|Andrew Tinsley||07/01/2022 17:55:26|
|1610 forum posts|
I have several tool holders that take cylindrical HSS blanks. I normally grind the blanks to an approximation of tool shapes that one would grind on a square section HSS blank. It never occurred to me to do otherwise. I suddenly thought that maybe I had got this all wrong and there were some crafty ways of grinding round blanks.
Have I been doing things wrong for all these years?
Edited By Andrew Tinsley on 07/01/2022 17:57:03
|Chris Mate||07/01/2022 18:36:37|
|136 forum posts|
How do your cylindrical toolholder clamp, do you grind a flat section in it and scew it secure in toolholder which will bring it same position everytime you re-install it in holder, and then grind the front tip angles & shape, or can it move around and you have to set it each time-?
Edited By Chris Mate on 07/01/2022 18:37:00
|42 forum posts|
Way back when I was an apprentice we would use round blanks for small (say below 3/8in dia) boring tools and I still do. If you start with a round piece you've got less metal to remove to make the tool.
I would not normally use a round blank for external turning. One of the times I would use such a tool is the using up of a broken end mill to make a special (one off) tool.
Chris, no I would not grind a flat, just position by eye. Hold the tool in a V block or split square holder.
Edited By elanman on 07/01/2022 19:34:19
|Andrew Tinsley||07/01/2022 19:56:31|
|1610 forum posts|
Perhaps I should explain a little more. I have made several swan neck tool holders, which I use on my shaper and lathe. I always get an excellent finish from this type of tool. I use round tool steel because it isn't possible to use a broach when making these tool holders, much simpler to drill a hole!
I don't normally grind a flat on the tool, preferring to align it by eye. I assume that grinding the tool shape is similar to that used on square section tools, just wondering if I am missing something?
Swan neck tools are hardly ever seen these days, which is a pity, as tool chatter is frequently a topic of discussion. If folk tried a swan neck tool when they have chatter problems, they might be amazed at the results.
|John Haine||08/01/2022 10:25:44|
|4621 forum posts|
One way to make the grind easy is to use a tangential holder.
|Andrew Tinsley||08/01/2022 10:50:28|
|1610 forum posts|
I do use a tangential toolholder and I experimented with a version to take cylindrical tool bits. Due to the extremely large radius on the tool (If sharpened in the conventional tangential way), you can only take very small cuts I didn't find that the surface finish was any better than for the swan neck tool, which could take much deeper cuts and still give an excellent finish.
It would seem that there isn't any special way to grind round tool bits, apart from grinding conventional shapes. So it looks as though I have been doing the sharpening correctly for all these years!
8461 forum posts
Do you mean a holder like this Andrew?
Sparey calls it a 'Spring Tool Holder' and a 'Screwing Tool Holder'. He says it 'greatly helps towards the production of clean well-finished threads'. Also, 'certain well-informed persons have gone so far as to say that it is the only tool by which perfect threads may be cut in the lathe. This is doubtless an exaggeration, but...' He's enthusiastic.
My hero L H Sparey doesn't mention anti-chatter, or using the tool for other than screw-cutting. He explains: 'In use advantage is taken of the "spring" of the tool by occasionally traversing the thread at the same lathe setting, so that a fine, polishing cut is given. This will produce perfect work.'
Got me wondering why they went out of fashion, and why Sparey says they're only used for cutting threads?
Can't comment on grinding round HSS tools - I find it hard enough angling square blanks correctly. I am cack-handed though.
|Andrew Tinsley||08/01/2022 16:15:03|
|1610 forum posts|
That is the type of toolholder that I use. In my case, the hole is considerably larger and the slit shorter. The tool itself is made from 1/2" X 1" gauge plate.
I started to use such tools on an old round bed Drummond lathe, which was very prone to chatter, from I presume, general wear. The swan necked tool completely eliminated the problem and left an excellent finish I had the same problem on a Myford 7 and again the swan neck tool cured it. New bearings and a bed regrind stopped the chatter and I could then use normal tooling without the dreadful chatter marks.
