Sharpening brazed carbide tip tools for the lathe.

I have been getting good results from my lathe by roughing out with brazed carbide tip tools and then making a 0.05mm finishing cut using auto feed. If I want an almost mirror finish then I can use a sharp HSS tool for the finishing cut using auto feed.

The carbide tips I have do not last that long before giving a bad finish so they need touching up. I thought a few passes with a diamond file or honing on a diamond stone might do the job but it does not work. That could be down to poor technique !

I have bought an Ozito 6 inch bench grinder and I was going to order a 100 grit green wheel. But then I read online that a green wheel will not do a good job of putting a really fine edge on carbide and that a diamond wheel is a necessity for this.

Your thoughts on this would be welcome. Of course I could just switch over to indexable carbide tools and forget about sharpening brazed carbide tools !

I have thought about putting the carbide tools in a vice and using the dremel tool with a diamond cutting wheel as a grinder. Has anybody tried this ?

Edited By Brian John on 12/10/2015 14:56:41

2 cents

I've always used a green grit wheel and found it fine, 80 grit

Carbide needs as much support as possible under the cutting edge to stop it chipping easily

The blue 10mm shanks have worked best for me. 8mm flexes too much and chips

edit:

The carbide tips I have do not last that long before giving a bad finish so they need touching up.

Sounds to me like you may have microflexing chipping developing on the cutting edge, carbide lasts for an outrageous amount of time when it has good stiffness, (making hss redundant for many basic roughing out tasks)

Edited By Ady1 on 12/10/2015 15:07:11

I too use a 'green' wheel, followed by a diamond hone or file. Try looking at the edge with a lens, amazing how rough they come off the wheel.
Make sure the wheel cuts vertically, (same direction the work will be turning) if you grind the tool 'horizontally' it can weaken the edge.

Edited By john carruthers on 12/10/2015 16:33:08

I'm not sure it's a good idea to be grinding carbide regularly unless you observe appropriate H&S precautions.

A combination of HSS and insert tooling seems to be popular with many folks.

Yes, I am starting to think that these carbide tools might not be worth the trouble. I might give the green wheel a miss for now and buy some indexable carbide tools instead. The bench grinder will still come in handy for sharpening the HSS tools.

The only time I have had problems with them chipping and cutting badly is when I have ground too much clearance angle on them. It's best to keep that angle at around 7 degrees which means that the centre height has to be set with some care - over centre wouldn't be a good idea.

The other problem I had was on an ML7 chipping them and inserts but that was down to the lathe.

I don't have much of a problem getting a decent finish with a 60 grit green wheel but as I mentioned before I haven't used them for a long time now. It's mostly been on cast iron for tooling and parting off blades converted to screw cutting bits mainly for use on HSS.

Are you turning aluminium and it's sticking to the tool ? If so it's easy to flick it off with something - sharp knife. If you want to use carbide on aluminium you will probably be better off using inserts - some would say ground and uncoated ones but the more recent ones are uncoated and micropolished. It can melt and stick even then. The easiest way round that is to reduce speed. No coating may seem odd but aluminium oxide is pretty abrasive stuff and aluminium oxidises very quickly. Instantly is often mentioned.

If you honing them it's best to put the hone on a flat surface and feel the sides of the tool flat onto it and move along the cutting edge if you can as that way your unlikely to round off the cutting edge = fatal. A bit of thin oil makes them cut more efficiently.

John

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Brian, from my limited experience green wheels are slower than diamond at dressing the brazed carbide tips. Another thing I noticed was that they were inclined to slightly round the cutting edge. That might have something to do with the soft bond on the green grit wheels.

All in all, I found that the cheap diamond laps/stones from the like of Aldi/Lidl did a good quick touch-up on the tips. I'd keep an eye out for one that was box shaped with four different grit sizes along the 4 sides. At about £8 they are great value and seem to last well. Using the finest side, 200# I think is fine for final dressing the edge and the tool cuts cleanly. Personally I gave up on the green wheel for dressing tips after using the diamond stone.

I use a 4" diameter diamond wheel (used) and sold to me for £5 about 30 years ago by a friend who was an optician and was disposing some of his surplus tools on his retirement. It has served me well and I use it regularly. It leaves a mirror finish and a sharp cutting edge far better than I could get with a greengrit wheel and/or honing. I have also recently been given a set of 8 cutting bars with clamps to hold inserts. The inserts are square and the tool bars are set at different angles both right and left hand. The inserts are both black and white and are in plastic trays and look like they are ceramic, Are they able to be used for turning metal or can they only be used for softer materials such as plastic? Can someone please advise!

Thank You RDL

At the smaller, more economical, Model Engineer affordable end of the range the quality of the carbide can be very variable. Seems to be some element of "whatever we can get this week" in the suppliers production plans. Certainly no active, focused, material development aimed at small lathe applications. As ever the problem with carbide is that its admirable strength and durability when kept under decent compressive loading is counterbalanced by fragility if it ever gets into tension. The Sandvick "Why Climb Mill" paper which Neil very kindly linked to in another thread makes it clear that even today clearing the very fine exit end of the chip when normal milling can rapidly blunt cutters seriously reducing life. Hmmn. Fine chip. Short life. Sounds about where Brian came in.

