Reprinted with permission from MLS Machinery, Inc.
Edge sanders have a table that is horizontal while the sand paper turns in a vertical plane moving between two drums, similar to the stroke sander where the sand paper travels in a horizontal plane. The part to be sanded is manually pushed against the sand paper while it sits on a horizontal table; the sanding done is only on the edge of the part. These machines come in different lengths normally four or six feet is the standard. Some of these machines have oscillating heads which will move the sand paper up and down allowing more of the paper to be used, giving longer life to the paper. In the standard machines normally only; one part of the paper is used causing quick wear and tear on the sand paper.
Stroke sanders are similar to the cross belt sander, and are normally manually operated machines. The sanding belt goes across the table which is manually operated; the part is put on the table and the operator has a small handle which controls a shoe that he pushes down onto the part as it is pushed manually through the machine. The operator pushes the table in and out and holds the shoe on the piece while it is being sanded. When he finishes, he lets the platten (shoe) go (it is spring loaded) and removes the part.
Drawer sanders have two large belts that travel up and down, opposite each other. Once the drawer is assembled, it is placed into the machine and the two belts are manually brought towards the drawer sides; once sanded, the two belts are then moved apart from each other and the drawer is taken out (mainly used for drawer sides in very high end furniture).
Mould sanders sand parts which have come out of a moulder and need to be finished and smoothed. These machines might go in line with the moulder. It might have a number of heads, three to six being the most common, and each sanding head or block could be set at different angles, sanding different parts of the moulding as it passes through; for example, picture frames, floor board mouldings, door frame mouldings, window parts, etc. Some of these machines will use the Vonnegut head (discussed under Profile Edge Sanders), or use Fladder wheels which have little fingers of sand paper flapping around that rotate; these Fladder wheels can get into little nooks and crannies. They can also use Scotchbrite Buffing Wheels.
Profile edge sanders can be very expensive machines. These machines will sand edge work, which can be very complicated, depending on the profile. These machines almost look like an edgebander, where a continuous belt feeds the part past the numerous sanding stations. Different applications can be done to the edge at the same time as the part passes through the machine. The various stations can be comprised of either buffing wheels and/or miniature (what we consider) wide belt sanders that can be placed at different angles to the edge for different angled work where very detailed or complicated parts require sanding. Profile sanders can also be single head machines that are completely manual. These machines look like a shaper but have a round sanding head pre-manufactured to the same profile or shape as the part that is going to be sanded. The sand paper is actually glued to this pre-manufactured head, called Vonnegut heads. The Vonnegut heads can also be used on the larger through feed profile sanders, or as well, on Mould Sanders. Profile sanders can be very long machines depending on the application and are normally very difficult to set up. Some of these can be double sided machines, capable of working on two edges at the same time, similar to the double sided edgebanders.
Rotary Sanders are becoming far more common today and are used to a large extent in the finishing and sanding of kitchen cabinet doors, interior and exterior doors especially if there is surface work that has been done on the face of the door, such as a moulding which protrudes from the door or a groove that goes below the surface of the door that require sanding before finishing. These machines ostensibly work as a conventional sander that is they might have a vacuum table and a feed mat that feeds the part through the rotary sanding head. Rotary Sanding heads sand the product from the top and come in various configurations depending on the manufacturers of the machine. The original machines had a main rotating arm (vertical) with 4 horizontal arms coming off the main arm which could accommodate one or two rotating sander heads each. These sanding heads are made from strands of sand paper that follow the contour or raised portion of the part. The original machines had only one rotating arm with 4 or 8 sanding heads.
In later years the same machine was available with 2 rotating arms, one behind the other and instead of only 4 or 8 rotating heads, these machines would have 8 or 16 heads. These machines have become far more sophisticated but the concept has still remained the same, head configurations are varied, with some producing better finish than others. Some of these machines now also have the same type of sanding heads in a vertical position so that the parts can be sanded on the edges as they go through the machine.
Denibbers are in most cases for getting into crevices and removing fine hairs and fibres remaining on the wood after the parts have been manufactured. Denibbing sanders in most cases are like a panel cleaner where a brush with fine strands of thin fibers are attached and the head rotates in a circular motion to remove excess fibres.
Finishing Sanders are as their name implies mainly for doing the final finish of a product. Finishing Sanders can be a combination of a larger machine that has numerous heads and the final head or two are used with a fine grit of sand paper being over 150 grit to get a smooth finish. These machines can also be stand alone machines that have one or two heads and will be used just in the final finishing process such as a cross belt / wide belt sander.
