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Gordon W	21/12/2009 15:49:45
2011 forum posts	Can some experienced person give advice on what material to use for what I call rough turning? Problem is most of my stuff is made from scrap of unknown quality. I am just trying to turn a disk in 3/8" steel which I have hacked with angle grinder to near round. A HSS tool blunts very quickly, an insert tip breaks very quickly so forget them, a brazed carbide seems best, but any sort of intermittent cut soon cracks the edge. I can't avoid int . cuts, any ideas please?
Circlip	21/12/2009 17:09:15
1723 forum posts	You COULD quite easily start a carbide/HSS flame war with this one Gordon, BUT, HSS is sharpened using a conventional grinding wheel so you can have more stabs at the offending material without damaging Carbide tips or inserts. Problem with unknown materials is just that. As a newbie, (And to be asking this question doesn't take rocket science to work out) you should restrict yourself to materials with known properties before commiting yourself to rubbish (In material terms). Once you've got how to sharpen tools to machine KNOWN properties, then you can deviate. Basically you've told us it's Metal. Turning speed?? Coolant?? What colour are the chips coming off?? What SHAPE are the chips?? I'm NOT mocking OR taking the ------- micky, but these are salient features. MOST Carbides don't like intermittent cuts, but I'm not discounting them, It's just that I preferr to do it properly and use HSS. Regards Ian.
mgj	21/12/2009 18:04:46
1017 forum posts 14 photos	Probably you have a piece of toughened heat treated steel and its gong to be a bastard from start to finish. HSS ground for tough materials will do it as Circlip suggests. or you get a proper tip designed for tough materials. Angles for grinding the right sort of tool are in the ME handbook You could try just heating it to red heat, holding it there for 10 minutes per inch, and then allow to air cool. Might soften it. If it doesn't I think I'd invest in a chunk of 220M07 and enjoy my turning. Edited By meyrick griffith-jones on 21/12/2009 18:05:45
Ian S C	22/12/2009 01:03:55
7468 forum posts 230 photos	How slow can you go?Some of the Chinese lathes don't go below 120rpm,I find with some of the rubbish that I get I'v got to get into back gear and 60rpm is fast enough.I try to keep away from old half shafts etc,but some times can't avoid flame cut stuff with hard edges,normally use carbide tips on that stuff and keep it hard at work so that it does'nt rub.Ian S C
Don Brymer	22/12/2009 05:37:58
9 forum posts	Gordon, First question, can you file the material with a sharp flat smooth file? If yes, you will be able to turn the work with HSS. For the diameter mentioned try a starting spindle speed of around 150RPM or perhaps less, with cutting fluid or straight cutting oil applied with a small paint brush. If no, then a carbide insert may be OK, but increase the spindle speed to 1500RPM or higher. Try to get the depth of cut under any surface irregularities. If the insert is constantly chipping you could be using a finishing grade insert or the spindle speed is far too slow. I think that the HSS is the better option, but do not grind the tool rake angles too acute. Limit the angles to 8 to 10 degrees. Regards, Don.
Circlip	22/12/2009 08:54:21
1723 forum posts	I keep re-reading the O/P but keep missing the diameter. Which line is it on?? Regards Ian.
Les Jones 1	22/12/2009 09:26:47
2292 forum posts 159 photos	Hi Ian, I can see your frustration at not being able to get the information from Gordon that is required to be able to help him. We had the same problem getting in information about a switch last week but the information was eventually supplied. Les.
Eric Cox	22/12/2009 09:54:06
557 forum posts 38 photos	Why use an angle grinder on something as small as 3/8" Dia. The heat generated would have an adverse effect on the material. Next time use a file or cut a blank with a hacksaw 7/16" or 1/2" square and turn to round.
KWIL	22/12/2009 10:43:53
3681 forum posts 70 photos	I seem to think it was 3/8" thick. If you cut it slightly oversize with the disk cutter then there will be material to turn without the intermittent cut that kills tools!
Circlip	22/12/2009 12:11:13
1723 forum posts	That seems to be two of us that are "Thick" Kwil.
