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Milling SFM or RPM

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chris stephens	23/02/2011 01:11:41
1049 forum posts 1 photos	Hi Guys, Time to ask a question of you more experienced at milling than I. What is the recommended SFM for HSS, oh, and I am using a 10mm cutter. TIA chriStephens
Ramon Wilson	23/02/2011 07:53:49
1655 forum posts 617 photos	Hi Chris, We need to know the material you are cutting first.The speed varies with the material to be cut. As a guide the cutting speed for mild steel can be taken as a basic 100 FPM - it can vary either side of this depending on type. RPM is worked out with Cutting Speed (CS) x 4 Dia of Cutter The softer the material the speed increases and vice versa. Hope this helps Ramon
chris stephens	23/02/2011 15:58:07
1049 forum posts 1 photos	Au Contraire, mon ami. I asked the cutting speeds for milling HSS, as I could not find a recommended one in any of my books. I require a shape that would take forever by grinding so thought I would mill it instead. chriStephens
Ramon Wilson	23/02/2011 17:39:41
1655 forum posts 617 photos	Well Yes I did read it as that Chris but I have to admit as I've never seen anyone actually mill it in its hardened state I thought you meant the other. 'Eats Shoots and Leaves' springs to mind. We did use to make the odd press tool parts from it in it's annealed state. Cutting speeds were well down using HSS cobalt cutters but the actual SFM I'm not sure, probably around 30 to 40 f/m. Despite having heat treatment facilities for normal tool steels this used to have to go out for treatment. I take it it is annealed. If not I doubt you will mill it at all even with carbide but I may be wrong there as so much has moved on in the carbide world since I packed up. It's not a material that is usually machined other than by grinding which is probably why there's little reference to it in any of your books. Sorry - There I was thinking I was being helpful Regards - Ramon Edited By Ramon Wilson on 23/02/2011 17:41:33
Richard Parsons	23/02/2011 17:55:00
645 forum posts 33 photos	I have a copy of the Machinery Year Book dated 11^th edition 1942 and the American Machinists Handbook 5^th edition dated 1932. The Machinery Year Book refers to ‘cemented tips’ the other talks about Tungsten Carbide tips. Neither mentions machining HSS. The best trick is to start slowly with a fine cut and ramp the speed up carefully in small steps until it ‘jibs’ at the cut then slow down a bit. Raymond your formula Cutting speed X 4 / Cutter diameter. What units are the cutter diameter in? Inches, feet or what? All the best Dick
mgj	23/02/2011 18:11:25
1017 forum posts 14 photos	And hardening HSS is not normally undertaken by us amateurs. You couldn't look at a slightly different route? Like grinding (slowly) , spark erosion etc. Or just using a hard tip in a softer carrier, or even gauge plate. Having said that, in the Sandvik cataloge there are tips for superhard alloys. These are the HRC 60 series - all with negative rake. Funny loking things. While I'm sure they can be got, I doubt you'd buy single ones, so it would be a box of 10 , and doubt you'd see much change out of £50 (guess). Sorry don't have one to post you. They do also do H series milling cutter tips in ANSI sizes - I daresay the speeds and feeds will be on the box! Take pleasure in the fact that after you have bought, at vast expense, the tipped endmill, and the H sries inserts, with the expenditure of only another £50 or so, you can use the ensemble for milling steel. (I mention that in passing) (And for those , not CS I hasten to add, who have trouble fininshing light alloys and bronzes to a superfine finish, the Glanze endmills and the APKT series (Sandvik Coromill 390) tips are the perfect answer, especially in the radiused corner versons. A mirror finish comes as standard.) Edited By mgj on 23/02/2011 18:13:29 Edited By mgj on 23/02/2011 18:14:10
chris stephens	23/02/2011 18:47:30
1049 forum posts 1 photos	Hi Guys, Thanks for replies but I just went ahead and did the job. I used 800 rpm for the heavy cuts and upped it to 1100 for finishing. I used a four flute 10mm solid carbide end mill, 3or4 £s from Jenny at JB, and the HSS was bog standard use as supplied 3/8"HSS, Cleveland brand I think. For future reference, milling HSS is quite easy, probably safer too as there is no dust, only chips. What I wanted was an "L" shaped piece about an inch long, which I now have. If I had an EDM device I would have used that, but I don't so I didn't, but this might be another reason to think about getting/making one. MGJ may have an inkling of what I wanted a special shape for, if he thinks of that German site (no not porn, for those of you with a dirty mind) I put him on to. If the project pans out SMEE members should be able to see it a week on Saturday as "work on the table" chriStephens
Ramon Wilson	23/02/2011 19:26:13
1655 forum posts 617 photos	Well Chris 'tis true you can learn something every day. That's very interesting to hear. I would never have considered it but there you go - 'it's in the pudding'. Just as a matter of interest what kinds of cut were you taking and how did the cutter stand up to it in total? Ramon
chris stephens	23/02/2011 20:05:07
