No 7 Jointer - How flat is flat?

[Dissolve]

Hi,

I just purchased a damaged No 7 Jointer plane from Rutlands, It had a scuff at the end of the sole which was quickly removed with a very light file and touch with some 1000 grit wet and dry.. That has no bearing on what I'm questioning.

I'm using my bevel edge straight edge (This is straight, it's been checked recently against a very reliable surface plate) to check the sole and it seems to have a bit of a belly near the center of the sole. It's only very slight, but I would much rather have a slight hollow to lap than a bump, how much is acceptable? The plane was labelled as being brand new aside from the scuff on the toe, so if I measure it with feeler gauges and it turns out to be unacceptable I dare say I'll have a delightful exchange with them next week!

What would you guys consider an acceptable tolerance?

 

[dzj]

If you are satisfied with how it works, then the tolerance is acceptable.

 

[Corneel]

Get a file and remove the belly.

 

[custard]

Unless you get a Karl Holtey plane you're very unlikely to have a sole that's so flat that you're unable to measure any deviation. Most quality makers seem to have a standard of +/- 1.5 thou. I think that Veritas have a slightly different quality standard and say their soles run from 0 to -1.5 thou, in other words it may be slightly hollow but there will never be any belly.

Personally I find that a bit odd as I'd much rather have a bit of belly than a bit of hollow. With hollow the iron takes a deeper cut when it first engages but then tapers out. There is a counter argument, that you tend to apply most downward pressure towards the centre of the plane, and that effectively bends the sole a fraction and removes any hollow. I hear that but for my money belly still is better than hollow.

Anyhow, the real message is you'll probably never find a totally flat sole, so provided you don't have a total banana you're better off asking yourself "does this plane do what I want it to do?" And if the answer is "no" then start thinking about identifying the problem and figuring out how you're going to remedy it.

 

[marcros]

The British standard I think is 2th +\- it may be 1 1/2 th but has been quote on the forum a few times before.

 

[Corneel]

The Britisch standard (anyone kow which standard? All I can find is the Clifton information about this, but they don't mention exactly which standard they are talking about) is +/- 1.5 thousand of an inch. Clifton uses a precise straightedge and 0.075 mm feeler gauges. Particular attention should be paid to the area in front of the mouth of course. A bit of a hollow behind the mouth doesn't matter, but a belly overthere tends to lift the iron out of the cut, which disturbs the ability to set a fine cut.

A hollow over the entire length of the plane makes it very difficult to create a straight edge with this plane. A bit of a convex sole is less troublesome, but it shortens the effective length of the plane.

I would first test the plane though to see how it works. When you can't set the plane very well to a fine cut, I would work on the belly behind the mouth. The area behind the mouth is the least important of the plane sole, so using a file makes it perfect, allthough the looks won't be so great. When you have a precise straight edge as as a refernce, this procedure is much more precise then rubbing the plane back and forth on a piece of sandpaper and many times faster. A combination of methods is also a good idea. File the very convex parts, remove metal where you don't need it and use the sandpaper on a very flat surface for the last bit of fine tuning.

 

[Graham Orm]

Get a file and remove the belly.

Helpful.

Whatever you do DON'T touch it with a file.

 

[Cheshirechappie]

The relevant British Standard (BS3623:1981 Specification for Woodworkers' Metal-Bodied Planes) is available for purchase here - http://shop.bsigroup.com/SearchResults/ ... 's%20plane - or it can probably be viewed in the library of a subscribing organisation such as the central branch of a Public Library. (Before anyone throws a wobbly about the price, bear in mind that the BSI is not a publicly-funded body. It's effectively a non-profit making company incorporated under Royal Charter, so it has to make an income to support it's activities, and the work of putting together standards and checking that all the information in them is correct is pretty painstaking. Hence, you can't just read standards online, you have to pay for the information one way or another.)

