Making parting off tools

[Graham MeekParticipant @grahammeek88282]

Posted by Tony Pratt 1 on 07/07/2022 15:20:15:

Posted by Graham Meek on 06/07/2022 11:07:06:

The front rake angle is the killer as regards a problem with digging in.

This is the blade holder I made for my Emco Maximat Super 11 lathe. This was the second blade used in 40+ years. The blade is 13 x 2 mm section, it has a dovetail section and is only ground on the front at 10 degrees.

The section of the blade means the swarf is turned on its side as it leaves the cut and it never caused a jam. I now use an 8 x 1,5 mm on my Emco compact 5, with the same style holder. Parting off is carried out with the carriage locked and at normal turning speeds.

I hope these notes help,

Regards

Gray,

Hi Gray, I hope you are well? I'm slightly puzzled, I understand the 10 degrees front rake but what about the top of the parting blade, is its face parallel with the lathe bed but no back rake angle?

Tony

Edited By Tony Pratt 1 on 07/07/2022 15:21:43

Hi Tony,

I hope all is well with you?

Not so good this end, more importantly as of the this morning Jean's health, and in recent months mine, are both taking a nose dive.

Regards

Gray,

Generally,

My observations on parting tools might not suit everyone's view point, but they have worked for me and have never given me any breakages or jams.

The Top edge of the parting tool blade is left with the ground dovetail face, and it is parallel to the plane of the bed surface. The angle of the dovetail face has two functions in the cutting action. The most important is, as the edge is sloping it turns the chip immediately it leaves the cutting edge and puts the chip on its side. Thus the swarf is narrower than the cut and cannot jam up.

The second advantage is that even with the parting blade ground square to the lathe centre-line it still has a pip-less parting action. As the tool is in effect producing a very shallow cone. As the cutting edge is really a product of the dovetail angle and the ground square edge.

A lot of people grind the top face flat, or with a slight top rake. This not only looses the above advantages but it also is reducing the width of the blade due to its in-built tapered section. It also restricts how deep the blade can penetrate the work. As the unground blade above the new ground top face is now wider than the cutting edge. It might not be much, but it is enough to give you a bad day.

The Front rake angle if it is too sharp, allows the blade to penetrate the work very easily. This in my view is what causes the dig-in, as there is no, or very little resistance felt on the feed handle. This results in too big a cut and a jam, dig-in, or breakage. If a moment is taken to think about it. A true vertical face would not cut, and by not cutting it cannot dig in. As the Front rake is increased the tool is allowed to penetrate the work, depending on how much this increase is, equates to how easily the tool can be fed into the work. Hence my opening sentence here. Some resistance to the cutting tool is a good thing in my book.

As I said these are my rationale, it is based on my experience, and advice given to those apprentices in my charge . Even on the smaller Compact 5 I use now, I still have the same set-up, and have been recently parting off 16 mm bar, (BMS & Silver Steel) at 330 RPM with no problem.

Regards

Gray,

[Tony Pratt 1Participant @tonypratt1]

Hi Gray, thanks for the swift & concise response, I will have to do some experimenting. Sorry to hear about the health issues!

Best wishes,

Tony

[DMBParticipant @dmb]

I didn't make mine, I purchased ready made holder and blade. Unfortunately I cannot remember where from but it looks like the holder shown in RDGs Myford set. It's a taper sided wedge bar that holds the tool in the correct position within the holder. As I didn't buy the set, I wonder if it wasn't RDG but another supplier. I have just looked at Arceuro and Chronos and drawn a blank. I clamp it in the QCTP on the topslde and slacken the tool post, run saddle up to stationary chuck and hold the blade against the face of the chuck to align it and tighten the tool post nut. Running the S7 at reduced speed on the VFD, generous supply of cutting oil and no trouble parting off steel. Frying pan type sound.                                                                                                       I have a casting + drawing from Reeves for the rear parting off tool post to Geo. Thomas'design, which I will get round to making up sometime with small changes as follows. A small plate screwed to the left hand side at the bottom to act as an alignment stop against the LH side of the cross slide. A  T – nut full width of base + a bit on the RH side of the base to make it quicker and much easier to fit on to the cross slide. Should then be able to just wack it on and have it aligned all in one go.

Edited By DMB on 07/07/2022 19:41:15

[DMBParticipant @dmb]

Just been in workshop and recovered parting toolholder and blade. No markings on the toolholder which is holding a blade marked RDG 3/32 x 1/2 x 4" HSS. So it was RDGs but I don't recall buying the set. Very pleased with it, having previously bought what turned out to be inferior designs elsewhere.

[VicParticipant @vic]

I’ve tried several types of parting tools and these are without doubt the best I’ve tried so far. If it’s really hard stock then I’ll use an insert parting tool.

[Michael HorleyParticipant @michaelhorley72278]

Posted by Rowan Sylvester-Bradley on 06/07/2022 11:02:09:

Is this type of parting tool satisfactory?

LINK

There seems to be nothing much (except the taper) to keep the carbide tip in place, and nothing to stop the tip being driven deeper into the tapered recess.

Thanks – Rowan

I use that one on my S7 and it works perfectly in the front or rear tool post.

[Tony Pratt 1Participant @tonypratt1]

Posted by Vic on 07/07/2022 20:27:02:

I’ve tried several types of parting tools and these are without doubt the best I’ve tried so far. If it’s really hard stock then I’ll use an insert parting tool.

Where did you get them from?

Tony

[DiogenesIIParticipant @diogenesii]

Chronos Chipbreaker blades ?