1049 forum posts 1 photos	Hi Ramon, I take the first E (Experimental, sometimes shorten when I am about to 'mental) in SMEE seriously , so I give things a go to see if they work, no one looking over my shoulder to say "you can't do that", I only find out from others that I can't do something when I have already done it. I took an 5 x 5 mm corner out of the 3/8 sq. Roughly each pass was 2 wide by 0.5 deep, give or take. I could have taken bigger cuts but sympathy for the machinery and the neighbours ear drums stopped me trying. Another reason for small cuts was the way I was holding the HSS, I did not want to strain the mill vice holding such a small piece of metal. The cutter seemed to be cutting as well at the end as the beginning. Even if it was blunted, I would only have to take the end few mm's off to restore it, another reason for small cuts. Although it worked out as well as I had hoped, let us not forget that HSS is a hard material and perhaps should only be machined by experienced idiots, to quote the Goons. I now know why there are no machining speeds published! I nearly forgot to say sorry for the confusion, I can easily see that there is room for a misunderstanding, especially if you have never tried milling HSS before. Certainly it seems that milling this material is not common in the home environment. This is not the first time I have tried it, I take the top dovetail of standard parting blades with an endmill, but that is only a very small job. The finish, by the way, can be better than by grinding., almost polished which some could say means that the cutter was rubbing not cutting, but I have the chips to prove it was cut. chriStephens
Ramon Wilson	23/02/2011 20:38:29
1655 forum posts 617 photos	Thanks Chris, Whilst I do believe that you should prove things to yourself I'm sure some would agree that this is one area where percieved wisdom would not likely be challenged. Just goes to prove one should look at everything with an open mind. I find your comments on the state of the endmill and the (relative) ease of which it cut very interesting. I certainly can't think of a situation where I would need to do likewise but I shall have no hesitation in trying if I do. Whether carbides would be gripped sufficiently to prevent shattering in my home made collets remains to be seen (unlikely I would think). Because of the limitations of my mill I tend to use small (HSS) cutters at shallow cuts but high feeds and as you say the cutters are easily reclaimed. You are obviously well experienced, which I was not aware of so my apologies if my answer seemed in appropriate. Regards - Ramon
chris stephens	24/02/2011 00:08:20
1049 forum posts 1 photos	Hi Ramon, Without open minds we are limited by what others know, and as we know no one knows it all. As for "well experienced" certainly I think I am out of the newbie category, but I fully and freely admit that I am largely self taught. There is therefore the possibility of gaps in my knowledge, and I do not know of them because they are gaps. Those that know work seem to think I am reasonably proficient, but perhaps I just exude talent. The reason for the OP (original post) was that I always try to find the "correct" way first (if there is one) before experimenting. No point in re-inventing the wheel, is there? Thanks again for trying to help. chriStephens
Ian S C	24/02/2011 10:03:02
7468 forum posts 230 photos	The more I do , the more I realise how little I know, I would not have thought it possible to machine HSS, I'v spent hours grinding the stuff. Ian S C
Andrew Johnston	24/02/2011 12:06:29
7061 forum posts 719 photos	Hi Chris, I must admit that I mis-read the original post too; I thought it was about machining with a HSS tool. It is very interesting that you machined HSS with a carbide mill. There is quite a lot about machining very hard materials, up to about 60Rc, on the professional machining forums. I assume that HSS falls into this category. Turning in particular seems to call for the use of ceramic inserts rather than carbide. Being curious, I have a few questions. I assume that the HSS was hardened, so about 55-60Rc? Did you use coolant, or machine dry? Lastly what chip load per tooth did you use? I don't have a need to machine HSS at the moment, but it's very useful to know it can be done. Thanks for posting the results. Regards, Andrew
chris stephens	24/02/2011 13:37:15
1049 forum posts 1 photos	Hi Guys, Although I have done the procedure I do not consider myself an "expert", on second thoughts if no one else has done it, that does give me a certain credibility. I understand why there is a touch of disbelief that milling HSS is possible, after all it is the stuff you normally machine with. Yes, the material was normal of-the-shelf 3/8 Sq.HSS as used for turning tools. It was machined dry with a solid carbide four flute end mill at about 800 RPM for roughing. The material is hard and carbide end mills are brittle, so shock loads are not recommended. I am apparently blessed with a good sense of "feel" when machining and if you do not have it, I would be careful how you approach the job. Try to keep two cutting edges in contact with the work, in the same way and for the same reasons that you do with a hacksaw blade. Smaller cutters are, I think, a better option than those big things with replaceable tips. Another thought is that you will be working on small pieces, which will have to be held tightly, this can put quite a strain on a milling vice. The more rigid your mill the better, and listen to what the cutter is telling you, the less it shouts a protest the more it likes what you are doing. Last recommendation, but certainly not least, face shields are HIGHLY recommended, you have been warned. All I can suggest, to any who wishes to try, give it a go but do it gently. If you have a source of cheap carbide mills try one, but I would not try with one if I had bought it at full retail prices. chriStephens
mgj	24/02/2011 17:36:29
1017 forum posts 14 photos	Well done for busting an old wives tale- like others, I wouldn't have tried it. I guessed it could be done with these special tips - I suspect the difference between them and a plain carbide mill would be the strength of the cutting lip.allowing greater speeds.Even so, it seems a bit adventurous. Looking at that tool - does it offer an advantage over the GHT version carrying a carbide bit. - ground to shape with a green grit wheel?.
