Drilling 1.375 hole

[heeler]

I am trying to drill a hole that is 1.375" +or- .010 for 4.2" deep and then it is 1.308" +or- .002 for another 1.3" for 5.5" deep total. They have given me a 1" thru the tool coolant HSS drill, 1.307" core drill HSS, and a 1.375 core drill HSS. They claim that this is how they've done it in the past. I have been unable to get acceptable results. Would anyone have some suggestions for feeds and speeds. This is in 7050 T7451 aluminum and the tools are 9 - 10" long.

 

Thanks

Glenn

[Eric S.]

I would prefer to mill it out or use a boring head. If you have the tools?

just a thought

[heeler]

I don't have an endmill long enough or boring bars long enough.

[MACHINEMASTERG]

???? whats a core driLL ?????

[heeler]

I't basically a 4 flute drill that is suposed to hold a tighter hole tol.

[Eric S.]

so how many parts do you have to make?

Can you afford scrap?

[Vector]

G0 G90 X0 Y0 S1600 M3

G43 Z2. H1

Z.1

G98 G83 Z-5.5 R.1 Q.05 F12.

G0 Z4. M9

G91 G28 Z0 M5

 

Vary the rpm from 1000 to 1800, and feed from F8. to F20., depending upon setup and machine. Use lots of coolant. Shorten the peck from Q.05 to Q.025 if needed. Keep hole clear of chips.

 

Good Luck

Vector

[Part Factory]

I've had good results using spade drills from Allied Machine (1-800-321-5537). These drills are economical single piece insertables and are ported for TSC. The 1.375 +/-.010 portion can be accomplished in a single push within tolerance. The 1.308 is a two step process of drill then ream to hold +/-.002 reliably. I usually exercise the tech team of the tool manufacture for the proper cutting values. Also, I have built great relationships with tool suppliers by having them supply a test tool and cutting parameters. This is a "Try before you buy" program.

[iowajim62]

Hi heeler,

Try this for giggles.

Mill open 1" hole 1" deep and then drill with 1" drill all the way thru then mill open to 1.375 and then drill 1.375 4.2 down.

Now flip over and get on location and mill open to 1.308 with endmill and don't use last core drill. Good luck.

HTH

[Rekd™]

quote:

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They claim that this is how they've done it in the past.

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My first response to this statement is usually something along the lines of "Maybe it's time to get current with the 21st Century".

 

There's lots of better, faster, more accurate ways to achieve this.

[heeler]

quote:

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There's lots of better, faster, more accurate ways to achieve this.

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Give me some ideas. Now I have a manager who says that it should only be done on a CNC jig bore machine. I have never had to drill holes this big and deep before. I have usually just been able to mill them in.

[Nominal]

What is "unacceptable" about the results that you get?

[mikeb]

before i make a comment about tooling(and i would, really, i would), how many pieces, can you purchase tooling, do you have a budget, is time a large factor?

[heeler]

quote:

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before i make a comment about tooling(and i would, really, i would), how many pieces, can you purchase tooling, do you have a budget, is time a large factor?

---

Usually there is not a problem. Just depends on the job and due date.

 

quote:

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What is "unacceptable" about the results that you get?

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The wall finish is really gouged. It really chatters as we drill. More so at the top than at the bottom. It is really gouged at the top for about 1 - 1.5"

 

Even if they decide to jig bore this job. I would like to have functional ideas for the next time. It always seems like the really hot jobs are the ones that nothing seems to want to work.

[mikeb]

well, without knowing more about the set-up, i would go with a brazed carbide tip drill for the 1.375 hole, take it to depth, ~ 1-9/32" brazed carbide drill to depth for the 1.308 dia., semi-finish and bore or ream.

 

i keep all those tools in stock, so its no problem for me. the brazed carbide virtually eliminates the need to spot a hole. if it was going to to be a very large quantity of parts, i would suggest something else. the brazed carbide drills are not cheap.

[chris m]

heeler

 

I think the reason you are getting gouging and bad chatter is that it sounds like you're drilling into a hole that has already been drilled nearly to size. It has been my experience that big drills don't like going into exisiting holes.

 

The spade drill mentioned before would work, Allied drills are good units, takes a lot of thrust though. I personally like inserted drills (UDrills) for any big holes, they work terrific, just $$. If I had to do that job I would definitely try to bore it; that is a BIG overhang for a relatively small boring bar but in aluminum you could probably get away with it.

 

Sorry I couldn't be more help.

 

C

[rchoward]

thru spindle coolant is a helper... a big helper

 

a u drill can bore as well as drill (sanvik is nice)

 

spade drills are good for sure if cash is a concern but the hss insert will wear up the flank

 

use big feeds... a .1peck will take forever to cut and rapiding up and down into the hole is lame.. try feeding into the hole and working with neg clearance

 

thru spindle coolant helps... oops just said that

 

is the bottom on a right angle? where the holes merge?

 

don't send a big drill into a predrilled hole

 

consider working from both side tour ratios are not as bad as some i have worked with good results

 

comes down to how many holes u need and how much each hole is worth... hard job to do cheap cheap quick and dirty

 

just my 2 cents

[jeff]

The spade drills mentioned earlier work great for me.

They are inexpensive and normally drill on size to about .01 over with a pretty good finish too.

You CAN run a bigger drill into a previously drilled hole with one exception,the pilot hole needs to be about the size of the web on the main drill.

You don't want to push the 1.375 drill into a 1.25 hole.

Try using a 1/2 drill for the pilot and then balls to the wall.

If the drill has carbide inserts,do not pilot drill,drill from solid.