Diamond tool holder.??

.

They are not too shabby at facing off either.

Here is a link to youtube taking off a 1mm cut to remove excess material in an interrupted cut on an eccentric for the James Coombes I am building.

**LINK**

Nick

On the subject of upside down parting tools, there aren't many lathes that are designed to withstand a lifting of the slides (including the saddle) by the cutting force, so I concluded that for my Bantam at least, any rear-mounted parting tool should be operated with the lathe in reverse and the tool not inverted.

If you look at the assembly drawing / exploded parts list for your machine, you will see what arrangement is used to restrain the saddle against this vertical (upwards) movement. It's usually fairly minimal and primarily intended for locking the saddle at a single point. Unless you have this saddle lock adjuster tightly nipped up (which isn't ideal in terms of wear), there has to be vertical slop in there and the horizontal location by the bed Vee's will also suffer from any such vertical movement .

On the cross slide, there is a firm and direct contact between the horizontal underside faces of the slide and its base in the "normal" direction. With cutting forces in the reverse (upward) direction, the slide is instead held by the angled gibs with some slop ie much less well defined and rigid.

I can only assume that in some cases, the additional slop and springiness resulting from running the tool upside down actually helps to reduce the likelihood of judder, most likely combined with light cuts. However, if you were asked to demonstrate exactly how the tool position is positively defined / constrained, I suspect you'd struggle. Generally speaking, rigidity and control seem to be the safest way to prevent "rubber pants" moments during heavy parting operations.

Murray

No stringy swarf on that, what material is it? Lovely finish on it as well.

Hi Vic,

It's EN3

Nick

Hi Murray, I also have a Bantam and agree about the forces involved, When people talk about lifting and tool post bending etc they tend to forget the weakest part of the set up that is the parting tool itself, which is going to bend long before the tool post. On a Bantam parting is no problem in the conventional manner but some top rake helps with the peel effect.

Have you tried a tangential parting tool? They have a limited depth of cut, depending upon design, but within its range they work great.

chriStephens

Chris

No, I bought a 3mm Korloy Sawman indexable parting tool as you can see from this album. Works really well. I use a few hundred rpm and power feed with coolant and it doesn't flinch. I'd forgotten that I made a Youtube video of it.

I wouldn't go back to HSS now except for very narrow grooving. I also wouldn't try to operate it upside down! I am going to get some "H01" grade inserts for parting aluminium and light alloys - although it parts these OK with the steel cutting inserts, the material sometimes doesn't clear fully, resulting in snagging and poor finish. Cutwel sell single inserts online.

I also have a Korloy KGT tool which not only parts and grooves but is also designed for normal turning operations. I've got inserts for both steel and light alloys and it's pretty darned good.

I have to admit I often use an indexable boring bar for both internal and external turning. The internal operation is pretty obvious - but for external turning I move the tool behind the centre line and reverse the machine. In this way, when you have the top slide at 45 degrees for chamfering, you can use the same setting for both internal and external chamfers. That avoids having to keep swinging the topslide back and forth. You need to swap out the boring bar for a proper turning tool when you have more than an inch or two of overhang or if you want to make proper heavy cuts.

When using the machine in both directions like this I like to sanity check that the power feed is the correct direction. I always try to use the power feed and feed stops where possible so I can get a decent finish and a reasonable rate of material removal.

Murray

Edited By Muzzer on 12/12/2014 20:50:33

Hi all,

Really interesting thread!

Can someone please tell me the correct size to get for an ML7 using the Chronos QCTP holders?

The War Office, (aka the missus) has promised to get me these for Xmas!

Cheers and Season's Greetings to everyone.

Martin

Details here Martin.

http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=6&Itemid=19

If you are using e.g. 12mm tools presently get a 12mm version.

Nick

Hi Martin, might I suggest you get the later version that allows you to keep the tool post square to the work, so you don't have to keep re-squaring it when, for instance, parting.

The original has to be kept angle, a compromise for threading, which is something not discussed under this title so far. For starters a tangential threading tool does cut very freely and cleanly especially with flank feed threading, if that happens to be your preferred method. Anyone else tried this tool for threading?

chriStephens

I have, I normally feed in using the compound set over to whatever angle the thread type dictates and it works fine but with two problems which stem from the quite steeply angled cutting face which make it difficult to line up the tool to the work using a conventional "thread gauge" and also the back face of the thread dosen't clean up so well as a flatter topped cutter when giving the final couple of "straight in" passes using the cross slide.

Does anyone else have a different threading technique when using one of these?

Paul

As much as I like it for conventional turning I won't be using it for threading.

I can't stand all that winding in and out so I'll be making one of these plus a grinding jig.

http://mikesworkshop.weebly.com/swing-up-tool-holder.html

As much as I like it for conventional turning I won't be using it for threading.

I can't stand all that winding in and out so I'll be making one of these plus a grinding jig.

A 10 pound vernier DRO on your cross slide simplifies threading because of its accuracy

You can skim down another couple of hundredths of a mm if required

Paul - you are not legally obliged to have the sloping top to the tool so you can grind it flat topped if you like.

A swing up toolholder is great if you are using a mandrel handle or have a lathe that reverses quickly but a retracting tool holder is better for a lot of purposes.

That's another job on the list!

Bazyle, using the Eccentric Engineering supplied jig and instructions will only produce a sloping topped threading cutter, what do you use to produce a flat topped one? do you have some type of custom jig?

Paul

Hi Paul, with the flank feed (off set top slide) method, if you set the top slide to exactly half the thread angle all you need to do is align the leading edge of the tool with your thread gauge, the trailing flank is taken care of by the in-feed. It would help a little if you grind the tool slightly under thread angle to give some small amount of clearance. It also helps to not take very deep cuts to reduce any "steps" in the trailing flank. A final pass or two straight in only really works with a form tool type tool.

Hi Vic, how about getting a cross slide stop, it would help with your understandable aversion. I have an Eccentric style tangential type threading tool on a swing up tool, amongst many others including a copy of the Victorian original, which again works well. I seem to recall demo-ing it on the SMEE stand at Ally-Pally a few years ago, some of you might remember as it seemed to draw quite a crowd.

chriStephens

My Lathe isn't the most accurate (or rigid) Chris so on the rare occasions I've carried out single point threading I've done it on a "trial and hopefully no error" basis - or put another way I sneak up on it and frequently check progress with a suitable nut! I do have a cross slide stop, comes in very handy. I think the flip-up holder will make things much easier for me.

I always understood that the top-slide should be set over at half the thread angle Chris

But then I started watching the videos of Marc Lecuyer (The Lazy Machinist in Canada) on YouTube and as a result (in future) I will be setting my top-slide at just under half the thread angle.

His explanation is that setting slightly "under" does no harm to the thread form but setting "over" (even slightly) does and that because it is quite hard to set exactly on the half angle - it's much better to set it "under". He goes through this in some detail here;

**LINK**

The rest of his videos are also very well worth watching by the way.

Regards

IanT

Hey, Chris, I remember that show. Our club stand was just over the aisle and I waited for the crowds to die down to see what was so interesting. Of course there was nothing as the crowd dispersed only when you stopped.