Drilling Blanks

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dfurlano

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I put a lot of time into a pen blank that I was going to use for an Emperor pen. Well finally look at the size of the large tube and realize I don't have much to work with. The blank is round but only about .1 inch from the final dimension. Anyone have any techniques for centering a hole that precisely?

The blank is Amboyna burl and the drill needs to be 37/64 for a RB kit.

Any suggestions welcome.
 
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Draw diagonal lines from corners, where thet cross should be exact center. Slow and easy of the drilling to prevent possible drift. May need to reconsider and use an oversized blank.
 
Maybe I'm missing something here.

Wouldn't it have been easier to drill for the tube and glue the tube in place before turning?

If it where me I'd save the blank that needs a smaller tube.
 
There are devices for finding centers on round. I use one for most of my turnings. But with as little extra wood as you have to work with everything will have to be absolutely exact. And a burl is especially unforgiving. Good luck.
 
Use a ruler and mark a line from one point to the other creating an X on the end of the blank. The middle of the X will be your center point.

Also, are you using some sort of clamp device to hold the blank?
Are you using a drill press?

When my blank is locked in place and drill press off, I make sure the center of my drill bit makes a small mark on the middle of my X. When doing this I know its going to be the right way.

Hope that helps

Ron
 
Draw a line segment anywhere on one side of the circle extending off the edges. Get a square and draw a line perpendicular to the other at exactly the place where it contacts the edge of the circle. If you draw a line between the two points where the lines extend off the circle, this will split the circle exactly in half. Do the same somewhere else on the circle, and the intersection of the two constructed lines will be the exact center.

Another easier way; support a pencil on a block of wood or something until it's close to the centerline of the part. Rotate the cylindrical part under the pencil. This will draw a tight circle which will be the center.
 
If you have a scroll chuck and a jacobs chuck I would drill it on the lathe. See attached picture. Best way to find the center and drill it straight.



<b>Image Insert:</b><br />
200561315653_DrillingA.jpg
<br />
 
Bruce,
And you thought you would never use you high school geometry. May I add your post to my collecton of "when will we ever use this stuff" questions that I share with my math students? Give BRuce an A+ in geometry.
Do a good turn daily!
Don
Originally posted by btboone
<br />Draw a line segment anywhere on one side of the circle extending off the edges. Get a square and draw a line perpendicular to the other at exactly the place where it contacts the edge of the circle. If you draw a line between the two points where the lines extend off the circle, this will split the circle exactly in half. Do the same somewhere else on the circle, and the intersection of the two constructed lines will be the exact center.

Another easier way; support a pencil on a block of wood or something until it's close to the centerline of the part. Rotate the cylindrical part under the pencil. This will draw a tight circle which will be the center.
Click to expand...
 
If it already round as suggested and you only have 0.1 to play with outside of your drill bit then I hate to say it but you might be up a creek. The problem is not accuracy, it is the pressure you have to clamp the sucker in with on a bit that large to drill it out. I don't think you will be able to hold it well enough with out causing enough pressure to crack it when you come to the bottom. I hope I am wrong. Good luck and blast me with a nanananana if you get it done.
 
This is the blank. The reason I did not drill it first was because of the way I constructed the inlays. I think I have enough to grab at the end so I don not have to drill all the way through the blank. But what I am thinking about is drilling it in several increasing diameters to try any minimize it breaking.

Anyhow for posterity (just in case...). This was for a friend, hence the "M" and I was going for something close to a cigar look. heres a picture:

 
&gt;Bruce,
&gt;And you thought you would never use you high school geometry. May I &gt;add your post to my collecton of "when will we ever use this stuff" &gt;questions that I share with my math students? Give BRuce an A+ in &gt;geometry.
&gt;Do a good turn daily!
&gt;Don

Don, if it can help your students, then by all means! I'm pretty good at that stuff. In college, I had a 3 dimensional geometry class. There was an exercise where you had to draw the third view of an object when the other two were given. I saw there was more than one way to interpret it. I made 18 cardboard models of 3D shapes that could work given those 2 views. The prof said I didn't need to be in there and exempted me from the course! [:I][:D]
 
My thinking is pretty much the same as Shane's. I think the forces created while drilling will very likely tear the blank apart. The following is sort of cumbersome and will require some close work on your part; but I think it might(?) work. Find a big scrap blank and drill it out to the diameter of your "GOOD" blank. Then glue your good blank into the scrap blank. Using one of the methods mentioned previously, identify the center of the original blank and drill it. Glue in the brass tube and then "CAREFULLY" turn off the scrap wood down to the original blank.....probably should use sandpaper when you get close unless you are real good with a skew!!!

My experience with burl is very limited; but the ones I've done seem to not want to hold together very well. I think your chances of drilling this blank without some external support is not real good. If you have a lot of time in this blank, you may also want to consider having someone stabilize it before you try to drill it??

Best of luck!!!

BTW, very nice job on the inlay!!
 
