Inlay curve cutting board, did I mess up?

[Patrick Irish]

I don't have a bandsaw and wondering if I messed up making this curved cheese board.
I made a pattern on 1/2" mdf (should have used 3/4) then cut the pattern out with my jig saw. I then sanded the curve section on the mdf smooth so the bearing on the router bit will follow nicely.

I clamped the template down, followed it with my bearing bit cutting about 1/4" into the cutting board. The picture shows the channel isn't 100% even.

I then cut down the middle of the routed channel with my jigsaw so make halves.

I then used a bearing bit on the router table to flush trim the left over from the jigsaw cut.

I clamped it together with the 2 scraps I have noticed a gap in the middle. Will adding another piece of thin stock fox that?

Not sure what happened. Guessing the jigsaw or sanding the mdf template wasn't right.

Do each halves of cutting board have to fit together/line up in order to for the final glue up to work and match?

I can always square the board off I figure. This lil project makes me want to get a bandsaw and an oscillating sander.

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[Steve Demuth]

Patrick,

For some reason I can't see your photo, but the short answer to your question is that you want to fill the channel created by the original router cut with material of the same thickness as the router bit you used. If, for example, you used a 1/4" bit for the original channel, then you need to have 1/4" strip as the infill.

The reason is simple: the original channel is 1/4" wide everywhere in a direction perpendicular to the the curve of the cut. But when you slide the two pieces together without the infill strip, you're moving them perpendicular to the long axis of the board, which in most places is a different direction than the cut perpendicular. The cut perpendicular varies everywhere along the cut, so there are going to varying gaps when you slide the boards together. But fill the gap with the same width material as the original channel, and voila, no gap. The infill material will have to stretch a little around the curve, but if it's narrow material, that's not a problem. In the picture I've attached you can see this clearly because the effect is exaggerated. The red distances are the uniform perpendicular-to-the-channel 1/4" cuts. The yellow distances are the ones you close by sliding the halves of the boards together perpendicular to the long axis. The reason for the gaps you see is obvious - no gap on the parts of the curve where tangent to the curve is parallel to the long axis of the board, large gaps where the tangent is at a steep angle to the long axis of the board.

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[Malcolm McLeod]

... followed it with my bearing bit cutting about 1/4" into the cutting board.
.... Will adding another piece of thin stock fox that?


The radius that the bit cuts is different on each side of the turns. The curved piece of "thin stock" that you use should be the same width as the router bit you used.



Do each halves of cutting board have to fit together/line up in order to for the final glue up to work and match?


IMO It will certainly last longer and look better if the curves match with minimal joint lines.

[Patrick Irish]

The radius that the bit cuts is different on each side of the turns. The curved piece of "thin stock" that you use should be the same width as the router bit you used.



Some reason the width cut from the router bit was not the same. Believe I used a 3/16" bit. I don't think it's a consistent 3/16" gap from start to finish. I'm trying to figure out why that is so I don't make that mistake next time. Maybe I over sanded the valley of the MDF template?

Right now clamped together there is a gap, about 1/16" I think, but no gap on the ends, only in a small middle section. By adding another 1/16" thin stock, how will that affect the board? I'm figuring it may take it out of square but shouldn't be by much. I can re-square it with a miter gauge.

[Steve Demuth]

Read my earlier post - it explains why you see the gap. The infill has to total up to the 3/16" width.

[Malcolm McLeod]

Read my earlier post - it explains why you see the gap. The infill has to total up to the 3/16" width.

^^^
+1 - If you used a 3/16" bit to cut the groove, then 'fill' it with 3/16" thin stock.

[Dick Mahany]

As others have said, just be sure the material that you use to replace the the material removed for the gap adds up to the same thickness as that which was removed. When I made the board below, I was amazed at how poorly the two pieces fit together after the curve was removed. I placed pieces of thin strips together to replace the "wasted" material, and when clamped up, all was well.
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[Gail Ludwig]

This thread is exactly why I LOVE sawmillcreek!! My next project is going to be inlay cutting boards --but haven't started yet. Reading this thread was the "ah ha" moment. I didn't think clearly through the process, but I am sure reality would have hit when I tried to put my inlays in and have the board match. So to carry this concept further, if I want to put in a 3/4 inch inlay, I must take out 3/4 inch. Or 5/8 inlay, 5/8 router cut --etc. Correct?

[Dick Mahany]

So to carry this concept further, if I want to put in a 3/4 inch inlay, I must take out 3/4 inch. Or 5/8 inlay, 5/8 router cut --etc. Correct?

