This puts things into perspective :

For that $885 price I would have to be drilling literally millions of holes a year to justify it.

As for putting nice neat round holes in soft materials at high speed that's where 3 - 5 flute tooling bits come into play.

Personally if it was me I would be looking at standard size commercial production tooling bits used for high volume metal drilling work being any decent ones of those can drill thousands of holes in aluminum at high RPM without wearing out and when they do they are easily resharpened with common bit sharpening practices.

That, or the same type of high speed high volume production metal working bits with carbide tips rather than being solid carbide.

What are you making and how many holes over what timeframe are you dealing with?

 

You are going to have 8 layers of plywood spinning at 5000 RPM? That could be dangerous. Have you thought about spinning the bit?

Sorry had to say it.

Well, I have worked around people (most often managers and bosses) who would see no problem in approaching it that way so it is possible.

Same with having spent near $300,000 custom product transfer conveyor system to move a product from production stage 3 to stage 4 packaging (end stage then to pallet and out to the warehouse on forklift from there) instead of just moving production stage 4's single machine over to sit next to production machine 3's output point which the company maintenance crew, me and three others, could have done in a day Vs the 2 weeks production shut down the custom conveyor system took to build in place.

 

He needs a special drill bit that's 4 1/2" long to drill through 4" of plywood which would make the 4 1/8" and the 5 3/8" bits too long to work.

I've looking for bits of those lengths in several places, and can't find them.

 

I would have to be drilling literally millions of holes a year to justify it.

Yup... that is the case here... several hundred thousand holes a year are being drilled with that machine.

What are you making and how many holes over what timeframe are you dealing with?

The machine drills holes in special-length plywood (up to 30 ft) which is later used as a template for manufacturing a product that I'm sorry to say I can't disclose here.

 

Yup... that is the case here... several hundred thousand holes a year are being drilled with that machine.


The machine drills holes in special-length plywood (up to 30 ft) which is later used as a template for manufacturing a product that I'm sorry to say I can't disclose here.

Then your first option of 200 to $350 each isn't so bad. Each hour you spend looking for a cheaper bit is another hundred dollars to any bit you eventually find. I'd spend the $300 per bit and call it a day - considering the customer isn't buying drill bits, they are paying for several hundred-thousand holes.

They are also paying for reliability - Down-time to change bits is time they are paying for a maintenance worker but, most of all, it is time they are NOT making product.

 

Then your first option of 200 to $350 each isn't so bad. Each hour you spend looking for a cheaper bit is another hundred dollars to any bit you eventually find. I'd spend the $300 per bit and call it a day

Yeah.. I was afraid it would come to that... but I had to give it a try anyway *sigh* ... thanks for your help!

 

Amazing how replys and answers change when one supplies relevant workable information regarding what their end goal is.

 

Amazing how replys and answers change when one supplies relevant workable information regarding what their end goal is.

True... but I was trying to avoid explaining the details...

I just watched a chapter of House. And it's funny because it's always the same thing. His patients never tell him the whole truth trying to protect their privacy.

 

True... but I was trying to avoid explaining the details...

I just watched a chapter of House. And it's funny because it's always the same thing. His patients never tell him the whole truth trying to protect their privacy.

Yup, if you are going to start a thread, it should have 30 minute of comedic exchange or 60 minutes of dramatic exchanges.

 

True... but I was trying to avoid explaining the details...

New to getting help on internet technical forums huh?

This is how I would have approached the issue.

" I have a manufacturing system that CNC gang drills holes in a plywood stock about 4 inches thick using high speed (5000 RPM drill motors) doing hundreds to thousands of them at a run and need to find a more suitable drill bit for the work.

Presently I drill two sizes of holes of XX/XX and YY/YY diameters with standard two flute HSS drills but they tend to wear and produce less than idelay round holes.

So does anyone have any recommendations for a more suitable/durable drill bit that will last longer and produce a nicer finish?

Here's the basic drill bit specs I need to find a close match to. (see attached drawing.) "

 

Actually I'm the one who designed it... and it's been working reliably for the last 12 years. And it's got two Milwaukee routers functioning as spindles. The bits are changed manually, btw.

