Shell Auger.

[abrown]

I am attempting to bore a very long, straight hole from the end of a turning. It was suggested to me to use a shell auger for the pilot hole (3/8"), but I have no information about what RPM to use or how much force to apply to achieve a reasonable feed rate without burning the wood. I am feeding it through a 3/8" hollow center.

Just making some trial cuts, I did notice that it bores very slowly. This isn't production, so I am not worried about time. However, I don't want to have to spend an hour to bore a 12" hole.... Any suggestions on using this tool would be appreciated.

Thanks,
Andy

 

[Jim Carroll]

When using the shell auger or any other type of long hole boring tool generally the slower you go the better it is.
Try to get your speed of the lathe down to 300rpm. When feeding the auger into the timber push the auger in till it touches the wood use your fingers as a guage against the tailstock by puting them up against the tailstock them moving back an inch. Once you have pushed the auger up to your fingers withdraw the auger to remove the shavings. It is not wise to do any more than this each time because if you do the auger will bind up and you will not be able to remove it from the turned peice.
You keep going through this process till you have gone all the way through or till the auger runs out of reach and you have to invert the peice so you are drilling in from the other end. It does not take as long as you think a steady pace is all that is required.
Trying to go any faster will generate too much heat and the auger will not work properly and bind up in the timber.
Some timbers will drill easier than others and some will drill straighter than others. Unfortunatly there is no way to avoid run off. If you feel it starting to run sideways then invert the timber and come in from the other end.
Usually on lamps you try to pick timber that has fairly straight grain anything with a swirly grain will be hard to drill as the drill will try to follow the grain.When drilling in the drill press you sometimes notice the drill wanting to go a little sideways due to the grain and growth rings.
You may be better to rip the peice down the centre and route a groove then rejoin. Unfortunately with the swirly grain you may see the join.

 

[john lucas]

You didn't sayy how long a hole you were trying to bore. I found that i had to sharpen my auger since it didn't come from the factory sharp enough. I used a diamond hone and polished the edges. That made it cut straighter. As was said before clear the chips often.
If you have trouble getting the hole perfectly centered simply bore the hole first. Mount the piece between these holes and then turn it.
On really long holes the lamp auger that I have simply won't stay on center. I'm talking holes that are 38 to 48 inches. On shorter pieces 24" or less it is close enough but still wants to follow the grain even if you feed it extremely slow.

 

[abrown]

Thanks for your comments. I'm trying to bore ~14" into soft maple. When you sharpen the tool, do you primarily focus on the front face?

Thanks,
Andy

 

[Andrew]

How straight are you wanting this, Andy? Are we talking just straight enough for something like a lamp cord or a peppermill? Or straight enough for use as a handle (where you'd put some steel pipe through this hole for example)? Or very very straight as in making an instrument like a flute?

There's different ways of doing it depending on the answer to the above.

If you need it really straight, don't rely on simply drilling the hole and then putting the holes between centers (if that's even possible in your situation) to start turning it. You'll likely find that that hole isn't straight from one end to the other. Bits, even shell augers, deep drilling bits (rifle barrel bits), etc. flex as they get deeper into the material along with being forced one way or another by the material (grain in wood) being drilled. So, you'll be starting out fairly straight for a few inches but then the hole veers off and you get a curve. That curve is still there even though you're putting the blank between centers (exit holes). Messes up musical flutes big-time among other projects where very straight holes are required.

 

[abrown]

I am actually trying to make a flute (2 piece). I did a 7 inch practice section last night. My first attempt resulted in burning and binding (probably off center). This was feeding the auger as slow as possible at 400 rpm. My second attempt was much better. I used the 3/8" auger for 1 inch segments at a time, then followed up with a half inch drill to bore it out. I didn't chase the 3/8 auger hole all the way to the end, but left about 1/2 inch to restart the auger. This cut down on heating and required force on the auger dramatically. As a result, the boring went faster and straighter. By the time I finished boring out to 11/16" and removed it from the lathe, there was no noticeable run-out at the ends. Is there a good way to measure runout at the interior, other than to cut it up?

 

[Andrew]

The quick and easy way that I do it when I'm making my straws (which requires an extremely straight hole for 16" of length) is to use a very rigid piece of rod to run up through the hole. I use HSS but you could use anything that isn't going to flex. If it flexes, it's not going to be as easy to tell when it binds or touches the walls.

I dip a rag into some blue pigment (you could just color the rod with a marker or something too but make sure it's not going to disturb any finish you'll apply later) and wipe that onto the rod all over. Then I push that rod up into the hole. If there's any resistance, binding or slop then it's not straight. If that doesn't seem to be a problem, I'll run it through from the other end and check it. Might be straight enough for your purposes though. You'll have to decide what's acceptable for your situation.

After pulling the rod out, I'll check the blue pigment that I applied to the rod to make sure that the "scrape pattern" is fairly even along it's length. If there's one side where the blue has been taken off more than another, then it's not quite straight either but I didn't feel it when pushing. It might work for my uses but often it's not.

I have no doubt that there are tools and machines to measure interior hole runout but I've not used one. The rod works pretty well. Just have to find one that matches your hole exactly.