Author Topic: Getting a good finish  (Read 3095 times)

Offline Stuart

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Getting a good finish
« on: October 15, 2012, 04:15:07 PM »
First don't shot the messenger

I hade a job in the lathe today which involved boring a hole 0.75 inches dia in a piece of 1 inch square stock 3 inches deep through not blind


I was using  one of the tipped boring bars that are common in the merchants store  ( Glanze omega at el )  my HSS bars are either to short or to big

as I stated with a 0.5 inch drill the boring bar was small and well extended the finish was terrible look like I had used a rusty nail ,

so  on when  a new tip the one they sell for steel no improvement tried it fast, tried it slow, tried it dry, tried it with cutting oil  still a very bad surface , but as the finish size was getting near desperate measures was call for.


the hole dis. still required the middle size bar  so a quick sort in the tip draw and I found some of those tips they sell for non ferrous metals nice and sharp with a good rake ( supplied from the  dunstable outfit )
so one it went the cutter it just hissed and the finish was superb, by this time I could get in with the larger bar with the NON ferrous tip on the results were the same a good ridge free smooth finish in the bore

now I realise that these tips would not hold up for any heavy cuts but for finish work they work fine on Steel

I do not Know the grade but it aint EN1A  it must be a form of GGQ   ( Good ? General Quality ) unmachinium

again its one of the thing that goes against the book but it got me out of a mess today

may be worth a try next time I have some nasty lumpy steel to turn


Stuart

My aim is for a accurate part with a good finish

Bogstandard

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Re: Getting a good finish
« Reply #1 on: October 15, 2012, 08:31:11 PM »
Stuart,

If you have a mill boring head and can hold the part OK, I find that boring in the mill gives a far superior finish and size just using the crappy brazed tipped boring sets you can buy.

If I want ultimate finishes and sizes, then I use the HSS 'German' types of boring bars.

Top few on this page

http://rdgtools.co.uk/acatalog/TOOL_S_FOR_BORING_HEADS.html

John


Offline Stuart

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Re: Getting a good finish
« Reply #2 on: October 16, 2012, 08:19:13 AM »
thanks John for the info

Stuart
My aim is for a accurate part with a good finish

Arbalest

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Re: Getting a good finish
« Reply #3 on: October 16, 2012, 10:27:19 AM »
Yes, thanks John. Not seen those type before.

Bogstandard

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Re: Getting a good finish
« Reply #4 on: October 16, 2012, 11:52:11 AM »
The 'German' types of boring bar are the type that you can very easily make yourself using silver steel, but I am a great believer in not making tooling if it is available commercially much cheaper than it would cost me in time and materials to make them myself.

If I needed more robust ones, I would have to make them myself, as the ones I have seen available at reasonable prices are only in the smaller sizes.


John