Large Forstner Bits.. Exposing the MYTH

[John Thompson]

I have always heard larger Forstner bits require very low speed. I am getting the new Steel City 17" Variable Drill Press and someone noted it was a "loser" when they found out the variable speed was from 500 rpm to 2500 rpm as they said they run large Forstner bits and they should be run at 300 rpm or under.

In 37 years of WW.. I have heard this often and many will argue the point adamantly and most agree.... And I was concerned getting a DP that starts at 500 rpm as I mainly run Forstner bits and run them around 400 rpm with OK results.

But.. is what is thought to be the "Holy Grail" on rpms for those larger bits "really" the Holy Grail? I set out to find out today while waiting for a glue-up to dry. I mounted a 2 1/8" Forstner and used 4/4 or 1" stock. A piece of pine and a piece of oak. A plunge and lift to keep the bit cool and and not over-power it to avoid grab and too big a bite. I started with 240 rpm and ended at 990 rpm. The results might surprise you.. really surprise you.

At 240 rpm.. the bit grabs and sqeals.. I made it to 1/16" in oak and 1/4" in soft-wood after I allowed 6 squeals. Unsatisfactory with the bit completely stopping...

At 350rpm.. proved the same squeal and grab making it to 1/4" in oak and 1/2" in pine. Unsatisfactory as the bit completely stopped several times...

At 390 rpm... got completely through without much squeal or grab so it was OK...

At 510 rpm... basically breezed through with no squeal and little grab and left a clean cut.. OK with one star..

At 650 rpm.. a repeat of 510 as got through with no squeal and little grab and left a clean cut.

At 990 rpm... basically poor performance and got through the oak only 1/8" before the squeal.. excessive grab to the point of the belts trying to jump pulley track. Stopped before they did. Completely unsatisfory at this speed.

At 600 RPM I got a super clean cut with no grab.. no squeal and no real slow down other than an occasional release to clear chips. The cut and speed at which it cut was as close to perfect with that monster bit as it gets.

So... I found 600 rpm to be as close to perfect as I am going to get. Between 390 rpm and 650 rpm was in range but the 600 was almost perfect. I was surprised as you might be also. But.. don't take my word for it or pass it off as he's full of it. Go try it yourself.. forget what you have heard repeatedly as I have... then past judgement.

Since I mainly run Forstners on my press.. it is now set to 600 rpm and will stay there for that task . And... Hello Steel City Variable Speed... when can I expect you?

Sarge..

[Mitchell Andrus]

The better the bit, the faster I run it. Good bits tend not to rub and burn, so speed makes a better cut. YMMV

[Bob Mircetic]

I applaud you for taking the time to actually test what is generally considered established fact.

However, I don't know if you can jump to the conclusion the 600rpm is perfect for *all* forstners, as I imagine different bit sizes would generate different results.

[Clifford Mescher]

Did you mention the type and manufacturer of the bit? Clifford.

[Roy Hess]

Interesting post. My old Sears drill press also starts at 500 rpm. I have a full set of Forstner bits which I use frequently. They are not even a "quality" set. I have always run them at 500 rpm in Oak or Ash, and they work fine.

Never thought of it any other way :o

[Pete Bradley]

Thanks for that. I recently had some smart guy acting as if I was some sort of hack for using a DP that "only" goes down to 470 RPM. After years of excellent results, it came as a surprise to me that I was actually doing it wrong. ;)

Like you, my experience is that slower isn't necessarily better especially if speed is necessary to eject chips.

Pete

[Mike Henderson]

At the woodworking school I attend, they teach that if your forstner bit is burning the wood, you need to increase the rotational speed.

So they agree with what you're saying.

Mike

[John Thompson]

Mitchell.. the 2 1/8" bit I used was a carbide tipped Ole Hickory which were made by Oldham. The bit was brand new as I have never had the call to use a 2 1/8" in my WW projects and I mainly build large carcass items even though I have had the set for years.

I can use a more expensive bit tomorrow as I have CMT forstners and hollow mortise chisels. But.. what I found is definitely contrary to the better the bit.. the faster you can run them. What I found is that there is definitely a too fast and a too slow. So.. at this point I can't agree with you but I wll re-test... 240 - 510 - 600 - 990 tomorrow and if I find different... I will get back and say so.

Sarge..

[John Thompson]

I applaud you for taking the time to actually test what is generally considered established fact.

However, I don't know if you can jump to the conclusion the 600rpm is perfect for *all* forstners, as I imagine different bit sizes would generate different results.

As I stated Bob.. I don't want you to jump to "any" conclussion.. go test the smaller bits tomorrow and see what you find. I only used the large bit to see if the 500 rpm limitation on the Steel City Variable would be reason to re-nig on it. It was not and it really surprised me.

