Celtic knot question - Woodworking Talk - Woodworkers Forum
 
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post #1 of 7 Old 03-04-2012, 10:23 PM Thread Starter
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Celtic knot question

I'm attempting to make a pen with a celtic knot in it. I've got the basics, but every time I try to drill the blank, I manage to crack it and it breaks in half on me. Very annoying. Hopefully someone can shed some light on the topic and tell me what I'm doing wrong.


I make a 45 degree cut into the blank, then glue in a kerf sized sliver of another type of wood (currently paduk sandwiched between purple heart) into the cut and clamp it all back together. I don't use a lot of force with the clamps; just enough to keep things together while the glue dries. Two hours later, I make another cut, and add another sliver. Rinse and repeat till I have all four in and the piece back together. Usually I get the last piece in around 10:00 or 11:00. Then I go to bed and let it dry till the morning. It gets a full 12 hours to dry before I attempt to drill it and continue the pen, but somehow I always manage to break things along one of the glue lines. Then, of course, the blank is trash so I have to start again.

I'm using Titebond III as the glue. Is that the wrong glue? Should I wait more than 12 hours for it to fully cure? Would a 5 minute epoxy work better? I typically spin the blank on the lathe and use a drill chuck with the bit in the tailstock to drill the hole through it. I spin the blank around 750 RPM typically and make slow cuts. Should I be spinning faster or slower? Should I try to drill faster?
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post #2 of 7 Old 03-05-2012, 12:23 AM
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Try a brad point bit and don't drill all the way through. Start your blank a bit bigger and then cut it to length after you drill.

That bowl was perfect right up until that last cut...
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post #3 of 7 Old 03-05-2012, 08:35 AM
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OK I will try to add some of my observations which I found from making these. But first a couple questions. When you say it breaks in half, does it break along one of your glue joints??? If so what woods is breaking??? What wood is the main body??

The reason I ask is you are using some very oily woods for the inlays. I do not know because you did not mention what wood you are using for the main body of the blank. But if that too is an oily wood that also can be a problem. I have found over the years there is no better glue for wood products than yellow wood glue. You are using Titebond III. That is a good glue but it is a more weather resistant glue. I like to use either the original or titebond II. The titebond II will give you abit more open time. What I would do and I always do when using oily woods is to wipe down the joint with acetone brfore gluing. I wait a minute or two for it to dry and then add a good amount of glue. I also roughen the glue surface abit with 120 grit paper. When you cut oily woods such as purpleheart you get such a smooth surface and the grain pores are all closed and glue has a hard time penetrating oily wood.

OK that is the glueup portion. Now the drilling. Being you have all different species of woods and the grain patterns are running at 45 degrees and different directions you will get alot of outward force when drilling. A couple things I would do and these are little tricks I have learned over the years. First a shap bit is needed. I do not like brad point bits but use machine bits. I always use a center bit first so that I make sure the hole is in the center of the blank or else the designed will be off. I like to step drill for my tubes. That is start with a 1/4" bit and work my way up to proper sized bit needed.

A couple of tricks that work. When I get the blank all glued up, and it has dried, I drench the blank with thin CA glue all over the joints. This adds strength. I will on occassion if I know the blank is very prone to breaking I will wrap the blank in 2" gauze and again wet it down with thin CA. Now the gauze will help in the stregthening process. Another trick is to wrap the blank in thin pieces of scrap wood all the way around on 4 sides. All this will be turned away after you drilled the blank. This how segmenters do their blanks and essentially that is what a celtic knot is a segmented blank.

I would drill at a slow rate and continue to clear the hole from chips. Heat is your enemy when it comes to drilling into glued joints. If your get too hot you run the risk of melting the glue. I like to cool my drill bit of with denatured alcohol when drilling woods or acrylicks or metals too. Just wipe the bit down after it is pulled out each time with a wet cloth soaked in denature alcohol. Works well.

Hope some of this helps. Look forward to seeing the results. One other note. The woods you chose will turn brown over time even when you top coat with CA. So the color difference you see now will not be the same at a later date. Just so you are aware of that. Take care and have fun.

John T.
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post #4 of 7 Old 03-05-2012, 09:49 AM
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Good suggestions JT. Since I don't turn many pens I can't relate to all of them but have had glue problems with Paduak and other oily woods. Wiping with acetone seems to work well for me.
When drilling pens with wood that is either glued together or has swirly grain that runs out through the sides, I find one of the V shaped clamping jigs that supports the wood all the way around when in the vice really helps.
Of course you can't use one of the those if you drilling on the lathe. for that I have a set of long jaws that will hold about 90 percent of the pen blank between it's 4 jaws. This keeps them from breaking.
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post #5 of 7 Old 03-05-2012, 03:38 PM
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I have made celtic knots in S& P Mills, game calls, wine bottle stoppers and pens. The quality of the cut is number 1, letting the glue dry for at least 8 hour before you make your second cut, I wait until the next day. I figure 1 day for each cut. I want the waxpaper to be almost dry when I remove the clamps. I use wax paper to line the form which holds the part aong with the clamps. I have use brad point bits since 2003 and have not had a problem. I am not sure how long the piece is you are cutting to make the knot but if the cut is not square you will only have glue and not wood to wood contact. Most of my cuts are 30 to 35 degrees. I apply clamp pressure to the sides as will as the length. I use titebond III most of the time.
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post #6 of 7 Old 03-05-2012, 08:43 PM Thread Starter
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I made another attempt yesterday and instead of trying to cut only 90% of the blank and squeeze the knot in there, I just cut all the way through and clamped it back together. Same 2 hour intervals for getting the knot in, then overnight before drilling it. Worked out pretty well and I have my first celtic knot pen to show for it. It's not as good as I'd like, but I'm happy with my first one. Now if I could get a decent pic of it to show off...
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post #7 of 7 Old 03-05-2012, 11:53 PM
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Way to go Itchytoe. I always cut mine all the way through. I have even made some with acrylic sheet material. On oily woods I used alcohol rather than acetone.
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