How to set up Planer Thicknesser Knives archive

Friday 30 October 2009

Alan Holtham shows you how to set up the knives for optimum results


Planer-thicknessers require very accurate setting up if you are to get the best out of them and many new users are nervous of the process, consequently leaving knives in far too long and soldiering on with blunt blades instead of taking them out for re-sharpening. Not only does this result in a very poor finish, but a blunt planer is more difficult to use safely because the timber bounces around rather than cutting smoothly.

The difference between a planer working well and working badly is minute in terms of blade adjustment. It cannot be overstated just how important this setting is, as incorrectly set knives result in a machine that either won't plane at all, planes tapers or takes big scoops out of the end of the work. With correctly set blades the timber should plane perfectly from end to end. You should not need to leave it overlong and then cut off the dodgy bits after planing.

Do not assume it is properly set up straight out of the box. Rough handling in transit can be enough to knock the tables out of line and affect all the settings.

Sniping and jamming

The most obvious indicator of a badly set blade is sniping, where a large scoop is taken out of the end of the board as you pass it over the planer. It can be caused by poor feeding technique, but is usually the result of the blades being set up too high in the block.

If the blades are very low the timber will jam as it hits the end of the outfeed table. If they are only a fraction too low the cut will gradually taper away to nothing as you pass the timber over the block. No matter how many times you repeat the cut it will always taper off.

Both these symptoms are easily cured, but you need to work very carefully and make minute adjustments until it is right. Be prepared to make several attempts to get it spot on, but the effort is well worthwhile as the planer feels totally different when it is cutting perfectly with both knives properly set.

Before you make any adjustments it is vital to unplug the machine.

Next, drop the infeed table well down to get it out of the way, because all settings are made relative to the fixed outfeed table.

Slcken off the retaining bolts on the locking wedges by winding them into the wedge. Only use the spanner provided with the machine, particularly when you are tightening up. Do not think that you will get extra pressure by using a longer one. It is deliberately short to stop you over-tightening and stripping the fine threads on the locking bolts.

The design of the tapered safety wedge means that the blades cannot fly out even if they become loose, so do not go mad with the tightening pressure.

You will need to wind the bolts well into the wedge before you can remove the whole assembly, but it will eventually come out as one unit.

Blade types

Essentially there are two types of blade, thin double-edged disposables or the thicker re-sharpenable ones which may or may not be double sided.

The advantages of disposable blades are that once the holder is set up they slot into position without further adjustment, they are double edged so you get two sets with one pair, and they are the best option for beginners.

Re-sharpenable blades may be cheaper than a new set of disposables but they have to be reground to obtain a fresh edge, must be reset each time to account for loss of width by the grinding process, and there is a longer, more involved, changeover period.

Blade alignment

Whatever the type of blade though, the alignment process is the same.

Start by cleaning the blade slot to remove any trapped shavings. Use some oil or dry lubricant on the wedge-locking screws so they revolve freely without the aid of a spanner. If they are not really free you cannot subsequently judge how tight you get them as you tighten up.

Also check that the height adjusters on either end of each wedge are revolving freely for easy adjustment.

Replace the new knife and locking wedge back in the block, taking care to fit the knife over any locating screws or lugs. Tighten up the locking bolts until the knife is held in place securely but is still loose enough to move as you alter the height adjusters.

Wind the height adjusters well in so the bade is really low. Also check that the end of the knife lines up with the end of the block.

The height of the blade has to be set just a fraction higher than the rear outfeed table, and we are talking thou here, not millimetres.

The traditional but far from foolproof way is by using a small strip of wood with two marks on it about 3mm apart. The theory involves setting the strip so that the first mark is in line with the edge of the table, then rotating the block by hand when it will hopefully pick up the wood and move it forwards a fraction, dropping it down so the second mark now lines up with the table edge.

If it moves it too far the blade is too high, and if it does not move it far enough the blade needs to be wound out.

Setting devices

Some machines come with a setting device, the best being a simple metal template that fits over the block.

All you have to do with these is wind out the knife until it bottoms in the notch of the cutout and is perfectly aligned.

Of course, this assumes the rear table height has not been altered relative to the cutter block, but it is pretty reliable otherwise.

You can buy magnetic setting blocks which work well, although working round them on the smaller machines is a bit awkward.

My setting method

The method I now use is much simpler and requires just an aluminium rule and piece of paper. The thickness of the paper represents how much the knives should project above the rear table.

Put the paper on the table, lay the rule over the block, bring the cutter out until it just touches the rule, then repeat at both ends of the block to get the knife in straight.

If at any time you wind the knife out too far, do not just wind the adjuster back in as there will still be some backlash in the thread. Instead wind it well in and then set the height as you wind out again. That way the knife will be seated properly on the adjuster. Always adjust by winding out.

Check and recheck either end then tighten the locking screws starting with the middle ones and working out to the edges. Repeat the whole process for the other knife, remove the paper and make a trial cut. If it scoops they are too high, if it tapers they are too low.

Do not worry if you have to make several attempts to get it right as the setting is so critical. You will also soon learn the difference in feel if one knife is fractionally higher than the other. When they are spot-on the planer feels totally different and you will get a perfect finish right up to the end.

Woodworkers Institute

Tagged In:

Alan Holtham , Knives , planer-thicknesser , infeed , outfeed , blades

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Troubleshooting Problems With Thicknessers

Regular serrations over the surface may be due to the metal infeed roller pressure being set too hard, crushing the wood deeper than the cutting circle of the cutterblock. This never happens with rubber-coated rollers. Try slackening off the pressure slightly with the adjusters.
With rubber feed rollers the coating can sometimes twist on the central spindle to form a lump. This results in a very jerky feed and leaves widespread dirty marks where the rubber grips intermittently. If the wood stops feeding altogether it may be that you are taking too heavy a cut or the board is slightly tapered and has jammed. Reduce the depth of cut and it should start feeding again.
If you get a scoop at the end of the board make sure there is support as it comes out of the machine. Either hold it up or use a roller stand. Particularly long pieces will oscillate up and down as the amount of projection out of the machine increases, leaving ever-deeper scoops.
Feed in only one piece of timber at a time. Unless you have a sectional feed roller never place several narrow pieces of different thickness together because the thickest piece could lift the infeed roller clear of the thinner ones which could then be fired backwards.
Indentations and bruises on a thicknessed board can be caused by poor chip clearance at the cutterblock, with dropped shavings being pressed into the cut surface by the outfeed roller. Check that the dust chute is not blocked and always connect to an extractor. If chippings are allowed to accumulate on the thicknessing table an odd one may become trapped under the board, resulting in a long score mark down the length of the underside, so always feed the work onto the end of the thicknessing table to push any chippings out of the way.