Reprinted with permission from MLS Machinery, Inc.
An abrasive planer is similar to a wide belt sander (to be discussed under Sanders Wide Belt). They basically take the wood and plane it down to an acceptable tolerance or an acceptable thickness. When raw lumber or panels arrive at a plant they can be oversized in thickness and might therefore have to be machined to size. Once the parts have gone through the abrasive planer, they will have been brought down to the thickness the operator wants. As an example, should you want to work with solid wood and have its final size 3/4” thick, it might come in from the suppliers of the lumber at 7/8” thick; it could also be substantially oversized, in which case the abrasive planer would be used.
If it is not tremendously oversized, a standard wide belt sander could be used. Abrasive planers work very similar to a wide belt sander. They have a rubber mat which is used to feed the material, be it solid wood or a panel, through the machine. The wide belt, abrasive planer uses almost standard sand paper, excepting that it is very rough (40-80 grit), therefore it is called an abrasive belt.
There is a top drum which is used to drive the belt, and a bottom drum which is the part that actually comes in contact with the material. This abrasive belt rotates around the top drum and the bottom drum. The top drum oscillates, allowing this wide belt to move backwards and forwards, thereby using different parts of the belt so that you do not get a wear pattern on the same part of the belt itself. In the case of a single top belt abrasive planer, if two sides of the material have to be planed down, the part has to be flipped and sent through the machine a second time on the opposite side.
Abrasive planers are available in a top version as well as a bottom version. The top machine will sand from the top of the part and the bottom version will sand from the bottom; therefore, you could have one behind the other and in one pass plane top and bottom. Whatever belt mechanism you have on the top, as described above, will be exactly the same as at the bottom. Some abrasive planers can have two heads, one behind the other. Abrasive planers come in widths of anywhere from 12” to 72”; the width size is determined by the belt width not the belt length. The difference between a wide belt sander and a wide belt abrasive planer is that the planer does the initial rough work to bring the material down to size and the wide belt sander, which normally does not have as high a horse power as the abrasive planer, is used for finishing work. However, the basic construction of the two machines is the same.
The main differences between a wide belt sander and an abrasive planer are:
1) Abrasive planers have much higher horsepower;
2) The drum on an abrasive planer is steel, not rubber as in a wide belt sander.
3) To feed heavy oversized rough material some use a hydraulic feed mechanism.
4) Abrasive planers are for rough work. Wide belt sanders are for final finishing.
There are now combination machines that do the two processes in one. There is a planer head on the machine as a first head followed by one, two or three wide belt sanding heads.
This relatively new technology uses a helical head or spiral head as the planning head which is much quieter that a conventional planning head. On these types of heads the knives which are small segmented knives one next to the other can be rotated and/or replaced if one breaks or if one is no longer sharp.
Planers fall under the category of standard machines; however, there are some quite sophisticated planers used for volume production. Planers for small shops are normally quite small with low horsepower and normally just plane from the bottom to get the wood down to the required size, similar to what we saw under Abrasive Planers.
Abrasive planers have belts while these planers have knife cutters which are attached into a round circular cutting block normally having four to six knives per block. These have to be sharpened on a regular basis to make the machine perform properly; therefore, many planers have grinders attached to them so that the knives can be ground directly on the machine without having to remove them or send them for sharpening.
Planers are predominantly used in the solid wood industry. If operators are planing down many narrow pieces at a time, it is advisable that the feeding mechanism has what is called sectional feed. A sectional feed mechanism has small independently operated sections that push the pieces of wood through the machine. This allows an operator to put a three inch thick and a three-and-one-half inch thick piece of wood through the machine at the same time without worrying that the thinner or thicker piece will not feed, or possibly get stuck. If these were non-sectional feed, either one piece would stop the machine or the other would not feed while the thicker piece was going through.
Some planers are two sided which cut from the top and bottom at the same time. Companies that have single planers and want to plane both sides of the material to get it down to a pre-required thickness would have to feed the piece through the machine twice. Most machines will open up to 8-12" in height and horse power's can vary anywhere from 5 to 7-1/2 HP for the small shop to 18-50 HP on some of the larger units.
Planers can also be four sided, which will plane the top, bottom and two sides all at the same time. Some planers can have multiple rip saws attached to them at the outfeed end so that the piece can be planed and ripped into smaller pieces all in one operation. Some cutters that are used on the more expensive machines are called helical heads which are circular, spiral cutting heads that are very expensive. These helical heads are very quiet as opposed to the standard cutters which are noisy.
Most planers will feed the material at between 25' per minute to 300' per minute on the larger units. Companies that produce 2"x4" or 2"x6" lumber (known as "Re-man" operations), they can have planers that will feed up to 2,000' per minute.
A relatively new innovation in the planer category is a sander/planer combination machine. This machine will normally look like a conventional sander but the first head will be a helical planning head followed by one, two or three wide belt sanding belts all fed through the machine by a conventional sander feed mat.
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