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Deep boring or horizontal drilling.

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CDarby67

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#1
Hello,
I have projects in mind where I need to create a part that is essentially a tube. I certainly can find material to use as a base but in some instances the final dimensions I need can not be made from stock material. The part lengths are between 8-16" in most cases. I need either 0.75" or a 1.0" I.D.

What is the best way to mill that part? Do boring arms reach 8-16"? If drilling horizontally is recommended, are there bits that reach 8-16"? Flipping the part end to end is a thought - is there a best practice when doing this kind of approach?

Thanks,

Clint
 
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#2
Clint,
not knowing what you have to work with (machines) it difficult to answer your question. Boring/drilling on a lathe would be my choice only because I'm setup to do so. I would more than likely drill then flip the work. If critical, I would drill undersized and bore to final dimension.
Give us more information like O.D and machine/s you have.
 

CDarby67

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Firestopper,
thanks for the reply. Sorry, I should have known to be more specific.

I have access (local makers shop) to a machine lathe with a swing and length way beyond me needs. Of course there is a tailstock, with otions for live and static centers.

I will be making various parts from T6061 aluminium for stage props - Star Wars light sabers. I have 1.5"o.d. 1.0" i.d. material. That will suit ~75% of what i will make. There will be times I need to mill parts with a much wider o.d. 3.5" - most of those parts will be less than 3" in length. The rare occasion for a solid piece that has portions of the length (8-16") flaring to 1.5" o.d. to perhaps the 3.5" o.d. will arise. Those pieces are what I wish to prepare for.
The end products can be very elaborate. The attached photo is no my work. I do not plan to copy this design but the level of skill to create something this beautiful is a desire; this work is my inspiration.

Thanks,
Clint
 

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JPigg55

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#5
As said, it depends on how critical the bore is.
Typically, a steel boring bar has an extension capacity of 4 times its diameter and carbide can extend
8-10 times its diameter beyond the holder.
The issue is flex in the bar. The further the bar sticks out from the holder, the less force it takes to deflect it by a magnitude of 4.
As an example, given a 1/2" steel boring bar sticking 4" out of the holder will flex 4 times the amount that the same bar would if only sticking out 1" from the holder for an equivalent force applied. Taking lighter cuts will reduce the tangential force applied and reduce the flex.
Another thing to consider is that a carbide boring bar is way more expensive than a steel one.
 

JimDawson

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#6
Long drill bits are available. Normally when I want to drill a deep hole I just build a drill extension and either use a Silver & Deming (reduced shank) type drill or turn down the shank of whatever size drill bit I need. I've drilled 1 inch 24'' deep this way. Given that your requirement is 3/4 or 1 inch a Silver & Deming style drill bit would be the easiest.

Drill an on size starter hole to get the hole started straight, then use the extension to finish the hole. Drill maybe 1/4 inch, then pull the drill out of the hole, clean off the chips and lube. Rinse repeat until you complete the hole.
 

David S

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#7
I don't want to be a knob, but the stiffness of a boring bar is actually proportional to the diameter^4 / length^3. So you can see that given the same diameter, a longer boring bar will have way more deflection than a linear prediction. Short and fat is always the best.

David
 

Mitch Alsup

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#8
The issue is flex in the bar. The further the bar sticks out from the holder, the less force it takes to deflect it by a magnitude of 4.
If you double the length the boring bar sticks out from the tool holder, it will deflect 4 times as much.

If you double the diameter of the boring bar, it will deflect 1/8 as much.
 

P. Waller

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#9
One compensates for the deflection in a boring bar, chatter is the biggest problem with a bar extended many diameters. Many companies make vibration dampening bars, these will be well beyond what a home shop person is willing to spend.
Dorian for example, I have never used one of these so can not say if it actually works.
http://www.doriantool.com/wp-content/uploads/sec-d-deep-hole-boring-2015.c.pdf
 

projectnut

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#10
We used to drill holes up to 27" deep in our shop. We didn't have many problems, but then again we had special bits to do the job. We used a series of different length bits. They were all parabolic and coolant through to better clear the chips. Even then it was a relatively slow peck and clear process. Believe it or not the best results were with hand sharpened bits. Even though they looked perfect to the naked eye there was enough difference between a hand sharpened one and a machine sharpened one that the hand sharpened one cleared the chips better.

I was told it was because even with the best hand sharpening job there was a slight difference in cutting angle and land width. Rather than both sides creating an equal size chip one side would create a slightly smaller chip. This allowed the chips to clear more readily. All holes were reamed to final size. I don't remember the exact sizes the holes were drilled to but if memory serves correctly they were about .002" undersize. Also I'm not totally convinced that the reason the hand sharpened drills worked better was because they cut more on one side than the other. All I know is it worked, the job got done, and the customer was happy with the results.
 
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