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Parting problems

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Michael Foden15/08/2012 21:47:42
24 forum posts

Can someone recommend a reasonably priced indexable parting tool ( £20 -£25 ) that will tackle 1.5" diam mild steel without problems.

In the past I have used a rear toolpost with 1/16" x1/2" blade inserted in a holder (Eclipse ). There have been no problems with brass or Magnesium, but these are the only metals I have worked .

However, with the mild steel, It very quickly starts to chatter, no doubt due to the blade flexing, even though there is minimal blade projection.

I have been looking at Glanze (from Chronos ), & a similar tool from RDG ( make unknown )- both within this price range. Tool will be for ML10.

Thanks

Mike.

David Littlewood15/08/2012 22:12:20
533 forum posts

A bit out of your price range, but the best parting tool I have used by a country mile:

**LINK**

If it's too much for you, well, might help convince some other readers!

David

Versaboss15/08/2012 22:26:12
483 forum posts
55 photos

Martin, a bit off-topic I know (*), but I would be very very interested to know where you can get Magnesium (rod or tube) in sizes suitable for turning. Not even on Ebay did I find that, and there are lots of 'exotic' stuff to find there!

Greetings, Hansrudolf

(*) cough, cough, tons of articles about parting off already on the 'net, imho...

speelwerk15/08/2012 22:52:13
439 forum posts
2 photos

Seems a bit much for 12inch, but if you are in need of it.

**LINK**

Ady116/08/2012 00:47:52
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5065 forum posts
734 photos

You only need one thing for parting

lathe stiffness, and some power

Without stiffness you are totally stuffed

minute amounts of chatter will make parting off a nightmare

Springbok16/08/2012 01:45:27
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879 forum posts
34 photos

This subject has been done to the death a number of times, could I reccomend that you do a search on this and other forums and you will find all your answers.

Good luck
Bob

Clive Hartland16/08/2012 07:30:55
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2812 forum posts
40 photos

1/16" sounds a bit thin for 1.5" steel, I would recommend something a bit wider and stiffer.

I use a 3/32" blade on my ML10 and close to the chuck will do a 1" depth cut with ease @ 800rpm using brush applied WD40.

Keep close to the chuck, keep even constant cut and make sure the cutting edge of tool is correct, tipped tools will not alleviate chatter !

On a seperate note, has anyone found that steel lately has bands of harder materiel in the depth of the metal when cutting ? Recently I found at about 1/8" in, a hard band that was like a sheath of hardness through the metal.

Clive

Edited By Clive Hartland on 16/08/2012 07:33:50

Harold Hall 116/08/2012 09:03:02
418 forum posts
4 photos

Ady is right, stiffness of the lathe is all important when attempting to part off. However, when it comes to lathes being used in the home workshop many will be on the borderline so to speak. In this case, mounting the parting tool in a rear toolpost is the only option. Where is the tool mounted on your lathe Michael.

For many years I used the one mentioned by David and can confirm that it is good. I did though often feel that one with a narrower width tip would be better at smaller diameters so purchased the Glanze 2mm wide tip from Chronos. This I have used both on my Hobbeymat MD65 and now extensively on my Super seven with very good results.

Incidentally, the tips on my parting tools are the only tips that I attempt to sharpen. When they are showing signs of becoming blunt, using a fine diamond hone, or file, on just the front face will bring new life to it.

Is there any possibility Clive that the tool is above centre, even very slightly, as this will cause the tool to rub and stop cutting at small diameters. For this reason I always set all my lathe tools marginally below centre.

Even this though is self defeating at very small diameters. Having to turn around 100 decking nails for a model Monmouth wagon that were about 0.010" diameter, the tool needed to be on centre +/- 0.000" and definitely not above centre else the tool will just rub.

Harold

David Littlewood16/08/2012 11:48:03
533 forum posts

Harold,

For really fine work - in my case, O gauge loco building - I find one of these mini-thin grooving and parting sets: **LINK** is the best thing I have used. Eye-wateringly expensive at normal catalogue price, but no-one pays those, you can get a good discount by entering a simple code (which I can't remember offhand!) but even better, they are on special offer at around half price about every other month in the sales flyers.

David

PS The sets are on page 523 - link seems to go to the previous page whatever I do.

Edited By David Littlewood on 16/08/2012 11:51:08

Michael Foden16/08/2012 13:18:46
24 forum posts

Thanks to all for replies. Obviously some of these tools are beyond my price range, but the answers give me something to ponder.

I did do a search on this forum for parting tools, but nothing came to light.

 

Mike.

P.S. Have sent P.M. to Versaboss as I have some Magnesium.

Edited By Michael Foden on 16/08/2012 13:20:38

Russell Eberhardt16/08/2012 13:39:19
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2728 forum posts
86 photos

Mike,

To answer your original question, I have the Glanze tool and while it may not be the best it works for me. For smaller sizes I tend to stick to home made HSS tooling.

The difference between front and rear mounting isn't just rigidity but, due to the geometry, a rear mounted tool tends to move away from the work when it deflects while a front mounted one moves towards it which causes digging in. Thus , for a light or worn lathe the rear mounted one works best.

Russell.

Michael Foden16/08/2012 16:06:27
24 forum posts

Hi Russell

My lathe is a Myford ML10 in first class working order. As noted in my original post, I suspect that a 1/16" thick blade will not tackle larger diam. mild steel.

I note that the Glanze type tools will operate from the front, & the advange with the design, as far as I can see, is that the blade is supported from underneath whilst cutting. This is not the case with the inserted blade tool which I have been using - OK for brass & alloys, but not for steel.

But, since posting, I have also tried a 12mm sq, parting tool ,tip about 3mm wide( used from the front of the lathe ), could be HSS or carbide, I'm unsure. It is razor sharp, & cut beautifully when a portion of the tip was in use, but started to chatter when the full 3mm made contact. This leads me to suspect that the problems maybe with the mounting of the work.