But.. it won't take you that long to draw a conclusion using various size bits. It is a sad day if we have to depend on someone else's word on a WW forum as frankly.. experience walks and BS talks. But you can't always distinquish between the two sitting behind a computer desk.

So... by all means run you own test and report back what you found as I did. The whole thing took about an hour waiting for glue to dry.

Fair enough... ?

Sarge..

[John Thompson]

Did you mention the type and manufacturer of the bit? Clifford.

The brand is Ole Hickory I have had for years. The 2 1/8" was new as I have never had the call to use one that large on furniture. I definitely have on construction but that is played on a whole different playing field.

I can run some CMT's tommorrow as I purposely used the cheaper carbide set I have. Personally.. I really don't think it will matter greatly but just a guess at this point.

Sarge..

[John Thompson]

Thanks for that. I recently had some smart guy acting as if I was some sort of hack for using a DP that "only" goes down to 470 RPM. After years of excellent results, it came as a surprise to me that I was actually doing it wrong. ;)

Like you, my experience is that slower isn't necessarily better especially if speed is necessary to eject chips.

Pete

I have always admired your knowledge with machinery, Pete. So.. I am glad to be of help and I should have done this sooner as it took about an hour. I have a feeling "they" were more assuming than speaking from experience as I also for years believed what I read but settled on 390 rpm on my machine. I shoud have tried it at 510 rpm which is a big improvement and the most improvement on my DP came at 600 as mentioned. 650 was OK but it started to do some grabbing. 990 simply was pitiful.

Again I am glad I did it and will pursue some smaller bits tomorrow as I use the 1/4" - 3/4" the most but I have a hunch I will find that somewhere around that 600 rpm range on my machine will be the mark. Keep in mind I do not have a rpm run-out but the belts were good and I left the lid propped open to make sure there was no slippage to throw off results.

Regards...

Sarge..

[Sonny Edmonds]

I've watched tons of trainees misuse a drill bit in presses and by hand, trying to learn.
One thing you have omitted, or overlooked, is the amount of pressure you are exerting on the bit at any given RPM. :o
That will make one hell of a difference to anybody trying to follow your results.
I've watched, stopped, and taught apprentices proper bit pressure before, during, and after they burnt bits.
I always find that one true "Achilles Heal" to most summations about wood related work lack consistency in the material itself.
Charlie Browns Oak isn't going to be anywhere near the same as Fred Flintstones Oak. ;) :D
Unless you can make allowances for Material, Tool material, Pressures used, and accurate RPM applied, it really becomes a moot point.

Kinda like me with my results of measuring my air flow at my machines. Not really worth a poot to anybody but me. Because it is doubtful the results could be duplicated in another's shop. :) ;)

[John Thompson]

At the woodworking school I attend, they teach that if your forstner bit is burning the wood, you need to increase the rotational speed.

So they agree with what you're saying.

Mike

The only time I have ever had burn was at high speed Mike. One day I didn't feel like changing speed and dropped a 3/8" in at over 1700 rpm. That 3/8' dis-tempered and was junk. I replaced it and latter bought a premium set of carbide bits but frankly.. as long as this cheap set is sharp they cut just as well as the CMT's.

But.. tell your school there is a too slow. Try that bit in hardwood at 240 rpm and the bits squeals and then stops as there is not enough rpm to fight it's way forward.

Sarge..

[Jason Whitaker]

John,

excellent post and very interesting to read your results. I have been making some decorative candle holders and using a 2 1/8 bit probably about 30 times in the past two days in woods like walnut, padauk and purple heart... and I have to say you are absolutely correct. My DP only goes down to 600RPM but I find that my cuts are clean, w/o burning and are relatively easy to make....And the bit I am using is not great quality, though it was brand new and relatively sharp. And I thought I was doing it all wrong too.....

[John Thompson]

I've watched tons of trainees misuse a drill bit in presses and by hand, trying to learn.
One thing you have omitted, or overlooked, is the amount of pressure you are exerting on the bit at any given RPM. :o
That will make one hell of a difference to anybody trying to follow your results.
I've watched, stopped, and taught apprentices proper bit pressure before, during, and after they burnt bits.
I always find that one true "Achilles Heal" to most summations about wood related work lack consistency in the material itself.
Charlie Browns Oak isn't going to be anywhere near the same as Fred Flintstones Oak. ;) :D
Unless you can make allowances for Material, Tool material, Pressures used, and accurate RPM applied, it really becomes a moot point.

Kinda like me with my results of measuring my air flow at my machines. Not really worth a poot to anybody but me. Because it is doubtful the results could be duplicated in another's shop. :) ;)

Sonny.. I am not a beginner or apprentice and do have a clue after WW for 37 years on what type pressure to apply to a drill bit and how it responds to a given piece of wood. I work in my shop 4-8 hours a day.

