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Internal grooving help required.

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Dave Harding 108/06/2019 00:15:47
147 forum posts
4 photos


I need to machine an internal groove in aluminum. The groove needs to be 10mm wide and 2mm deep. The workpiece is 100mm OD and 87mm ID.

So plenty of room to work. I am struggling to find a tool to do it with.


Jeff Dayman08/06/2019 02:24:53
2189 forum posts
45 photos

Made the one shown below from a broken tap with the end ground to suit. It is set in a cross drilled mild steel bar. A tapped hole in the end holds a setscrew to hold the tool. You could make one a bit bigger of course but I would not try and cut the 10 mm width with a 10 mm wide tool. Better to make a smaller tool and move it along the 10 mm cut , doing a few passes to reach 2 mm depth. Hope this helps.


Paul Lousick08/06/2019 02:43:05
1868 forum posts
666 photos

What about one of these ? AU$15.94 on ebay.


mgivr2016 boring bar.jpg


JasonB08/06/2019 07:15:32
21632 forum posts
2493 photos
1 articles

I do the same a Jeff. For that sort of size work the tool along the 10mm length increasing the depth as you go rather than taking plunge cuts

not done it yet08/06/2019 07:29:14
6438 forum posts
20 photos

Yep, boring bar. Bought in, modified or made. Your choice of spend or use existing items.

Nigel Bennett08/06/2019 09:57:49
423 forum posts
11 photos

For reasons that escape me now, I once did a small job where I bored the groove OD into the bore with a slot drill, and then pressed in a little turned slug to create the groove. It depends on how much load you will have on a pressed in slug if you go that way.

Nigel Graham 208/06/2019 13:09:58
1772 forum posts
22 photos

My first choice would be a tool similar to the one shown by Paul, and it can be in HSS: a standard boring tool. Ensure the face of the tool is parallel to the axis to give the groove equal depth along its width.

The type Jeff illustrates is fine but does need plenty of room beyond the groove. A long-proven alternative capable of working right into the corner of a blind bore, holds the cutter in a hole at 45º across the end of the bar, with a grub-screw that protrudes less than the cutter. Obviously for a square-section groove the cutter itself is ground back at the corresponding 45º.

Tasks like this would be greatly facilitated by saddle or cross-slide stops in both directions. (Depending on lathe and set-up, the rear stop could be the tailstock, or a bar held in it.)


Recently I carried a somewhat similar task in PVC, where I needed not a groove but a narrow ridge, to make a special clamp with partially-closed bore for a corrugated plastic hose.

I experimented with something like that shown by Paul, by turning and filing, then hardening and tempering, a silver-steel cutter held by central countersunk screw onto the end of an existing mild-steel boring-bar. It was not very successful, but I think only due either to the "insert" shape not being quite right, or it slipping.

Certainly a field for further experimenting, but not original. I'd copied the idea from a trade text book from pre-carbide insert days, for a HSS-equivalent in profiling and threading tools.

Jeff Dayman08/06/2019 14:08:20
2189 forum posts
45 photos

"The type Jeff illustrates is fine but does need plenty of room beyond the groove."

Nigel, the OP does mention the ID is 87 mm and that there is plenty of room.

But If depth was an issue the boring bar layout that Paul suggested would be better.

Clive Brown 108/06/2019 15:49:50
723 forum posts
34 photos

p1020542.jpg A couple of home-mades that can cut close to a blind end. One is made from 3/8" silver steel by offset turning in a 4-jaw independant chuck followed by filing and hardening. Silver steel nowadays seems a rather under-valued material for cutting tools but it's fine with proper use.

The other tool has a 3/16" dia toolbit. This is clamped by drilling the bar lengthways and inserting a clamping rod which is tightened by a grub-screw accessed from the mounting end of the bar. A G H Thomas design for his boring head IIRC.

Edited By Clive Brown 1 on 08/06/2019 15:50:24

Edited By Clive Brown 1 on 08/06/2019 15:52:04

Edited By Clive Brown 1 on 08/06/2019 15:52:28

JasonB08/06/2019 15:55:21
21632 forum posts
2493 photos
1 articles

You can also use they style shown by Jeff and myself that is drilled for most of it's length and has a grub screw at the "blunt end" that pushes a rod that in turn bears on the tool. This needs very little clearance at the end and is also said to damp vibration.

Or you can slit the end and use a screw that goes top to bottom to clamp the cutting bit.

Dave Harding 109/06/2019 12:39:30
147 forum posts
4 photos

That's an interesting video thanks for sharing.

Dave Harding 109/06/2019 23:37:45
147 forum posts
4 photos

I eventually got the job done using an ISCAR miniature boring bar.

old mart10/06/2019 13:53:31
3411 forum posts
210 photos

The grooving insert holder in Pauls post is for MGMN inserts which are commonly available widths of

1.5, 2, 2.5, 3, 4 and 5mm. Each width has a dedicated holder, and the inserts also fit in left and right handed parting off tools. I believe the grooving tool shanks only go down to 16mm, limiting the minimum hole size and are too big for smaller lathes. The tips are commonly Chinese, but Korloy also make them. The inserts are double ended.

Edited By old mart on 10/06/2019 13:54:34

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