Re: A funny story re Lathes & precision finishing

Post #41,681 by dmarker2 6/8/02 9:55:41 PM 6/8/02 9:57:54 PM Reply	Re: A funny story re Lathes & precision finishing I am sure there are still a lot of machine shops around, I suspect no where near what there was per capita in the 1940-50s (mostly war effort) But one story I was told by a guy in california who made a hobby lathe years back, called the Taig Micro Lathe which was for the hobby market. I was fascinated with how he built these things - the small base (a flat bed) was made from a hollow aluminium extrusion & filled with a special concrete mix that gave them the needed rigitiy. But on to his story ... He had formerly (in the early 1970s, run a machine shop producing precision components for the govt for use in missiles. The tolerances were incredibly tight & the polished finish was a critical part of the job. In his small machine shop he had a reputation for producing polshed surfaces that defied the statistics & the govt kept sending teams to look at why his shop was consistently better at the job that the larger and important volume producers. He had one big lathe that was supposed to be used for the finishing off. It was specially approved by the govt for the job & he would not get contracts if he didn't have that required machine. But what he could never tell them was that he and his staff actually did the finishing off on an older unapproved (& never likely to be) lathe out the back & that their perfect finishes were achieved by using cigar ash as the finishing compound. I really enjoy that story as a kind of 'John Henry' up yer nose at 'officialdom' when it comes to machinery. The fact that he never told the govt is a nice twist to the story. Cheers - Doug Marker Edited by dmarker2 June 8, 2002, 09:57:25 PM EDT Edited by dmarker2 June 8, 2002, 09:57:54 PM EDT Expand All History
Post #41,683 by Andrew Grygus 6/8/02 10:46:11 PM Reply	I had a sort of opposite problem In the Aircraft industry, landing gear hinge pins are considered to be rather critical parts (for some reason). For a particular pin, I read the specification up and down and sideways and wrote a detailed manufacturing plan for inside manufacturing steps and exactly which outside vendors would be used for certain steps we were not equipped for. Every time I had a batch ready to go, the Menasco source inspector tried to reject them because "they didn't look like the parts everyone else was making". That's because ours were the only ones made to spec. Everyone else had to kiss grind after shot peen to hold tolerance. This is a very big no no. Shot peen needs to be the last step before hard chrome, because any touch of grinding negates the positive effects of the shot peen. But my parts "looked different", so every time we had some to ship we had to call in his supervisor to buy them off. [link\|http://www.aaxnet.com\|AAx]
Post #41,688 by dmarker2 6/8/02 11:20:46 PM 6/9/02 12:03:11 AM Reply	Re: I had a sort of opposite problem That is interesting - 'They don't look right" so don't want em. Sheesh Am interested as to what the 'shot peen' process involved. Am guessing that peen means 'hitting' & shot implies using ball bearings to do the hitting ? am also guessing that this was a hardening process after machining. Cheers Doug UPDATE#1 LOOKED IT UP ON THE WEB ... Shot Peen Forming [link\|http://www.curtisswright.com/segments/metal_treatment/shot_peen_forming.asp\|Shot Peen forming] Peen forming is a dieless forming process performed at room temperature. During the process, the surface of the workpiece is impacted upon by small, round steel shot. Every piece of shot impacting the surface acts as a tiny peening hammer, producing elastic stretching of the upper surface and local plastic deformation that manifest itself as a residual compressive stress. The surface force of the residual compressive stress combined with the stretching causing the material to develop a compound, convex curvature on the peened side. Parts formed by peen forming exhibit increased resistance to flexural bending fatigue. Another distinct advantage with peen forming, unlike most other forming methods, it that all surface stresses generated are of a compressive nature. Edited by dmarker2 June 9, 2002, 12:03:11 AM EDT Expand All History
Post #41,696 by Andrew Grygus 6/9/02 12:47:31 AM 6/9/02 12:58:20 AM Reply	Only the last sentence is relative Shot peening of (very hard and not at all formable) critical structural parts is done with very tiny steel shot at high velocity. The objective is to create those compressive stresses on the surface, similar to the stresses induced in tempered glass. Grinding after shot peen tends to relieve these beneficial stresses through removal of material and heat, and introduces microscopic cracks and unwanted grinding stresses. Properly, there should be a heat cycle after grinding operations to remove the stresses produced by that process, but any such heat cycle would also remove the beneficial stresses from shot peening. On the other hand, shot peening can be used to relieve grinding stresses if a heat cycle is not possible due to metalergical (temper) requirements. [link\|http://www.aaxnet.com\|AAx] Edited by Andrew Grygus June 9, 2002, 12:58:20 AM EDT Expand All History
Post #41,710 by tonytib 6/9/02 3:33:29 AM Reply	Taig is still around, but in Arizona They are still making tabletop lathes and mills, at [link\|http://www.taigtools.com/\|Taig Tools] A CNC version is available at [link\|http://www.microproto.com/\|Micro Proto] for around $2,000. [link\|http://www.sherline.com/\|Sherline] is probably the best known hobbyist lathe and mill company. Sherline does have some advantages, such as the availability of DROs and continuous speed motors. CNC conversions are available from other suppliers, and are, IIRC, over $2,000 for a complete system. Similar (bigger but less precise) tools are available from China, e.g. Grizzly ( [link\|http://www.aerocom.ws/bedair/Grizzly.html\|here is one Grizzly web page] ), Harbor Freight, etc. For dedicated CNC use, I'm most impressed with [link\|http://www.maxnc.com/\|Max NC], also in Arizona. Their models aren't much more than Taig or Sherline, but are available with servo motors, for example. The manual table top mills seem to be roughly $500 - $1,000 (DRO is more), with CNC models at $2-3,000. A used full size manual mill would typically be $3-5,000, but has many problems for home use (3 phase power, often 480V, a weight of about 2,000 lbs, etc). I don't have any experience with these, but a friend who has used the Sherline says it's hard to do precision (meaning 0.001" or better) work with it, and that the real thing (Bridgeport) is much better. Tony Who is slowly learning the Pro/Desktop free computer aided solid modeling program (and it's pretty good for a free program -- and no, I ain't going to become a ME -- but I might buy a table top mill or CNC machine)

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