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Boring Question

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Chris03/02/2010 19:52:44
87 forum posts
13 photos
I am just dabbling with my first attempts at boring using a good quality boring bar with carbide tip. The tip is well centered and I have about 2" of the bar protruding from the tool post.
Early attempts have brought up the strange occurance of the tool cutting more as I withdraw the tool than when it is fed into the bore. Is this common? Is one supposed to move the tool a few thou off the surface before withdrawing?
Fortunately I have discovered this problem on some scrap thick walled tube before tackling my expensive castings. You guys have taught me something! Caution before enthusiasm.
mgj03/02/2010 20:24:53
1017 forum posts
14 photos
Yes - always will. Caused by flex in the tool and/or a reversal of torque taking up slack in the bed alignment. - push and the saddle will rock one way  pull and it will rock t'other. So it will always take a small bit more on the back cut.
 
How to get over it. Doesn't matter while you are roughing, but stop roughing some sensible distance short, and then take a cut, in and out AT THE SAME SETTING. Then measure and having taken all spring out of the tool you can use that measurement. When you are getting close you run the tool in twice and out twice, at the same setting and then measure.
 
Failing to do that will mean you will cut oversize, and you will be pissed off, and you will then have free membership of the club to which we have all belonged at some stage.
 
I will rough plough to say .050 short on dia. Remove spring, cut .025. Remove spring x2. (as above). Finish with 2 cuts of about .012", removing spring completely x2 as above. Last cut I measure before each outward pass, just in case.
 
Good sharp tool, its very very accurate. Fail to take the spring out and you are all over the shop.
 
(dimensions in inches - is there anything else? )
Clive Foster03/02/2010 20:35:37
3135 forum posts
109 photos
Generally something to beware of.  The amount depends on the boring bar diameter, shape of the tool tip and depth of cut.  Reason is that during the forward cut there is a force trying to push the bar sideways out of the cut.  Due to the unsupported length and relatively slender nature of a boring bar it almost invariably will be pushed out unless the cut is very shallow.  On the return the bar springs back against the previously cut bore making the unwanted cut.
 
To reduce the effect use the thickest bar you can and withdraw the tool out of cut during the return movement.  When finishing to size take spring cuts at the same feed setting to work out any effects of boring bar deflection.  Normal practice is to accept the effects when rough turning making sure there is enough material left for spring cut(s) when finishing to size. Really its a question of getting to know your tools.  Don't get into the habit of taking teensy weeny cuts.  Job takes forever and by the time you are ready to finish off the tool will be less than sharp so you'll not get a good finish.
 
Clive 
Mark Smith 304/02/2010 04:16:38
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175 forum posts
36 photos
Good thread, thank you; cleared a few things up for me too.
Mark
Circlip04/02/2010 10:56:30
1510 forum posts
Learn how to grind tool steel and chuck the carbides Chris. Use largest boring bar you can fit. "Sharp" carbides are a contradiction.
 
   Regards  Ian.
Chris04/02/2010 11:19:23
87 forum posts
13 photos
Thanks to you all. Glad it has helped someone else as well. I sometimes feel my questions are so basic they are a bit embarrasing. Would like to grind my own tools  Ian, must try to get someone in the local club to give me some lessons. Off to the shed now to put the wisdom of Meyrick and Clive into practise.
Chris.
John Wood104/02/2010 12:12:45
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116 forum posts
Excellent thread and resulting gen invaluable to the novice.  I found just the same problem and have worked out how to get around it which, I'm glad to say, is pretty much exactly as Meyrick says. Boring seems to be one of those operations which gets easier with experience so having realised the basic principles I am turning my attention to the cutting tools themselves as I'm sure my poor grinding is not helping. Am building a Worden cutter/grinder at the moment which should help a lot.
 
Keep going........John
James Burden04/02/2010 12:24:39
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98 forum posts
12 photos
Hi,
 
I found the Model Engineer digital archive on the homepage quite useful - Model Engineer Issues Vol 143 - George Thomas' articles on boring tools.
 
