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 Author | Topic: Carbide drill rescue (Read 166 times) |
daveb1
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|  | Carbide drill rescue
« Thread Started on Oct 8, 2009, 3:29pm » | |
Hi all,
I snapped the tip off a center drill(HSS) in a bevel gear as I was setting up to ream it out. Will a carbide drill go through this tip to clean it out??
Thanks
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Dave Barker |
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Dan Rowe
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| | Re: Carbide drill rescue
« Reply #1 on Oct 8, 2009, 8:29pm » | |
Hi Dave,
I hope some one has a better answer then I have. I know the sound of one of those breaking in a work piece.... nasty sound.
It will just ruin a good carbide bit by chipping it. There might be some types that are used in hammer drills that can take the punishment but I have not tried that type.
My usual method is to fracture the embedded bit with a center punch or some other suitable piece of hard steel that will reach the broken bit end. Work out the pieces with tweezers or needle nose pliers if they will fit. This does not leave a pretty sight which is why I hope some one has a better method.
I have heard of using EDM to remove broken taps in a work piece and if you know some one that has one of those it will work.
Good luck Dan
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trainlarry
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| | Re: Carbide drill rescue
« Reply #2 on Oct 8, 2009, 8:47pm » | |
Dave,
If you have a hole clear through the gear already, you can try and punch it out from the other side. If you were just starting a hole, you can try prying out the tip with a pick or small jewelers' screwdriver. Do not use a carbide drill, as it probably will break off also, or it will chip and be worthless. Use a carbide end mill instead, and go slow. If the gear is not steel, (brass, bronze, etc.) get some alum from your supermarket spice section, and dissolve as much as you can in a non-steel container or bowl of hot water. You only need enough solution to cover the gear. Keep the water hot on the stove, and watch the bubbles from the broken tip as it is dissolved. If the gear is steel and all else fails, you can anneal the gear and tip, and then you will be able to drill it out.
Larry
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kenrinc
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| | Re: Carbide drill rescue
« Reply #3 on Oct 8, 2009, 10:46pm » | |
Oh man, been there. Heartbreaking. Take a deep breath and get a pair of loupe's on and take a look at what you have. I just did this a couple weeks back when drilling the two holes at the front of the main frame (1.5" scale). I spent the rest of the evening getting out that piece of carbide. What I did was start banging on it with the tip of a center or prick punch. I would hit it at all different angles trying to dislodge it. After awhile, believe it or not, it came right out using a scratch all. Other times I've had to heat it up with a torch (with a broken tap) but I'm not convinced that did anything. You have to get even HSS really hot to do anything for you.
Ken-
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daveb1
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| | Re: Carbide drill rescue
« Reply #4 on Oct 9, 2009, 8:56am » | |
Hi all
Thanks for saving me the cost of a carbide drill. Possibly I can drill holes around the tip. If this can be done it should be an easy matter to pry the thing out. Off to try!!
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Dave Barker |
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daveb1
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| | Re: Carbide drill rescue
« Reply #5 on Oct 9, 2009, 2:13pm » | |
Hi all
Success! I managed to drill 3 holes around the edge of the broken tip. Then pried around but couldn't budge it. Finally took the broken center drill rechucked it in drillpress and went for broke. It must have dislodged the tip before it shattered, because the tip was gone. Finished reamming and all looks well.
Thanks for the help.
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Dave Barker |
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kenrinc
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| | Re: Carbide drill rescue
« Reply #6 on Nov 4, 2009, 4:42pm » | |
Just finished breaking a tap doing the holes for the pedestal binders (1.5" scale). Broke off well in the hole. I mulled over this for awhile, partly because I was so pissed, better to back off and think about it but in the end I had a bunch of used carbide endmills I had bought on ebay. Took a 1/4" endmill with a 3/8" shank (you need the stiffness) and with the speed way low I plunge milled right through it. I tried an 1/8" endmill at first but it wanted to skid and break off. The bigger mill was way better. Of course I had to tap the hole 5/16-18 instead of 10-24 but hey, it works and nobody will see it.
Ken-
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trainlarry
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| | Re: Carbide drill rescue
« Reply #7 on Nov 4, 2009, 9:19pm » | |
The worst sound in the world is hearing a drill or tap break. There are tap extractors available that can help to successfully remove broken taps, especially the bigger sizes. Learning how to tap properly will minimize tap breakage. The usual cause of tap breakage is over-torquing it, caused by either a tap that gets jammed because of chips, or a tap that is started crooked, jams, then gets over-torqued and snaps. Dull taps will break also. Use spiral tip or gun taps for through holes to help push the chips out of the hole. Blind holes are always a cause for consternation. I do 2 or 3 turns, back out 1 or 2 turns, then continue, to help clear the chips. For best results, and peace of mind, I use spiral fluted taps for blind holes. The spiral flute helps eject chips back up the hole, not packing them in front of the tap. Expensive, but worth it. Most importantly, always guide the tap to start straight. The best tap wrench to get is the General brand 'T' handle tap wrench with guide. The guide fits in a drill or mill chuck. Using that will always start a tap straight. Lastly, always use a good tapping fluid. The hardest part is learning what the proper torque is for a given tap, and to not exceed it. Proper tools, and a few simple rules, will help remove thread tapping as the most dreaded part of the job.
Larry
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Dan Rowe
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| | Re: Carbide drill rescue
« Reply #8 on Nov 6, 2009, 5:23pm » | |
There is a useful tool for extracting broken taps all the way down to a #4 or 3mm. These are made by the Walton Co. see: http://www.waltontools.com/products/extract-machsc-hand.htm
I have rarely had to use my set but when needed they are worth the money spent and then some. If it was a small tap wait until the next day.... until your nerves have settled down.
I use a lot of taps smaller than this all the time and they are the ones that give me grief. I have just switched to thread forming taps for the small stuff. I do not have enough experience with them yet but a larger hole is used and the tap is stronger. They are only good for ductile metal but my main use is silicone bronze castings or gunmetal.
The tap hole size is OD - 1/2 the pitch for 75% thread engagement not the usual OD - pitch for 75% threads for cutting taps.
There is an information article in the MSC catalog about thread forming taps and a formula for different percentages of thread engagement.
Dan
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