Got a wobbly plane?

You’ve got a wobbly plane?
“Just flatten it on a piece of abrasive stuck on a piece of flat glass

Thats how the advice goes. There is however, I feel, rather more to it than that and its to that little bit of that more to it that this article is dedicated.
Why then should we bother doing it, all of this flattening, faffing about? Well the truth is that a plane, or any other shave making tool come to that ,has a blade set in a jigged surface. The jigged surface in this case is the bottom of the plane, or the sole of the plane. This sole has got to be as flat as you can make it.

Until very recently, planes have been only more or less flat. Older planes were really good because they had cast steel bodies that had settled and were no longer wriggling around. Modern planes were always a pain in the neck because they were brand new, had been cast quite recently and though you could spend days flattening the damn things, within a few weeks they had resumed their steel banana configuration. So a gap in the market opened thats been promptly filled by the likes of Lee Neilson and Clifton to provide planes that are pretty damn flat, so all this plane flattening lark, fooling around with sheets of glass and abrasive paper had, I thought, dissolved into the mists of time.

But it keeps rearing its arm wearying head as people find nice, reasonably priced old number 7 Records, or quite frankly dont want to spend as much on a posh Lee Neilson plane. So the abrasive paper and sheet of glass comes out yet again. But as I said in the first sentence, theres a lot that can go wrong in this process and I thought that hopefully for the last time I shall put this down as we may have found at last a method that deals with all the problems.

The problem in essence is this.

In order to create flat surface on the sole of your plane, you need a flat surface to bear the plane against. Now the flattest surface we can find is a sheet of glass, but that sheet of glass itself, is neither inflexible nor abrasive. So you have to find a surface upon which it can be placed that is itself pretty flat. Weve used until now great slabs of MDF, bench tops and dead flat cast iron machine tables, but all have had their problems. We now use the wooden top of a storage cabinet that is about 11/4 thick.

This is a fairly rigid surface and wont bend under the relatively light pressure that might occur when flattening a plane on a glass. On the top of this we place the sheet of glass. Now this is a 15 mm thick sheet of float glass. The difference is that its placed upon those blue plastic pads that are used by glassmakers to separate sheets of glass. Each of those pads are of identical thickness and if placed carefully around the area of the glass can provide support at 100 mm centres. This is sufficient support to allow the glass to do its job.

The glass does its job…

The glass is secured at the four corners with small blocks of wood and paper shims, which you will see as white strips under the blue plastic supporting pads, are used to adjust the sheet of glass and its relationship with the workbench top. Its good practice to check that flatness of the glass periodically as the plastic pads do get compressed and if you are bearing down on the glass during an operation the configuration of the glass can change. So when you change the paper check the glass for dead flatness. Remember if the glass isnt flat theres no chance of you getting your plane flat, and that is the object of your exercise.

To check the plate glass for flatness, use your straightest, longest straight edge. We have in the workshop at the moment a 36 inch Starrett straight edge fron America which is proudly owned by one of my students and borrowed repeatedly for this process. It cost several arms and several legs so I dont think well be owning one in the future, but will in the future make do with a slightly lower quality straight edge. The key thing with the straight edge is also that is its straight, and unquestionably straight. Ive known people spend 200 on a 3 straight edge, but I have kept my spending down to just under 100 and got something that Im pretty happy with.

Less than this and I begin to get worried as there are some pretty poor straight edges being sold by mail order companies, especially one not too far from here. I think its foolish to buy measuring tools that are inaccurate to a degree that will effect the quality of your work and this is a case in point. Straight edges and squares are at the very core of your pursuit for accuracy. So watch out when that 30 straight edge pops up in the catalogue or on the web site.

To check for flatness we use a straight edge combined with a feeler gauge. If you can pop a very slim shimmy like feeler gauge under the blade of the straight edge when its sitting on edge on the glass, then you know you have to shim the glass up with a strip of paper. Put the paper where the plastic feet sit and it will do the job.

….with some Abrasive help

Your next task after setting up the glass is to attach an abrasive paper to that glass. Weve found in the past that we cant just attach it at one end and work away from the attachment as the slightly curved nature of the abrasive paper will give a greater wear down either edge of the paper resulting in a slightly convex plane sole across its width. (This can also occur in other situations, but Ill come to that later).

To overcome this, we fix the abrasive to the glass over its whole surface. Weve tried using double sided tape, but that sticks like s..t to a blanket and changing the paper is then a time consuming and solvent inhaling nightmare. Weve tried using a photo mount but that again throws a fine mist of lung clogging solvent into the air, so one of our students, Will Gordon, came up with the novel solution of first placing masking tape on the glass, applying double sided tape to the masking tape and then applying the abrasive to the double sided tape. This sounds long winded but has the benefit of being absolutely accurate which is important in this consideration and easy to change the abrasive once it becomes worn or damaged.

First lay the three strips of masking tape, down the glass. We use 2 rolls of tape and lay them with a slight gap between each strip of tape. You can then take the cap iron from your plane and use it as a burnisher to flatten further the masking tape onto the glass. Once this is done, lay probably four strips of double sided tape on top of the masking tape being very careful to not allow any dust or wood chips to raise the surface. This has got to be done carefully as we are after flatness here and flatness is a very unforgiving objective.

Next cut off a piece of abrasive paper. We are using 120 grit aluminium oxide abrasive cut from a roll. Remove one end of the backing paper from the double sided tape and fix the abrasive at one end. Be careful to align the abrasive carefully and then pull the backing paper out slowly as you lay the abrasive down onto the glued surface. If this is done fairly smoothly and quickly rather than slowly and carefully you will get a better result. You should find yourself now with a dead flat sharp abrasive surface that can be used to prepare your plane. (I told you that there was more to this than just flattening a plane on a bit of glass with abrasive stuck on it didnt I)

but you’re till having problems?

Mind you, you can still go wrong at this stage. The coarser your abrasive, the less accurate the flattening process is going to be. Weve determined that 120 grit is about as coarse as we like to go even though this can be a quite slow and laborious process if the plane is long and the curvature in the plane is pronounced. Christian who you can see in these photographs is flattening a quite nice antique number 7 bench plane which is quite a long plane and hell probably do this over 3 or 4 sessions as it can get tiring and mind disturbing after a little while. Mark the underside of the plane blade with a black felt tip pen with a series of parallel lines across the width of the plane about every 2 or 3 inches.

Now back the plane iron well back, but leave it attached in the frog of the plane. Set yourself up in planing stance and quite gently rub the plane the full length back and forth along the abrasive. Your objective now is to wear the abrasive out evenly all over. Do not just rub the plane up and down the centre of the abrasive. This will give you a worn out centre to the abrasive with a track on either side of very sharp abrasive. As you depart every now and again from that central track, the sharper abrasive will wear out the edges of your plane giving you a slightly convex plane sole across its width. Its difficult to achieve this and requires immense carelessness, but Ive seen it done more times than I would care to mention.

You will see very quickly the plane sole become shiny in some areas and is left dull in others. The dull areas are the parts that are not touching the abrasive. Your determination now is how long are you prepared to go on flattening this plane to get those areas to touch the abrasive. Its not absolutely essential that all parts of the sole of your plane are absolutely dead flat . What is important is that the toe and the heel are touching at the same time and the areas around the blade are touching. It would be nice if the bits in between were touching, but these three areas are the ones that have got to touch if the plane is to do its job properly.


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