James
Ramon Wilson04/02/2010 13:02:24
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1319 forum posts
382 photos
Following the good advice and procedures from Merrick and Clive which is definitely the way to go about the operation (whatever type tooling is used) I would however agree  with Circlip regarding using HSS tool steel.
 
The problem with virtually all carbide insert tipped tools is that they are prone to rapid wear if not worked at their optimum rate. This normally leads to the final fine cuts being 'pushed off'' and nothing happening at all - especially if the material is a little prone to work hardening. This leads to the unwary (and sometimes the not so-definitely bought the tee shirt on this one!! ) putting on further 'one thou' cuts until - whoops - the tool digs in and takes the bore undersize. This can even happen with a brand new tip which becomes really frustrating.
 
They are of course 'attractive' aquisitions and do have excellent uses - roughing - especially cast iron and the tougher steels but I believe nothing will beat that well sharpened HSS tool for the finishing and/or sizing cuts.
 
Many years ago I made GHTs boring bar set and can thoroughly recommend it. Well worth the time spent. The bars use small pieces of inexpensive round HSS which are even more inexpensive if the shanks of worn FC3 cutters are used. - incidentally many of my lathe tools are made from these - the bits held in 1/2 x 3/8  gauge plate holders with a 4BA caphead. Quick to grind too.
 
The other thing made for boring was a set of 'between centres' boring bars - these are excellent for producing a parallel bore and eliminating the possiblity of 'push off' induced taper'. I have some pics if that will help anyone.
 
Hope this is of use - Ramon
 
 

Edited By Ramon Wilson on 04/02/2010 13:31:24

Circlip04/02/2010 14:43:40
1510 forum posts
NEVER feel  embarassed about asking questions Chris, within three answers you can have very easily about a hundred years of combined experience. The answers are not always the same but neither are they ALWAYS contradictory, they may even answer questions you didn't know you asked, but it's a bit like Woolworths used to be, pick and mix, YOUR choice.
 
   Regards  Ian.
mgj04/02/2010 17:54:27
1017 forum posts
14 photos
Well this is kind of taking us back to the old thread on sharpening.
 
I'm less fraught about carbide than some. I agree abrasion can be a worry, but if it is apply FEED.  Also my carbide boring bars have centre holes for coolant, so I can feed coolant right to the tip at the bottom of a bore. - again wear seems to be less of a problem.
 
A good sharp HSS tool is very good in steel, particularly as, on the back cut, a brand new edge is brought into play. I think carbide (the right carbide?) is better in iron.
 
I am sure that John is right - you really NEED a tool a cutter grinder. It doesn't have to be a Quorn or a Stent,  but you do want something (like the Hall set up)that will hold an applied angle and cut/grind  it properly. Many I know will say they can grind this or that by hand. Possibly they can, but I'd further suggest  that until you have tried the real McCoy finish polish ground on a 60grit wheel, you ain't in the hunt.
Ian S C05/02/2010 10:41:29
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7468 forum posts
230 photos
Just in from the workshop,I'v been boring holes in cast iron using one of my home made boring bars,This tool has a carbide tip from a circular saw blade this tip holds its edge and cuts like HSS. It has 5 deg front and side rake, and zero top rake, it just gets a touch with the diamond lap every now and then. Ian S C
Chris07/02/2010 11:16:02
87 forum posts
13 photos
Hi to all who have helped. Spent yesterday converting a small, old drill stand found in the scrap box at work into a tapping stand. T'aint pretty as it is made almost entirely from re-cycled bits but everything is a nice sliding fit courtacy of your help.
Meyrick, What is "the Hall set up"? Perhaps you could PM me, although it may be relavant to this thread.
Chris.
mgj07/02/2010 12:27:55
1017 forum posts
14 photos
Oh sorry - Harold Halls book Tool and Cutter Grinding (Myhobbystore)
 
In that he shows how to make a tool and cutter grinding set up, based on an ordinary bench grinder. Sort of expandable, so you start with a rest for lathe tools and then add to the kit so you can sharpen drills, endmills and quite a lot else too. A Quorn its not because it would be difficult to make taps dies multiflute reamers etc (but then who does on a regular basis?), but its quite simple and it looks like a pretty handy item, and I bet it works well.
Circlip07/02/2010 13:06:06
1510 forum posts
And if Richmond digs out  the series of articles by "Duplex" in the 1948 M/Es "In the Workshop" the original grinding jig will be shown.
 
