Accurately laminating curved pieces

[Bob Daniel]

Hi folks!
Something on my mind for a while now, haven't had any luck chasing it down, then I remembered Sawmill Creek. Duh.

I've seen projects where you cut matching curved pieces at the bandsaw, say from maple and walnut, stacking the two workpieces so you get matching curves. I'm imagining a maple bread board with a curvy walnut line through it. And vice versa.

Well, anytime you cut something on the bandsaw, you need to sand to remove the irregularities left by the bandsaw blade. But by the time I sand the two matching edges at the drill press sanding drum, I can't imagine they would be an exact enough match for an accurate edge-to-edge lamination.

Is it "just" a matter of fine-tuning the joint manually? Or am I missing a trick here somewhere?

Thanks in advance, cheers.
Bob.

[David DeCristoforo]

You only need to get the first piece perfect. Subsequent pieces can be flush trimmed using the original piece as a "template". I clean up the outside face on a stationary belt sander and then run it between a "fence" and sanding drum to fair the inside. The setup is similar to this:

http://www.sawmillcreek.org/attachment.php?attachmentid=127628&d=1252615041

[Van Huskey]

I use hardboard to make my pattern then use a pattern bit in the router. You can also use a pattern following sanding spindle on your DP.

[Bob Daniel]

Of COURSE!! Thanks!! The pattern thing is the piece I was missing. Seems obvious now... many many thanks, now I'm excited!
Cheers,
Bob

[mreza Salav]

You only need to get the first piece perfect. Subsequent pieces can be flush trimmed using the original piece as a "template". I clean up the outside face on a stationary belt sander and then run it between a "fence" and sanding drum to fair the inside. The setup is similar to this:



Maybe I am missing something, but if the original question was how to get "matching" curves, (as in a male/female arc where one is convex and one is concave) then you cannot use flush-trim router to get a perfect fit. I can see how to make an exact "copy" of a curve using flush trim but not a "matching" curve.
I have had this problem and my solution was way more complicated.

[Van Huskey]

Maybe I am missing something, but if the original question was how to get "matching" curves, (as in a male/female arc where one is convex and one is concave) then you cannot use flush-trim router to get a perfect fit. I can see how to make an exact "copy" of a curve using flush trim but not a "matching" curve.
I have had this problem and my solution was way more complicated.


I think he did want exact copies. You can make exact copies with a pattern, mirror "copies" with a flipped pattern and curves that fit within each other with a pattern as well (but there are more complications with that depending on the piece). It seems what you are talking about is a mirrored curve which is made by flipping the pattern no extra sweat. Then again I am pretty sure I don't know what you mean by matching since what ever you have in mind is more apparently more complicated.

[Bob Daniel]

Sorry if I wasn't clear in my explanation. I'm imagining a breadboard design with, say, a slightly S-shaped walnut "racing stripe" through the maple, maybe an inch wide, running the length of the board. Maybe two matching stripes, meaning a stripe of maple in between the two walnut stripes. Or at its simplest, for the sake of argument, maybe just a half-maple, half-walnut board, with a curvy joint line where they meet.

So maybe I need to prepare perfectly mating patterns on the hardboard, one for each half of the final mating workpiece? And don't I then have the same problem of getting them perfectly mating? (Although much easier to fine tune a 1/4 inch hardboard joint than one-inch maple).

And assuming the patterns CAN be made perfect, will that translate into perfectly mating workpieces, if the pattern routing goes well?

Thanks, cheers.

[Keith Westfall]

So maybe I need to prepare perfectly mating patterns on the hardboard, one for each half of the final mating workpiece?

That will work. I recently did that, took some sanding with the OSS and holding them up to the light to check the fit.

Get your patterns, trim your wood with your router, and then keep them for next time and away you go.

After the glue up, no gaps! Hopefully...:D

[Van Huskey]

The two side by side S shapes is a little harder and I jsut spent about 30 minutes on a post explaining ti an just about the last sentance (I am using new laptop) hit control instead of shift and the letter I hit closed my browser... argh. When I have a chance I will explain it again.

[Van Huskey]

Edit "I misunderstood some of your post so I talk about things outside the scope but clear it up at the end of the post in the other edit!"