Yes, that is correct. It isn't as intuitive as we would think, but it is simply a matter that cutting two curves with a router bit yields different curvatures on opposite sides of the bit. The curvatures don't fit well when touching each other because they essentially have different radii.

Another way to visualize it would be if one was to rout a full circle from a larger board. Once the circle was cut out, it would only touch the surrounding remaining board on a single point if they were to be in direct contact. Even though those gently flowing curves in cutting boards are not true radial curves, the same principal still applies.

[Steve Demuth]

Yes, that's right. And, just so you're clear, the bit with which you create the original channel must be 3/4" in your case. You can't do this by taking a template, routing out a narrow groove, then moving the template and routing a second groove so it's 3/4" away. If you do the latter, the pieces will fit perfectly with no infill, and not at all once you try to add your 3/4" of pattern infill.

If this seems like I'm beating a dead horse here, it's because I've had the exact conversation I just wrote down in the past. "But the groove is exactly 3/4" wide; why doesn't my 3/4" worth of pattern infill fit?"

[Prashun Patel]

Patrick writes,

"Some reason the width cut from the router bit was not the same. Believe I used a 3/16" bit. I don't think it's a consistent 3/16" gap from start to finish."

The other guys have explained why the two halves won't mate. However, the channel should be an even 3/16" throughout - before you jigsaw it. If the edges of the channel are not perfectly parallel then is it possible that your router moved during the cut? You can minimize that tendency by cutting a shallower channel, say 1/8" . That would be easier to control perfectly.

[Patrick Irish]

Thanks everyone for the replies.

Steve's explanation is little much for my psych major/psychologist for a day job mind hahah!

I measured the bit and it was 1/4" bit. I planed the thin pieces of stock down to .25 and I still have a gap as noted in the first picture below. The 2nd picture is thin stock that measures like .270 or so. Still have a gap along the top swoop.

I understand the concept of replacing what I routed out with same thickness in thin stock in order for it to fit and get the grain patterns to line up.

Here's the link (http://www.finewoodworking.com/membership/pdf/17882/011233068.pdf) I followed on doing this. Only difference for me was using a jigsaw and sanding the MDF template by hand with a folded up piece of 5" circle sandpaper. I think my issue was my template wasn't perfect which transferred over in my routing.

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[David J Blackburn]

It's possible you don't have proper clamping pressure, or that the inlay isn't consistently 1/4". As long as the template is smooth - and looking at the cut, it sure seems smooth enough - it can't really be messed up. Try Adding some more clamps closer to the gap. There is not good clamping pressure at the top of the gap in your pictures. Remember that the clamping pressure comes out from 45 degrees in both directions, and eyeballing it looks like the clamping pressure is coming directly down the curve or just short of it. In something like this you should have a ton of clamps on it.

My two cents, for what it's worth.

[pat warner]

CTR, (complimentary Templet routing (http://patwarner.com/images/templates_cover_shot.jpg)), is tricky stuff.
It can be a 3 step process. A master templet is created. From that, 2 working templets are created. And from that, the work is generated. Whatever the cutter diameter was that rived the working templets, is then added to one of the work pieces. And if any joinery is to be added, then that too is added to one side of the work. All the while, keeping the parts (geometrically) as close to the master as possible. And there are ways to get it nearly exact.
Bottom line: With a 3 step approach, you have the templets for the future, less guess work, but more complication.

[Grant Wilkinson]

It looks like you are using plywood in your last two pics as a test of the gap filling idea. You may want to check the thickness of the plywood. The big box stuff around here is seldom, if ever, of consistent thickness.

[Cary Falk]

Just looking at the pictures it looks like the curve is not smooth and that is causing the gaps.

[Steve Demuth]

Patrick,

I think the remaining gap is due to imperfect tracking when routing your original channel. Not much you can do about it at this point unless you want to re-rout the groove. That's not a trivial task, but it's eminently do-able. You need to align the two board with the gap mostly closed (say down to 1/8") and the template on top. Fasten everything very firmly so it absolutely can't move from the router pressure, and recut a shallow groove over the 1/8" gap that removes some material from both sides. Then you can recut the full groove using your trim bit. If you do everything right, stay on track, you'll have what you want in the end. I've fixed up more than one routing accident this way.

Edit: Patrick PM'd me and I explained this further. I advised him to actually glue the two halves together with some scrap infill, before rerouting the groove with a slightly larger bit. This way he won't be further frustrated by tearout caused the inevitable unsupported climb cuts routing the coordinated, but not solid, two halves.