granite worktop offcut for lapping plate?

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Wouldchuk

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Morning all - I was chatting to a guy in the pub who runs a worktop company, and offered me an offcut of granite to use as a lapping plate for planes.

I've not taken him up yet as I wanted to check - is worktop-grade granite flat enough for the lapping of plane soles? Considering I am a hobbyist... I should think they are, to an acceptable standard for me at least.....

And what is the ideal sort of size - I've a No 7 as my largest plane. I dont want to have something larger than I need.

Any advice gratefully received.

Tim
 
Wouldchuk":1o3asglh said:
Morning all - I was chatting to a guy in the pub who runs a worktop company, and offered me an offcut of granite to use as a lapping plate for planes.

I've not taken him up yet as I wanted to check - is worktop-grade granite flat enough for the lapping of plane soles? Considering I am a hobbyist... I should think they are, to an acceptable standard for me at least.....

And what is the ideal sort of size - I've a No 7 as my largest plane. I dont want to have something larger than I need.

Any advice gratefully received.

Tim

I don't believe (what woodworkers call) lapping of soles is a good technique for making them flat, and I don't trust worktops to be flat enough to be involved in a laborious process without at least some hope of a successful outcome.

If your goal is to be within 1-2 thou, you must know that your reference is (in fact) BETTER than that.

BugBear
 
Perhaps the first thing to establish is whether or not the planes actually need lapping. It's a lot of work, and there's no point spending the time and effort aquiring equipment, setting up and doing the job if they don't need it.

To check, sharpen up the iron of each plane, fit the cap-iron nicely, set the plane up and try it doing the work it's designed for. If your smoothers will take a fine, whispy shaving and leave a clean, polished surface on wood, they're flat enough. If your No 7 will dress the edges of two boards longer than the plane so that they match nicely with just a hair of light showing at the middle of their length, and it'll dress the surface of a board flat and true when tested with a (woodworking) straightedge and winding sticks, it's doing what it was designed to do, and doesn't need flattening. With a jack plane, you have a little more latitude - if it'll take off a nice, thick shaving to bring a rough surface true, or thickness a board, it's doing what it should. The same applies to joinery planes, mitre planes, shoulder planes and what have you - test them out by using them, and if the results are good, the plane needs no lapping.

By the way - it's surprising how many problems can be cured by sharpening the cutting iron - a dull iron can give all sorts of wierd effects, some of which may be wrongly attributed to other plane faults by the newcomer.

It's certainly true that there are a few planes out there with soles that are of unacceptable flatness, but most planes are good enough for duty. You'll soon find the rogues by using the plane - if it just won't take a fine shaving no matter what you do with the adjusters, then the sole is suspect. However, I repeat - those planes are a minority.

One of the problems with using things like granite worktop is that you don't know how flat it is to start with. It may be as good as a certified surface plate, or it may not. You therefore run the risk of inadvertently making your plane soles less flat than they were. A slightly better bet is a piece of float glass, which being made by floating on a bed of molten metal, will be about as flat as things can be made without resort to very sensitive measurement and correction. The glass still needs to be laid on something flat, though - to some extent it'll conform to any humps and hollows on whatever it's supported on.

The only way to be sure of 'flatness' is to use equipment of known, and certified, flatness - a proper engineer's surface plate or engineer's straight-edge. Neither are cheap or readily available (to the average woodworker, anyway). To be sure of a good job, taking any plane that exhibits faults to a properly equipped machine shop for surface grinding is probably the best solution (Ray Iles can offer such a service, I believe). To expand a little on Bugbear's point above, doing the job by 'lapping' at home with extemporised equipment will almost certainly give a plane sole with convexity both in length and width, which whilst preferable to sole concavity, won't produce 'flatness'.

In summary - sharp iron, nicely fitted cap-iron, try the plane out. If it does what it's supposed to, job done - no further action is necessary.
 
Right ho - I shall probably pass that offer then.

The particular reason I was interested is as I've an old Bailey No 7 which has a very noticeable highspot just behind the throat and it's never cut right, despite new iron, new chipbreaker and attention to all these from me and also my father in law, who has a lot more experience than me. His advice was to see if I could try and have it reground, but any local engineering firms have turned their nose up at the job.

I inherited the plane, and it's getting to the point where I may just look to buy something new and save myself the time and work involved in trying to fettle up something quite so wonky.
 
Wouldchuk":2wjc7otv said:
The particular reason I was interested is as I've an old Bailey No 7 which has a very noticeable highspot just behind the throat.....

Ah - that's definitely a rogue plane! There are others that crop up from time to time with the same fault - I gather it's quite a common failing on the Calvert Stephens 88 plane that Record made for a while. However, lapping probably won't help in this instance.