First, with good patterns and some moderate skill on the router table with a starting pin and good quality pattern following bit you should be able to get an excellent mate without much if any sanding, actually the more you sand the more you will goober up the fit when dealing with multiple nesting pieces.

There are two basic ways to approach this either with full thickness boards or inlay, I would probably do inlay but you sound like you are doing full thickness which is particularly cool if you see both sides. So I will deal with the full thickness approach. The first thing here is how it is going to sit in the field, if the S shape runs the full length of the breadboard it makes it much easier if you want the S to sit in the middle of the field surrounded by a third "base" wood that is a whole other subject that I can address if need be. (after finishing the post I will NOT be addressing this! if you want it sitting in the field not running from side to side go the marquetry approch!)

Lets deal with the single S from two different woods first since it is easier. For this you need a single S pattern (make it longer than the actual S you need), draw your S onto the hardboard either directly or from another pattern you make from paper or cardboard use a double marking compass to draw the initial pattern so the sides stay parallel. (You may want to leave a short flat section section at the very middle of the S so you have a short section of parallel straight lines, you will see why in a second) Cut this pattern out of the hardboard and sand it to get just the shape you want everything else will reference from here.

When you are there and your pattern is finished stack one piece of each wood on top of each other and tape them with double sided tape, then tape the pattern on top in the same manner or you can just draw the pattern on, then take this stack to the band saw or use a jig saw to cut out the rough shape (with a jig saw definately draw it on then tape the pattern on before the next step, hopfully you have a bandsaw since the thin S could be a pain with a jig saw) , then go to the router table and cut out the two pieces stacked on each other using the pattern bit, depending on how wide you went with the cut take your time and don't hog it all off at once.

Now you have two identical S shapes in your two woods, take the pattern off but leave the two pieces taped together then use a saw to cut them in half (if you have the flat section in the center where you cut they will mate fine, if you have a continious curve they will probably have to be joined then they will have to be sanded a little). In any case once they mate correctly then you need to join them to make your full S. This full S now becomes the pattern to cut the two patterns you need to cut the panel it sits inside.

Take this full S and mount it to another piece of hardboard and use the thinnest pattern cutting bit you can find to follow the S. The key here is you are actually cutting the hardboard into 2 pieces each with one side of the S cut into it. At this point you should have two pieces of hardboad that will be used as the patterns for cutting the panel so the S fits in the middle. Note the pattern will sit inside the S perfectly BUT will have to slide up, the wider the bit the more it has to slide up and the longer the S needs to be over the finished size. To see what I am saying get a piece of paper, tape two pencils side by side so they draw parallel lines, draw and S on a sheet of paper then cut out both lines (the waste piece of paper in the middle represents the kerf of the router bit) then when you mate the paper you will see you have to slide one sheet up to fit, thats why you need to start oversized. Now you should have one pattern for each side of the S.

Now on to the panel. I would make it in two halves and make these much longer than needed especially the first time you do this! So take one half of the panel and tape one of the hardboard patterns you just made to it orienting the side of the S the way you want it. Rough cut the edge with a jig or band saw then off to the router table to cut that side with a pattern bit. Now you should have one side and the S, they should mate without much work but they will sit offset as I mentioned above. Now repeat with the other half of the panel and the other pattern. The key here is making sure the pattern is taped onto the uncut panel at the proper angle. If you want the S "square" to the panel AND you started with a quadralateral piece of hardboard to make you patterns you can just reference of the outside edge of the panel or a glue line. This is important for the first pattern as well I just didn't think to mention it above. If you want it to sit at an angle you can do that as well but I won't make a long story longer!


You should now be able to mate all three pieces together and glue them up, once dry you will need to cut the mismatched ends off. To make the first cut since the opposite side will not ride square against the fence you will need to use either a miter gauge with a long enough fence, a miter sled or a RAS or CSMS with enough capacity.

Once finished you can reuse the patterns with one caveat, if the blade used to cut the S in half is not the same kerf in the future the two panel patterns will be off.


Now IF you get what I am saying (not sure anyone will) you should be able to extrapolate how to make the second mating S. Assuming the sides of your S pattern have perfectly parallel lines another S shape cut from it will nest in the first one fine but will be offset. If they aren't you can go about making another pattern using the mating edge of the first. As you can see IF you make a really accurate first S pattern it is all easy from there.