  Regards  Ian.
Jeff Dayman07/02/2010 13:17:28
2225 forum posts
47 photos
"you really NEED a tool a cutter grinder. "
 
Nonsense. They are a 'nice to have' luxury item for 90 percent of what model engineers do. If a beginner follows published tool angles reasonably closely, and develops his hand grinding skills by practicing, they will be able to produce good work. I do agree that beginners should forget carbide tools until skills with HSS are developed. If you want one carbide tool in case of a piece of hardish cast iron, fine, but for most ops HSS is great.
 
Machinery's handbook and Tubal Cain's The model Engineer's handbook both have useful sections on tool grinding, and again most angles are not critical. Far more important is tool nose radius, which no one talks about. Grinding these by hand is a skill acquired over time with much practice.
 
I would much rather see beginners spend money on reamers taps dies etc and spend time making models than making tool grinders.
 
JD

Edited By Jeff Dayman on 07/02/2010 13:20:28

mgj07/02/2010 14:56:12
1017 forum posts
14 photos
You don't NEED a TCG - I do apologise. You are quite right. Of course you don't  for most things - it just as easy to go and buy carbide.
 
HSS is great.
 
Yes it is - but how do you grind it accurately so you get a decent finish and a consistent setting angle every time, without pissing about. This time it rubs and last time it cut. While it can be done doubtless without a TCG, the fact of the matter is that most people are amateurs, and don't have the skill of the Gods of model Engineering, nor given the age of many, do they have the time available to acquire them. In any case, they'd probably prefer to be making something rather than be standing by some offhand grinder acquiring hot fingers.
 
And if nose radius turns you on - personally I've never had much problem getting a mirror finish since I made a TCG - rather than spending half the evening practising, you can just break the tip with a stone -triangular Engineers India for choice. (or a fine diamond lap). Its not often, frankly that a specific nose radius is called for - and if it is, for instance for a bearing groove - then you HAVE to have a TCG - or go to carbide.
 
The next point is that many don't actually have a decent offhand grinder, plus diamond and stone dressers. So for them HSS is a pain and indexed tips a  blessing. However the interesting thing I find about TCGs is, in talking to people, you always hear how they survived without one, but just how damn glad they were to have made one - because having good tools transforms ones turning drilling and milling capabilities.
 
Hopefully beginners will be making what they want to make, independently of what you and I may think.  Still as we all know, as each shiny new Model Engineer presses the go button on his new lathe, there is a very significant amount of tooling that he will need to make before he can start making models (or anything else) conveniently. Since his experience will be limited, and his knowledge of what a cutting tool should look like dubious, and his ability to sharpen it almost non existent, a set of carbide tools and a TCG is probably not a bad place to start - even if he grows out of it later.
 
So yes, you do NEED some kind of effective tool grinding equipment, beyond the plain vanilla offhand grinder.  (Sorry - you may not, but the rest of us, less expert, do)
 
By the way - can you four facet sharpen to that standard by hand - such that it cuts dead to size and dead straight, and is self starting too?  Yes I'm sure you can. 



Edited By meyrick griffith-jones on 07/02/2010 15:17:16

Ramon Wilson07/02/2010 15:24:07
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1319 forum posts
382 photos
Ahh Merrick you pipped me to the post!

Have to admit that whilst what Jeff is saying is possibly provoking to some I have to agree with most of what he says.
 
I set out to build the Quorn when it was first published and was well into it when I had the opportunity to purchase a virtually unused Clarkson T&C grinder at a very reasonable price from my works. I then sold the Quorn to well known ME 'toolmaker'  Dr Peter Clarke and then, (after equiping it with an expensive single phase motor), over the next several years proceeded to use it  just once and that was to reduce the diameter of a cutter for a 'special'.
Eventually that too was sold, strangely enough to another doctor, about two years ago. No doubt there will be time I guess when I may regret that but so far it hasn't occurred.
 