But I do agree that pressure will play a role. This was done with a with moderate pressure and release to allow the chips to omit at lower speeds to attempt to avoid the grabbing. At the mid range the same pressure but found that the bit was not grabbing so I continued until I felt the slightest grab or squeal and then release.

At the 990 rpm the bit began grabbing after about 1/32" inch and grabbing so hard the belt felt and looked like it would jump track as I propped the lid open to watch for slip.

So.. if you read carefully this is not a cut and dried "this is the way it is" or "follow my results" in all conditions thread. Merely what I found and what I found was that the myth about using slow speed on large mortise bits is a fallacy as far as I am concerned.

But... I also challenged and encouraged you.. him.. them to go find out for yourself in lieu of taking my word that I have discovered the "Holy Grail". I haven't nor did I say I did.. simply that you don't believe everything you hear and accept it if any doubt. Just try it for yourself and the truth will be revealed about how your machine acts.

And frankly what I have found is most definitely worth something to me. If others have a look they may find out that it could also mean something to them. If it doesn't so be it...

Sarge..

[John Thompson]

John,

excellent post and very interesting to read your results. I have been making some decorative candle holders and using a 2 1/8 bit probably about 30 times in the past two days in woods like walnut, padauk and purple heart... and I have to say you are absolutely correct. My DP only goes down to 600RPM but I find that my cuts are clean, w/o burning and are relatively easy to make....And the bit I am using is not great quality, though it was brand new and relatively sharp. And I thought I was doing it all wrong too.....

Be careful Jason but... just for fun try one at around 1000 rpm and then jump to 1700 or so.. And be real careful and ready to release as I have a feeling it will grab hard if too much pressure is applied. Just a guess.. mind you. :>)

Sarge..

[Brian Effinger]

Very interesting, Sarge. Thanks for posting it.
I know that "your milage may vary", but this is a great starting point for anyone else (like me :) )to give some speed a try and see what works for him or her.

Brian

[Wilbur Pan]

At 240 rpm.. the bit grabs and sqeals..

At 650 rpm.. a repeat of 510 as got through with no squeal and little grab and left a clean cut.


I certainly don't doubt your results or your conclusion, but I have an idea as to why you were seeing grabbing and squealing with your drill press at 240 RPMs.

There have been two ways to slow down the speed of a drill press through the ages. The way it's done today is with some sort of electronic speed controller, which is what I'm going to guess is what you have on the drill press that you ran this test on. (If your drill press has a pulley speed change mechanism, then ignore everything I'm going to say from here on. ;))

The advantage of this method is that you can dial in the exact RPMs that you want. The disadvantage is that as you drop RPMs, you drop torque. So it may be that the reason your Forstner was grabbing and squealing is that at 240 RPMs, your drill press was barely being able to push that Forstner through the wood. As you ramped up the speed, you were providing more torque to your Forstner, giving you better performance, until you got to the point where you were burning the wood.

The old school method is to use step pulleys and change speeds by moving a belt from pulley to pulley, which is what I have on my 1940's era Walker-Turner drill press. The disadvantage of this method is that you only have certain speeds that you can run your drill press at. The advantage is that you are not going to lose power/torque at low RPMs. So it may be that the "big Forstner=low RPMs" rule came from those days, when you could very well burn out a big Forstner at low RPMs, because at low RPMs you were still providing a lot of torque. I don't have a 2 1/8" Forstner, but I would not be surprised that if you mailed me your Forstner and your test wood, that I would wind up with burning at 600 RPMs with my old drill press, simply because my drill press is providing more torque at the same RPM due to the step pulley speed change mechanism.

Similar issues occur with lathes and woodturning -- as you drop RPMs with a electronic drive to rough out that big bowl blank, you lose horsepower and torque. But if you have an old lathe with a step pulley, it's less of an issue.

Bottom line -- you should check it out for yourself.

[Bill Huber]

The Steel City 17 inch drill press they have on their will go down to 215 rpm by their chart.
This is a chart right from the manual, it also shows the speeds you should use for different types of bits and woor.

106319

[Sonny Edmonds]

Simply stated, John, is that if you are going to "expose the myth", you need some solid science to back up your findings.
Medium pressure to who? (Whom?)
What I stated is all real world truth. And Charlie Browns woodpile is certianly going to have different wood in it than Fred Flintstone's woodpile.
If you are going to "Expose the myth", I'm going to ask for some real hard facts.
And I'd do, and have done, the same with apprentices, and long term veterans of many a trade.
I didn't ask for any puffed out chest banter. I merely stated you need more finite details.
Medium pressure, for example, doesn't mean squat to me. 70 pounds of pressure does. 10 pounds does.
Medium torque on a bolt is of little value. 30 foot pounds (or pound feet, if you will) is a repeatable referance for anybody reading the post.
But medium pressure can have a very wide range.
And I haven't started on RPM referance... According to whom? Who amoung us has a tach on their drill press?

