Prevent Drill bit wondering

[turbominij]

Hi all

Wondering if anyone can give some tips and tricks they use for keeping drills on track in a milling machine

What I’m about to do is drill and ream a 3/16 hole through 5/8 bar stock as part of the eccentric straps I’m making for Pansy

This will be for the yoke end where the expansion links go

My setup currently is in the mill with a end stop and the hole lightly centered using the dro

Drilling that deep is likely to cause me issue so what tips and tricks do people have for keeping thing on track

….

What I’m thinking is deep centre drill,Then through with a small 2/2.5mm first then one size under for the reamer

Would I be better stopping half way and drill from the other side knowing that the centre will be milled away to make the yoke And then ream the holes once the centre is removed?

Thanks in advance for all help

[uuu]

Use new drills. Of a decent make. They'll cut a lot straighter than a poorly sharpened one.

Wilf

[92220]

Use a centre drill, and then, as Wilf say above. Use a 4.5mm new drill and take small drill cuts. When through, open out to your 4.7mm and then use a 3/16" reamer. Don't just push the drill through in one go. That almost always leads to drill wander because too much end loading on the drill, will cause it to buckle slightly and this is the start of 'drill wander'.

Bob.

[JonL]

When there is a risk of wander I "peck" the drill through. I don't know if it actually works but it seems to. It could be an old wives/machinists tale. A variation on what Bob is suggesting I suspect (although he provides a reasoned argument unlike me!).

[Shawki Shlemon]

I would use cutting fluid and remove the swarf few times by relieving the pressure on the drill bit .

[tony9f]

In a situation like this I would start by centre drilling just deep enough to make a hole bit not chamfering it, then following up with a small drill a tad bigger than the pilot and drill right through. Next I would open the hole out to any size that comes up just under 5/32" or 4mm then put up a slot drill or end mill and run through with that. It is going to be more rigid than a drill and will not follow the hole but it gives you a true hole to follow with the next drill.
The rest can be opened out by a succession of incrementally larger drills that should follow the previous hole until you are at the stage when you can put the reamer through, ideally a machine reamer but by this method you will have the basis to accurately ream by hand.
I know it all sounds a bit of a faff but in my experience sometimes it pays to be patient and take things slowly. This is the method I use when I want to make sure that the hole is true. Drills are notorious for running off because the chisel point will not centre itself unless they are ground to have a point as in 4 facet grinding. Split point drills may give the same effect.

Hope this helps

Tony

[turbominij]

The pecking at the work makes sence I generally do that clearing chips regularly on any hole I do and step up in sizes.


Interesting idea with the end mill il see what mills I have and if I have anything close

Brill thanks for the advice what drill bits do people recommend being “decent” I obviously don’t want to spend stupid money on them by also don’t want to by rubbish for the sake of a little money

[uuu]

I use mostly Dormer drills. I'm lucky to have a 0.1mm increment set - so there are some that get a lot of use and others that are fresh and ideal for situations like this. They're not costly individually.


Wilf

[simplyloco]

Jun 2, 2024 10:25:41 GMT JonL said:

When there is a risk of wander I "peck" the drill through. I don't know if it actually works but it seems to. It could be an old wives/machinists tale. A variation on what Bob is suggesting I suspect (although he provides a reasoned argument unlike me!).

Agreed. I wouldn't be without my lever tailstock, it makes life so much easier. I don't miss the long screw at all!!!
John

[uuu]

Having made reference to poorly sharpened drills above, it's worth noting that the knack of bringing a used drill back to life is worth learning. Alas I haven't quite got it. But John (the Pump) has, and it's a joy to see him tickle a drill back to life freehand on a grinder. His racks of drills all cut well and true. And he keeps a separate set for brass, with the helix stoned off to present a square edge. I must practice more.

Wilf

[jasonb]

I use a spot drill to start holes rather than a ctr drill. I Also have a reasonable range of stub drills in all the commonly used sizes, as these are shorter and stiffer they don't tend to wander as easily. At that size I would just spot and then go in with a 4.5mm stub drill then follow that with a 3/16" machine reamer.

Use decent drills I use the Dormer A022 Stub drills and their A002 Jobber Length. These are split point and you can actually use then without spot/ctr drilling first but for accurate parts like valve gear I would still spot the positions.

[suctionhose]

I spent a fair portion of my first year apprenticeship divided 1:6 between sweeping swarf for the whole machine shop and drilling on the radial drill.

My boss would never allow pilot drilling because the second drill would cut close to size and wear the lands off the drill. Worse; the radial was just outside his little office and to where did he burst out of to vent fury when pissed off but...you guessed it: the radial drill!

Once a drill started to squeal in holes due to wear you had to chop an inch off and resharpen. We were drilling thousands of holes up to 2 & 3 inch diameter - expensive drills - and the boss knew the value of them by the inch of their length.

Yes he was a hard man but oh what I learned. Interestingly, drilling is about the most efficient rate of metal removal in the machine shop.

Blundering holes through metal, even with a keen eye and a well ground tool, is not meant to be precision engineering; it's just metal removal.

My boss said, "If you're not removing metal you're not doing anything!" A simple truth that guides my productivity even today, 50 years later.

All that said, if nothing better is available, then a drill can be tweaked to drill on size, even slightly undersize at a pinch and true.

Worse came to worst we'd grind the corners off - like 30 deg and then a small land at 60 deg - which really had the drill follow a pilot hole tightly. Not the same as reaming but it did get a few jobs out the door!

We used some deep hole drilling experts a couple of times and they could drill a 3/4" hole though 8ft of steel and you could slide a bit of 3/4 bright mild round straight through!

So back to model engineering. Best friend: start on centre. Use centre drill or spotting drill but short and positive position for starting the flexible drill off. Hold the centre drill in a collet rather than a chuck...

Reamers are your friends - if the start is on position - but a slot drill or better still, a single point tool will correct any run off.

Dee bits are easily made at home and are marvellous for producing a straight, on size hole (a finish cut through a pilot hole of course).

[turbominij]

Just reporting back
Brand new really sharp dorma drills (Amazon 10x 3mm £1.88 bargain!! ) did the trick with cutting oils pecking at it to slowly go through and clear the swarf

Managed to drill through the 5/8 bang on center precisely where I needed to

[ianholder]

No doubt everyone will say this is wrong, but I have recently been doing exactly what the original poster is doing. I set it all up on the mill so the centre drill was on the centre line and went straight through with the centre drill. The first one was a test to see if it worked and on examining the hole it was perfectly smooth all the way through, better finish than some of my reamers, and a 3/16th dowel pin was a perfect fit. Whether your centre drill is long enough for 5/8th thick you will have to check. I can only say it worked for me.

[92220]

A centre drill will work....up to a point. The problem is that they are very short and have nowhere for swarf to escape. That can lead to overheating. IF you find that the centre drill idea works for you, length is not necessarily a problem, just the availability of sizes. I have some long centre drills, sizes 2 and 3, which are 100mm long. I usually 'peck' through with a new twist drill (I bought a new set of Presto 0-1/2" in 1/64"s and 1.0mm to 10mm in 0.1mm steps, not too expensive!) and that is 0.2mm smaller than the hole I want. When that is through I then finish off with either a reamer, if I want a decent finish to the hole, or a new drill of the wanted size, for just a drilled finish hole. Drilling through with 0.2 smaller drill, and ending up with a truly aligned hole will also allow a new drill 0.1mm smaller, to drill through and follow the original hole perfectly, for smaller diameter holes. As with any new engineering procedures, "practice makes perfect".....hopefully!

Bob.