Bits for deep boring

[Brian Holcombe]

Looking to learn from those with more experience in this regard. I typically do this sort of deep boring with a brace and auger bit, however I have a fairly critical installation coming up that needs some serious accuracy.

I will be using a Bridgeport milling machine to do the boring, but I am interested to know which type of bit is the least effected by deflection in the cut.

I have some ideas, but I'd prefer not to color the responses, only thing of course is that I would like the bit to be initially shorter, then once the cut proceeds about halfway I will be able to add an extension and bore the remainder.

Thank you
Brian

[Adam Herman]

In wood? with the super rigid setup in the bridgeport I do not think you will have any trouble getting extreme accuracy, better than the wood will hold due to MC change even with quality HSS drills. If in metal, cooled sintered carbide, face spotting and work holding are important. Make many plunges and be sure to clear the chips.

I have never encountered a bit extension that does not create a bunch of wobble.
look into getting a gun drill, the drilling head is a larger dia. than the shaft reducing overall friction and heat.

[Patrick Walsh]

Funny brian i kinda just went through part of your problem this weekend.

I installed the BenchCrafted CrissCross and Classic leg vise into its leg and chop. The crisscross mounts to both the chop and leg with a 3/8 metal rod that travels through the leg and chop catching a hole in top of the crisscross brace.

Benchrafted suggests these holes be bored straight through the leg and chop all in one shot as to assure proper alignment.

Had i just built my bench with standard 5-6" legs this would had been eash peasy. But no i have 9 and 9.95" x 5.5" legs on my bench.

The solution. A drill press and two bits. The first a standard length brad point bit to get the whole started. I bored down with this bit deep as would allow and then backed the bit out. All the whil my work oiece is clamed to the drill press table. I then swapped for a 12" 3/8" standard bit as it was all i could source off the shelf in a pinch. I cranked down the table till i could get the bit in the arbor then cranked the table back up. To my suprise it was a piece of cake as my previouse hole aligned my new longer bit.

I had to crank the table up a bit more as the bit still would not make it all the way through my work piece.

In the end and to my suprise i had perfectly alighned holes side to side. It was a big hail mary moment as much work had gone into that leg and the coresponding stretchers and lefs that had already been mortised, tenoned and fitted.

I know this is not the exacting precision you are looking for but somehow in my little pea sized brain the two related.

The drill bit extension sounds like something we should all have around our shop..

[Cory Newman]

I did the same thing with my benchcraft leg vise a couple weeks ago. Mine didn't turn out as good as yours, but will still be functional.

[Patrick Walsh]

There is a bit more to my story Corey.

As not to derail Brians thread i will update my bench build thread and you can read all about it there if interested..


I did the same thing with my benchcraft leg vise a couple weeks ago. Mine didn't turn out as good as yours, but will still be functional.

[Brian Holcombe]

Thanks for the replies. It seems I left out some key details.

The holes I need to make are 1"~ diameter. I'm boring into side grain wood.

Patrick, that is a good idea, maybe two bits is the key to it, and dump the idea of an extension.

[Larry Edgerton]

I have a good set of ship auger bits with a removable center screw that I use for that purpose. I use a Clausing DP. The ship auger bits are guided by the bore.

I would consider starting the hole with a 1" bit in a plunge router if they are square. I made a jig for that using a 1 3/8" guide bushing and a template that the bushing just fits into to locate the router.

What you making?

[Malcolm McLeod]

Other critical details (at least in my mind) are:

1-How deep? Best accuracy will be if a single bit of preferred style will reach the finished depth.
2-Is it a thru hole? And, can you start from both sides? (....might prevent blow-out.)
3-If not thru, what are your requirements for the bottom: Flat? Taper OK (like on a twist drill)? Will a self-feed center-screw/brad-point cause issues?

Forstner are my go-to for precise clean holes, but may not give you enough depth. My advise would be stay away from extensions if possible, as they generally don't fit in the same sentence with 'precision'.

Gun-drill certainly has the reputation, but I've not used one.

I have tried 10"L thru holes in cypress with 1" self-feed ship auger bit in a big hand drill. It is VERY difficult to keep the hole even close to aligned. It might have worked better if I had started them straight(er) with a Forstner, but couldn't get a 22ft beam in the drill press.:(

[Brian Holcombe]

I may work this from two approaches, I can create a start in the Bridgeport but may or may not be able to make my depth. The depth is not set in stone but at least 8" and likely not more than 10".

These holes are blind and they need to be aligned to one another so a plunge router is out, it will reliant upon too narrow a surface.

[Patrick Walsh]

Hmm,

The 1" hole adds a whole nother real of complication to this.

If i was you and could source a 1" x 10-12" bit i would go the route i went.

At first i thought it was a recipefor disaster and the i was destined to fail. I actually though i would have better luck starting the hole on the DP then finishing it with a hand drill.

Once i got my first hole started and the table cracked down, longer bit put in then indexed back into the starter hole i was sure a mess would surely ensue. Much to my suprise the drill bit just started spinning and the work piece did not move even a hundred thousandth.

I had marked my hole on both sides in the event i had to go in from both sides. When i was done i was able to use a pair of digital calipers and a combination square to see that even though my center mark was drilled away i was indeed still on exact center.

In retrospect it came down to two things, good layout and the time to secure my workpiece to the DP table. The second part was a DP with zero runout and a arbor completely 90% to the table in all directions.