If you said you found these things to work for you, it would be a plausable thing. But exposing the myth?
Stand ready for challange and question about it. :)

[John Thompson]

I certainly don't doubt your results or your conclusion, but I have an idea as to why you were seeing grabbing and squealing with your drill press at 240 RPMs.

There have been two ways to slow down the speed of a drill press through the ages. The way it's done today is with some sort of electronic speed controller, which is what I'm going to guess is what you have on the drill press that you ran this test on. (If your drill press has a pulley speed change mechanism, then ignore everything I'm going to say from here on. ;))

The advantage of this method is that you can dial in the exact RPMs that you want. The disadvantage is that as you drop RPMs, you drop torque. So it may be that the reason your Forstner was grabbing and squealing is that at 240 RPMs, your drill press was barely being able to push that Forstner through the wood. As you ramped up the speed, you were providing more torque to your Forstner, giving you better performance, until you got to the point where you were burning the wood.

The old school method is to use step pulleys and change speeds by moving a belt from pulley to pulley, which is what I have on my 1940's era Walker-Turner drill press. The disadvantage of this method is that you only have certain speeds that you can run your drill press at. The advantage is that you are not going to lose power/torque at low RPMs. So it may be that the "big Forstner=low RPMs" rule came from those days, when you could very well burn out a big Forstner at low RPMs, because at low RPMs you were still providing a lot of torque. I don't have a 2 1/8" Forstner, but I would not be surprised that if you mailed me your Forstner and your test wood, that I would wind up with burning at 600 RPMs with my old drill press, simply because my drill press is providing more torque at the same RPM due to the step pulley speed change mechanism.

Similar issues occur with lathes and woodturning -- as you drop RPMs with a electronic drive to rough out that big bowl blank, you lose horsepower and torque. But if you have an old lathe with a step pulley, it's less of an issue.

Bottom line -- you should check it out for yourself.

Good info Wilbur.. but I have step pullies. Our drill presses may have different HP motors also which might (?) come into play. The reason I suggest each person to find the range THEIR Machne works best at with the pressure and method they use.

Again.. good info

Sarge..

[John Thompson]

The Steel City 17 inch drill press they have on their will go down to 215 rpm by their chart.
This is a chart right from the manual, it also shows the speeds you should use for different types of bits and woor.

106319

Hey Bil.. I did not test on the Steel City 17" but on my current drill press. The standard 17" will go to that low rpm but the newly introduced (be out soon) Variable speed range is between 500 rpm and 2500 as I double checked today with Jim Box of Steel City who is sending me the new 17" Proto-type introduced at IWF in Atlanta to field test for them.

Someone mentioned the 500 rpm on that machine as being a "loser" in another thread because they said you run large forstner bits at 300 or below. And not the first time I have heard it. Well.. I found out different today as I felt if true.. that would be a draw-back on getting that press.

But what I found out is there is a too slow and a too fast from my press even though it will probably vary from machine to machine. But.. at this point I have confidence that 500 rpm bottom end will be fine to run forstners and that below 400 rpm the performance was poor. Simple as that really.

Sarge..

[John Thompson]

Simply stated, John, is that if you are going to "expose the myth", you need some solid science to back up your findings.
Medium pressure to who? (Whom?)
What I stated is all real world truth. And Charlie Browns woodpile is certianly going to have different wood in it than Fred Flintstone's woodpile.
If you are going to "Expose the myth", I'm going to ask for some real hard facts.
And I'd do, and have done, the same with apprentices, and long term veterans of many a trade.
I didn't ask for any puffed out chest banter. I merely stated you need more finite details.
Medium pressure, for example, doesn't mean squat to me. 70 pounds of pressure does. 10 pounds does.
Medium torque on a bolt is of little value. 30 foot pounds (or pound feet, if you will) is a repeatable referance for anybody reading the post.
But medium pressure can have a very wide range.
And I haven't started on RPM referance... According to whom? Who amoung us has a tach on their drill press?

If you said you found these things to work for you, it would be a plausable thing. But exposing the myth?
Stand ready for challange and question about it. :)

Sonny.. I am going to ask you go back and read the orignial post.. read it very carefully. The title is Large Forstner Bits.. Exposing the MYTH/

Simply stated.. I simply wanted to find out if the Myth I have heard for years and accepted by many of runniing large forstner bits at low speed was a must as I am getting a machine with low end of 500 rpm. I personally found that to be a myth..

