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Old 01-21-2010, 05:04 AM   #1 (permalink)
 
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Angry Celtic Knot in Brass - Difficulties

Experimenting with BRASS INLAY (2x10 mil) for Celtic Knot. I know this is pushing it so far as thickness is concerned. Any guidelines for drilling, gluing, clamping in vise and turning? My first attempt to drill the blank resulted in a disaster. I used a parabolic bit and did not place the knot far enough down into the pen vise. Voila! The butt joints of the knot did not hold and the wood blank sort of exploded at the knot. I know I forgot to rough up the brass sheet before gluing with medium CA. Next time I'll rough it up and use epoxy. Previous results with all-wood knots worked out fine as long as the drill was properly centred in the blank.

H E L P!

Added Note: Perhaps someone can comment on the use of different profiled drill bits. The parabolic bit looks like it would bite into the metal inlay rather than cut it. Same with the brad point. Maybe regular profile is better.

Jan 21/10 - Thanks very much for your feedback so far.

Last edited by Dave Talbot; 01-21-2010 at 12:23 PM. Reason: adding detail and thanking contributors so far
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Old 01-21-2010, 07:13 AM   #2 (permalink)
 
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Try annealling the brass to soften it somewhat. If it is a piece of stock from the local hardware store, they usually have a fair amount of hardness to them.
You also do need to create a scratch coat on the surface for adhesion.
Lastly, even though it takes four days total to do the blank, try epoxy instead. Just mix up barely enough to do your bonding.

Last edited by JerrySambrook; 01-21-2010 at 07:16 AM.
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Old 01-21-2010, 08:31 AM   #3 (permalink)
 
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I agree with the epoxy, I did not let it cure completely and the blank exploded........a couple times......
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Old 01-21-2010, 09:06 AM   #4 (permalink)
 
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A trick that I picked up from seeing pics of Eagles works in progress.

Once you have the blank ready for drilling, Wrap it in string so you can't see any of the blank, then douse the string in CA. This will provide extra support around the entire blank while drilling and will allow you to simply turn the string off once you are on the lathe.

You can use other things instead of string, but it's cheap, easy to find, and strong.
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Old 01-21-2010, 10:19 AM   #5 (permalink)
 
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I will add; always put a support block under the blank while drilling, otherwise when you hit the spot where the knot comes together the blank will come apart!

If you can visualize the blank, the knot will look like two four-sided pyramids arranged tip to tip.

If the hole is very large, drill in steps. (drill 1/4", 3/8", 1/2" etc.) This reduces the stress on the blank and reduces the chance of chips exploding the blank. They just fall out the bottom.

Hope this helps.
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Old 01-21-2010, 10:20 AM   #6 (permalink)
 
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Quote:
Originally Posted by Russianwolf View Post
Once you have the blank ready for drilling, Wrap it in string so you can't see any of the blank, then douse the string in CA. This will provide extra support around the entire blank while drilling and will allow you to simply turn the string off once you are on the lathe.

Mike; That is an excellent suggestion!!!
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Old 01-21-2010, 08:44 PM   #7 (permalink)
 
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Since you are cutting the metal at an angle, using a drill bit also cut at an angle means your tip won't be trying to cut the metal, just the wings. Lots of heat which weakens the glue joint.

I always use brad-point drill bits when doing metal segments. Works great and I've never had one come apart yet. (((( KNOCKING ON ALL THE WOOD I OWN )))
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Old 01-21-2010, 10:07 PM   #8 (permalink)
 
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Did you ever think about making a jig to hold your brass and pre-drill it before you insert it in the blank? Another tip is to drill the brass with your bit before you put it in the jig. This makes the hole fairly close to the final size. The jig then holds the brass stock and lets you turn a round hole into an elongated hole.

I took a hard maple blank. Drilled it with the same size bit the real pen blank will need. Then cut it like it was the final blank with the cut being at the exact angle the celtic knot will be cut. Drill the brass stock with the proper bit flat-wise and you have that round hole. Then set the brass in the saw slot. Center the brass stock in the jig making sure the hole is in the center. Place one drop of CA to hold the brass in the slot if loose. Drill the blank again this time drilling the brass at the correct angle. When your take the brass back out you will have a elongated hole as the drill bit goes through the brass at the correct angle. I cheated the other day and made my jig with three slots. I could create three brass stock inserts at a time with an elongated hole that was perfect for the celtic knot. Do just one at a time as you start out.

Make sure you glue the stock in the final blank with the elongated hole in the right direction. I mark the top of the stock with a marker so I make sure I get the elongated hole in the right direction. I never cut all the way through the blank. Just 7/8's the way through. The slot holds the brass stock but the blank must be exactly square or the knot gets lopsided.

Now I have two ways to drill a celtic knot blank. Like most I have cut and glued repeatedly and then try to drill the entire blank. Hard to hold your breath that long as slowly and carefully you drill a blank that you have spent ten hours working on. One slip, one misstep and you have scraps.

You can pre-drill your brass stock as detailed above and most of the stress areas in the center of the blank will not have a solid brass mass that has to be drilled out. It will be a almost perfectly centered brass stock with a hole already where you need it. You need to drill it as normal but most of the danger areas are already drilled out as the brass stock is all got one hole in each. If you centered it properly your drilling is almost never a problem. Almost.

Now when I get real concerned I drill the final blank end to end before I start. The blank must be exactly square. Then as I cut and glue the brass stock I put a cork shim down the hole in the blank. It centers and holds the brass stock while the glue cures. It is easy to drill the cork stopper right back out and leaves no mess in the blank. Turn, cut, glue, remove the cork, chase with a drill bit and repeat until done. Then just chase the blank hole one more time and you are ready to glue in the brass tubes.

I know it is a lot of steps but it is simple if you just think outside of the box. I do scuff the brass to give the glue a surface to stick to. I guess all mu brass has been soft already. Must use extremely sharp tools.
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Old 01-22-2010, 11:20 AM   #9 (permalink)
 
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Default Pre-drilled Brass

WOW! What a brilliant "out of the box" idea! I'm grateful and thanks very much. I'll try it.
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