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Drill heat treated 4340


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I am drilling about 20 holes in heat treated 4340 and I am having problems with the drill breaking on every other part.

 

Drill size #40 (.098)

speed 600 RPM

Feed .4 ipm

peck .025

depth z-.400

 

I am pre drilling with a #2 center drill and the # 40 drill is held in a keyless chuck. I have tried both HSS black Ox and Cobalt drills and have not had much luck with either. The drill is getting plenty of coolant, and the drills are spinning true within .001. Any advice would be greatly appreciated.

 

Merry Christmas,

 

Justin

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Thanks for the replies. With what kind of drill Toolman. Also do you have any reccomendations that are not to expsensive. Maybe a certain brand, material, tip angle, coating, etc. Unfortunately one of the areas my company likes to cut costs in is tooling and it can be hard to convince them to buy higher quality tools.

 

Thanks again.

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Eric I totally agree about the cheap tool issue. When this job is finished I will have to add everything up, lost time included and show my boss how much he didn't save us. The hardest part is getting him to take the risk of buying something a little more exspensive, but if I can show him how it is less exspensive in the longrun he will be all for it. I will look into that OSG VPH-GDS

 

Thanks

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quote:

You may want to look into Guhring drills also.


As you can see, there are lots of options.

Hardmill is right, guhring makes excellent drills too.

next time you have a lot of holes like this to do, call a rep in and they could help you out. Sometimes they even give guaranteed trials (you don't buy the drill unless it proves to be cheeper in the long run) idea.gif

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quote:

I find that centre drills can be harmfull sometimes. Maybe try a spot drill with the correct angle

I agree with this 100%. I'd use a 120° carbide

spot drill to spot the holes. The 60° walls

made by a center drill can damage the cutting edges of the drill.

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we drilled 3550 hloes in pre h/t 4340, using 1/16 dia. guhring drills 5/8 dp. changing the drill every 70 holes. with only 4 broken drills.

 

$8.44 per drill. then we tried a cheaper drill on the next part. $ 1.75 per drill same speed and feed. 3550 holes 20 broken drills. $500.00 t0 burn out the broken drills. I think the extra money for the drills pay for them selves.

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I have found when drilling hardened material that it is best to not center drill so deep that the major diameter of the hole created is as large or larger than the drill. Just drill deep enough to clear for the web of the drill. If the corner of the drill is what contacts first, you will wear the corner off the drill and cause it to bind and break. I drill hardened H13 (52-56RC) quite often with HSS drills down to .020 diameter.

 

+1 on the stub drill.

 

Cheers,

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