A couple of other things. The "kink" in the middle of the S can be made as tight but not tighter then the size of the bearing on the router bit. I would make a long graceful sweeping S though as it makes things easier.

One other way to do this is IF you make a long very sweeping S is to do a lamination for the S. Make a one sided pattern in the hardboard which would look like one of the second two patterns you cut above then use it to cut your oversized (lengthwise) panel so it now has an S cut in the middle and "nests" but it will be slightly offset due to the kerf issue. Then rip a bunch of thin strips out of your two contrasting "S" woods then glue them into the panel so you see an S made out of contrasting "plywood". You would probably have to do this in steps a few strips at a time but you can use the other side of the panel as a caul for each glueing step then when it is wide enough just glue the last strip to the other side of the panel. Could be a very interesting look. Heck with enough time you could make an entire panel out of it, cut it square and face it with solid wood, very cool but VERY time consuming.

In any event when you have the panel glued up flatten with your perferred method depending on what sanders you have.

I like this idea (and I am stealing it) and have it in my sketch book now and WILL use it some time in the future, just wish I had a opening within the projects the LOML has lined up for me to try it sooner. I see a buffet with four doors having a S running through them vertically probably in walnut and maple and the same S running front to back on the top. However, knowing my wife and how she likes to make things harder she will want the S in the top running lengthwise...


One final note is paper is your friend, cut lots of little S shapes to see how patterns come out when cut and how pieces cut from them fit together. When you need to use both sides of the cut to make two mating patterns use the two pencils taped together (or a double marking compass) to magnify the effect a kerf has on the mating of the parts.

Man I hope this makes sense but I am resonably sure it doesn't to anyone except me. My wife constantly reminds me that I speak "Van" and make a simple concept sound stupid hard since I can't help but add every detail I can think of and rarely in a coherent manner.


Edit, I just reread your post and I went far deeper than I needed to!!! For the half and half board just cut out one S with the thin router bit in hardboard then use the two patterns to rout the edges of each half, they will mate but again offfset. If you want one stripe of say walnut inside the maple then follow my steps above for the "half and half" S but just make one with no need to cut it in half and no kerf issues (wish I had read that right the first time and saved myself some thought). For the three stripe version I would suggest doing my two stripe method above with a thin slice of maple pressed in while gluing in my plywood fashion above. Think I covered it all now.

[jim gossage]

I think this should work. If the curve is completely symmetrical, you can flush trim the pieces taped together, and then flip one upside down and then end to end. They will then fit together, but only if the curve is completely symmetrical. If you want a more random curve, prepare a template for your curved part from 1/4" MDF, about 3 or 4" wide. Get one side perfectly smooth with the curve you want, and then use a jig to trace that curve about 3 or 4" away from the first. You might be able to use the system that Dave DeCristoforo outlined to get the second side smooth and paralell to the first side. You now have a piece 3-4" wide with matching curves (e.g. looks like a flat snake). You then use opposite sides of the curved template to flush trim route your cutting board sides. Then, use the cutting board sides as cauls to compress your laminations. I would cut the lamintations a little proud and then clean them up with a drum sander. This way, if a lamination slips during glueup, you won't have a depression to fill in.

[jim gossage]

Now IF you get what I am saying (not sure anyone will) you should be able to extrapolate how to make the second mating S.

Sorry, but that one flew by me like an incoming scud! Of course, it is 5am. Got some pictures or drawings?

[Van Huskey]

Sorry, but that one flew by me like an incoming scud! Of course, it is 5am. Got some pictures or drawings?

Yeah thats what I afraid of, it makes perfect sense in MY head but it is something you really need to show someone. I don't have the computer skill required to do the drawings quickly and don't have the time to actual do one and takes pictures along the way. I was hoping that if someone followed along making it out of paper they would get it but alas I am probably wrong and might have been better off saying nothing! PLus because I misread the post, before my edits I was talking about a different idea and it all just went sideways. I am confident what I have in my head will work and is easily repeatable but the first time you do it will take a lot of time and steps to get the patterns you need. Your idea is a peach as long as you get perfect curves onto the first pattern, without something like a CNC machine I could never do that, so my convaluted way takes out any need for a precise first pattern since everything references off actual cut edges your curve could be simply hand drawn and everything would fit and the free hand cuts and sanding you have to do to make the first S pattern do not have to be to any tolerance other than just visually appealing.

