Archive for January, 2010

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…

Hacksaws and files

A little discussion about specific tools for those people who are considering making a plane by hand – first and foremost, make sure you have a good high-tension hacksaw, and be prepared to use it a lot.  There are any number of sources for these – and my local home center even carries a fairly good one.   I use 18 tpi blades for almost all steel work; 24 and 32 tpi blades are nice to have around for work on copper alloys, and thinner work. I’ve had good success with Starrett and Lenox bimetal blades, but I think any good quality blade is probably fine. I lubricate my hacksaw blades with parrafin – the same chunks I use for plane soles – and have never felt it necessary to try anything else. I should also say that I am very quick to toss blades when they show signs of wear – I’m doing enough work with the hacksaw as it is without fighting my tools on top of it.  I will often go through as many as half a dozen blades in the course of making a smallish bench plane.
With respect to files, there are two types that I think are indispensable for planemaking, neither of which are typically found in the average wood shop.  The first is a barrette needle file – shown below left.  Barrette files have teeth in only a single face, with safe knife edges and a safe back;  these are key to getting crisp corners and filing any acute angle.
The second type are pillar files.  Pillar files are toothed on two faces, and have safe ‘edges’ that are precisely ground perpendicular to the faces.  At least one of your pillar files should be of a narrow type – I have a stash of 3/16″ 00 cut narrow pillar files (shown at right in the photos above) – this is in my hand more often than any other single file I own. If you have the resources, it’s nice to have a few larger, and also finer cut pillars as well, but they’re not strictly necessary.
 You can also make very usable ‘versions’ of these files with a bench grinder and a few typical files from the local home center… grinding safe edges at an acute angle (30 degrees is a good place to start) on a 6′ or 8″ mill file will get you into most of the corners.  Add a few sizes of triangular saw-sharpening files for getting into small spaces, and you have a very capable file set that will let you do almost anything you’ll need to in making planes.  Personally, I think the step-up to more dedicated – and higher quality (read: swiss pattern) files is well worth the cost, but for someone just dipping their toes into the planemaking waters, I see no need to take on any more expense than absolutely necessary.
Whatever you’re using for files, please be sure to lubricate them properly and clean them from time to time.  The most convenient form of lubrication I have found for files is simple blackboard chalk. A couple of swipes against the teeth will do wonders for keeping the file sharp and free of metal dust, and will give you much cleaner results.
For cleaning, I use a small file card and the occasional dental pick to remove obstinate bits of metal.
About three or four times a year, I soak my most-used files overnight in a mild citric acid bath to freshen them up. Once a year or so, I send a batch of well-worn files to Boggs Tool in southern California, who do a magnificent job resharpening them.  
I have a pretty extensive cabinet of at least 40 or 50 files, all of which get used at least occasionally — but these two files are capable of covering at least 75% of the work I do on planes.  Having a wider range of files available makes many things easier or faster, but it isn’t a strict necessity by any means.
One final bit of information regarding safety: please don’t even think about using any file without a handle on it.  You can buy a range of sizes, or there are plenty of good ways to make a handle for next to nothing. I don’t use them myself, but I know many people who swear by wine corks as handles.  It doesn’t matter what it is as long as it keeps the pointy tang out of your palms.

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.

Song for the sneckless

One of the previous commenters had asked about some details on snecking blades.  The sneck is a very nice addition to a blade, particularly on low angle miter planes, as it provides a very handy means for reducing blade projection without having to strike the plane body itself.

The method I use to sneck miter blades is simple:  just add a supplementary thickness of steel at the rear of the blade.  It’s a very easy process, but it’s a nice introduction to peining and rivets, which are critical to constructing dovetailed infill planes.

Here’s the annealed O1 stock I’m going to use for the blade. 

This is 1″ wide, 3/16″ stock, and I’ll cut another section of steel the same width, about an inch long, to use as the sneck – in this case I’m using 1/8″ for the sneck, but you can use a thicker sneck if you prefer. The mating faces of both pieces of steel should be nice and flat to ensure you get a clean union between the two – the goal is for the blade to look like a single chunk of steel at the end.  I lap both pieces on a granite surface plate to about 220 grit.

Next, drill the holes for your rivets. I’m actually prepping four snecks here, as I want to make a few spare blades.  Two pins are more than adequate for a steel union of this size – I’m drilling to 3/16″, and I’ll pin with O1 drill rod of the same size.
 
Make sure you use the sneck itself to register the holes in the blade, and drill those as well.  On the top of the sneck and the bottom (face) of the blade, you want to taper the holes just slightly to give the peined rivets someplace to ‘grab’ and join the steel tightly.  I use a tapered hand reamer – they are readily available from most industrial supply houses.  Here’s a shot of tapering the sneck:
 
Once all for tapers have been reamed, cut your pin stock – leave about 1/16″ extra length for peining – and assemble the bits and pieces together for peining.  Here is the assembly before peining the rivets… note that my ‘fitting’ is hardly precise – but it’s completely acceptable for my needs as I’ve left myself plenty of extra material for filing and grinding off during final shaping :
 
I forgot to shoot pics of the actual peining, but it consists of striking the pins numerous times (several dozen strikes on each side of each pin) forcing the excess material into the reamed tapers. Peining is far from difficult, but it does require a little finesse to strike hard enough to move the metal, but not hard enough to deform the parts you don’t want to deform, or introduce unnecessary stresses.  My advice would be to always err on the side of ‘too soft’ as I’ve yet to see anyone who didn’t start out striking much harder than necessary.  When it comes time to pein the shell of the next miter plane, I’ll try to get into some more detail on the techniques you can use, but for simple rivets like these, it’s mainly just a matter of aim.
Once completed, it should look something like this (I’ve done some rough shaping already in this photo):
 
