Mounting boring bar in the lathe

[Mick BaileyParticipant @mickbailey28509]

After decades of using old-style square stock boring bars in the lathe I decided to buy a round type with inserts S10K-SCLCR09 as a ‘make weight’ to get an order value over the postage threshold.

I was expecting the flats along the tool to give alignment of the tool tip when mounted in a conventional tool holder but was mistaken – they’re at an angle to the top surface of the tip. What’s the reason for this?

Presumably I need to make or buy a tool holder to mount it in a conventional tool post.

[JasonBModerator @jasonb]

The inserts are intended to slope down towards the tip of the insert, this is to ensure the edge of the insert does not rub.

Just clamp it by the flats on the shank

See on the table here where the angles are given, steeper as the minimum hole gets smaller. It also shows you that the cornet of the insert should be what you set to ctr height

[Peter Cook 6Participant @petercook6]

Long thread on the same subject here

 

[Mick BaileyParticipant @mickbailey28509]

I see. It’s a different approach to the angles ground on my regular boring tools. Good job I asked.

[Mick Bailey]

On 14 October 2024 at 10:44 Mick Bailey Said:

 

Presumably I need to make or buy a tool holder to mount it in a conventional tool post.

A guy on YouTube made one the other week. He just clamped a block of steel in his toolpost and mounted a drill bit of the correct size in the chuck to drill it for the boring bar. Milling a block of steel to fit the toolpost was the longest part.

[David George 1Participant @davidgeorge1]

This is my boring bar holder which is bolted straight on to thr saddle and replace the toolpost.  The centre of the hole for the boring bar is on center height which is the centre height of the tip which is inclined down to suit the tip cutting shape.

 

 

 

 

David

 

 

 

[Mick BaileyParticipant @mickbailey28509]

I’ve got a suitable block of steel so I’ll do something similar. I tried the bar out today on some 304 stainless and the finish is really rather nice, so I’ll get some different sizes and semi-retire my old boring tools.

 

[David George 1Participant @davidgeorge1]

I was making some nuts for a replacement set of main bearings and found that I could use the bar holder for screw cutting as well.

David

 

 

[duncan webster 1Participant @duncanwebster1]

That’s nice, another one for the todo list

[Nigel Graham 2Participant @nigelgraham2]

An excellent idea – and thank you for showing us complete with drawing, which of course can be adapted for other lathes.

My “To Do List” has long had a centre-height gauge with two steps, for setting either the front or rear tool-post, but I’ve rarely gone wrong by sighting the tool against a centre as in your photo.

This shows something that’s never occurred to me: are these boring-bar holders designed so the insert tip is on the diametral plane of the bar itself? Hence allowing your system to work without needing height and angular adjustment? The clamp screws would hold the angle by gripping on the flat. (Though the system necessitates a certain degree of tool standardising by the user.)

[Nigel Graham 2]

On Nigel Graham 2 Said:

are these boring-bar holders designed so the insert tip is on the diametral plane of the bar itself? Hence allowing your system to work without needing height and angular adjustment?

See the link I posted in the first reply, you can see that the shank is central when tip is on ctr height. The actual end that holds the insert sits lower.

[David George 1Participant @davidgeorge1]

The center height of my boring bar holder is bored on the center height of the the lathe as the cutting edge in on the center height of the diamiter of the bar on all diamiters so it is possible to actualy bore the holes on the lathe with drills, reams or boring bar mounted in the spindle. I have also thought of having a bush or two to fit smaller boing bars into existing holes it would just need further taped holes with smaller screws to hold the bar. when you put a boring bar in as the holder locates in the T slot in the cross slide it is always square to the job you are turning and as you tighten the screws just slightly rotate the bar untill it is nipped and it will be on center height then fully tighten the screws.

[JasonBModerator @jasonb]

David, could you not put three holes in the sleeve to allow the existing clamping screwed to pass through and bear on the actual bar. Or make some screws with the ends reduced in diameter.

[David George 1Participant @davidgeorge1]

Thanks Jason the idea of making screws with a reduced diamiter is a great idea sometimes I dont see what is obvious to do and save work.

David

[David George 1Participant @davidgeorge1]

I have made a bush as Jason suggested and as I had bought a 6mm shank 8mm boring bar at the show.. The screws were already machined at the end to give a flat face to clamp the boring bar on centre line.

No problem just unclamp the toolpost slide off and slide on the boring bar holder.

David

 

 

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