Ian Bradley recommended the swan neck tool for use on a shaper and I use one on my Viceroy shaper and it has proved to be a good choice. The Ian Bradley recommendation was for a forged swan neck tool, presumably made from carbon steel and hardened and tempered, rather than the more modern hole and slot type.
|Thor 🇳🇴||08/01/2022 17:17:16|
1597 forum posts
I have made a few tool holders for round HSS toolbits, and I try to grind a small flat for the grub screw. This is also used when grinding. I have also made one swan neck tool holder for a small parting off blade, this tool has worked well on my small lathe.
|Michael Gilligan||08/01/2022 17:30:13|
20052 forum posts
[ pedant alert ]
”Sparey says they're only used …”
or should that be “Sparey only says they're used …” ?
|Clive Foster||08/01/2022 19:10:31|
|3099 forum posts|
The most economical, and strongest, way of grinding round tool-bits is to use a holder that gives a permanent positive rake. As is common on J&S, Armstrong and other makes of (square) tool-bit holders for lathe use.
For such alignments the basic grind involves putting a flat on the top of the tool reaching down to just below the centre of the bit. The angle of the flat relative to the bit centre line being whatever is needed to give the desired back rake angle relative to the work when the bit, and its carrier are mounted on the tool. The two sides of the tool bit are then shaped in the usual way to give appropriate angles and clearance. A certain amount of care is needed to ensure that the ground sides intersect the flat top. Not usually aproblem in practice unless you plan to take deep cuts.
This method is not practical for all tool shapes and applications but where it can be used it is very economical of material becuase the tool only needs to be ground back just enough to remove wear. Conventional grinding with back rake always consumes more material. Eventually the tool becomes too thin so it has to be cut back and grinding started over. As the business end can normally be no more than half the blank diametr thick the tool is inherently weaker.
Realistically repeatable grinding and shapin of round tool-bits requires holders to place the tool at the correct angles when the holder is sitting on the grinding rest.
Digressing into a very much "do as I say, not a s I do thing" but I'm convinced that most neophytes would do well to have a small selection of holders arranged to put appropriate angles on tooling when place on a flat grinding rest perpendicular to the wheel. Versatile and useful though it is the conventional tilting table "Hart style" rest designed in many variants by folk such as Howard Hall, Duplex et al needs a certain apprciation for 3D geometry to properly understand its use.
I'm sure that many beginners would prgress much faster if there were designs for a small set of holders to reliably produce sharp, adequately functional, tool shapes. Five or six ought to do it, three might well be enough. Assuming MEW were to print an article describing such a holder set along with the typical performance of such tooling it would make assistance through the forum much easier.
"I'm using an MEW No. 5 tool ....... and have these issues ...... on a...... cutting ...... " becomes much easier to answer than a simple description of the problem. Whether changes to speed, depth of cut et al or suggesting that an MEW No. 4 tool would be more appropriate. Folk with unspecified tooling could be directed to an appropriate MEW No tool and asked to report back. The point being that the holder ensures the tool is sharp.
Edited By Clive Foster on 08/01/2022 19:10:49
|Clive Foster||08/01/2022 20:00:42|
|3099 forum posts|
Ooops. Error in second paragraph of previous post.
"The angle of the flat relative to the bit centre line being whatever is needed to give the desired back rake angle relative to the work when the bit, and its carrier are mounted on the tool."
The angle of the flat relative to the bit centre line being whatever is needed to give the desired back rake angle relative to the work when the bit, and its carrier are mounted on the machine.
Original isn't quite wrong but multiple meanings of "tool" makes hard reading.
|duncan webster||08/01/2022 21:59:53|
|3919 forum posts|
Back in 1983 Ian Bradley described the manufacture of a Target tool grinding jig. One of these target but made from bar stock. Scroll down to the bottom of the link. It looks like it could make tool grinding less hit and miss. I've got a scan of the article if anyone interested
Edited By duncan webster on 08/01/2022 22:01:22
|Michael Gilligan||09/01/2022 06:49:44|
20052 forum posts
It’s a bit late for Sparey, Dave … but you might like this:
Ref. __ https://pounceatron.dreamhosters.com/docs/misc/Armstrong-Catalog-THB49-1947.pdf
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