Archive for the ‘towell’ Category

Towell Miter update – infills and edge treatments

Before I pein the shell of the miter, there are a few more things that need to be done. The first is to fit the front and rear infill blocks, which are much simpler to refine to shape before the sole and sidewalls are joined.

I’ve covered most of what I have to offer on shaping the infill blocks in a previous entry, so I’m not going to go into much detail here, other offering a small point regarding the pitch of the infill bed – ideally this should be an exact match for the pitch of the metal ramp it’s going to meet. In practice, though, it is vital to understand the tolerances for ‘exact’ in this application.  In short, if the infill bedding angle is even a tiny bid  lower than the ramp’s, the plane will work poorly if at all; A slightly higher pitch on the wooden bed, however, is not only acceptable, it’s even advantageous. In this situation, there will be a very slight gap under the blade at the junction of metal and wood, with the blade very solidly seated at the top of the bed and the mouth.  This way, when the wedge is set,  the blade will be very tightly ‘sprung’ in place, with extremely good registration at the mouth — which is by far the most critical point. I shoot for a very slightly steeper bed than ramp angle – and by slightly, I mean 15-30 minutes (1/4 -1/2 of a degree).

One feature of the Towell plane that I really like is the shape of the front infill escapement. It rises from the plane’s throat in a gentle ogee, which is fairly common, but just below the top there is a single bead which forms a perfect surface for your thumb in use.

Here are the infill sections after sanding (no escaping abrasives in planemaking, unfortunately) and the first coat of french polish.

 
The other operation I need to address before peining is the final finishing of the front and rear sections of the plane, which will be much much harder to work on once the plane is assembled.  I flatten and sand the front plate and rear curvature at this point, proceeding through 320 grit. 
I also cut the front and rear sole radii, and finish the front and rear top surfaces as well ‘. The sides of the plane will be lapped and cleaned up after peining the shell and pinning the infills in place. I also take the opportunity to draw file and sand the subtle radius along the top edge of the plane.
Here’s the shell, ready for peining:
And with the infills in place:
Finally, I shape and grind the blade blank to get a better picture of the final appearance.
From here, there is nothing left to do but continue building french polish on the infills and get ready to pein the shell.

Towell miter – sole assembly

OK – now the plane shell is starting to move along.  It’s time to prep the sole assembly and cut the tongue and groove for the mouth. This part of the plane construction is only applicable for bevel-up planes, and doesn’t generally apply for bevel-down planes — which are the vast majority of infill planes.

For a bevel-up plane, however, we’re looking for an extremely fine, tight mouth – and the only reasonable way to do this with ‘conventional’ tools is by splitting the sole in two, then rejoining it once the ramps have been fit. The first step, then, is to split the sole in two right where the mouth would be, and shape the ramp and rear of the mouth.

Filing the Ramp
There is really no secret to filing this ramp other than to be very very patient and painstaking. Once it’s  close to the final level, draw-filing gives very clear indication of where the high spots in the ramp are, and where it is out of flat. This process is not nearly as difficult as it might appear at first glance, but it definitely requires patience… this ramp is the most critical single point of support for the blade in the final plane, and should to approached accordingly. Did I mention patience?

I’m using a 22.5-degree bedding angle, with a sole thickness that is 5/16″ (.3125″) thick.  Some quick trigonometry calculation give me the following:

          TAN(22.5) = .3125 / x    [where 'x' is the run of the ramp]
          x =.3125″ / TAN(22.5)
          x = .754″

so I mark out the rear of the ramp at 3/4″ from the mouth. In order to make it simpler to cut and file at the angle I need, I position the sole piece laterally in my vise at exactly 22.5-degrees — this way if I saw perfectly horizontally, I know I’m hitting the proper ramp angle.  This makes it simpler to hacksaw the series of comb-cuts to remove the bulk of the material for the ramp.

Here are some closeups of the cuts from front to back – ideally they should get as close to the ‘lines’ as possible, but they mustn’t go over or I’ll be left with a nasty mark in my bed.  And nobody likes that.

