502 forum posts
OK I need to buy a boring tool and I'm looking at RDGs selection of tipped tools.
First off, are tipped tools any good, I have been told that they are inferior to ground HSS tools? (My ground HSS parting tool broke )
And secondly there are half a dozen similar bars all with different tips which all have different letters eg CNMG, TNMG16, CCMT09, DCMT07 etc etc
Whats that all about then?
|David Littlewood||29/11/2011 22:28:36|
|533 forum posts|
There was a very comprehensive database on interchangeable carbide tooling in a past issue of MEW, which explained all the code letters. You have to make sure, obviously, that the holder and the tips are meant to fit together.
In essence, CCMT are fat diamond shaped tips with an angle of about 80 degrees at the business corners - 2 can be used in a conventional holder. CCMT 0604 is a useful size, as a lot of outside turning tools also use them. A third pair of digits tell you the corner radius, e.g. CCMT 060402 has a 0.2 mm corner. You can also get roughing tools which use the other two corners when you've bust the two main ones!
DCMT have a much sharper working corner (I think it might be 40 degrees, but I'd have to check) and is quite useful for profiling.
Those two are probably the most useful for our puposes, at least IMO, others may have a different view.
|Clive Foster||29/11/2011 22:34:26|
|2459 forum posts|
First off inserted tip tools are, in general and massively oversimplifying, designed and engineered to work best for fairly specific jobs under fairly specific conditions. This means industrial strength machines and, usually, CNC speeds and feeds. In particular they are mostly made to work on what can be called the back side of the spindle hp per unit volume of metal removed curve where going faster and working harder means you shift more metal per hp. Fine with full enclosure and mechanical chip conveyor but somewhat worrying with an open machine, especially in the home shop. Under industrial conditions each tip edge usually lasts only a few hours, often less, but the amount of metal shifted in that time is impressive.
At home its much more comfortable to work at relatively low metal removal rates, on the front side of the curve where hp needed goes up faster than metal removal rate. HSS tooling works fine in this region. The general run of Model Engineer machines have neither the strength, speed or power to drive industrial rated tip tooling into their design operating range hence the perception, in some Model Engineering circles, of tipped tooling being inferior to HSS. If you insist on using something outside its design operating range poor performance should be no surprise so its only to be expected that a randomly chosen insert will not give of its best.
There are approximately a zillion different types of insert out there. All the major makers produce lots of data enabling the informed purchaser to select a decent insert for the job. All that data and choice is a major, major headache for the normal guy. Best answer is to go to a specialist, such as Greenwood Tools, who will be able to advise you on a suitable style and grade of insert that will work well on your machine. At home you will almost certainly be running the insert outside its design envelope but it will last a lot longer. I understand you now have a Smart & Brown model A which makes life far easier as you have decent speed and strength so could run some inserts to their design loading.
The RDG tools sets look nice in the catalogue but I don't know how well they are made. Proper location of inserts is essential or they will break quite easily. Also I see no specifications as to maker, material and detail shapes of the supplied inserts nor any details of speeds and feeds. All vital information. I personally would not deal with a firm so unprofessional that they cannot be bothered to supply such. A bit better than the no-name E-Bay cheapies who don't even know the type of insert, assuming its a standard that is. One such supplier not only offered non standard inserts but was unable to provide replacements!
Parting tools are much easier. Just buy one of reputable make. Mine is a Kennametal with 3 mm wide inserts.
In my view best bang per buck in the home shop lathe tooling is HSS bits in properly used Armstrong / Williams / J&S (best) holders along with a decent size grinding table and nice set of templates so that you always sharpen to the same angle. Proper use of the tool holder means that, except for the occasional difficult job, the shank of the toolbit is either at 90° to the lathe axis (normal turning) or parallel to it (facing). The holders are bent to facilitate this. If you have a simple tool height gauge its easy to leave the holder mounted and interchange bits as a very poor mans QC system.
Edited By Clive Foster on 29/11/2011 22:35:21
1026 forum posts
I've been cutting metal for over 50 years now and I agree with Clive, Used lathes from Dean Smith & grace down to my Myford and was around when disposable tipped tools were in their infancy.
They are OK but really designed for industrial use and frankly I find I get better results with high quality HSS tool blanks ground free hand. I use Eclipse or other top brand tool blanks and grind my own on an offhand grinder.
Tonight I turnd a component with 4 different diameters all to a limit of 0.0005" with HSS. I have tried this in the past with tipped tools and on small machines they stuggle to hold close limits--good for roughing out though! The brazed tip tools can be sharpened to a keener edge if you have the gear, of the disposable ones I have tried on the Myford I fined the Sumitomo give the best results but they are expensive.
I do like the full form screw cutting tips though and they work well.
|1008 forum posts|
Well I have to say I use SECO tips on both the 6" and the Myford. Intercahngeably with HSS, at HSS speeds and feeds, when it suits. I get a very good finish, and I regard Ok for dimension as +/- .0002".
