Wood movement question about using a bridge to hold a wedge

[Matthew N. Masail]

I was playing around with a design for a bevel up woodie due to a fellow creekers interesting wenge plane
when I thought "why not use a bridge to hold the wedge in a bevel down plane too?"

by bridge I mean like an infill miter plane.
http://www.daedtoolworks.com/


I would make it thicker, it's upper half leveled with the top of the plane. would certainly be solid, easy to make from the middle section off-cut when making a laminated plane, and even if I make it rather massive it wouldn't block the view anymore than a krenov style one. it would also move a the same rate as the rest of the plane.


But glue alone is not enough, even with hide glue I wouldn't feel right about it if the plane wasn't for me.


So I thought the best thing would be to have two 1\4 inch dowels going from one side solid through to the other.


Here is my question, will gluing the dowels in inhibit healthy movement in a laminated plane? if so what might be the outcome? I'm having a hard
Imagining it.

[bridger berdel]

I doubt that movement in the pin would be a problem.

[Kees Heiden]

I think it would be a problem because if the cross grain. Can't you mortice it into the sides?

[Matthew N. Masail]

I think it would be a problem because if the cross grain. Can't you mortice it into the sides?

I suppose I could, but part of the reason for wanting dowels it to strengthen the cross grain of the bridge. what kind of problem do you think it might cause?

[Jeff Heath]

If the bridge expands, it will blow the cheeks of the plane out, or cause cracks in the body of the plane. At the least, you'd have to run the grain 'across' the body of the plane, but then you're dealing with a different kind of issue. As the wood expands and contracts, it's going to loosen or tighten on the wedge.

If you use a metal, like brass, you've solved your problem. That's why cross pins are not glued in, so they can allow for the plane to expand and contract.

Jeff

[Kees Heiden]

What Jeff sais.

[Matthew N. Masail]

even if the bridge is from the actual center section cut out?

like this
https://www.google.co.il/search?q=wenge+plane&tbm=isch&tbo=u&source=univ&sa=X&ei=mWEoU9G6Joap7QbYpYGgCg&ved=0CCkQsAQ&biw=1242&bih=585#facrc=_&imgdii=_&imgrc=lU1Wy3tMglI7mM%253A%3By-5D34T_343SQM%3Bhttps%253A%252F%252Fs3.amazonaws.co m%252Fljimg%252Fmi89vlt.jpg%3Bhttp%253A%252F%252Fl umberjocks.com%252Freplies%252Fon%252F2277002%3B50 0%3B223

how is it differant from the front and back blocks of the plane itself?

[Jeff Heath]

I misunderstood what you were trying to accomplish, and went back to look at the photo links you posted to.

In theory, I think it will work, but in practice, I personally wouldn't like it because you're going to have a difficult time passing anything but the smallest of shavings if you make the bridge stout enough to hold up to the pressure of the wedge. I'm just guessing at this, obviously, since I've never tried it. I made a few laminated planes with cross pins, and I've already broken 1 of the cross pins because of wedge pressure. I haven't sat down and done the math on a vector force diagram (disclaimer in case the techie police show up here) but there's a lot of force caused by the wedging action, especially if you're using the plane to take heavier cuts, and you pound your wedge in tighter to compensate.

I say, give it a whirl, and you'll find out pretty quickly for yourself.

As a planemaker, I enjoy trying to stretch the envelope of what is presently being done. While I spend most of my time making traditional style bench planes, I also like to throw in a few curve balls here and there to see what works, and what doesn't.

A lot gets said on this site about traditional thinking, and how smart they all were 250 years ago, and why fight that thought process (as it pertains to woodworking and tools), and I only buy in to that to a certain extent. I'm guessing that 99% of my customers to not stand before their benches all day long working rough timbers by hand. Most have a smoothing plane or a jack plane for an hour or two, at most. Ergonomics aren't as important in that case as they were to an apprentice in 1776 that was planing rough timbers to dimension given to him by the master.

It's a different world altogether now.

Make it, and let us know how it performs.