At this point, I would now whack out the ‘tines’ and then file to the final ramp surface as precisely as possible.  I wanted to show the method here for the benefit of anyone who wants to try this for themselves — but as I am a weak man who is currently suffering a nasty bout of tendonitis, this is where the siren-song of the new mill became too much to resist. I milled out the bulk of the waste (though the surface still needed some final filing to get it just-so)

The final results are hopefully the same, whether using a mill or a pillar file – a nice, clean, and very flat bed. Here’s what I have after some very careful finish filing:

Tongue and Groove 
Next, I open the groove for the tongue and groove joint that will register the two halves of the sole together. First I mark out the groove – roughly 1/3 the thickness of the sole, and about 3/16″ deep.  I put the sole piece back in my vise, this time perfectly vertical, and with the depth of the groove right at the top of the jaws to give me a guide to saw to:

Then carefully, I saw for the front side of the groove:

Once I’ve gotten to depth, I flip the piece in the vise and saw for the other side, taking my final cuts across both sides of the groove.  Then I refine both sides with files.

Here’s the final groove:

Now it’s on to the front half of the sole. The front piece is filed similarly, but I use a 45-degree angle for the throat piece. Additionally, I leave 1/4″ of extra material for the tongues that will register the front and back portions of the sole together.  I’m cautious to do a lot of test-fitting to ensure the joint fits properly, and that there is as little ‘step’ in the sole from front to back as possible – I’ll have to lap out whatever differential there is at the end.

H
ere’s both halves of the sole, ready for dovetailing:

Dovetailing the sole 
Finally it’s time to cut the dovetails to join the sidewalls to the sole.  In the interest of brevity, I’m not going to detail all the cutting and filing operations here – it’s been well-covered in earlier entries.  One important item to keep in mind, though, is that when joined together, it’s important that the dovetail joints force the tongue-and-groove joint closed, rather than open – so when marking out, I want to ensure the joint is very tight.  I put the sole assembly in a parallel clamp to force it tight, and carefully mark out all the dovetails directly from the sidewalls:

From here, it’s back to – you guessed it: more hacksawing, and much more filing. Finally, though, after a lot of filing, checking fit, filing some more, and checking fit again…

I get to another  milestone… the sole and sidewalls are now fitted, and all of the metal joinery for the plane is now complete.

 The mouth is consistent across the plane, and just a sliver of light – this is good, as it means I’ll be able to lap it open to the size I want once the plane is finished.

Now it’s time for a break – I’ll put the front and rear profiles on the sole next, and then (at last) I get a chance to actually work with some wood. Definitely starting to look more and more plane-like now.

Towell Miter – bending and peining the sidewall/bridge assembly

When last we left our humble plane-to-be, it was in heaving anticipation of finally being bent into shape, finalizing the shape of the sidewalls and bridge assembly that is so critical to the design. This is, quite frankly, one of the most nerve-wracking parts of planemaking… the bend needs to be carried off with a high degree of precision in order to end up with a proper fit to the bridge, and a square, properly formed shell.

Getting Bent 
Until recently, I did bending operations using a simple wooden or steel form and a vise, in the way Bill Carter demonstrates on his site ( if you’re not familiar with his work, you should take the time to GET familiar with it — he is as close to a ‘hero’ as I have).  This works quite well, with a couple of limitations;  first of all, you are basically limited in the length of the plane, which generally needs to be less than the capacity of the vise you’re using. My modern taiwanese vise has an opening capacity of just under 5″, and my old Columbian 504 opens to a bit over 6″ — neither is nearly enough for this plane.  Also, when you get to stock over 1/8″ thick, the vise method becomes much more physically difficult, requiring a fairly sizable lever to get anywhere.  The biggest problem with a plane the size of the Towell, though, is in tweaking to get the final degree of precision.


So earlier in the fall, I made a modest investment in a ‘compact bender’, which avoids some of those limitations. To be honest, I wouldn’t really recommend it to most people – it’s far from ‘necessary’ – but if you intend to do a lot of this sort of work, it’s worth the $80 or so I plopped down for it.

 As a general ‘rule’, I find that it’s relatively straightforward to get within 1/16 of an inch of the desired symmetry. Unfortunately, however, 1/16″ is nowhere near close enough for proper fit – so I need to be able to correct the bend somewhat to get it ‘just so’.  With smaller stock of 1/8″, this is fairly easy to do gently hammering in a vise as Carter shows at the link above.  With a 3/16″ sidewall of tool steel, however… not so much.  In order to tweak the bend in the location I needed to, a little creative fixturing was in order, as shown below:

It was very fortunate for me that I had come into the t-slotted table pictured here just prior to this point.  It came attached to a number of other bits of metal, but for the purposes of this operation, the table and the clamping setup shown were all I needed.  More on the ‘rest’ of the table a bit later…

If you look closely, though, you’ll see how this works, letting me very precisely adjust the bend at the lower part of the rear curve without risk of losing the straightness of the plane sides — in this case, pushing the ‘top’ side of the plane a smidgen further forward to bring it into exact symmetry with the other side.  The Bessey clamp worked just fine, though it was probably operating at the limits of torque it’s capable of.  At any rate, this got the plane body to just the shape I needed, ready for the bridge and front plate to be inserted, and the whole assembly peined.  First, though, the bridge needs to be shaped and finished.

