Hey all I have run into the need to do a small diameter Gun Drill thru a 8"to 10" 5/8" shaft. this shaft is hardened but not all the way thru. The tolerances are pretty loose but I would like to do it as well as possible. I have a 48" import lathe and a 60" Logan and I have the proper bits. Do any of you have any pointers? This would be most dificult one I have done in my short career eeeerrr hobby life.

Wayne

How loose are the tolerences required? As far as I can see, if your lathe is fairly tightly centered, you shouldn't have any problems with it coming out properly.

A nicely started center drilled hole will set the pace for error over the length of the part. How round is this part?

A nicely started center drilled hole will set the pace for error over the length of the part. How round is this part?

It is a hardened ground shaft and I only need to get a fluid passage through the center and retain as much strength as possible. I have not measured for run out of the part but the machines are both pretty tight.

Wayne

if it is strictly fluid passage just drill from both ends. From the exterior you will never see if the bit wanders off center.

Well I am going to drill it tonight. Here is my plan it worked last night on a 5/8" x10" steel rod. let me know if you see anything I should be aware of.

chuch rod in lathe and start with a Cobalt centering drill.
Use new regular 1/8" bit to drill as deeply as it will.
Use 1/8" X 8" reduced shank drill bit to drill to center +
Flip shaft in chuck and repeat.

Other than going slow and using lots of coolant what else should I watch out for?

Wayne

OK that was 3 1/2 hours I will never get back. I got it done but it was not easy. I ended up having to go 13.5" with a 1/8" hole. I centered and started with a Cobalt centering bit and drilled a couple inches with a Cobalt bit. Then I used an 1/8" x 12" long drill bit to go 7" from one side and 6.5" from the other. That thing was a hard SOB I could only drill 3/8" or so before the bit needed sharpening and nothing I did would stop the thing from chattering. When the two holes connected they were off just a bit which caused a bind and broke 1/4" off the end of the bit. I had to grind a length of drill rod to slide into the hole and knock the broken piece back the way it came in. Oh well I got it done, thanks for the help only 3 more to do.

Wayne

One thing that may lessen the chatter is to clamp a small lathe dog onto the drill and support it with the compound. An inch or two from the end of the part your drilling. As you feed in you'll have to move the dog, but it's should help dampen the vibration until you have most of the bit in the tool. Don't let the swarf load up in the flutes, back it out and flood it with coolant (wd-40 if that's all ya got).

Also, how much material did you have sticking out of the chuck?

One thing that may lessen the chatter is to clamp a small lathe dog onto the drill and support it with the compound. An inch or two from the end of the part your drilling. As you feed in you'll have to move the dog, but it's should help dampen the vibration until you have most of the bit in the tool. Don't let the swarf load up in the flutes, back it out and flood it with coolant (wd-40 if that's all ya got).

Also, how much material did you have sticking out of the chuck?

I am not following how to support the dog with the compound??? I tried everything from making rubber dampener bushings that clamp on the bit to supporting the bit with a steady rest. Nothing helped much. I think it was a torque load unload thing on that long skinny bit.

I could get about .125" drilled before the flutes loaded up, any more and the swarf would start to pack tight making backing off a chore. I had a hollow ground 1/8" bit but it broke with the first chatter. I did the rest with a sears special.:D

The Coolant pump ran the whole time heat and lubrication were not the problem I don't think.

Since the shaft had a bit of runnout I only let about 1.5" stick out of the chuck. that worked best for centering and seemed to be the sweet spot for reducing chatter.

thanks for the help

Wayne

Clamping a small lathe dog on the bit and laying the L shaped drive portion onto the top of the compound (or any solid, fixed part of the lathe) was what I had in mind.

My thinking was it should effectively shorten the length of the bit, limiting the twisting and hopefully the chatter. If it does do any good it'll only be temporary. Once there is enough bit in the hole it'll be useless.

I assume you played with the spindle speeds and tool feed rate? What's the ID of this hole?

Clamping a small lathe dog on the bit and laying the L shaped drive portion onto the top of the compound (or any solid, fixed part of the lathe) was what I had in mind.

My thinking was it should effectively shorten the length of the bit, limiting the twisting and hopefully the chatter. If it does do any good it'll only be temporary. Once there is enough bit in the hole it'll be useless.

I assume you played with the spindle speeds and tool feed rate? What's the ID of this hole?


I got it:D great idea on the lathe dog. I used a peice of 1/4" steel strap with a 1/8" hole drilled in it on the compound to keep the bit true. I could adapt something with a dog to keep it from twisting and keep the bit true.

You assume correctly I had lots of time to play and nothing worked.

As posted above 1/8" diameter hole thru a 13.5" hardened shaft.

I thought the shaft was only case hardened but it must be through hardened cause it was a tough SOB. I drilled a regular steel rod the night before for practice and it went really smooth less than 30 minutes. The real thing ....well not so much.

Thanks
Wayne

Too late, but a carbide tipped Lexington taper length drill would have held an edge longer, probably enough. The only problem would be sharpening it if you needed.

Too late, but a carbide tipped Lexington taper length drill would have held an edge longer, probably enough. The only problem would be sharpening it if you needed.

I have 3 more to do, where do I get such a bit? I have a 8" 120 grit diamond wheel on an old facing lathe I sharpen with. I could probly sharpen a carbide it I needed to.

Thanks
Wayne

A few companies make carbide tipped drills, Lexington Cutter is just one of them that I use for work. Try J&L Industrial or other machine tool suppliers.

A few companies make carbide tipped drills, Lexington Cutter is just one of them that I use for work. Try J&L Industrial or other machine tool suppliers.


