Drilling and Tapping Mild Steal (A36)

[zstuf]

I operate a CNC Mill in a small shop that has 2 CNC Mills.

We need to Drill & Tap A36 Mild Steal using the CNC Mill.

Current process is using Morse taper drills on a manual machine.

We want to minimize the coletts and holders needed for each process.

We are looking at 3 fluted carbide drill and ER colett to match. This will require 9 coletts just for the drills, per machine. I am looking for a better option.

The drill sizes and taps are as follows......................


DRILL DIAMETERS MAX DEPTH

1. 1.0625 or 1 & 1/16 3.25”
2. .8125 or 11/16 2.25”
3. .6875 or 13/16 2.0”
4. .5625 or 9/16 2.0”

DRILL DIAMETERS TAP SIZE

1. .4375 or 7/16 ½” - 13
2. .5312 or 17/32 5/8” – 11
3. .6406 or 41/64 ¾” - 10
4. .7343 or 47/64 7/8” - 9
5. .875 or 7/8 1” - 8

We have had Some success with Sandvick 880 series changable insert drills.

We have also burned up a couple of drill bodies.

Searching for options.

We do not have spindle coolant, flood only.

I would apreciate any feed back possible.

[davereagan]

Hello,
I have a few thoughts. From my recall, your tap drills for 3/4"-10 and 7/9"-9 are small, which will make the tapping torque and stress go way up. 21/32" is the standard tap drill for 3/4"-10 and 49/64" for 7/8"-9. That's 1/32" different than 47/64, which is a lot of extra material for the tap to cut. Three fluted drills are for cast iron and sometimes aluminum and are considered weak for steel drilling. Two flute drills with split point are the way to go, whether it's HSS, cobalt or carbide. Flood coolant should be fine if you have some soluble oil in it. (not full synthetic) 10% concentration is a lot better for tapping than 6%, which is often the case. It can mean the difference between a borken tap and not. What kind of machine do you have? Is it 40 or 50 taper? geared head? A lot of 40 taper machines can't push a 1" drill at the correct feedrate without a 1/2" hole drilled to begine with. If I weren't doing holes in the high hundreds, I would just use cobalt split point screw machine length drills. This eliminates center drills and a tool change. Are the holes through? Spiral point taps are the only way to go for that. If you want to make a ton of holes fast, consider a Tialn coated carbide split point drill like a Garr or Titex.

Dave

[dertsap]

Hello,
Three fluted drills are for cast iron and sometimes aluminum and are considered weak for steel drilling.

three flute drills work extremely well in mild steel , I've used them many times , a single 1/2" drill in 1018 punched from 1500 to 3000 holes before it had to be changed , these were used to replace a drilling then reaming operation , the drills stayed withing our tolerance of .0005 and had an excellent finish

[zstuf]

I am operating a 1985 Hitachi Seiki VA 55 II with a 50 taper, Fanuc 11M controls. The 40 Taper machine is a Chinese made Virticle Machining Center that about 3 to 4 years old, also running Fanuc, 16m I believe. I am assuming that both machines can handle rigid tapping at this time, we will adjust to spring loaded tap collets if rigid tapping does not work.

We are looking at 10 to 50 part runs. That's less than 100 holes and 25 taps per run. All holes & taps are thru. We run 4 outside holes for every tapped hole. Right now we are looking at OSG 3 Flute carbide drills and rigid tapping with OSG taps, but that was one suggestion, we don't need to get fancy, the cobalt split point screw machine length drills will probably work well for us.

I don't know why the current process uses 49/64" drill for the tap, we may change this for the rigid tapping, thank you for this...... it helps.

[zstuf]

dertsap,

Are you using carbide, is there a coating?

Our shop does not need to consider high tolerances, but the 1500 to 3000 holes before sharpening sounds good.

[dertsap]

they were carbide tialn coated Garr , personally I hate garr tooling but they worked ok for what we used them for

[dertsap]

for your larger sized taps I'd suggest making sleeves if necessary and put them into solid holders , a 7/8" tap can easily spin in a collet holder and destroy the collet , and or the tap and part