tipped tooling

I dont seem to be able to get on with tipped tools , I just bought a new boring bar but it leaves a poor finish , I tried a couple of others as well similar result , A HSS tipped cutter works fine . , I have founf similar results on plain turning , on cast and on steel . I am using a Culchester Bantam so plenty of power , Where an I going wrong please

Can depend on many things, some of which:

Are they brazed tips? (notoriously poor out of the box if cheap. May need sharpening.)

Are they inserts? Could be poor quality cheapos, or too large a radius on the cutting tip.

Also depth of cut. Carbide does not like light cuts. Needs some work to do. Great for taking deep cuts and shifting metal. Some operators then use HSS for the fine finishing cut. Or the CCGT type inserts with a ground edge that cuts finer.

RPM. Need to spin faster to get the best out of carbide.

Feed. If too fine will let the tool rub and give chatter.

Centre height wrong?

Too much tool holder overhang?

Wrong insert tip radius?

Wrong speeds and feeds?

EDIT - hopper posted whilst I was typing! 

Edited By David Standing 1 on 23/02/2020 09:24:55

Where does one start? Is your Bantam properly adjusted, so there's no play in the slides, etc.? Have you got an appropriate tip for the material and intended depth of cut? Are you running the tip within its designed speed, feed and depth of cut range? Is the tip geometry appropriate for the job? Is the material just a b*st*rd to machine anyway, and getting a decent surface finish is going to be a challenge? The Bantam's relatively slow top speed may be way too low for small dia. work too.

Not a helpful answer, perhaps, but tipped tooling is so complex, with so many variables, that you could be 'going wrong' in so many ways. Homework required?

[edit] Bother! Beaten by others. Now irrelevant...

Edited By Kiwi Bloke on 23/02/2020 09:56:02

Where are you based I thought that is someone is local to you they could have a look and it may be just a second pair of eyes can help.

David

Boring bars are possibly the worst (or best) test of a tool tip. They have inherent long overhang, need to fit in the minimum diameter hole and are often not the stiffest material around. I’m not too surprised if your bores are less than 25mm diameter. With only 1600rpm, the lathe likely needs to be at top speed for that size hole.

I’m afraid ‘new’ does not mean a lot to me. Especially if of asian origin. I have a couple which were new from china but have been mostly replaced with older, stiffer ones. Look at both the cutter holder and the tip, along with the speed is my advice - all other things on the lathe being in good adjustment. Boring is probably my least liked job with the lathe - unless using a boring head.

I know that the more support a cutter can have, the better it will perform. That is why I like to use my larger mill as a horizontal, whenever practical/possible - even though changing from vertical to horizontal involves some heavy lifting!

Hi all, with regard to brazed tip Tungsten Carbide & butt welded HSS tools, they were never intended to be used as supplied, at the end of the production line in both cases I believe there was a man who picked up each one & showed it a grinder & said "this is a grinder, you may need to become acquainted with it at some point", indeed if I had a pound for every one that I ground for myself or other people I could have retired at the age of 25! So, if you can't grind them yourself or find someone to do it for you then put them aside, you will get far better results using small section HSS bits in home made holders with a bench grinder with half way decent tool rests as advocated by Mr Harold Hall etc,or indeed the Diamond Toolholder advertised on this very page! PS do not insult this cutting media by tip toeing about, it is capable of cutting at the read heat of steel so remember its called roughing out for a reason!

Cheers Bob H.

So assuming this is for the redwing then 1.5" borein CI should not be too much of an issue for access and doable with a thick bar, something like a 16mm shank tipped one is what I would be using with a 0.2mm CCMT insert for clearing it out with about 25tho DOC. Finish cuts I would swap to a CCGT insert or sometimes a stout 25-28mm bar with an HSS toolbit. Quick hone and off you go.

Even if you only have a Bantam 800 you will have sufficient speed.

The bar I was using is a RDG indexable 16 mm diameter , Yes its a 4 inch x 1 1/4 bore , I think my trouble is taking it too slowly, speed and feed and too fine a cut, But working to a size fine cuts are a must for me , I am not an engineer . just a self taught guy . I think I will stick to the HHS unless its something really hard .

