Before I start could I just say that I still have not yet received th highly recommended amateur lathe books from Amazon, therefore I am stil in the dark to a certain extent. So please, once again, forgive m ignorance, and if you can?t do that, then pretend you haven?t read thi thread and don?t reply!
After considering the advice given to me previously, I purchased cheap 8 piece set of HSS tools from RDG to practice on, but I? confused about the so called ?finishing tool? which is pointed.
I am trying to get the best possible surface finish on a brass tes piece. I assume a high chuck speed combined with the lowest possibl feed rate? I cannot see how you can achieve a good finish with pointed tool. Surely you are just creating a very fine thread eve under these conditions, therefore the surface of the piece feels rough I found an old tool with a semi-circular form, which I assumed woul give a better finish ? it did ? an almost mirror finish.
So my question is: How do you get such a finish with my ?pointed finishing tool (or any other tool other than one with a cutting fac which is wider than the ?pitch? of the feed rate?
Also, and anyone point me to a good online explanation of *exactly* ho to use the thread pitch indicator on the Myford ML7?
You're working in brass that's why ...totally different to machining steel ...
Sorry....I cant look over your shoulder ...you may be burnishing it with the side of the tool ...if it's really shiny
yup I've found that rounded tool does brass ok ...
Pointy tool is for taking very fine cuts off steel to finish it. when doing this set speed faster and feed slower ... sometime by means of screw cutting gearbox...to get slowest feed. for final cut only
dont over-do the speed or you will burn the HSS tool out on steel.
Garth, as Mark rightly suggests, you are going between brass and steel and each have different angles for lathe tools.
A brass lathe tool will have a flat top whereas a steel lathe will have a possible 7 to 17 degree slope. Again, I am unsure about what you mean by 'pointed' If you have a pointed tool you will a. quickly destroy the point and b. cut a thread.
Can I then suggest what I would do- writing a DIY set of instructions with a blindfold on and my arms tied? ( OK, lads, the guy needs help. Come in if you want) Look in your HSS tool bits for a lathe tool with a top slope of 7 degrees, A taper back of 7 degrees where it will traverse the steel and say 7 degrees on the edge. That sort of thing and one which does not involve grinding. You will have a point- which will attempt to cut the steel or a say 1/16th rounded point. Get a decent oilstone and round off the point but don't tilt the lathe tool so that you round the top of the tool. The top of the tool should be so sharp that you can pare your thumb nail with it. If you aint got to this stage, stick with it till you have. It may be easier if you use a waterproof felt tipped pen and watch the black corner rub off, all shiny. Now is the time to set the lathe at dead tool height. In other words, if you put a centre in, the cutting bit of the lathe tool will be right on the centre point. Shim it, up or down and the tool should not project more than half an inch from the holder.
Set the lathe to run in first gear- and use your hands not power and go gently with a weeny cut of 5 thous.
A little short of time tonight so I'll give you a very quick answer if that doesn't help I'll try a longer version. Firstly if you have bought the 8 piece HSS set from RDG is doesn't in my opinion include a "finishing" tool and yes I do have a set. It is front of me still in the wallet. If you look here:
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A little down the page it shows a set of tools, you will see that it includes two finishing tools both of which have rounded, not pointed ends. The difference between brass and steel finishing is the radius of the end, relatively small radius for steel and larger one for brass. As already mentioned for best performance the clearance and rake angles are also different. A finishing tool can also have a small flat end and as long as it is short enough not to induce chatter will work very well. These changes are quite subtle and the difference between a turning and finishing tool can be as little as maybe a .5mm radius on the end. In fact many tool tips will have radius on th ecorners corners of maybe 0.02mm or 0.04mm. So it is not a case of going from a point to a 10mm radius. As has already been said at high speed on steel that sharp pointed tool supplied will not last long, the end will burn quickly unless you are taking extremely small cuts.
To be honest, I would not use what they call the straight finishing tool without grinding a small radius on the nose first say 0.5mm. As Norman says this can be done on an oil stone with every success. Some would grind the very end of the point into a small flat again say
0.5mm across and that will also produce a good finish but I find the radius more flexible and less sensitive to small angular errors when setting the tool.. Your point about getting a fine thread instead of a mirror finish is correct, even if you think the finish is superb if you look at it under sufficient magnification you will see evidence of the tool path. As you said a fairly high spindle speed and slow consistent feed is good for brass. With steel then slowing it down can work better. As Mark has mentioned if you have a large contact area you could be burnishing the brass to get a shiny finish, while this looks good to the eye it will give you problems later if you try to machine like that to a very tight limit on the finished diameter.
