Advice on cutting 16mm diameter groove on the lathe

[Steven ShandParticipant @stevenshand77617]

Hi,

 

I’m looking for some advice on tooling. I want to cut a 16mm diameter groove around an aluminium part, a simple pulley style disc. At the moment I’ve been using a ball end mill with the part mounted on a rotary table on my milling machine. This kinda works but is slow, difficult to set up and the finish isn’t great.

It seems like I really should be doing this on my lathe but I’m not sure of the best tool for the job. I think I should be able to use a circular insert on an indexable tool. I think an RCMT16 is what I need and although I’ve found inserts for this I’m not sure what holder will work with this insert. I’m a little bogged down with the charts showing compatibility. My tool holder has a 12mm capacity.

Can anyone help on this and point to an example of a tool holder that would work with an insert I’ve described?

Many thanks.

 

[JasonBModerator @jasonb]

What lathe do you have as a small one won’t have the grunt or rigidity to handle the amount of tool engagement that a 16mm dia insert will require.

I’d probably work out a few co-ordinates to rough out the waste and then make a form tool either half round end or maybe a 1/4 of the circle and do one side at a time.

[Steven ShandParticipant @stevenshand77617]

Thanks. I have a Warco WM290. I did wonder if it would have grunt for the job.  A half round profile is probably a good plan. I’d like it to be really accurate though hence buying something that was dimensionally correct would be preferred over creating and maintaining a tool myself.

[noel shelleyParticipant @noelshelley55608]

A form tool after roughing out to somewhere near, but why the need for such accuracy ? Made some pulleys for a winch which were in steel this way. Good luck. Noel

[Steven ShandParticipant @stevenshand77617]

but why the need for such accuracy ?

 

They are support wheels for a roller bender. It’s very thinwall tubing that’s being bent and if the tube isn’t really well supported then you end up with slight deformations in the tube. Sounds like it could be quite a rough fit but it really can’t unfortunately.

[Martin Johnson 1Participant @martinjohnson1]

Why are you using a ball nose cutter?  Use a plain 16 dia end mill, plunge into the side and then rotate the work.  A 16 cutter working on the side face will rip metal off pretty quick.

Martin

[Martin Johnson 1]

On Martin Johnson 1 Said:

Why are you using a ball nose cutter?  Use a plain 16 dia end mill, plunge into the side and then rotate the work.  A 16 cutter working on the side face will rip metal off pretty quick.

Martin

Thanks. I did try that setup but I think from memory (I’ve tried a lot!) the issue was that I didn’t have the clearance to get the 16mm end mill fully engaged in the part. Perhaps a longer endmill would have worked. I’ll look again at that.

[noel shelleyParticipant @noelshelley55608]

AH YES ! Bending thin wall is never easy and even with tight formers there is a limit. Again, good luck. Noel.

[JasonBModerator @jasonb]

You could mount the pully on an arbor so it stands further away from the  rotary table and then your existing cutter may do. It is something you often need to do when cutting gears.

The right type of ball cutter would also work and they can be setup for convex as well as concave. Mine would need some modification to do the size and depth you need but it is an option.

[DC31kParticipant @dc31k]

An option might be to use a 5/8″ cutting tool and do the final finishing with abrasives. That would put a good surface finish on the roller, which could be difficult to achieve with other methods.

Having both imperial and metric tools in mind could give a wider choice for buying something.

Delrin might also be an alternative material and allow use of tools designed for woodworking.

[Ian PParticipant @ianp]

I made several black Delrin rollers with semicircular grooves for a sliding door to run on 25mm diameter SS tube for a ‘designer’ kitchen.

I used parts out of my scrapbox, the two black horizontal bars are clamped to the tubular spacer and the lower bar is fastened to the lathe cross slide with the single hex bolt. The HSS cutter bit is mounted in a cross drilled hole in a bar free to rotate (hand turned with the lever at the top)

If I was doing the same thing again I would probably use a small boring head mounted on a spindle running in a journal fitted to the toolpost. Big advantage of a boring head is accurate radius setting.

Ian P

mbvjhv

[Clive Brown 1Participant @clivebrown1]

I’ve made aluminium pulley sheaves using a silver steel form tool. Turn the disc with, say, a 12 – 14 deg. inc. taper for front clearance. Hardening & temper might not be needed for a one-off. Cheap as chips.

[Clive Brown 1]

On Clive Brown 1 Said:

I’ve made aluminium pulley sheaves using a silver steel form tool. Turn the disc with, say, a 12 – 14 deg. inc. taper for front clearance. Hardening & temper might not be needed for a one-off. Cheap as chips.

 

That looks perfect actually. I’m not sure why I didn’t think of that. Thanks.

[Andy_GParticipant @andy_g]

You may find that a full radius form tool chatters horribly.

There’s the option of ‘machining by numbers’ by making plunge cuts with a smaller radius insert – this is a 6mm diameter insert cutting a 20mm radius.

Steps of 0.2mm between passes meant that minimal hand finishing was needed to blend the surface:

 

(More info here )

I have a spreadsheet that can calculate the coordinates if you are interested in this approach.

[Ramon WilsonParticipant @ramonwilson3]

This very topical!

Only last night I did exactly the same for the same reason only mine was 9.5 dia (3/8″ actually). The shape was formed by grinding the radius on a piece of 3/8 sq HSS freehand on the bench grinder and plunging straight in. No issues were found in cutting and the form produced is certainly good enough to form the copper pipe around.

Personally for 16mm I would make a circular cutter from silver steel and mount it to a piece of bar – certainly accurate  and sturdy enough for a one off – I made those in the pic for turning gear cutter blanks – the cutter has a spigot that is juts loctited innto the holder and have done others where the cutter is held on by a central screw much like any insert tooling

hope that’s of use
Tug

 

 

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