Make sure you’ve completely filled the tapers filed into the rivet holes so you don’t have gaps after cleaning up, and be careful not to dent the surrounding metal if you can help it – it will make the lapping much easier if you don’t have to remove a few thou of surface to remove the dents.
Now it’s a simple matter of grinding and lapping the assembly to its final form.  I do the majority of stock removal with files and a 12″ disc sander, and then lap to the desired sheen — in this case, only up to 180 grit, as I like to leave some texture on the blades. 
Here is the blade after shaping, ready for heat treating:
 

And that’s all there is to it.&nbs
p; Start to finish, including cutting the blade stock, I’d say this took about two to three hours to do a batch of four blades to the point of having them ready to heat treat.  A single blade would probably be do-able in an hour or less once you get used to the process.

Please bear in mind that there is no reason you can’t add a sneck to a blade after heat treating, but the hardened blade makes drilling and shaping much more difficult.  However, an annealed sneck on a hardened blade is not an issue at all in my experience.

Finally, here’s a shot of the blade after heat treating, in place in a small miter plane.  Also pictured is the coffin smoother (with the older LC screw) I briefly showed in a previous post, which someone else asked to more photography of.

Hope that helps with the basics of snecking.  I’ll be posting the first sequence of prepping the Towell miter plane later in the week.

Independence Day

First – A Personal Note

Happy New year all. Thanks to everyone who ‘gently prodded’ me about getting it back in gear.

Long time since last blog entry?  Yup.  What can I say – holidays at the best of times are busy, and if you have young children like we do, you’ll know that it also brings a severe increase in activity of the local TLF  (Toddler Liberation Front) cells.  Our home has been a haven for this crafty and disarming organization for the past several years, and the new recruits (codename:  the twins) seem to have stepped up their mobility this year, as evidenced by a remarkable uptick in the organization’s chatter, and a few very close calls.  One day I’ll be able to tell the tale of the Christmas Eve Pasta Offensive, but this is not the time or place.

The long and short of it is that it was easily the most wonderful, and also the most hectic, Christmas season I can ever recall having.  Ever seen a 4-year old’s face when she first sees the  hoof-strewn mess that Santa’s reindeer made of the cupcakes she left them? Ever had that sense of wonder interrupted as an overactive pair of fifteen month olds exploit the moment of freedom to finally topple the 9-ft. Yuletide Tree crammed into the 8-ft tall family room?  Well, then you obviously understand.

New toy for Daddy

At any rate, the season also brought the addition of a new piece of machinery at the toolworks — one that marks a rather nice personal milestone:

The Daedworks’ own metal lathe – a WWII era Montgomery-Ward branded Logan with a 10″ swing and 24″ between centers. I know it’s not specifically a woodworking tool, but it’s significant as it allows me to bring the last outsourced bits of my planes in-house. Until now, I’ve had all the lever cap screws for my bench planes made by the extremely talented Johnny Kleso (known as rarebear to many).  You can see a couple of videos Johnny’s posted on YouTube.  Well worth a view for anyone interested, especially the Acme threading videos. Johnny’s lathe time is limited, though, and he’s stopped taking outside work with the exception of a couple of his old friends. So I’ve been considering how to move forward for a few months now, and finally decided I should just learn to make ‘em myself.

So two days before Christmas, I picked up this Logan and the past two weeks of shop time have been devoted to setting it up, calibrating and aligning everything, and learning the rudiments of turning metal, knurling, and single-point threading. As an added benefit, this acquisition also lets me finally shift to using Acme threading on the lever caps, something that is fairly labor- and time-intensive, and is frankly rather costly to have someone do for you. The learning curve has been pretty steep, but so far I’m happy with the results.  Here’s the first screw I’ve finished in the Bronze I prefer to use:

 
And another shot of the screw, in place in a coffin smoother I finished around Thanksgiving:

I’m not completely satisfied with the knurling at this point, but I think the step to Acme threads makes up for it.  As I said, overall I’m quite pleased with the results.

Of course there are other things you can make on a good metal lathe as well…

I’ve freehand-turned a few plane hammers on my wood lathe in the past, but the results with a good metal lathe are really a notch up.  This one is also the first time I’ve been able to incorporate a design feature I picked up from Jameel Abraham — a threaded post mount for the wooden head.

There are so many advantages to this, I don’t know where to start. In addition to making it incredibly simple to replace a worn wooden head, I can also keep a couple of replaceable heads in different materials – soft wood, harder wood, and perhaps (if I can work out the details) rawhide, which is the preferred material for adjusting wedges in a miter plane. All in all, a nice secondary benefit;  this is easily my favorite of the plane hammers I’ve made over the years.
And now, this:
 
Next project, which I’m going to document all the way through, is a full-size miter plane based on a beautiful old Towell Miter from the collection of Joel Moskowitz, who
is one of my best secret (or once-secret, I suppose) sources of information.
I am done with most of the basic layout for the plane, which is about 10-1/2″ long with a 2-inch iron and a single-piece sidewall construction. This is going to be the first large-scale mitre plane I’ve done, and it should give me the chance to try out some new ideas.  It’s a classic design, and Towell’s cupid’s bow bridges have been the model I use for a while now — they’re superb. Towell’s original, top – the last bridge I did, below it.
More soon, as I get to the serious work of hacksawing and filing. I’ll try to cover everything about the plane as I progress over the coming weeks.
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