And if you read carefully I clearly stated I did not want anyone to take my work but go into their shop and do it on there machine to find out for themselves if they also concluded it was myth. I am not writing a book on drill presses.. not attempting to make a usuable chart for others to follow.. not attempting to teach others the correct way.. not trying to do anything scientific.

I am simply passing on information I found out for my needs to decide on a particular drill press with 500 rpm low end. I simply put out a challenge fore each person to find out if they felt it was myth or not. I found out that my current press runs large forstners best between roughly 500 and 600 rpm.

Please don't attempt to twist what I did say into something more complicated that what I said. I don't need to provide scientific facts.. I don't need to define medium pressure. I simply needed to know if it was myth or not to make a decision. I have done that for myself and presented what I found which I consider at this point to be a myth.

I challenged All to find out for themselves by actually doing it and not just taking someone else's word. Life is simple until someone finds a way to complicate it. There should be no complication here if you read carefully.

Sarge..

[Jeff Bratt]

Thanks for sharing these results - it's always nice to see some real-world data to back up opinions. If you you test any more bit brands or sizes, please pass the info on. I would guess that the smaller bits will have a faster optimum speed - but maybe that piece of conventional wisdom also needs questioning!

[Dewey Torres]

Thanks fos putting this together. I can tell you put much time and effort into it!

[Greg Pavlov]

John, I use a 16.5" drill press with a 1/2 horse motor and run Fostners (cheap Rocklers) at 590 (pulleys). I haven't used anything wider than 1 3/4", tho.

[Larry Edgerton]

I have taught myself for the most part, and I have always sped up the DP for wood until it feels comfortable. I have no idea what RPM I am at as I have a Walker Turner with a variable speed clutch setup, no belt changes. This setup will go very slow, you can almost read the bit. I think that 500 may be too fast for some steel drilling operations, and certianly way too fast for a fly cutter, so to me I think that as an all around tool, 500 is too fast.

Are you proving the tool, or are you justifying the deal you have made with Steel City? Throw a fly cutter in there at that speed and you will have a dull cutter in a heartbeat.

I would agree with a 2 1/8 that 600 would be about right, now try it with a 3 5/8 bit. The teeth are traveling at almost exactly twice the speed, and I think you will find that you are now too fast at 600. If you want your teeth to travel at the optimal speed that you yourself have come up with, you would need 300 rpm.

You can say the you never use that size, but I do........

[Mike Heidrick]

John is one awesome dude that is determined to come to the truth for sure in any endeavour!!
Few questions I have....

How do you prove what speed the DP is really travelling at? I am taking it for granted my DP is spinning at the speed the chart says it is spinning at. I have never truely measured it at.

Is it only for Forstner bits in wood that you will need the low speeds for?
Ever cut into steel with your machine? Will you need the low speeds for that?
What about hole saws or circle cutters?
What about the larger multi-spur bits?
What about larger bits in tile or glass or acrylic?

What about using some of the larger brad point bits in hardwood?
What about tapered bits?

Are the forstner bits used in the test saw tooth type or rim notch type? Would that make a difference?

[Jason Roehl]

A quick check on RPM of drill presses. If your DP has a nameplate on its motor, the speed on there will be pretty close, because it's based on the 60Hz power we get here in the U.S.A. That motor drives the rear pulley stack on most DPs. From there it's all about the ratios of the pulleys, which can be physically measured if you so desire.

Thanks for the info, John. I once assembled a log stair system, and had a whole bunch of holes to make with a Forstner bit. At first, I tried to go slow with my VS corded drill (this was an on-site deal, no DP available). I ended up at higher speed and pretty high pressure, switched between my corded and cordless drills--the batteries would die on the cordless and the corded would get too hot to hold (several dozen holes, it's been a while, so I don't remember for sure). :eek:

[Steve Rozmiarek]

Good stuff, Sarge. Makes me feel a little better about being lazy and not changing speeds all the time!

[John Thompson]

I have taught myself for the most part, and I have always sped up the DP for wood until it feels comfortable. I have no idea what RPM I am at as I have a Walker Turner with a variable speed clutch setup, no belt changes. This setup will go very slow, you can almost read the bit. I think that 500 may be too fast for some steel drilling operations, and certianly way too fast for a fly cutter, so to me I think that as an all around tool, 500 is too fast.

Are you proving the tool, or are you justifying the deal you have made with Steel City? Throw a fly cutter in there at that speed and you will have a dull cutter in a heartbeat.

I would agree with a 2 1/8 that 600 would be about right, now try it with a 3 5/8 bit. The teeth are traveling at almost exactly twice the speed, and I think you will find that you are now too fast at 600. If you want your teeth to travel at the optimal speed that you yourself have come up with, you would need 300 rpm.

