Author Topic: parting of made simple  (Read 6586 times)

Offline stirling lad

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parting of made simple
« on: November 02, 2014, 10:22:47 PM »
I saw this video from latheman on utube...
I thought his explanation about the blade being knocked clear of the work piece seemed wrong if he was cutting dead on centre but i gave it a try anyway,,,,,,, and it was AMAZING!!!!  i've never parted of anything so quickly,,, ok, ive only tried brass so far but what a difference... just by turning the cutter up-side down...
https://www.youtube.com/watch?v=-RZRq0olsxM

has anyone else done this ?? ..

...mike...

Offline wheeltapper

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Re: parting of made simple
« Reply #1 on: November 03, 2014, 07:09:29 AM »
seems to me just the same effect as a rear mounted toolpost.

Roy.
I used to be confused, now I just don't know.

Offline DavidA

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Re: parting of made simple
« Reply #2 on: November 03, 2014, 08:22:58 AM »
Mike,

I can't watch the video at the moment,  problem of some kind. Getting error messages.
But from what is written it seems like you turned the tool upside down and ran the machine in reverse.  Is this correct ?

Problem is that if you do this on a machine with a screw on chuck then there is a very real risk of unscrewing the chuck during the operation.

Dave.

Offline Arbalist

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Re: parting of made simple
« Reply #3 on: November 03, 2014, 08:38:07 AM »
Thanks for posting that Mike. I've been meaning to try one of these on my Lathe.

http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=31&Itemid=45

Roy, many of us can't easily fit a rear toolpost on our Lathes so this is a good option.

Good point Dave but I think most mini lathes like mine don't have screwed on chucks. One to look out for though.

I'll certainly be trying this as soon as I can Mike, thanks again.  :thumbup:



Offline BillTodd

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Re: parting of made simple
« Reply #4 on: November 03, 2014, 11:48:23 AM »
Quote
I thought his explanation about the blade being knocked clear of the work piece seemed wrong if he was cutting dead on centre but i gave it a try anyway

He is right. The problem is that a parting-off cut requires considerable cutting force, enough to bend the machine (tool post top-slide cross-slide etc.) . The geometry of the machine means that as it bends it pushes the tool further into the job creating even more cutting force - a vicious circle that, with a parting blade*, usually results in a stall ,broken blade or worse.

Changing the direction of the cutting force, either by cutting in reverse (watch that chuck!) or using a rear mounted tool-post will bend the tool away from the job.

There are parting-off versions of the ancient spring-tool design that can do the same automatic backing off task.

Bill

*Chatter is caused by something similar.  Chatter occurs when the tool springs back out of the work as the thicker chip breaks. The combination of springiness and mass of the machine parts, means that is plunges back into the work and so the cycle starts again  - only reducing the cutting force will stop the cycle so oil, reducing cutting speed, changing cutting edge etc, will help to stop the chatter.
« Last Edit: November 04, 2014, 07:16:32 AM by BillTodd »
Bill

Offline studders

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Re: parting of made simple
« Reply #5 on: November 03, 2014, 10:12:48 PM »
I don't know if it was just my eyes playing tricks but to me it looked as though the cross slide or top slide was being pushed up quite a bit.

Offline dawesy

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Re: parting of made simple
« Reply #6 on: November 04, 2014, 05:26:50 AM »
One thing I've found that helps is if it's a large dia I'm parting is make the first cuts a bit wider as it helps lessen drag on the parting tool.
Lee.
wishing my workshop was larger :(

Offline Manxmodder

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Re: parting of made simple
« Reply #7 on: November 04, 2014, 07:21:52 AM »
You're right Lee,that extra side clearance is certainly helpful when using the parallel sided hss blade type.
 If using the carbide insert tip type the insert is dovetail tapered to provide side clearance with the widest point being at the cutting edge.....OZ
Helixes aren't always downward spirals,sometimes they're screwed up

Offline Arbalist

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Re: parting of made simple
« Reply #8 on: November 04, 2014, 08:59:32 AM »
These look pretty good, particularly the Mode A profile type with the deep chip breaker.

http://allianceglobaluk.com/products/empire-regrindable-blades/

I've contacted the company and they will supply direct. The HSS PM2N is 24.96 and PM2N Mode A are 28.98 ex VAT plus postage for orders under 100.

Offline Jonny

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Re: parting of made simple
« Reply #9 on: November 04, 2014, 02:47:01 PM »
I don't know if it was just my eyes playing tricks but to me it looked as though the cross slide or top slide was being pushed up quite a bit.

Quite correct noticed it straight away that's why those machines are flimsy. He has the feed just about right, notice taking a cut withdrawing, another sign of flex or movement.

$90 in Aussy link plus a decent cutter and expensive shipping might just as well have the real deal from likes of Seco, Manchester, Iscar, Arno, Kennametal etc and not have to bother sharpening every cut off with hss.

