Quality Finish

[martyn nutlandParticipant @martynnutland79495]

Hello

I wonder if the experts could give me some advice on obtaining a high quality finish on a part.

I'm making track rod ends for a vintage Austin Seven. As many, many of you will know; on an Austin Seven a fork on the end of the track rod clenches a steel pin by means of the ubiquitous cotter pin, then the steering arm/track rod arm has a bronze bush to pivot on said pin.

I'm using EN16T at diameter +/- 9.5mm and for mechanical rather than purely cosmetic reasons I'd like to achieve as near to a glass-like finish as I can. Recently I used some steel described as 'polished' from my supplier here in continental Europe (the excellent RC Machines in Luxembourg) but found the tool tended to tear the surface and leave it rough how ever sharp the insert or light the cut. I don't want that to happen again.

I won't be tryng to harden the pin in any way – the mileage doesn't warrant it.

Any advice and many thanks in advance. Keep well.

Martyn

[martyn nutlandParticipant @martynnutland79495]

Getting a ‘glacial’ surface on a part

[Paul LousickParticipant @paullousick59116]

What tool are you refering to ? And a photo of the part would be helpful for advise on what to do as I have never seen a track rod for an Austin 7.

Paul.

[JasonBModerator @jasonb]

Posted by martyn nutland on 23/08/2020 07:40:13:

found the tool tended to tear the surface and leave it rough how ever sharp the insert or light the cut. I don't want that to happen again.

A decent depth of cut to make the insert work will often result in a better surface finish, plus a reasonable feed and tip radius.

Failing that work through the grits with abrasive.

[KettrinboyParticipant @kettrinboy]

On 16t steel I would go with a HSS tool with say a 0.4 mm rad put on with a stone and use a quality cutting oil , works on all the usual alloy steels like 19/24/36b ,and the finest feed your lathe will do, if you turn a fine finish then polishing is quick and easy.

[Howard LewisParticipant @howardlewis46836]

For the ultimate, turn to about 0.0125mm oversize, and then polish with emery and oil, using finer and finer grades, possibly 600 wet'n'dry., until you are at the required size.

Being an Austin 7, you will actually be aiming for an imperial size, of course

Howard.

[Nick HughesParticipant @nickhughes97026]

I've had some good results Roller Burnishing shafts, by replacing the Knurls in a Clamp type knurling tool, with Deep Groove Ball Races.

Nick.

[Nigel McBurney 1Participant @nigelmcburney1]

Use HSS tool with about 15 degrees top rake,small radius on tip and hone with an oilstone,soluble oil is ok though a drop of liquid ROCOL helps, reduce speed to 40 to 50 feet per minute.

[Dave HalfordParticipant @davehalford22513]

Martyn,

I've found inserts for alloy CCGT32.51-AK H01 will give a much better finish on teary steels, they are really sharp.

[Martin KyteParticipant @martinkyte99762]

Turn as fast as possible.

regards Martin

[ChrisBParticipant @chrisb35596]

An HSS tool ground as a shear tool will give you a mirrior finish. The depth of cut should be minimal say 0.02mm and preferably supported at the tailstock end as this will generate some sideload.

[Mick B1Participant @mickb1]

Posted by Nigel McBurney 1 on 23/08/2020 09:34:28:

Use HSS tool with about 15 degrees top rake,small radius on tip and hone with an oilstone,soluble oil is ok though a drop of liquid ROCOL helps, reduce speed to 40 to 50 feet per minute.

That's more-or-less what I do too.

[martyn nutlandParticipant @martynnutland79495]

Many thanks all. HSS, fast, light, lubricant, stone. Got it.

M

[Brian Sweeting 2Participant @briansweeting2]

Use a shear tool to obtain a smooth finish then fine abrasive.

[Tim StevensParticipant @timstevens64731]

When you get the surface to the stage that it is silvery and you can barely see scratches, spin it fairly fast and apply a rage with metal polish (Solvol AutoSol used to be favourite) or use bodywork finishing products. This will produce a much more brilliant surface – like chrome but still only steel.

Quite why such a surface is required I'm not sure, though.

Cheers, Tim

[martyn nutlandParticipant @martynnutland79495]

Many thanks again for all the good advice.

I didn't know about shear tools which seem essential to the process.

Strangely enough, Tubal Cain has a whole video on making them and I'm now studying this.

Martyn

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