Effects of high angle frog

[ivan]

Alas, I was too young to learn all my handskills from Grandad, a joiner who worked in the huge, then newly built, late victorian and edwardian "luxury" houses on the south coast, in his younger days. But he always said 50 deg planes were for hardwood, and thus I got myself a couple of LN bench planes with the higher angle frog.

From time to time people question if increasing the bedding angle from 45 to 50 actually makes any useful difference. On an awkward grained sample today, (with frequent reversals) where the 50 deg will take whispy shavings in either direction, the same plane and blade with a 45 deg frog stutters and pulls out the surface. Planing improved at 45 deg with a resharpen, but not for long.

Grandad's hair-close cap iron also minimises the need to raise the bedding angle for a clean surface, so you still get a nice polished surface straight from the plane.

 

[matthewwh]

Bedding angle (or effective pitch) can make a massive difference to the surface produced by a plane, although IMHO exchanging the whole frog is a rather long winded way to go about it. Swapping out the blade in bevel up planes works well, but I find them less ergonomic than bevel down ones, and with very little effort higher and lower pitches can be achieved with a standard 45 degree bevel down plane.

Honing a small back bevel on a spare plane iron has the same effect as a steeper frog but it's less expensive and can be swapped in and out in seconds. I tried a 5 degree (york pitch) back bevel initially, but found 10 degrees (cabinet pitch) made a much bigger improvement - to the extent that even burrs would yield a smooth surface, let alone the odd knot or two.

To achieve a lower effective pitch a standard 45 degree bevel down bench plane can be skewed to the direction of cut (the same principle as walking up a hill diagonally to reduce the incline). This does reduce the width of the shaving but can be very helpful, particularly where there is a large disparity in hardness within the timber - zebrano for example.

 

[Karl]

Bedding angle (or effective pitch) can make a massive difference to the surface produced by a plane, although IMHO exchanging the whole frog is a rather long winded way to go about it. Swapping out the blade in bevel up planes works well, but I find them less ergonomic than bevel down ones, and with very little effort higher and lower pitches can be achieved with a standard 45 degree bevel down plane.

Honing a small back bevel on a spare plane iron has the same effect as a steeper frog but it's less expensive and can be swapped in and out in seconds. I tried a 5 degree (york pitch) back bevel initially, but found 10 degrees (cabinet pitch) made a much bigger improvement - to the extent that even burrs would yield a smooth surface, let alone the odd knot or two.

To achieve a lower effective pitch a standard 45 degree bevel down bench plane can be skewed to the direction of cut (the same principle as walking up a hill diagonally to reduce the incline). This does reduce the width of the shaving but can be very helpful, particularly where there is a large disparity in hardness within the timber - zebrano for example.

Matthew

I agree about the effects of the increased cutting angle - going to 55/60 degrees on difficult timber gives excellent results.

WRT skewing the blade reducing the EP of the cutting edge. On one of his DVD's, Rob Cosman planes some birds eye maple with a standard angle LN smoother, using a skew action. And with no tearout. I've never really understood how this works, because you would expect the lower EP to increase tearout on such a timber.

Cheers

Karl

 

[matthewwh]

Hi Karl,

The decision about how to approach a specific piece of timber is part science and part guesswork/experience/trial and error.

The science bit is that with steeper pitches the chip breaks away from the underlying timber right at the cutting edge (referred to as a type one chip) this works well on consistent density timbers and copes nicely with reversing grain. The extreme example of this is scraping, with the blade at more than 90 degrees to the surface.

A type two chip - produced with lower pitches - splits away from the underlying surface before the cutting edge reaches it, so the wood is being riven rather than shaved. The extent to which that splitting occurs can be controlled by setting the mouth opening, with a very tight mouth you can achieve almost the same effect as a type one chip even at a low angle which is kinder to softer timbers or timber with a wide variation between hard and soft patches.

The dicretionary bit involves 'reading' the specific board that you are working, even to the extent of treating different sections within the board in different ways. If the background timber on Rob's board wasn't hard enough to cope with a high angle approach then the lower angle / tight mouth approach would be entirely appropriate.

The type of tearout you get can help you to determine which way to go, if you are getting fluffy fibres on the surface from reversing grain use a higher angle. If the blade is skipping across the surface of a really hard timber try less projection and a higher angle. If the blade is tearing chunks of harder timber out of a softer background use a lower angle and a very tight mouth.

 

[ivan]

The point of the 50 deg high angle frog is that if you plane hardwood, you keep it fitted all the time.