Shaping the Cupid’s Bow bridge.
Shaping the bridge for a wedged plane is one of my favorite tasks; in general, the ‘sculptural’ elements of the plane are the most fulfilling to me, and I look forward to them. Forming a Cupid’s bow is not difficult, but it helps significantly if you ‘slave’ its dimensions to fit the tools you have — specifically, I try to make sure the concave curvature matches one of my round files, preferably a size I have both roughing and finishing cuts of file in.
I’m not covering the procedure in detail, but the setup I use to make these should give anyone interested all the information they need to make a very solid attempt at one of these.

Notice the angle of the bridge in the vise, which means basically all file work is done with the file perfectly horizontal. Once I’ve roughed out the entire shape, I refine it with contoured sanding blocks (available from any number of sources).

I generally like to finish the cupid’s bow itself to a pretty high polish – leaving the rest of the bridge with a coarser finish of about 320 grit or so.  I like the counterplay between the textures, and find it really draws the eye into the decorative feature.

A few minutes with abrasives on granite surface plate to finish the flat surfaces, and the bridge is done.  I finish the underside as well – if for no other reason than to be SURE I have removed all the burrs from the underside of the bow,  which can wreak havoc on the finish of the wedge otherwise… or so I’ve been told.

Assembly and peining:

In order to slip the bridge in place, I need to open the body slightly.  I use the jaws on my machinist’s vise as a spreader to do this.

Then, using the vise to close the plane up, I can insert the front plate into its dovetailed ‘home’ and the sidewall assembly is ready to be peined together.
 The first section I pein is the bridge tenons – this brings the back half of the plane into alignment, and closes up the sides tight to the bridge. You can see the ‘gap’ at the lower side of the bri
dge here; if I’ve tapered the mortises properly, the peining process will automatically close this up and leave me with a very tight fit.

Once the bridge is peined, I can turn my attention to the front plate.  The front side of these dovetails is a bit of a pain to pein closed, as there is no way to ‘back up’ the hammer blows on an anvil.  The best I’ve managed to come up with is to pein it with the sidewalls pinched in my bench vise, readjusting the plane every minute or so as it slides down the jaws a bit. This is the reason I spend so much time making sure this particular fit is extremely tight when cutting the front plate joints — if I have to close up even a small gap, it can take literally hours to get enough movement to do so.  The goal is to have a joint that is tight enough already that I only need a few minutes to close up the small seams from the front:

Once the front of the plate is piened, it is extremely secure in its ‘seat’, and I can safely pein the sides of the dovetails without concern for pushing the plate outward. 

At this point everything looks good, so I grind off the rest of the excess material. This is one of the nicer points in making a plane like this, giving me my first glimpse of the overall ‘form’ of the final plane.
 
 

So far, so good – now it’s time to start work on the sole.

Towell Miter – front plate and bridge

This entry will cover the remaining steps that need to be accomplished prior to bending the sidewalls.  The front plate needs to be fabricated, and the dovetails cut for joining it to the sidewalls, and the bridge needs to be completed to the point of fitting the tenons to the sidewalls.  After that, its simply a matter of cleaning the interior surfaces, and then I’ll make the bend.

Front plate

This is a pretty self-explanatory process – first I need to cut the plate to size, then cut the dovetail joints to fit it to the sidewalls. The sizing of the plate is fairly straightforward – it’s the height of the sidewall pieces above the dovetails – in this case, the sidewall stock is 2″ wide, minus 5/16″ for the sole, and another 1/16″ for peining material.  So the remainder is 1-5/8″ tall (I measure the piece itself as a check).  In width, the plate needs 2-1/8″ for the interior of the plane, with 2 x 3/16″ for each sidewall, and an additional 1/8″ for peining material on either side – this gives me a width of 2-5/8″.