As for the plane itself, I'd agree with custard. Try the plane out first and see if it does the job. Plane the face of a board flat with it (woodworking flat, not engineering flat), joint and fit the edges of a pair of boards as for a table-top, and see if it'll take shavings when very finely set and it's full length engaged on the workpiece. If it does those things, it's flat enough. If it won't, then the way the plane performs (or won't perform) will probably tell you where the significant faults lie. Don't do any correcting unless the plane really needs it - or send it back as unmerchantable with photographic evidence of what it won't do.

I'd also agree that a slight (very slight) convexity in length is better than a concavity, when dealing with 'acceptable' deviations from absolute flatness. The exception to this is a lump behind the mouth - but try the plane out first and see if it works OK. Remember, we're woodworkers, not metrological toolmakers.

 

[MMUK]

Just to add to the above, a #7 isn't a finishing plane anyway so IMV, you can be slightly more lenient with tolerances.

 

[Corneel]

First, thanks a lot Cheshirechappie for the reference. I am curious what's all in the standard. The description on the Clifton website doesn't make much sense, because they don't adress the area just in front of the mouth. In their description it is allowed to fly 3 thou high in the sky, which is the worst condition within their standards. For a jackplane it doesn't matter, a jointer more so.

Get a file and remove the belly.

Helpful.

Whatever you do DON'T touch it with a file.

This is how planes can look like if you don't care about cosmetics, only function. The idea was picked from the Japanese planes. Btw, this is not my picture, it is from Caspar Labare, a Dutch cabinet maker. I did the same treatment to my #4 and it performs quite a bit better now. This is a cheap and quick way to get the three neccessary points of contact in one line, the front, in front of the mouth and the rear of the sole. You do need a good straightedge though to check your progress.

 

[rafezetter]

has the sole been filed leaving the 3 main areas proud, so they can be levelled out?

 

[Dissolve]

So what are the red flags to look out for? By that I mean where is it must critical to have clearance/nothing that resembles a bump?

Obviously a large convex clearance around the mouth would result the iron having be protruded further to make a full shaving, but what should I look for most critical?

I haven't lapped the sole yet, I've just removed the burr that the scuff left at the end of the sole.

 

[Corneel]

has the sole been filed leaving the 3 main areas proud, so they can be levelled out?

Yes. This saves a lot of lapping work.

 

[Graham Orm]

has the sole been filed leaving the 3 main areas proud, so they can be levelled out?

Yes. This saves a lot of lapping work.

Interesting....I take back my previous comment, never heard of that before.

 

[Corneel]

Maybe we should add a warning: Don't do this to your LN planes. :mrgreen:

 

[Graham Orm]

I'm still not comfy with the idea. Whilst it cuts down on lapping, and probably friction whilst planing, there will be a period on every stroke where the blade will cut deeper until the un-filed rear of the sole reaches the work, then it will lift the blade a couple of thou and you will get a ridge forming.....surely?

 

[Sheffield Tony]

According to school physics, friction doesn't depend on surface area, just the force and surface properties. Sort of figures because reducing the contact area increases the pressure on the remaining surface. SO ... what were corrugated soles all about ?

 

[MIGNAL]

I'm still not comfy with the idea. Whilst it cuts down on lapping, and probably friction whilst planing, there will be a period on every stroke where the blade will cut deeper until the un-filed rear of the sole reaches the work, then it will lift the blade a couple of thou and you will get a ridge forming.....surely?

It works. I use the method on the English wooden planes that I have - two hollows along the length of the Plane. In the correct places. Of course I can just use a Cabinet scraper rather than a file.

 

[bugbear]

According to school physics, friction doesn't depend on surface area, just the force and surface properties. Sort of figures because reducing the contact area increases the pressure on the remaining surface. SO ... what were corrugated soles all about ?

I suspect school physics is ... incomplete. I note that formula 1 cars have tyres whose size and lack of tread appears
explicitly designed to maximise contact area.

BugBear

 

[bugbear]

What would you guys consider an acceptable tolerance?

A practical rule of thumb is flat to the tolerance of the thinnest shaving you're planning to take.

BugBear