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24mm end mill for 16mm collet?

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Jim Mason12/04/2021 14:35:56
7 forum posts

Hello all,

I'm hoping you experts can point me in the right direction. I have some 3mm 304 stainless steel laser cut plates that I fix 24mm OD bearings into. These are lasercut with the hole undersize, and currently I open the hole out using a 24mm blacksmiths drill with a 12.5mm shank so it fits in the mill chuck. This isn't brilliant as it deforms the steel and results in a loose fit. If I could go through with an end mill instead the finish and fit are much better.

I only have up to 16mm collets, and it looks like a 24mm cutter with 16mm shank is as rare as hens teeth. Does anyone have any alternative solutions that might work?

This is all to be done on an SX3 mill with MT3 taper.

JasonB12/04/2021 14:51:06
20443 forum posts
2267 photos
1 articles

Boring head, that will allow you to fine tune the fit.

Or a 24mm Rotabroach cutter in a 19mm MT3 collet

Edited By JasonB on 12/04/2021 14:56:56

Martin Connelly12/04/2021 15:01:54
1705 forum posts
181 photos

I would consider one of these Ø24mm Hole Saw Cutter High Density Carbide Teeth for Stainless Steel Metal available for about £10 when searched for on line.

As an alternative at a higher price Ø24mm Rotabroach mini cutter and matching arbor.

Rotabroach mini cutters

You need the RA118 arbor for cutters over Ø21mm.

Rotabroach are more expensive but are made to accurate diameters.

The pipe fitters where I used to work used them on 316L stainless pipes in preference to drills.

These types of hole saws are better for sheet metal than drills when the diameter is a multiple of the thickness as is the case here.

Martin C

not done it yet12/04/2021 15:36:33
5853 forum posts
20 photos

With your machine in its current state of fettle, motor-wise, I would suggest the boring route is likely the favoured plan. How much undersized are the holes? If substantial, the blacksmiths drill may not do you motor brushgear much good, btw.

JasonB12/04/2021 15:39:41
20443 forum posts
2267 photos
1 articles

Step drill would be another option if you can live with the inaccuracies of a drilled hole. But I would still opt for the boring head, if you get then rough laser cut to 23 or 23.5mm it's just one light cut to clean up the hole to exact size.

SillyOldDuffer12/04/2021 15:40:40
7131 forum posts
1571 photos

+1 for a Boring Head. Slower than a hole-saw or drill, but precise and unlikely to chew up. The other advantage is a boring head will open a hole to any size wanted within the limit of its swing, which is wide!


Tony Pratt 112/04/2021 15:55:53
1503 forum posts
7 photos

For a bearing I would recommend a boring head.


Jim Mason12/04/2021 18:06:37
7 forum posts

I've never heard of a Rotabroach but that looks the thing for me, I'll give that a go. Thank you all for your helpful advice.

Ady112/04/2021 19:01:45
4345 forum posts
675 photos

Boring head/bar for anything over 16mm imo

I've used a boring bar at high speed to 40+mm in steel

it comes off like gossamer with a fine feed  and leaves a nice finish

Edited By Ady1 on 12/04/2021 19:04:32

duncan webster12/04/2021 21:36:35
3179 forum posts
55 photos

If you only ever want to bore 24mm you can make up a boring bar to go in the 16mm collet and fiddle with the cutting bit till you get the right diameter. No more difficult than using a between centres boring bar on the lathe.

Mike Poole12/04/2021 22:53:36
2963 forum posts
70 photos

Tungsten carbide will machine the shank of a HSS cutter, it is a bit heavy going but it can be done.


John Reese13/04/2021 02:25:03
906 forum posts

If drilled hole tolerance is acceptable try a 3 or 4 flute core drill. On thin material a 2 flute drill tends to make a 3 lobed hole. The core drill would eliminate the lobing.

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