Inagine a plane with a hollow in the length of the sole, so that the toe and heel are in contact, but the mouth area is clear of the wood (that's also a fault that crops up, usually on newer planes). In this instance, lapping will help, since the two points in contact with the lapping surface are 'high' and need removing. However, it's almost impossible to lap something with only one high spot. Balancing a plane sole on just a high spot is just asking too much; there must be some other part of the plane sole in contact with the abrasive, so that part will be abraded too, even though it's not a high spot. Hence, you end up with a convex-soled plane.

To tackle the high spot with only simple 'home' equipment, try the following. First, check the sole with as good a straightedge as you've got - even quite a short one will do, such as the blade of a 6" engineer's square, to find where the high spot is. Check along the edges of the sole too, since the side webs may well have kept the casting straighter there, so the high point may not extend to the sides. Mark the high spot with something like a Sharpie (or chalk or soft pencil, if they'll take on the smooth plane sole). Then start to address the high spot with a smooth cut file, but be careful which file you select. You want a 'flat' file, not a 'hand' file - the 'flat' ones have a very slight belly in their length which you can see by looking down their length. (They're called flat files because they're used for filing flat, not because they are flat. They usually have tapered, curved sides too, so that you can tell them from hand files - which are flat!) By using the flat file with a bit of finger pressure over the part you want abraded, you can control where you take metal off.

Be a tad careful how you hold the plane in the vice. Plane sole castings are thin, and vice pressure can distort them a little and give false flatness readings when you're checking with the straightedge. It may be better to do the checking with the plane free of vice pressure.

If you don't have a flat file to hand, you can make a pretty good substitute from a stick of (say) 1" square wood, with one (or more!) faces planed to have a slight belly, and then a piece of coarse emery cloth or wet-and-dry glued on.

With the weapon of choice, attack the hump. Go a bit cautiously at first and CHECK FREQUENTLY with the straightedge, so that you can gauge how fast metal comes off. You can pile in a bit more enthusiastically once you get a 'feel' for the job. To start with, DO NOT file anything away from immediately behind the mouth. Do this bit last, if it needs it. What you want ideally is a plane that touches at toe, heel, and around the mouth.

When you get it flat to your satisfaction, you can either leave the sole with abrasion marks, or dress the whole length with fine wet-and-dry wrapped round a block of wood or cork sanding block. That's more for appearance's sake than effectiveness. A careful rub on the float glass lapping plate would clean up the sole surface too, now it's flat; but it's not a really necessary step.

Finally, fit blade and cap-iron, and try it out. Adjust as necessary. With any luck, that's a job you'll only ever need to do once on any metal plane.

Hope that helps!
 
If it has a bump behind the mouth I wouldn't fret too long and just grab a file, any file, and remove it. It doesn't matter to the function of the plane when you create a bit of a concavity in that spot, or when you leave scratches. If the scratches are too unsightly, then rub a bit with some sanding paper. A bump in that spot is bad, a concavity is no problem.

But get a real straightedge first when you start metal working like that. A steel ruler or extruded piece of aluminium is most probably less straight then you plane sole.
 
Grand - nothing ventured, nothing gained! I've a proper Veritas steel straightedge so will run that across and get a sense of how high and where and then see what I can do with a file.... thanks v. much.

t
 
first, is it real granite of plastic granite. Most are reconstituted stone chips in resin. Personally I would use plate glass for a straight edge.
 
As another approach to removing a "hump", an engineer's scraper might be at least as good as a file, since you can concentrate on the area needing attention, without any danger of damaging other parts of the sole.
 
Hi All I have a piece of granite worktop ( proper granite not reconstituted ) and its about 2 1/2 ft long. I think its pretty flat - I can get a 2 thou feeler under a straight edge laid across it so its not to engineering standards but probably OK for woodwork. I have used it a few times but the main problem with it is that it is HEAVY to manoeuver round the workshop.

To take a few thou off the bottom of a plane I would reccomend using an engineers scraper - a modified old file will do - once you have removed the hard skin it is fairly easy to remove material from just where you want.

Best of luck --------Arnold
 
I use a piece of 25mm melamine faced, MDF with abrasive paper glued to it for flatting my oil and water stones. I also use it to flatten the soles of my planes; if they ever need it, but again we are in the realms; as Capt. Mainwaring would say.

I don't have time to flatten plane soles to the nth degree. Not enough hours, as they say. I can buy a new LN or Cliffie and know they are going to be flat enough for most of us. So for my older clunkers, if they are flat right across the width, at the nose, around the mouth and at the heel then I am happy. I'm not the world's best woodworker, but I'm happy enough with what I get from my planes. If I found a 'hump' in any of my second-hand planes, then it would be my fault for buying it. I'd dismantle it and keep the bits. The body could make a nice doorstop.

Now, I just noticed the wind has ripped the felt off my shed, so I have to go and tend to that! :cry:

Regards

John
 

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