 
 Once the plate is cut, I need to clean up the cuts from the hacksaw.  I used to do this work with files, but I find I get results that are as good (and much quicker) with a good 12″ disc sander:
 
With the plate square, it’s a simple matter to mark of the ‘tails’ that will join the front plate to the sidewalls.  This joint is responsible for holding the bend in place, and experiences some fairly good lateral stress, so I feel that tails on the front piece are really the only sensible choice here.  At any rate, I’m going to include less and less ‘cut’ and ‘file’ pictures, but I’ll still include them occasionally.  Here are the dovetails being cut:

and then they’re filed.  Flip the plate and repeat.  Next, mark the ‘pins’ from this piece at either end of the sidewall stock… pay close attention to the orientation that will result after the bend – there is nothing more frustrating than cutting a perfect dovetail that is flared in the wrong direction, scrapping a sidewall piece you’ve already got a half-dozen or so hours into… or so I’ve been led to believe.

Here’s the fit of one side.  Ideally, you want this fit tight enough that it requires some light hammer taps to seat or remove the piece – that makes for very easy peining later on.  In reality, you can get away with a good bit more slop than that, but it’s a lot more work later…

 
 The only thing remaining is filing secondary dovetails.  These dovetails are done in 3/16″ stock – not nearly as thick as the sole – so I’ll use a ‘conventional’ full-depth taper for them.  Here they are marked out:
 
and filed:
 
At this point, all of the operations on the sidewall pieces are complete, except cleaning up the interior surface.  It is all but impossible to adequately clean up the inside of an already-assembled plane, so I want to put a final finish on the inside now.  I use PSA sandpaper on a large granite block for this – and for the interior I’ll sand to 220 grit. You can go higher than this if you prefer bright and shiny, but I  I like a little texture to steel. The finer you abrade the steel, the more fingerprints and dirt will stand out and interfere with the surface aesthetics, so bear that in mind if you wish to use a higher grit for your surfaces… I will say that almost without exception, I have tended to back off on my surface treatments over time – I’ve rarely, if ever, felt I needed to shift my regimen to a higher degree of polish.  This is largely a matter of taste, though, so use the finish that suits your sensibilities.
Here is the sidewall, now with all the cutting and filing completed, and ready for the bending operation:
 
 But before I actually do the bend, there’s just one more task I want to finish.

Bridge tenons
It is infinitely easier to fit the bridge tenons before bending the sidewalls, so I cut the bridge piece from 5/16″ stock, and cut/file the tenons in place.  I will finish the actual shaping of the bridge a bit later, but for now I want to get the fit for the bridge correct before I bend the sidewalls up. The tenons themselves are really straightforward – cut, remove some metal, file a bit and – voilá!  The only tricky part of this exercise is filing the shoulder in place on the tenons.  Once I’ve got the tenons themselves cut I have to remove about 1/16″ of material from the top face of each .  This gives a nice shoulder, and a substantially nicer aesthetic fit to the bridge when the plane is completed. Here’s one side of the bridge, ready for the shoulder operation:

What I’ll do is use the vise jaws as a guide to cut to depth with my hacksaw – this will make it much easier to get the filing depth correct in a minute. I’m careful not to cut deeper than my 1/16″ depth, as cuttin
g beyond that point will substantially reduce the strength of the tenons:

Once the cut is made, I use the jaws again as a guide, this time for a pillar file used horizontally to remove the face material from the tenons ( you can’t actually see the tenons behind the file, but trust me – they’re there.)

Once you’ve gotten to depth, flip the bridge and repeat on the other side.  A few test fits and refinements, and you’re left with the bridge piece looking something like this:

Be certain you have a perfect test fit on either side of the sidewall piece (and pay very close attention to orientation).  You want a fit that is easily pressed in place without much resistance, but not too sloppy – you must be able to get the bridge in place after the bending operation without too much trouble.  Here is one side’s test fit:

 
And now I’m finally ready for the nervewracking step of bending the sidewalls.  I find everything prior to the sidewalls is accompanied by a silent prayer that the bend goes off well – it’s not unheard of for a bad bend to mean all of the work to this point is basically scrap metal, so there is a bit of apprehension in building up to it.  
I’ll cover the actual bend in the next installment, as well as inserting the bridge and front plate.