Here's the thing:

• The drilling has to be done at high RPM so as to leave a clean-cut hole, plus the operation is much faster.
• A spade bit won't leave a nice and sharp edge in the wood being cut, plus there's no way for the chips to evacuate when drilling 4" of commercial pine plywood.
• If HSS bits are used:
  • The holes won't come perfectly round, and will be quite oblong, even at much lower RPM, and even if TIN (or Cobalt) coated bits are used.
  • The bits' sharpness won't last more than a couple of hours, and the wood will start to smoke. Whereas a solid carbide bit will stay sharp for up to a year.

• In the 12 years that the machine has been working, there has never been an accident. A bit broke once (and only once) due to overuse and lack of sharpening maintenance (you can tell by the smoke being produced while drilling). When that happened, the bit stayed inside the wood, and didn't fly out. And the bit is protected by a tube (used to vacuum the chips) that also acts as a shield.
• As for adapting a commercially available solid carbide bit, I had looked into that years ago, but either a 1/2" shank was not available for those diameters, or the length was not long enough. Maybe things have changed, so I'll go and look into that again.

Any suggestions (and even critique, I know you guys mean well and are trying to help) will be thoroughly appreciated.

Thanks again all for your help.

Your experiences are different than mine. I don't understand how a carbide TWIST drill is/does make a rounder hole than a HSS TWIST drill. The geometries of both drills should be the same. If not get a good, not Chinese made or hardware store drill that is the same flute and point geometry as your carbide that your using. There is a difference between say a Chicago Latrobe or Cleveland drill and a hardware store one. If you have and know a carbide bit works, where did you get the one your using now? I've drilled many a hole in phenolic, and in even brake shoe linings for relining old car brakes that are much more abrasive than pine plywood without a problem with just a HSS bit

If your smoking the wood maybe your feed rate isn't right for your drill speed?

There's only two types of drills that I've found that cut a truly round hole in wood, a Forstner bit and a spur/brad point bit. https://www.google.com/search?q=Forstner+bit&ie=utf-8&oe=utf-8 https://www.google.com/search?q=spur+point+bit&ie=utf-8&oe=utf-8

Over the years in the trades I've silver soldered many shanks on drills and never had a problem with them.

 

I don't understand how a carbide TWIST drill is/does make a rounder hole than a HSS TWIST drill. The geometries of both drills should be the same.

The thing with HSS is that it's not as rigid as carbide is, and it tends to bend and wobble a little at those RPM's, that's why they don't leave a good round hole.

There's only two types of drills that I've found that cut a truly round hole in wood, a Forstner bit and a spur/brad point bit.

That's a very interesting option, I wonder if those bits can be found in carbide too. I'll do some googling and then get back here. Thanks for the suggestion.

 

This is how I would have approached the issue.

Yeah, maybe I should've been more specific from the start. I owe you guys that much at least. Guess I'll have to work some more on my communications skills.

 

The thing with HSS is that it's not as rigid as carbide is, and it tends to bend and wobble a little at those RPM's, that's why they don't leave a good round hole.


That's a very interesting option, I wonder if those bits can be found in carbide too. I'll do some googling and then get back here. Thanks for the suggestion.

Didn't answer the question about where you got the carbide your now using. And that goes into your first answer here, if your thinking a carbide drill will be more "rigid" than a HSS drill my experience say no. If any thing a full RPM it will wobble more, due to the weight difference between the two. Any wobbling of the drill is due to the fact your using a router as a spindle. A router is designed, bearing wise, to have it's tool 'close coupled' to its tool holding device or chuck. Not having the tool sticking out ~5". Look at router bits, there short. The bearings and shaft in a router are small compared to a drill spindle.

Was also thinking of this over the weekend, the chip clearing and smoking/burning of the drill bit. How often do you retract the bit during the drilling? Drilling that deep in wood or any material requires the drill to be retracted occasionally. How often depends on the chips being produced. The flutes on a twist drill are only meant to move them away from the cutting lips and to give less surface area to rub on the hole created. Not to completely evacuate all chips as they a being created.

 

Didn't answer the question about where you got the carbide your now using. And that goes into your first answer here, if your thinking a carbide drill will be more "rigid" than a HSS drill my experience say no. If any thing a full RPM it will wobble more, due to the weight difference between the two. Any wobbling of the drill is due to the fact your using a router as a spindle. A router is designed, bearing wise, to have it's tool 'close coupled' to its tool holding device or chuck. Not having the tool sticking out ~5". Look at router bits, there short. The bearings and shaft in a router are small compared to a drill spindle.

