Tuesday, 6 May 2014

lapping & accuracy

A common question I hear is how I flatten the sole and sides of a plane. Most people assume that I have a milling machine, surface grinder or some other mechanical process. I don’t - I lap them by hand. I do use a bench mounted grinder to grind off the proud parts of the dovetails and pins, but other than that - they are lapped by hand. The next question usually has to do with accuracy and there is often a level of skepticism about how accurate they actually are. The implication being that hand lapping could not possibly be as accurate as a surface grinder or other mechanical machinists process. 

Here is the process I go through - I will use an A11 style mitre plane as an example.


Here is the mitre plane after being piened together but before the infills have been installed. It shows the dovetails before grinding.  The photo below shows the plane with the infills installed and the dovetails and pins ground down from the bench grinder. 







I have several different lapping surfaces in the shop. The one in the photo above is a piece of marble inset into the top of the cabinet. I use an automotive sandpaper made by Norton called A275. It is normally used to abrade paint and fiberglass but is by far the longest lasting, least loading paper I have tried. I use a 3M product called Super77 which is a low tack spray adhesive to hold the pieces in place. Once the pieces are worn out, just peel them off and re-apply new ones. Expect to pay about $1 per sheet. As a point of reference, I have used 12 sheets (of 80 grit) so far, and 4 more will finish it off tomorrow. $16 to flatten the sole and sides is pretty good value for money in my books.



In addition to the 2 marble lapping surfaces, I have two 4" thick, 12" wide, and 36" long granite surface plates. I use one of them with A275 attached to them, but only for the final lapping with finer grit(s). The second one is kept clean and is used for measuring and reference.

The other important items are accurate measuring tools - for square and flatness. 


  

The square is one of a set of 3 I bought at the first Woodworking in America. They are in wonderful condition and have knife edges on the inside and outside of the blade. I am always on the lookout for more but have yet to find another.  

The other tool is a Russian straight edge with a very fine knife edge. Here are a few photos of it.






 It is frightfully accurate. Here is a shot of the straight edge on the sole of the mitre plane facing the sun coming through the window. The second photo shows the effects of a 0.001" feeler gauge under one corner. Click on the images for a larger view.




 



As I am lapping, I keep my Starrett square handy and check the progress often. I will use a Sharpie marker to mark spots that are high or if a side is out of square. I make adjustments to my hands, stance and pressure to bring things into square as I am lapping.

Once the lapping on the first (marble) surface is just about done, I still check using my Starrett in multiple places, but I also like to place the plane on the Granite plate and push the knife edge square up to it. This is just another way to cross check that things are in fact square. (It is also important to dust off the reference surface plate before placing the plane and square. Even one piece of loose grit can really screw things up).




 The square pushed up to the sole...



 ... the square pulled back a couple thousandths of an inch to show the light gap (click on the images for an enlarged view).

I check the plane in several spots to make sure it is square across the length of the sole. The only light gaps should be the micro gaps left by the scratches from the individual pieces of grit in the paper. A knife edge square makes things so much easier to see and will reveal gaps that a flat edged Starrett will not.

Hand lapping is physically demanding work, and may not be for everyone, but it is fairly low cost, and with practice, patience and a deliberate watchful eye, is certainly capable of producing excellent results.

It is also good exercise.



(the almost finished mitre plane)

20 Comments:

Anonymous Anonymous said...

Very interesting post - thanks for sharing your knowledge

6 May 2014 22:32  
Blogger Kevin Brehon said...

Thanks for this post. For me, the metalworking parts of plane making still hold a lot of mystery. Every little bit helps.

6 May 2014 22:58  
Blogger Konrad said...

Hi Kevin,

The metalworking part often seems tricky for people who are used to working with wood. The approach I took was to think about metal as a strange wood with strange working properties. You can do almost anything to metal that you can do to wood... you just need to work a bit differently and with different tools sometimes. This approach has served me very well - maybe unconventional, but it worked for me.

cheers,
konrad

7 May 2014 05:53  
Blogger pmelchman said...

Old school, slow and easy wins every time. Thanks for the insight.

Patrick Melchior

7 May 2014 06:55  
Blogger pmelchman said...

Old school, slow and easy wins every time. Thanks for the insight.

Patrick Melchior

7 May 2014 06:56  
Anonymous Anonymous said...

Konrad

An excellent post that reveal much of the thinking behind your exquisite level of work. I too enjoy the metalworking part of "woodworking" in great part due to my early years in the pattern shop of a foundry, and I hope to write and blog more about metalworking int he woodworking shop. Nothing exotic, but sometimes pot roast is preferable to something fussily elegant.

Don Williams

7 May 2014 07:12  
Blogger Richard Wile said...

As an owner of planes from all the major contemporary planemakers, the workmanship and tolerances of all of them are incredible. The means to the end is not apparent in any of them and really should not be an issue - and it isn't. Thanks Konrad for the insight into another way to skin the same cat...