[Matthew N. Masail]

Thanks for the encouragement Jeff!


I don't think it will be a problem strength wise at all, it fact most of my cross pins are a piece of wood with metal rod going through.
I have only ever broken one (the wood) due to in being only 0.5mm thick below the dowel. 1-3mm holds up perfectly so far. the bridge should be much stronger than this
but we will see. I feel the same way as you about experimenting, this is my hobby and fun right now, doesn't matter to me what they used to do, if if I'm doing what's been tried or any of that... this is my joy so I'm going for it. worst case it doesn't work out... I have a dozen or so planes that are an ergonomic nightmare..:rolleyes:

[Jeff Heath]

Just a thought....

Try making your cross pins out of one piece of wood, and use a round tenon cutter on the ends to produce the round dowel. It's quick, easy, inexpensive and leave you with a stronger cross pin.

If you already knew that, then please ignore this public service announcement. :D

[Matthew N. Masail]

Well... the reason I never tried doing that is because I don't have a tenon cutter, and I got comfortable doing it the other way. I might be coming to the US in the next few mouths for a wedding so I should (will) get one, but..... we will see how the bridge thing turns out, if it works well it will probably be stronger than both cross pins.


I'm not sure about the grain direction, here is what I did today, still haven't glued it in - that will be at the end after cutting through the sole from the top:


285103


I've been thinking it would be much smarter to have the end-grain pointing toward the top of the plane, that way the length of the bridge is long-grain and the width is short grain but supported by the dowels that pin it after gluing. the width of the bridge will still expand\contract the same obviously. however doing it that way I lose the end-grain contact with the wedge which it tougher. I'm not so worried about it contractin expanding on the wedge, but should I? as long as the angle stay all is good I think...

Here is one with a metal rod and a wooden pin, it does work... but it's not as solid as I want
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[Mark Kornell]

Matthew,

What makes you think glue wouldn't be strong enough? With a cross pin, all of the wedging force is directed into a relatively small area of contact where the pin presses against the hole in the cheek. With the glued-in bridge, that same force is spread over a much greater area (the total area of the glue joint). That is all that is holding the "bridge" in place in that wenge plane. While the plane is only three years old, it has been under constant tension and shows no signs of fatigue.

Something you might want to consider is how shavings will clear the plane. If I made a mistake when I built that plane, it was making the opening too small. I could have made the opening 50% larger and/or dished it out a lot more without any compromise to the structural rigidity. You could dish out the lower portion of your wedge and bridge and the top of the toe to create a fair amount of room.

In terms of grain, I took care to match the orientation as closely as possible as if the openings around the bridge had been drilled/chopped out - so that wood movement wouldn't be an issue. Dunno if it makes too much difference, but it can't hurt. In your pic above, it seems like you are very close.

Something to ponder is traditional planes with cheeks holding in wedges with excavated throats - see one of Derek Cohen's for reference: http://www.inthewoodshop.com/ShopMadeTools/BuildingaStrikeBlockPlane_html_m14442b72.jpg
(from http://www.inthewoodshop.com/ShopMadeTools/BuildingaStrikeBlockPlane.html)

What you are doing is not all that different in terms of how forces get applied, other than that you are joining the cheeks together with a bridge. Given the ubiquity of this design in pre-metal plane eras, I think it is clear that the full bridge isn't really necessary.

[Matthew N. Masail]

Hi Mark, Thank you so much for your insights! I mean, you are responsible for this you know. . . :)

I guess your right, I mean if the glue is strong enough to hold the bridge on musical instruments...
but than again I know myself, I'll worry about it and glue creep is still a possibility. I might glue it in, dowel it, then cut out the middle
section to create abutments, than just taper the bottom of the abutments. essentially gluing it in as a bridge give perfect alignment for both sides.

I could have made more room, your right, but it's a short plane and I didn't want the opening to be too big. I did make sure the angle of the bridge is 90 degree to the sole or less, so it shouldn't effect shavings much.

Thanks again for your response, you gave me a bunch of things to think about.