I use a couple of those in a rear toolpost, I find I have to grind the top of the blade flat to obtain better chip clearance (which is poor with this type of tool) and plenty of cutting fluid. The 3/32" blade is fairly sturdy and will part up to 2" dia or so, I have the 1/16" blade tool also which is good for small diameter work and saves on waste because of the narrow cut. Both need the cutting edge re-shaping to be optimal (a bit more top rake, and I make mine hollow ground). I wouldn't like to operate either in the normal position on the topslide because of the poor chip clearance, I used to get frequent jams also like this, in my experience back toolpost only for these.

There seems to be a whole branch of our hobby devoted to parting off in hobby lathes and if you have the time to read it all there is more written on the subject than any other topic I know. Many experienced and learned model engineers recommend a rear mounted tool post as the answer to parting problems but I've never been convinced enough to go to the trouble of making one. I use a similar parting tool to the one you have and after a little practice have few difficulties with it.

I make my parting cuts as close to the chuck as I can, I have the apron and top slide locked, I have the parting blade, tool clamping bolts and toolpost firmly tightened and the workpiece tight in the chuck; in short, making everything as rigid as I can. I have the blade oilstone sharp and keep the speed down to around 200 RPM whatever the diameter of the job. I use plenty of flood coolant on steel and have an old 2" paintbrush handy to clear swarf if it starts to build up. Once I start the cut I keep the tool cutting but without forcing it into the workpiece.

Regardless of what others may say, I find the above practices work for me on my Warco lathe although I haven't tried parting anything more difficult than mild steels, brass and cast iron. Hope this helps.

Jim

I have a few of those types of cutter/holder which are all ground to different widths.

I put a lot of top rake on the cutters, even to the point of a sharp radius right up to the cutting edge.

Try running slowly, say 120rpm on a 2" (50mm) dia bar. If you have coolant use it. once the cutter starts to cut try to keep the feed even and at a steady rate.

Sometimes it depends on what the material is as well.

Hope that helps,

Brian

Hi PH,

If you can start to part off OK then have problems, it might be that your tool is not 100% square to the work, or you have not ground the front of the tool perfectly square to the rest of the blade. I know some folks advocate grinding the front at a slight angle to aid a cleaner pip-less finish but on a thin blade it will tend to flex and cause a jam which in turn might cause the blade to break., certainly it will cause noise as it rubs the cut.

Are you using any lubrication when you part off? Even a few drops of neat cutting oil will improve the cutting action, flood cooling is not necessary unless the work starts to get unacceptably warm.

Another thought, have you set the cutting edge too high? Dead on centre or very slightly low( the merest of smidgeons) is important. Being too high is fine to start with, but the smaller the work gets the front will start to rub until it can no longer "dig" in, thinking of which the front clearance is important, too much will allow the edge to dig in too much which is not good. Too little clearance will stop the tool cutting, you need a fine balance between the two (and any back rake) to suit your lathe, material and your "touch". If you get the balance wrong, the tool will tend to self feed and pull the blade into the work, which will take up the feed screw backlash, and certainly cause a dig in and may break the blade.

Personally I have a similar tool to yours, but Eclipse brand. I have it mounted in a holder that is set to give 6 degrees of rake, this in turn is held in a QC holder. Naturally I can only use it for parting smaller stuff, recommended max depth for 1/16 blade is 5/16-3/8 but i often go a little deeper, it's all about "feel". By max I mean that that is the limit to how much blade is protruding from the holder.

In years to come you will wonder why you ever had problems with parting, keep practising and you will eventually get the "knack"

chriStephens

Fizzy has got it in one.

I use both insert tooling and HSS tooling for parting off. Here are my rules:

1. If it doesn't need to move lock it, ie, lock the top slide and saddle

2. Run at a sensible speed, eg, for 2" diameter steel I'd run at 300-400rpm

3. Flood coolant for everything except cast iron, brass and plastics

4. Don't bother with tapered tips, you'll get a pip on the work anyway

5. I use a minimum feedrate ot 4 thou/rev, or higher, even on materials like stainless steel; my personal preference is to part off under power feed, but that is more controversial

I've just made 650 5/16" diameter aluminium spacers, each one of which was parted off from bar stock by hand, no power cross feed on the repetition lathe, using a parting tool ground from 5/16" square HSS. Out of interest I've dug one of the curls of swarf out of the bin to measure it's thickness – 0.3mm, or 12 thou. Parting off the spacers was done at 1100rpm.

Regards,

Andrew

Chris H, Nice work that rear tool-post & fittings. Good photos too. Regards, Bear.. P.S. How do some correspondents get the return key to work?

Just a little point has the tool got side clearance? Else the top edges of the tool will rub more and more as it cuts deeper. I would think that just stoning off the top corners, back to the cutting depth may help.

Frank

Petro,

VFD stands for variable frequency drive. It is a box of tricks which is used to drive a 3-phase motor (much smoother and more efficient than a single phase one) and to allow the speed to be varied on the fly (i.e. by twiddling a knob, not stopping to change belts or gears).

I can confirm the the Q-cut sold by Greenwood Tools will fit quite comfortably in a size S00 Dickson toolholder (Myford 7-series size). I can also confirm, as a previous gent said (can't see previous page while typing this) that it's the best parting tool I have used, and I've tried quite a few. It's not just a bit better, it's in a different league; you can easily part off under power, and without resorting to backgear.

It is however vital, whatever tool you use, to get it absolutely perpendicular the the bar being parted, or it will rub on the side as it goes in.

David

Edited By David Littlewood on 15/05/2013 16:06:31