drilling holes on round steel shaft

woodguy2 · Dec 6, 2019

Let me preface this by stating I'm a woodworker, using a basic drill press, with limited knowledge of machining steel.

I'm needing to drill several hundred .17" holes in .5" 1045 steel shaft. The holes need to be pretty accurate, as they're to align a mortise on a gear for a key to prevent rotation. I'm using a jig made I built with a drill bushing. Photos of the jig are attached.

I did a few samples to make sure this was possible for me, and they went fine, but when I started to drill the batch I encountered a problem. It seems like I must have hardened an area or something like that.I's like to understand what went wrong, and how to be sure to avoid it.

The problem seems related to drill speed, and perhaps the stock I received for some of the shafts was harder than the samples I drilled previously. Within the first few seconds I encountered resistance, and then I forced the feed, and it became clear something was wrong. The bit was misshapened from the incident.This was at about 3000 rpm's. Was that too fast?

I was able to resharpen the drills (by hand and eye, certainly not good as new) and drill a few holes at lower rotation (about 500 RPM) speed on other shafts, but I want to avoid whatever happened to ruin the new drills.

What rotation speed should I use for this? I used WD-40 as lubricant --would proper lube make a difference? I used cobalt drills , 135 degrees, from Mcmaster --would different drills help? Any advice here would be appreciated!

kenton · Dec 6, 2019

I would run the drill at around 2000 RPM and find a better cutting oil. I like Mike-o-cut or tapmagic.

GregSY · Dec 7, 2019

The good thing you're doing is buying bits from McMaster. At least you know they're good.

3000RPM is too fast.

Anytime you drill a radial hole in a round shaft, it's hard to keep the bit from walking around until it breaks the surface. If you had a mill, a good vise, and a spotting bit or end mill you'd be home free. But I guess you don't.

I'm not sure the oil is doing much for you but WD40 is probably at the bottom of the pile in terms of viscosity...I'd look for something thicker.

kenton · Dec 7, 2019

I might also look into adding a drill bushing to your fixture. A drill bushing is a hardened piece of steel tube just slightly larger than your drill bit, to keep your drill bit from wandering while you drill.

McMaster-Carr

PocoLoco · Dec 7, 2019

You are on the right track, with the bushed jig. Some tips would be to use a flatter angle, like 118, or more on the drill. It will support the edge better. And use a cutting oil, the dark brown stuff they use for threading pipe. Engine oil will work in a pinch. Wd40 is a dry lube in a thin vehicle meant to evaporate. Keep the drill cutting, i mean making chips. If it stops cutting, stop and sharpen it. You will get plenty of practice sharpening drills. You will find some rods are harder than others, try a carbide masonry drill, sharpened to the high speed drill geometry. I know some here will cry foul at this, but it works. As for speeds, experiment with it till you find a good speed. I would try 1000, but 2000 as suggested is probably ok. Starting with a few extra rods, knowing some will not turn out well, is also good practice.

wheels17 · Dec 7, 2019

A properly sharpened masonry bit works surprisingly well. I was trying to get a hardened shaft out of a blown up jetski pump, and it was destroying up all my conventional drills, HSS and Cobalt, from reputable manufacturers. I put a truly sharp edge on a used masonry drill, used good cutting oil and high downward pressure. It cored it's way right down the shaft, stayed centered in an un-piloted 8D hole, and was spewing a fountain of blue chips. Really surprising.

A suggestion for an improvement in your design. The square key pressed into a round hole requires tight tolerances if you expect to have a fit without slop. I'd suggest that you change over to spring pins. They have a good tolerance for hole size deviations and are much cheaper than key stock. That looks to be about a 1/8 key. Amazon can provide 1/8 x 3/4" pins Monday for under a quarter each in a lot of 25:

Amazon.com: Prime-Line 9187793 Slotted Spring Pins, 1/8 in. X 3/4 in, Plain Steel, 25-Pack: Home Improvement

1/8 x 1" pins in a lot of 100 are $13.59 with free shipping. Longer delivery, though.

