Parting off - front or rear

John Ward sells an extended and T slotted cross slide for the South Bend and SB Clones (like Boxfords). My Raglan has only a short cross slide as standard but the John Ward long slide that he produces for the Raglan is ideal for rear toolposts.

Today i had a play with some new parting tools - one from eccentric engineering and another from a local tool supplier The F.O.R tool by eccentric uses T shaped blades and the other the conventional wedge shape blade .

Both of these are mounted upside down in the toolpost ( QCTP) and i ran the lathe in reverse , if you have a screw on chuck you will have to use them in a rear toolpost . I started out with some 30mm 6061 T6 round bar running at 250rpm and neat soluable oil for cutting fluid . I followed the advice on sharpening the blades as supplid by eccentric enineering - use the side of the wheel to give a 4 deg relief , many use the front of the wheel which gives a concave grind and too much relief .

FIrst cut with the F.O.R was going ok but the chips looked like they were tearing out and not cutting well so i switched over to WD40 with an immediate improvement - the soluable oil didn’t seem to like aluminium and i also tried some trefolex ctd spray which worked ok and i repeated the same process with the other blade with similar results .

Next up was some bms at 20mm dia and as in the first test i tried the neat soluable oil and this led to my first jam up but fortunately I didn’t have the qctp clamped too tight so the holder popped up and stopped any damage ( mental note : don’t tighten the qctp lever too tight as this acted like a safety device and stopped the blade breaking ) . I reset everything and tried the ctd spray which worked better , I didn’t bother with wd40 as i never considered it as a cutting fluid for steel ( i was seriously mistaken on this ) .

Now that i seemed to have it going in the right direction I thought i better bite the bullet and try some larger dia steel , this time 40mm roundbar of unknown composition - i had machined it before so knew what it cut like . I didn’t try the soluable oil on this for the first cut as i knew from the previous tests it wasn’t the best so so ctd spray was used first .

I did the first cut in two stages with no dramas with either blade and considering the t shaped blade is only 2mm wide i was quite surprised it didnt wander or break ( i would learn a little later that this blade is one tough little blade ) and the other blade is 3/32 wide . Anyhow i parted of two disks with each blade with no issues and i did switch between ctd spray and soluable oil on both the last disks but i could hear a difference in how the blade was cutting so soluable oil went back on the shelf .

I did one last test with both blades using power cross feed and found the constant feed seemed to help a little , on the last cut using the wedge blade for sh#ts and giggles ( or possibly tears ! ) i thought i would try WD40 just to see what happens - You wouldn’t believe it but it worked better than any of the other stuff i had tried by a country mile ! I then set up the t shaped blade and tried it using WD40 and got exactly the same result so half way through i reached for some RP7 spray which caused an immediate seizure ripping the blade upwards along with the toolholder . Fortunately it didn’t damage the blade or holder but it did open my eyes ! You would think all those types,of sprays are all the same but not so ! I reset everything and started the cut again using WD40 and it cut all the way perfectly . On the last two cuts i cuts i did i cut through in one pass and was pleasantly surprised that the thin t blade came through with flying coulours ! The t blade has a slight concave grind along its top edge to help curl the chip in to clear the sides of the groove - the wedge blade has a convex v on top with the apex offset and I don’t know if this is intentional or not so i left it on there and it did seem to fold the chip and feed it out to one side of the groove .

Cutting speeds :

alloy 200- 300rpm for 30mm bar worked ok

steel 120 rpm for 20mm and 60rpm for 40mm dia ( i did switch up to 120rpm about half way through on one cut but didn’t see any gain other than alittle time saved but at the risk of a jam up so I don’t feel it to be worth it

So what did i learn from all this ?

Oils aint oils so don’t be afraid to try something else . I don’t know why WD40 worked so well on steel but RP7 caused a seizure ?

Speed isn’t everything so slow it down - with turning , speed and feed will give different surface finishes with parting it doesn’t matter I don’t think you can’t go too slow with parting .

The qctp can be used like a safety device by not cranking the locking lever closed too hard .

The relief angle on the front of the tool shouldn’t be too much , around 4 deg is more than enough will help stop dig ins , use the side of the grinding wheel to sharpen the blade not the periphery which gives a concave grind , more relief angle and a less support under the cutting edge .

If you have powered cross feed consider using it as it gives a nice even feed .

In my opinion the inverted parting tool running either at the from or the rear definitely lessens the damage caused from a dig in and it is even better if you use the qctp as a safety device .

Note: the F.O.R blade holder has a sliding wedge design so to can adjust the blade height ( about 1mm in height ) without having to use shims - this is a really handy thing for those who don’t have a Quick change tool post.

Disclaimer : i have no affiliation with any of the companies or products i have mentioed and ALL of the products mentioned were paid for by myself at full retail price .

Good evening,
I bought a Myford leadscrew handwheel to mount it as an apron handwheel on my ML10, instead of the stock ball handle.
The leadscrew handwheel has an index ring cast on its periphery that I wanted to remove.
I took one of these:

the name is something like "MGEHR1010-2 Grooving Turning Tool Holder" (there are several sellers, I chose the cheapest one with 10 inserts, around 7 GBP including shipping costs):

I set the tool in the front toolpost right with a try square and proceeded in lowest backgear (48 rpm) as the cdiameter was 86mm: the operation completed perfectly, with the proverbial "sizzling bacon" sound, and in the end I could remove the cast iron ring.

Admittedly Myford cast iron seems a nice material to machine, but I never had the impression to reach the limits of safe operation and the 2mm insert finished in as good as new conditions, though, when the ring was almost severed, the cut was interrupted each time it met the spokes of the handwheel.

