Author Topic: Sharp Tooling  (Read 195 times)

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Offline IanT

Sharp Tooling
« on: Dec 15 2019 12:54 »
I mentioned this in another thread - but in case anyone is curious, I thought I'd explain how I 'hone'

The tool is 'shaped' on the grinder - that is to say it is given its clearance and cutting angles. On my tooling, I tend to use the same clearance angles for lathe tools (7 degrees) with a bit less on shaper tooling (3 degrees). I work mainly in mild steel and non-ferrous - so generally use about 10 degrees for side and back rake on steel and zero rake on brass.

The tool 'tip' is also shaped dependant on its required use (roughing, finish, chamfering, parting, facing etc) or perhaps some kind of forming.

More detail of all of this can be found online - but the only provisio I would make is that many of the tables published are for Industry where they specify different angles for this, that and the other material. Much of this is designed to get the best use out of a tool over prolonged and hard use - e.g. to lessen tool changes. We generally don't have to worry about much of this - provided the tool is sharp.

Having 'shaped' the tool - sometimes you can just use it straight off the grinder, which I often do with my Diamond tool holder for instance or for a roughing cutter. But where I am taking 'fine' cuts (e.g. smaller work or close tolerances needed) a honed cutting edge will help.

So how to do it?

Well, these days I always try to use the front (curved) face of the wheel. It is good practice to do so but also has another advantage. It also curves the cutting face - how much depends on how much above the grinding wheel centre line you hold the tool. But once you have that slight curve, then honing is very simple, because you have two raised edges to reference - and you are not honing a large area but just the two edges (much easier & quicker). I always hone off the machine btw.

I will attach a photo of a finishing tool that I use on my shaper - as I think you can see the two honed edges quite clearly in it - but the concept can be applied to most cutting tools. Obviously, only the top edge cuts, the other being clear of the work. So if you are having trouble getting a fine finish or want to turn very small parts - then try this approach and I think you will find it helpful.

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Jon_C

Re: Sharp Tooling
« Reply #1 on: Mar 09 2020 09:07 »
Hi,

Sadly I think this is something that comes as shock to people new to lathe work.
1. that you can make your own cutters. (instead of insert tooling)
2. That to get a decent finish on the work, the tool needs to be honed.
3. there face when you show them what the cut looks like :D

I always hone the tips, whichever tool it is that im using, it increases the strength of the tool by enlarging the thickness of the cutting edge, while also improving the finish by "polishing" the work as it passes. I don't have the luxury of a stent or quorn cutting tool, not even the coned wheel. Just two plain old boring grinding wheels, Even so most of the tools that are required for building locos can be done on these shop bought simple grinding wheels.

Harold Hall also shows on his website a device that can be made to assist the precision grinding of the tools which is built from bar stock, bolts in front of the grinder, and allows precise increments of movements to grind perfect tools every time.

Offline cabbage

Re: Sharp Tooling
« Reply #2 on: Mar 09 2020 09:19 »
Hmmm... I have only ever used wolframite tipped tools - either brazed on or replaceable. I have never made HSS cutting tools except for my fly cutters. I own Seig made clones and the DC motors max out at 150W. It the wolframite gets a bit blunt I tone them up with a diamond block.

Given a preference, I make my wheels from steel bar slices rather than cast iron. I have just finished six iron tender wheels and it was just repellant!!!

Regards

Ralph

Offline IanT

Re: Sharp Tooling
« Reply #3 on: Mar 09 2020 09:29 »
I should probably have also mentioned that I do use insert tooling Jon but generally for specific work...

I use HHS tooling for small parting operations but for larger stuff, I have a back-mounted parting tool that even on my somewhat worn S7 will go through 2"+ of mild steel like butter. The shaped head would be difficult to grind in HSS. Downside - it takes a 3mm wide cut and I've broken tips in interrupted cuts (e.g. square stock)

I also have insert tools for screw-cutting. This is mostly laziness - I can grind the required angles in HSS but inserts are the exact shape and do last well, as only used occasionally.

Finally, I have a selection of insert boring bars - 6mm to 16mm diameter. Bored two sets of bronze cylinders last year, had problems with both - but one used a very strange core material and just killed my HSS tool. The insert (finally) solved the problem. However, small HSS are still very useful,

IanT
Nothing's ever Easy - At least the first time around.

Offline Jon_C

Re: Sharp Tooling
« Reply #4 on: Mar 09 2020 10:07 »
My comments aren't to any "old hands" out there that have years of experience. I'm a member of quite a few facebook groups, and the number of new blood to machining that straight away look to buy insert tooling is quite astonishing. Also the number of those newbies who don't know that the tool needs to be honed, and cant understand the reason they are getting such poor results, when the tool is practically screwcutting the work.
When new to the hobby of model engineering money is usually tight, and the acquisition of a lathe often a costly expense, to then double the outlay on all the accessories at once, and buy insert tooling, quick change toolpost ect its often enough to put people off. When a simple bench grinder and HSS blanks ground and honed on an oil stone, is sufficient for most applications, a couple of carbide tools in addition to help get under the sink of castings then switch over to HSS for a fine finish.

I don't have anything against insert tooling, I'm a yorkshireman with a large young family, and don't like spending money. HSS is undoubtedly cheap. For anyone starting out, the idea of honing is not explained fully, my comments where intended to add to those of Ian's, and direct people to the fixture for grinding HSS tooling on Harold halls site, something which may be helpful to others who might struggle to freehand grind tools.

Offline IanT

Re: Sharp Tooling
« Reply #5 on: Mar 09 2020 10:41 »
No I don't do Social Media Jon I'm afraid.

I went on FB when a family friend went off to live in Canada for a while and we used to follow them until they returned. Then I tried to remove myself from it but years later I still get annoying messages from them - "So & So 'liked' this or that music or video" etc (generally something I care less than zero about) with 'So & So' being someone I barely know that FB seems to think is an intimate friend of mine.

Never mind, I can still hit 'Delete' without that much effort I guess...and there is no Internet in the Shed at all - just a old radio left tuned to Classic FM. Not especially a classic music fan but it doesn't intrude when I'm working - it used to be Radio 2 but I can't stand the constant 'chattering' on there these days...

Obviously getting really miserable in my old age...  :-(

IanT     
Nothing's ever Easy - At least the first time around.

Offline cabbage

Re: Sharp Tooling
« Reply #6 on: Mar 09 2020 13:29 »
Being a child of "sanctions" I never knew what money was until we emigrated to the UK... As for "Classics FM", I am the proud owner of a set of headphones rated at 25W and a headphone amplifier capable of driving them to levels I can hear(!)

The kitchen sink engineering background music is pure Prog Rock and Heavy Metal. I also assure you there are advantages to being the deaf parent of a would be teenage musician...

Regards

Ralph