,
where D is the diameter of the drive wheel in mm, N is the engine revolutions per minute.
If a three-phase motor is used, but connected to a single-phase 220V network, then its calculated power when connected in a delta with a working capacitor is approximately 1.5...1.6 times lower than the nominal value. This must be taken into account. For example, according to calculations, an electric motor with a power of 800 watts is required, and the motor will be used three-phase, but on a 220V network. Then the required power of such an engine will be equal to: 800 * 1.6 = 1280 watts.
The optimal choice is a single-phase motor with a speed of at least 2800-3000 and a power of at least 800 watts. With such an electric motor, it will be possible to process hardened steel on a grinder, and not just sharpen “pencils.”
We recommend reading:
How to choose and glue grinder tape.
If an open-type motor is used in the manufacture of a belt grinding machine, as in washing machines, then you should think about protecting it from abrasive and metal dust. Such protection can be made from a 5-liter plastic bottle or any other plastic container.
How to make rollers for a belt sander
If you know a turner, then you should not have a similar question. Well, if there are no such acquaintances, then this information will be useful to you.
There are several ways to make videos.
It is convenient to make the drive roller from a sheet of plywood. First, circles of the required diameter are marked, then they are cut out using a jigsaw. After this, the plywood circles are glued together.
Glue the plywood circles together.
After gluing, the central hole of the roller is drilled to match the diameter of the electric motor shaft. Now you need to make a keyway in the hole. It is easy to do with a file.
Making a keyway in a plywood roller.
Driven plywood roller with keyway.
Then we put the roller on the electric motor and grind it using a chisel, a large file or an angle grinder (grinder) with a grinding wheel.
We grind the plywood roller with a grinder.
To make the drive roller slip less, it can be treated with liquid rosin.
The easiest way to make driven rollers is to simply assemble them from bearings of a suitable diameter on a shaft. Partially threaded bolts can be used as a shaft. Bearings need to be sealed, otherwise they will quickly become clogged with dust and fail.
You can use timing belt rollers from your car as rollers, but don’t buy new ones, ask them at any service station. It is only desirable that the rollers be flat without shoulders. These beads can cut the edges of the tape.
Another way is to cut the rollers with a crown made from a sheet of plywood and glue the resulting washers together. You can additionally secure them with self-tapping screws. Afterwards, inside the roller you need to drill two holes on both sides of the roller for the bearings. The depth of such holes should be equal to the width of the bearings. It is convenient to drill such holes using a wood drill bit. When the holes are ready, we drill a through hole in the center of the roller for the roller axis. The diameter of this hole should be slightly larger than the diameter of the inner race of the bearing, otherwise the bearing will jam inside the roller.
After this, the roller is almost ready, all that remains is to sand it on the outside and give it the desired shape, if it is a barrel-shaped roller.
Plywood roller.
We sharpen the roller using a grinder.
The rollers can be made from round caprolon or another name for this material is polyamide-6. The process of making a video is no different from the previous ones. We cut the workpiece to the required length, drill holes with a feather drill for the bearings and grind it on the outside using a grinder.
Another way to make driven rollers is to use couplings from a polypropylene pipe. Barrel couplings are available for sale. For example, a Czech-made coupling d 32 Wavin Ekoplastik.
Plastic plumbing coupling.
This photo clearly shows that this plastic coupling has the shape of a barrel.
Bearing No. 201 fits well under this coupling. The bearing can be pressed into the coupling using a vice.
If you need to make a straight driven roller or you couldn’t find a barrel-shaped coupling, then you can make a roller from two straight couplings. If necessary, this roller can be ground to a barrel-shaped state.
Diagram of a roller made of two plastic couplings.
Parts for making a grinder roller.
For one roller you will need two plastic couplings with an internal diameter of 32 mm, three bearings No. 201 and washers for the M12 bolt. First, the plastic couplings are cut, on one side, so that the distance from the edge of the coupling to the inner rib is 5 mm. We need the bearing to be able to enter the coupling only half its width, that is, 5mm. The bearing should rest against the internal rib of the coupling.
The photo shows a plastic coupling marked before cutting.
After cutting the couplings, use a vice to press the bearing between the two couplings. It will be inside exactly in the middle of the future video.
Now we put washers and press two bearings along the edges of the roller.
We place washers between the bearings.
All that remains is to sand the outside of the roller.
We grind the roller using a grinder.
I recommend watching a video on this topic.
