Small diameter turning tool question

Hi,
Chronos have this neat looking tool for turning small diameters on their website at <http://www.chronos.ltd.uk/cgi-local/ss000001.pl?page=search&SS=sdtt&search.x=0&search.y=0&search ¬TION&PR=-1&TB=A>
(or search for SDTT from <http://www.chronos.ltd.uk ).
I was thinking of making a cross between this and the GW Thomas retractable threading tool, and I just wondered whether anyone here knows any reason why the inserts pictured on the Chronos website should appear to be made from copper ? I mean I know that is probaby what they are made from :-), but why copper ? I'd have thought bronze would be more normal here, no ?
Thanks,
--
Boo

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wrote:

As far as I recall, the inserts have to be made to suit the diameter if the work. Unless there is a regular use for a diameter, there is no reason why steel, cast iron, plastic or wood could not be used! I recall Sparey used wood and 'Cleeve' used steel and cast iron- so there is a sort of precedence. I got lost on the GHT thing because this is for screwcutting and obviously was designed to retract in and out only a thread depth. GHT DID a parting off tool for small diameters and he did a rear parting off tool- and I made both. Regarding his small diameter parting tool, this was illustrated but no steady is shown. Frankly, if the blade is razor sharp, I would agree with him. Regarding the rear parting tool and its blade, I couldn't grind the suggested top ( or bottom) vee and settled for a curved one- which works fine.
Maybe I have gone off at the wrong tack. If so, I apologise
Norman
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On Wed, 7 Jan 2009 10:43:16 -0800 (PST), ravensworth2674

    Not true, Norm....it retracts about a quarter of an inch.....but it's too bloody cold to go and check properly. :)
Of course, if you were referring to a girt thread like as what John S produces to keep the lid on his kipper-case, that might be different. --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Well, it's like this, yer 'oneur!
I keep looking at this ear contraption in GHT's book- which is in my snow hole-laughingly called a workshop.
Sorry, but it is the 'roundtuits'
'Harengs'heeds. loaves of breed, and aal manna' o'things! Sung in Craster- wheere the real kippers come from
Cheers
Norm
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Sorry to hi jack the thread but just looked at the link on Chronos in Firefox but getting no pics. Exploder shoes them. Is this Firefox or Chronos web page ? Anyone else having these problems.
BTW that design works fine I have been using a larger one today to turn some 12mm bar down to 7/16"
John S.
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Yes, John, and I am using Vista. Thought that it was ' the pirate king' thing Had to re-Google and go thru' the Myford bits to get somewhere. See they are doing this 'black box thing' More hi jacking- works well- thanks for the help in getting them
Cheers
Norman
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On Wed, 7 Jan 2009 14:23:13 -0800 (PST), John S

Seeing it all right in Firefox from here. Try a CTRL-R to reload and see what happens.
Would a small roller box not be simpler to adjust for different sizes?
Mark Rand RTFM
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Possibly easier to adjust, but also a bit harder to make and the diameters I need are all pretty small (3mm and 4mm at the moment) which makes small enough rollers hard to source and the roller bearing pins a bit flimsy.
Where do you stand on the copper question as a matter of interest ?
--
Boo

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On Thu, 08 Jan 2009 00:16:51 +0000, Boo

Copper's crap to machine and a lousy bearing material :-(
Mark Rand RTFM
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Well I won't use that then :-)
--
Boo

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Nope, still not working on that page but others work, the page looks wrong, it looks like a pure text page.
Roller box would work but I was just lazy, I set a tipped tool up to get to 7/16" then screwed a piece of brass bar onto the side of the tool and drilled it 12mm with a drill in the chuck.
To use it I set the toolpost square and offer the hole in the brass bush up to a 12mm dowel pin in the chuck. As long as it's minus 2 to plus 10 it's OK for the job it has to do but it's 120mm long so it's beyond the limits for a roller box in the turret. One day I may replace it with a 12mm bore sealed bearing.
John S.
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John S wrote:

Dunno if there's a problem with FF but I couldn't reliably get the URL to load either and I use FF (hence the product code in my original post).