I think I have the answer... buy a freakin CNC machine.

[mreza Salav]

I think he did want exact copies. You can make exact copies with a pattern, mirror "copies" with a flipped pattern and curves that fit within each other with a pattern as well (but there are more complications with that depending on the piece). It seems what you are talking about is a mirrored curve which is made by flipping the pattern no extra sweat. Then again I am pretty sure I don't know what you mean by matching since what ever you have in mind is more apparently more complicated.

By "matching" male/female I mean two pieces curved (say half circles) that are going to be joined/glued together; so the glue goes on the "outside" of the one piece and on the "inside" of the other one. I don't know of any way of building these two copies with just using a flush bit/pattern bit (as simple as described above) IF the pieces cannot be flipped over. I encountered such a situation recently where I had a curved piece (on the top section of the crib in the following link) and to attach the stiles I had to get a matching curve on the top of the stiles:

http://www.sawmillcreek.org/showthread.php?t=133526

Here is a thread for a similar question and the solutions:

http://www.sawmillcreek.org/showthread.php?t=129952


Sorry if I wasn't clear in my explanation. I'm imagining a breadboard design with, say, a slightly S-shaped walnut "racing stripe" through the maple, maybe an inch wide, running the length of the board. Maybe two matching stripes, meaning a stripe of maple in between the two walnut stripes. Or at its simplest, for the sake of argument, maybe just a half-maple, half-walnut board, with a curvy joint line where they meet.



I don't think with a flush pattern bit you would get a perfect fit here as
that can be used to make an exact "copy" of a curve.

(http://www.sawmillcreek.org/showthread.php?t=129952)

[Prashun Patel]

Not sure this hacked powerpoint pic makes sense:

Make a template of the edge (t) and screw it to a wide support (base) with a support piece (s) the same width as (t) about 1" from the edge of (t). (s)'s shape is not critical as long is it basically follows (t) but allows bit clearance.

Using a flush trimming bit (r), mount the one piece of yr top (a) to the jig, and route its edge.

Then mount the mating piece (b) onto (s) and route it flush - making sure to keep the bearing riding along (t).

It then won't matter what shape or symmetry or smoothness (t) has, you'll create 2 perfectly mated pieces.

[Bob Daniel]

Great Googly Moogly, you guys are awesome! Since 11 a.m. is, in a sense, my 5 a.m., I won't say much more right now besides THANKS!! Lots of detail to go on here. It started out as a hypothetical question, pretty much, but now I feel like I should go get the materials and get building!

Of particular interest was the idea of the offset caused by the kerf... never thought of that, that could've spelled trouble... I've be sure to leave lots of wiggle room...

[Bob Daniel]

Shawn, that's interesting. As I understand it (I think) then you're using the SAME edge shape to route BOTH the inside and outside of any shape, so no issues with making perfectly mating templates, there's just the one... this is fundamentally different than the other approaches discussed, I think.

This would be a handheld router situation, as you've drawn it, yes?



Not sure this hacked powerpoint pic makes sense:

Make a template of the edge (t) and screw it to a wide support (base) with a support piece (s) the same width as (t) about 1" from the edge of a. (s)'s shape is not critical as long is it basically follows (t) but allows bit clearance.

Using a flush trimming bit (r), mount the one piece of yr top (a) to the jig, and route its edge.

Then mount the mating piece (b) onto (s) and route it flush - making sure to keep the bearing riding along (t).

It then won't matter what shape or symmetry or smoothness (t) has, you'll create 2 perfectly mated pieces.

[mreza Salav]

Not sure this hacked powerpoint pic makes sense:

Make a template of the edge (t) and screw it to a wide support (base) with a support piece (s) the same width as (t) about 1" from the edge of (t). (s)'s shape is not critical as long is it basically follows (t) but allows bit clearance.

Using a flush trimming bit (r), mount the one piece of yr top (a) to the jig, and route its edge.

Then mount the mating piece (b) onto (s) and route it flush - making sure to keep the bearing riding along (t).

It then won't matter what shape or symmetry or smoothness (t) has, you'll create 2 perfectly mated pieces.

