Issues parting off

[Bangkok Mick]

My tool tends to pull towards the chuck causing parting off to result in a concave on one side and a cone on the other. I have tried offsetting the tool in either direction and also tried tool upside down and lathe in revers with this issue still persisting in the same direction.

Can anyone shed some light on this problem?

Cheers Mick

[DavidA]

All I can suggest is that either your tool isn't ground dead square or or it isn't square to the job,  or both.

But I suppose you have checked those.

You do have clearance on the tool flanks ?

Dave.

[Meldonmech]

  I agree with Dave, make sure your tool is square to the lathe bed, by setting it against the face of the chuck. When grinding your tool, clamp a piece of hard wood to the tool rest of your grinder, set square to the face of the wheel. Then hold your tool against the wood when sharpening. Make sure the grinding wheel face is dressed square to its sides. Also check that your tool post is not turning during parting off. Let us know how you get on.

                                                            Good Luck  David

[Bangkok Mick]

Hi Dave,

The tool is tapered towards the bottom to prevent it from grabbing, this is a standard pre shaped tool shape not my own design.

U do not understand the meaning of clearance on tool flanks, can you please explain.

Cheers Mick

[Bangkok Mick]

Thanks David I will re look at my set up

Cheers Mick

[DavidA]

By clearance on the flank I am assuming that the top surface of the tool narrows slightly towards the body.  I.e the actual cutting edge is slightly wider. Some tools are parallel and I find this gives a tendency to rub on the inside edges of the cut. I your tool wasn't dead square it could lead to the cutting edge being pushed off to one side.

The other thread that is talking about parting off may be helpful.

Dave

DavidA

[Manxmodder]

Mick, the other thread on parting tools is here: http://madmodder.net/index.php/topic,10183.0.html

Also,I agree with what others have said,if hss parting tools aren't ground properly and evenly sharp along the full width of cutting edge then they have a tendency to drift to one side rather than cut square to workpiece.....OZ.

[studders]

Is the saddle locked and the topslide firm during parting? 

[chipenter]

When I have had this problem it has always been the top face has a corner rounded , so that one of the corners of the tool pushes away from the blunt corner it dosen't take mutch .

[dawesy]

Make sure the tool is perfectly parallel to the work and that the carriage is locked off. Looks like slop somewhere.
Parting off needs everything tight.
Also check the tool is sharp and band on centre.

[75Plus]

Keep the blade as short as possible. Too much blade exposure allows flexing to occur.

[Jonny]

The tool is tapered towards the bottom to prevent it from grabbing,  Mick

I have a few of them and they all do the same thing.
You can sharpen left, right or neutral it makes no odds the blade veers off left to right as its going into the job.

Have a look in other thread about parting off, maybe worth trying one of those T hss types and only leave the amount of tool hanging out to do the job. ie 1/2" protruding to part off 1" dia.

[hermetic]

You realise that it is always best to lock the carriage (saddle) when parting off.I used to be ter
Phil.rified of doing it before I learned to lock off the carriage, now I'm only very afraid!

[Arbalist]

You realise that it is always best to lock the carriage (saddle) when parting off.I used to be ter
Phil.rified of doing it before I learned to lock off the carriage, now I'm only very afraid!

Agreed, I lock everything I can before parting on my Lathe.

We could get away without doing this on the Harrison's at work but small machines don't like it!

[mechman48]

Hi Mick
I Had the same problems; as with other comments parting off seems to create fear & trepidation for a lot of guys.. keep the tool as short as needed, lock the saddle up, ensure the tool is square (90* ) on to the work, set dead on centre height, also make sure that your compound slide is snug & any backlash is eliminated, use plenty of coolant / cutting oil, keep it flooded or well oiled ( not in the usual sense ( ) once you start cutting keep the tool moving don't stop /start otherwise any slack that has been taken up by the downward forces will reappear & will have your parting tool tend to dig in again.

I have taken the plunge & forked out for a insert tip type parting off tool.. comes as a block plus blade (26mm) & 1 tip.. has improved my confidence no end, & have now parted off up to 2" aluminium bar    on autofeed at approx' 300 - 400rpm with the slowest power infeed on the cross slide. For steel I have made & used a rear parting off tool with the machine running as normal & a HSS blade, much better as the cutting forces are directed downwards on to the bearing bottoms/headstock casting.
The link for the tool I bought (usual disclaimer)...

http://www.rdgtools.co.uk/acatalog/Indexable-Parting-Tool-3mm-x-19mm-blade--10mm-shank--2534.html   

George.

[Bangkok Mick]

Thanks George,

I think last week my tool was getting blunt so I will try again with all the advice this thread has offered. I think I will also invest in one of those insert type cutters as they seem to be the recommended way forward.

Cheers Mick

[Stilldrillin]

Mick.

I'm sure the answer is in the above postings. But which one, I don't know! 

From my own, mini lathe experience. The tipped tool from RDG was just as bad, as all the other tools I have owned.

Here's the project....... http://madmodder.net/index.php/topic,2759.msg29242.html#msg29242

Parting didn't really settle down, until I had taper roller bearings. A carriage lock. Dixon type toolpost, and dedicated parting tool.

Somewhere here, I think...... http://madmodder.net/index.php/topic,7759.msg83052.html#msg83052

The tipped tool? Somewhere under the bench. Unloved. Unused....... 

David D

[Bangkok Mick]

Thanks David, good to know before I go spending funds.

Cheers Mick

[dawesy]

Following the advise in a video on YouTube I've successfully parted off 25mm 316L stainless with a cheap RDG hss tool. No chatter or wobbling. One of those ' confirm everything three times before you start'tgings I think.

[Fergus OMore]

Years ago, I made up a rear parting tool to the design of George Thomas and despite changes from one lathe to another, it has never faltered.
I simply followed the 'words and music' and ground up and ordinary Eclipse HSS parting off blade. Well, almost
The top- which is really the bottom has a specified Vee kerf of 140 degrees and I was windy about doing the trick without a T&C( then) and I settled for a rounded kerf done with cheap Chinese pillar drill going 'flat out' with a worn thin and rounded angle grinder disk. After all, it is only a kerf of of an inch- which will part off 2" round. Thomas, the great pedant Guru specified a front edge of a male vee of 140 degrees which is a far easier task. And then when it all blunted, I simply ground the front edge flat.

With it running- in the the Myford forwards- 'cos the chucks unscrew- it peels off up to 2" in a continuous narrowed ribbon- downwards.

As I said, dead easy and really, what is all the fuss. Whether a tool is a penknife or something more exotic, it is only cutting- or not.

I didn't invent it- nor did Thomas, some Gezira Gizinta did it in Ancient Eygpt at the time of the Pharoahs -when he stuffed his dead Mummy

[Phody]

Mick
The problems with parting off are many once overcome the process works without fault. I have a Myford ML(speed)10 and part off 30mm bar with no problem even from the front.
Fist the bearings must be in good order, second the parting tool must be sharp, ON CENTRE line, Square on to the bar and the speed correct. I find that changing speed as the diameter reduces helps. Use a light cutting oil and proceed with the cut in asteady motion. All the slide must be clamped to prevent tool wander. I use a combination of tools - The Quick cut from Greenwoods, groud HSS (square stock) and quality parting blades. 7deg top rake works for me. I'm about to make a tool holder like the Geoge Thomas/ Ian Bradley design so that I dont have to cange tools.
Hope this helps
Phody