1/8" x 3/4" Roll Pin/Spring Pin Medium Carbon Steel Black Oxide Pk 100: Amazon.com: Industrial & Scientific

Green Machine · Dec 7, 2019

1350 rpm is 60 sfm, should work well with intermittent lube application. Second on the masonry drills suitably sharpened, I used to use those to drill holes in hardened die steels all the time. Just don't overheat them drilling too much, or the brazing seems to get weak and the tip will break. I use air to keep them cool, and chips cleared out.

michiganbuck · Dec 7, 2019

I would guess that your drill chips are accumulating in your drill fixture at the place between the part and the bushing and causing too much heat so aiding the possibility of work hardening or burning up your drill point. You may need to do more pecking (in and out) to pull chips and get coolant in.

You might consider a parabolic split point drill for smaller chips and faster chip flow. Or a carbide drill as it can/might tolerate more heat.

For speed I would start at 1000 and work my way up/faster until I found the sweet spot. (Very fast RPM also tends to lessen the coolant getting into the job.

With your drill fixture,You might make a different drill bushing with using a drill rod piece, radius the part close end to match the part OD, Hand harden it to cherry and quench, then press/glue it in so it near touches the part.

A 1” steel square stock fixture block held in a clamped down vise with the hard bushing radiused at the touching the part end so little chance for chips getting in so packing between. Perhaps a another drilled hole next to the drill bushing where pressured coolant can go in.

For speed I would start at 1000 and work my way up/faster until I found the sweet spot.

woodguy2 · Dec 7, 2019

Wow, so many great suggestions. It seems like too high speed was the main culprit, causing work hardening that then ruined the bit. I also realized from research that there's a danger of work hardening occurring at the very end of the cut, which I also experienced, where the small amount of metal left can heat up with a combo of too high rpm and too fast a feed.

Great suggestion on the spring clips! I'll give that a try . It will make assembly much easier, having the radiused surface to enter the mortise, rather than the square edge of the keys. Also allows for smaller hole in shaft, which should be easier to drill. And they're available in many more lengths than machine keys.

Is the suggestion for masonry bit (which needs to be custom sharpened, right?) over carbide tipped just about cost saving?

This forum is so helpful, getting advice from experienced pros.Really grateful for the advice!

L Vanice · Dec 7, 2019

A split point drill was mentioned, but I will add that that type drill is excellent for drilling into a round rod. The parabolic flute feature is fine, but not necessary for starting and continuing to drill. They will start on a curved surface and drill straight even without a guide bushing. Of course, the bushing and fixture is certainly ideal for making multiple parts.

Buy them by the dozen and do not expect to re-sharpen them to the original split point geometry. But they can be re-sharpened to a conventional point for other uses.

The masonry drill for hard steel is certainly a tried and true trick, but you need experience and a good diamond wheel to sharpen them to cut steel. And most masonry drills have the fluted shaft smaller than the carbide tip, so they do not get guided by a bushing unless the bushing is right up against the workpiece. And that carbide tip is usually not a very true running or accurate diameter, which again makes it unsuited to using in a guide bushing. Masonry bits are available in 1/8 and 3/16, but probably not .170". But the 1/8 size would work fine with a 1/8 roll pin.

Larry

litlerob1 · Dec 7, 2019

PocoLoco said:
You are on the right track, with the bushed jig. Some tips would be to use a flatter angle, like 118, or more on the drill. It will support the edge better.

135° is "flatter" than 118° FYI.

OTOH, if the masonry drills that people are recommending are the ones I'm picturing, they are Carbide tipped so 60-125 SFM is painfully slow. But it won't hurt the Carbide, so whatever. Also not sure if anyone mentioned it, but feed, feed, feed. Once your hole is started, I would be putting as much pressure on the Drill as I could, before it bends and breaks.