I am not sure I understand your steps correctly or not, Are you saying (a) and (b) will be the mating pieces? It seems to me with step one, you get a "copy" of edge of piece (t) on piece (a). Fine. But I cannot understand the rest.

One thing that I think is critical is to account for the thickness of the bit when making matching pairs otherwise the curves will be different.
Here is how I do/did it:

Suppose I have a piece "A" with a curve on the edge and I want to make a matching pair for it.

1) Since I don't want to change "A", first make an exact copy of "A" on another piece using a flush trim bit. Call this "B". so "B" is identical to "A".

2) Use a rabeting bit, and cut a rabit of, say 3/8" into the curve of B.
Then using a flush trim bit complete the rabet on B; so now the curve on B
is 3/8" offset from the original curve.

3) Take a wide piece of MDF (to make a pattern out of) and a flush trim bit which is 3/8" (which is the same amount of off-set created on B). You can replace all these 3/8" with 1/2" if that's all you have, or 1/4". Now follow the new curve on B to cut into the MDF; you get two curved pieces on MDF; one is identical to B and the opposite is the matching curve of A.

4) Use the MDF pattern and a flush trim bit to transfer it to whatever piece you want to be the matching pair of A.


The purpose of step 1 is to account for the thickness of the bit used in step 3.

I hope it makes sense now.

[Prashun Patel]

(a) and (b) are mating pieces.
By routing on the other side of the bit, my (b) will be the mirror image of (a). (b) needs to be clamped down, and you have to route in the opposite direction as with (a) else you'll be climbing the cut.

If you already have (a) cut, then you can use that as the template for flush trimming (b). You just need a support piece under (b) that's at least as thick as (a).

Yeah, this'd be only for a handheld router. I was thinking tabletop, where the pieces might be too large for an r-table anyway.

[Bob Daniel]

One thing that I think is critical is to account for the thickness of the bit when making matching pairs otherwise the curves will be different.

Wouldn't that only apply where the curves are tighter than the radius of the bit? Otherwise, shouldn't it just follow the curve? Isn't that the pattern bit's whole point, to match the pattern? Getting confused again....:confused:

[Derek Hansen]

Not sure this hacked powerpoint pic makes sense:

Make a template of the edge (t) and screw it to a wide support (base) with a support piece (s) the same width as (t) about 1" from the edge of (t). (s)'s shape is not critical as long is it basically follows (t) but allows bit clearance.

Using a flush trimming bit (r), mount the one piece of yr top (a) to the jig, and route its edge.

Then mount the mating piece (b) onto (s) and route it flush - making sure to keep the bearing riding along (t).

It then won't matter what shape or symmetry or smoothness (t) has, you'll create 2 perfectly mated pieces.

YES! Thanks Shawn!

Edit* Aww nuts Mreza is right.

[mreza Salav]

(a) and (b) are mating pieces.
By routing on the other side of the bit, my (b) will be the mirror image of (a). (b) needs to be clamped down, and you have to route in the opposite direction as with (a) else you'll be climbing the cut.

If you already have (a) cut, then you can use that as the template for flush trimming (b). You just need a support piece under (b) that's at least as thick as (a).

Yeah, this'd be only for a handheld router. I was thinking tabletop, where the pieces might be too large for an r-table anyway.

I am sorry but I don't think you'll get perfectly mating pieces this way.
You simply are not counting for the thickness of the router bit.
The radius of the curve on (a) and (b) will be different by exactly the thickness of your router bit. They won't fit perfectly.

If you think carefully about it you'll see what I mean.

[Bob Daniel]

I am sorry but I don't think you'll get perfectly mating pieces this way.
You simply are not counting for the thickness of the router bit.

I'm not sure I understand why. Seems to me you could use a two-inch radius router bit (if there were such a thing) and still the left and right pieces would match because they're cut using the same template. As long as any inside corners aren't smaller than the bit radius, then the bit radius is not even in play. Just like carving out a bowl with a bowl bit, the diameter of the bit is only potentially a factor in the corners, and only if the bit radius is bigger than the desired corner radius. In that example, actually, the bit radius will BE the corner radius, like it or not...

