How Long Does A Drill Bit Last?

[Kody]

Very interesting reading the above. If I were doing the job, I would power feed the drills all the way. No counterbalance or other stuff. The problem starts when the drill begins to break thru the lower surface of the steel plate. With no proper control of the feed and pressure, the drill can plunge into the last of the hole and break. IMO it would be far better to power feed the drill all the way with a constant feed rate. For me, I would hand sharpen the drills as I can sharpen a drill to very exact requirements for any material being drilled. My own personal problem is that I sharpen the drills (up to 1/2" dia.) so good that they cut to exact diameter and often jamb or wont go into the same hole I just drilled. I have to grind the drills so they cut a couple of thou too big. (Yes, really!)
The choice of cutting fluid is critical and must not be taken lightly. I have witnessed many trials of cutting fluids when I was in the USA and an incorrect choice can lead to big dissapointments. It is absolutely essential to run the drill/s at the correct speed for the material being drilled. If you use a "pilot drill" or a "center drill" to start the hole, only drill down untill the hole is at full dia. This means that if you use a center drill to locate the hole and start it, dont drill more than 1.5 to 2 mm deep. Dont drill down to the 60 degree angled section, it's simply not needed. A better way to do the job would be to use a short "stubbie" drill. This is a drill about 50mm long and when chucked up, the extended drill is only about 25 or 30mm past the chuck jaws. Having the drill sharpend correctly would help the swarf to clear from the flutes. The width of the "chisel" point is also critical for easy penetration, long life, accuracy and cutting efficiency. If nothing else, you will certainly end up knowing how to sharpen a drill correctly.

Kody

[Woodlee]

Dewalt "Pilot Point"?

Great drill bits. Must get some again. I used them years ago and they drill a really quick neat hole and don't grab when breaking through.

http://cgi.ebay.com.au/DEWALT-29-PIE...mZ290296157095

Nev

Yep that's them ,but mine are called Extreme and I was told they only come in metric sizes .
So much for the salesman ,knowing his product

Kev

[Ashore]

Very interesting reading the above. If I were doing the job, I would power feed the drills all the way. No counterbalance or other stuff. The problem starts when the drill begins to break thru the lower surface of the steel plate. With no proper control of the feed and pressure, the drill can plunge into the last of the hole and break.
This is true if the feed is not constant though the breaking of a drill I find hard to believe
IMO it would be far better to power feed the drill all the way with a constant feed rate. For me, I would hand sharpen the drills as I can sharpen a drill to very exact requirements for any material being drilled. My own personal problem is that I sharpen the drills (up to 1/2" dia.) so good that they cut to exact diameter and often jamb or wont go into the same hole I just drilled. I have to grind the drills so they cut a couple of thou too big. (Yes, really!)
1. If you can grind a drill to drill 2 though oversize , whatever you are doing now you can change jobs and make a zillion dollers a week if by hand you can alter your sharpening technique to sharpen a drill by hand to have exactally the same size flutes and then alter this by two thousants of an inch your hand sparpening would be something to behold
The choice of cutting fluid is critical and must not be taken lightly. I have witnessed many trials of cutting fluids when I was in the USA and an incorrect choice can lead to big dissapointments. It is absolutely essential to run the drill/s at the correct speed for the material being drilled. If you use a "pilot drill" or a "center drill" to start the hole, only drill down untill the hole is at full dia. This means that if you use a center drill to locate the hole and start it, dont drill more than 1.5 to 2 mm deep.

Wouldn't this depend on the size of the center drill and the length of the teat on the end


Dont drill down to the 60 degree angled section, it's simply not needed.

The whole idea of a centre drill is the two diameters if you dont drill to the second diameter why use a centre drill , makes you wonder why quallified engineers bothered to invent the center drill and why they have been in production for the last 60 years or so
A better way to do the job would be to use a short "stubbie" drill. This is a drill about 50mm long and when chucked up, the extended drill is only about 25 or 30mm past the chuck jaws. Having the drill sharpend correctly would help the swarf to clear from the flutes. The width of the "chisel" point is also critical for easy penetration, long life, accuracy and cutting efficiency. If nothing else, you will certainly end up knowing how to sharpen a drill correctly.

Kody

Mate everyone loves good advice thats why most post on these forums but lets be real you may well be a great quallified machinest with many years of training and I appreciate that but what you have posted to me does not as a quallified engineer with over 40 years in the industry does not ring true for the reasons I have outlined
Rgds

[Woodlee]

Id have to agree with Ashore here ,I fail to see how you can hand grind a twist drill to cut under size .I have knocked the corners of a twist drill cutting edge with a honing stone to make it drill on size , the side flute edges work like a reamer and clean off what the cutting edge corner didn't remove.