chris stephens	24/02/2011 22:53:44
1049 forum posts 1 photos	Hi MGJ, As I have said before, not being a time served machinist I don't know the "limits", to me if I think it should be possible I find out by trial and, hopefully not too many, error. Of course I could have used the surface grinder to fashion the bit I wanted, but all that dust and grit did not appeal. Next time I will use a 1mm thick angle grinder disc to remove the bulk, which will leave me with a still useful piece of metal, and finish with the job on the mill. You mean the one from Germany? I was not looking at their version of the GHT retracting holder, just the HSS insert for threading. I have now made the holder for the bit I milled but not added the clapper box part yet. So far the insert worked as well as expected in a normal threading fashion, you can't beat sharp HSS for clean cuts. Tomorrow should bring forth the other parts, all being well. I will bring it down to SM for your perusal, if it works. If it doesn't you will never hear about it again. chriStephens
mgj	25/02/2011 17:34:41
1017 forum posts 14 photos	Be interested to see. If it doesn't work to well you can borrow my GHT one. They are actually rather good, and with a x slide stop would make a difficult to beat combination. I don't have the x slide stop, but then I don't do a lot of screwcutting nowadays. - last I did was a 16 TPI buttress thread and nut for the TEs brake mechanism, and that was nearly a year ago..
chris stephens	26/02/2011 01:37:14
1049 forum posts 1 photos	Hi Mgj, Thanks for offer, but I have a GHT, as well as another, design of retracting tool holder and I am still looking for something better. While the GHT does exactly as it should and was quite fun to make I feel that there is a better form of cutter. So far a simple cross stop is by far a better option than either retractor because you can choose which cutter you want to use. The cross slide stop is also so much quicker to make. Can't quite see why you would want a slide stop for use with a retractor, but then we all work differently, thank Heavens. The recent developments of the clapper box type tool holder by John "Bogstandard" Moore and John Stevenson shows great promise, but again it is the actual cutting bit that I find leaves a touch to be desired. The best cutter I have encountered so far is the Eccentric style, but the German one looks good and is quite neat. Now I have a CS version of it, (thanks to milling HSS) which also works well, and all I need to do is add the clapper part .This last week I have cut several 7/16 and 1/2 BSW threads in Mild, as well as EN24T and screw cutting the thread is a lot easier, on the parts, than using a die. When it all works out I shall convert you to a screw cutter of distinction. chriStephens PS I can feel an article coming on. "screw cutting not for beginners"
mgj	26/02/2011 08:42:04
1017 forum posts 14 photos	I'm a great fan of the eccentric style, but its not so hot in brass or bronxe - not with a standard sharpening jig anyway. Also, the different POV comes from never having to cut many threads. Everything has been a one off. I think, had I not been given the GHT holder that I'd still be using a standard cutter and offset on the toolholder (or not for smaller threads), just because of the investment per task. I've never used them but what about these tipped threading tools. They should cut pretty well. The interestng point for me is the matter of devlepment - most of our modeling type literature is now quite old, and a lot of it also dates from the era of carbon steel tools - or its heritage does. It all works well enough, but there is very little about the way tooling has developed and the opportunities that creates. (We could all I suppose start doing all our cutting on the back toolppost since it works so much better than the front!) Edited By mgj on 26/02/2011 08:43:18
chris stephens	26/02/2011 12:45:20
1049 forum posts 1 photos	Since you ask, carbide thread cutting inserts can be very good, but with limitations for the home user. Inserts fall into two categories, those that cut full form threads and those that just cut the "V". Clearly, full form are only for a specific pitch although diameter does do matter. Partial form inserts will cut a thread up to a Max pitch which is limited by the width of the "V" ground on the insert. As with all one-size-fits-all something has to give and with these inserts it is that the root of the thread is too sharp. This "too sharpness" will show itself by you having to cut deeper than the charts would suggest, but we are now getting a bit too involved for a forum post. 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. Failure on either point will result in a chipped tool. I have used these tips in a clapper box thread cutting holder, as well as standard holder, with success. The only real advantage over home ground is the "full form"which will give a notionally perfect thread form, but then most of use can live without this as long as the nut fits. I will briefly add that inserts do save having to grind good 60 or 55 degree tooling (I don't think the make BA ones) but then this is why I am interested in tooling that only needs sharpening on the end, in much the same way that Tangential tooling only needs grinding on one face to restore a perfect edge. You could say that a little development allows laziness at a later date, but then that is the underlying reason for most of the industrial revolution. chriStephens

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