You can say the you never use that size, but I do........

Having been around restoration of old muscle cars and machinist Larry.. I think that 500 is too fast for "some" steel drilling operations also. But.. that might be better answered by a machinist. I am going to keep my current step pulley DP just because I do some metal work to cover that issue if it comes up. At least for the moment...

I can probably only get around $150 maximum for it and it may prove more worth by keeping it. I had the same issue when stepping up to a large BS. I kept the smaller one as I could not get what I felt it was worth and it could be used to dedicate to a much smaller blade for currves. That proved to be the best call I could have made.

I personally never use over a 2 1/2" bit on a DP as I personally chose a less thrilling way with wood. But.. once I get it I wil have to test the "big boy" bits as some do use them on the DP as you. I already have an opinion on the issue but until I find out for sure... that will go unsaid at the moment as it is just an opionion.

Sarge..

[John Thompson]

John is one awesome dude that is determined to come to the truth for sure in any endeavour!!
Few questions I have....

How do you prove what speed the DP is really travelling at? I am taking it for granted my DP is spinning at the speed the chart says it is spinning at. I have never truely measured it at.

Is it only for Forstner bits in wood that you will need the low speeds for?
Ever cut into steel with your machine? Will you need the low speeds for that?
What about hole saws or circle cutters?
What about the larger multi-spur bits?
What about larger bits in tile or glass or acrylic?

What about using some of the larger brad point bits in hardwood?
What about tapered bits?

Are the forstner bits used in the test saw tooth type or rim notch type? Would that make a difference?

How can you prove the speed.. without proper equipment you can't as there are too many variables. All the speeds I have mentioned are what are listed on my current DP chart and what the manufacturer says is the speed.

Do I feel that is the exact speed. No... but it is approximate and the reason I say to do it on your machine to find out what works best for you based on what your machine chart indicates is the speed. Again.. nothing scientific here as I really don't see a need. Just a problem I will have to face. I found the solution I was looking for concerning Forstners which is a large part of what I do on a DP.

I have printed out the list you have ask questions on, Mike. I can't answer them concerning the Steel City 17" Variable as I don't have the machine to seek the answers yet nor am I looking for them at this point. Finishing the two pieces that went into glue-up yesterday is my current agenda.

But.. when I do get it (god willing and the creeks don't rise) I will attempt to test each of the above you have mentioned. They are good questions for any that cross over to other than wood and those that do spin large bits which I don't.

So.. you will have to be patient and I will re-iterate to not expect scientific backed data to be thrown out. Just simple test to determine if it will or it won't or does it fall somewhere in between with a given material.

Regards...

[John Thompson]

A quick check on RPM of drill presses. If your DP has a nameplate on its motor, the speed on there will be pretty close, because it's based on the 60Hz power we get here in the U.S.A. That motor drives the rear pulley stack on most DPs. From there it's all about the ratios of the pulleys, which can be physically measured if you so desire.

Thanks for the info, John. I once assembled a log stair system, and had a whole bunch of holes to make with a Forstner bit. At first, I tried to go slow with my VS corded drill (this was an on-site deal, no DP available). I ended up at higher speed and pretty high pressure, switched between my corded and cordless drills--the batteries would die on the cordless and the corded would get too hot to hold (several dozen holes, it's been a while, so I don't remember for sure). :eek:

You're welcome Mike.. and that goes to all that chimed in with constructive opinions......

I have attempted to use forstners in a hand held drill also but corded. Not the easiest task you can tackle as I found you had to cant the drill from side to side to so the lead cutter would catch the wood as holding exact speed with a variable hand drill is almost impossible.

The result of those holes was needless to say.. somewhat over-size due to the canting left to right. Just my experience as there may be someone that can cut one accurate with a hand drill but it certainly isn't me. :)

Regards...

Sarge..

[Clifford Mescher]

Mitchell.. the 2 1/8" bit I used was a carbide tipped Ole Hickory which were made by Oldham. The bit was brand new as I have never had the call to use a 2 1/8" in my WW projects and I mainly build large carcass items even though I have had the set for years.

I can use a more expensive bit tomorrow as I have CMT forstners and hollow mortise chisels. But.. what I found is definitely contrary to the better the bit.. the faster you can run them. What I found is that there is definitely a too fast and a too slow. So.. at this point I can't agree with you but I wll re-test... 240 - 510 - 600 - 990 tomorrow and if I find different... I will get back and say so.

Sarge..
You will always be able to run carbide at higher RPM's then high carbon or HSS bits.Clifford.

[John Thompson]

Mitchell.. the 2 1/8" bit I used was a carbide tipped Ole Hickory which were made by Oldham. The bit was brand new as I have never had the call to use a 2 1/8" in my WW projects and I mainly build large carcass items even though I have had the set for years.

