Parting tool problem

[Chris MurphyParticipant @chrismurphy94983]

Hi all,

as you can see in the pics, I bought this RDG parting tool that someone recommended and it looks a really good tool. The only trouble is, is that the cutting point is a little bit above the centre of the work, so it’s not cutting at all really, more like rubbing.

my question is, is there anyway I can get this on center point or have I wasted my money. I don’t have a milling machine to reduce my toolpost holder.

I also bought the hss parting tool, this seems to struggle too, but as it says on the side of the tool, it’s more a grooving tool than a parting tool.

any advice.

regards

chris m……

Mod edit, rotated photos.

Edited By SillyOldDuffer on 23/08/2022 15:09:12

[Chris MurphyParticipant @chrismurphy94983]

[Anonymous]

Grind the top of the toolbit down until it is on centre height.

Andrew

[noel shelleyParticipant @noelshelley55608]

Put the holder in the lathe and machine away an amount of metal that will drop the blade to centre height. Hacksaw or grinder will also do the job. Noel

[Howard LewisParticipant @howardlewis46836]

Have you got a 4 jaw chuck?

If it will not weaken the holder too much, mount that in the chuck and face off the lower side of the holder, enough to bring the tip down to centre height.

IMO, don't grind top, rake on the blade, to reduce the risk of dig ins. But do lubricate when parting off

Howard

[SillyOldDufferModerator @sillyoldduffer]

The pictures show the blade tool is much too high. Three choices I think:

1. Modify the holder, as per Howard. Easy with a milling machine, but a challenge on a lathe for a beginner. If the holder is soft I'd file it. (And curse every second wasted doing it.)
2. Grind the tool down from the top, as per Andrew. Only objection to this is the need for a grinding wheel and the skill to use it. I'm prejudiced against grinding HSS because I'm not very good at it. After lots of practice I can just about manage, but it's never a happy experience.
3. Buy the next size down so you can get on with learning how to part rather than stop to learn how to modify tools first! Modifying tools is well worth learning, but it often requires advanced techniques a new learner hasn't got to yet. I'd buy my way out of the immediate problem and come back to grinding and milling later. They both need to be tackled in due course, and fixing the tools as described by Howard and Andrew is a suitable project.

Dave

[JasonBModerator @jasonb]

As well as Andrew's suggestion you could do as many older lathes did and not use the 4-way but clamp directly to the topslide with packing to bring it upto height.

[Howard LewisParticipant @howardlewis46836]

If you adopt Jason's suggestion of an easy way to solve your problem, do ensure that the tool is square to the work!

Howard

[JasonBModerator @jasonb]

That really applies for however you hold the tool, if you don't have the 4-way square on or don't have the holder square in the 4way you are likely to get the same problems as clamping directly to the topslide.

[Clive Brown 1Participant @clivebrown1]

Note that if the parting blade is tapered, then grinding from the top will reduce the cutting width. The tool can then be fed into the work, without risk of jamming, only to the extent of the ground length.

The "grooving tool" looks to be a poor shape, far too much rake on the top face. I'd grind it back and perhaps put on a much shallower rake of, say, 5 deg. or so.

[Mick B1Participant @mickb1]

On my old Myford Speed 10, I found that machining the underside of the toolholder would leave me with insufficient support, so I put the 4-way in the vertical slide I had, and milled away about 1/8" thickness at the bottom of the tool post slot instead to get the parting tool to centre height.

It meant I had one toolpost slot pretty much dedicated to parting, but that didn't produce any issues I remember – and if it had it would've been easy enough to pack it back up again with strip.

[DMBParticipant @dmb]

Hi Chris and everyone,

Look back through my previous posts and you will find that I recommended the tool shown in your photos. However, I use the blade in the QCTP holder supplied by RDG and mounted on the QCTP, allowing height adjustment, which your 4way toolpost doesn't.

John

[DMBParticipant @dmb]

Look under "Thread: parting tool trouble" my posts 4th & 5th August 2022. All I can say is that the PT blade, holder and QCTP works OK for me on my Super7.

