Inserted Carbide Parting-off Tool

[Brian Rupnow]

So--I have to ask---I have read a lot of various reports about carbide inserted parting off tools. I have only ever used HSS parting off tooling, and it scares me right to death every time I use it. I know the correct set up, speeds and feeds, exact center height, lock the saddle, use lots of cutting fluid to flush out chips, keep the tool at exactly 90 degrees to the central axis blah, blah, blah. I know how to sharpen my tools and the correct relief angles required.--And even so, about one time out of five the blade digs in, the lathe gives a mighty groan, and either the belt slips, the tool breaks, it pulls the piece out of the chuck, or I manage to slap the e-stop button and then go and change my shorts!!!!--I do NOT want to mount an upside down -run my lathe in reverse-mount my parting off tool on the wrong side of the saddle cut off solution. I want to know from people who really have and use inserted carbide parting off tooling.--Is it really better? My 10" x 18" lathe has speeds ranging from a low of 115 RPM (which I generally use for parting off) to a high of 1620 RPM in about 6 available "stages", and it doesn't lack for power. I do not have flood coolant. I do not have power feed on the cross slide. If the inserted carbide parting off tooling is really that much better, I might just be able to afford the seemingly outrageous price they want for one. I find that for 95% of the parting off and grooving I do, that .093" (3/32") seems to be about right. The largest stock I would ever part off is probably 2" diameter steel.--Opinions, please.---Brian

 

[kuhncw]

Hi Brian,

I've used an Iscar Self Grip SGFH 19-2 inserted cutoff blade for quite a few years. They are pricey, but the blade works well for me. I've used the blade in an 11 inch Logan and now in my 13 inch Sheldon. There are other brands and cheaper blades. I can only comment on the Iscar. This blade carries a narrow insert in the 0.093 or less range. I sometimes drip some tapping fluid or cutting oil into the cut.

Chuck

 

[modelman1838]

I bought one of these carbide insert parting off tools about 16 years ago when they were first available for the smaller lathe such as the Myford super seven. It does work really well and you can part off quite large diameters of about 2 ins at much higher speed even without coolant. I think they score by having the best rake and clearance angles for the job built into them, achieved by many years of experimenting. They really do work.
Hugh.

 

[Swifty]

I have been using a 4mm wide carbide parting for years as well as a HSS one. I found that the carbide is too wide for most of the smaller diameters, too much chatter etc. so most of the time I have been using the HSS one. Recently I bought a QCTP and a set of 16mm shank tools to suit, one of the tools was a carbide parting tool, it is only 3 mm wide and it works great. Depending on your diameter and material, I feel that you speed is too slow when parting off. Generally I use a speed af about 550 RPM, mostly in brass and aluminium, but also when required, in steel as well.

Paul.

 

[Brian Rupnow]

Okay Paul---You just made me google it.--And the answer is surprising to me. 17 foot per minute for cast iron, 57 fpm for brass, 83 fpm for aluminum, and 37 fpm for mild steel. That is recommended speed for parting off with an HSS parting off tool. Based on parting off a 3/4" (19 mm) shaft, that would be 87 rpm for cast iron, 290 rpm for brass, 422 rpm for aluminum, and 188 rpm for steel.

 

[Brian Rupnow]

I'm impressed!!! I just parted off a piece of 3/4" cold rolled steel at 210 rpm, which is as close as my lathe can get to 188 rpm. It went very smoothly, and far better than the 115 rpm I have been using for the last 5 years!!! Big head-slap for me.---Damn--I should have figured that out 5 years ago. I still think I will pursue the inserted carbide blades though.

 

[Brian Rupnow]

This is the .093" HSS cutting tool that I used to make that cut.

 

[bazmak]

Hi Brian,the variable speed lathe is great for nudging the speed while cutting
The carbide blades are good but i prefer HSS.What i have found is that you need an increased top rake angle for steel something like for alum.Even so i still avoid parting off or hold my breath
Usual fault for digging in if everything is set correctly is lack of ridgidity
or play in slides etc.The tool you are using looks good with large inbuilt top rake.For large Dias i also cut so far ,withdraw and move the compound/saddle sideways a couple of thou to the waste side for extra clearance

 

[Swifty]

One of the biggest problems of parting off is, the surface speed decreases as you get near the centre, fine if you have constant surface speed, but not the usual thing. I seem to break tips on blades always as it gets towards the centre, and lose surface speed. I have to admit that I'm a bit of a speed demon when it comes to machining speeds, guess I'm just impatient.

Paul.

