Lowest possible Bevel Up Bed Angle???

[Dan Barr]

All,

What is the lowest possible Bevel Up Bed angle a plane can have?

any stabs would be better than none. All i ask is that you explain your rationale.

My guess is in the 3 to 10 degree range by limitation of the strength of the bed itself.

cheers

dan

[Bill Houghton]

zero, as demonstrated by Lee Valley: http://www.leevalley.com/wood/page.a...64&cat=1,41182.

If you mean held in an actual plane body such that there's plane body below the iron, then I suspect the answer is partly, "how much are you willing to spend?" The 12 degrees that Stanley and the other makers settled on as a minimum back in the gray cast iron days is prone to chipping, but works very well. By using some more exotic metals (not a metallurgist, me, but I envision a titanium plane body), you might be able to get lower.

I think you would soon reach the point of diminishing returns, though: any improved benefit would be outweighed by increased cost.

[Sam Takeuchi]

0. Flush plane has no bedding angle. Neither ancient Egyptian plane (pre-Roman) also had 0 bedding angle. It had a copper (or bronze, I don't know) blade attached to a wooden body. Blade was laid flush to the sole in a bullnose fashion.

[Dan Barr]

for nothing.

Gentlemen,

I do appreciate your clever answers. while they are "potentially" correct, I am trying to find out the actual limitations of Beds and bed angles. (both wood and metal)

while 0 is a nifty answer, it is not allowing a bed to exist. therefore, to wit; your answer is not pertinent to the question. you might say "aha! you are not actually talking about a bed though." but alas, I am inferring existence of a bed through the use of the term "bed angle". otherwise, i would ask "what is the lowest angle that a plane can cut at. (to which the answer would be the honed angle of the iron, due the flush plane)



Thanks and cheers,

dan

[george wilson]

I made a miter plane in 1970 whose angle was so low,I COULD NOT GET IT TO CUT!!!!!. I shouldn't have been such an extremist! So long ago,I can't recall the angle now. The plane was fabricated from 1/4" brass half hard sheet.

[Raney Nelson]

I don't like going below 15 if I can help it, and certainly not 10. The problem is the clearance angle of the blade - once the fibers move past the edge, there is a degree of springback. If you don't have enough clearance angle, this can force the blade up, and out of the cut. It can also increase the wear rate of the bevel.

a 0 degree bevel won't take a shaving other than to remove high spots. That is a very limited application for a plane - most bench planes are also used to remove material in a consistent fashion.


edit: with respect to your later clarification about being mostly concerned with beds - I think there's a reason that we don't see any beds lower than 12 degrees. With wooden planes, it's unusual to see much under about 20 degrees. But I still think clearance angle is the more limiting factor when dealing with metal planes. I also think this is the reason you see 45 degrees as the lowest commonly used pitch for BD planes in the west (leaving 15-20 degrees clearance for common bevel angles of 25-30). In japanese BD planes, 38 degrees is the lowest I've run into, and sharpening with the blades for these planes is considered absolutley critical because of the possibility of clearance issues.

[Joel Goodman]

As stated the clearance angle is the issue. You could prove this to yourself by putting back bevels on a low angle block plane and see where it stops working well. But what about wooden spokeshaves -- don't they have an essentially 0 clearance angle?

[Dan Barr]

yes

spokeshaves have 0 degree beddig angle because they have no bed.

back bevels dont really equate to my question. I am wanting to know the lowest bed angle possible on a Bevel up plane.

a bevel down plane would equate to your instance of honing back bevels.

i think the answer is that any angle can be used as long as enough pressure can be put close enough to the edge of the blade so that the blade cuts into the wood.

this being the limiting factor; the amount of pressure on the blade, what is the lowest possible bed angle? at a few degrees (1-5) the thickness of the blade (typically .125 +/- a little) will not be strong enough nor will the bed, to exert more pressure than the resisting force of the wood. i suppose that the blade would bend up off of the bed slightly.

however, i believe that a lower angle can be achieved through a thicker blade. this would lend strength to the cutting edge from a further distance

--from a further distance because no material will be able to withstand that amount of pressure on a 1 degree sliver of a bed. the blade will have to be secured "further away" on the bed, relying on the structural integrity of the blade to keep the cutting edge in exact position under great pressure.

hmmm...

dan

[Joel Goodman]

I think you are ignoring clearance angle issues and focussing on the mechanics of the plane body. I think the cutting issues are the real ones. Larry Williams has some strong opinions on clearance angles in some older threads about BU vs BD.

[Raney Nelson]

While a LA spokeshave (potentially) has a zero clearance angle, that clearance angle is constantly adjsuted 'on the fly' by the angle you're using the shave at. Try using one flat to the wood - you get nothing. And 1, 2, 3, or even 5 degrees usually doesn't work any better - because of clearance angle issues. At a low angle you'll start to get the blade intermittently diving into the cut, then being pushed back out, etc etc. until you raise the angle to the point that clearance angle is high enough to negate the push from springback of the wood fibers. At that point, you start getting the sort of shavings you' hoped for...


Dan - Can I ask why you're asking this? Are you planning to do an experiment of some type on this, or to make a plane? I ask because I believe Bob Strawn has actually made a plane with some degree of adjustment to the bed in order to test this very thing, and might have something to add here (if he's reading this).

[Shawn Patel]

My instinct is as you drop much below 12 degrees, the bed offers too little stability to be useful.

Rather, it might be easier to use a 0 bevel bed and a thicker blade honed to a sharper angle.

