Tearout when thicknessing, some Qs

[ivan]

The usual advice (apart from reading the grain) is to hone the blades, perhaps with a back bevel, take small cuts under 1mm down to perhaps 0.3mm, and maybe dampen the surface with water to swell / tighten the fibres, and slow the feed rate if you're lucky enough to have variable speed.

Tried these today (except feedrate) thicknessing some longish lengths* of curly maple when it ocurred to me that the very light cut approach might be compromised by my serrated infeed roller..... Mine bites in so that a 0.2mm pass just removes the marks. I think a fine pass makes the tearout worse, the feed roller's cross grain "nicks" making a weak point encouraging the problem. Possible?

Try a fine pass only if you've a rubber infeed roller?
Is this reason for choosing a rubber infeed roller?
If you can't aviod reversing grain, is a 10 to 15 deg back bevel a real advantage?
Should you get a backbevel ground at sharpening time?
How set serrated infeed roller pressure?

Thoughts gratefully received!

* could not cut shorter

 

[OPJ]

If you're machine has a serrated feed roller then, you should be looking to remove no less than 0.5mm in a single pass. Otherwise, as you've discovered, the roller will dig in and mark the surface. Shavings and chippings that get caught up in the feed rollers and 'recycled' through the machine can also leave dents on the surface. Make sure you have good extraction! Taking shallow cuts should also help here.

Rubber-coated feed rollers won't dig in like the serrated ones so, you could possibly take even finer cuts, if you really wanted...

If you were prepared to flog your current machine in hope of buying a Scheppach though, I reckon you'd be better off saving a little extra still and buying a Jet drum sander, to complement your thicknesser! :roll:

Not sure of whether adding a back bevel is an advantage in this situation. That's normally reserved for hand plane irons, where you'll save a lot of time otherwise spent flattening the back of the iron. Next time you drop your blades of for sharpening, you could ask them to try regrinding the bevel at 60° - I've heard that this is a better angle for getting a good finish on hardwoods but, as yet, I haven't tried this myself.

You don't really want to start messing with the tension on the feed rollers if they're already doing their job and feeding the wood through consistently, as they should.

 

[Ironballs]

I had some flame maple for a guitar top that I had to put through the big thicknessers at college, these will normally put a good finish on all but the most difficult woods but I was still getting some tear out. Finer cuts seemed no better than deeper cuts, so I just took it close to where I wanted it to be and broke out the smoothing plane

 

[Steve Maskery]

For figured timbers like this a thicknesser is a blunt instrument, unfortunately. The only way I am aware of to do this is to sand like mad.

Now if we lived in more enlightened parts of the world you could look to replace your knife cutter head with a Shelix one. You need to emigrate, I'm afraid. Australia or USA is your only hope, AFAIAA.

One day, one day.

Now perhaps I should buy a little CNC lathe and a job lot of WC tips and.......
S

 

[Philly]

Ivan
I'm sure David Charlesworth had some advice in his first book on tuning up the thicknesser. I'll have a look if you don't have the book?
Cheers
Philly

 

[ivan]

I was really thinking more about best P/T technique than the best solution for the troublesome maple.

Philly, done that; it was DC who grumbled about commercially PAR brought by his students with surface divots 2mm deep, as an intro. He also suggests back bevel, he hand honed his on knives ground to 35 deg. (This gives same efect of high angle frog) The more scraping cut means limiting max cut as more power is needed, and very light cuts down to 0.3mm (he says) reduces tearout. If I remember he had a Multico planer at that time. My experience tends me to think the Multico must have had a rubber infeed roller (DC didn't say). The pattern of pock marks I was getting with light cuts, sat very guiltily beside a strip put through a second time (to record the cross grain serrations from infeed roller). Where's DC gone? Not here, not F&C.

NIgel Voysey's book on wood machining suggests 10-15 deg back bevel (on 35 deg) when planing anything other that straightest of grained hardwood. Standard block is almost always designed for softwood, he says. My knives are 40 deg the same angle they came with, I tried slipstone-ing a backbevel as per DC. I get the impression Voysey has his knives ground with the 2 bevels at sharpening time. Wondered if anyone had tried this technique. Presumabaly the backbevel doesn't need to be much wider than a shaving thickness.

Folks on the other side appear to belt sand if any tearout appears, don't bother to 'fiddle about', but alas no wide belt (or even drum) sander here.

 

[ivan]

PS
Steve, I think I've seen something similar (to shelix) in some literature here recently, but at considerably more expense, thus binned. It might have been JKO (?) the German firm, Wealden have some of their replaceable tip router cutters and spindle tooling. This latter includes a spirally mounted "tip" planing head, although the cutting edges are lined up with the block axis, not the helix, so no skewed cutting.

If it's serrated roller for carpenters and rubber for cabinetmakers, my P/T has a rubber outfeed roller, so could fit a spare as infeed.

 

[noddy67]

Hi Ivan. Did you ever sort out a solution to this?
In a similar situation with some brand new blades on a Felder thicknesser trying to thickness some troublesome Ash and am getting terrible tearout. I have had one suggestion of putting on a 10 degree back bevel on the planer blades but wanted to ask around a bit more as the blades are expensive.

Would welcome your thoughts.

Cheers