The first picture looks 'wrong' to me, the tool boat should be nearly horizontal, maybe like that to get the centre height right? As it is the 2 clamping screws are going to have edge contact only & will not be very secure. More detailed advice from others will follow I'm sure.

Tony

Certainly looks wrong to me and I don't even use arear tool post, the tool should be horizontal or the whole thing pointing downwards slightly towards the work. That way you don't need to grind that nasty notch into the tool, it's left flat and the incline of thetool gives you a few degrees of positive rake.

Hmmm, got to say I don't care for those boat adjusters. Sworn at rather than sworn by! They're prone to wander, fiddly to set to height and mess with the rake.

Wandering will be worse used that way round because the cutting forces lift the boat and bear on the two fixing screws, which are also canted where they press on the spacer, yuk. If the lathe is run in reverse, with the tool the right way up, the cutting forces press down and the post is more rigid. Alas, Myford lathes aren't top dog for rear parting because the chuck is likely to unscrew when they run in reverse.

I'd dump the boat in favour of a flat rear tool post which is shimmed to height. The plain post eliminates a lot of problems, even used upside down. (I expect to be told boats are easy when you know how. Even if it's my fault I don't trust 'em.)

Parting off tends to wander at the best of times. The tool has to be straight and stiff.

Dave

This is much more rigid than the boat toolholder. The base block has a shallow slope enabling the cutting tool height to be adjusted.

Alan

William,

The rear tool post shown by. A J is a far preferable set up. Mine,I think, is even better. It is of fixed height – made that way for my particular lathe, I expect. I can remove or replace the whole caboodle, without fear of altered cutter height.

With the blade always held parallel to the cross slide, any extension (or retraction) for parting different diameters is a simple affair. I always keep the extension to a minimum. Nor does sharpening the blade alter the cutting height.

I originally purchased a QCTP with several tool holders (supposedly better value by an amount, but not in hindsight). I wish I had not because the parting tool holder was at an angle – just a PITA in use! I’ve since modded that particular tool holder for a different purpose.

As an aside, I’ve never used the push-type knurler, either, which was also bought at the same time – as part of a set of tools to fit that QCTP). I was caught out twice in the same day, but won’t make the same mistake again.

Hi Guys,

This is a picture of my "Norman" patent rear tool holder with a 12mm X 2mm blade in a holder. It is horizontal and set exactly at centre height. The tool holder can be used on the front tool post as well.

William

Your new set up looks much more promising. But as has been said the grinding does not look good. I wonder if you need a finer grit wheel.

Arc do "Parting tool blocks" for holding blades which might suit if the dimensions are okay.

Also, your original set up with a square section tool can work okay if you get a proper HSS parting tool
(ie a parting tool shape ground on the end of a piece of square section HSS, all the ME suppliers do these) rather than the grooving tool you were using. All provided you pack it up (down?) to centre height and near horizontal. Blades are more versatile but if you only need to part off smallish stuff the square HSS parting tool works okay and might be easier to fit to your holder.

Boats are not popular, as has been said, but the one you have is more rigid than the original diecast myford offering. I think the newer ones are hardened steel so may not be easy to drill for dowels. Parting tools, once set, are often left alone for extended periods so it may be okay to just adjust the tool, packing and boat, then clamp up tight, and not fix the boat at all. You may have to experiment with these things.

Good luck!

Rod

Whether a grooving tool, or a parting tool, each SIDE of the tool needs to have clearance. (Which is why a parting tool narrows from top to bottom if you look at it from the front. When mounted inverted in a rear toolpost, it narrows from bottom to top )

Assuming that you intend to continue using the boat holder:

Rather than grind the top face of a parting tool to bring it down to centre height, I would grind the whole length of the bottom face. If need be make up a holder with a deep enough groove so that when the holder contacts then grinding wheel, the tool is at correct depth. In this way, any errors will have minimal effect on the angle at which the tool sits.

You could mount the Boat in the 4 jaw chuck and turn the required amount off the flat face on which the tool sits. This might be the more accurate way of lowering the tool to centre height.

How much to remove?

Since the blade is tapered, you will need to make a clamping piece with a taper to match that of the blade so that when clamped the wider, cutting face, is horizontal in BOTH planes.

The clamping screws will bear on the upper face of this clamping piece.

If you do not have milling capability, you will need to file the taper. The blade can act as your gauge.

Mount the parting blade on the boat, using your new clamping widget, (to cater for the taper ) and measure the distance between tool tip and centre height. If in doubt take off a little bit too much. You can shim UP but not DOWN.

(Although the tool is mounted inverted, the logic is still to start with the tool below centre height and shim to bring it UP to centre height, just as in a front toolpost )

Remove too little and it will still be below centre, but cannot be shimmed to bring to centre height..

Grinding a parting tool with the front face at an angle (viewed from above ) should allow parting off so that there is no pip on the parted off piece. BUT the swarf is wider than the groove being machined, and so liable to jam, particularly with large diameter workpieces as the groove deepens.. Hence the advice to grind the front square to the blade. So when presenting the blade to the wheel to grind the front clearance, keep the blade at right angles to the wheel. The radius of the wheel will provide front clearance, without it being excessive.

Excessive clearances leave less metal behind the cutting edge to conduct away the heat so that the tool heats up, softens, and wears more quickly.

HTH

Howard.  Predictive spelling!!!!!!!!!!

Edited By Howard Lewis on 23/07/2021 16:02:03

William

I was concerned that the grooving tool might only be intended for shallow grooves and lack side clearance, and so be part of the problem. If it works use it.

Howard has covered all the other issues so your set up should now work ok.

Let us know how you get.

Rod