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SpiderMan
12-11-2002, 01:14 PM
I acquired a piece of Atlas LBM rod stock the other day, and decided to try making a few ferrules from it. Because LBM has a reputation for brittleness, my first thought was to pre-drill a small hole and follow it up with a boring bar. Soon discovered I didn't own a boring bar small enough, so my second option was a gradually-increasing twist-drill diameter for achieving the necessary results.

To make a long story short, I have about five or six ferrules with hairline cracks. No good ones. My best process so far is to leave about 1-1/2" of material protruding from the chuck jaws (so as not to chomp down on the drilled stock), go up to 5/16" in three drill steps, and use a cutoff tool to collect the result.

Well, I can get almost done on the final drilling, but somewhere around 3/4" into the stock I always hear that little "tink" that tells me a crack just popped in. I'm going very slow and withdrawing the drill many times to clear chips and allow for cooling.

What's the deal? Can this stuff only be bored, not drilled, to such a diameter (5/16" in a 0.562" rod)? Or do they just distribute the rod stock as a joke? Is my sample defective?

SpiderMan

Rod
12-11-2002, 02:13 PM
Spidey, obviously I'm not a cue maker. Two things, why not lightly clamp the stock in near flush with the chuck? Possibly a split point drill cut at 135 to 140% may help.

SpiderMan
12-11-2002, 05:36 PM
Rod,

Tried that first, before I saw how tricky this was. Clamp with any force at all and the drill bit will bind as material is relieved from the inside and lets the walls flex a little. Clamp light enough to prevent this, and the stock spins. This stuff heats up very quickly and there's a lot of friction with the sides of the bit.

I need a tiny boring bar, or a bit ground so that it cuts slightly larger than it's own body.

SpiderMan

TonyM
12-12-2002, 12:38 AM
Hmmm, I've never had the problems that you are having.

I'll tell you what I do:

Center drill first- I use a 5/16" to 3/8" diameter center drill. You want to create a center with a large enough conical portion to help guide the drill.

Don't step drill LBM. I either just go straight with the 5/16" diameter twist drill (Titanium Nitride coated only!), or I go a bit smaller, and then ream the hole to 5/16" (very slow speed for reaming).

Experiment with different feeds and speeds. LBM is sensitive. Don't go too fast.

Let me know how it works out for you.

TonyM

Fred Agnir
12-12-2002, 09:00 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr> My best process so far is to leave about 1-1/2" of material protruding from the chuck jaws (so as not to chomp down on the drilled stock), go up to 5/16" in three drill steps, and use a cutoff tool to collect the result.<hr /></blockquote>
Any chance your bits are dull? And what kind of bits are you using?

I'd opt for the small boring bar, but what do I know?

Fred

Rich R.
12-12-2002, 09:12 AM
SpiderMan, I have never drilled LBM, but I have drilled other brittle materials, including glass.
I may be way off base here, so take this with a very large grain of salt.
Along with a slow speed, you may want to try some lubrication, like WD-40.
Unfortunately, I do not know if the WD-40 would have any adverse affects on the LBM. Some other lubricant may be a better choice.

SpiderMan
12-12-2002, 10:09 AM
Tony,

The difference in what you said and what I've done is the step drilling. I assume that you tried that and had problems? If that's the case, then next time I'll try drilling in one pass.

When you do a drill/ream, how much undersize do you drill for LBM? Seems like a reamer might cause splits much the way as a step-drill operation.

SpiderMan

SpiderMan
12-12-2002, 10:13 AM
Rich,

I'd be afraid that a lubricant would remain on the material and adversely affect glue adhesion. That's why I wanted to get a small boring bar - the heating seems to be friction with the drill sides, which would be absent using a boring bar.

SpiderMan

SpiderMan
12-12-2002, 10:16 AM
Fred,

I'm using standard twist drills, new and sharp, but Tony seems to think that the problem is going up in steps rather than single-pass.

SpiderMan

Fred Agnir
12-12-2002, 11:32 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr> Fred,

I'm using standard twist drills, new and sharp, but Tony seems to think that the problem is going up in steps rather than single-pass.

SpiderMan <hr /></blockquote>
Thinking out loud, what happens if you rest in between passes? Let the thing cool down and recover before the next assault.

Fred

SpiderMan
12-12-2002, 12:54 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> Fred,

I'm using standard twist drills, new and sharp, but Tony seems to think that the problem is going up in steps rather than single-pass.

SpiderMan <hr /></blockquote>
Thinking out loud, what happens if you rest in between passes? Let the thing cool down and recover before the next assault.

Fred <hr /></blockquote>

I've taken up to an hour to drill the last pass. Drill 1/8", pull out and clear chips, let cool, drill a little more, etc. Always a hairline crack before 1" deep.

SpiderMan

BLACKHEART
12-13-2002, 12:12 AM
ARACHNIDBOY CHECK YOUR E-MAIL

caedos
12-14-2002, 10:00 AM
Is it possible to use a ferrule's length of stock at a time, drill 50%, reverse it in the chuck/collet, and finish it from the backside? In my very limited knowledge of such, there might be some runout as the material spins that is causing a vibration. If the material is brittle, it could be that instead of heat causing the crack. Or I could be totally off base.

Oz

TonyM
12-14-2002, 01:50 PM
Yes, I don't step drill. But I also use a fairly slow speed and feed. And the drill is sharp (I sharpen it right before I use LBM) and Titanium Nitride coated.

I use about a 0.010" undersize drill before reaming. And I use a very slow speed, and feed for reaming. You can't push LBM very hard, as it will crack (as you found out!).

Tony

Barry
12-24-2002, 05:17 PM
Try using soap. An old bar of Dove may work .