Towell Miter – secondary dovetails and Bridge mortises

This entry will cover the layout and cutting/filing work for the bridge mortises and secondary dovetails on the sidewall stock.  First, the bridge work.
Bridge mortise layout
The layout of the mortises for the bridge are absolutely critical to the final outcome of the plane. Variations in layout from one side to the other will at best require some serious finagling to correct.  At worst, they will make the sidewall unusable and require starting over from scratch.
To ensure symmetry, I produce a simple template indexed precisely to both the top and the front edge markings on the sidewall stock.
This is a one-time-use template, so I’ll make it out of graph paper.  To lay out the mortises, first I need to establish the angle the bridge will lie in with respect to the sole.  The blade will be bedded at 22.5 degrees, and the bridge needs to be at an angle a bit higher than that to accommodate the wedge.  I like to use a wedge angle of about 8 degrees, so I’ll use 30.5 degrees as the bridge-to-sole angle. To get the vertical placement correct, I want to register the bridge of the bed, leaving enough room for both the blade and some wedge thickness.

The bed location is easily drawn in, referencing the working drawings for the plane.  From those, I establish a baseline for the wedge by marking out a 30.5-degree line directly from the rear of the mouth, where the bed meets the sole – from this line I’ll establish the amount of offset I’ll need to accomodate the blade and wedge.  You can see the baseline in the photo below – it’s the dotted line between the bed and bridge.  I’m planning a 3/16″ blade, so I am using 1/4″ of offset from the ‘baseline’, which should allow for a reasonable wedge thickness as well.  Please note that the offset should be marked off perpendicular to the bridge baseline – not perpendicular to the sole.  

The bridge itself is 5/16″ thick, so I lay out a second line 1/4″ above the bridge line – this line is 1/16″ shy of the top of the bridge to allow for a shoulder at the top of each tenon – then I place the mortises within the space I’ve defined.  I’m planning to use a bridge that is about 1-1/2″ long, so I lay out my mortises 5/16″ wide with 1/2″ space between them. 

 Here is the paper layout:

Now, I cut this layout out for use as my template, paying special attention to the index lines, which are the front and top edges of the sidewalls.  These are what will ensure I’m laying the mortises exactly symmetrically.  First on the ‘left’ portion of the sidewall :

Then I flip the template front-for-back and mark the right side of the stock:
At this point, as a self-check I scribe a pair of 30.5-degree lines on the stock to coincide with the top and bottom of the mortises. These are a good double-check to ensure the template markings are set in the proper plane.
The mortise layout looks good, so it’s on to the secondary dovetails.

Laying out and filing secondary dovetails

One of the interesting things about the Towell miter is the appearance of the dovetails on the sidewalls.

If you look closely, you’ll see that each dovetail is actually only ‘flared’ in the lower 1/8″ or so – the top 3/16″ of each joint is perpendicular to the sole. This is the first time I’ve seen this on a plane – my best guess is that Towell used this technique because it greatly reduces the size of the gaps at the top of each joint, which must be peined shut later on.  With such a large sole, a full dovetail would be quite a chore to close up, and is really not necessary for strength purposes.  I think this is somewhat of an aesthetic compromise, but it is a very interesting feature and I’m going to emulate it here; since the plane is steel-on-steel, the dovetails are not particularly visible after lapping anyway, and it strikes me as an interesting technique to try out.

The layout for these is a bit more work than conventional full-depth secondary dovetails, but the basic premise is the same.  I scribe in a second ‘baseline’ 3/16″ from the bottom of each tail (1/16″ of this is my peining excess), and mark in the dovetailed portion to this line. Above the line, I mark vertical lines to the top of each tail.
The measurements for this feature are selected in part to fit the tooling I have – my smallest pillar file is about 3/16″ wide, which will fit the ‘flat’ portion that needs to be filed perfectly. First, I file the flared portion of the joint:
Then I file each flat, trying to keep the two surfaces matched up properly:
And that’s the process. Conventional dovetails are done the same way, but the flared portion continues all the way to the top of the joint – making the process a fair bit simpler and faster.
Cutting and filing bridge mortises
 
