Over the past few weeks, I’ve been working up a project that’s been on the ‘to do’ list for well over a year now: prototyping an M2 mitre . The plane itself- shown above – is a new size designed around a 1-1/4″ blade, placing it dead-center between the two sizes I’ve offered to date. Overall I’m quite pleased with the size, which is an excellent all-round compromise for small-scale work.
The other development I incorporated in the plane, which is the real subject of this post, is a new (to me) blade holding mechanism. The technique, which I’m referring to as a screw-drawn wedge, employs a traditional wooden wedge and metal bridge, but with the addition of a screw through the bridge to aid in securing the wedge. This is not the most common method for securing a blade, but it is a tried-and-true technique that I believe was first used by Norris in some of its thumb planes, chariots, and shoulder planes.
One thing that I think worth noting is that in this mechanism, the screw has a very different function than the screw in a lever cap does. Where the lever cap screw is the primary means of forcing down-pressure to secure the blade to bed, in the screw-drawn wedge it is still the wooden wedge that provides this primary force. The screw’s role here, at least as I implement it, is actually to locate and secure the wedge in its position. In order to facilitate this, the screw is terminated with a cone, which in turn sits in a precisely mated bronze seating point inset in the wedge. When placing the seating point, it is actually offset by a small amount (on the order of .030″, or 1/32 of an inch) such that as the screw is tightened, the taper of the screw draws the wedge further down to ensure the wedge is set quite securely. In this regard, the screw’s function is somewhat analogous to a drawbored mortise and tenon joint.
While it may at first seem that the rationale here is increase the holding power compared to a conventional wedge, that’s really not the case – the simple wedge has been adequately holding blades on its own for centuries just fine, thank you. The screw in this system is effectively performing the same function as the final tap of the wedge with a mallet: setting the wedge.
So what are the advantages? Well, as with most things it’s a bit of a tradeoff. As I’ve said, it’s not as though the traditional wedge and bridge design needed any ‘fixing’, and in terms of actually securing the blade in place the two methods work more or less equally well. To my mind, the primary rationale for using the screw-drawn wedge is that it allows the user to adjust the blade without needing to reset the wedge. The tradeoff part is that once the plane is built, the wedge tension cannot be properly adjusted on the screw-drawn wedge by any means other than altering blade thickness – and in this application, a thickness difference of 1 or 2 thousandths of an inch is quite significant. In practice, this ‘disadvantage’ has much more to do with plane-making than plane-using, but it does make replacing blades a trickier proposition in the long term.
So do I have a feeling as to which system is ‘better’? Well, personally I probably prefer the aesthetics of the traditional design just a bit – and since I’m quite used to using a mallet for all the adjustments and setting needed, the screw isn’t much of an advantage for me. Having said that, though, I do think that for many users the screw-drawn schema will be more convenient in both the short and long term. Over the next few months of using this plane and my others I’m sure I’ll develop some more opinions about it, but for now that’s about it.
Finally, just to be clear here — there is absolutely nothing unique or new in this system. As I’ve said, I believe the technique originated with Norris long before my great-grandparents were born. Additionally, several modern makers have been using the technique for years: Karl Holtey, Konrad Sauer, and Wayne Anderson have all been making planes with it for years. However, I do think that there’s relatively little information about how it actually functions out there, and since it is not necessarily intuitive I thought it worth a blog entry.
Besides – it’s the first actual planemaking content I’ve had in six months now. Man oh man it’s nice to have a shop again.
J says
This method would clearly require parallel sided irons right? In parallel sided irons, isn’t there a tendency for the wedge to back out with low planing angles and heavier cuts? http://www.toolsforworkingwood.com//Merchant/merchant.mvc?Screen=NEXT&StoreCode=toolstore&nextpage=/extra/blogpage.html&BlogID=190&BG=1 This would seem to prevent that (with a sheer pin), even if its theoretical in a light cut miter plane.
When adjusting more coarse wooden planes with a mallet (my experience), it seems straight forward, whacking toe-heel and what not, with an infill miter I assume another (more delicate) method is used, right?
Richard Wile says
While the manually adjusted wedge is the “traditional” approach, I find it takes far more finesse to make it work. To my mind, this approach of Raney’s eliminates one of the variables in the adjusting process, thus avoiding the wedge slipping out of place while being adjusted, which is often followed by the cursing stage of getting a plane adjusted.
