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

Hi,
I am new to CNC machining and was wondering if it would be possible to drill a 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 and a link to a PDF showing dimensions of this tool. The threads contain cams to further complicate the process of machining.

http://imlafrica.com/Anleitung_Zuwachsbohrer_eng_02-2009.pdf (Schematics on pages 3 and 4)

Thanks for the help,
Jack

Sorry, the link to the PDF is actually http://imlafrica.com/Anleitung_Zuwachsbohrer_eng_02-2009.pdf

The link didn't work, but the short answer to your question is; Yes it can be done.

The longer answer is; it won't be easy or cheap. Just accept that part right now. Don't pursue it if you think you can cheap out on a project like this.

You say "new to CNC machining" does that mean you are a grizzled, gnarly old manual machinist? I think not, because the ones I know wouldn't ask the question.

You will need specialized tools, and specialized knowledge of D.H.D. and if your lucky a machine that is good for this kind of work. Much deeper, much smaller holes have been drilt.

R

Why would you even consider boring from the solid. I would start with a piece of DOM tubing with tool steel welded on the screw end and alloy steel welded on the back end.

that's what a gun drill is for

72bwhite said:

that's what a gun drill is for

Click to expand...

+1
Find a good gun drill shop to do the work for you.
I think you'll find the costs don't even compare to buying the tooling required.

I'm with Illinoyance on this one. Make the boring/cutter head from tool steel, and the shank from inexpensive standard tube. Vastly easier, faster and cheaper. If you absolutely require 0.256" bore rather than a common 0.250" bore, it would be pretty cheap to get a made-to-order reamer and braze it to as long an operating shank as you require.

That tool is made out of multiple pieces.. A cutter head.. A tube.. And some crap
on the end to hold it.. Either welded or brazed.

Increment borers undergo a ton of friction and torque when drilling into hardwoods, especially if they are long. Are you sure that a standard DOM tube would hold up to those forces? I have never heard of a reamer or brazing. I just joined a club on the university I am attending that has various CNC machines such as lathe and mills. I attached three screenshots of the page I was referring to on the PDF. Also, here is a video demonstrating the use of an increment borer (skip to 8 minutes) Tree Coring Part 1 - YouTube.

Thanks,
Jack

Bendak said:

Increment borers undergo a ton of friction and torque when drilling into hardwoods, especially if they are long. Are you sure that a standard DOM tube would hold up to those forces?

Click to expand...

If you're used to playing with wood... How strong "metal" is is quite amazing...

A crappy shitty 5/16 grade 2 bolt you can buy down at the hardware store for about 15 cents will
lift a car before it breaks (hopefully), around 2 tons...

A grade 8 1/2" will support over 10 tons...

It would only take 2 grade 5 or grade 8 3/4" bolts to lift an empty 737. 4 of 'em if its
at Max take off weight.

Rotational is a bit different, but you get the idea...

I'd bet my left nut (that's my favorite one) that the shank is just crap tubing brazed or
welded onto that head.. MAYBE somekind of alloy steel, but I doubt it..

Take a torque wrench with you out into the woods and see what you come up with.. Report
back, and some body here smarter than I am will crunch the #'s for you and tell you what you
need.. If you don't have a torque wrench.. Length and weight is all you need, hanging a bag a
known distance off center with some rocks will get you a ball park figure.

Now making that screw on the end... That's going to be the real challenge.

What do these things sell for?? I can't imagine there is a massive demand. No matter
what the cost.. Its an interesting project.

Thanks for the info!
Increment borers have a wide range of costs depending on the length. A standard 16" borer bit costs around $200 whereas a 28" borer bit costs $660. They are manufactured up to 40" in length, although realistically, most use none longer than 18". They say that they use a special process of hardening and tempering the steel but they may only be referring to the tip (which appears as one piece with the shank although I could be wrong). I'll see if I can find the torque with the bag and rocks. The torque applied probably maxes out at around what the average human can produce (for very hardwoods not often drilled into) with a 16" handle for a 16" borer bit, and so on for longer bits. I suppose I'll need to use a CNC mill for the "cammed" part of the thread.

Thanks again,
Jack

0.25"ID/0.375"OD tubing is widely available in both low-carbon (A513) and low-alloy (4130) steels in North America. This is very close to the diagram's 6.5mmID/9.2mmOD, and I suspect the diagram was taken from a design originally in Imperial (inch) measurements.

Yield strength of A513-1 as-welded tubing is in the range 38,000 to 45,000PSI (sorry for non-metric units) and A513-5 DOM tubing is 60,000 to 70,000PSI. 4130 tubing, in the annealed or normalized heat treat conditions likely in tubing rather than drawn bar, has similar yield strength as A513-5 DOM tubing. Given the strength equivalence of A513-5 and 4130, the only reason to buy the 4130 is to do additional heat treatment which could bring the yield strength into the 100,000 to 140,000PSI range. To put those numbers in perspective, O1 tool steel (which is a very basic high-carbon steel like 1095), when heat treated to 50RHc, has a yield strength of very roughly 200,000PSI.

