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Is the tool tip dropping.?

If the tip drops below center height it will then dig in and as the work rotates be pulled into the job by any backlash there is making it even worse . Things will then go south quicker than you can blink.!

I learned this the hard way. My problem turned out to be the toolpost actually moving under load that was causing the dropping tip.

Nick

The tool position is far left of the cross slide ways. I suspect the whole topslide is deflecting to the left causing the tool to drop. Can you reposition the topslide to keep the tool over the cross slide ways?

My parting tool is in the same place as that shown by JasonB, and I have no problem parting off. However I lock both the top slide and saddle. The backlash on my cross slide is rather worse than the figure quoted by the OP.

With an carbide insert parting tool I use a minimum feed of 4 thou per rev, otherwise the tool seems to chatter. Some years ago I bought some Glanze boring bars, which are fine, but the supplied inserts were very poor. I don't know if the Glanze inserts have improved since then.

Andrew

Page 19 Using the Small Lathe by Len Mason " NEVER part off between centres unless you want to engineer a front- page smash up"

Brian

Title of thread is Parting Problems not cutting a deep groove . I agree cutting a groove and then using a hacksaw is the way to go to cut through large diameter material . I solved my parting problems by tacking out the backlash .

Brian

For a start en 3b is not the best of materials to part off,I would rather part off tougher en 8 any day. The rigidity of the tool is a major factor.and a correctly sharpened HSS tool or a good insert tool from a proven supplier,both well lubricated makes further improvement. A genuine Dixon toolholder can all to easily deflect under load ,the tool dips and moves to the left then digs in, a rigid single tool holder or a big 4 way tool will improve matters. The design of the lathe is another factor,width and depth of the cross slide,type of gib fitted and stiffness of headstock. I have owned a round head Colchester master and now have a later master 2500, same centre height , the bed width is wider, the cross slide is wider and the v ways deeper, cross slide backlash about the same as the nut is adjustable, the bed is a lot deeper.with the same Dixon tool post ,when parting off with the Round Head Colchester dig ins were frequent and tools broken,worst machine for parting off that I have worked on, the square head master is a vast improvement ,parting off is easy , I did make a solid tool holder for the round head which improved matters. The basic rules often ignored is that the parting tool should only protrude as far as necessary to part off the job,the top slide should not overhang its bottom slide,tool should be lubricated,soluble oil is ok, the parting tool should be as close to the chuck as possible for maximum rigidity. Do not use too wide a tool.The work speed should be half of normal turning speed for that material (HSS tool) During my training I never saw anyone use power feed for parting off on a centre lathe, auto lathes and modern CNC is a different matter and they are vastly stiffer machines.Parting off with a tailstock centre in position was always regarded as a no no!! ,(cut off bar with a power hacksaw),for novices on here don't do it ,a lump of 40 mm bar rotating at speed can be dangerous if it breaks free.

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It was a Dickson 'clone' that I had problems with moving under load.

I understand the genuine items are a first rate product. But the clone I had was a disgrace. So bad that I don't even have the audacity to shift it on ebay. It 'looked' the part with being nicely finished but in reality the internal cam action was a very poor in finish and bad manufacturing size causing the locking cam action to loosen under load.

Where out of curiosity did you get your clone from.?

Nick

As Phil says it was completed by hacksaw, also I would not want to be making that cut without tailstock support – the weight of the long length of bar would tend to tilt down and close up the cut which would definately cause a smash up. And as for the alternative of cutting at the far end

It was just a photo that was already uploaded, it was the same EN3B, its almost an identical lathe and dia was about the same so I was not far off on the other criteria. Maybe you could post a pic of yoursetup parting the same material?

For the benifit of the thread title here are a few bits of slightly smaller 32mm bar that were parted off without centre support.

From the picture, that is not parting off between centres. The work is held in the chuck and supported at the other end by a center. Whilst I would withdraw the centre for the last bit it's unlikely to cause much grief if it does part through.

Martin