Travelling Steady.

Edited By mgj on 11/03/2011 18:14:15

Edited By KMP on 12/03/2011 10:56:46

Keith

PS Still to crack the formatting when cutting and pasting from Word

Edited By KMP on 12/03/2011 12:33:44

Graham, mgj, Hi,

Sorry no subterfuge intended, I am neither a “Rocket Scientist” or a “50 years on the dials” man. My background is in Aircraft but includes large machine shops repairing worn or damaged parts.

I have no issue at all with what you say but feel that we need to put it in context for the typical “home workshop”. As you say, only luck will see you with a “round” bar off the shelf but it will not be straight either. My concern would be if Geoff, on his new machine with an unfamiliar rest can better the errors one would typically find on the OD over a long (?) length. If the leadscrew is less than 13” (shows my age) long I would suggest Silver Steel would be a reasonable starting point but again not perfect. I would have suggested EN8 (BS 970 080M40 Carbon Steel) or even better 226M44 (BS970) listed as "USACUT 45". Now I am wandering and suspect those type of details will not bother Geoff at the moment.

I totally agree with your and mgj’s comments on burrs but, once again, we must put it in context of someone who is developing his skills. I have found in helping others into this wonderful world that “sharp tools” is something they either learn instantly or after a period of struggling. For some reason many see tool grinding as a “black art” or something that needs a Quorn and the ability to use it (I have yet to build one myself but it is on the “to do” list). The tipped tool path is fine but one needs to select the insert carefully as the cheaper variety for general use will not be that sharp, unless one has found the newer generation of “aluminium” positive rake tips that are sharp and superb on most of our materials. I can’t really recommend as I do not know what the thread angle is being produced, 60 deg would be easier.

Again, I agree with your comments on finger tip wear, but the newer engineer also has other factors to contend with. Chip removal is often neglected particularly where no coolant flow is available or is inadequate. A problem on subsequent cuts but can cause havoc when they get between fingers and work. I find cheap paint brushes invaluable particularly if I am using cutting oil. One other major issue is with using any old “mild steel” whatever that is; I have seen some round bar that would not cut cleanly with the sharpest tool.

Sorry Geoff if I have confused the issue for you and profuse apologies if in my assumptions I have put you on the wrong part of the learning curve. I am guilty of always starting with the very simplistic but in this hobby without someone looking over your shoulder, the basic can be the most difficult to pick up. Most writers on the subject are at the other end of the curve.

Keith

Thaks Gray - but now I'm going to disagree with the idea of silver steel for leadscrews. Its only half an apology, because one of ther other recommendations was IMO the best selection. (Maybe SS wasn't your recommendation?  )

Edited By mgj on 13/03/2011 16:41:12

Edited By mgj on 13/03/2011 16:44:56

Edited By mgj on 13/03/2011 16:49:14

Edited By mgj on 13/03/2011 16:58:01

Gray, mgj, Terry, Hi

Gentlemen, and I thought we were getting on so well. In Graham’s defense twas I, I suggested that Silver Steel could be an alternative. In my defense, I didn’t recommend it and suggested En8 or 226M44 both of which I have found superb for this application. The suggestion was nothing to do with its toughness or hardness but was in relation to having an accurate, consistent outer diameter to work with rather than to have to surface a long slender bar. My own experience of Silver Steel is that it certainly needs more careful selection of speeds and feeds but, in its normal (soft) state, it machines better than many of the alternatives. As mgj says there is no need to harden it in fact life is made much more difficult if you do. I have found that with a, sharp tool, SFM at the lower end of the range, and with a positive depth and feed all will be OK. For small tasks I tend not to use lubricant and have found “suds” better than oil if necessary. It certainly doesn’t like any rubbing or “dust” cuts with a blunt tool, hard spots will quickly appear. So if you tend to creep up on a finished size, leave it alone and pick one of the other suggestions. Do though make sure you actually have En1a, En8 et al, as many suppliers are apt to take liberties when supplying our small needs.

Mgj, one day we might explore the wear rates of two mirror surfaces when under load without a pressure oil film, but Geoff’s thread is not the place I feel. You will also have to promise that the maths are kept out of it.

Edited By KMP on 13/03/2011 18:38:08

Edited By KMP on 13/03/2011 18:41:09

Edited By mgj on 13/03/2011 19:23:08