R

PocoLoco · Dec 7, 2019

Yea, have not used one of those little angle thingies for maybe 40 years, i just sharpen them by hand till they cut the way i want them to. Flatter angles work better in hard metal, but require more pressure. Drill press should have enough pressure, hand drilling requires steeper angles to cut freely. And keeping it cutting is key, once it stops, its over. Sharpen and try again.

rogertoolmaker · Dec 7, 2019

Cutting speed formula

woodguy2 said:
Let me preface this by stating I'm a woodworker, using a basic drill press, with limited knowledge of machining steel.

I'm needing to drill several hundred .17" holes in .5" 1045 steel shaft. The holes need to be pretty accurate, as they're to align a mortise on a gear for a key to prevent rotation. I'm using a jig made I built with a drill bushing. Photos of the jig are attached.

I did a few samples to make sure this was possible for me, and they went fine, but when I started to drill the batch I encountered a problem. It seems like I must have hardened an area or something like that.I's like to understand what went wrong, and how to be sure to avoid it.

The problem seems related to drill speed, and perhaps the stock I received for some of the shafts was harder than the samples I drilled previously. Within the first few seconds I encountered resistance, and then I forced the feed, and it became clear something was wrong. The bit was misshapened from the incident.This was at about 3000 rpm's. Was that too fast?

I was able to resharpen the drills (by hand and eye, certainly not good as new) and drill a few holes at lower rotation (about 500 RPM) speed on other shafts, but I want to avoid whatever happened to ruin the new drills.

What rotation speed should I use for this? I used WD-40 as lubricant --would proper lube make a difference? I used cobalt drills , 135 degrees, from Mcmaster --would different drills help? Any advice here would be appreciated!

The formula for cutting speed for High Speed Steel drills.
RPM = 4 x the cutting speed / diameter.
The cutting speed for:
Low carbon steel = 60
Brass = 80
Aluminum =200

4 x 60 / .170 dia. = 1411 RPM.

Sulphurized Cutting Oil is best on steel.

118 degree drill point.

Good Luck
Roger

Tony Quiring · Dec 7, 2019

Another suggestion for your fixture.

Carefully active and punch marks for holes on end and side of a chunk of steel block.

Drill hole lengthwise for stock and from side through the first one.

If you miss shift a bit down the block and drill again.

This makes a gapless fixture.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Mike C. · Dec 8, 2019

Start the hole with a center drill, then swap to the twist drill. The twist drill will walk all over on the curved surface, a center drill is very rigid and will give you a good start. Definitely too fast, as has been said already. Quick rule of thumb, 500rpm for a .500 (1/2") hole. You can work out from there, 100rpmn for a 1/4", 2000 for 1/8:, 250 for 1", 125 for 2". You can figure in between sizes from there. Keep the drill cutting and keep pulling it out every 1/8" or so to prevent clogging, especially after it's halfway through.

litlerob1 · Dec 8, 2019

rogertoolmaker said:
4 x 60 / .170 dia. = 1411 RPM.

Sulphurized Cutting Oil is best on steel.

118 degree drill point.

Good Luck
Roger

12/Pi does NOT equal 4.

If people are going to post mathematical formulas, at least do it accurately. If the student chooses to round the value up, that's on them. Sorry, it's a pet-peeve.

R

DDoug · Dec 9, 2019

Mike C. said:
Start the hole with a center drill, then swap to the twist drill. The twist drill will walk all over on the curved surface, a center drill is very rigid and will give you a good start. Definitely too fast, as has been said already. Quick rule of thumb, 500rpm for a .500 (1/2") hole. You can work out from there, 100rpmn for a 1/4", 2000 for 1/8:, 250 for 1", 125 for 2". You can figure in between sizes from there. Keep the drill cutting and keep pulling it out every 1/8" or so to prevent clogging, especially after it's halfway through.

If the OP constructed a proper drill jig with a simple drill bushing, it can be done in one shot.

or simply buy a pump jig and apply the proper sized drill bushing:
Adjustable Cross-Hole Drill Jig - HAND | 61-251-305 | Travers Tool Co., Inc.

Don't like the price ? I see them used all the time, plus, how much time are you spending cranking "wing nutz" on/off ?

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