I can use a more expensive bit tomorrow as I have CMT forstners and hollow mortise chisels. But.. what I found is definitely contrary to the better the bit.. the faster you can run them. What I found is that there is definitely a too fast and a too slow. So.. at this point I can't agree with you but I wll re-test... 240 - 510 - 600 - 990 tomorrow and if I find different... I will get back and say so.

Sarge..
You will always be able to run carbide at higher RPM's then high carbon or HSS bits.Clifford.

Thanks Cliff as that is something that never crossed my mind. I simply used what I had to determine if I could get away with low speed 500 rpm. But.. when I do some testing with the SC.. that would have to be held accountable for any that run HSS. I really wasn't aware anyone made forstners in HSS anymore but I don't get out of the shop as much as I should.. but I'm not complaining. :)

Sarge..

[John Gornall]

As a new engineer just about 40 years ago I worked for a large manufacturing company studying cutting tools. A cutting situation would be recognized and I would test to find the best edge material, cutting speed, and rate of cut. The "best" was concluded based on speed of cut, quality of cut, tool edge life, and cost of tooling. If I was testing a 2.125" diameter forster bit I would start by getting a selection of bits in different designs and different steels. I would then start cutting holes in a specific type of wood. At first the feed rate would be constant with only the rpm being varied for each cut. The feed rate would be controlled by maintaining a constant amperage to the cutting tool - constant torque. A series of cuts would be made at increasing rpm to determine the "best" rpm. This would be repeated for each different bit. Then the feed rate would be increased and the test repeated and so on. By collecting a lot of data on time to drill a hole of adequate quality, life of cutting edge, and cost of tool I would make a recommendation on which bit to purchase for production.

In the case of a 2.125" diameter high speed steel forstner bit in oak if I was to go back to my old knowledge and make an educated guess of suitable rpm I would multiply my guess at a suitable cutting speed in feet per minute of the outside cutting edges of 350 times 4 and then divide by the bit diameter 2.125 and get a speed of 660 rpm - interestingly close to results reported above. A carbide bit would be a little above 1000 rpm.

Most people I have observed run drill bits in wood far too slow. I run my pocket hole step drill at 2250 and I watch others using cordless drills at 1200 with poor results. I use an air drill for 1/16th inch bits at 10,000. The smaller the bit the higher the rpm needed.

[John Gornall]

There is so much detail I could add - this part might be usefull.

In cutting steel we also tested cutting lubricants as another variable. I highly recommend waxing some of the surfaces of your forstner bits such as the outside and the chip slots. As to what kind and how much wax - you'll have to test.

[John Gornall]

My mind keeps going back to the old tests. Another thing of interest is that we kept records of the temperature of the cutting edge. Carbide bits when cutting in steel worked better when hot - there was less friction as indicated by an increased cutting volume at the same torque. Ceramic edges when cutting steel needed to be hot enough that the edge glowed red.

[Clifford Mescher]

You will always be able to run carbide at higher RPM's then high carbon or HSS bits.Clifford.



Thanks Cliff as that is something that never crossed my mind. I simply used what I had to determine if I could get away with low speed 500 rpm. But.. when I do some testing with the SC.. that would have to be held accountable for any that run HSS. I really wasn't aware anyone made forstners in HSS anymore but I don't get out of the shop as much as I should.. but I'm not complaining. :)

Sarge..
John,
From what I see thumbing through the catologs, High carbon and HSS are still domineering the market with carbide available at a premium price. Most of my forstners are HSS with a few of my favorite sizes made with carbide. Clifford.

[John Thompson]

As a new engineer just about 40 years ago I worked for a large manufacturing company studying cutting tools. A cutting situation would be recognized and I would test to find the best edge material, cutting speed, and rate of cut. The "best" was concluded based on speed of cut, quality of cut, tool edge life, and cost of tooling. If I was testing a 2.125" diameter forster bit I would start by getting a selection of bits in different designs and different steels. I would then start cutting holes in a specific type of wood. At first the feed rate would be constant with only the rpm being varied for each cut. The feed rate would be controlled by maintaining a constant amperage to the cutting tool - constant torque. A series of cuts would be made at increasing rpm to determine the "best" rpm. This would be repeated for each different bit. Then the feed rate would be increased and the test repeated and so on. By collecting a lot of data on time to drill a hole of adequate quality, life of cutting edge, and cost of tool I would make a recommendation on which bit to purchase for production.

In the case of a 2.125" diameter high speed steel forstner bit in oak if I was to go back to my old knowledge and make an educated guess of suitable rpm I would multiply my guess at a suitable cutting speed in feet per minute of the outside cutting edges of 350 times 4 and then divide by the bit diameter 2.125 and get a speed of 660 rpm - interestingly close to results reported above. A carbide bit would be a little above 1000 rpm.