The funny part of my story is that i set out to do ths on my own DP. When i went to set the whole opperation up i acame to the conclusion my DP had excessive enough runout that i was destind to fail. My DP table was also not close to 90% to the table at full extension. The table has no adjustments and i have yet to take the time to shim a sacrificial piece atop it. For most of what i do non of this matters much. A good DP is high on my wants/needs list.

Anyway last minute i made the decision my DP was not up to the task ans made a call to a uncle. An hour and half later i was in front of a new DP checking the runout so forth and so on. It was took me a half a dam day to drill two holes. Being all came out well it was well worth my patients but man was i cussing all kinds the whol way through. Had i made a mess of my leg and chop i would had really been in much worse shape. All in all i got lucky i think?

Anyway thats enough out of me.

[Malcolm McLeod]

Maybe one of these? A bit pricey, but if you have to, you have to... (https://www.mscdirect.com/product/details/33012857)

[Brian Holcombe]

Ah, thanks for the insights. I'm forming a plan now which of course may change slightly as things progress.

[Brian Holcombe]

Maybe one of these? A bit pricey, but if you have to, you have to... (https://www.mscdirect.com/product/details/33012857)

Length of cut is 2.5", too short for this job.

[Malcolm McLeod]

Length of cut is 2.5", too short for this job.

You'll be using as a drill and it IS center cutting and can go ~9-10". You'd have to drill and retract many times to clear the chips - - because of the length of cut.

[Larry Edgerton]

These holes are blind and they need to be aligned to one another so a plunge router is out, it will reliant upon too narrow a surface.

Before there was a Domino in the house I had a T shaped base plate for the big PC that I used to make quick and accurate dowel holes on edges. Actually worked better than the Domino, just not as convenient.

[Brian Holcombe]

You'll be using as a drill and it IS center cutting and can go ~9-10". You'd have to drill and retract many times to clear the chips - - because of the length of cut.

I'd have to disassemble the entire setup to retract that bit to clear chips. I appreciate the thought but I think there may be a better solution out there. $250 is also more than I would like to spend in order to solve this issue.

[Malcolm McLeod]

I'd have to disassemble the entire setup to retract that bit to clear chips. ....

Whatever bit you select, keep in mind that a Bridgeport knee mill will allow you to use the full quill travel, plus the vertical travel of the knee. Combined, it should eliminate the need to disassemble. I've seen machinists reach into seemingly impossible places with a well thought out setup. - - Hope it helps.

[Prashun Patel]

Can you bore the hole as deep without the extension.
Then use an extension to drill a smaller diameter hole through to final depth.
Finally, attach your original bit to the extension and ream out the hole to final width.



I use this method when drilling dog holes in my bench - not because I'm afraid of deflection, but because it makes it SO easy and resistance-less to drill to deep depths. The reduction in resistance might (my theory) reduce the desire of the bit to deflect.

[Brian Holcombe]

Malcolm, I'll continue to keep that in mind, as I have for the past 14 years that I've worked with this machine. :D

Fixturing to the machine is not the issue. I was looking for specific types of woodworking bits best known to minimize deflection and maximize chip evacuation. I assumed Forster but was looking to double check unless there was something significantly better.

Maximum underhead is 16" and the piece will likely end up at 10-12"~. Which is why I expected to need to cut then drop the longer bit in to finish the cut.

[Malcolm McLeod]

:oI have come to know you as 'The SMC Neander Guy'; had no clue of your metallic skill set. :o I'll shut up now. :o

[Prashun Patel]

...and don't try to school him on scotch either, Malcolm ;)

[Malcolm McLeod]

...and don't try to school him on scotch either, Malcolm ;)

The gauntlet has been thrown..... it's on!!

[Brian Holcombe]

Hahaha! Ok, we may as well steer this one well off the rails. I'm an Islay man and I like long walks on the beach (the second part is a lie :) )

Bunnahabhain 18 and Lagavulin 16 are my go-to's.

[Malcolm McLeod]

We're all allowed some claim to :eek:fame...
357706
...my cousin.:D And not a sassenach.:cool:

Anybody else?;)

And anybody who likes the Lagavulin is welcome in my home ... with a bottle in his pocket!!

[Brian Holcombe]

Awesome! That's got to have some good benefits. Also, good to know that I'm in good company on this board.

[Grant Wilkinson]

I've read that flute makers use gun drills for deep, straight bores.Would that work for you?

[Roger Nair]

To be on point with the O.P. and the derailment, consider the Scotch eyed tee auger, still available from the UK.

As a former timber framer, I would layout drawbored peg holes and drilled the holes before cutting the joints. I used several bit types and achieved predictable results, namely twin spurred solid center Irwin bits, single spur ship auger bits from various sources and triple spur Wood Owl bits. Lengths from 12 to 18 inches. Sharp spurs are, imo, one absolute key getting a clean bore. Other key are directional control and boring through perpendicular to tangential grain. I used drill frames of two types and several jigs to focus the bit. The simplest is a block five or six inches thick with a perfect bore through the block. Layout the bore on both sides and center punch. Insert bit through the bore in the block, find the centered punch hole with the feed screw and clamp the block to the workpiece. Drill halfway through and flip the stock and repeat process. Accuracy depends on crisp layout and regular surfaces. Or one could just bore through with a block clamped of the side where the bit comes through. to prevent blow out.

[andrew whicker]

https://www.mcmaster.com/#standard-drill-bits/=172fyd9

?

Not sure if a drill bit on your mill would be good enough.

[Brian Holcombe]

Thanks for the insights.