I like them too.

Edited By DiogenesII on 08/07/2022 15:34:02

[DMBParticipant @dmb]

[duncan webster 1Participant @duncanwebster1]

Anyone know where I can get eclipse type 5/16 blades from without a mortgage. The blades sold by RDG are not the same, they have flat top and bottom

[DMBParticipant @dmb]

Photo above is RDG Toolholder that I now use in preference to previous naff designs sold by other suppliers, in my opinion. The blade is 3/32 x 1/2 x 4" HSS. It's flat topped. Works perfectly for me on my Super7. One small problem is the need to set it up square to the work, meaning the blade is pressed against the face of the chuck then tighten toolpost clamp nut.

As stated in my previous post, I'm looking into machining Reeves' GHT design casting to affix the same Toolholder to the rear toolpost with two mods; a small steel strap plate screwed to the LH side at the bottom to act as a stop against the LH side of the cross slide and a T nut full width of the casting base + a bit to speed up insertion of same into the T slot. I will be only using the casting as a base and not having the swivel top part – just a clamp to make the whole as rigid as possible.

[DMBParticipant @dmb]

Duncan,

Read my posts – I find RDG ' s flat top and bottom blades perfectly satisfactory.

John

[DiogenesIIParticipant @diogenesii]

Posted by duncan webster on 08/07/2022 20:40:13:

Anyone know where I can get eclipse type 5/16 blades from without a mortgage. The blades sold by RDG are not the same, they have flat top and bottom

5/16 – is that depth, width, or typo?

[Ketan SwaliParticipant @ketanswali79440]

Posted by duncan webster on 08/07/2022 20:40:13:

Anyone know where I can get eclipse type 5/16 blades from without a mortgage. The blades sold by RDG are not the same, they have flat top and bottom

ARC does similar to eclipse type, but the smallest width is 10mm rather than 5/16. Here is the link.

Ketan at ARC

[duncan webster 1Participant @duncanwebster1]

won't fit my existing holder unfortunately. I've doctored an RDG blade using a diamond file, but I'd prefer an original

[HopperParticipant @hopper]

The very slightly concave top on the Eccentric Engineering T-section blades gives a beautiful long curl of narrow swarf that falls out of the groove without jamming. Definitely superior to any other parting blade I have ever used, although they were all flat on top, not angled like Gray describes in his "dovetail" post above.

[Tony Pratt 1Participant @tonypratt1]

Unfortunately all eccentric blades are out of stock

Tony

Edited By Tony Pratt 1 on 09/07/2022 07:14:03

[HopperParticipant @hopper]

Posted by Tony Pratt 1 on 09/07/2022 07:13:24:

Unfortunately all eccentric blades are out of stock

Tony

Edited By Tony Pratt 1 on 09/07/2022 07:14:03

Very eccentric! Supply chain issues to Australia still have not recovered from Covid. I believe the blades are made in the USA and there have been massive problems with shipping from there. I had several bike parts returned to US sellers as undeliverable. But as posted above, there is a UK supplier of similar T section blades with the concave top.

[Anonymous]

This is what steel swarf looks like when using an insert parting tool:

The swarf is slightly narrower than the insert and considerably thicker than the selected feedrate.

See this discussion: Parting Off

Andrew

Edit: Messed up the link

Edited By Andrew Johnston on 09/07/2022 11:59:16

[HopperParticipant @hopper]

Nice pic there Andrew. You can really see the curve in the cross-section there. No wonder it does not jam in the groove!

[Howard LewisParticipant @howardlewis46836]

The T section blades perform the same function as taper sided blades, providing side clearance.

The flat top provides no Top Rake, although a holder with the groove machined at an angle (a la GHT ) will set the blade with top rake.

As Graham warns, grinding top rake onto a tapered blade reduces its width, and the depth to which it can enter a workpiece. So that doesn't sound to be a good idea..

A parting tool,or insert with a groove in the top will produce U section swarf. which should be narrower than the groove and so be less likely to block with swarf.

Mounting a parting blade inverted in a rear toolpost uses gravity to encourage swarf to fall out of the groove, again, reducing the risk of blockage and jamming.

The advice to maintain a steady feed is good, it is never good to let a tool rub and generate heat. I have now become so overconfident that I often use power cross feed with the rear toolpost mounted parting tool.Seems to produce a better and flatter surface than manual feeding.

Howard

[Graham MeekParticipant @grahammeek88282]

The Multifix tooling on the Hardinge I worked during the 70's came with a parting blade which had more of a "V" shape ground in the top face for the length of the blade, so these types of tools have been around for sometime. I have been trying to remember the make of the blade but with no success. I do remember it was only about 11 mm high.

GHT did try a parting tool ground like this as well as one ground with a shallow inverted "V" on the Front Rake. The latter is something I have tried, but found a straight face to be just as good when using a dovetail shaped blade. The end goal is trying to get the width of the swarf narrower than the cut width. The inverted "V" might seem the wrong way to go, as the cutting edge is longer than the width of the tool, but the secret is in the fact that the bottom of the "V" hits the work first before the outer edges. This forces the centre of the swarf to rise up from the tool and thereby reduce its width.

The problem with power feeding is the change in the peripheral speed as the tool nears the centre, with a constant feed rate. On the Hardinge this is easy to overcome as it has a variable feed. On larger lathes like the DSG, VDF and Colchester this does no seem to matter so much, as on these machines you do have the facility to change feeds on the move as it were.

Regards

Gray,

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