[Dan Barr]

Hello gents,

My aim here is to understand more about the mechanics of panemaking in general. More specifically, the limits of such considerations. i.e. bed angle, wedge angle, lengths, etc.

some of this is physics 101, but, I havent cracked a physics book in some time and translating some of this to physics will take me more time than hopping on SMC and asking the community.

I'm embarking on building all my own wooden planes. But before i jump in I want to think about things and have them worked out a little. I know jumping in will teach me plenty. I did a mark up of all the lines on a block of wood last night for making a very narrow smoother. no particular purpose other than playing with tools before i went to bed. just doing that reinforced numerous tidbits of knowledge that I had picked up but would otherwise never write down in my own studies. those types of things you just take for granted.

anyway, I'm mostly exercising thought processes.

Cheers,

dan

[Larry Williams]

Dan,

Old low angle wooden planes with bevel up irons, like miter planes and shoulder planes, were bedded at 20º. Every one I've ever seen failed structurally. You can see the cracks coming off the back corners of the mouth on the plane Joel Moskowitz recently blogged about : http://tinyurl.com/ykpl678

or the crack off the back corner of the escapement of this commercially made British boxwood shoulder plane:

The problem is that the wedge on these planes exerts its pressure at an angle too close to the natural cleavage lines of the wood and wedges put a lot of force on things with very little pressure on the wedge.

History holds an interesting lesson that may help you understand clearance angles. In the late 18th Century, most dedicated planes for shooting miters were strike block planes. Strike block planes are bevel down and bedded about 40º which is a structurally sound design. Strike block planes were replaced by miter planes. Wooden miter planes, like the one Joel shows, were bevel up and required a stop to close the mouth and some other features like longer irons that increased the cost. The 1829 J.Wilkes catalog that Joel mentions lists both the strike block and miter plane--the strike block cost 3 shillings and the wooden miter plane sold for 9 shillings, three times as much.
You can see both types in this illustration taken for an old David Stanley auction catalog:

The miter plane is above and the strike block is the lower plane.

This leaves me with a big question. Why did a structurally inadequate plane replace a structurally sound one that sold for one third the price? I believe the answer is that the strike block is pushing the clearance angle limits with only 15º of clearance when the iron is sharpened at 25º. At the time trade practice was to freehand grind the bevel before honing and those grinders didn't have tool rests. Their bevel angles were hit or miss. Our experience making a strike block began with the iron beveled at 30º and the plane just didn't function as it should. It had to be forced to take a shaving and tended to act dull. The surface left by the plane was burnished and not the dull looking open pored surface one wants a plane to leave. The plane's behavior improved radically when ground and honed at 25º because the clearance angle increased from 10º to 15º. Free-hand grinding just isn't accurate enough to keep the needed clearance angle and the strike block plane would be prone to clearance angle problems. I think that's why the miter plane replaced the strike block plane.

Your question, "What's the lowest possible bed angle," depends on a lot of things centering on clearance angle. The minimum clearance angle varies depending on the sharpness of the iron, the bevel angle of the iron, the angle of attack or angle at which the shaving is deflected, the type of wood being cut, the depth of cut. One thing I know is that my 55º bedded bevel down smooth plane just doesn't work properly if the iron is sharpened at 35º. 20º simply isn't enough clearance and this is when it's sharp and taking fine cuts in a dense wood with low fiber deflection.

Can one force a plane to work when there's not enough clearance angle? Yeah, usually. It depends on a lot of things. It won't work properly and will require you to work harder than you should. Both control and surface quality suffer.

Wood fiber deflection ahead of a cutting edge and its springing back to its original position after being severed is interesting stuff. It works with you by giving control of paring chisels or the previous example of a wooden spoke shave. When it's not working with you it's best to leave clearance for it. If you don't you'll end up fighting your tool and work.

[Raney Nelson]

Originally Posted by Dan Barr

Hello gents,

My aim here is to understand more about the mechanics of panemaking in general. More specifically, the limits of such considerations. i.e. bed angle, wedge angle, lengths, etc.

some of this is physics 101, but, I havent cracked a physics book in some time and translating some of this to physics will take me more time than hopping on SMC and asking the community.

Dan,

Your mention of physics made me chuckle. My degree is in physics, and I can tell you with absolute certainty that my experience with physics was basically worth squat when it came to planemaking. The reason for this is that while a plane behaves according to the same laws of physics as the rest of the universe, the truth is that wood is such an idiosyncrtic material, and working it is fraught with the sort of 'irregularities' and multiple variables that drive physicists to distraction. Wood is just not a cooperative substance when it comes to reductionism.

The most instructive things I've ever done to learn more about planes and making them is to copy well-established designs, preferably those that were in use back when wood was worked by hand all-day, every day, by an enormous community of craftsmen whose livelihood depended on knowing what they were doing. John Whelan's book is probably the best overall source of information I've seen, unless of course you manage to corner Larry Williams at a show somewhere, and ply him with gifts to get him to drop some instructive little tidbits like the one above.


edit - It occurs to me that some might read this post as implying that I'm chuckling at you, Dan, and that isn't what I meant at all. So just in case - I want to clarify that what I meant was that I laugh when I remember how frustrated I felt at many points, because things didn't seem to act the way I thought they should, and some of what I was learning just didn't seem to make sense to me.

[Jim Koepke]

Have been enjoying this thread. Up early today since I could not fall back to sleep this AM.

For some reason my side rabbet planes came to mind this morning. Most likely something to do with cutting sliding dovetails.

Anyway, was thinking that those may be the answer to what commercially made planes have the lowest bedding angle for a bevel up plane design.

According to the Lie-Nielsen, the bed angle is 8° with the blade bevel at 25°.

They will develop cracks if used too roughly.

jim