Cheers,

Massimo

I just found out something interesting as I was struggling to get a stable cut groove or even part off in a 50mm 6061 or 6082 aluminum bar, just using a Chinese 3mm carbide insert - rated for aluminum, which is just not the case as you will see later - tool in forward direction. Toolholder similar to the one in the post from Massimo above. I am using a 200x1000mm lathe with a 1.1kW motor and coolant flow straight spraying in the cut. The thing chattered all the way from 100rpm up to 1000rpm. N way to get it clean.

I converted the lathe to CNC a while ago and probably lost a bit ridgidity in the X-direction due to the limited dimensions of the ball screw, dictated by the small space underneath the cross slide. If i remember well, chatter on parting off or grooving was also there before the CNC conversion. So it had to be something else as many pro-CNC lathes are parting off at 1000-2500rpm without problems.

But then I read an article that makes a lot of sense from a dynamics point of view and it clearly shows how the toolpost dynamically flexes the wrong way ( most toolposts are fixed at the base side ) causing the tool to dig downwards in microscopically and release back accordingly. This elastic kind of spring-movement is the major cause of the chatter we see and hear. When using the normal setup that is.

So I reversed the tool and rotation, mounted the tool even a tad above center and tried again, at 1000rpm! Very much less chatter but still not satisfactory to my standards. It could have worked but it felt llike not cutting optimally.

Then I went on and sharpened the carbide so that the slightly convex front side below the cutting edge became flat to even a little concave. Leaving a razorblade sharp edge with negative geometry, theoretically the best one for aluminum. This time, no chatter, clean cuts, huge chips of 0.15-0.2mm thick, very often breaking in small pieces of a centimeter or so, avoiding birdnesting most of the time. Birdnesting was still there when cutting lightly though. So in order to get the chipbreaker in the carbide insert to do its work, one needs to push for heavy cuts, which makes sense.

So, this thing ran at 157m/min surface speed with coolant and it works just great. You need coolant because the one time i did not use it, the cutting edge has tendency to weld up quite fast with aluminum and the part became burning hot. The limit would be something like 250m/min cutting speed but for safety reasons I don't want to exceed 1000rpm on this CNC setup ( barely enclosed lathe and fairly large and heavy workpieces ).

Hope this helps for some of you facing similar issues and avoid time consuming research and trials.

I no longer use the topslide on my Warco 250MV because everything is so flexible. I certainly cannot use the quick change tool post for anything other than with a light boring bar. I have a solid block of steel set on the cross slide with the 4 way tool post set onto that. It is about as rigid as one can get. I have made it so that most tools, such as indexible ones do not need shimming.

I have a 25mm deep cut off tool holder & I mount a 13mm* 2mm exide tapered steel blade in it. I just grind a bevel on the front that looks right & touch it up with a stone. The holder obviously does not fit in the tool post so I bolted 15 * 15 piece of bar on the side. I then milled it to 12 deep such that it fitted in the tool post & the cut off blade sits dead centre.It has a very slight curve in the bottom & by tightening the 3 clamp bolts unequally I can force the blade up or down .25mm as it rocks in the tool post by a few of thou. That gives me a solid holder in a solid tool post.

I find it works OK on steel at 180 RPM,with lovely curled chips if I can maintain an even feed. I would like to run slightly slower, but the lathe keeps stopping, as the variable speed is carp at low revs

As for cutting oil I find that chainsaw blade lubricant seems to work OK. I have found a particularly "sticky" one. Not sure of grade or make. They sell it locally

It depends on the work you do and your priorities. I use my vertical slide a lot on my Warco, and a rear tool post would just make mounting that a load more complicated, plus I don't have enough need for rapid parting-off, or enough difficulty doing so, to justify making one.

I too replaced my Warco 290V top slide with a solid CI block & didn't like it at all, I found it very restrictive with no swivelling facility, I also use a rear tool post so I couldn't fit the top slide back on as & when needed. My solution was to completely re-machine the Warco top slide to a decent stand of workmanship & I am now very pleased with it, plenty rigid enough now for heavy cuts, you can indeed make a 'silk purse out of a sows ear'.

Tony

I thought this was a wrinkle for spindles running in bronze bushings.

Normal wear on the bushing is at the top.

By putting the parting off tool at the back upside down you could use the unworn bottom of the bushing.

If you have tapered roller bearings then it is for fun only.

I like fun.

I could be completely wrong about this, but not about the fun part

I use this vertical parting tool on my Stepperhead lathe

https://www.youtube.com/watch?v=S8HvS13L7MU

and a rear mounted HSS parting tool on my Chipmaster

Both work well

Alan

Nice to learn how we all try to get around some fundamental rigidity issues on our - mostly - smaller lathes.

The setup with the front rotatable compound Z-slide is flexible but a disaster in terms of rigidity. My posting above is about keeping the possibilities of this compound slide, having a fast Dixon-type of toolchanger and still being able to do some fast and heavy cutting in groove or part-off from the front side. And with CNC running things. Plus coolant spraying. For CNC runs, I lock up the compound slide with the four hex side screws. Not ideal.

To compensate for that flexing tower I need to part off in reverse as mentioned before.

I need the Dixon and the compound in some cases, otherwise I would have replaced the toolpost and compound assembly by a solid steel block instead like some of you have done.

Next step is CNC internal /external threading large diameters with a servo spindle and a modified controller.

FWIW, having had problems with parting iff in the front toolpost on a Myford, after making and fitting a rear toolpost , never looked back.

When I changed my lathe, one of the first jobs was to make a four way indexing rear toolpost.

Am now so confident, with a very old HSS blade, that I often part off under power!

Trying a carbide tip parting tool, in the front toolpost resulted in jam ups, and finally damage to the holder!

Howard