John

[duncan webster 1Participant @duncanwebster1]

I wouldn't go modifying the toolpost, if you remove enough metal to get the tool point down to centre there will be nothing left. you can get a 5/16" deep parting tool otherwise identical to the bottom picture. RDG might do you a swap. It's only 1/16" wide as well, which might make life easier on what looks like a ML7, notorious for parting issues. I'm sure mine used to laugh when it saw the parting tool coming out.

[HopperParticipant @hopper]

Send your  tool and holder back to RDG and exchange it for a smaller one that that will fit your Myford. The RDG site says this one should but obviously it doesn't.

But first, check that if the mounting block attaches to the main parting tool holder body with two cap screws, sometimes the holes are offset so if you flip the block over it will lower the tool height.

If the other tool, labelled Grooving Tool, cuts an 8mm wide groove, it is way too big. 8mm tool height would work ok with packing though.

Edited By Hopper on 24/08/2022 02:31:58

Edited By Hopper on 24/08/2022 02:33:28

[not done it yetParticipant @notdoneityet]

I can’t remember, now, what I got with my first lathe nearly thirty years ago.

I do remember that I was using some brazed carbide cutters (some of which were useless, but I was not aware of the quality issues and them needing proper sharpening!).

However, the lathe was fitted with a 4-way tool-post so I found how much shimming was required to get the cutter to centre-height, then selected a single thick spacer/shim which raised the cutter to a few thou below centre-height. That was initially retained with the individual cutter and later glued to it. That meant I only needed to store that cutter with a shim that raised the cutter that last few thou. Simples, really.

I always use the largest cutter/holder that I can, the smaller ones (mainly HSS) are used when space is limited – or for less tool grinding. Think about it – HSS is generally used for light cuts, so do not need to be that big, and many light-weight/worn lathes will flex when making heavy cuts, altering that careful centre-height setting anyway. Adding a QCTP simply exacerbates any flexing of the whole system.

One problem, with thin tools/cutters arises when the cutters are extended, by users, to reach further. A lot of hobby beginners just don’t think about these potential issues. So little wonder that these issues keep arising on the forum.

[Dave HalfordParticipant @davehalford22513]

I thought the standard answer to a post with the words 'parting' and 'problem' in it was to fit a rear upside down tool post, especially with all those empty T slots.

[Graham MeekParticipant @grahammeek88282]

Rather than modify the blade holder you have would it not be better to talk to RDG and exchange the holder for one of their smaller blade holders. A blade which is 10mm high will probably fit better than your current set-up.

It needs to be remembered that Myford machines were designed around the use of 1/4" to 5/16" HSS tool blanks.

The opening shot of the ground parting tool has far too much top rake. I do, and have always used zero top rake.

Regards

Gray,

[not done it yetParticipant @notdoneityet]

Oops! It looks like my post above may well should have been posted on another thread by this member. Apologies, for listing it on another of his many threads.

[Chris MurphyParticipant @chrismurphy94983]

Hi all,

update on my parting problem.

I managed to grind down the RDG holder and the cutter was just a fraction higher,a very tiny amount.

I’ve been trying it all afternoon and still no success.

I’ve tried different speeds, selected the back gear, moved the cutter in and out, cut as close to the chuck as I can.

still a complete waste of time. I’m doing something wrong, I just wished I knew what.

this is the only issue I have with using the lathe, oh well.

the lathe is a Myford ml7 btw.
anyway thanks for the replies.

chrism…….

[roy entwistleParticipant @royentwistle24699]

Is the lathe going forwards ( don't ask )

Roy

[Tony Pratt 1Participant @tonypratt1]

chrism, we need details the more the better for a diagnosis, pictures or a video would be even better.

Tony

[Howard LewisParticipant @howardlewis46836]

If the cutting edge of the blade is above centre height, even "A fraction" it will rub rather than cut, and you will have problems.

ANY tool mounted above centre height will not cut, it will rub.

Set the blade at centre height, with no top ,rake and life should be a lot simpler.

Howard

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