Thread: How Long Does A Drill Bit Last?
21st Feb 2009, 09:08 AM #1
How Long Does A Drill Bit Last?
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?
What is the name of the the twist drill bit that has a small centre drill on the cutting tip?
21st Feb 2009 09:08 AM # ADSGoogle Adsense Advertisement
- Join Date
- Advertising world
21st Feb 2009, 09:24 AM #2
To answer the second question first, Bob, is It a "centre bit" that you're thinking of? For drilling the centre hole in metal for lathe work.
To answer the first, I've been told that if you have the skills to get your drill bit sharpened properly, and have the right amount of pressure on it during drilling so that a consistent curl of metal is spun out of it, a type of self-sharpening process takes place and drill bits can last for ages. But we need someone like Ashore or Woodlee to confirm or deny this.
21st Feb 2009, 09:50 AM #3
What about Auto sharpening? Put one of those drill doctor thingos within reach of the CNC and get it to go there for a touch up every 20 or so holes?
21st Feb 2009, 10:31 AM #4
MMMM how long is a piece of string?
There are many variables that will play the field here ,what type of material you are drilling , speed of the drill , feed rate ,coolant and the angle that your drill is sharpened.What type of material the drill is made from ,ie HSS , Cobalt HSS or carbide, stellite.
One would need to make sure your sharpening angles are correct for the type of material ,and that your speed and down feed are at the correct rate.
One helpful source for such information is Suttons who make twist drills.They have or had a small booklet full of information on such matters .
As far as auto sharpening goes ,I guess a certain amount of wear on the drill would achieve this , but the geometry of a correctly sharpened drill presents the cutting edge to the material at such an angle to enable it to cut much like a chisel , behind the cutting edge is the rake angle which is clearance for the cutting edge .To sharpen a drill you need the grind the whole face down along the rake angle . As the cutting edge on a drill wears it become slightly lower than the rake angled face behind it which causes rubbing rather than cutting .
Coolant is important for not only removing heat from the cutting edge , but also a lubrication for both the cutting edge and the drill swarf .Swarf that packs tight into the flutes holds heat ,can jam between cutting edges up along the flutes and the job and creates more heat and possible breakage of the drill
Center drill maybe , but I have a set of Dewalt Extreme drills I bought just recently ,I thought they would be good for wood drilling,as brad points .They have a smaller diameter starting tip to start the hole for the larger true diameter of the drill.Much like a step drill for counter boring holes for socket cap screws.They are murder on acrylic , absolutely grab the material and cause major havoc.Lousy on wood too ,I mean they drill holes ok ,but cause chipping and splintering on exit holes.
I was planning to do a review on them and post in the forum.
Just thinking on how we sharpen drills ,I use a bench grinder and use a coarse and fine wheel for finishing ,then straight to the job with no thought on the condition of the cutting edge .To my mind it must be a series of grooves much like a serrated knife ,would the cutting be better if it was honed to a finer edge like we do to our wood chisels , plane blades and lathe tools?
Kev."Outside of a dog a book is man's best friend ,inside a dog it's too dark to read"
21st Feb 2009, 10:36 AM #5
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.
21st Feb 2009, 10:46 AM #6
why would you need a CNC drill press/machine?
ok as for the drills i know that there are charts you use when programing the NC's showing the RPM the feed, size of the drill and i think you need to consider the material you are using ........if you use these calculated feeds and speeds then the drill bits will last a very long time for most applications so much so i dont think you need to worie about them going blunt oh and i would be using a proper cutting oil ......um yeah i dont think coolant should be needed would just make more of a mess. if you have to drill lots of holes for stuff why dont you get a gang of drill presses will be so much cheaper and maybe put auto feeds on the quills so you can get that good feed into the material oh and buy good D-bits Sutton is good we use them at work.
you really haven't given us much info as to what you want to do with this CNC, is it for commercial use or home use? what kind of jobs do you want this for? what material do you want to drill?
hope i can help
21st Feb 2009, 12:07 PM #7
The cnc drill is for drilling hundreds or thousands of holes in mild steel plate and RHS etc,
The cnc will only speed the actual drilling process a little bit.
But as it can be set and left to do the drilling it eliminates many man hours of work, freeing time up to do other tasks.
Using pilot drill bits should mean lower probability of wandering,eliminating centre punching and layout times.
Cnc also gives repeatable accuracy.
Thanks to everyone for all the excellent advice
Thanks Nev, I couldn't think of the name of the Pilot Drill Bit.
21st Feb 2009, 12:11 PM #8
less than 15 seconds some times Bob especially if they are 1/8" and less
They break far to easy
21st Feb 2009, 12:16 PM #9
Pretty well what every one has said if you get all the variables right coolant, speed, feed, for the material you are drilling , drill cutting angle , type of drill and material the drill is made from
It also depends on how you are sharpening the drill , by hand or machine sharpening
BTW are you going to set this cnc up and walk away or will you be monitoring it , you can see a drill getting blunt by the shavings that are comming off their colour size etcAshore
The trouble with life is there's no background music.
21st Feb 2009, 01:28 PM #10
I'd prefer to let the cnc drill do it's job while I go & do something else.
As a drill bit gets blunt it will take longer to drill a hole given the same feed pressure,
So the obvious feed method may be by counterbalance with an cnc rewind.
When the time to drill increases too much its then time to resharpen.
It may be better practise to swap drill bits each say 1000 holes and avoid dulling problems that way.
I usually sharpen by hand but it may be desireable to machine sharpen the cnc drill bits.
21st Feb 2009, 02:00 PM #11
The machine sharpen is the way to go that way the drill is constant and you can work out a suitable time interval to change.
When I was working with one we changed the tools with each run and never made that many , usually 100 max , a lot of stuff was 1 off for a specific task , the last cnc stuff I worked with was in the early 70's when it was in its infancy and Newcastle steel works only had 4 cnc machines and I worked on one for 3 months as an apprentice, so I am curious as to how you monitor feed pressure , is the feed not a mechanical amount ,Ashore
The trouble with life is there's no background music.
21st Feb 2009, 04:47 PM #12
That's why I'm considering a mechanical feed using a counterweight (cable and pulley is simple & reliable) which is merely released by a cnc controller and reset to up (home) position by a cnc motor.
21st Feb 2009, 05:02 PM #13
What thickness material are you think of drilling,you would probably have to peck.
21st Feb 2009, 06:49 PM #14
3mm and 6mm thick steel
21st Feb 2009, 09:03 PM #15
To detect a blunt drill bit: surely the drill motor would draw more current, so some form of current monitor would send data to the CNC controller board & computer. When the current draw falls outside a certain range, it stops drilling & signals for human intervention. This should also work for other sorts of machine problems too such as broken drills.
The latest FWW has a similar setup shown for their saw blade test, they use a 'clamp on' type of multi-meter to measure amperage drawn by a table saw.
By bannock in forum GENERAL & SMALL MACHINERYReplies: 2Last Post: 21st Jun 2008, 09:09 AM
By Dean in forum WOODWORK - GENERALReplies: 2Last Post: 26th Nov 2007, 09:56 AM
By JB in forum HAND TOOLS - POWEREDReplies: 6Last Post: 22nd Jul 2006, 09:43 PM
By BassTeQ in forum HAND TOOLS - POWEREDReplies: 18Last Post: 9th Sep 2005, 10:16 PM
By kenmil in forum WOODIES JOKESReplies: 5Last Post: 5th Apr 2004, 12:49 AM