[mreza Salav]

I'm not sure I understand why. Seems to me you could use a two-inch radius router bit (if there were such a thing) and still the left and right pieces would match because they're cut using the same template. As long as any inside corners aren't smaller than the bit radius, then the bit radius is not even in play. Just like carving out a bowl with a bowl bit, the diameter of the bit is only potentially a factor in the corners, and only if the bit radius is bigger than the desired corner radius. In that example, actually, the bit radius will BE the corner radius, like it or not...

Imagine the piece (a) is a half disk with radius 2". If you use a 3/4" thick bit then the mating piece (b) will be a half circle with radius 2+3/4" which is clearly not matching (a).

[Prashun Patel]

I think you are right, Mreza. It's easiest to see yr point if the template were a perfect circle. (a) would have a diameter equal to (t), but (b) would have a diameter (a) + (r).

To correct for this, then I ask you, can you do it like inlay template kits?

First, you route (a) with the template on top, using a bushing with an offset equal to the radius of the router bit.

Then for (b), you remove the bushing, and route it like I said below.

This seems to work for inlays. Would it work here?

[mreza Salav]

I think you are right, Mreza. It's easiest to see yr point if the template were a perfect circle. (a) would have a diameter equal to (t), but (b) would have a diameter (a) + (r).

To correct for this, then I ask you, can you do it like inlay template kits?

First, you route (a) with the template on top, using a bushing with an offset equal to the radius of the router bit.

Then for (b), you remove the bushing, and route it like I said below.

This seems to work for inlays. Would it work here?

It would work, but the mating pieces you get, none is the copy of the original piece you started with (i.e. (t)).
What I said was, if you have a curved piece (t) and you want to find a mating piece for it then you have to following something like the steps I mentioned.
What you said (using router templates) gives you two mating piece none of which is a copy of the one you started from (t).
So if you had a 2" disk to start with you'll get two mating pieces each with radius 2+3/4', say.

[Van Huskey]

My way will NOT work correctly. It was very late and I saw some issues but couldn't completely think them through. The kerf is the killer. You need that "Atom Splitter" molecular kerf blade which I need to get around to inventing. Sorry for all the misinfo.

[David DeCristoforo]

Sorry...somehow I thought you were stacking pieces, not mating them. Templates and guide collars are the way to go for this. But here's another "trick" that's a bit "down and dirty". If you stack a couple of boards of contrasting colors and stick them together with some sort of temporary bond (hot melt, two sided tape, etc.) you can bandsaw a mild curve, separate the layers and the pieces will match closely enough to get a tight glue joint. You have to make the cut in one smooth motion so as not to alter the kerf. And if you are trying to follow a true radius, it can be difficult. Also, the tighter the curve, the more difficult it is to get the pieces to glue up cleanly. So like I said, a mild curve is best for this "technique".

[Prashun Patel]

What you said (using router templates) gives you two mating piece none of which is a copy of the one you started from (t).


Understood. I guess one could cut (t) a little small, or for the application, being off from the template by this much just might not matter.

[mreza Salav]

Aside from the method I posted in post #18 (which works; I have tried) the "other" trick David suggested works to some extend too.
To get an even better joint (when the two pieces are stacked up) I would use a scroll saw. The thin blades on scroll saw are much more forgiving than the blade on a bandsaw and the joint's will be a lot smoother too.

[Bob Daniel]

Imagine the piece (a) is a half disk with radius 2". If you use a 3/4" thick bit then the mating piece (b) will be a half circle with radius 2+3/4" which is clearly not matching (a).

Okay, I see now. Thanks. In the example of the same template being used twice, yes indeed, the router bit diameter does come into play, being a whole bit-width away, or collar-width away, from the template during the second pass...

I think... going to play with quarters and pencils... test it out...

So we're back to this, I think:

1. Layout a gentle S-curve on hardboard, cut on bandsaw as accurately as possible.
2. Finesse both pieces of the hardboard until they mate perfectly, and are smooth. (Which is still the hard part, and a variation on my original question!!) Label them left and right.
3. Use "left" template to create first curve within the glued-up maple breadboard workpiece.
4. Use "right" template to prepare mating walnut piece. Glue walnut to maple while you have two flat edges for clamping.
5. Use "left" template again to create the other edge of the walnut stripe, say an inch away from the now-glued-up edge.
6. Use the "right" template to clean up the cast-off edge of the maple from step 3.
7. Glue up this final maple piece, and you now have a maple breadboard with a curvy stripe of walnut.
8. Optional: use the templates to cut matching curves in the outside edges of the final piece, parallel to the stripe.
9. Route any final details (juice groove, finger grip, chamfered edges) and call it a day...