Thanks for the input

There is obviously something amiss here. Coincidentally I have just machined some cast iron with a carbide tool and got a almost mirror finish so carbide and cast iron can get on with each other.

Its only really possible to make suggestions as to what would improve your results if we knew where you were starting from. Details of the actual boring bar, which insert it has, hole diameter etc?

Ian P

Edit after seeing your reply. Tip type still applies

Edited By Ian P on 23/02/2020 11:05:17

What rpm, feed rate and cut depth were you using?

And the way us (muddle) engineers do it is to bore (and maybe hone or lap) the hole so it has a nice smooth, parallel finish but don't worry about getting it the exact size. Then machine the much-easier-to-deal-with piston to fit the existing bore to the precise clearance desired.

Edited By Hopper on 23/02/2020 12:13:14

".… carbide doesn't like light cuts..." I hear this often and its just not my experience, particularly with the sharp aluminium cutting types. You can make the finest cuts with these and get beautiful finishes. The chips are so fine they are just a dust on the top of the tip.

Am I missing something ?

Gerry

.

I think all you are missing, Gerry, is that the quoted statement is out-of-date

MichaelG.

Plus 1

The other thing that is also often mentioned is the need for high speed. While this can be true for a lot of carbide tooling it is not needed for the sharp polished inserts. I use this type of insert most of the time on a lightweight machine and they cut well at a wide range of speeds.

Doug

Plus 1 to that too.

Ian P

I echo whats been said about polished inserts,i also use **gt polished inserts on the little Sherline & get a mirror finish running fast or low speeds. The **mt inserts also give pretty good finish but not to the level as the **gt polished inserts give.

" You can make the finest cuts with these and get beautiful finishes."

Must remember that, - especially when turning Stainless.

Regards Ian.

Some time ago, I bought a set of brazed on carbide tools for the lathe. Even when sharpened on a diamond lapping wheel, they were still poor. They got binned and I have used nothing since but proper industrial inserts. The only time HSS goes near the lathe is in the form of drills. Getting the grades right can be a problem, inserts for steel are not sharp and are useless for finishing cuts, but excel with deep cuts. If you dare to make a finishing cut of 0.025" deep, then the finish will be good, but not so with a 0.002" pass. As already mentioned, there are sharp inserts made for aluminium, which are as sharp as HSS, but a much more sophisticated profile, they are capable of cuts on steel down to 0.0005" depth or less. Another advantage of using tooling with indexable inserts is the consistent tip height, so if your Bantam can use 20mm square tooling, with a shim, then that shim will be correct for all your tools except boring bars. I keep each size of boring bar in its own box with a shim to suit it.

+1, except I recommend experimenting as well.

I've found getting the best from carbide inserts needs more care and attention than HSS, and put this partly down to their tip shapes being highly engineered to perform best in particular circumstances. Production work often means powerful machines driving harder and faster than most of can manage or want, with inserts lasting hours or minutes of rapid metal removal rather than days of pootling.

My HSS experience suggests chatter and poor finish are best managed by slowing down and taking lighter cuts. Counter-intuitively, carbide wants the opposite - some combination of more speed and/or deeper cuts. I initially failed to push carbide hard enough - it felt wrong - until advised to go for it by Andrew Johnson. Perhaps I should have taken more note of the fact that carbide is typically worked 5 to 20 times harder by industry than they push HSS!

Although it's true that sharper carbide inserts do well at HSS speed and DOC, I believe these also do better when pushed rather than mollycoddled. Not enough data to confirm, but it seems to work.

Be good if someone tried all the combinations of inserts at hobby speeds and powers and wrote the results up for common metals. HSS as used by professionals and amateurs followed much the same rules and the resulting advice is consistent. Not so with carbide inserts. Today there's a much bigger gap between amateur and professional practice, and most carbide research I've seen is squarely aimed at the pros. Inserts are complicated - there are far more carbide insert tip profiles available than Sparey ever described!

Dave