Mike.

KWIL16/08/2012 16:50:16
3549 forum posts
70 photos

It could be that the tool is not truely square to the job and the sides are rubbing. One advantage above all of the inserts is that they curl the swarf inwards towards the middle of the kerf which helps to prevent side jamming.

Harold Hall 116/08/2012 19:46:21
418 forum posts
4 photos

Thanks David for highlighting the Mini Thin inserts, I have been using these for around ten years with a double turret on my rear tool post, one side with a Glanze parting blade and the other a Mini Thin insert in my shop made holder. I agree though, even the tips are expensive.

If any reader has earlier copies of MEW or have access to the digital copies the holder can be found in issue 107 page 29. It is one of the few articles of mine that are not on my website, perhaps I should take this as a prod to put it there.

I too though had a problem with the link, it only showed the top of the page and when I attempted to move the cursor over the page to move it up the cursor just disappeared. I went back ot MSC's home page called up the catalogue and placed the page numbers 522 and 523 from the keyboard and it worked fine. Funny things computers.

Harold

Michael Foden16/08/2012 20:09:36
24 forum posts

Think I may be on track to answering my parting problems.

For years I've used an inserted Eclipse HSS blade in a very sturdy rear toolpost, & this has coped with non ferrous very well, even though blade is 1.5mm thick.

I have now actually measured my 12mm parting tool at the tip, & find it is 4.5mm thick at the cutting edge, not 3mm as mentioned in previous post.

So I've concluded, rightly or wrongly, that one blade is too thin & one too thick. Have ordered a Glanze carbide indexable tipped tool with a 2mm thickness. This is supported underneath , so I am hoping for good results.

Watch this space.

Mike.

mgj16/08/2012 20:32:25
1017 forum posts
14 photos

I'm sorry but it is simply not true that a rear mounted parting tool moves away from the load. That old chestnut has been around for years, and I am afraid that a lok at the vectors involved prove that is oversimplified and wrong If it was right the tool wouldn't jam up at the back - and it can.

Draw it up - its easy to see.

img.jpg

 

The force acts at right angles to the face of the tool - on the top rake.So it has 2 components - some downwards(at the front) and critcally, some inwards Put that point above centre at the rear and you create a situation where you have an inwards force pulling into thinner material if things go wrong so its tending to unload. Put the tool below centre then you have an inwards force digging into thicker metal.

Do the same drawing from the front, and you can see the forces are the other way around but otherwise identical. And you would expect that since the tool and the job have no idea where they are.

What  is needed is an argument that explains how it jams both front and back, and why its less likely to jam at the back. And thats pretty simple, once you look at the mechanism.

Waht you have to do is take off the inwards force - take off the rake, you remove the inwards vector and it doesn't jam. Look at the commercial indexed tools and they are all almost zero or negative rake.

How does it work - You dig a tool into the material, you generate that inwards force, but the feed is greater than that inwards force so the tool is kept under control in the backlash gap - its jammed against the feed nut, and it cant move forwards. Reduce the feed, the cut is insantaneously identical, but that pressure is removed - it is now free to pull in, which it will in the backlash in the feed nut. Which is why most of the time these jam up occur when the operator is being careful

If you get rid of the rake and maintain a steady feed, you find that jam ups are a thing of the past. I have apile of tools and kept putting on rake, because it looked sharper. Bought about 10 different models to try to solve the jamming problem. The identical tools, reground don't jam any longer - no top rake. And I don't part off from t he back any longer. If anyone wants a genuine Myford rear parting toolpost they can have it. It is perfectly useless and offers no advantage. PM me!

 

Why doesn't it jam up at the back so much - less feednut backlash, because normally that face on the screw is only ever used to retract a tool under no load. But put enough rake on and it will jam at the back, and very easily - that I promise. Got that tee shirt.

 

BTW tools have to be straight etc as well - thats understood. As is the fact that tools must give vertical glearance. I do agree though that the Sandvik 2.5mm tool as fitted to the Kit Q Cut cuts better than the GTN2 fitted to the Glanze and others.  But not by much, and hte GTN is a lot cheaper and made by many people.

Edited By mgj on 16/08/2012 20:35:06img.jpg

Edited By mgj on 16/08/2012 20:38:08

Edited By mgj on 16/08/2012 20:43:54

Stub Mandrel16/08/2012 21:42:16
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4315 forum posts
291 photos
1 articles

For what it's worth, I think the issue is entirely dwn to chip clearance problems or side rubbing leading to poor cut, followed by grab. Reason? Aparting tool cutting full width on the end of a workpiece won't ever jam up, despit making the same cut and taking the same load as when parting. the thing that causes the problem is being in a groove.

The solutions are manifold, and it's clear that adding rigidity helps by limiting tool flex, but that's addressisng symptom, not cause.

neil

blowlamp16/08/2012 23:07:29
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1595 forum posts
102 photos

Stub Mandrel has the answer.

Rear mounted HSS bladed tools may be less likely to jam, because gravity and coolant helps to eject the swarf out of the groove, but if you use one of the modern replacable insert style tools, you'll find that they can be used at the front too, with no loss of function, as they shrink the width of the chips and also have better clearances built into their geometry.

All parting problems are down to swarf log-jams in the groove.

Martin.

Chris Trice16/08/2012 23:53:18
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1375 forum posts
10 photos

That's my experience too, and would also suggest that backlash in the feedscrew also plays a role. Excess backlash allows the tool to be pulled in when it starts to 'dig in' instantly causing a jam or broken tool. I worked in a workshop once where the backlash on the cross slide and top slide of the lathe was truly dreadful and it was nigh on impossible to part anything off.

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