Sound like a plan, kind of? Step 2. still concerns me...

Cheers, Bob.

[Bob Daniel]

I think... going to play with quarters and pencils... test it out...

Okay, I did that. I used a large circle (mug) and a small circle (coin). I drew an arc using the mug. Left the mug in place and using the coin to represent the router bit collar, followed the arc of the mug with a pencil on the far edge of the coin, representing the second cut described in the diagram. It creates a lovely PARALLEL arc, like the opposite shore of a curve in the river, but not a MATING curve.

Geometry wise, the second arc is of a circle with a radius larger than the first circle by an amount equal to the diameter of the coin (router bit). Interesting....

So, used as part of a different process, I can still see it being a very useful technique, maybe even as another way of solving this same problem. Haven't quite figured out how yet, exactly, but still food for thought...

[Van Huskey]

This has been bugging me but I am out of town and can't do it hands on BUT here is my early morning shot at it...


1. Make a 3/4" MDF template of the S, you need something thicker than hardboard, you will see why in the next step. Be aware that this is a pattern to make the patterns so the final cut will be similar but the radius of the curves in the final product will be slightly different.

2. Place the template on another 3/4" piece of MDF and use a 3/4" pattern following bit to cut the S curve out of the MDF so now you have two pieces of MDF, they then become the patterns for each of the sides. You need the 3/4" thick original pattern because you couldn't hog out enough material at once to get the pattern cutting bit to sit against 1/4" material and I think you want 3/4" MDF to make clean patterns for the next step.

3. Now here is the trick, you need a bushing and straight bit that puts the edge of the straight bit EXACTLY half of the width of the pattern cutting bit away from the edge of the new patterns. When you have that the rest is easy. If my sleep deprived brain is right and you use a 3/4" pattern bit to cut the two patterns then a 1/2" OD bushing and a 1/4" straight bit should put the bit edge 3/8" from the pattern and exactly in the center of where the pattern bit ran.

4. Place one pattern on one of the wood species and route the S (all the way through) using the bushing and straight bit, then use the other pattern on the other species of wood and cut again with the bushing and straight bit to form the other half of the panel.

5. Now you should have two pieces that mate together.

In essence you are cutting each piece of wood in the exact center of where the pattern cutting bit ran through the MDF. Assuming I am not crazy this should work.

Assuming this does work then you can extrapolate how to make more complex multiple S patterns but it gets more complicated.

Somebody help me with this I am on the road for 2 more weeks and I need to know... so I can sleep!

This all does depend on the accuracy of the bit and bushing sizes and the router runout and being tunes to perfect concentricty with the bushing/bit.

[Bob Daniel]

Sorry Van, I thought we had this sorted... this is where I left it, in my mind: (pasting my list/plan from earlier post)

1. Layout a gentle S-curve on hardboard, cut on bandsaw as accurately as possible.
2. Finesse both pieces of the hardboard until they mate perfectly, and are smooth. (Which is still the hard part, and a variation on my original question!!) Label them left and right.
3. Use "left" template to create first curve within the glued-up maple breadboard workpiece.
4. Use "right" template to prepare mating walnut piece. Glue walnut to maple while you have two flat edges for clamping.
5. Use "left" template again to create the other edge of the walnut stripe, say an inch away from the now-glued-up edge.
6. Use the "right" template to clean up the cast-off edge of the maple from step 3.
7. Glue up this final maple piece, and you now have a maple breadboard with a curvy stripe of walnut.
8. Optional: use the templates to cut matching curves in the outside edges of the final piece, parallel to the stripe.
9. Route any final details (juice groove, finger grip, chamfered edges) and call it a day...

(end paste)

[Bob Daniel]

I'm re-posting this, my "final" (current) plan/checklist at the root level, since the thread is getting a bit heavily nested... thanks again for all the thoughts, and taking the time to respond...