I do have a Quorn and ground HSS - mostly now for specific shapes and profiles. With a high rake angle I can take about 200 thou on a single cut on the Myford feeding by hand, without causing it pain, so that deals with roughing steel.
I have heard all this stuff about being only suited to CNC rates etc. Perhas it does. but not in my workshop.
Tipped parting tools are a can't live without item.
|1289 forum posts|
I agree with mgj, you can use positive rake tipped tools in a small lathe. I find them very useful when turning hard material or material with hard skin or hard spots (castings). I recommend you try a tipped tool in your lathe, especially for roughing cuts. You can then use HSS for the finishing cut.
1935 forum posts
I have hardly ever used tipped tooling except on cnc lathes. They are expensive to maintain, individual tips are not cheap to replace, they are really intended for industrial work hence quality tips are usually sold in packs and not individually. They are relatively brittle and easy for a novice to break being susceptible to chipping. If you are having difficulty turning with HSS, indexable carbide tooling will not make the problems go away, just more expensive.
As for parting, HSS is perfectly satisfactory and the problems are either with the machine or the operator. A novice is better off with a rear mounted toolpost with a proper parting blade mounted upside down. In that case, the tool tends to lift away from the work whereas with a front mounted tool it tends to be pulled under the work especially as the diameter gets smaller thus getting forced under the work, digs in and breaks - simple. If you don't believe this I can produce force vector diagram analysis which shows how this happens, it is not magic, just plain old physics, pm me.
I would persevere with HSS until you are proficient. Learn to grind the proper rake and clearance angles for the job in hand. Master craftsmen have been doing this for many years quite successfully. It is not an easy skill to learn but is simpler than riding a bicycle.
By the way, you need indexable tooling just as the amateur snooker player or golfer thinks he needs the same equipment a professional has. Nice to have but won't improve your game, just more expensive to play.
As for the tip designation (CCMT etc) these are codes which are derived from these tables.
Edited By Terryd on 30/11/2011 05:54:35
1935 forum posts
Hi again Wolfie,
I forgot to mention that if you do buy a cheapo set from the usual suspects make sure that you can get the tips individually. I was given such a set with a lathe purchase and when one tip chipped and I tried to buy one replacement was told that they were only available in sets to suit my particular range of tools. The salesman's gruff comment was "that's how the Chinese supply them". Hence I'm back to HSS, and won't use that supplier again.
|612 forum posts|
I made my first from 10mm of silver steel and bought a chunky 15mm one
I use my own handmade HSS inserts.
Never had a problem, rough boring is one of the easiest things you can do on a lathe because the tool support is directly over the lathe bed.
I would definitely recommend the cheap and cheerful route, if you haven't done boring before then you're going to have a few unintentional internal collisions as part of the learning curve before you get a "feel" for boring.
A leadscrew clutch is very handy for long boring jobs, and once you get around to it, internal threads.
Edited By ady on 30/11/2011 08:15:14
|612 forum posts|
(My ground HSS parting tool broke )
Had problems myself with high speed parting.
Any kind of stiffness error and yer goosed, bam!
I started to part using my backgear, it does take longer but its miles easier, and I always part from the rear, not the front.
One big advantage was no heat issues if you use the backgear, so you can part thick aluminium bar really easily.
Edited By ady on 30/11/2011 08:22:23
|Ian S C||30/11/2011 09:18:20|
7468 forum posts
My first boring bars were 1\4" and a 3/16" Eclipse, look like little hocky sticks. Over the years since then I'v made my own, some ground out of solid HSS, others from grade 8 or better bolts, for HSS inserts old taps, center drills are good. One way to make a little carbide tool,either internal, or external is to braze a tip from an old circular saw blade to an old high tensile bolt suitably shaped. For some heavier work, on steel that has been gas cut, and has a hard edge I have a boring bar made from a 24 mm grade 10 bolt, with a used tip from the face cutter on my mill brazed on, the tip is 16 mm triangle. Ian S C
1935 forum posts
From your experience do you think silver soldering would be strong enough to fix an old saw blade tip? I have an old tipped blade I could use for this purpose. I did think about cutting a section from the blade with tip intact and using that for parting, do you have any views?
502 forum posts
Its not so much the use of said tools thats the problem, I'm trying to save myself a long laborious job grinding the tools on my small bench grinder.
It only has two wheels like any other and one is a wire wheel and the other is a fairly fine stone which is taking ages and ages to remove metal from HSS.
Yes I know I could change the wheels over each time but thats a big hassle as well for two reasons. One is that I have to dismantle the whole guards set up to get at the nuts at each end of the spindle.
And secondly and far more of a pain is that for some insane reason I can't hold the wheel at the other end so I can do the nut up, because if I do it undoes the nut at its end (opposite threads???) and I struggle to get either of them done up properly. There doesn't appear to be another way of holding the spindle so I can do the nuts up
Edited By Wolfie on 30/11/2011 11:08:45
|Ian S C||30/11/2011 11:54:43|
7468 forum posts
Terry, I cut the insert out of the blade with a hacksaw, then filed it down till the brazing showed, I then placed it in a prepared groove in the tool, I used(I think) bronze rod as filler, just a little fraction of that, the insert is only about 5 mm long by1.5 or 2 mm sq. If you look at the tips you will see that they are angled alternately left and right, so you are best to chose the correct one for the tool that you are making. Tried making a parting tool by just cutting a rectangle out of the blade, but when I tried it the brazed joint let go about half way through a 1" dia bit of hot rolled steel.
