Drilling O1 for small parts

[Steve355Participant @steve355]

Morning

Perhaps this should be in the beginners section, but I made such a hash of this I thought I’d reach out for advice. I have a fiddly little part that I need for one of my projects. It’s a wood plane blade adjuster, a little bottle-shaped thing. Being part of a tool, and potentially under stress, I thought I’d make it from O1 and harden it before installing it the device.

It’s basically a piece of 0.25” x 0.218” x 0.482” tool steel that needs to be drilled and tapped twice for M4 (despite what the drawing says I ended up tapping it in both holes).

I cut rough blanks and dimensioned them using the surface grinder. Lucky I have that.

I made a pretty decent job of punching the hole locations accurately.

Thats when the fun started. I broke several bits and a tap. The problem seems to be work hardening. I dialled back the drill speed to 200rpm, and tried annealing the work in sand to keep it malleable. I did it in the end, but on the 4th try.

I used plenty of cutting oil but I don’t have a coolant system.

Does anyone have any tips for drilling small fiddly holes in O1? I’d really like to be able to do this quickly with minimal fuss.

Thanks

Steve

 

 

 

 

 

[Tony Pratt 1Participant @tonypratt1]

Are you using good quality cutting tools with sharp edges? Cheap or blunt tooling just won’t do it in O1. Make sure you keep the pressure on when drilling, if the tools rub work hardening can be an issue.

I’ve machined a lot of O1 back in the day and used coolant for drilling and cutting oil or similar for tapping, finally a 3.3 mm HSS drill should be run at around 900 rpm.

Tony

[renardiere7Participant @renardiere7]

Steve,  generally you shouldn’t have any difficulty drilling and tapping O1 in the annealed state. I suspect what’s happening is that you have inadvertently hardened the steel by getting it too hot while grinding it.  You will either need to go much easier with the surface grinder and/or use a coolant while grinding. A small spray bottle with soluble oil can work very well for surface grinders that are not set up for coolant.

Good luck

 

Alan

[JasonBModerator @jasonb]

What was your original drilling speed? 200 is very low I would be at around 1000. You might even get away with going upto 3.4mm which would make tapping a bit easier though should still not really be a problem at 3.3 with a drop of tapping fluid.

I tend to drill on the mill, finding the edges and then positioning the quill so no need to punch and more accurate positioning.

Decent split point drill and the same for a spiral flute tap and I don’t think twice about drilling and tapping Silver steel or gauge plate.

[John HaineParticipant @johnhaine32865]

The only feature of the part that actually needs to be hard is the pin. You might have cut that from silver steel and loctited it into a close fitting hole in the block. The block itself might actually be better made from hard brass, it would slide better and the screw could be smoother.

[bernard towersParticipant @bernardtowers37738]

Im with John on the brass or even a piece of colphos even though the drawing calls for stainless!. Could also be made from a piece of 0.218 round.

[Martin ConnellyParticipant @martinconnelly55370]

I like the idea of re-engineering the design as suggested by John, it is possible to make use of more modern options such as Loctite that were not available when parts were originally designed. Another option to add to John’s idea is to single point thread the pin at one end and thread the hole and use a thread locking compound to secure the pin.

On the subject of drilling it is always better to use something with power-feed on a tough to drill material that can work harden and to use a feed per rev suited to the drill diameter. This may mean that you could end up setting it up in a lathe to use the carriage drive to achieve this if you do not have a suitable drill or mill to do it. If you don’t have a means of holding a drill in a lathe’s tool holder an option is to link the tailstock to the carriage to drag it along at the correct feed rate. I think I have seen people showing how they did this in either magazine articles or internet videos. For a 0.13″ drill going through a material thickness of 0.25″ I would opt for a stub drill as well. I always have a few Ø3mm and Ø3.3mm stub drills ready just to start holes off without any wandering of the holes. I don’t use a punch for much apart from setting up odd shapes in a 4 jaw chuck.

Martin C

Edit. I have been looking at the drawing and I now think the drawing is suggesting putting a pin into a clearance hole and that the drawing is unclear on this point.

 

[Martin Connelly]

On Martin Connelly Said:

….

Edit. I have been looking at the drawing and I now think the drawing is suggesting putting a pin into a clearance hole and that the drawing is unclear on this point.

 

So it does!

[renardiere7]

On renardiere7 Said:

Steve,  generally you shouldn’t have any difficulty drilling and tapping O1 in the annealed state. I suspect what’s happening is that you have inadvertently hardened the steel by getting it too hot while grinding it.

 

Alan

This was my first thought.

[Steve355Participant @steve355]

The drawing does suggest putting a 4mm pin in a clearance hole (planning to use loctite). However, this hole failed initially (drilling) and I realised that a 3.3mm tap hole, being smaller than 4mm, would be easier to drill on the tiny area on the top of the workpiece – and so it was.

The drawing erroneously says stainless – that’s just the drawing template.

When I look at a part of a Veritas hand plane that has a similar purpose(see below), it’s clearly extremely robust and made of some sort of tool steel. That’s why I chose O1. I’m not sure my design is right but I’ll refine it once I have a prototype working (or not!). Brass would be easier!

Originally my drill was running about 900 rpm. Which ironically sounds like it was about right. Trying to reduce the RPM to reduce the heat wasn’t the right move and I can see why now.

Funnily enough I’ve done quite a bit with O1 in the past, and I’m always amazed by how soft it is in its annealed state.

I think in fact my drill bits may be poor. I need to order some probably 3.4mm good quality bits.

In fact, having considered the suggestions, and looking at the Veritas design I think I may be better off turning the thing out of “hard brass” as someone suggested, or bronze. Then there’s only one hole to drill…..