(pasting my list/plan from earlier post)



Layout a gentle S-curve on hardboard, cut on bandsaw as accurately as possible.
Finesse both pieces of the hardboard until they mate perfectly, and are smooth. (Which is still the hard part, and a variation on my original question!!) Label them left and right.
Use "left" template to create first curve within the glued-up maple breadboard workpiece.
Use "right" template to prepare mating walnut piece. Glue walnut to maple while you have two flat edges for clamping.
Use "left" template again to create the other edge of the walnut stripe, say an inch away from the now-glued-up edge.
Use the "right" template to clean up the cast-off edge of the maple from step 3.
Glue up this final maple piece, and you now have a maple breadboard with a curvy stripe of walnut.
Optional: use the templates to cut matching curves in the outside edges of the final piece, parallel to the stripe.
Route any final details (juice groove, finger grip, chamfered edges) and call it a day...


(end paste)

[Richard Dragin]

If you have two perfectly mated pieces and then place some laminations between them you won't have matched radius' anymore. Depending on your next step after the glue up, making them perfectly smooth may be a waste of effort.

There are some really long winded posts in this thread so excuse me if this has been addressed.

[Bob Daniel]

If you have two perfectly mated pieces and then place some laminations between them you won't have matched radius' anymore.

Not laminations, as such... I'm going to route each edge with either the left or the right template, as I described. You're right, if I was to "wrap" a thin piece along the edge, it would build up the radius. But that's not what I had in mind. Thanks for the response, cheers!

[Richard Dragin]

I guess the title of the thread threw me off.

[Bob Daniel]

I guess the title of the thread threw me off.

hehe, good point, my bad... :o

[Van Huskey]

Sorry Van, I thought we had this sorted... this is where I left it, in my mind: (pasting my list/plan from earlier post)



I did see that and really was trying to work it out in my mind in a way that does not require any fitting work, as this is where the problems come in. I knew there was a way to do it without ever having trial and error come into play. It certainly won't hurt my feeling if you go with the other approach, as I put the thought into it as much for me as anything. I just hate trial fitting it is usually when I really screw things up! But, then there are a lot of people (I am sure you included) that are a heck of a lot better at freehand things than I am, if I don't have a jig I can't sweep sawdust! :o

[Bob Daniel]

I had a start on it today... I laid out my curve on a piece of hardboard, cut it on the bandsaw.... I wandered off the line here and there, but decided not to worry, it looks organic enough to get away with it, and if I sanded back to the line, I'd never get them to mate perfectly... as it was, just a very light sanding and they still mate... now I have my left and right templates, I should be good to go... "knock wood", haha...

[Van Huskey]

I had a start on it today... I laid out my curve on a piece of hardboard, cut it on the bandsaw.... I wandered off the line here and there, but decided not to worry, it looks organic enough to get away with it, and if I sanded back to the line, I'd never get them to mate perfectly... as it was, just a very light sanding and they still mate... now I have my left and right templates, I should be good to go... "knock wood", haha...


Patience is a virtue I do NOT have. If I can stick it in a machine and make it do my will I HAVE to find another way. One reason I will never be a neander...

[pat warner]

Can be done entirely with routers. Moreover, with compensatory cuts, the glue line can be tee & geed (http://patwarner.com/images/fish.jpg).
Takes patience, tools, many templets, and algebra 1.

[Van Huskey]

Can be done entirely with routers. Moreover, with compensatory cuts, the glue line can be tee & geed (http://patwarner.com/images/fish.jpg).
Takes patience, tools, many templets, and algebra 1.


This is SOOO funny, I almost posted the other day "where is Pat Warner when you need him". The fact is what made me realize that it could be done with just a router was the scene in your "The Versatile Router" where you show the animation of bushing cuts not having the same radius as the template. It just popped in my head this AM and I thought thats what I need, something that has a different radius as the template...

[Bob Daniel]

Well, I'm giving up, for now...

I have what I thought was a pretty decently mating pair of curves, on hardboard templates. No daylight at the join when I hold them up together. Then I routed a final workpiece from each template, a "Left" in maple, and a "Right" in Walnut. Held them together: daylight through the join... even when clamped, couldn't get them to mate perfectly... hmmm...

Anyway, I'll save the templates and try again in the warmer weather (unheated shop)... for now, I'm going with straight-line racing stripes...

I'll also re-read some of the ideas in this thread, see if I missed something... thanks again folks...