Nice plane BTW :-)

Rich

7 May 2014 10:23  
Blogger Konrad said...

Hi Patrick,

I agree fully with the sentiment of slow and easy and old school, but there is a funny thing that often happens. It starts off slow and easy, but it usually speeds up and skills and confidence increase and suddenly it is fast and easy. This is one of the surprising things I have discovered - handwork seems to know no limits to speed whereas a machine has a much more limited pace.

cheers,
konrad

8 May 2014 05:41  
Blogger Konrad said...

Thanks Don,

I look forward to reading about your experiences with metalworking. I was initially nervous about metal working but planemaking has opened up many doors for me - the biggest one being the initial fear of working with metal in the first place. Once you start, you look at objects very differently knowing you could probably make things you would have overlooked earlier. It is quite liberating.

Love pot roast!

cheers,
konrad

8 May 2014 05:46  
Blogger Konrad said...

Thanks Richard,

This is something that Karl and I have talked about many times - the very different ways in which we work. We have some very common goals but quite radically different ways of getting there. I suspect we would accuse the other of being nuts:) But at the end of the day, if your process accomplishes what you are after (and is appropriately accurate) it does not really matter how you get there.

cheers,
konrad

8 May 2014 05:56  
Blogger Chris Bame said...

Hi Konrad,
Nice post on accuracy. I often wondered what was a good reference, 4" of granite ought to do it : ) Going to have to look into the paper you mentioned too. Thanks for sharing. Really liked the cabinets with the inset marble tops.

Cheers Chris

13 May 2014 12:41  
Blogger Konrad said...

Hey Chris,

Yeah - 4" granite pretty much covers it:) Those cabinets are a funny thing - quite a few people comment on them. They are just utilitarian storage with Ikea pulls. I have been meaning to replace the pulls because every time I lap on that side of the cabinet, I often catch my pants pocket on one of them and tear it off! Either that or whack my knee cap:)

Let me know if you can find the paper or not. It is made in Canada and I assume it is available in the States.

cheers,
konrad

15 May 2014 20:34  
Blogger raney said...

In the states, A275 is known as "champagne magnum"

Someone in the marketing department at norton us undoubtedly wakes up with a laugh every morning over that little bit of buffoonery. I can only assume that Screwcap old thunderbird was deemed a step too far.

Anyway, I get mine from Jamestown distributors over the webs.

Great post Konrad. I do have a surface grinder but have also found hand lapping much more accurate.

29 May 2014 06:54  
Blogger Owen Crane said...

Hi Konrad - I'm wondering how your sidewalls/bottoms are made? You aren't hacksawing and filing these to shape are you? I don't know anything about metalworking, but went back and read every single post you've made and have learnt a lot - great blog - and there are lots of things you do I didn't know were possible but that seems especially crazy. I showed your work to a metalworker friend and he thought it must be cnc/waterjet/laser or something to that effect, and looking at sidewalls like the 28.5" jointer, I had to think it might be likely. Also I think in all the years, you haven't covered that? Are your sidewalls and soles outsourced? I assumed you must be doing things in a similar way to holtey - but his blog is all full of pictures of milling machines and cnc's...I also noticed he uses the cnc on his knobs and totes, so maybe your approaches are more different than I thought at first. Anyhow would really appreciate some feedback on that!
Great work, as much as it seems comical at this point in my life to own a plane worth as much as yours....one day I will have one.
Thanks!
Owen

14 June 2014 17:46  
Blogger Konrad said...

Hi Owen,

Thanks for the note, your comments and questions. Just when I thought I had covered every aspect of planemaking, you have pointed out an area that I may not have touched on enough.

The sides and soles are cut with waterjet. Waterjet and not laser. I have cringed when a few people have employed a few laser cutting outfits thinking they were saving money. Laser cutting 01 tool steel is not a good idea - you are effectively heat-treating the edges and filing and piening will be a nightmare. Waterjet cutting is a little more expensive, but it can cut 01, bronze or even a heat treated blade. The cut is not 100% perfect, but it is fairly close and the amount of hand work to get everything perfect is worth the expense when compared to hand cutting with a hacksaw. I know - I did that for the first 3 years. I don't regret it at all - it was great practice for sawing and there are still times now when I will hacksaw a quick part or make a modification. It is amazing how accurately you can saw with some practice under your belt!

After waterjet cutting, there is a lot of hand filing and fitting, but there is no machining or milling from that point forward - the waterjet eliminates the grunt work.

All the wooden parts are cut in my show on a bandsaw and then various other saws (mostly handsaws), files rasps and chisels. It is the woodworking aspect of planemaking that drew me into it in the first place - I view metal as a strange wood with strange properties and proceed that way. It may be unorthodox, but it has severed me quite well up to this point anyway.

cheers,
konrad

16 June 2014 21:49  
Blogger Owen Crane said...

Ah cool, - Thanks for the response Konrad - no idea how you manage to build this stuff and keep us all informed at the same time.
Cheers,
Owen

16 June 2014 21:58  
Blogger Caleb James said...

Another good post. Thanks for sharing!

20 June 2014 14:28  
Blogger Konrad said...

thanks Caleb - glad you enjoyed it.

cheers,
konrad

20 June 2014 14:55  
Blogger pmelchman said...

Konrad,

what lubricant do you use when you use the sand paper? Simple Green, plain water...oil? or nothing.

patrick melchior

26 June 2014 20:50  
Blogger Konrad said...

Hi Patrick,

I don't use any lubricant when lapping on the sandpaper.

cheers,
konrad

26 June 2014 21:16  

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