Drilling Hybrid Blanks

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montmill

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I'm making my first pens using hybred blanks that I've made using alumilite slow resin. The cherry burl was stabilized before pouring.

I painted the brass white before inserting it in the blank. I first drilled with the recommended 12.5 mm drill bit but found the painted brass wouldn't go in the blank. I opened it up finally finishing with a 1/2 inch imperial bit. Even at that the painted brass was very snug when I glued it in with two part epoxy.

Is this something you've run into as well? I wonder if the drilling melted the alumilite causing the smaller opening? I didn't investigate to see if the pinch was with the wood or the alumilite.

Thanks for the feedback.
 
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There are two things that help in situations like this, once you get comfortable trying different size bits:

1. keep a chart at hand to see what is the next size up in a drill bit without getting too large.
here is the link to a chart in our library:

Conversions - (Colored) MM Equivalents by Tenths, Fractions, Decimals, Number & Letter Drill Sizes

This Colored Conversion chart will print on (2) 8.5" x 11" sheets of paper or back to back, if your printer allows it. I've Laminated it also. It includes MM Equivalents by Tenths, Fractions, Decimals, Number & Letter Drill Sizes. Uploaded...
www.penturners.org

2. As finances allow, see about a SET of metric bits in .5 mm progression to 13mm, AND also get a Set of bits to 1/2" or larger in 1/64" increments.

That will cover a whole bunch of sizes, and allow one to increase the size just a tiny bit without over sizing. The chart will help figure out the next actual size up, which might be metric or inch.

Harbor Freight used to offer a 115 piece set that covered "Numbers" "Letters" and Fractions up to 1/2". They don't offer it now. Amazon does have them but the least expensive set are now north of $100.
 
It makes no difference if you drill Hybrid blanks, acrylic blanks or wood blanks, Heat from drilling can cause reactions. Make sure you use sharp bits. Make sure you drill slowly and withdraw and clean hole often. With some materials a lubricant is needed. I have never run into that one because I follow the first 2 strictly. To cool the bit I use Denatured alcohol. Works very well. Then after the hole is drilled it would be wise to let sit and cool off or return to normal. Before you glue the tube in, run the tube in the hole to see if it is too tight. If so you may need to redrill using the same bit or step up a size. As mentioned a fully equipped set of bits MM, English and numbered work well. Now if painting of the blank is needed because of transparency then I suggest you always paint the blank. Spray paint is the easiest and thinnest . Others use various methods and works for them. Some people color the epoxy too. Painting the tube is a waste of time in my opinion. Over the years I found that painting the inside the blanks covers the transparency. I will though add color to the epoxy. Again any way you do this always try insertion before gluing.
 
Agree with @jttheclockman - paint the blank not the tube. Spray paint is the best. You are not looking for a thick buildup of paint, just the color to hide the brass. Don't forget to also consider the color to be a possible accent or highlight vs just using it to hide the brass. Drilling with the least amount of heat is key to preventing distortion. Either prevent the heating by adjusting your drilling process, and/or cool it as you go - I use water in a spray bottle. Keep the water off your lathe bed ways with a towel or some carboard.

As for sizing the hole, as Hank @leehljp said, use the chart to get the next possible upsize drill when you need it. You don't want the hole to be sloppy, so pick as tight as you can, but allowing a little extra room for good paint and glue coverage is a positive. Metric drills combined with letter drills can give you a bit more flexibility than imperial bits, just make sure they are decent quality and sharp!
 
All the above is sound advice .

I would also add drill slowly and withdraw and clean the bit frequently. Any resin build up or glue traces on the drill bit will increase friction and cause heat. A sacrificial piece of plywood under the blank assuming drill press use , also helps prevent blowout .
 
Drilling hybrid or solid synthetic materials can build up heat. I neglected withdrawing and cooling the bit at first; had the fun and games of cutting a synthetic blank off the drill bit. I don't recommend it.
 
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