Repetitive work I will put a rear quick release tool post on and gang the tools up one being an upside down parting/grooving tool. Does same job and don't have to stop and restart in reverse direction. Is it any better, dubiously.

Offline bp

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Re: parting of made simple
« Reply #10 on: November 04, 2014, 08:17:06 PM »
I've been parting off backwards on my minilathe for years.  The blades I use are HSS 1mm thick and 1.6mm thick from A.R Warner in the USA.  The toolholder was deliberately kept as small as possible to reduce overhang.  Works a treat.  Obviously you need to be careful with old fashioned (ducks behind cover) lathes with screw on chucks.
cheers
Bill

Offline Arbalist

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Re: parting of made simple
« Reply #11 on: November 05, 2014, 04:15:35 AM »
Might just as well have the real deal from likes of Seco, Manchester, Iscar, Arno, Kennametal etc and not have to bother sharpening every cut off with hss.

No not really, most of them don't make holders for mini lathes like mine.

Sharpening one edge on a HSS parting blades is hardly a bother is it?!

I do have and use insert tooling for some turning and parting but prefer to keep my options open by using HSS tooling as well.
Unless I'm turning hard stuff I find HSS is much cheaper as well.

After having an insert parting tool block not fit my Lathe very well I wouldn't buy another one, I'd just buy the blades and make my own block like I did for the last one.

Offline Jonny

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Re: parting of made simple
« Reply #12 on: November 05, 2014, 09:13:57 AM »
Might just as well have the real deal from likes of Seco, Manchester, Iscar, Arno, Kennametal etc and not have to bother sharpening every cut off with hss.

No not really, most of them don't make holders for mini lathes like mine.

Sharpening one edge on a HSS parting blades is hardly a bother is it?!

After having an insert parting tool block not fit my Lathe very well I wouldn't buy another one, I'd just buy the blades and make my own block like I did for the last one.

Buy cheap expect problems, just saying the Ozzy link works out around same price as a decent tool complete. Didn't even pay that for the 32mm Iscar and tool block or any of the other 8 parting tools each. Use one and you will wonder why you struggled.
Why constantly remove blade to keep touching it up, not ignoring the fact of different angles and its effects, then setup each time hardly cost effective unless diy. By the time faffed about touching the hss up I could have done the job. HSS blades has more tendency to veer off, have loads worthless free to good home.
I turn with mine, great finish cant do that with HSS without flex.

Offline Arbalist

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Re: parting of made simple
« Reply #13 on: November 05, 2014, 10:35:40 AM »
Good for you John but there are plenty of hobbyists on here that do things for fun not to earn a living removing metal. I'm one of those and I'm glad when folks post links to tooling more suitable for the hobbyists on here. If I had to earn a living with my Lathe or Milling machine I might a agree with you but then I probably wouldn't waste valuable time posting be on here telling folks that anything other than insert tooling is a waste of time.

Offline stirling lad

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Re: parting of made simple
« Reply #14 on: November 05, 2014, 03:42:45 PM »
  I'd just like to thank Bill Todd for his explanation of how the blade clears the work piece .... I now understand how it's different..even though it's still on centre... thanks for that Bill.. :thumbup:..

 in his video the bloke uses one of these insert tools,,, i can't afford that stuff but it still worked a treat with an ordinary hss blade..

DavidA  yes your right,, sorry i forgot to mention that the lathe is run in reverse...
   ...mike..

Offline Arbalist

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Re: parting of made simple
« Reply #15 on: November 06, 2014, 04:38:40 AM »
Chronos now sell similar blades separately from their holders. Not in the same range of sizes sadly but the ones they have are much cheaper.

https://ad101.infusionsoft.com/app/linkClick/6577/67d540a1df70e80c/4522827/f0e1fdfb2cd7d43c


Offline Jonny

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Re: parting of made simple
« Reply #16 on: November 06, 2014, 04:09:28 PM »
Missing the point Arbalist I had to start some where and did it for fun for around 20 years so know both sides.

Parting was always a problem best avoided by using either a decent Sandvik tool or many of those hss cobalt blades even Eclipse that will wear before it actually parts off some materials. No way could I bring myself to fork out for a decent brand (Iscar) parting tool but knowing what i know now after trying loads of designs, it was part of the problem, the other was machine flex the root of all evil.
The point being is that decent non Chinese tipped tools last the job having little flex without wearing out and different styles cut better than others so would be pricey finding the right tool.

Offline Arbalist

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Re: parting of made simple
« Reply #17 on: November 07, 2014, 10:21:59 AM »
You're still speaking for yourself and the way you work. Some folks on here would struggle to use insert parting tools on their modest size machines so they use HSS.

As a point of interest I use both insert and HSS turning and parting tools.

I also don't believe insert tooling is the only answer as the link I posted earlier suggests.
The products they sell are clearly aimed at industry not hobbyists.

http://allianceglobaluk.com/products/empire-regrindable-blades/

I think it's best we agree to disagree on this one Jon.