Wolfie, to rough grind, an angle grinder can be a good help, clamp the HSS in a vise, with not too much protruding, finish it with the bench grinder,just take your time. Before you start on the HSS, it might be an idea to get a bit of square (6-10 mm), and practice on that, unless you are confident to go staight in on the HSS, It becomes easier with practice. Ian S C
2314 forum posts
Do you really need a wire wheel on your grinder?
You say that your wheel is a fine grade so why not replace the wire wheel with a coars(er) stone - you can then rough out the shape with this and finish/restore edges with the fine wheel.
|Clive Hartland||30/11/2011 12:23:05|
2612 forum posts
Wolfie, forget the tipped tools for the moment, when working the lathe you always need tools of a certain shape.
It would be better to get yourself a decent two wheel grinder and then you can shape you HSS blanks as you want them.
Also get a green grit wheel for carbide tools later.
The best boring tools are of the 'Bar' type and sometimes have removable heads.
You will need a 'V' block to clamp them in or a block with a slot to clamp them.
1935 forum posts
The shaft on a grinder should have a RH thread on one end and a LH thread on the other. That is so that the stones don't unscrew themselves in use. Hold the opposite wheel when tightening, not the nut, otherwise it will undo as you have found out, as I said, it does not have to be over tight and use paper washers for goodness (and safety's) sake.You do not need to tighten the wheels up too tightly, otherwise you risk causing unwanted stress in what is a relatively brittle wheel with the possibility of it bursting at high speed - not a sight you want to see, believe me.
Here is a safety leaflet on grinding wheels, including how to mount them. If you never read any other manual read and follow this one your eyesight or even your life may depend on understanding these principles. I would like to have the opportunity to keep on trying to answer your questions for the foreseeable future.
I would keep a decent quality set of wheel on the grinder and swap the wire brush when needed. Better still do as I do and buy a second inexpensive grinder and dedicate that to a wire brush one end, with a pigtail and polishing mop on the other. Much cheaper than indexable carbide tooling. I am lucky that I have a large garage workshop and am able to dedicate a moveable trolley to grinding.
I often dedicate a session to grinding tools and then only need to touch them up on the fine wheel or with a diamond hone when they are dull. You don't really need to do much grinding when you have a basic set of tools ready ground up. Apart from special form tools, very few shapes are needed - about 6 basic shapes including a threading tool. For boring I use a number of different size bars, each with a short piece of round HSS in a cross drilled hole.
Edited By Terryd on 30/11/2011 14:55:06
1443 forum posts
Lots of good info on HSS tooling here.
If you're after a really good 'use it for everything' carbide insert, that rips the swarf off like there's no tomorrow with most material (free cutting mild steel, brass, aluminium etc.) and leaves a super finish, then have a look at the pics of some 0.2mm nose radius 55 deg inserts in my album.
These were bought from JB Cutting Tools and I use them on my Clarke CL300 lathe and are on 8mm x 6mm shanks. Larger size shanks are available.
They are razor sharp and only £2.50ish each - I'm still using the first edge of the first insert and that's after some extensive use on all sorts of materials.
I'm afraid that I'm not too impressed with the tool holders (SDJCR/L type) from the same supplier, but for only £15.00 (inc 1 tip), you're not going to get Sandvik quality.
|Donald Wittmann||30/11/2011 17:59:17|
|40 forum posts|
What you should be aware of is unless you have a large rigid lathe with plenty of HP behind it then avoid any inserts that end in the letters MG as all the inserts ending with those, are Negative inserts and really require lots of HP and rigidity.
here are some of the culprits, CNMG, DNMG, SNMG, VNMG. there are also a few others that are not so common.
|1008 forum posts|
Could be. OTOH the Myford handles WNMG inserts beautifully.
Not often you find 3/8 negative rake tools, but these I bought from Myford with the lathe many years ago.
The WNMGs are an industry standard, so I can buy them singly for about £5 each, and that gives me 6 edges since they are double sided. (5mm .8mm nose radius). Very cheap - magic for castings.
Cut beautifully on a small lathe.
Most of the tipped parting tools use negative rake inserts, to prevent dig ins. All the Chronos ones come with ISCAR GTN2 clones as standard, and they are negative rake. you can get positive rake tips if oyu want. I can't remember hte numbers, but then, personally I wouldn't want positve rake on a parting tool. - zero at best or slight negative. Stops that inwards vector which causes did ins andf makes everyone chase around with rear toolposts.
Negative rake ground (HSS) tools are (or have been) recomended for copper - always use them on bronze, and zero rake on brass.
Horses for courses.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.