Tight plane mouths and tearout

[Crooked Tree]

My tuppence worth:

I have a Stanley SB4 (a present, now used for rough work since I bought a 1960s Record No.5) which is bevel down and does not even have a chip breaker. I have always been surprised at how well it works, despite the comments in the old books. It seems to perform OK in pine and oak. although I guess that it might struggle in something more exotic. The blade is slightly cambered by default - I think thath the oil stone may need flattening!

 

[martin99]

It is worth bearing in mind that it wasn’t Stanley or Bailey who started using or invented the cap iron. All of the traditional English and Scottish wooden and infill bevel down planes use one. These also use heavy irons so I am inclined to think the cap iron does have merit and this seems to be confirmed in the research in Derek’s link. Karl Holtey isn’t convinced but he is increasingly making bevel up planes which is a different and simpler arrangement as only the EP and mouth play a role. I had never previously thought of the cap iron as a heat sink but I am not sure how relevant this is so long as the steel doesn’t get hot enough burn the wood or loose it’s temper – not things that I have ever had a problem with.
Jon.

Quoting Mr G from the dark side:
"Some doubt about the function of the cap iron.
i've come to the conclusion that the cap iron has just one essential function, which is to transfer pressure from the wedge (in a woody) or the lever cap (in a steel plane) to as near to the edge as possible. For obvious reasons IMHO."
I think I agree with that.

 

[woodbloke]

It is worth bearing in mind that it wasn’t Stanley or Bailey who started using or invented the cap iron. All of the traditional English and Scottish wooden and infill bevel down planes use one. These also use heavy irons so I am inclined to think the cap iron does have merit and this seems to be confirmed in the research in Derek’s link. Karl Holtey isn’t convinced but he is increasingly making bevel up planes which is a different and simpler arrangement as only the EP and mouth play a role. I had never previously thought of the cap iron as a heat sink but I am not sure how relevant this is so long as the steel doesn’t get hot enough burn the wood or loose it’s temper – not things that I have ever had a problem with.
Jon.

Quoting Mr G from the dark side:
"Some doubt about the function of the cap iron.
i've come to the conclusion that the cap iron has just one essential function, which is to transfer pressure from the wedge (in a woody) or the lever cap (in a steel plane) to as near to the edge as possible. For obvious reasons IMHO."
I think I agree with that.

The reason is to support the edge in a BD plane and to prevent 'chatter' whilst in a BU plane the edge is supported by the bed, hence the chipbreaker isn't needed...not that it could be fitted anyway.

As for agreeing with Mr. Grimm...I need another wee dramm - Rob

 

[David C]

Referring back to Brian's post, I don't know where this idea that you can't have a tight mouth and a close set cap iron/chipbreaker comes from.

It is perfectly possible to have both in a 45 degree bed plane. If one draws a crossection of the throat this should be clear.

Shaving traps or choking only happen when something is not prepared correctly. Usually the front edge of the CB, or perhaps the front edge of the throat.
Best wishes,
David Charlesworth

 

[Steve Elliott]

I agree with David C that it's possible to have both a closely-set chipbreaker and a fine mouth without causing problems with shavings getting clogged.

In most cases it's not necessary to set the chipbreaker extremely close. Using a sharp blade and taking thin shavings are my first choices for dealing with tear-out. A higher effective pitch is helpful when planing difficult hardwoods but a high EP will leave a cloudy-looking surface on some softwoods. A fine mouth and a pitch of 45 degrees or so is more likely to leave a good surface on softwood.

As for a fine mouth, one advantage that hasn't been mentioned is that a fine mouth makes it easier to judge blade projection. If I'm setting a blade to take a shaving .001" thick or less it's easier to feel the blade projection or to sight down the front of the plane to see it if the mouth dimension is small.

 

[Derek Cohen (Perth Oz)]

... A fine mouth and a pitch of 45 degrees or so is more likely to leave a good surface on softwood.

As for a fine mouth, one advantage that hasn't been mentioned is that a fine mouth makes it easier to judge blade projection. If I'm setting a blade to take a shaving .001" thick or less it's easier to feel the blade projection or to sight down the front of the plane to see it if the mouth dimension is small.

Absolutely, Steve.

As we all know, softwoods generally do not like to be scraped and are left with a fuzzy surface. As the cutting angle of a smoother approaches that of a scraper, this effect is progressive. I have, however, achieved good surface finishes with a very sharp 60 degree cutting angles on both BU and BD planes .... and no chip breakers

Setting the blade projection is probably the only real reason for a fine mouth on a shoulder plane (used for this purpose) since endgrain does not tear out.

Regards from Perth

Derek

 

[Modernist]

Referring back to Brian's post, I don't know where this idea that you can't have a tight mouth and a close set cap iron/chipbreaker comes from.

It is perfectly possible to have both in a 45 degree bed plane. If one draws a crossection of the throat this should be clear.

Shaving traps or choking only happen when something is not prepared correctly. Usually the front edge of the CB, or perhaps the front edge of the throat.
Best wishes,
David Charlesworth

I agree but you made an earlier comment which confused me

We no longer relieve the front edge of the throat here, (we used to when I wrote book 1). If the C/B edge is accurate there is no need, and the use of a honing guide is much more certain than the method shown in book 1.

I think that refining, rather than perhaps "relieving" is beneficial in ensuring a clear passage for the shaving in the area of the cap iron (depending on the quality of the plane). I am still not sure what you mean in the quote above.

 

[David C]

Yes, sorry, clear as mud.....

In the distant past when first book of articles was written we used to file and polish the front edge of the throat, at 15 degrees forward angle.

Over time I developed a better way of preparing the front edge of cap/chipbreakers, using a honing guide to ensure that they are never steeper than 45 degrees. So we no longer slope the front edge of throat, but do continue to lightly file if necessary and polish.

I can now set as fine a mouth as desired, even down to 4 thou", and the CB as close as possible for fine work in highly figured timbers, with no risk of choking.

The cap setting is more difficult to quantify, but I think I can get to between 8 or 12 thou".