 

[SillyOldDufferModerator @sillyoldduffer]

I look at three things when jobs go wrong.  They are: the material; the machine; and the man.

Material:  Is Steve’s metal really annealed O1?  I don’t believe O1 work hardens.  (My book says O1 machines well (about 90% as well as mild-steel) and doesn’t warn against work hardening.  I’ve had no trouble machining Gauge Plate.)   Other tool-steels do work-harden, so maybe Steve has one of them, not O1.    Brass cuts best with very sharp tools so I only use new drills on it.  A drill used once on steel is unhappy with brass, but drills eventually too blunt for brass still cut steel, so use ’em for that!  Not sure about Bronze except it tends to grab and break drills.

Machine:  O1 being a shade harder than mild-steel makes it more important to use sharp drills, cutting at the correct speed.

Man:  The ‘correct speed’ is a combination of feed-rate and RPM, down to the man.  Rule of thumb for mild steel, RPM = 10000 / diameter in millimetres.   So a 3.4mm drill should be spun at 2940 RPM – much faster than Steve’s 200 and 900RPM.  Though RPM isn’t highly critical, getting it wrong feeds the other main ways of blunting tools:

• Feed-rate too high.  Overstresses the cutting edge and rapidly blunts it, generating more heat than swarf.   If a hasty gorilla with a headache is at the controls, put something in his tea to calm him down!
• Feed-rate too low.  “Pussyfooting” blunts the cutting edge by rubbing rather than cutting.  This forum put me wise to this mistake, and I found twist drills suddenly lasted about 20x longer!

These two main faults are compounded by not using enough cutting fluid.  It lubricates the cutting edge as it penetrates into the metal,  keeps the edge cool and helps eject swarf. Failing to clear swarf regularly means it minces under the cutting edge, also causing rapid blunting.

There’s a balance to much of this:  get the RPM about right, then adjust the feed-rate, then tinker with cutting fluid for best results.  I dislike flood cooling because of the mess, and squirt CT90 into drill holes from a spray can rather than a brush because the blast helps eject swarf.  Another balance is how often drills are pulled out to clear swarf.  Experiment to find what works best for you.

Taps and dies should be reversed a quarter turn to break swarf ribbons.   In my experience taps usually break because they’re not straight in the hole, so I avoid hand-tapping.  Instead the tap and tool are held at right angles by the lathe, mill or home-made tap holder.  Take extra care to remove swarf when tapping.   Some get the balance right intuitively, many have to practice.  The late John Stevenson advised the rest of us to take up knitting…

🙂

Dave

 

 

[Steve355Participant @steve355]

[Tony Pratt 1Participant @tonypratt1]

Dave,

I would suggest your 2940 rpm is way too high for O1 Tool steel, mild steel yes. Steve355 is going to be royally confused.

Tony

[JasonBModerator @jasonb]

Well just to show there is nothing too different when drilling & Tapping O1 Gauge Plate here is one I have just done.

5mm thick GFS

3.3mm Dormer A022 Split point stub drill, 1250rpm run dry. No spot or punch mark

M4 Spiral Point Tap from ARC 160rpm, drop of CT90

Small or large part should make no difference as the drill and tap won’t know how much metal is around the hole and one mans small is anothers large! Not sure how grinding could have hardened it, possibly got it hot but you would have needed to quench it to make it hard but I suspect the vice/chuck holding it just kept it cool enough. Probably a poor drill bit.

[Steve355Participant @steve355]

Thanks for that Jason, that’s my issue – it should be easy!

I don’t think the surface grinder hardened it at all, I agree that it’s likely my drill bits were poor/blunt. I need to invest in a few decent ones.

[renardiere7Participant @renardiere7]

Small or large part should make no difference as the drill and tap won’t know how much metal is around the hole and one mans small is anothers large! Not sure how grinding could have hardened it, possibly got it hot but you would have needed to quench it to make it hard but I suspect the vice/chuck holding it just kept it cool enough. Probably a poor drill bit.

 

I don’t think the surface grinder hardened it at all, I agree that it’s likely my drill bits were poor/blunt. I need to invest in a few decent ones.

 

Really!!  There is such a thing as grind hardening, and tool steels such as O1 particularly in small sections are vulnerable as they are generally easily hardened steels. It’s a surface effect and the steel does not need to be quenched, O1 steel will still air harden.

The classic example is chainsaw grinders. Chainsaw teeth are normally in a softish state to allow hand sharpening with a file but it just takes heavy handed use of a chain grinder and you’ll get the teeth hard enough to strip a brand new file.

[JasonBModerator @jasonb]

Thanks, I’d not heard of that before. Though the OPs ability to ctr punch the part suggests it was not that deep or hard, maybe just enough to take the edge off the drill.

[NealebParticipant @nealeb]

I once spent a long time chasing a similar problem, although I was only trying to drill something like EN3B (forget actual spec but ordinary black mild steel) from a local supplier. Never had problems with their steel before but just couldn’t get a 3mm or so drill through the stuff. Changed drills a couple of times – still struggled. When I checked the drill, it seemed to have lost any kind of proper cutting edge. Couple of new drills later, still no success. Then I looked at the tip of a new drill straight from the box. Badly ground – would have probably cut better run in reverse…

Those were brand new from a UK online seller, although other sizes from the same source bought at the same time were OK. So, even if new drill, might be worth checking. And I now buy from Arc Euro…

[JonParticipant @jon]

01 otherwise known as silver steel or guage plate all harden when hot.
M2 and M3 can be iffy but M4 with quality non chines cheapies should plough through in seconds under power or not.

A poor or blunt drill may have generated the heat but suspect the grinder. Only buy branded, Guhring, Hertel, Dormer etc even those have grades for the application.

 

[Author]

Posts