 

[Niels Abildgaard]

A rather expensive but foolproff way:

http://www.homemodelenginemachinist.com/showthread.php?t=10176

 

[goldstar31]

I've used the rear parting tool as described in Vol 142 of Model Engineer and later in George Thomas's epic Model Engineers Workshop Manual for years now and I used a lolloping along 200 or 350rpm in using a a simple Eclipse hss. I've used it on a far from perfect old Myford ml7 and then a 918 and now a Myford Super 7B which I restored. Within limits, the speeds are no issue but the maximum diameter of round is 2". I use lard oil which I have advocated for 'ever' which is what traditional turners used until it became too expensive for cost accountants( Grrrrh!)

The only trick or difficulty is grinding the 1" kerf along the top of the blade. I first used my tool and cutter grinders but most workers do not have one and one to do the 140 degree kerf. So with care, the kerf can be 'ettled'( the auld Scots from the Alliance Francaise- atelier) using a drill press with a worn cutting off disk.

That kerf, I must assure you is the secret of parting off. The blade, be it angled or not gets a ribbon of steel( or whatever) and as the ribbon comes off- downwards it jams in the kerf. And the thing breaks unless it is narrowed- using the rounded or vee'd kerf.

AS I repeat, the GHT tool post gets a very neat thin ribbon of swarf and provided the work is supported, one can cut an absolutely smooth face almost to the centre.

GHT- for whom I have a high regard as a brilliant model and professional engineer overdid the need to do the front cutting edge at an angle of again 140( male) degrees. I did it- it worked fine- but the regrind which only requires a lick was left as flat cutting edge.

If people want, the kits for both the Myford size and laerger are from Hemingwaykits but mine is just from bits of scrap.

There is NO mystique, black art or the need to have ( and try to regrind carbide). I can regrind carbide but don't.

I hope this helps

Norman

 

[gus]

I find the 1/16" HSS Parting Tool from LMS to be quite suitable for my Sakai Mini Lathe. With dobs of Tapmatic Cutting Fluid and not so greedy digging in,I get good results cutting steel, brass,C.I. etc etc. Very important to keep groove wide to prevent tool seizing. It is important to have tool sharpness maintained. If it doesn't cut well, its about time grind sharpen.
For aluminum,I use Tapmatic Tapping Fluid(for aluminium only).
My luck is bad with carbide insert parting tool. Or perhaps I should rewind and check what went wrong.I still have the Japanese parting tool.The inserts is expensive.:wall:

 

[purpleknif]

Been doing this stuff full time for thirty years and the whole secret to this tool is clearance. Mostly on the back side.

 

[goldstar31]

It would be interesting to learn the views of those who have actually made and used a Thomas rear tool.

I've had mine about the same length of time as my Quorn- about 1974.

Regards

Norman

 

[GLCarlson]

do NOT want to mount an upside down -run my lathe in reverse-mount my parting off tool on the wrong side of the saddle cut off solution.

Given that a lot of history -and experts, GHT for example- think that this is the OPTIMAL method, why not? I understand some concern with a threaded spindle (vs Camlock), but the rear mount solves that. There is a hypothetical risk to the saddle dovetails, but while I've seen that discussed, I've never seen a report of the dovetails actually being damaged by the lifting forces.

I'm genuinely curious: why would one rule out a time-tested method, used by many with reported good success, which solves all of the problems one is having with the "classic" method?

FWIW, I've been using an upside down parting tool on my lathe for 30 years- it fails safe, isn't finicky, and works great.

 

[Brian Rupnow]

Best reason ever--There is no room on my lathe to put one.

 

[goldstar31]

Brian
Point taken about room but GHT in his pedantic and infinite wisdom catered for such eventualities and did drawings for 'overhang' on both the shorter saddle on the ML7 and the Drummond( which I both owned!)

For others who are following the discussion, my 918 or 9x20 or actually a 920( Ugh!), I had a subtable of steel to use the Myford tee slotted designs. I had several very useful Myford and GHT bits and whilst Myford slots are awful, I re-iterate, I wasn't going to dispose of them when a bit of steel solved the problem.

Good luck- anyway.

Norman

 

[GLCarlson]

Best reason ever--There is no room on my lathe to put one.

I confess that hadn't occurred to me! Also reassuring- you haven't identified some non-obvious but horribly important reason to avoid this approach. I'm always worried I've missed something when an expert absolutely rejects a method.

 

[bazmak]

I have used a rear tool post for parting off and it works well.May make another
as i have room and the T slots on the C4.My only dislike is that as an old school engineer i like to see and hear the chips,it tells a story.With high speed machining and CNC its fast and blind.You start with a blank and finish with a part the in between is a blur

 

[Brian Rupnow]

GLCarlson---You're calling me an expert?--Good Lord man, I just fumble along with all the "want to be" machinists out there. I AM an expert design engineer. I am a novice at this machining business.---Brian