Another way to get a good finish from a pointed or small radius tool is to angle the tool so that the trailing tool edge is almost parallel with the work, at least for the first mm or so. If you look at the RDG set (No 4) which is a corner chamfering tool, it can be angled so that the trailing edge (right hand side) lies close to the work and will in effect give you a different radius when cutting. You can experiment a little with this and you will see that it affects the finish and if you take it too far so that all of the trailing edge is in contact with the work it will cause chatter. Again the actual cutting corner can be rounded off with an oilstone to improve the affect.
If you visualize the straight finishing tool as they call it with a small nose radius ground on you will see that changing the angle that you present the tool to the work from 90 deg to say 45 deg will give you a different radius at the actual cutting point. With a little trial and error you will soon find a suitable position for differing materials.
I'm running out of time Garth but changes to cutting tools are subtle and depend on many angles, speeds, feeds and the material of course. There is no perfect finishing tool for all materials, cutting steel; brass aluminium will all require something slightly different. You will soon learn what works for you but if you think about it, part of the original advice you received was to go to HSS just so that you could make these changes and learn the effects.
Apologies if this isn't spelt or phrased corectly but I really need to be elsewhere.
At no point do I want to cross Keith's path. Quite simply I was looking for Deckel stuff and was ploughing my way through YahooGroups and the various sections like the 3 Quorn ones and then the ToolGrinding one.
Following the debacle with Magicalia, much of the old classic stuff has gone but there is a still bit in ToolGrinding which gives shapes and angles in the Files Section. I would suggest that you join as many of these sections as you can. Unquestionably, it is really about tool and cutter grinders but you have to understand what goes onto to a tool and cutter grinder- which goes onto your lathe- etc etc.
Now Garth, I had a struggle to get things to download but you will have to be patient. You will get great info- I promise.
Don't ever worry about "crossing paths" that's the very best way to learn I've found. Every time I've encountered another path I've learnt something useful. I'm also willing to admit that many, many times I've been (and still am) embarrassed by my own lack of understanding but that improves with the help of others. Open discussion is the key and anyway SWMBO says I should have no trouble accepting that I'm wrong because it happens so often, who am I to argue? If we can get enough intersecting paths in Garths' route he will pick up on one and be away.
I think one of the main points that beginners have a problem with is that there is no "one best" tool for any one job really, if there was, we would all be using the same half a dozen or so pre-ground tools. One of the issues (IMHO) with the set that Garth has got is that many of them are ground with "chip breakers" on the top surface and in my experience that confuses the various angles that beginners need to get their head round. I still feel that if Garth would let us know what area of the country he is in, someone would spend an hour "looking over his shoulder" and the issue quickly resolved.
Norm, I agree with you that there is much to be learnt from the avenues you suggest and it will be a path that Garth would be wise to follow as he progresses. However, the problem with getting too involved with the tool grinding theory early on, is that it can appear very complex and there can be problems with getting your mind round the tool in three dimensions unless you can see and touch it. In our apprenticeship we had 6" square example "tools" that made the angles very obvious even to us dullards. I suppose the other issue is that many of the "essential" angles can be compromised if other aspects are altered at the same time to compensate. I would never usually machine steel without top and side rake but I have a rounded "finishing" tool that only has top rake (ground for other than steel no doubt) and as long as you keep it very sharp, exactly on centre and take small (dust) cuts slowly it produces a superb finish. Of course I have another straight tool with about 40deg negative side rake and very little top rake and that also produces a fine finish and is not critical on centre height at all. I can't and wouldn't argue with the experts who tell us that the best tools are ground accurately on a T&C grinder but I would say in the practical world, much good work can be done with "nearly right" tools that are simpler to produce when one is starting out.
Norm, I am "guilty as charged" of over simplifying a fairly complex subject but we need to get Garth started. My other concern is that I sense that Garth is experiencing a little frustration that the theory is not matching the practice and I suspect he is finding our advice a little contradictory and difficult to follow. One of the advantages of these forum is that if you are able to identify it, "there is plenty of advice out there and most of it has value". The major disadvantage of these forum is, if it is all new to you, "there is plenty of advice out there and most of it has value", but which bits are best for me? Hopefully, little bits of each of our ramblings will stick and in a very short time Garth will be able to pass on his own hard won experience. To be honest we all try to shortcut this learning and development period and get on to the interesting bits. It's very easy to forget that in most apprenticeships many many hours are spent either learning to grind tools for a range of jobs or in today's production world learning to select and set the right tip. There just is no shortcut, the knowledge and experience must be developed.