Of course the absolute sharpness that can be got on a cutting edge is heavily dependant on umpteen parameters like grain size, bonding and gawd knows what else. Its fairly clear that as you approach the ultimate possible sharpness there is is pretty much nothing holding the carbide grains on. Which obviously sets the limit to how sharp a usefully durable cutter can be before the edge crumbles away. Our smaller machines inevitably suffer more from vibration, minor deflection, speed instability etc than industrial types which clearly won't help as every vibe, however small, puts a tension load into the cutter. Worse for really tiny cuts as there is pretty much nothing to load up and stabilise things.

Worth examining your methods to see if you can get good finish from deeper cuts. If I go below 0.5 mm (20 thou) its 'cos I've cocked up in measurement, tool grind or material selection (must stop buying from Crap But Cheap Metals Inc). Generally 50 thou, 1mm (ish) cuts for pretty much every job works OK for me giving a reasonable balance between finish, cutting time and chip handing. I rarely need to remove so much stock that the extra two or three passes at 1 mm compared to really exploiting the machine capacity are significant.

Clive

Excellent observations, Clive ... especially regarding edge sharpness and carbide grain size.

Carbide grade [and, of course, quality control] is very significant.

For an example of what can be done, on the small and costly scale; the video on this page [from Eternal Tools] is worth a look.

MichaelG.

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Edit: I wish I knew what Carbide they use for those gravers !!

P.S. ... This looks promising.

Edited By Michael Gilligan on 12/10/2015 22:38:32

Edited By Michael Gilligan on 12/10/2015 22:44:11

I fully agree with Breva, green grit will do it, but tends to leave a rough coarse edge, and takes longer, the white fine diamond wheels give a smoother edge, faster!

Phil

The green grit wheels are a fairly hard bond and useless on other materials such as HSS and glaze quickly because it can't break the bond down. This is assuming it's a green grit wheel intended for use on carbide.

Of late I've put down failure to obtain a sharp edge on what ever it is comes down to wheel wobble. I have more than one grinders, one has no wobble. It's seems to be getting harder to get wobble free wheels that will dress easily. I mounted 2 recently on a grinder that locates them accurately. One's ok with a degree of run out that would be easy to dress out. The other far from it. I've not checked yet but the bore must be seriously out. I'm getting the impression that most companies prefer to sell junk.

In terms of brazed tip tools it will probably pay to buy of a company that does supply to professional users and has done for some time rather than being a pure tele sales type outfit that know diddley squat about what they are selling. I've come to that conclusion on indexed tips too. The brazed tip ones always used to have a grade stated - invariably cast iron grade. That's down to the grade of carbide and cutting angles.

On thing for sure if the edges are chipping on what is essentially a new lathe there is something very wrong with the tools. Most of these types of cutter should have angles suitable for interrupted cuts and should take way more HP than Brian can apply.

On sharpening in general if Hopper gets nice sharp HSS tools Brian should look very carefully at what he uses to do it with and the abrasives. The source is also likely to be useful.

John

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It's often lack of HP that causes carbide tips to chip, you need a constant loading on the tip. It's best to take a relatively shallow cut, say .020"/ ,050", and a fairly high rate of feed to keep the edge working, it's roughly the opposite from how you work with HSS.

Ian S C

I didn't have any problems using them on a Taig Ian. I had to mill the shanks down on it to get them to fit. I put the ML7 problems down to rather loose headstock bearings. That seems to be correct. Due to the clearance angle on them I think a bit under centre is important. Thou's as usual but if the bearings are loose the work will lift anyway and then it becomes important to keep the feed rate up to keep it firmly up.

John

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I have decided not to order a green wheel or a diamond wheel. I am going to give the brazed carbide tools a miss. I will order some indexable carbide tools and see how they go. They seem to be far more economical and give less trouble. The HSS tools will be kept for finishing cuts.

Brian how do you arrive at the indexable ones being more ecconomical. I have brazed tip tools that have been sharpened on the grinder many times and touched up with a diamond stone many more times so just the cost of the tool and a bit of wear on the green wheel. With decent tips working out at say £1.00+ a corner you will very soon have covered the cost of a brazed tip tool etc.

I've suggested Brian use these which work out at just under a £1 a tip with VAT but the cheap holders that they will fit usually come with coated gp ones of the same type or more usually worse.

**LINK**

Use - aluminium and stainless finishing. That should cover most things.

Your correct though Jason. Brazed tip should work out a lot cheaper as little should need grinding off.

Edit - The 4 corner versions cost about the same but holders may be a problem at Brians size.

John

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Edited By John W1 on 13/10/2015 17:01:36

Should not be 6mm square holders for the CC** 06**** tips are easy enough to come buy, I have a few.

Also bear in mind Brian's toolpost does not swivel so tool holder really needs mounted along or across the lathe axis. A right hand holder for the CCMT/CCGT tips can face and turn without needing to move it in the toolpost.

Not sure Jason I thought it would take 10mm / 3/8in holders but could be mistaken. On a Taig I used to use it to mill down the shanks on the smaller brazed tip tools. Also a 1in holder milled down to 1/2 in or so on another lathe in the very early indexed tip days.

The sets come V pointing forwards, angled, left cut / face and right cut / face. He might have problems facing with V forwards. Maybe some one could mill down holders for him if needed.

He can alter tool angle with the compound slide. He needs to look at that aspect carefully before buying.

John

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I thought I might start with these :

**LINK**

Or this set has a boring bar which will be required for my Stirling engine kits :

**LINK**

The two sets have different shaped indexable tips. I am not sure of one shape is better than the other.

Edited By Brian John on 13/10/2015 18:03:36