Gordon W	22/12/2009 14:17:31
2011 forum posts	thanks for the advice everybody. My fault didn't give all relevent facts, this particular job is 5 1/2" dia. x 3/8" thick. I thought I'd cracked the job with a brazed tip, 90 deg. point with a 1mm rad. was cutting ok until back edge cracked off. Would love to use free cutting steel of known quality, but can only get it mail order and at a huge price.I did put the part in the stove overnight and this may have helped. This is a re-accuring problem with me, think it will be best to buy some 1/2" hss blanks and just keep grinding them up.
mgj	22/12/2009 18:11:29
1017 forum posts 14 photos	I dunno Gordon. A lot of the cheapo HSS blanks are not much more than monkey metal. Better to buy a couple of GOOD HSS blanks (ouch because they will cost) and then buy the right steel for the job. Be cheaper in the long run. Good HSS is pretty pricey.
Paul Boscott	22/12/2009 19:04:47
99 forum posts 21 photos	Gordon Have you considered mounting your disk in the lathe covering up the slide ways and using the angle grinder bracketed off the tool post to get the part concentric with the lathe so there not any lumps on it to start with? Then treat it like a casting a make the first cut slow and deep enough to get under any local hardening you may have caused Yours Paul Boscott
Gordon W	23/12/2009 10:24:30
2011 forum posts	Thanks to all. I had thought about grinding in the lathe and may do so next time, or make a sort of crude rotary table. I do know about tool grinding etc. but for ind. type work and am new to small model stuff. I think some of the problem is cheapo tools, and esp. HSS. This job now done, it may help someone else to tell what I did;- 1) fitted a leadscrew handle for long. feed, this better than power feed, and much better than using the rack to hand feed. 2) found some very old pieces of 1/2" sq. Hss ,ground LH & RH tools with minm. relief on all faces and good rad. on point, as suggested. 3) used neat oil to cut. Am fitting big pulley to get a lower speed as my eastern lathe has 120 rpm as the lowest. I had just thought origenally, that there may be some modern stuff that I did not know about, or some old stuff.
Nigel McBurney 1	25/12/2009 11:42:42
1101 forum posts 3 photos	Hi The worst of the common materials to machine are steel water pipe then rolled steel plate,they are not really tough but very stringy.forget carbides use good hss with 15 t0 20 degrees rake and SLOW cutting speed ,around 40 to 50 ft per minute using soluble oil or even slower on the first couple of cuts,if as you say your lathes bottom speed is 120 then you are attempting to cut rough steel at at nearly 200 ft a minute which will destroy any tool,your lathe speed should be 25 to 30 rpm.I know there is some low quality hss around,but no hss will last on good steel if you exceed 100 foot a minute surface speed,possibly 120 on soft leaded freecutting material,the tougher the material the lower the speed,thats why carbides were introduced,to enable higher speeds to be used to keep cost down,but they are intended for use on suitable machinery and nice clean known materials under ideal cutting conditions,not rough jobbing engineering .thats why a Myford and my Colchester have low bottom speeds of 25 rpm.Use ordinary soluble oil at 20 to1 mix,The above is not theory I earn my living on jobs like this. ps dont go using grinding wheels and angle grinders on your lathe.
Gordon W	26/12/2009 13:47:32
2011 forum posts	Thanks for that Nigel, yes I've met the tough water pipe as well, but beeing small dia the cutting speeds could be low. New pulley just about ready to fit, should get down to 70 rpm, as low as I can easily get. HSS ,How do I know what I am buying? Prices for 1/2" sq. x3" long seem to vary from £2 to £10 ,just assume the dearest is best? For interest the old piece I ground up to do my job is marked Goodyear, I'm assuming it was a form tool for tyre moulds, but maybe not, good steel anyway
Ian S C	27/12/2009 10:51:51
7468 forum posts 230 photos	Hi Nigel,don't know what water pipe is made of in the UK,I machine water pipe here in NZ as for any mild steel,it cuts ok,I'v used it for cylinders in model hot air engines,the bore comes up nicely.Ian S C
mgj	27/12/2009 15:26:18
1017 forum posts 14 photos	Ian I rather agree. Not sure of the spec - just a common or garden low carbon mild, but its often in the drawn state so its work hardened and a bit stringy. If its being a bit feminine, then I just anneal it - like anything else that's tough (or most else- there are some materials which won't soften, but they are relatively rare). Mind you, with the right tip you can machine armour plate quite easily and to a good finish, at quite reasonable speed, even in the toughened state. All of these things are just a matter of having ones act togehter.
Ian S C	29/12/2009 04:58:14
7468 forum posts 230 photos	Only problem I'v had with water pipe was once when boring it the weld let go.I took it out of the lathe,ground a V down the seam,clamped it up and welded the outside of the seam,put back in lathe,finnish bore.Ian S C

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