Boring a 0.256" by 16+" - 30+" hole through M2/A2 tool steel

[Bendak]

Hi,
I just joined a CNC machine club at the university I am attending and am new to CNC machining. How would one go about drilling a 0.250" - 0.256" diameter by either a 16+" or up to 30+" hole through M2 or A2 HSS tool steel? My goal is to make a large increment tree borer. I have attached pictures of the tool and its dimension along with a link to a video demonstrating the use of an increment borer. The threads contain cams to further complicate the process of machining as shown in some of the pictures.

Video link: (Skip to minute 8)

Thanks for the help,
Jack

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[Superman]

Why does the tubing material have to be A2 or M2 ?

the spiral bit should be harder ( and maintain sharpness ), but the tube could be "off-the-shelf" stainless tubing ( anti-rust)

And braze the two together

[Bendak]

I guess that could work as long as the tubing can stand up the the torque required to drill torque hard wood (which can be pretty tough at times). According to the company located in Sweden, the borer bit is made from hardened steel which may or may not include the actual shaft. Someone else told me that Sweden has a company called Sandvik which produces many high yield "unobtanium" alloyed tubes. But if the stainless tubing meets my needs then I guess ill go with that after checking in with the guys more knowledgeable than me at the university.

Thanks,
Jack Ruddat

[brian257]

I would think readily available 4130 tube, possibly heat treated if needed would be good with the auger bit on the end of it. Welding on the bit if it is a different material than the tube will mess with the heat treating though unless you got an alloy of tip that just happened to need to be heat treated at the same time and temp as the shaft.

[hanermo]

There are multiple options, accuracies, and often very high costs involved.

The desired or needed straightness of the bore is the biggest cost.
It can increase the cost 100x or more, depending.

Some drivers, some examples.
Pre-drill, then bore the holes, to 5-20x D, or about 2.5" in this case from both ends.
A 3 micron TIR/straightness is typical, 2 um is easily done with medium-high end stuff, 1 um is easily done by those who know how and charge accordingly.
About 100/200/500$ per bore cost / accuracy. So far.

A gundrill would follow the bore, wander very little.
Add 100-500$.
Maybe 0.1 - 0.01 mm, depending, along the bore. Typical 0.02-0.04 mm perhaps.

The bore could be straightened, via any nr of custom tools/fixtures/setups if 0.02 mmm +/- or 0.001" is not enough.
CNC-controlled grinders, lapping, laser interferometry could control hole size and straightness to any level You care to pay for.

I am 99.99% sure I can make the hole 30" deep in A2 from both sides and a small workpiece, over a time of approx 6-12 months, to 2 micron in straightness, and 1 micron in TIR.
Overall.
About 200-400k€, depending.

Anyone with a gun-drill can punch your hole, for perhaps 200-600$.

Endless errors/caveats.
It will not end at *exact* center at the other end if done one way (helps straightness).
Does this matter and how much €€ ?

Straightness is critical in €€.
A hole started from both ends, at Your proposed 1/4 - 30" = 120 D/L ratio, will not be straight by any means.
Or uniform, or cylindrical.
But it can be, cheaply, a very(fairly) accurately sized hole at both ends, and along the length (not so cheap but doable) via
- reaming
- double reaming
- cylindrical roller sizing/burnishing

I can see all sorts of custom tooling and tricks to get near 1 um overall.
Everything undersized by x um, of course, so the last finish sizes everything.

Frontal bores of 10xD == 60 mm, used as pilots for custom boring heads, for the next 60 mm bore depth, undersize just a bit.
Using laser interference metrology, it is possible to measure the real straightness of the bore.
And by using cnc live-tools of boring-by-angle it is perfectly possible to straighten/adjust bores to any direction/size desired.
Next-pass conventional tools will then follow the avg base hole.

Recap.
Any conventional gun-drill setup can make the hole pretty well for 100-600$.
0.01 mm or better in size, pretty straight in the hole, not ending at centers of workpiece.
One can get both ends and avg sizing Very Good for 500-2000$ more.

If You need an *accurate* hole and have $$$ money, I would be happy to do so.
If You just need a hole punched, I would decline the job.
If You wanna do it on your own, make a gun-drill setup with pumped oil.
If you wanna make parts/assys and money, use reject barrel-blanks for this part of the job and don´t do it yourself.

[Bendak]

Since I only have access to what my university has (CNC lahtes and mills, etc (but no gun-drill)), I think I resort to buying the pipe and then machining it from there with the threads either welded or brazed on. The borer has to be straight enough not to get stuck in the tree which is probably fairly loose in terms of tolerances, perhaps even +/- 0.5-1mm. This is really just a school project for a club I am in. I would rather buy the stock and machine it myself then pay over $600 for a real 28"+ increment borer.

Thanks,
Jack Ruddat

[mactec54]

Since I only have access to what my university has (CNC lahtes and mills, etc (but no gun-drill)), I think I resort to buying the pipe and then machining it from there with the threads either welded or brazed on. The borer has to be straight enough not to get stuck in the tree which is probably fairly loose in terms of tolerances, perhaps even +/- 0.5-1mm. This is really just a school project for a club I am in. I would rather buy the stock and machine it myself then pay over $600 for a real 28"+ increment borer.

Thanks,
Jack Ruddat

If you look close at the original one you will see that the screw end has been welded on to a tube, as suggested 4130 tube or stainless steel tube would work, laser or Tig welding should do the trick, if using 4130 the screw end could be made from the same material and hardened

[brian257]

For a large variety of 4130 tubing in lengths where you won't have to buy and ship a whole very long piece check Pilot Supplies and Aircraft Parts from Aircraft Spruce. 4130 tubing is very common in homebuilt aircraft.