Planing & Thicknessing Technique

[Anonymous]

Ever since I have been using a planer and a thicknesser, I have been a stickler for following the correct procedure in squaring up and dimensioning a rough sawn board. I have always been particularly conscious that the thicknesser will not give a flat surface, just one that is parallel to the opposite face.

However, the other day I needed a load of 8' lengths of 20mm square walnut battening to finish off a job. The only board available was an old 2" one which was twisted, cupped, bowed and consequently still on the rack after a couple of years. Being in a hurry and of the opinion that as I was only making battens it didn't really matter I dispensed with the planer altogether.

After feeding the board through the thicknesser a dozen times or so alternately flipping it over and spinning it round lengthways I found to my surprise that my board was now perfectly straight and flat. I have to say that I was only taking a fine shaving off on each pass and that my thicknesser is an old Wadkin with quite long infeed and outfeed tables.

So is the received wisdom wrong or was I just lucky?

 

[Scrit]

You were lucky-ish. The thinner the stock the more it will be flattened by the feed rollers and the less wind you'll actually take out of a board because it will just spring back after thicknessing. Thicker material is less likely to be flattened out by the rollers and so you're more likely to get a straightening of the stock, however, it will come at a greatly increased risk of the stock being ejected from the machine as the result of kickback, so I wouldn't recommend that you continue this practice. In any case a planer will take off much more stock in a pass than a thicknesser ever can.

In the late 19th century (particularly in the USA) it was common to rough saw on a band/ripsaw then pass through a thicknesser (or panel planer) or even a 3-side moulder (for T&G boards) as materials up to 1in thick could simply bent to fit then nailed down...... This is one of the reasons you sometimes find Victorian buildings with T&G boards rough sawn on the underside.

Scrit

 

[Anonymous]

Makes sense about the thicker material Scrit, but what do you mean by kickback? I've experienced it on a table saw, which is why I always use a riving knife and crown guard, but not on a thicknesser, which on the face of it would appear to be one of the safer machines in the shop.

Brad

 

[Scrit]

Hi Brad

Well on a thicknesser work is pressed down against the table and fed through by a pair of powered rollers above it, the infeed one being either serrated steel or rubber-coated whilst the outer one is generally smooth steel. The cutter block rotates against the direction of feed, meaning that the block is in effect trying to throw the workpiece out of the infeed end of the machine at all times. It is normally constrained from so doing by two factors - the constant pressure/feed action from the infeed roller and the presence of anti-kickback pawls or fingers in front of the cutter head.

In normal use the variation in thickness of a given piece of timber end to end or side to side isn't too great, and that combined with the weight of, say a plank means that there isn't the power to eject the timber which is constantly under feed/pressure. However, when you feed through small section stock, and particularly long, narrow materials, especially warped stuff, you run a much greater risk that the contact between the infeed roller and the material will be lost. Add to that the possibility that warped stock can rock as it is fed through because it has no stable flat bottom surface. If this occurs whilst there is any cutting action on the timber the cutterblock can catch and throw work out of the infeed side of the machine with some considerable force. Operators have been known to break fingers, etc when this happens although personally all I've ever had is blood bruises, but then I don't stand behind the stock. That is a kickback on a thicknesser. They do happen, particularly with badly warped/twisted stock, reaction timber, etc and especially at the start of the thicknessing process, and/or where no face planing has been done prior to thicknessing, and they are exercerpated by feeding over-long pieces through the machine - another reason for following the old joinery approach of crosscut to length, rip to width, plane, edge then thickness.

Scrit

 

[Anonymous]

Well, I guess I am lucky then - on two counts!

That I haven't had a kickback experience on the thicknesser.

And that old Scrit is there to explain it all!

Methinks I'll carry on doing things by the book.

Thanks Scrit and Happy Christmas

Brad

 

[scooby]

Add to that the possibility that warped stock can rock as it is fed through because it has no stable flat bottom surface

I remember making that mistake when I was an apprentice. I had to make a similar size bead/batten. I ripped it down to around 1/8" oversize, passed it though through the thicknesser and was greeted with a bead, when looking at the end grain, resembled a parallelogram. In the case of the timber I was machining (glazing bead, so only 2 sides showing) I found it better to rip oversize, plane face and square edge on the the planer, then get the finished size on the dimension saw.

I've never encountered kickback on a thicknesser, I've seen it happen to someone and although, in my opinion it wasn't as vicious as saw kickback, it didn't look fun.

 

[Anonymous]

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[Anonymous]

4 o'clock on Xmas Day morning, Scooby!

What is it?

Late night & not gone to bed yet?

Insomnia?

Or the delight of young kids getting you up in the middle of the night to excitedly rip open the carefully wrapped parcels of tat you've just mortgaged yourself to buy?

I was expecting the last one in my house, but it's 7.30 and all is quiet! The little ******* are getting older at last!

Happy Christmas
Brad

 

[Scrit]

You get around the rocking prob by putting it concave side down on the table so it is more stable..... .... if you planed it perfect on both sides you'd end up with 18mm instead of about 23 mm, from 1" sawn boards.....

For bowed in length I'd agree, but what about timber in wind? Normally what I do on the planer is just to make enough passes to get a flat enough surface to allow me to thickness, rather than try for a perfect surface on one side. I agree that going straight through the thicknesser with an ex-1in board will work, at least with softwoods which do tend to be a lot more flexible, as the feed rollers will handle it, but it won't take out wind - if it goes in in wind (or for that matter bowed in length), then it will come out the same way. Whilst the technique you outline is adequate for ex-1in softwood floorboards or skirtings which will be nailed to something solid (like a building) I'm most certainly not in favour of using that approach with timbers such as thicker hardwoods to be used in cabinetwork where you are dependent on having true, straight, parallel stock to start with. Possibly another influence on me has been the amount of production woodwork I have done where having straight, true stock off the planer/thicknesser is taken as a prerequisite to producing accurate end pieces.

Scrit

 

[scooby]

4 o'clock on Xmas Day morning, Scooby!

What is it?

Late night & not gone to bed yet?

Insomnia?

Or the delight of young kids getting you up in the middle of the night to excitedly rip open the carefully wrapped parcels of tat you've just mortgaged yourself to buy?

I was expecting the last one in my house, but it's 7.30 and all is quiet! The little ******* are getting older at last!

Happy Christmas
Brad

Hehe, It was the first reason mate. Stopped drinking at around 3am, and thought it was best I had something to eat and drink plenty of water before getting some kip. So thought I'd spend the time here whilst eating

Had to be up early Christmas Day morning too, so only got about 4 hours kip.

Happy Christmas
Jon