Problem- Trying to drill many #8 holes.

[ErnieD]

Hi,

I am trying to drill many holes through .500 thick 12L14 with a #8 drill using a Tormach PCNC1100 milling machine. I am running the spindle 1800 RPM's amd feeding 4.5 IPM. The holes are larger at the top (drill entry side). What am I doing wrong?

Thanks,

ErnieD

[Delw]

are you spot drilling them first? if you are then you have a bad drill.
if your peck drilling your drill has run out, is not centered or you have a bad drill.

how much bigger whats your tolorance? 12L14 cuts like butter

[egyptandjustice]

Hi my name is Jerry and I am new to this forum. I am just starting my apprenticeship in the field and dont know much. But I would say that your bit is brobably dull, causing slow feed and It may be walking toward the top of the hole causing it to be bigger. Have you tried putting a split point on the bit?

[cam1]

Hi: Rule of thumb: anything deeper than 3D of drill is considered to be a deep hole... you could center drill with a #0 center drill, then drill peck your way through with a high quality, yes high quality drill. the split point is only an advantage if you choose to ignore center drilling.Small drill, high speed, low feed...no frr lunch in the universe for precision.
The rule of 3D rears it's ugly head a number of times in the trade.
No worries C12 is the easiest material to drill aside from your finger.

regards

[Belding]

Originally Posted by cam1 the split point is only an advantage if you choose to ignore center drilling.

They take a lot less pressure to push through.

[cam1]

Good point, I stand corrected.

regards

[kalmah]

Do you do center hole before drilling ?? If not, your drill MUST have a web thin if you don't want to have a hole diameter to large at the top.

[egyptandjustice]

Hey I'm learning alot from you guys but I do have a few questions. What is frr and 3D mean. Please excuse my ignorance.

[davereagan]

No one asked a couple of really important questions. Are you using a screw machine length drill? This makes all the difference. It will still have plenty of flute depth for 1/2" material, but there would be no need for a center drill and the loss of time. A jobber length drill will wander around without a center, which explains the larger top side of the hole. Also, using a split point is important too for not having to center drill. I would raise the feed rate to atleast 9 inches per minute. That is only .005" fpt, which I use in 1018 CRS. Your material is nearly twice as easy to cut. Are you using flood coolant? I would probably drop the revs down to 1500 and not even peck drill. Also, make sure your runout is under .003" at the end of the drill if you can. McMaster.com has a split point cobalt #8 drill for $2.87 and you could do several thousand holes on one drill if you flood with soluble oil. The part number is 28765A58. Their UPS ground shipping is really reasonable, starting at $4.25 for Michigan. The guy who gets paid big bucks for making a couple holes perfectly thinks a lot differently than the guy who gets paid a little per hole for many holes. I happen to be both guys. LOL.

Good luck,
Dave

[dertsap]

holes that are larger at the top are due to one of a few factors , no spot , dull drill , drill has been ground improperly and is offset , crap built up on the drill due to poor chip extraction and rubbing the edges of the hole wearing the top of the hole open ,drill is too long as was pointed out already , pushing the drill too hard , cheapo drills made from inferior materials


change the drill and try again

[g-codeguy]

Originally Posted by egyptandjustice Hey I'm learning alot from you guys but I do have a few questions. What is frr and 3D mean. Please excuse my ignorance.

Based on the context, frr is misspell 'free'. As in no free lunch. 3D means 3 times the diameter. Thus a #8 drill's first peck would be .597 deep.

Apparently I am doing something wrong, as I find this rule to be true only with smaller drills. Try going 1.5 inches deep in 316 SS with a 1/2 inch drill in one peck. Doesn't work for me! Nor will it work with 52100. If anyone knows how it is done, please enlighten me. I would love to know how.

[cam1]

The rule of 3D basically states that any hole deeper than 3 X the diameter of the drill, should be treated as a deep hole. It does not imply the depth of the first peck.
I usually go in at least 1.5D on the "first peck" to avoid chatter, as the drill generally pilots itself on it's diameter at 1.5D. After that, I usually reduce the peck depth. The depth of peck is a variable that's workpiece and tool geometry dependant ie don't peck into work hardening materilas, and softer materials like aluminium tend to get long stringy chips on too deep a peck....

regards

regards