Best regards
Keith
PS There I go wrong again, I thought I had fiinished for the night but SWMBO says that's not the case.
Thanks for all the comments. If you look at this link :
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The sets at the top of the page show eight tools. The tools in questio are the finishing tool (I think the 'pointed' one, third from the left) and, the threading tool (again, I think, the asymmetrically pointed one seventh from the left).
OK so the finishing tool is symetrical viewed in plan, and has som rake angle on the top of the tool, BUT I did not realise that thi finishing tool would need modding. Rounding the nose as Norm suggeste will certainly improve matters significantly, but I am at a loss t know why someone would sell this as a finishing tool when it will quit obviously give a poor finish. This is what confused me last night. I they had said 'this tool must be radiussed to your requirements' the fair enough, but there was no such instruction.
The threading tool is asymmetrical in plan, and has a flat top - n rake angle (for some reason unknown to me). I have tried setting th leadscrew to 1.2 mm pitch and running the thread tool along some M1 threaded bar just to check that I am doing the gearing correctly. Th result was fine - after taking up the initail backlash, the too followed the existing thread perfectly, and the thread angle looke spot on. Part of my initial question was how the hell do you do mor than one pass of a thread tool (assuming you need to do several cuts t get the correct depth), and how on earth do you use the thread pitc indicator device? I have read the Myford Manual, but this seems aime at people who have previous experience of thread cutting.
You are practising on brass Garth ..you will almost always get a good finish on that no mater if you used a cold chisel in the tool post ..... have a go on mild steel black bar .this is the worst to get a good finish on ...and will show up the tools for what they are .
Forget about the thread dial indicator for now ....it's for advanced speedy thread cutting .....you get the same results going slow for now, stopping at the end of the cut.....taking tool out of cut at the end of the cut . ...noting dial reading .......then reversing ....and not taking it out of thread cutting mode .....stop........put back into cut .....advancing beyond last reading by a small amount. start. take as many passes as you like ......but don't undercut ............leave small core sticking out of the bar as lead- in ......this core is the same as the thread core ....should be prepared before you start..and can be taken off after .......
YOU ALSO should prepare a core at the end of the cut ....this is your manoeuvring space at the end of the cut. you also need to use the tailstock centre or live centre ...if your bar is sticking out of the chuck some way .........corresponding to it thickness....so there is no chance of bar flexing.
I have a shaper finishing tool that I ground that produces a wonderful finish on steel (completely different from the cast iron shaper finishing tool that I also have). I keep thinking that I should try it in the lathe to see what it does there...
Garth, The delightful thing is that we are all right although we differ a bit here and there. It is called finding your own personal equation. Going back to George Thomas, you will get a better insight when his books arrive as he is one of the gurus. We lesser mortals are struggling to express our selves properly. In the meantime, I would concentrate on plain turning rather than screwcutting and if you have these 'pointy tools' they were probably ground by people who are far from clued up. Mark Jones, Keith and I have been at it- making mistakes and learning from them.
Moving to Mark Rand, I suggested to Garth that he armed himself with GHT, Sparey and Bradley and whilst GHT had a Union T&C, he did most of lathe tool grinding on a quite simple grinder but honed by hand and gave very pedantic instructions even to the type of 'oilstone'. OK, we can now buy diamond stuff with fascinating grits and ex production tool and cutter grinders for 'shirt buttons' but old GHT and the old mob were able to produce exhibition quality stuff on their ML7's. I have already confessed to owning a plethora of grinders but I now have shaky, limp all sorts of things including fingers.
Mark, one thing I forgot to mention about my "prize" tool and I know you will understand from one of your earlier posts, it is (whisper this) carbon steel?? and bloo*y hard too. Only gets to come out of my treasure box on high days and holidays and hasn't actually seen the grinding wheel for many years. Just gets a good stoning to keep it in line and of course very careful use.
I have to admit I never (yet) cracked grinding shaper tools, all of mine used to leave the furrows "clear and wide". I just put it down to lack of practise on my part. I wonder if grinding tools is really a great art form and we all have one "masterpiece" in us.
Keith has reminded me of the quality of tools. Not necessarily shape or how ground or honed but what is in that chunk of metal which is poking into a lump of metal- rotating round and that. Garth,one does have favourite tools like Keith's. It does suggest that some lathe tools bought from discount sources( polite me) will not hold up in the hurly burly of machine work.