Ok I ordered one but had a question. Every carbide tipped drill bit I could find specificly said "not for use on hardened steel" I know sometimes things work differently than the manufactures recomendations but I am concerned about trying to get a broken carbide tip out of a 6" deep 1/8" diameter hole. any thoughts.

I got the one from Lexington cutter by the way
Wayne

Ok I ordered one but had a question. Every carbide tipped drill bit I could find specificly said "not for use on hardened steel" I know sometimes things work differently than the manufactures recomendations but I am concerned about trying to get a broken carbide tip out of a 6" deep 1/8" diameter hole. any thoughts.

I got the one from Lexington cutter by the way
Wayne

"Hardened" is relative. So is surface feet per minute. On something fairly hard I'd keep the sfpm to a minimum. This will help avoid chatter, carbides worst enemy. Between 25 and 40 sfpm, good oiling and clearing the chips, the tip should stay solid. 40 sfpm is 1220 rpms for an 1/8" drill.
The only issues I find with carbide tipped drills is the hook angle or lip angle. They tend to be not as helical as the rest of the flutes. A mild lip modifacation for more angle will also help break the chip.
Peck the hole and feel for chip bind, any sense of binding will need chip clearing.
I could suggest two other types of drills for this that work really well.
Cobalt extended shank;
These drills are rugged and take a beating. The extended shank will give you around 1.0" of flute, more than enough because you need to clear the chips very often. It will also give you more torsial rigitity.
I may have mis-spoke on taper length, they may chatter more due to torsial loads trying to unwind the helix, if you push them too hard.
Titex TFL coated drills;
These drills are amazing. I don't know if they're made in extended shank but I've never seen a better working drill. I use them 410 stainless, monel, inconel, finico, nickle, copper, 304 stainless, tullurium, titanium, etc.......

Drill specs I'd suggest;
135* point angle
Not split point
Extended shank
25-40 sfpm
Castrol's Moly-Dee cutting oil
Drill thru feel

The biggest allie on your side is time, be patient.

"Hardened" is relative. So is surface feet per minute. On something fairly hard I'd keep the sfpm to a minimum. This will help avoid chatter, carbides worst enemy. Between 25 and 40 sfpm, good oiling and clearing the chips, the tip should stay solid. 40 sfpm is 1220 rpms for an 1/8" drill.
The only issues I find with carbide tipped drills is the hook angle or lip angle. They tend to be not as helical as the rest of the flutes. A mild lip modifacation for more angle will also help break the chip.
Peck the hole and feel for chip bind, any sense of binding will need chip clearing.
I could suggest two other types of drills for this that work really well.
Cobalt extended shank;
These drills are rugged and take a beating. The extended shank will give you around 1.0" of flute, more than enough because you need to clear the chips very often. It will also give you more torsial rigitity.
I may have mis-spoke on taper length, they may chatter more due to torsial loads trying to unwind the helix, if you push them too hard.
Titex TFL coated drills;
These drills are amazing. I don't know if they're made in extended shank but I've never seen a better working drill. I use them 410 stainless, monel, inconel, finico, nickle, copper, 304 stainless, tullurium, titanium, etc.......

Drill specs I'd suggest;
135* point angle
Not split point
Extended shank
25-40 sfpm
Castrol's Moly-Dee cutting oil
Drill thru feel

The biggest allie on your side is time, be patient.

Thank you:D that is way over my head but I will try to put your advise to good use. I'll let you know the outcome.

Wayne

Real gundrills are really confusing.
http://www.sterlinggundrills.com/images/dm6.gif
The point is not on center. :D

Real gundrills are really confusing.
http://www.sterlinggundrills.com/images/dm6.gif
The point is not on center. :D

Wow how in the hell does that work?????

I called a company in kansas who said they could gun drill 1/8" holes but they wanted a months pay to do it. I figured it was worth a shot to do it myself.

Wayne

it goes really fast and has coolant that goes through the tool to blast chips away. Make a hell of a noise sometimes..

It cuts a nice hole because it is solid over more of it's length than a drill bit which has material removed for the flutes, same reason a 2 flute tap is stronger than a 4 flute...more tool around the core.

Doing small shit almost always takes longer than large things...if time is on your side then like mentioned in then out, clean, in then out. clean repeat a few hundred times and you can get a fairly nice hole.

I would also get an extended shank drill...chatter is bad. Get a Drill Dr.

Wow how in the hell does that work?????

I called a company in kansas who said they could gun drill 1/8" holes but they wanted a months pay to do it. I figured it was worth a shot to do it myself.

Wayne

They're mostly a PITA.
The gundrill has a hollow cored shank with a carbide tip. The tip is ground specifically for moving chips down the v-notch outside the hollow core. The hollow core supplies cutting oil at very high pressures, the smaller the drill, the higher the pressure...obviously.
The tip's point is located 25% away from the outside diameter.
Example; .250" diameter gundrill's tip is .0625" from one side. The short side is ground at 23* whereas the long side needs more angle to clear the coolant port. That angle is also dependant on material and feedrate.
If you were to stop the drill and cut the work piece in half, the profile in the face of the hole would be in the shape of a "W".
The work piece is held on the ends in a way to insure coolant doesn't escape during or after the drill sequence. The gundrill is guided by a hardened drill bushing (usually honed to perfectly fit the drill) for the start of the cut.
I ran an Eldorado gundrill for years and very glad to be free of the noise when drilling hardened materials. :eek:

Hey all FYI I tried again last night using the tips you guys have offered and got one finished in just over an hour. Lathe speed was too slow, I had the reduction gears on the drive and was only getting 1/2 the speed I though I was. Been a long time since I used the machhine without them I had forgotten they wer on there. When I got the speed to 900 rpm it cut nice and no chatter. I only had to sharpen twice.

Thanks for the help
Wayne