Most twist drill's will drill over size ,unless you creep up on the hole size by using pilot holes one or two sizes under , and the last one you use is closest to the desired hole size so the drill just cleans the hole out to the desired size.If you want a really accurate hole drill under size and then ream the hole with a reamer.

The idea of the 60deg angle on the center drill is to make a centre to locate the tail stock center for machining long shafts where you need support .It is also used for starting twist drills when drilling shafts in the lathe ,not much point (no pun intended) only drilling 2-3mm deep , when you have a nice angle there to help center and start the drill.

Of course the center drill can be used in the drill press also for accurately locating holes and easy starting of twist drills.


Kev.

[new_guy90]

I'd prefer to let the cnc drill do it's job while I go & do something else.

I usually sharpen by hand but it may be desireable to machine sharpen the cnc drill bits.

YOU CANT LEAVE THE CNC TO JUST WORK!!!!!!!!!!!!!!!!!!!!!!! ok heres the think if something happens the CNC doesnt know and it will keep going what if it was say the job slipped and it was drilling holes out the places it was meant to drill! stop thinking you can just leave it there are so many problems that can go wrong it will need to be supervised when ever it is on.

now i assume its for industrial use so are you looking to convert a drill press to do the work or do you want to completely make a new drill? if you want to leave it alone (which you shouldn't do) then an auto feed and clamping system will be needed right? so what kind of job are we talking about, like extruded rails say 50mm to 100mm wide? or plate steel with varying sizes? the former would be the easiest to make you could uses something like an automated bandsaw converted for use with the drill, if you want to do plate well............... your better off getting a conventional CNC mill but you will need sooooooooooooo much more for that

for a CNC and the jobs you want to do i would buy good quality and get a drill sharpener it will just help so much.

when you give us a clearer picture of what you want to do then we can give better advice and sorry if i went a bit over board

Patrick

Edit: if a CNC could detect a blunt drill then all the commercial CNC's would have it, if a bit is blunt then the servo would just keep pushing it and really bugger the drill...... if your trying to measure if the servo is working to hard then there is sort of a way .......look at the "CNC cookbook" they guy who runs that website did something similar for his mill but that was to measure if the gibs were to tight and strain on the mill while cutting .........have a look its a great site .........im not sure about the counter weight myself but it could work

[echnidna]

Its for drilling the holes in the posts on this website.

Its 50 x 50 x 3 RHS

If I setup the cnc I may as well do plates too

[new_guy90]

ok yeah i see what you mean but i really think a CNC would be more trouble than its worth .......maybe get your self an apprentice for these jobs lol. since the holes are at on a few different lines (i can see 3 parallel lines of holes) in my opinion i would get 3 good pillar drills and bolt a vices to each, 1 for each line, then set some jig stops so you can drill each hole in its place......... then its a matter of running each part in each drill to get what you want. i really think a CNC would be over kill for such a job as you would just be throwing money down the drain for a machine that is not very useful and will not save you much time (in my opinion) as for the auto feed well that sounds like it will save time and be easier for the operator. just get something simple like that counter weight but dont get computers involved its just not practical, a foot pedal would in my mind be very handy and hey why not just use some pullies to do it? if you use a counter weight then to increase the feed all you will need is to do is add more weight and if the bit is dull then you will be able to see it (the counter weight is no longer sufficient to supply the force needed for the drill bit to cut properly so it will feed slower and maybe stop cutting)

ok thats just my opinion, i think the kind of work you need it for doesn't need it so why bother when a simpler solution is at hand.

good luck

Patrick

[Kody]

Hi Ashore
with 40 plus years in machining your comments are hard to figure. However, why run a center drill down into the 60 deg angle section when It's not really required? I only use the 60 deg cutting edges when I need a "turning center" or If I simply must have the tapered hole to form a chamfer in a special hole. No problem, I see we all do our own thing the way we have had the best success and thats the important part.
As for sharpening drills by hand, I had to make an extension for a 1/32" dia. HHS twist drill using a 2" length of silver steel. The 1/32" drill was soldered into the end of the silver steel shaft. I then had to sharpen it so it would drill hundreds of holes that conformed to a tolerance of +0.0005 to +0.001. The hole formed a bearing for a very small shaft. Every tenth hole was tested with "Go/NoGo" plug gages. The original drills were made in a tool room, were very expensive and were broken every 3 or 4 days at the most. The drills I made were shaped and sharpend by hand using a high power eye glass (a watchmakers loupe) and an ultra fine diamond hone. They lasted for 3 to 4 weeks and they ran all year in production at 20,000rpm.

