Trouble drilling a hole...

[Michael]

Fresh on the heels of dbrandow's query,

I'm having trouble drilling a small hole in some 7/32 music wire, which I think is SAE 1095. Trying to put a 3/32 hole thru the diameter at two places.

First I tried in the drill press with the old bit in the index. It cut about 3/16 down and stopped cutting. Figuring I had a dull bit I replaced it with an Irwin Cobalt bit. Same problem, the bit cuts just a little and stops.

The slowest speed on my drill press is about 620rpm, a bit fast for metal I know. 3in1 oil is being used in copious amounts. I tried the same hole in the post drill, and the bit just bends.

I'm about to try resharpening the Cobalt bit, but haven't had much luck sharpening such a small bit.

Did I dull the new bit that fast? Does 1095 workharden that fast? I'm ready to try hot punching the hole, if I can make a punch that small, and if I can keep the music wire straight, or annealing the hole locations and trying again with another new bit.

Any help would be appreciated.

thanks,

Michael

[MattBower]

I don't know what's causing your problem. I do know that a traditional anneal (heat well above critical and allow to slow cool) on 1095 could make your problem worse, not better. 1095 has excess carbon. A traditional anneal will let it gather along the grain boundaries in the form of coarse cementite, or iron carbide, which can make the steel very hard to drill. It's not uncommon to see people complaining about not being able to drill annealed 1095, for exactly this reason. Instead, you might want to try to spheroidize the steel. But that's something I've only read about, and don't completely have a handle on. There's lots of info out there on the bladesmithing sites, though.

[pkrankow]

Work hardening of the surface. The bit gets 1 revolution without cutting and it is done. Add some baking soda or chalk to the hole and see if that does the trick. The hardened layer is very thin, but thick enough to prevent drilling. The abrasiveness of the powder will break the hardening layer and let the drill work.

Phil

[Swamptroll]

Fresh on the heels of dbrandow's query,

I'm having trouble drilling a small hole in some 7/32 music wire, which I think is SAE 1095. Trying to put a 3/32 hole thru the diameter at two places.

First I tried in the drill press with the old bit in the index. It cut about 3/16 down and stopped cutting. Figuring I had a dull bit I replaced it with an Irwin Cobalt bit. Same problem, the bit cuts just a little and stops.

The slowest speed on my drill press is about 620rpm, a bit fast for metal I know. 3in1 oil is being used in copious amounts. I tried the same hole in the post drill, and the bit just bends.

I'm about to try resharpening the Cobalt bit, but haven't had much luck sharpening such a small bit.

Did I dull the new bit that fast? Does 1095 workharden that fast? I'm ready to try hot punching the hole, if I can make a punch that small, and if I can keep the music wire straight, or annealing the hole locations and trying again with another new bit.

Any help would be appreciated.

thanks,

Michael

Try thinning the web and changing the angle of the point to 135 degrees

[JNewman]

620 rpm is not too fast for that small a drill bit. I would go to an industrial supplier and buy a couple of new drill bits the size you need. The quality of drill bits sold at big box stores is in a death spiral. Buy your drill bits the same place as the machine shops do. Rather than using oil use WATER when drilling. The coolant most machine shops use for milling and drilling is mostly water.

[Michael]

Thanks guys, I'll try the chalk/baking soda trick first and then give the regrind a try.

[BIGGUNDOCTOR]

If the music wire is in a blue temper it is probably too hard for your drills. I work with some spring stock at work, and I use carbide drills. For a HSS drill, cutting speed would be in the neighborhood of 70x4 divided by the diameter of the drill. With hard stock, start with that, and go slower from there if needed. I haven"t had any problems with steel work hardening under a spinning bit. With Stainless, yes. You may try using a center drill first, then your bit. With the center drill you can keep the pressure on due to the higher rigidity.

Change the angle of the cutting edges, and leave the back rake shallow to prevent the edge from chipping to easily. Use plenty of cutting fluid/oil. The water and baking soda will work, and it won't rust up the tools, but there are better options. I have yet to be in any machine shop that uses straight water for a coolant. Some cutting fluids are water based, but they have a lot of additives in them. 1,1,1 Tri Chlor works excellent-if you can find it, and have plenty of ventilation when you use it, and DO NOT USE ON ALUMINUM. I have found that some solvents like brake cleaner can work wonders for some applications. High sulfur pipe cutting oil is good, and both of these are readily available. If you have any machine shops around you may be able to get some cutting oil/fluid from them.

You have 2 things working against you here.

#1 The material is in a hardened condition.

#2 Being round doesn't help. The surfaces are compacted in the forming process adding some hardness. Plus add in when the drill starts to break through on an interrupted cut it can chip the drill flute tips.

If it was me, and I don't have my solid carbide drill handy, I would anneal the part to be drilled, drill, and re-harden/temper if need be. Being a thin section it will cool quick, maybe too quick. If it is too quick, you can heat another larger chunk of steel that will hold some heat, wire them together, and put both into the annealing medium-I use wood ashes.

[Michael]

thanks for all the tips guys. the baking soda/water combo helped a lot as did regrinding that tiny bit to a slightly wider angle. I really need some close work glasses if I'm going to be sharpening up any more of those little bits. Finishing up the first hole took about 30 minutes. Regrinding the bit twice for the second hole and the bit snapped just as it poked thru the other side of the music wire. I was able to drive the shard back out with a centerpunch and clean up the hole with a needle file.

thanks again for all the help. Knowing it could be done was instrumental in getting it done.

Michael

[BIGGUNDOCTOR]

One thing that you may want to do next time is to make a backing piece that fits the wire diameter. Just pick a new spot each hole, so that when the drill starts to pass through the wire it is still cutting steel (the backing piece) I do that when I have to cut half a hole, or half a thread in a piece.

[HWooldridge]

Useful website: http://www.winsloweng.com/articles/drillChart_content.htm

Useful formula from the website: RPM = Surface ft. per min. divided by drill dia. multiplied by 3.85

Recommended drill feed for tool steels is 15-20 SFM. Subsequently, 15/.094*3.85 = 614 rpm, so you were very close in your initial approach. However, drill breakage is often due to a low spindle speed and can be improved by raising RPM.

I'm glad the job is already done to your satisfaction; my comments would have been: 1) Use a carbide drill bit around 1200 rpm with a relatively high feed rate and lots of cutting oil 2) Drill a 7/32 hole lengthwise in a piece of brass or aluminum (might have to ream it enough to admit the wire with minimal clearance) 3) Cross drill a 3/32 hole into the center of the first one 4) Position the wire in place and drill through the second hole again. This approach is similar to BIGGUNDOCTOR's recommendations but completely encapsulates the wire.