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Milling SFM or RPM

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Andrew Johnston26/02/2011 12:58:58
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Posted by chris stephens on 26/02/2011 12:45:20:
 
A quick summary of inserts, great for cutting a thread if you have cut a run-out groove or have CNC, or quick reflexes, to withdraw the tool at the same point each time.
 
Or an Ainjest high speed threading unit.......not that I've found them particularly easy to use.
 
Regards,
 
Andrew
mgj26/02/2011 13:01:22
1017 forum posts
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Thanks Chris.
 
A rounded runout groove is IMO mandatory - I wouldn't/ don't thread cut without one - nothing to do with runouts and everything to do with strength and stress raisers.
 
I have an SDJCR tip which is a 55 deg tip, but I suspect thet even with a groove, against a biggish shoulder the tip may yet be too fat to be able to place the groove correctly - unless the bits being bolted are thick enough. ie one is making a bolt rather than a screw.
 
I don't have a problem grinding a decent cutting tool - I put a touch of side and top rake on, but I am a bit lazy and haven't done the sums to make the angular correction. (Which means I haven't applied such a correction, which I should)
 
A lot depends on whether one has good sharpening kit. Despit its limitatiojns the tipped route is probably a good way to go for the person who cannot control angles precisely, for whatever good reasons. I think the tangential route is also good because . with minimal kit one can grind a good thread cutting tool - but then of course there is always the internal thread to be cut.
 
 

chris stephens26/02/2011 19:38:11
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Hi Andrew,
If you have a spare one lying around I would be willing to do a test run to see how easy or not they are to use.
 
 
Hi MGJ,
As you may remember I do have a Quorn, but if I can sharpen with a simple jig and a double ended grinder that is always my preferred route. I absolutely agree that if someone can't grind a complex shape that another route must be taken, be it a Tangential tool or speciality tips. I don't as a rule think that general purpose carbide inserts teach the newbie much about accurate machining, but that is their choice.
 
We have not mentioned thread milling yet. This is another of my long term projects, I bought the milling cutters years ago, both 55 and 60 but have not had the time to build the equipment to hold them. The thought of cutting a thread in one pass does still appeal though.
chriStephens
 
KWIL26/02/2011 19:45:10
3681 forum posts
70 photos
Chris, They do make BA ones, Posithread (located in UK!). Greenwood Tools can help you source these.
chris stephens26/02/2011 20:02:04
1049 forum posts
1 photos
Hi Kwil,
Thanks for the info but I can't say that I have any pressing need right know, but the details will be filed away.
chriStephens
chris stephens26/02/2011 20:02:05
1049 forum posts
1 photos
Hi Kwil,
Thanks for the info but I can't say that I have any pressing need right know, but the details will be filed away.
chriStephens
mgj26/02/2011 21:01:47
1017 forum posts
14 photos
As I said, I have no experience of screwcutting with tips, and I get very good results with HSS. OK I'm not so red hot with tip radii - I just break the tip with a stone but still work to .64 is it of the pitch for depth. The alternative being .8 something of p. Its an accurate pich neatly cut thread, perhaps a bit functional WRT to depth, but as always its better to be approximately right than exactly wrong.
 
I have to say I have never worried about the potential of carbide tips to shift metal, though at those speeds operating life is often in modelling terms, uneconomically short.(15-20 minutes in some recommendations.) I accept I "under use", but I just use them interchangeably with HSS. I can take shaving cuts if I need to, (in 220M07) though I am aware of Sandviks reccomendation that the final cut should always be =/> the tip radius, and I do try to organise it that way if I feel like it.
 
What is handy for me is that, as a person who doen't have a lot of modelling time, I can (at a price) spend time making rather than sharpening. I still have specialist tools to sharpen, and drill bits of course, but they are a lesser task.
chris stephens26/02/2011 21:57:33
1049 forum posts
1 photos
Hi MGJ,
Do you know you are beginning to persuade me that I ought to spend a little, or at least some, time model making instead of tool making. For me though there can never be too many tools. You have to agree that tools are useful and while models can be things of beauty but once you have proved they work they tend to be left on the mantle shelf for others to admire. Traction engines excepted but a little out of my price range at the moment or the foreseeable future.
Anybody know next weeks winning Lotto numbers?
chriStephens
Andrew Johnston26/02/2011 23:07:29
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Chris,
 
I do have an Ainjest unit lying on the bench. But I think they're specific to a given lathe, so unless you have the same lathe as me you will not be able to try it out.