Not new, but I think an excellent way to go and why I will be getting this feature on my new mitre from Raney.
Great work.
raney says
@J
Hi J,
That’s a great observation, and one I puzzled over a bit myself when I first started researching and making mitres. Yes – the screw-wedge method does indeed require parallel irons in order to work properly.
Joel’s blog post you referred to is pretty much in line with my experience. Please note where he points out that in a properly fitting wedge, the forces on the blade are nowhere near overcoming the force of the wedge. This is certainly my experience, even in coarse-use planes such as a fore – a well-fit wedge is a very very strong force.
Having said that, though, for wooden bench (and moulding) planes I do prefer tapered irons; the reason, though, has more to do with adjusting the irons, and getting the irons out of the plane than with finding any needed increase in holding power.
One of the biggest advantages to the tapered irons as used in western wooden planes is that it’s extremely easy to remove the iron – just tap the iron down and it drops right out through the mouth. This can be important, because in most bench planes the wedge is only designed to be driven in, not out – so removing a blade is not especially easy – you would have to whack the heel of the plane several times to loosen the wedge.
Overall, I tend to be of the opinion that either method works just fine – but that fitting wedges in tapered blade planes is a bit less sensitive, and tends to remain effective much longer even with wood movement. For that reason, they were traditionally dominant right up until the point where parallel plane blades were becoming significantly less expensive to buy. Then, a batch of watered down plane designs started to show up.
So for my purposes, I’m only making planes where the wedges are fit extremely precisely. And – perhaps more importantly – using infill materials that are as close to devoid of movement seasonally as one can get. So using parallel blades is quite acceptable in this application.
Finally, because these mitre planes are bevel-up, I think that any advantage of a tapered blade is effectively negated by the fact that if the blade is pushed forward too far, it will crash into the mouth, potentially causing it damage. So having a blade come loose in the forward direction is quite as problematic as having one come loose in the opposite direction.
Hope that all makes sense.
As to your comment about adjusting infill planes – I do know some people who adjust infill planes with hammer taps, but they’re not generally in posession of particularly nice infill planes. Adjusting in this way does cause damage over time. I’ve never found it necessary, as one can easily adjust blades only in the ‘down’ direction, and in the mitre planes I make (where this is much more problematic), I include a sneck that makes withdrawing the blade quite easy and predictable.
Hopefully that addressed your comments – sorry for the long-windedness, but it seemed worth delving in a bit.
Trevor Walsh says
Can I just say that that is a sexy bridge/wedge shape?
J says
Thanks Raney for more info. You could have slapped that with another pretty infill pic and you could have gotten credit for back to back content entries. Really appreciate your assistance, and your entries (even those without official plane making content.) It amazes me the subtleties of the few variables in the simple machine (or jig) that is a plane and how the parts interact. Learning and understanding the valid (and less valid) combinations of irons,caps,angles, mouths, soles, body materials is very interesting and I think that as the new age of toolmakers document their findings (and everyone seems to be sharing,) it’s making the sum even better than the parts.
Roy Mittmann says
Hi Raney, Wondering if you had any quick thoughts on why wedge fixed infill miter planes remained in common use, and wedge fixed infill smooth planes were largely replaced by screw lever caps. Is there a disadvantage in their use with smoothers that is not present with miters?
raney says
Hi Roy,
That’s a very good question. I’ll have to ponder it a little more, but my immediate reaction is that for me at least it’s probably aesthetic as much as anything. For me, the infill material really is the beauty. The metalwork is sort of the ‘frame’ around the artwork. And in a mitre, with a lever cap there is very little wood visible — front bun is it. To me, that looks really unbalanced. For smoothers, panel planes, etc, however, I love the look of a lever cap.
There are a couple of other ideas that I think may have some part in it, but if I’m being honest that’s the overwhelming reason I use wedges in mitres and lever caps in most everything else.
Konrad says
Hey Raney,
Really great looking plane. The bridge in particular is beautiful – and mirrored in the tip of the wedge – stunning.
Great design and great execution.
Cheers,
Konrad
PS – we will see about the 12/4 curly African Blackwood.