Problem drilling 5160

M

Marcus

Joined
Oct 4, 1998
Messages
622
I was trying to drill holes in the grip area of the 5160 knife I`m working on and ran into some problems. The 1/8" bit I used to make pilot holes and grip pin holes worked fine but when I went to anything larger I could only drill down 1/8" before the bit would stop cutting and start to squeal. I was lubing the bit as I drilled and didn`t let the bit get too hot. The bits are almost perfect except for a slight rounding of the extreme corners. The same bit goes through mild steel fine. I reasoned that I must not have gotten all the hardness out of the blade stock when I heated it. So I heated the grip area again to bright orange and let it cool on it`s own. The bits still don`t cut. BTW these are cobalt bits and all either new or only slightly used. I`m perplexed,what am I doing wrong? Marcus
 
Marcus first off I think your drill bit is bad, you can resharpen it if you didn,t take the temper out of it. The reasosn I think the bit is bad is I use cobalts bit to drill harden steel RC60 and it will work.

But I think you got other problems too. You said you heated up bright orange ok how hot is that? If it is not ~1440-1550 it will not do much. An easy way to get right temp is with a magnet, when it doesn't stick you are there. Now how do you cool it? I have found that air cool is to quick. I heat it up to temp and put it in a hot box to slow it down.

The hot box is just a metal box filled with vermiculite. I do it at least three times.


 
I ran into the same problem once when trying to drill a lawnmower blade, which is really tough steel. After ruining a drill bit, my neighbor, a retired millwrite, drilled the hole with his drillpress, but he turned it down to a much slower speed. Don't know why but it sliced through that tough steel like it was butter.
 
Don`t think the prob is the bits,I tried several new cobalt bits and they didn`t work either except forthe real small ones(?!). They`re not getting too hot either,I`m spraying lube on them constantly and they`re not discolored. They still have a sharp edge as well,except for a few thousandths at the extreme outside edge and that`s not even that bad. I`m sure I got the steel hot enough the second time as it was starting to puddle(waayyy past non magnetic,maybe too far past?). The cooling rate sounds like it might be the ticket. That might just be why it seems to grind so hard too. I`ll whip up a halfa$$ed hotbox tomorrow. How about a steel pan full of glass beading media? I can fill it half way up toss the hot blank in and cover it with a few inches of blasting media and a lid. I`m also going to check the Blades n Stuff tech notes and see what speed I should be drilling this stuff at. Thanks for the tips. BTW I did find a way around drilling the big "balance" holes in the drill press. I used the "HOT drill"
wink.gif
Marcus
 
I have not used glass beads, so I don't know how they will work. But anything is better than nothing. As long as it can handly the heat. I have used floor dry(kitty litter)some people use lime some use ash or sand almost anything that will slow down the colling will work, Some just better then others.
 
Hot boxes are a real good Idea. Lime works well also.. BUT If you are trying to cool a part slowly its a good idea to preheat the material in the box first. If its cool you can harden the part..
Next .. after annealing the part you may still have problems drilling the same hole..
If the hole has glazed it will be a tough time redrilling it.
You may want to slow you SFM down on the drill . Say 200 rpm or so when you drill 5160 from now on. If you want to save the part order a solid carbide spade drill and drill it with that. Take your time . Run the drill at about 1000 rpm with light pressure. Put a scrap of wood under it for cushion when the drill goes through the part so it dont chip. They are about 7-8 dollars . There nice to have around in case you run into stuff like this.. Then you dont have to stop the project to anneal.


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Thanks for the tips Darrel I`ll give them a try tomorrow. I wouldn`t have thought of heating the media in the hot box,I`d really have been beating my head against the wall with that one(trying to figure out why the steel was still too hard).
wink.gif
Marcus
 
marcus,
You said that you were drilling pilot holes first? You could be heating and glazing the material around those holes when you drill the pilot.
Do like darrel et al said and anneal the blade. Then, if possible, drill new holes full size in one pass, with as slow a speed you can get with your drill press and flooding with cutting fluid. No pilot holes.

