What are recommended feeds and speeds for deep drilling operation for 6061-T6 Aluminum?

[chohmanQ74YB]

I have a part which needs 3/8"-16 threads machined into 6061-T6 aluminum inserts at least 1" deep. I am currently using a 5/16" HSS steel with the following settings, but I am creating so much friction and heat that the aluminum insert block is heating up and deforming the other materials around including the foam and carbon fiber. I am using coolant.

What is a recommended speed, feed and pecking depth to reduce heat and drill a clear hole about 1.25" deep?

[chohmanQ74YB]

I have switched over to an uncoated carbide drill, but I am still unsure of the correct settings. I understand all of the guideline formulas, but what is the target range.

[programming2C78B · Accepted solution]

125sfm, 10-14 IPM, 25-50% peck. The chips should look like "6s and 9s" not long springs. 

[chohmanQ74YB]

Do the settings I previously had make sense of why it is heating up? The drilling operation barely formed chips with the .03" pecking depth.

Why so slow on the SFM? The 25-50% peck is of the total depth correct?

[programming2C78B · Accepted solution]

Because youre rubbing and not breaking a chip. Heat stays in the part and not carried out by the chip.

I find 200+ sfm causes our drills to not stay round/on location. 

No, the % is relative to your tool DIAMETER. The internet loves to say you can do 3xD in one peck, but it can cause issues in my experience.

I may be more conservative then it "can" be, but we also dont ever scrap any parts on .005" PCD/location tolerances and the chips break. Try it out. 

[chohmanQ74YB]

Thanks @programming2C78B 

I am going to do a test on a block and measure the temperature. I have yet to find good resources online which has lead me to my desired results. The best way I guess is to test yourself, but I thought I could use some sort of guidelines.

Do you have any noted rules, formulas or guidelines for drills? The main material for us is 6061-T6 aluminum.

[programming2C78B]

This was made off my real world experience with regular length HSS twist drills, spotted before with a 120* point

[chohmanQ74YB]

With your program settings I achieved "6s and 9s" but I also tested 4000 RPM at .3 peck at 15 IPM and I got long springs. What do the different chips represent?

[seth.madore]

6 & 9's are the desired chip, it means it's breaking the chip into something that will be easily flushed away. With an uncoated carbide drill, I'd be pushing it around 500sfm and maybe .005 to .010 FPR

[programming2C78B]

long story short, the longer the chip the more heat stays in your part and isnt taken out with the chip itself. The 6 means the chip is big enough to actually break itself and is what you look for in almost every material.

[chohmanQ74YB]

Ok makes sense thanks! Check out the chips from this test. The chips are noticeably different from test 1 to test 2 and based on what you guys are saying it seems that the higher FPR is better with chip formation and temperature. Let me know what you think!

Test 1

5/16" uncoated carbide drill into 6061-t6 aluminum with coolant

1500 RPM

15 IPM

.01 IPR

.078 pecks to 1.25" deep

Temperature of material: 84°

Test 2

5/16" uncoated carbide drill into 6061-t6 aluminum with coolant

4000 RPM

15 IPM

.0037 IPR

.300" pecks to 1.25" deep

Temperature of material: 91.3°

[seth.madore]

Any chance your machine has "thru spindle coolant"?

Either way, 1.25" deep in aluminum at .312" hole size is not even close to "deep hole drilling". If you're limited to external coolant only, then pecking is definitely the way to go (a G83 to get the chips out). 

[chohmanQ74YB]

No, the machine does not have thru spindle coolant. 

The settings I landed on:

3500 PRM

.0042 FPR

15 in/min

.25" pecking depth

The drilling operation settings produced spring type chips which seem to evacuate the hole, but its not 6s and 9s chips. The only test I was able to get the small 6s and 9s chips was when I ran test 1 at these settings.

1500 RPM

15 IPM

.01 IPR

.078 pecks

I know you mentioned pushing the FPR more with an uncoated carbide drill, perhaps that will allow me to achieve better chips versus what I have now.