Parting tool blade not sitting square

[gluhParticipant @gluh]

Hi, I am very much a newbie, but am fortunate enough to have a Warco WM180 lathe and a WM18 milling machine.

One problem I have is that when I tighten the blade in my QC tool holder using the rear Allen key, the blade always slightly rotates away from vertical. Am I doing something wrong? It doesn’t seem right, and makes parting off harder than I reckon it ought to be.

TIA

 

[David AmbroseParticipant @davidambrose86182]

I had the same problem when I started.  I had bought the wrong type of blade for that holder.
I eventually bought a parting tool that uses inserts, and clamps into the standard QCTP holder.  It works very well for me.

[gluhParticipant @gluh]

Thanks David; the holder & blade were bought at the same time from the same webpage, so not sure why it doesn’t “fit”.

https://www.arceurotrade.co.uk/Catalogue/Machines-Accessories/Lathe-Accessories/Tool-Posts/Model-100-Parting-Blade-Holder-2

I’ll ask them what type they suggest I use.

[JasonBModerator @jasonb]

Check you have the blade the right way round as many of them have slightly angled top and bottom edges so that they “dovetail” into the holders.

Was the notch already ground into the top?

[Andy StopfordParticipant @andystopford50521]

The angle ground into the top will tend to make it dig in, especially in conjunction with the built-in angle of the toolholder. The slightly smaller “000” series equivalent has the blade level, and it works fine with no top grind.

I realise this doesn’t help with your question, but worth mentioning since many older books show parting off tools ground in this way – in my experience, it’s a great way to cause dig-ins and broken tools.

[Mike HurleyParticipant @mikehurley60381]

A quick mail to Arc would be worthwhile. They’re nice helpful people and will advise you appropriately

Mike

[Clive Brown 1Participant @clivebrown1]

I’m with JasonB. Not certain, but it seems from the lower picture that that might well be the problem. I’m assuming here that the top-rake was ground in by the OP, thereby “handing” the blade incorrectly.

[Dave HalfordParticipant @davehalford22513]

Is possible the wedge is the wrong way round?

[Howard LewisParticipant @howardlewis46836]

Looking at the picture, the blade is definitely angled away from the body.

As suggested, check that the locking wedge is the correct way round. It should pull the blade towards the body, not away from it. It might even benefit from some filing so that it does pull the blade against the holder body.

With the blade off vertical, jamming is likely, and parting can make enough problems, without using the wrong set up

Having a large top rake, on a blade that is already set at a rake angle, by the holder, will also cause problems with dig ins.

FWIW, I use my parting in a rear toolpost, rather than what looks like a QCTP, with Zero rake on the blade, or the holder, and have almost no dig ins. To the extent that often parting off is done using power cross feed!

Tip

If feeding manually, keep up a steady, slow feed, and use plenty of lubrication.

My power feed provides 0.00225″/rev feed, and ordinary lub oil is applied by brush, or a slow drip feed of soluble oil.

It is taken as read that the cutting edge is set at centre height?

Howard

 

[David George 1Participant @davidgeorge1]

I made a rear parting off tool holder and the top nd bottom of the blade has an angle which matches the angle milled into the holder.

 

The blade is upside down as the toolpost is at the rear and the cutting edge is on center height.

David

 

 

[BazyleParticipant @bazyle]

The cross section of a parting blade should be a parallelogram. Sitting on its bottom edge it should lean to the right, so lean into the toolholder and the top edge will then be lower on the left than the right so the clamp also pushes it into the holder body.

The front cutting edge should be a little off-square seen from above so that the right hand corner is ahead of the left hand corner so at the end of the cut the part falls off leaving a small pip on the main stock but ideally nothing protruding on the part.

[Howard Lewis]

On Howard Lewis Said:

Looking at the picture, the blade is definitely angled away from the body.

As suggested, check that the locking wedge is the correct way round. It should pull the blade towards the body, not away from it. It might even benefit from some filing so that it does pull the blade against the holder body.

…………………

Howard

 

I have 250-207 holders, so the same design, but a size larger.
The locking wedge only fits one way, as the threaded hole is offset.
Also, its not designed to draw the side of the blade against the body, as the underneath of the wedge is flat.
Similarly, the vertical face of the tool slot is just that, vertical, so not designed for a tapered blade.
Mine came with a slab of flat HSS, to form a wide grooving tool.
The HSS Parting blade I use has a cross section more like a T shape, with a wider flat top, a flat bottom and parallel, but relieved sides as the upright part of the T.
It would take a smallish shallow insert blade tool OK, though the cross section of the blade would be a bit thin to be stable; it would also have to be one with flat top and bottom.

I do have other parting blades and holders for the Myford, which have the conventional tapered relieved sides, and sloping top and bottom, such that the angled nut pulls the blade against a slightly angled/off-vertical face of the holder.

Bill

[Ian PParticipant @ianp]

The blade holder from ArcEuro linked to in the second reply is a bit too versatile for its own good!

Its hard to tell from the website pictures but both the upper (the clamping wedge) and lower surfaces appear to have no ‘dovetail’ effect but look to be parallel to the toolholder base. It looks like the OPs blade is ground at the wrong end so the and the wedge clamp has pushed the (nominally, parallelogram shaped) blade downwards so the the blades lower edge is sitting flat against the lower seat.

I’m not sure how one parting tool holder can satisfactorily hold a range of blade widths and heights.

My experience with various single size blade holders is that even from new with the correct blade, the side clearance angles are not equal. I corrected an Eclipse holder by re-machining the holder underside at a very slight angle so that the blade stood exactly vertical giving equal side clearances. A Dickson holder also held the blade wrongly (no clearance on the the chuck facing surface of the blade) but as the whole block is hardened I resorted to gluing a 2mm wide strip of shim near the top of the blade recess (to cock the blade to the left slightly).