Maybe someone else will be able to to take some of my waffle and make it more scientifically sound. I did suggest that you rummaged in your newly acquired accessories that came with your lathe. I doubt that you will found the JonTom Special but the probability is that these blunt tools will be of higher quality which you can do something with. Repeating myself, you can hone one or two back to productive life.
GHT when the book arrives will mention his favourite manufacturers and he will go onto making carbon steel tools from silver steel( another heretic who should burn in Hell) whilst Martin Cleeve in Screwcutting in the Lathe will discuss other stuff from manufacturers. Me(?), the tite arsed git? I buy my (s)crap tools at Club sales and sort of recover them. I have one of those shirt button( now) shagged out old Clarksons which cost one arm, one eye and one toothbrush in the olden days- and my 'rubbish' is transformed.
OK, enough of me and my odd strange habits but in a few days time, the Harrogate Show will be on and instead of going around the glossy stalls go and have words with Club members about tooling. Digressing yet again, I went to the SMEE stall with Arnold Throp of Model Engineering Services doing a Rear Parting tool demonstration. Frankly, I wasn't interested as my GHT one works OK. On the stall was his old Kennet grinder and he was giving a lathe tool a magic touch up. As his firm sells Quorns, I wondered about the better machine. It was quicker with the simpler Kennet and the quality of his work was undiminished.
Maybe somebody else will try to follow my ramblings. I hope that I haven't been telling people how to suck eggs.
I am going to go off for another week of evenings and waste some meta again, so I will probably off-air again till next weekend.
A couple of observations/contradictions I've picked up, firstly:
Mark - Thanks for the thread cutting advice. OK with the ML7 how do reverse and re-cut when I don't have a reverse on my lathe? Presumabl I get to the end of the cut, disengage the clutch, then wind th leadscrew back by hand and then re-insert the tool by eye (or someho with the dti)? Using the tumbler reverse would presumably mess up th alignment?
The other thing is regarding tools and grinding. OK I now realise tha making or modding existing tools is part and parcel of owning a lathe and this is in itself a black art. This would imply that the inser type tools should be better all things considered. Surely with these, 'finishing' insert is a 'finishing' insert and a 'turning insert' is 'turning' insert and a 'threading' insert...you get the idea? N pissing about grinding radii and angles in three planes by eye? I hea the arguement about these inserts being more suitable for high speed high volume work, but surely that depends on which grade of insert yo get? As a learner I would think that at least having a consistent too geometry would eliminate one variable from the learning process - eve if it might give consistently below optimum results.
Keith - Good advice and offer to have someone who could tell me how t do stuff. Thanks for that, but I am really trying to teach myself a much as possible because I think making mistakes is a good way o learning hard lessons - sounds daft, but for me it has proved true! have an engineering PhD and have done all the cutting tool geometr theory in the past. I currently work in an aerospace manufacturin research facility, and have access to the most incredible machiner available (and a lot of stuff that is very much unavailable!) There ar plenty of people I could ask to come and show me stuff, in fact I coul get almost anything conceivably imaginable custom made in an superalloy or composite you could name, but I'd rather do it for mysel in brass or steel on my ML7!
A lot will be much clearer with the pictures in the books.
With no reverse in the lathe, use one of the numbers on the threading indicator, such as number 1, and only engage the half nuts at that number.
In truth, it often is not required to use a threading indicator at all, but if you are new, picking a single number on it, and using that will allow that to be a non-issue.
That does not cover the coordinating of the feeds of the croosfeed and compound, for threading, but that too, will be more than adequately covered.
Have you hunted about the web for a couple scanned copies of books applicable? South Bend's "How To Run a Lathe" is a good one, as is the Boxford equivalent "Know your Lathe"
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These two links have a pile of good information in them.
At the outset of the purchase of Dr G's ML7, I pointed out that the manual was available via the YahooGroups MyMyford site. I have just checked to confirm this as I have an original copy and have sufficient knowledge gleaned over the years to write about overhauling them.So I am not 'au fait'with scrabbling for information.
It would now appear that the reverse facility was omitted when Myford made his machine.
In the words of the great American humourist, O.Henry, an evasive answer is appropriate.
No, you must keep the relative position of spindle to saddle to maintain the correct pitch location. You will need to leave the gear train connected as well as the half nuts. Rotate the spindle backwards by hand and this will drive the saddle back to the start whilst maintaing the correct positional relationship.
Excellent link to the Boxford manual, thank you, I hadn't found it on line. I have an old and now tatty copy of the Boxford book but was looking to pick up another in better condition. Not necessary now, thank you very much.
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