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Boring out a hole in middle of aluminium disc

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Jak2g30/04/2021 09:56:35
36 forum posts
10 photos

Good day everyone

I have an 8 inch aluminium disc, 1/2 inch thick, that has an 8mm hole in the centre. I need to enlarge that hole to 19mm.

I have a myford super 7 and a warco GH universal milling machine.

Keeping in mind that I am fairly new to machining, I am having difficulty figuring out the best way to enlarge the hole. Lathe or milling machine? I have a faceplate for the lathe but given the size of the disc I think it would be fairly difficult to secure.

Any recommendations to set me on the right track would be greatly appreciated.


Mike Hurley30/04/2021 10:10:01
305 forum posts
87 photos

Depends on what tooling you have - i.e. a boring head for the mill? If so, by far the easiest way as you can clamp it to the table (standing off for clearence) however you can - the advantage you don't have to consider balance as you would if mounting it on a lathe faceplate. . If not, you'll need to mount it on the lathe faceplate (standing off for clearence) and use a boring bar, but consider the balance as your clamping fittings might cause a lot of machine vibration if too unevenly spaced / different weights etc - and if using high RPM


Edited By Mike Hurley on 30/04/2021 10:12:58

Thor 🇳🇴30/04/2021 10:10:07
1608 forum posts
45 photos

If you can drill a few holes in the aluminium disc so it can be clamped to the lathe faceplate you could bore it in the lathe.
If drilling holes in the disc is not an option, you could clamp it to the milling machine table (with suitable spacers between disc and table) and use a twist drill and then a boring head.


Howard Lewis30/04/2021 10:10:49
6032 forum posts
14 photos

Given the size of the disc, I would be inclined to use a boring head on the mill.

If absolute concentricity is not vital, a close fitting 8 mm mandrel in the centre hole can be held in a collet while the disc is clamped on parallels to the table.

If concentricity is absolutely vital, then the disc has to be centred by using a finger clock in the small centre hole..

If you feel brave, and impatient, you could try trepanning with a small hole saw, but being 1/2" thick, will require plenty of lubrication and frequent withdrawals to clear swarf.

The hole can then be bored out to 19 mm diameter, in stages.

If boring from the start, it is going to be a relatively slow job, and boring in all senses of the word, and not quick. The cuts will need to be small, probably no more than 0.25 mm at a time, max, with the final cuts being smaller, and possibly requiring several spring cuts to get to finished size.



Michael Gilligan30/04/2021 10:11:59
20112 forum posts
1044 photos

In your position ... I would probably do it in the lathe:

Fix the disc to a piece of melamine-faced board, with double-sided tape, and attach that to the faceplate with screws.

‘though ... Having a BCA with its large rotary table, I might use that.


Edited By Michael Gilligan on 30/04/2021 10:16:04

Edited By Michael Gilligan on 30/04/2021 10:30:49

John Haine30/04/2021 10:17:59
4639 forum posts
273 photos

Clamp it flat on the mill table with a pice of MDF or similar underneath it. Put a bit of 8mm ground steel in your milling chuck to locate the centre hole before you tighten the clamps. Then lock the slides before raising the spindle. Now you have the hole exactly on the axis of your mill spindle.

To open it out I would probably use a series of slot drills (depending on what you have), feeding slowly using the Z leadscrew (not the quill lever - lock the quill). Take it slowly and use some coolant. Depending on the precision you want, you could use a boring tool for final sizing.

I wouldn't rule out using the lathe though - if you can accept 4 holes in the material you could bolt it to the faceplate, use a similar technique for centering it. Then just open the hole out with drills and finish by boring. If your FP is nice and smooth and clean you could even superglue it in place, centering with a centre in the tailstock, holding the plate against the centre and running it quickly to clamp on the FP (best use slow set glue). Once bored, undo the FP and put the whole thing in the oven at say 120* C to release.

not done it yet30/04/2021 10:25:05
6748 forum posts
20 photos

AsThor, re mounting, but first is this hole important re dimensions? Simply drilling should get you to 19mm. Boring is better, especially if you need 19.0mm or higher precision/accuracy.

A 3/4 inch drill may well suffice, if 19.1mm is close enough.🙂

Jak2g30/04/2021 10:28:02
36 forum posts
10 photos

Thanks everyone. I can't drill any holes in the disc unfortunately or I'd definitely be putting it on the faceplate.


I don't have any tools for boring on the mill, but this is something I could get. I was thinking the lathe could have been quicker, given that the largest drill I have is well under 19mm, so I think I'll be boring it out for a while!


I do want to have good concentricity because I'll be using this as a lapping disc mounted to a 3 phase motor and vfd 

Edited By Jak2g on 30/04/2021 10:29:14

Michael Gilligan30/04/2021 10:39:41
20112 forum posts
1044 photos

I have just edited my earlier post ... because I had omitted the words “with screws”

That said: it would be better [for convenient adjustment in-situ] to put threaded inserts in the board, and use hex socket screws. Attach loosely and use the tailstock centre for positioning ... then tighten the screws.


Adam Mara30/04/2021 10:50:48
167 forum posts
3 photos

Depending on the precision required, how about a 19mm reduced shank drill bit from Toolstation @£4.69?

SillyOldDuffer30/04/2021 11:06:07
8513 forum posts
1914 photos

I wouldn't muck about! The easiest way is on the mill with a boring bar and boring head, and boring heads are so useful. No problem clamping the disc to the table with a spacer underneath and then centring the mill.

Otherwise not too difficult to do an a lathe; the hard part is centring the disc on the faceplate.

Others suggest clamping with sacrificial MDF underneath, I might try bolting the MDF to the faceplate and supergluing the disc to the MDF. Don't overdo the glue because the MDF has to be removed later. Acetone as a solvent works too slowly my experience, and heat is better.  I'd just warm the Aluminium disc up with a blow-lamp, or pop it in the kitchen oven : not too hot - about 150°C for a few minutes should do it.

I wouldn't worry about the time taken by boring unless speed was of the essence. Boring is accurate rather than quick, but it's not dreadful slow.


Edited By SillyOldDuffer on 30/04/2021 11:08:28

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