Casting – off center hole correction

[colin hamiltonParticipant @colinhamilton16803]

I’ve bought a cast iron handwheel for a project. It was supplied with a small (8mm) center hole. I need to open this up to 20mm for my application, which I was intending to do on the lathe. The only problem is the existing hole is way off (approx 3-4mm) and I was thinking was too far out to drill successfully.

What would be the best way to get the hole back centered?

Thanks Colin

[JasonBModerator @jasonb]

Bore it.

Depending on the size of your boring bar you may need to first open up the wonky 8mm hole which can be done by using a milling cutter in the tailstock chuck, say 10mm then 12mm before starting boring.

[Andrew CrowParticipant @andrewcrow91475]

Hi Colin, as the hole in the casting may be a bit rough you could mark out where the hole should be and then use a round file to get it approximately back on centre before boring to size.

Andy

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I’ve done what JasonB has said a time or two.

Regards Nick.

[cogdobblerParticipant @cogdobbler]

If you don’t have a milling cutter to hand, you could mount the job off centre on the faceplate or 4 jaw so the existing 8mm hole is running roughly true, then drill it out to, say, 12mm or so. Then set the handwheel rim to run true and bore out the now offset hole with a boring bar.

With your final hole being 20mm , you have plenty of “meat” to play with. If you mark out the 20mm hole to start with, you will know exactly how close to it you are drilling.

 

[noel shelleyParticipant @noelshelley55608]

Bearing in mind this is a casting I would be loath to use a milling cutter lest the casting had hard spots that could wreck the cutter. Grind up a tool bit to open up the hole, or try to drill out 1/2″ on a pillar drill then bore out to size. Good luck. Noel.

[FulmenParticipant @fulmen]

Another possible solution is to plug & glue the hole with the same or similar material.

[Howard LewisParticipant @howardlewis46836]

With a 20 mm hole the ultimate object, there is plenty of material to be removed, so the 8 mm cored hole being 3 – 4 mm off centre won’t matter.

DON’T attempt to drill it.  A drill will try to follow the off centre hole.

As already advised, Bore it. Even using a three jaw chuck, the resulting hole will be concentric within 0.1 mm probably.

Once the first 4 mm has been removed, with a boring tool, the hole will be 12 mm diameter, anyway, By that time, removing material from one side only, will be finished, and the bore will then be central, ready to be opened up to your desired 20 mm.

Howard

[old martParticipant @oldmart]

I would do it exactly the same way as cogdobbler suggests, assuming you have the equipment.

I would clamp it on the mill and stick a carbide endmill down on the centreline, but not everyone has that luxury.

[colin hamiltonParticipant @colinhamilton16803]

<p style=”text-align: left;”>Thanjs everyone for the help. I think I’ll be trying the cogdobbler solution.</p>
 

Cheers

Colin

[Nigel Graham 2Participant @nigelgraham2]

I’d treat it as a faceplate task, centred to the perimeter not the wonky hole or central boss.

Then use a small boring tool.

Faced with such small pilot holes, especially off-centre, I do not try to cut right through on each pass until the hole is large enough and concentric with the rim to allow that. The tool probably won’t penetrate far anyway.

Instead I nibble away at it as a series of shallow counter-bores taken to just beyond the eccentricity, working the base of the recess down a bit at a time.

It’s a slow, patient process, but does work!

Then swap to a heftier boring-bar to bring the now-concentric hole to size.

[duncan webster 1Participant @duncanwebster1]

If it’s 8 mm dia and 4mm offset the edge of the hole will be on the centreline, which will make a boring bar a bit difficult. Drill the existing hole out a bit bigger where it is will make life a lot easier

[Nigel McBurney 1Participant @nigelmcburney1]

Bore out the eccentric hole,but dont remove too much material at one pass,if too much cut is taken it will cause the boring tool to deflect and you will still achieve a wonky hole, to start on a 8mm will need a very small dia boring bar ,use  a larger boring bar as the bore gets larger.

[Dave HalfordParticipant @davehalford22513]

This is a handwheel that has already had a hole machined. Much like the ancient one probably used on valve I had to centralise properly to use it for a lathe drawbar.

The tailstock held milling cutter worked fine, no drama, just easy.

[colin hamiltonParticipant @colinhamilton16803]

Thanks everyone. I opened the hole up with a milling cutter and then finished it off with a noting bar. It all went super smoothly. Thank you for all the advice.

[not done it yetParticipant @notdoneityet]

As per several, above, the simple milling cutter option (followed by a reamer if the finished size was needed to be precise?).

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