Next, I drill and file open the bridge mortises.  The trick here is to drill out as much as you can without going over the lines, then file to the lines. I will sometimes use a jeweler’s saw to help remove some of the waste, but in this case I managed to get a lot of waste out with the drill.  If you don’t own one, I highly recommend investing in a spotting drill – I have a 1/4″ one that cost me $5 or so, and has lasted me two years without sharpening. Spotting drills are very short, with a solid round shank and a single flute, all of which makes them very stable, and nearly immune to ‘walking’ and distortion.  Ideally, you want one with a tip angle to match your standard drills, so you can start a hole and have solid registration of a twist drill when you switch over.  I center punch where I want my hole, start a shallow hole with the spotting drill and then finish the hole with a standard twist bit – with this technique, I find I have a remarkable degree of precision in drilling, which lets me remove as much waste as possible before I switch to files.
Once I’ve filed to the scribe marks, the last step is to file a taper on each edge of the outside to give some grip to the tenons when I pein them in place.
The last operation before bending is to cut the dovetails for the front wall – but for now I decide to do some cleanup and remove the layout fluid.  I deepen the scribe marks for the centerline and each end, as I’ll need these when I do the bend and cut the front plate dovetails.
That strikes me as enough for one night, so I decide to break at this point. Here is the sidewall stock as it is now:
Next comes the front plate, dovetails, bending, and the start of work on the two-piece sole.  It may be a few days before I get everything done and written up for the next installment, but it shouldn’t take too long. Stay tuned…

Towell Miter – design and layout

The Plane -
The plane for this project is going to be loosely based on a miter plane made by Robert Towell of London in the early to mid 19th century.  The original plane belongs to my friend Joel Moskowitz of Gramercy Tools and Tools for Working Wood, and I had a chance to take some measurements and photography of the plane last fall at his shop.  Joel, who is an avid historian of woodworking as well as a woodworker and tool collector, did a brief writeup on Towell and the plane on his blog; if you search his blog for ‘mitre’ (his preferred spelling – in the british tradition) you will also find quite a fair bit of other information regarding these planes, which are somewhat of a curiosity in that there isn’t a firm consensus as to what they were originally used for.  I’m not going into that area here – at least not now – but Moskowitz has offered some ideas in his blog.
This is not a project I would recommend for a first attempt at making an infill plane – there are several features of its construction that are somewhat advanced, and add quite a bit to its difficulty. Firstly, the one-piece bent sidewalls are tricky to form and fit infills to; Secondly, this is a bevel-up plane design, which requires a two-piece sole construction — one of the more challenging aspects of planemaking to get right in my experience.  Having said that, however, this plane does have a lot to interest people who are considering making a plane, as well as those who are perhaps already somewhat experienced planemakers.  It should also provide a fairly comprehensive picture of the basic processes necessary for all dovetailed infill construction.  For these reasons, I think it’s a solid candidate for a project  writeup – and I’m hoping it will provide a fairly accurate idea of what infill making entails, and some of the choices and problems that can come up in planning and constructing a plane from scratch.
Designsharpen those pencils and/or clean the lint from your mouse.
The first step in getting the design established is to make some dimensioned drawings, establishing at the very least the major angles and distances necessary to start laying out and cutting the sole and sidewall pieces.  I have some limited experience with Sketchup, but I still generally prefer graph paper and pencil for most of my construction drawings. This is largely a matter of comfort and preference, though – you should use whatever format you’re most at home with. Here is the rough construction drawing set I am going to be working from:
The next step for me is making some test bends in my steel bending fixture, establishing the setup I’ll be using and the radius of the curvature of the sidewalls at the rear of the plane.  This is necessary to ensure I have the proper layout of the sidewalls, which are all laid out, cut, and filed before the bending happens. While it’s a simple task to calculate the radius of the curve mathematically, there are two problems with using this as the only measurement – one is that the final curves will rarely match up to a perfect semi-circle, such that the final radius will almost always be somewhat shorter than the theoretical one;  the second problem is that there is always some degree of stretching and compression of the steel when it’s bent to a curve.  The bottom line is that you can get an approximate prediction of the length to allow for the radius, but in my experience it can be off by as much as 3/8″ from the actual results. A test bend using the same thickness of steel is the only reliable means of establishing the necessary length. I use inexpensive cold-rolled steel for these checks, which generally give results within 1/16″ of my final bend – quite close enough for my purposes.
I use a Grizzly compact bending tool, which I mentioned briefly in an earlier post.  This isn’t really necessary, however – planemaker Bill Carter, who’s made some of the most beautiful mitres ever produced, uses simple bending forms in a machinist’s vise for all his work.  The compact bending tool just adds a degree of simplicity and repeatability that I find helpful if you plan to make more than a couple of planes.
Laying out sidewall dovetails – pins first

