Parting off problems.

[sshire]

Every point made is valid. I know it's a bit busy but, keeping the cut wet is important. I use a lab wash bottle and keep enough pressure on it for continuous dripping.
When I got an insert parting tool, I had no end of problems. I called Aloris and the tech guy said if I'm not getting curled chips (as opposed to scrapings or dust) I wasn't pushing the tool hard enough. Sure enough, that solved the problem.

[Steamer5]

Hi Pete,
 For what it's worth from somebody else who struggled, and still is, & then resorted to hacksawing, before biting the bullet & having another go. I tried a tipped tool that was supplied with the lathe....after smashing a couple of tips gave up! The I got a QCTP that came with a HSS blade I very tentatively used it with ok results at as slow as I could go, 60 rpm, went well for quite a while UNTIL I hung too much tool out.....bang crash & it was time to switch off & have a beer to settle the nerves!
 Time passed & last year I invested in the Aussie made Eccentric Engineering FoR parting tool, also got there turning tools. The parting tool can be mounted front or rear, mines on the front the lathe run in reverse, a range of width of blades is also available. Since I started to use this I'm getting much better results, using a 1 mm blade, & like others inspired by the experts here to increase the feed, not at a level of some but faster than before, have tried stepping the speed to 120 & am finding it ok.......still find it intimidating!

Cheers Kerrin

[Gas_mantle]

Thanks for all the helpful replies.

It sounds like a lot of the problem is not feeding fast enough (and not at a constant rate), I'll give the blade a sharpen and give it another try later today. My only worry is that in the past by feeding faster I find the tool digs in to the point of stalling my machine, admittedly the fuse did it's job but it does suggest something is wrong with either the tool or my technique. (or both) 

It actually doesn't take long to hacksaw through but the parts are intended to be crank webs so I want the faces to be parallel and a good finish but sawing means I then have to turn them over and face off the reverse side which although not impossible isn't ideal on a 7mm thick part.  It seems to make more sense to part them off if I can.

[Jasonb]

If they are webs then I would want to turn them on both sides anyway, with the best will in the world your parting tool is likely to wander a bit and the finish won't be as good as a turned one.

Use the reverse jaws or packing to set the turned face against the chuck body true then skim the parted face, remove packing before switching on. Soft jaws would be better if you have them.

[Gas_mantle]

Hi Jason,

I guessed you have kind of solved the problem then 

I'm making a new crankshaft as the one I had made has had a few knocks and is no longer perfectly true, I had pinned the webs on and they can no longer be removed so I've decided to start it again from scratch - I can't remember how I made the last one !

I'll try parting them off as a learning exercise but face off the resulting parts as you suggest.

Peter.

[Graham Meek]

I may be too late with my observations but, here goes.

The parting blade shown in the open post has far too much "front clearance". I use a maximum of 10 degrees, this I feel is where a lot of folks go wrong. The more the front cutting edge approaches the vertical the less tendency there is for the edge to "dig in", but also the less tendency for the edge to cut. A shallower front clearance therefore adds some degree of support to the blade during the cutting cycle and reduces chatter.

Another pitfall is having a parting blade that is too wide for the size of machine. A wider blade is often chosen in the belief that it is stronger and less likely to break, which both points are true. Unfortunately the rigidity of the machine or the set-up quite often cannot support such a wide cut on a small machine.

I use a Seco HSS blade which is 2 mm wide on my Emco Maximat Super 11, and on the Compact 5 the bade is 1.5 mm thick. On the Hardinge I used to work many years ago the HSS blade was 2.35 mm and this would happily part off many of the exotic tool steels that we used. Where as on the Dean Smith & Grace type 17 we used a 3 mm wide HSS or 3 mm wide inserted tip which were just being introduced back then.

Lubrication is another important factor and I always use cutting oil for my home shop use. In industry we used a range of neat cutting oils to fully synthetic fluids, but the cost of these prohibits there use in my workshop.

Hope these few points help.

My best regards
Gray,

[Gas_mantle]

Thanks to all those who offered help, I've now successfully parted off the remaining parts 

Resharpening the tool helped a bit but I think the bulk of the problem was my lack of experience - I found that using a slightly faster feed and trying to maintain a constant rate helped considerably. I guess as a beginner it seems natural to take it cautiously and withdraw the tool at the first hint of a problem but wasn't the best approach.

As for the coolant as my lathe hasn't got it's own in built system so I'll knock up some makeshift arrangement that drips on to the work piece leaving both hand free to control the feed rate.

Peter.

[Chipswitheverything]

Hello Peter, you are certainly not the only one of us who has had a few "moments" when attempting parting off!

  Years ago I made up Geo. H. Thomas's rear parting off toolpost for my Myford S7. The head will accommodate a 1/16" and a longer 3/32" blade, both the Eclipse type.  The rear toolpost does have rigidity benefits as against the topslide and quick-change tool holder assembly on a smallish lathe such as the Myford.

  I find that one of the main difficulties in our "amateur" parting procedures is not being able to get a good flow of suitable lubricant to the cut down in the groove.  I use some Shell Garia H cutting oil, which is what GHT found by experiment was an effective lubricant, back when he wrote up his articles in the ME about parting off problems.  ( We went halves on a 5 litre can between us! ).  In industrial use, this sort of straight lubricant would likely be pumped over the job and pour into the groove continually, flooding the cut, with hugely helpful results: but as it costs about the same as a decent whiskey!, we tend to dab and drip in in the groove with a little brush!  We are not really keeping the cut interface lubricated, by comparison.
 
Agree entirely with Jason that the parted face will need a clean up cut in any case...

( While I was writing, see that you have had success!, hooray!, but I'll post anyway....)

Dave

[mklotz]

As for the coolant as my lathe hasn't got it's own in built system so I'll knock up some makeshift arrangement that drips on to the work piece leaving both hand free to control the feed rate.

Here's how I did exactly what you suggest back when I was encountering the same problems that have plagued you...

http://www.homemadetools.net/forum/parting-off-oiler-27738#post37592

[Gas_mantle]

It sounds like rear mounting the tool is a better set up but my small lathe doesn't have T slots on the cross slide so to do it I'd need to modify things and at the moment don't think I have the necessary skill to do that - it may be something I can look into at a later date. 

Marv, I like your drip feed lubricator - had originally thought of just rigging up a simple set up to attach to a DTI magnetic base but having seen your arrangement I think I'll make something a bit more substantial along the lines of yours.

Peter.

[Allen Smithee]

We covered this before:

http://www.modelenginemaker.com/index.php/topic,4229.msg78576.html#msg78576

AS