You (or someone else at your University) can do the strength of materials calculations to see what material properties are required of tubing of the specified dimensions to resist human-applied torque without deformation. All of those steels I mentioned will twist elastically the same amount under a given torque; increased strength does not mean increased stiffness. The question is whether the material will resist permanent deformation. You will also want to do a column critical collapse analysis, but based primarily on torque loading rather than exclusively compression loading. (I don't think that particular analysis is in my go-to "cheater" textbooks.)

BTW, if you read the text associated with the diagram, you don't want just a cylindrical hole all the way through the tool. The bore inside the cutter head is tapered, narrowest at the sharp end and enlarging toward the body of the tool to provide internal clearance for the wood core sample. You can't replicate that with a drill. You would have to profile ream, which would be a God-awful mess going essentially the whole depth of a 40" hole. If you were not already convinced to make the head separately from the shaft, that should be a clinching argument.

Bendak said:

I suppose I'll need to use a CNC mill for the "cammed" part of the thread.
Jack

Click to expand...

From what I can see that is Turned (lathe) part all the way, C axis for the "cams". I won't get into how to create the "spreader" function on a straight up 2 axis lathe, but it isn't big deal.

R

That first photo is a welded assembly like a gundrill; the weld has a visible gas hole. The thread is just a tapered thread, not hard to make at all on any CNC turning center, although you might have to grind a tool.
For the spreader "cams" you could leave a shoulder at the end of the thread and just make the shape on a bench grinder. It would be functional enough; you're just hand-cutting into a tree.

sfriedberg said:

0.25"ID/0.375"OD tubing is widely available in both low-carbon (A513) and low-alloy (4130) steels in North America. This is very close to the diagram's 6.5mmID/9.2mmOD, and I suspect the diagram was taken from a design originally in Imperial (inch) measurements.

Click to expand...

"SUUNTO" catched my eye over the pdf.
Might be metric, made in Finland(at some point) and all that
But seems like Swedes are the ones to blame after all:
Increment borers

Shaft material in other model is listed as stainless steel but that doesn't mean that it's your average 304 tube.
Swedes have Sandvik and along with it all kinds of high yield unobtanium alloyed tubes.

I guess I'll ask if someone can help me with the calculations for strength. Someone else mentioned brazing as an option. Is welding stronger than brazing? I did read that welding can only be between similar metals. A513/4130 and tool steel I assume are close enough to weld?

Jack

leaving clearance perhaps .oo5 and braze with a chip of silver solder makes a fair bond...

Bendak said:

Is welding stronger than brazing? I did read that welding can only be between similar metals. A513/4130 and tool steel I assume are close enough to weld?

Click to expand...

Welding is generally stronger than brazing, although brazing can be as strong as the parent metal. High-alloy and/or high-carbon steels (like tool steels) require careful procedures to weld reliably, not a chore for Joe Bob "I have a MIG and I'm not afraid to use it" Welder.

Both welding and brazing will have a problematic interaction with heat treatment here.

If you weld, you will have to heat treat the cutter end after welding. Even if you hardened the cutter prior to welding, the heat input from the weld would destroy the previous hardened condition. Possible exception (maybe not an exception due to small workpiece mass): friction welding.

If you braze before heat treat, the heat treat process will probably destroy your braze joint. If the cutter end is made from HSS (not O1, A2 or anything like that), you can braze after hardening the cutter and be done. If the cutter end is not HSS (or carbide) brazing is likely to have the same issues as welding. But getting a small chunk of annealed HSS and hardening it is going to be a lot more expensive and time-consuming (logistically) than getting an equivalent chunk of O1 or A2. I can harden and temper non-HSS tool steels in my own shop, but not HSS, which requires higher temperature hardening and tempering furnaces for heat treatment. In fact, my current hardening furnace would probably make a decent tempering furnace for HSS.

If I were producing these, I would weld, definitely. But my production line would be set up for the appropriate pre- and post-heat and immediate annealing required to weld tool steel, followed by a hardening heat treatment operation. For a one-off, I might decide otherwise.

So I could either braze pre-hardened HSS/carbide to 4130 or just Weld tool steel to 4130 and then try heat treating the borer. I might try the first option if I can find pre-hardened HSS/carbide. This will probably be a one-off job for myself as I don't plan on mass producing these.

Jack Ruddat

If you start with prehardened HSS or carbide, you will have to grind your external thread form and internal narrow cone. Possible, but not recommended unless your shop is a lot better equipped than mine is! In that event, you can start with the shank of an appropriately sized endmill for your raw material.