Most people I have observed run drill bits in wood far too slow. I run my pocket hole step drill at 2250 and I watch others using cordless drills at 1200 with poor results. I use an air drill for 1/16th inch bits at 10,000. The smaller the bit the higher the rpm needed.

Thanks for your in-put from the engineering side. I just came up from the shop but this morning I ran a 1/2" forstner through the speeds. It was from the same set and I was curious. The results were interesting and pretty much confirmed what you stated about smaller bits.

I got a very clean cut from 250.. 340.. 510.. 600.. 990.. 1250.. 1640.. 1920.. 2450.. and 3100. The low end cuts were much slower but fewer bit releases were required to clear chips. As soon as I got to the 1640 the bit did have to be raised more often to rid it of chip waste or scorching the wood starting occuring.

All the cuts were good in oak (I only did oak today) and I felt the most comfortable speed.. chip clear and feed rate around 990 to 1250. And I repeat.. that is what I felt or sensed personally... not what my neighbor might sense. Again.. there was no problem higher but you had to be more sensitive to chip scorth with the higher speeds which makes sense.

Again thanks as I am really only interested in what is and what isn't for my own needs. This has dis-spelled some things I believed and en-lightened me on others I didn't know.

Regards...

Sarge..

[John Thompson]

John,
From what I see thumbing through the catologs, High carbon and HSS are still domineering the market with carbide available at a premium price. Most of my forstners are HSS with a few of my favorite sizes made with carbide. Clifford.

I suspect you are probably correct in the other post about different metals requiring different speeds. I got to thinking about my Ole Hickory WW forstners and began to question if they are indeed carbide or HSS. I did a Google on them and it appears Oldham has quit carrying them as I can't find anything. I wanted to check the status of the forstners as I know for fact that OH had carbide router bit sets at one time.

I even looked on the carry case but it did not state carbide.. HSS.. etc. So it leaves doubt and I have no clue how to determine one way or the other.

Back to the shop...

Sarge..

[Clifford Mescher]

I think it is important to emphasize that alot of people buy cheap carbon bits that have to go slow because they get hot real easy. You can go faster with HSS. And you can go real fast with carbide. Clifford.

[Clint Schlosser]

I would like to weigh in with my personal experience.

I have a 4" and 3.5" forstner bit and I use it in my DP350 delta benchtop drill press. I run it at the lowest speed (500 i think) and I was able to bore out a Mug I was working on from Sycamore with a little patience and no grabbing, burning, or other issues. I will say that I was very careful about the pressure and the amount of chip collection I used.

I actually started the hole with a 1" bit and then went strait to the 3.5" and finish with the 4". This method worked for me but what do I know, being a weekend warrior. I might just be lucky to be alive or without serious injury.

[Jeff Bratt]

I wanted to check the status of the forstners as I know for fact that OH had carbide router bit sets at one time.

I even looked on the carry case but it did not state carbide.. HSS.. etc. So it leaves doubt and I have no clue how to determine one way or the other.

If the case doesn't say carbide - then I would be suspicious. If they are carbide bits, there will certainly be a brazed-on carbide piece at the cutting edge(s) that will be plainly visible. I cannot imagine a forstner bit being ground from solid carbide - that would be prohibitively expensive.

Please let us know...!

[Clifford Mescher]

Here are two 3/4" forstner bits. One on left is HSS and of course, carbide on the right. Clifford.

[Larry Edgerton]

John, I have to agree with Sonny here, you are making some pretty sweeping generalizations, and you should be called out because that is how misinformation gets its roots.

I think your heart was in the right place but your data was flawed.

The bit size you chose was not particularly large as I showed in my last post, the actual rpm was not established as fact, and the types of wood chosen were not particularly challanging. Add to that that there are many other possible drill press uses, and just this one point does not qualify what RPM a drill press should run at at all.

It would seem better to me to have a drill press that ran too slow than one that ran real fast. But that is just my opinion......

[John Gornall]

There's no doubt that each circumstance is specific in using cutting tools. That's why we did tests rather than just look up drill speeds and feeds in an engineering book. When production showed 4.5 million holes would be drilled in a certain type and thickness of steel our tests were justified because of the potential cost savings should we be able to drill twice as fast and use half as many bits.

The point here is simply understanding that when you drill a big hole in a wood of your choice and it isn't going well there are changes you can make that might lead to better results. Bit rpm, feed rate, a different bit design, lubrication, more chip clearance - give each a try. And of course if all else fails get out a chisel amd mallet.

I mention chip clearance - I find most forstner bits jam up in the chip slots - I grind a bit more clearance with my Dremel - seems to help a lot.