Disc Sander is a very simple machine that has a disc that comes in various diameter sizes e.g. 12” – 36” diameter. Sand paper in the same diameter is glued to the disc and the disc rotates around its own axis. The disc is normally in the vertical plane as an edge sander and the part is pushed against the rotating disc.
Miscellaneous sanders covers a whole cross section of different kinds of sanders.
Pneumatic drum sanders are small machines. These machines have an inflatable bag and one piece of sand paper, approximately 8" wide, wrapped around this inflatable bag (also approximately 8" wide); this drum just rotates around itself. These machines are used for sanding small parts which normally have to be done manually, such as the inside parts of chair legs and chair arms.
A wide belt sander is a sanding machine that sands down either raw lumber, once it has gone through different operations such as a jointer or planer, and has already been brought down to the approximate thickness that the operator requires; or, it will be used in the panel industry to sand down the final component parts, or sheets of veneered plywood.
Sanders are very popular machines; they are required in all forms of finishing. You have to have some sort of sanding to finish a product which can either be by a wide belt sander, or Miscellaneous Sanders, or you could have a whole crew of people manually hand sanding. Most wide belt sanders have a conveyor belt that passes through the machine. The part is put on this conveyor belt as it feeds through the various sander heads and comes out on the other side. The head configuration of sanders would vary depending on the operation. A wide belt sander would normally have quite a long belt (to be discussed later). The width of the machine will be determined by the width of the belt; therefore, when we talk about a 36" machine, the width of the belt would be 36" wide; or a 54" machine would have a 54" wide belt and so on. The length of the belt would be determined either by the manufacturer of the machine or what is required; the longer the belt, the better the belt life because it will have more surface area to do continuous sanding. These belts that are now, say, 36" wide could be eight to ten feet long and are joined together to form a constant loop. The belt fits around a drum on the top of the machine and then is looped around a drum or shoe (pad) on the bottom depending on the head configuration. On a top sander, the sand paper is above the feed belt; on a bottom sander it would just be upside down with the sanding belts on the bottom and a feed mechanism from the top. In most cases sanders will comprise one drum and one shoe or pad, but this is completely determined by the needs of the individual. It is possible to have a six head top and six head bottom machine with various head configurations.
The drum would normally calibrate, that is, bring the part down to the final required size, or do the rough sanding using a lower grit paper (the lower the grit the rougher the sanding paper); the second belt would be a fine grit paper to do the final finishing operation and the final smoothing of the part. The shoe or pad generally vibrates a little while the panel passes through and will do the final sanding, sometimes called polishing. A traditional machine for a solid wood application, such as component parts for doors would normally be two drums very close to each other to do small parts as well as long ones. The two drums would have different grits of paper, rough on the first and fine on the second head.
The horse powers will also vary, depending on the operation, somewhere between 10 and 50 HP would be the norm. In the manufacture of particle board, the sanders that are traditionally used would have three heads on the top and three heads on the bottom thereby allowing sanding on both sides of the particle board that has just come out of the press, at the same time. Kimwood makes a machine with a 125 HP top and a 125 HP bottom first head, and the other four heads being 100 HP each, giving a total of 700 HP. This is not the norm.
As discussed above, a top sander and a bottom sander could be placed in line behind each other, to sand both sides of a part in a single pass. Some sanders used in the veneering industry might also have what is commonly called a cross belt sander attached to the rest of the machine. This means the belt will go across the grain of the material instead of going up and down with the grain as the other belts previously described. This belt is very narrow, normally being approximately 6" wide, and travels across the panel as the panel feeds through the machine. The reason for this is that once the final shoe (sanding head) with the finest grit paper has sanded the part, fine hairs can still be left on the veneer. The cross belt head will make the fine strands (hairs) stand up. If the cross belt head is the first head, as previously discussed, it will make the hairs stand up and the next heads will remove these hairs. The cross belt can be either the first or last head and in some cases both.
Some sanders today are C.N.C. controlled, that is to automatically set the thickness for various parts or to allow numerous parts of different thickness to be sanded side by side at the same time. These machines have computer controlled sectional pads normally at 32mm from each other that operate by a scanner pre-determining the size of the part that is going through the machine. This, in turn, determines which pads have to come down to actually come in contact with the part. The C.N.C. control is also used for parts that have fancy edgework, the computer will determine the shape and activate the pads that are needed and will also determine how much pressure to put on the panel near the edgework.
Note the difference between an abrasive planer and a wide belt sander; they almost look identical but the heads in an abrasive planer are normally made of steel drums as opposed to a sander where the drums are rubber and in various forms of hardness. Abrasive planers normally have much higher horse power and will also have a hydraulic feed mat to feed the rough material through the machine; they take a lot of abuse. Sanding is a finishing operation while abrasive planing is a starting operation.
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