Once I have worked out the bend setup, it’s time to generate a dovetail layout template.  I  do this on graph paper with simple black markings for each of the ‘pins’ on the sidewall.  Notice that you only lay out half the plane, in this case from the front edge to the rear centerline – you’ll mark half of the sidewall, then flip the blank and mark the other side from the same template to ensure you have a nice, symmetrical dovetail arrangement. If you enlarge the next photo below, you can see the markings on the graph paper below the steel.
Now it’s time to start preparing the steel flat stock.  I’m using 3/16″ O1 steel of 2″ width.  Allowing 1/16″ of excess for peening dovetails to the sole, this should give me a final height of 1-15/16″ for the plane.  I cover the ‘outside’ face and bottom edge of the steel with layout dye, then mark off the front edges (again, leaving at least 1/16″ excess for peening the front wall on later) and the centerline.  Now I use the template to mark the dovetails off at the bottom of the face.  You can see the template and the already-marked blank below:
 
With straight-sided planes, I have some degree of choice as to whether the sidewall dovetails are the ‘pins’ or ‘tails’ — if I use pins here, the sidewalls will drop in to the sole from above;  if I use tails,
the sidewalls will slide in to the sole from the sides.  For a one-piece sidewall like that in this plane miter, however, the sidewalls can only drop in from above, so the decision is effectively made for me – pins it is.
On the face of the stock, I first scribe a line to mark the top of the dovetails – in this case, I have allowed for a 5/16″ sole and 1/16″ of excess, so this line is scribed at 3/8″ from the bottom.
With the template markings transferred to the plane, I use a square to extend the marks up the face of the stock to the line scribed previously. On the bottom edge of the stock, I then mark off the ‘flare’ for the dovetails as they will be seen from the sole of the plane.  My habit is to draw my templates to represent the outside of the sidewall, so each pin expands to the inner face at an angle of about 12-15 degrees, which I find to be a nice balance between aesthetics and ease of peining closed.  The photo below shows the completed dovetail layout.
 
At this point, I cut and file the dovetails as laid out.  There will be additional layout for the secondary dovetails later on, as well as the mortises for the bridge – but there is no reason to add to the complexity at this point.
Cut and file… repeat.
A few quick words about cutting and filing these dovetails… In many ways, dovetails in metal are more forgiving than in wood, because you can close up minor gaps during the peining process later on.  Having said that, though, it’s very much in your best interest to be as precise as you can at this point – particularly in keeping the pins perpendicular to the sole, and in keeping the baseline intact.  Every bit of precision at this point will pay off later on – and minor errors now have a way of magnifying into bigger problems later in the process.
I’ll try to add a post later about the types of files and hacksaw blades I like best for this sort of work, but when starting out you can make do quite well with a set of small Nicholson files if you grind safe and acute edges on a couple of them. I use 18-tpi bimetal hacksaw blades for cutting steel. One of the reasons I prefer O1 to mild steel is that it is much easier to remove waste from harder steels.  In the photo below, I have started comb-cutting the waste for the dovetails:
In general, I try to leave somewhere in the range of 3/32 – 1/8″ ‘tines’ between each cut.  This thickness of material is very easy to whack out with a cold chisel later on.  I actually use an old woodworking chisel with a flat bevel ground on it for this – it’s just the most comfortable and controllable one I’ve found for it:
The simple idea is to tap each ‘tine’ first to one side, then to the other.  Generally, two sets of direction changes is all that is required before the material snaps cleanly off.  In softer material such as mild steel or bronze,this does not work anyhere near as easily or cleanly – and it’s often much easier to just saw the waste out with a jeweler’s saw if you are working in those metals.  O1, however, is remarkably conducive to this.
Once the material has been broken off, it’s time for the file work.
 
Again – this can be very tedious work, but the more accurate you are at this stage, the more smoothly things will go later on.  A couple of hours work later, here’s the sidewall stock with the first-stage pins all cut and filed:
 The next step will be to lay out and file the secondary dovetails, and the mortises for the bridge.  This entry has already gotten long enough, however, so I’ll come back to that process in the next entry in a day or two. 
For those of you reading this, I would really appreciate feedback as to how helpful this is.  Questions are very much welcome, as are any comments on what is or is not helpful for understanding and following along with the progress.  My habit is to try to err on the side of too much information, rather than not enough – but if the entries are becoming too long and detailed please let me know.
Return top