Randy's idea of a surrounding support blank sounds promising. Dan, I've not had the bad burl experience he has, especially w/Amboyna, and its density would not lend itself well to stabilization. Just be slow and careful when drilling it out after gluing it into the new support blank.
 
I like the support blank idea. I was also thinking of dipping it in EPR but fear the heat of curing and shrinkage of the resin may damage the blank.

Probably go with the support blank. Stay tuned.

Thanks.
 
Originally posted by dfurlano
<br />This is the blank. The reason I did not drill it first was because of the way I constructed the inlays. I think I have enough to grab at the end so I don not have to drill all the way through the blank. But what I am thinking about is drilling it in several increasing diameters to try any minimize it breaking.

Anyhow for posterity (just in case...). This was for a friend, hence the "M" and I was going for something close to a cigar look. heres a picture:

Click to expand...

Nice!!

I'm working on a blank myself, while it has a different design than yours it's basically the same idea.

I use a lathe with a scroll chuck and a set of #1 jaws to hold the blank in place. No need to worry about centering the blank because it is automatically done. Straight grain wood is no problem, I can get a hole perfectly in the center every time. The problem I have run into is when I hit a section of wood where the grain running in a different direction. Sometimes the bit will wander off. This is the problem you will run into with your blank.

While the blank is spinning in the chuck, I take a skew and make a divot in the center of the blank. This helps the bit to find the exact center. I move the tail stock with the bit install and the quill locked down up to the blank and let it lightly touch the blank.

As soon as the tail stock stops dancing I lock it in place and start drilling to about a 3/8" depth, then I stop. I pull out the drill bit move the tail stock away and lock down the quill again. Now I "Push" the tail stock into the blank, using the hole I created as a guide and start drilling. I extract the bit every 1/4" inch or so. This works 99% of the time. Also, if you know how to sharpen drill bits, it would be a good idea to do so before you start.

BTW I run the lathe at about 750 RPMS (or what ever speed 1 in on a Jet 1236)

Good Luck!
 
Agree with Shane and Randy. The project sounds very problematic. A machinists trick I once saw was to embed the object in question in plaster of paris. This stabilizes the item to be worked on. I know, chucking plaster of paris might not work. Whatever you try, please share results, even if disaster strikes. It will still be a shared learning experience.
 
Randy has the right idea. Bore a nice hole the size of your blank and slip it in. I would also be sure to have something up against the bottom of the blank. Of all of the blanks lost while drilling the majority were large blanks with less than 3mm to go. Those large bits will catch an edge as it exits the bottom of the blank and KABOOM! [xx(] Good luck. That is a beautiful blank. If you chicken out it would look great on a Jr. Statesmen. That would give you a little more room to play.
 
Originally posted by woodscavenger
<br />...I would also be sure to have something up against the bottom of the blank. Of all of the blanks lost while drilling the majority were large blanks with less than 3mm to go. Those large bits will catch an edge as it exits the bottom of the blank and KABOOM...
Click to expand...

Shane made a good point and one I forgot to comment on. To prevent a blow-out, you might think about trying the following......or maybe someone has another idea?? When you get close to exiting the blank, stop!!! Reverse the blank and drill a small...maybe 1/4" hole from the other end. Then using:

1. a rat tail file or
2. a Dremel tool with a fine wood rasping cutting tool or
3. a piece of sandpaper wrapped around a nail(head removed) and chucked in a cordless drill or
4. whatever else you can come up with,

gradually open up the other end of your bore to the diameter of the brass tube. This will be a little tedious and you will have to be careful; but i think you could get an accurate opening without the danger of blowing out the blank. Going to this extreme may not be necessary if you have cut the blank "long" as many like to do.

Again, BEST of luck and let us know what you decide to do and how it turns out!!

P.S. And as Ron mentioned, do be sure you have a sharp drill bit. If you don't have one, you might want to invest in a Drill Doctor. One of the best investments I've ever made in shop tools!!! They are a little pricey at retail; but you can get some good deals on eBay and maybe Amazon dot com.
 
Originally posted by Randy_
<br />
Shane made a good point and one I forgot to comment on. To prevent a blow-out, you might think about trying the following......or maybe someone has another idea?? When you get close to exiting the blank, stop!!! Reverse the blank and drill a small...maybe 1/4" hole from the other end.
Click to expand...

Glue a piece of scrap to the back end of the blank.
Click to expand...
 
Two-flute end mills are center cutting and may be used to plunge-cut. Multiple flute end mills must be center cutting to enable plunge-cutting.
 
Originally posted by dfurlano
<br />Anyone ever use an endmill to bore out for a tube? I'm thinking that may be the way to go.
Click to expand...

I would think you could use a small one as a starter hole. Or drill a small hole, like 3/16", then ease a 1/2" endmill through it, then the proper drill bit.
I do like the idea of encasing the blank in something, even if you just drill a hole in a 2x4 the size of the blank, split it, then put it together around the blank with a couple of wood screws.
 
Isn't it amazing how you can read a topic and compleely miss an important point. A round blank, HMMMM try drawing a line from corner to corner to get the center.
 
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