liam.mccaffrey
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| posted on 12/2/09 at 12:21 AM |
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Treppaning (sp?) in the lathe
I need to do some trepanning on the lathe this week and wanted some advice from any one who had done it before.
Its into the end of a 3" brass disc and about about 6mm depth.
What speeds/lube etc. I am going to grind a tool specifically for this with proper inner and outer radii. What clearances and reliefs should I
use?
I know this a long shot but i thought it worth a shot. Cheers
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splitrivet
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| posted on 12/2/09 at 12:30 AM |
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I tried it it once I needed it like a hole in the head.
Cheers,
Bob 
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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Alan B
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| posted on 12/2/09 at 12:36 AM |
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Liam, use as little clearance as you get away with...you'll need the tool as stiff as possible, although the depth you need is not excessive.
I'd use simliar speeds and feeds as if you were parting. No lube usually needed on brass.
Should be pretty straightforward really, never really had any problems myself...just keep overhang minimised.
Alan
[Edited on 12/2/09 by Alan B]
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liam.mccaffrey
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| posted on 12/2/09 at 12:53 AM |
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been practising with parting today alan and managed to get a tidy groove into the brass maybe 10 mm deep (20mm overall). I was very pleased with it
actually as it was the first time in earnest I had tried. Bit chattery until i set the tool height ever so slightly above centre and plucked up the
courage to feed a little more firmly. It was quite smooth then
I can set it up with very little overhang thinking about it 
[Edited on 12/2/09 by liam.mccaffrey]
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ashg
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| posted on 12/2/09 at 02:53 AM |
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if your getting judder either the saddle is too lose on the bed or the gibs on the crosslide need adjusting.
when you set the tool height put the tool in the tool post then put a static centre in the tail stock. move the tool up to the point of the static
centre and set its height about 1/2mm above the tailstock centre.
you will want about 500-600rpm and a feed rate of about 1.5-2mm per min although the bigger the lathe the higher you will be able to feed.
you need to make sure the rpm doesnt drop with brass or you will get a poor finish.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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neilj37
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| posted on 12/2/09 at 07:41 AM |
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quote:
Originally posted by ashg
and set its height about 1/2mm above the tailstock centre.
Thats one of the things i remember from being an apprentice. When parting off or trappaning make sure that the tool is set slightly above centre to
stop it digging in and causing judder.
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David Jenkins
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| posted on 12/2/09 at 08:56 AM |
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No lubricant.
Tool shape is critical - you want ZERO rake on the top, or even negative rake. In other words, the top of the cutting tool should be horizontal, not
sloping down away from the work. If you use the tool shape required for steel then the tip will dig in - brass cuts by shearing rather than cutting,
so a zero rake tool works best. A tool for steel will judder and make nasty noises as it digs in, but the correct tool will hiss and throw a stream
of brass needles straight at you!
I would set the tip of the tool as near to the centre height as you can possibly manage.
This link may help.
[Edited on 12/2/09 by David Jenkins]
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liam.mccaffrey
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| posted on 12/2/09 at 10:40 AM |
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got it.... zero rake, slightly above centre, all slides and gibs are properly adjusted. As little overhang as possible
hissing and small needles
Will try it tonight and post pictures
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liam.mccaffrey
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| posted on 12/2/09 at 10:52 AM |
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I love the illustrations in that link beautiful.
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David Jenkins
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| posted on 12/2/09 at 12:20 PM |
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quote:
Originally posted by liam.mccaffrey
got it.... zero rake, slightly above centre, all slides and gibs are properly adjusted. As little overhang as possible
hissing and small needles
Will try it tonight and post pictures
Try at centre height first - you can always raise it later.
Oh - I forgot - high speed and light cuts. However, judge the speed according to what you're doing (but it'll be faster than the same job
in steel).
You'll know when you've got it right - you'll find little brass splinters in the skin of your hands for days (nasty little b*gg*rs!)
- hard to see and very irritating!
(only joking - I love machining brass 'cos it's so easy to get a nice finish).
There's a fair bit of brass and bronze in my little beast here...
[Edited on 12/2/09 by David Jenkins]
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wilkingj
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| posted on 12/2/09 at 12:28 PM |
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Excellent link... Thanks from me too
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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