Blades used in the Dickson are not a parallelogram section, more accurately they should be described as a trapezoid.

I quite like the clamping wedge idea of the Arc offering but not keen on the rake being built in. I prefer to be able to extend/retract the blade to suit work diameter without having to change the cutter tip height.

Ian P

[DiogenesParticipant @diogenes]

I’ve had the same issue using a tapered blade in a holder designed for ‘parallel’ blades.

My solution was to insert a shim (piece of piano wire / ‘wiper-blade strips’) to stand the base of the blade off to the side of the holder.

IIRC, GHT’s solution was to use grubscrews as adjustable standoffs.

[Ian PParticipant @ianp]

This is a close up of the rear of the ARC holder (snipped from the OP’s picture).

It looks like the top and bottom faces of the blade are parallel to each other, and the clamping force has rotated the blade so that blade bottom edge is aligned with the lower tool recess face. Turning the blade end for end will ‘sort of’ rectify the problem, but the blade will then only have line contact support as it appears the blade recess is parallel to the base of the holder

With a recess able to take 5mm wide blades, gripping a 1.5mm blade looks like a trial and error process.

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

Just for a change [?] … Amazon includes this useful little note in its listing of a holder with the same reference number:

For use with 1/2″ (or smaller) blades having parallel top and bottom edges

… although, of course, it would be more useful to mention that  the edges should be orthogonal to the sides !!

[ Artificial Intelligences please take note ]

MichaelG.

[Howard LewisParticipant @howardlewis46836]

The ideal section for a parting blade should be trapezoidal, as the sides tapering in towards the bottom provide side clearance, reducing the risk of jams.

Very often a jam means a broken blade, and at least a need to regrind.

My VERY old HSS parting blade has side clearance, and is ground with a small front clearance angle, to maximise strength and metal below the cutting edge to conduct away heat.

Mounting a parting blade, inverted in a rear toolpost, definitely reduces problem when parting off.

Howard

[Michael Gilligan]

On Michael Gilligan Said:… although, of course, it would be more useful to mention that  the edges should be orthogonal to the sides !!

Correction … With due deference to Howard: let’s make that “orthogonal to the perpendicular centre-line”

MichaelG.

[gluhParticipant @gluh]

Gosh – thanks so much for all of the replies! Amazing!

The blade is indeed a parallelogram, however, with the pointy end forward (ie as I had it), the tendency is for the blade to rotate when tightened. But I have just tried it with the pointy end facing backwards, and it remains vertical when tightened. So the rank amateur in me thinks that perhaps the pointy end was ground in to the wrong end at manufacture?

But anyway, a new holder & blade are being sent out by Arc today, and I will see how I get on. They have been incredibly helpful – I am _genuinely_ impressed with their help & service.

I’ll reply again when the new bits arrive in a day or two.

[JasonBModerator @jasonb]

That was my thinking with the blade, good to know Ian sorted you out.

[peak4Participant @peak4]

As I mentioned earlier, the 207 version of these holders have top and bottom of the tool holding recess parallel,  and at right angles to the vertical face. I’m writing vertical for ease, as that face is also parallel with the toolpost itself.
The wedges are flat bottomed, and not reversible, so designed for holding rectangular blades.
They slots are not tall enough to hold carbide insert parting blades.

Sorry if the photos are a bit dark, but you should be able to see that the front view of the left hand holder houses a lump of HSS bar 0.161″ thick, with sides parallel to about half a tenth. It’s 0.634″ tall with top and bottom square to the sides. This one does appear to have a slight angle to the base of the wedge, but it’s just damage to the front edge.
The right hand one holds a blade of T cross section, rather than trapezoidal, where the parallel relief on the upright part is about 0.040″ narrower than the cross bar of the T.
I just nip up the wedge, whilst temporarily inserting a 20 thou wire feeler gauge into the gap twixt blade and holder to keep everything vertical/parallel.

Bill

[peak4Participant @peak4]

Next one, also designed for this size of tooplost, is the insert blade holder; If the idea of holding trapezoidal parting blade with the centre line vertical  as opposed to just the right hand edge, it might not be ideal; I just don’t have one tall enough to experiment. In that case, as far as I can see, relief would only be provided on one side.
As you can see, it comes as a separate unit, which mounts into a conventional 202/201 holder, which works well enough, though at the expense of a greater overhang.

Top and bottom of the recess is clearly angled to lock a thin blade against the vertical side.
The insert blades I own,  have rounded, rather than single angles at top and bottom

Bill

[peak4Participant @peak4]

Now for the Dickson style.
The left hand one seems designed for ½” parting blades, though here I have an all hard hacksaw blade fitted to thinner parting/grooving.
The right hand one is obviously holding an insert tool blade, and works well.

Using my best tenths DTI, the vertical face, does appear vertical, and not half the included angle of a trapezoidal blade.

Bill

[peak4Participant @peak4]

Here we now have my Myford rear mounting toolpost, specifically designed with a dovetail to hold inverted insert style blades against a vertical face.
You still run the lathe forwards of course, but the load on the cross slide is different, allowing for a much safer cut with less chance of a dig-in.

There’s a couple of spare blades below, one showing a coated + uncoated tip; the other, for which I don’t have inserts, presents the tip with a different top rake.
Part numbers clearly visible, some blades will hold both 2 & 3mm wide inserts.
I normally only use the thinner ones on the Myford/Warco 720.

Bill

[peak4Participant @peak4]

Finally, this shows the shape of a trapezoidal HSS blade.
I’ve deliberately taken the photo from a slight angle to change the perspective a bit; the top and bottom angles are a bit shallower in real life viewed end on.

This would be the view from the rear of course; the sharp end is away from you out of view.

Bill

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