This is not to say they are not worth having or that they don't do a good job but just that like Jeff intimates they are not neccessary to be able to cut metal.
 
'Tis without doubt there are many very desirable 'bits of kit' very attractive to the model engineer - its down to paying money and taking choice in the end - but again I agree with Jeff perhaps much better spent on other items of more use.
 
Where I slightly disagree is in acquiring the skill to grind a tool. Like all things 'Practice makes ..... etc' and the more it's done the more experience is gained. Once an idea of the angles required are learnt for the various metals (and plastics) its easy enough to produce them by hand. One of the barriers often seen is to have to reduce a hefty lump of HSS to the shape required creating lots of heat, dust and sparks which is exactly how I saw it so long ago. When you consider just how small the area of a tool is doing the actual cutting  the size of (HSS) blank behind it isn't that important. As already said many of my tools are made from easily ground, totally free, FC3 cutter shanks fitted to steel holders. More than adequate for most tasks and especially for the fine finishing cuts so I guess I'm more than happy to be left out of the hunt on this one
On the basis of one pic etc,  with no offence grannies -

 
 
That said I'm a great believer in cat skinning and using each day to learn something so Ian SC's post on the saw blade carbide tipped tool is interesting. Is that brazed in Ian?
(Ian doesn't say but for those not certain carbide is usually ground using a much softer 'green grit' wheel before lapping)
mgj07/02/2010 19:21:49
1017 forum posts
14 photos
No offence taken - I just resharpen my FC3 cutters  and since I have only recently started to use them, I don't have so many spare...
 
How as a matter of interest would you resharpen a 12 tooth 21/2" diameter  shell endmill with spiral flutes?
 
Or even just an ordinary 1/2" endmill at what £12-15 a go for a good one incl P&P. Or a slot drill, an undersize slot drill being so useful and all. (Forgive me for being a bit uncertain about the price. I haven't bought one for years)

Edited By meyrick griffith-jones on 07/02/2010 19:26:24

Ramon Wilson07/02/2010 21:51:32
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1319 forum posts
382 photos
Oh that's easy Merrick, I'd jump in the car, nip over to my old place of work and get them to get it 'done' for me.
 
Now that's not being flippant just a fact because I have just one shell end mill and again used that just once since I was given it in 1980, quite recent too, to do the crankwebs on the Nova engine. I realise of course that that isn't an option that most can take but having said that most small jobbing shops have a regrind service they rely on and I'm sure if approached would be happy to help on the odd occasion such an item needed sharpening. It's how mine was sharpened! One can but ask. (If one can find a jobbing shop these days that is!!!)
 
However I take your point - but the thread is about boring tools not milling cutters. Of course you need a Tand C to sharpen endmills etc and it will save you a lot of money not to mention control of those specials but as has been stated so far it isn't really neccessary to have such a luxury to actually be able to machine metal. If the average guy hasn't got a decent bench grinder before his 'Tand C' I would venture to think the priorities are a little askew.The 'amateur versus professional', 'God of ME' etc shouldn't have to rear its head, for me it's about helping that amateur get a job done without their as yet to be acquired skills being a stumbling block.
 
And I really can speak from personal experience here for I began model engineering as a total amateur in 1972 when I struggled, really struggled for several years, to acquire those skills so desired but so elusive. Then in 1980 I gave up my offshore career to begin again and started from scratch in engineering to learn how to make a living as a 'machinist' something I was very passionate about doing. That early period was truly an eye opener for an amateur so I like to think I have not forgotten those roots and can see it from both sides - it sometimes is very difficult for the true professional to understand the dilemmas of the enthusiastic amateur as he takes so many things about the business for granted though believe me, I have seen some very 'professional' engineers make some appaling 'amateur' cock ups but we all make mistakes myself very much included!!.
 
I can only offer help to others based on what I have done in machining in the past - I have certainly not accomplished any great feat of model engineering - but I certainly won't comment on anything I haven't had any experience of. I hope my intentions will be seen as not to disagree but to offer an alternative in the hope that it helps someone. God, I've just retired, the last thing I want is to be controversial.
 
Keep on grinding
 
Best Regards - Ramon
 
 
 

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