Was also thinking of this over the weekend, the chip clearing and smoking/burning of the drill bit. How often do you retract the bit during the drilling? Drilling that deep in wood or any material requires the drill to be retracted occasionally. How often depends on the chips being produced. The flutes on a twist drill are only meant to move them away from the cutting lips and to give less surface area to rub on the hole created. Not to completely evacuate all chips as they a being created.

A good rule of thumb is that holes should not be more than 5x the depth of a drill bit diameter. This was demonstrated at a diamond tool show by Boeing and a tooling supplier. Oval holes, re-integration of chips into the cut wall through friction-stirring (friction welding) and overheating of the tool (short life) can result. Wood doesn't get redeposited like metal does but the lignin can come out of the wood and deposit a resin-coated mess on the tools.

Retracting often and cutting with significant force (pressure) will help keep the tool cool and chips flowing.

 

Retracting often and cutting with significant force (pressure) will help keep the tool cool and chips flowing.

That's the big thing (for tool life) in metal working too. Feed fast enough to put the heat in the chip, but not so fast that it rewelds to the tool.

 

That's the big thing (for tool life) in metal working too. Feed fast enough to put the heat in the chip, but not so fast that it rewelds to the tool.

Yeah, I had already implemented that into the machine. The way I did it is by constantly monitoring the current going into the router. If the current reaches a preset threshold, then the tool travels upwards a bit, so as to evacuate the chips and minimize friction, then it goes back in again, until a depth set point has been reached. Then it considers the drilling complete, and moves on to drill the next hole. This technique allows you to monitor the tool's sharpness too. This is because the duller the tool, the more "pecking" cycles are required because more current is being consumed to perform the same operation. When the number of pecks reaches a pre-programmed limit, the software reports that its time to change the tool.

 

With out seeing your machine, do you have a drill bushing or guide near the material to be drilled? This would help to keep the drill from wandering and wobbling at router speed. For a 11/16 drill bit that really is high RPM, even in wood. How about a PID type speed controller for that router? Seems to me that past(passed?) member the RB had a controller circuit on the site. He came up with it for one of his DIY CNC routers, when a regular 'dimmer' style didn't allow full torque from the router head.

 

With out seeing your machine, do you have a drill bushing or guide near the material to be drilled? This would help to keep the drill from wandering and wobbling at router speed. For a 11/16 drill bit that really is high RPM, even in wood. How about a PID type speed controller for that router? Seems to me that past(passed?) member the RB had a controller circuit on the site. He came up with it for one of his DIY CNC routers, when a regular 'dimmer' style didn't allow full torque from the router head.

No, the machine doesn't need a bushing to guide the bit. And yes, that is high a speed for a 11/16" drill bit, but it's even more important for the 21/64" bit, since it's thinner, and that's the bit that wobbles the most if I were to use a HSS bit instead. Trust me, carbide's rigidity is much higher than HSS:

Tungsten carbide is approximately two times stiffer than steel​

In the end, what I had to do 10 years ago was install a speed regulating circuit (designed by me) inside the router (a 3-1/2 HP Porter-Cable). This is because that router model can't function below 5,000 rpm. But the circuit's been working reliably ever since.

 

If it was me I would have went with common 1 HP 4 or 6 pole (~1050 - 1725) RPM three phase AC motors powered by off the shelf VFD units instead of high speed router motors.

To me the fact you have to use special speed control to make the routers run slow enough (and well under their rated power band) says you picked the wrong motors for the job to begin with.

http://www.engineeringtoolbox.com/drill-bit-speed-hardwood-softwood-d_1451.html

Going by the basic recommendations in the link the drill bits you have should never need to go above 1000 RPM in any type of wood let alone run at 5000 RPM.

To be honest all of this drill bit related problems sounds like the whole issue stems from poor research and design that should have been easy basic study work done well in advance of the machine ever having been built and now the idea of 'just throw more money at it until it works our way' is what's being looked at rather than stepping back and looking at it with basic well known and understood woodworking principles and setting it up to run with the correct type of motors to work in the proper speed range of the current drill bits.