Kody

[Ashore]

Hi Ashore
with 40 plus years in machining your comments are hard to figure. However, why run a center drill down into the 60 deg angle section when It's not really required?
Thing is why use a centre drill if you are not going to use it for what ir was designed , just use a small drill
I only use the 60 deg cutting edges when I need a "turning center" or If I simply must have the tapered hole to form a chamfer in a special hole. No problem, I see we all do our own thing the way we have had the best success and thats the important part.
As for sharpening drills by hand, I had to make an extension for a 1/32" dia. HHS twist drill using a 2" length of silver steel. The 1/32" drill was soldered into the end of the silver steel shaft. I then had to sharpen it so it would drill hundreds of holes that conformed to a tolerance of +0.0005 to +0.001. The hole formed a bearing for a very small shaft. Every tenth hole was tested with "Go/NoGo" plug gages. The original drills were made in a tool room, were very expensive and were broken every 3 or 4 days at the most. The drills I made were shaped and sharpend by hand using a high power eye glass (a watchmakers loupe) and an ultra fine diamond hone. They lasted for 3 to 4 weeks and they ran all year in production at 20,000rpm.
As I said sharpening by hand to that tolarence would be something to behold, even with a loupe my eyes wouldn't be up to it , I sharpen by feel and memory these days though I still get a better result than those comercial drill sharpeners
Kody

Yep we are all diffrent in our approach to a job , as long as the result is there , but thats what makes the world go round.

[blackfrancis]

Hi Bob

Many years since I worked in the trade but in my youth I did an apprenticeship in a factory that was full of CNC machines that were run around the clock. I never ran them much myself but paid attention to what was going on when I was there. There were several machining centres which drilled a large number of holes, about half inch. These drills were resharpened on a speacial machine which put the same edge on as a new twist drill has. I pressume they had a set schedual for changing the tools, but I often noticed that parts would be turned out that were discoloured near the holes due to the drill being blunt. That was with a flood of coolant of course.

With what you want to do you should be able to drill quite a few posts between sharpenings as the holes look like they are only through relatively thin section. I don't see any reason why you couldn't put a part in, leave it to be done and asses whether you should change the drill when you come back.

With regard to starting the holes. I'd be thinking about making a holder that only lets the drill protrode just enough such that it would be self starting.

Cheers
Steve

[echnidna]

Hi Bob

Many years since I worked in the trade but in my youth I did an apprenticeship in a factory that was full of CNC machines that were run around the clock. I never ran them much myself but paid attention to what was going on when I was there. There were several machining centres which drilled a large number of holes, about half inch. These drills were resharpened on a speacial machine which put the same edge on as a new twist drill has. I pressume they had a set schedual for changing the tools, but I often noticed that parts would be turned out that were discoloured near the holes due to the drill being blunt. That was with a flood of coolant of course.

With what you want to do you should be able to drill quite a few posts between sharpenings as the holes look like they are only through relatively thin section. I don't see any reason why you couldn't put a part in, leave it to be done and asses whether you should change the drill when you come back.

With regard to starting the holes. I'd be thinking about making a holder that only lets the drill protrode just enough such that it would be self starting.

Cheers
Steve

I should have thought of that , thanks

[new_guy90]

here just thought i would share this, the largest CNC mill at work has a table about oh 2m by 1m and i was told to buy new would cost 11million!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

back to the drills what brand are you using right now? it may hurt the back pocket but i would buy a some drills from the higher end of the market and work out what works best ..........and a drill sharpener got to have one of those

Patrick

[Ray39]

How Long Does A Drill Bit Last between sharpening.

I'm thinking of making a cnc drill for repetitive drilling, I'll setup a coolant/lubricant feed.

As I see it the biggest problem may occur when a bit goes dull and the computer keeps trying to drill more holes. I can't think of any way for the cnc program to detect a dull bit. So I expect the bits need to be retouched before they dull off. But how long does a bit last?

Next question,
What is the name of the the twist drill bit that has a small centre drill on the cutting tip?

Hi all
As a useless piece of information the correct name for a centre drill is in fact a Slocomb drill, no idea why it was named this way maybe he invented it back in the dark ages
Ray

[Big Shed]

Hi all
As a useless piece of information the correct name for a centre drill is in fact a Slocomb drill, no idea why it was named this way maybe he invented it back in the dark ages
Ray

Slocomb is to centre drill what Biro is to a ballpoint pen

http://www.mail-archive.com/sslivest.../msg01154.html