Secondly, because I was an idiot and made a stupid mistake when using the unit, it is now damaged and awaiting repair, when I get my enthusiasm back.

Before I damaged it, I found it difficult to engage the half nuts correctly. Once running it was fine and dropped out instantly in the same place. I was being cautious and running at about 550rpm, cutting a 1.5" diameter 12tpi thread. To be more precise, when I tried to engage the half nuts when it wasn't set up to cut an actual thread, everything worked fine. When it was set to take a cut, it didn't always seem to engage properly. Finger trouble on my part probably.
 
Regards,
 
Andrew
 
mgj26/02/2011 23:14:49
1017 forum posts
14 photos
Young Christopher...
 
For years I made nothing but tools. Let me loose in a tool shop with someone elses credit card and I go weak at the knees with pleasure. I love tools.
 
BUT,
 
I don't think that the person with a full time job can really do both satisfactorily. Ours is just not a hasty hobby, and if you take 3 years to knock up a traction engine, its going to take a lot longer, with a lot more forgetting of bits and potential loss of motivation if you have to do all the ordinary tooling, as well as the specialist stuff related ot that job.
 
Probably accidentally, I went about it the right way, in that for many years I made tools, and though I could yet make a lot more, by the time I started "modelling" there wasn't a lot I needed, other than a ball turning tool. Boring head, mill, rotary table, dividing head, decent coolant systems, machine vices - I had them all at reasonable cost and great accuracy.
 
For me its all about what one wants to do and what one enjoys. Tools, there is a great satisfaction in making the next one more easily using the one you have just made, but it does stop there.
 
A TE or a loco, you can tow kids, contribute at open days, burn coal, get dirty, and discuss engineering and the worlds problems for hours in a very relaxing atmosphere, once you have finishied a longish project. Metre Maid - she is running on air in 7 months, and I hope to have her tested and on track by the autumn, so that will have taken about 15months or so.
 
However, I found that, despite having loved and worked on the development of IC engines for a lot of my career, I just couldn't get excited about making one - not because it doesn't require skill though a single cylinder 2 stroke is hardly taxing either to make or design, but because they don't do anything on their own. You have to build an aeroplane or a boat to go round it and a lot of commercial people do it a lot better! The trouble is that, once you have run it, its done all its ever going to do. They don't have a life of their own, you can't watch all the bits work, and spectators get bored quickly. So they don't have an added entertainemnt value - for me.
 
I might make a stationary steam engine -a beam engine say, but much of the above applies to them. In model aircraft terms I can quite see why they could become a hangar queen as you suggest . But a loco or a TE - there IS added value, and a shed load of subsystems (pumps water lifters, injectors, overfilled boilers, cold fires etc etc)and you need to use all of them with some skill to keep the whole going. As you will discover when you drive the Little Samson soon - even the steering is rather feminine and prone to spite.
 
However, to go full circle - you ain't going to get a loco, even a simple one like Speedy or Pansy or Metre Maid/Sweet Pea, ready to a decent standard in 15-18 months if you have to stop for tooling.
 
So you makes your choice. Whichever you enjoy, this not being a rehearsal.
 
(What next  - a 4" Little Samson, and then a Duchess)
 

Edited By mgj on 26/02/2011 23:17:54

chris stephens27/02/2011 00:08:11
1049 forum posts
1 photos
Hi MGJ,
You know it's only jealousy on my part. Given the same credit card in your opening para. I would quite possibly buy a set of TE material and castings, but it ain't goner happen!!!
chriStephens
chris stephens06/05/2011 12:26:10
1049 forum posts
1 photos
Hi Guys,
As some of you might remember I was milling some HSS , well I have loaded a photo or two of what it was all for. You can see the HSS in its holder, it looks a bit untidy but I only used an oddment for the experiment. Before you lot ask, yes I honed the milled surfaces on a diamond plate to get rid of machining marks and the top cutting face was ground.
chriStephens
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