If you have to use the same holes, one trick that might get you through this one job is to pick up a cheap masonry bit that has carbide cutters and just run it dry with light pressure. I've used them to bevel holes, and you can do a lot before the carbide gives up and starts chipping off the bit.

madpoet
 
Darrel is correct. The spade drill will do the job. I use a spade drill for my detent hole in the tang of my blades. This is after the knife has been heat treated to 59-60 RC.


 
The glass bead media "hot box" worked fine. It took about 4 hours for the blade to cool from orange hot. I didn`t get a chance to try drilling it but I did take a file and grinder to it and it does seem somewhat better (ie.softer). Thanks for the tips,my knives are coming along nicely thanks to all the help. Marcus
 
Here`s an update on the drilling saga. Still no luck. Small bits whiz through,larger ones go so far and stop. The just sit there squealing. I may try a different brand/type of bits. The prob may be the drill press I can only set it down to 600rpm,could this be too fast? In the mean time I`m drilling holes for pins and burning out larger holes for balance. Lucky I`m good with a torch.
wink.gif
Marcus
 
ok how big of hole are you trying to drill?
your pilot hole should be no bigger then 1/3, your big bit needs at least 2/3 for it to drill right.
 
Good idea Darrel,I`ll try it on Mon. I don`t think the belt`ll stay on long if it`s more than 1 groove off so I still may not be able to get the speed slow enough,but it`s worth a try. Greg,my pilot holes were all 1/8". I tried just about every size drill in the index with them up to 1/2". Marcus
 
Thers the problem.. You can offset the pullys also by loosening the set screws and realinging the pullys. SFM x 3.14 / the drill diameter at 50 sfm = about 300 rpm. For the 1/2 in drill . Your burning them up. Try to get your speed down or buy a carbide drill.


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Web Site At www.infinet.com/~browzer/bldesmth.html
Take a look!!!





 
Hey Darrel how did you come up with that?
It could come in handy, heck I just look at the speed and guess is it to fast or not? I don't even know what speed I use. But I would like to know how did the numbers?
Where did you get 50sfm is that a rule of thumb? and what is it for other bits? I do get how you did the math just not the constant.
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Thanks again Darrel,that explains my prob. I`ll try moving the pullies and see what happens with bits in the smaller range and invest in a carbide drill or two for the bigger stuff. Gee, you`re a handy guy to have around.
smile.gif
Marcus
 
The machinerys Handbook has speeds and feed for most all metals. Its a bit on the expensive side 50.00 . But that being my trade for 27 years I have a few copies. It also has other info that is of great help. Like screw head sizes , body sizes, ect. IT has many subjects ... gears, screws, trig.
The book itself is about 4 inches thick full of all kind of info.

The story.
When first starting my machinist training the first rule was you had to know all the speeds and feeds for most materials.

The sfm I use was an average. It says 5160 then gives differnt hardnesses in the book. So it went in the middle. 30-85 sfm was recommended.. So i used 50.

The formula again is sfm x pi (3.14) / the dia

dia = drill dia, turning dia, end mill dia..
This book is availble from MSC or J&L industrial supply
Note SFM is a GENERAL starting point to caculate speeds of drilling, turning , milling..


------------------
Web Site At www.infinet.com/~browzer/bldesmth.html
Take a look!!!






[This message has been edited by Darrel Ralph (edited 18 January 1999).]
 
Thanks Darrel, I am going to buy that book! I think I will buy it with buy tool allowance. I work Maintenance at a factory and get $300.00 year allowance, The book will be my first thing this year.
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As Darrel posted, the spade point carbide bits work very well on hardened steel, and for my money, the HI-Roc (at about $12-$14 apiece) seem to last longer than the cheaper ones. I also peck at the hole, never allowing the point to linger in the hole.
Harry Jensen
 
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