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CENTER DRILL PROBLEMS

Tinyfxds

By Tinyfxds,
in Industrial Forum

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Tinyfxds Newbie

Tinyfxds

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I can never seem to get my center drill depths correct.  I have a chart that tells me how deep to send a center drill to get "x" diameter chamfer but when I go to verify it in Mastercam, it shows it's going too deep. Now it doesn't make a difference if it's a 60 degree or 90 degree it always shows that it's going deep.  I'm missing something here, could my center drills be built wrong?

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Tinyfxds Newbie

Tinyfxds

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I am not using tip comp for the center drill operation.  Everything I am finding shows that whether I use a 60 or 80 deg center drill Mastercam has it built correctly it just doesn't verify correct.

 

I prefer to use a 90 deg spotting drill.  It's much easier to control depth.  Some people, especially those doing production work, don't like that because of undue wear on drills, but for the work I do it's as close to perfect as I can get.

I was using a spot drill but we are having a problem with the drills walking a little bit.  We are using .098" diameter drills so we are thinking that the center drill option will work better

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Micromoldmaker Newbie

Micromoldmaker

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I was using a spot drill but we are having a problem with the drills walking a little bit.

I don't know if this would work for you: when I have small holes that need to be as straight as possible (core pin holes, eg)  I "bore" the drilled hole with an end mill that's slightly larger than drilled hole and smaller than reamed hole.  On small holes I do on occasion use a center drill; a new one that's very sharp and I only drill deep enough to start the hole, usually no more than .015 deep.

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Tinyfxds Newbie

Tinyfxds

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If your drills are 135 Deg point I would use a 140 Deg spot drill. I find I get the most accurately drill holes with them. That's what they are designed for. Center drills are designed to drill for centers, not for spotting drills.

I agree.  We are trying to work with what we got.  I like using 90 degree spot drills simply because a lot of the stuff we do calls out for a 90 deg chamfer on drilled holes but using a 140° would be a small inconvenience if the holes turn out correct.

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slyym Newbie

slyym

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I agree.  We are trying to work with what we got.  I like using 90 degree spot drills simply because a lot of the stuff we do calls out for a 90 deg chamfer on drilled holes but using a 140° would be a small inconvenience if the holes turn out correct.

 Yea I always liked using a 90 Deg cause you can chamfer with it too.

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Bob W. Apprentice

Bob W.

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If your drills are 135 Deg point I would use a 140 Deg spot drill. I find I get the most accurately drill holes with them. That's what they are designed for. Center drills are designed to drill for centers, not for spotting drills.

Agree.  I have done testing and the amount of drill 'walking' was the same when using a center drill or nothing at all.  When properly using a spotting drill (120 degree for 118 degree drill, engaging short of the shoulder) the holes were perfect.

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Sticky Newbie

Sticky

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Maybe a stupid question, but are you using the calculator for depth and entering the tip flat dimension? At the machine it will be correct, but verify does not show tip dia., just a point so it will verify incorrect. If you need an accurate verify you must build a custom tool.

 

 

I'd bet this is the culprit. What mastercam actually want to know is the web dimension. Why they call it a flat I don't understand, it's obviously not a flat.

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Newbeeee™ Community Regular

Newbeeee™

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On a close tolerance location, I'll put a tiny spot, then drill, then come back for edge break. I get zero walk this way.

Foggy, we run the OSG's in hydraulic Schunk holders. We drill, followed by a 90deg spot to deburr the hole (and all other milling).

We've never noticed an issue with drill wander (talking ally and stainless parts with positional tolerances of .002 tightest).

That said, we don't do any of that highfalutin work that you do :D

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Sticky Newbie

Sticky

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Absolutely agree, we drill lots of 15-20XD holes this way

 

What kind of drills are you using that go 15-20xd with only a spot as a guide?

 

We do like Newbee, we put a hole in the same diameter 1-3xd first before we stuff a 20xd drill in there.

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Eric@HorsepowerInc. Newbie

Eric@HorsepowerInc.

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What kind of drills are you using that go 15-20xd with only a spot as a guide?

 

We do like Newbee, we put a hole in the same diameter 1-3xd first before we stuff a 20xd drill in there.

Guhring, its the only way to go! Great quality in deep hole drilling. I actually contacted them before hand, they specifically said to use 140 deg. spot before hand only. Almost 1000 parts in on this one job in particular and I'm a believer. I will say I haven't got up to there recommended speeds and feeds, but very happy where were at. edit: I do want to state the no pre drill hole is a 3/4 dia. , we do however pre start the 17D hole only because it is a .296 dia drill and worried about breakage that other tooling would suffer from on connecting ports. Even so, we only pre drill .25 deep so we can enter/ ramp spindle and have at it without affecting the hole geometry as these are AN- ports.
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Sticky Newbie

Sticky

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Guhring, its the only way to go! Great quality in deep hole drilling. I actually contacted them before hand, they specifically said to use 140 deg. spot before hand only. Almost 1000 parts in on this one job in particular and I'm a believer. I will say I haven't got up to there recommended speeds and feeds, but very happy where were at. edit: I do want to state the no pre drill hole is a 3/4 dia. , we do however pre start the 17D hole only because it is a .296 dia drill and worried about breakage that other tooling would suffer from on connecting ports. Even so, we only pre drill .25 deep so we can enter/ ramp spindle and have at it without affecting the hole geometry as these are AN- ports.

 

So you are using a .75" drill that is over 12" long with spot only? And you get good size and hole location?

 

I have a job I drill .656" 13" deep in 4340htsr, but I put 1.5d worth of pilot hole in it before I crank that drill up, we feed it pretty hard too.

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