But did you make the steady bearing inserts of copper or just what was lying around ? (Somehow I think I know the answer to this in advance :-)
--
Boo

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On Wed, 07 Jan 2009 17:09:19 +0000, Boo

If you're extremely lucky it might be aluminium bronze, which is supposed to be very good in that sort of application and is a coppery colour. On the other hand, they might just have messed up the colours in the pics.
Tim
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Hi Tim, The man from Del Chronos said brass so I guess you were right about the colours being messed up. I didn't know aluminium bronze would be recommended as a plain bearing material, I will have to lay my hands on some and have a play...
Cheers,
--
Boo

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On Thu, 08 Jan 2009 11:28:41 +0000, Boo

Aluminium bronze would be rather wasted in the application unless large amounts of stock of the same diameter were to be worked on. In a case like that, an oil hole might help as well. It isn't the most freely machining material on Gordon's green earth.
Brass is easy. Mild steel is cheap, I've got 2.7metres of 40mm square cast iron that I'd use, due to my habit of buying full lengths of metal rather than the odd foot.
Mark Rand RTFM
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Sounds like overkill for me I will only use it occasionally to make parts in 5's off quantities.

I have some brass of a suitable diameter so brass it is...
Thanks to all who posted,
--
Boo

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I've just engaged in turning down "mild steel" (don't better than that) 4mm round to 3mm leaving a corner into the shoulder. What's the best tool profile / speed to get a good finish?
I've been using an HSS knife tool and it keeps picking up now and again spoiling the finish. (Even with Neatcut)
TIA
Steve
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Steve,
I was doing a few tests on my new (to me) lathe yesterday. With a very fine cut (0.025mm or 1 thou) and a very fine feed (0.03mm/rev) I was able to get a mirror finish on EN1A with a brand new CCMT TC tip. The speed was about 5-600 rpm on a 1/2 inch bar, so for your 4mm I would make that around 1000 rpm, but it's more important to pick a speed that does not cause any "chatter" which is ruinous to finish. (I have a variable speed 3-phase inverter drive, so can change speeds on the fly, though to be fair you are less likely to get chatter with such a fine cut).
You are unlikely to get such a fine finish by going straight from 3mm to 4mm (if you do, you are doing better than me and don't need any advice!).
You should be able to get a similar finish using an HS tool, but only if it is very sharp. The finish from a grinder is not good enough, you will have to hone it on a stone or diamond hone, taking care of course not to round over the edge. Use a RH knife tool with a small radius (but not less than the feed rate per rev) on the tip, this will help smooth the peaks and crests.
Finally, if you still cannot get the finish you desire, I find careful use of a number 4 cut Swiss hand file (or even better a number 6 cut) with a dose of cutting oil will give a very nice finish. *Do* however ensure you have a proper handle on the file, the injury to your wrist from the file tang if it catches is too awful to contemplate. Also make sure the file is cleaned of steel fragments at regular intervals (use a piece of 1/8 or similar brass along the line of the teeth) otherwise the fragments will spoil the finish.
David
--
David Littlewood

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writes

Thanks David,
I've been taking the same cuts as yourself, but the feedrate is much higher at 0.2mm /rev so I'll drop that down, though I can't to 0.03mm /rev with the gears I have. I've been running at 1500rpm. I've got some CCMT tips, but given the shoulder is only 1mm high on a 4mm dia, I really need a very small radius to get into the corner. I'll make sure the knife tool is upto snuff then have another pass.
The good news is when you are only taking 1mm off 4mm for a length of 6mm, scrap and time lost is trivial!
Steve
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Yes; remember, the effect you get on turning is akin to screwcutting on a small scale, and with a knife tool you get a sawtooth finish. The finer the feed, the smaller the teeth.

You can always try undercutting the corner (or, better from a fatigue point of view, chamfer the mating bore mouth).

David
--
David Littlewood

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