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Atlas 10F V42

Discussion in 'ATLAS, CRAFTSMAN & AA' started by timmeh, Jul 16, 2017.

  1. timmeh

    timmeh Australia isdownthashed. Active Member

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    On Saturday, finally got around to putting the Atlas back on it's screw jacks after rearranging the workshop a while back.
    On Sunday, power was out for a while, musta got bored, i dunno....



    Now I'll have to clean up reassemble. While its apart, I'll make some changes, do a bit of fixxy and get some better photo's of some previous repairs/mods.

    Already found something a little odd, Bolts/Holes for attaching feet to bed appeared to be 1/4"U.N. to me(Course for headstock end and fine for tailstock end).
    Closer inspection of the bolts says otherwise, with the course bolts measuring 6.75mm O.D. and the fine bolts at 6.7mm O.D.(1/4" is 6.35mm). The T.P.I. for the course bolts seems to match NC 20 but the T.P.I. for the fine bolts is nowhere near NF 28, maybe 26 T.P.I. not sure yet.
    Are these a special made by Atlas?
     

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  2. wa5cab

    wa5cab Downloads Moderator Staff Member H-M Supporter-Premium

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    Tim,

    I have no idea why anyone would have used coarse thread bolts on the headstock end and fine thread on the tailstock end. Unless it was wartime shortages. But my best guess is that the coarse threads are 1/4" BW or BSW (20 TPI) and the fine are 1/4" BSF (26 TPI). Why the diameter is a few thou over 0.250 I don't know. Can't be something like BA as 0BA diameter is 6MM and there is no fine and coarse. If you still have the bolts, check the width across the flats. BW bolt heads are larger than BSF which are larger than both UNF and UNC (which are the same). 1/4" BW hex head is 0.525" max. My 1943 Machinery's Handbook doesn't seem to list dimensions for BSF heads. There was once an A.S.M.E screw thread series with the #16 having an OD of 0.268. But the pitches listed are 22, 20, 18 and 16.
     
  3. timmeh

    timmeh Australia isdownthashed. Active Member

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    O.K. Have done a bit more ground work, definitely "off the shelf" or mass produced bolts. Confirmed that coarse thread is 20tpi and fine thread is 26tpi. Diameters are, as near as i can determine with a .05mm dial vernier, course 6.77mm(somewhere in the vicinity of slightly on the high side of midway between .266" and .267") and fine 6.71mm(a bees butt hair over .264")
    The hex headed bolt is 7/16 AF. I have come across a few oddball threads/diameters/pitches on fasteners and various components. I suspect you may be on the right track with wartime shortages, short on standard stocks and all that's available is specials(fasteners) for military purposes perhaps?
    It's possible that these sizes won't show up on a standard thread chart.

    Bit of a bummer, if one has a problem the next size up is 5/16, not a lot of meat left there after that.
     

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    Last edited: Jul 18, 2017 at 11:12 AM
  4. wa5cab

    wa5cab Downloads Moderator Staff Member H-M Supporter-Premium

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    7/16" across the flats of the hex head and 26 tpi and nominal 1'4
    ' diameter doesn't match anything that I can find. All that I can suggest is that if you have all of the original bolts, use them. If the problem is that you don't have enough of them, you have four choices. Locate and purchase 1/4" hex head BSF for the fine thread and 1/4"-20 UNC hex head for the coarse. Make the missing ones. Drill out and tap for a larger available size. Drill out and tap for a larger helicoil for some nominal 1/4" or 6mm diameter size.
     
  5. timmeh

    timmeh Australia isdownthashed. Active Member

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    I don't think 1/4" bolts would even take any tension in these holes, the coarse ones might tear the crests off. .014" to .016" is a bit much, no matter which way you might going on a fastener that size, i.e. clearance or interference.
    These fasteners are definitely mass produced and way to big for 1/4" threaded hole.

    One of the fine bolts here must not have been tapped right through(centre, at the end of the bed), has damaged the end of the bolt. A little troublesome coming out, more so going back in. It's in for now, but don't know how long for as I had run a 1/4" fine tap through the hole to clean up(OOPS) before checking sizes properly.
    Plenty of time yet to decide... fix one/fix all. Tis but a hiccup.

    Still, there is a lot to ponder. Why fine and coarse, why that way around(I would have thought vibration would have been more of an issue at the h/stock end)?

    Original plan was to fit some riser blocks between feet and chip tray/legs to give a little more clearance under the bed. Maybe modify the chip tray a bit to install a drain and catch can for oil and such.
     
    Last edited by a moderator: Jul 21, 2017 at 2:04 AM
  6. wa5cab

    wa5cab Downloads Moderator Staff Member H-M Supporter-Premium

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    I've never actually had my hands on an Atlas 10". only on several of the 1/2" way 12". What is the minimum thickness of the material that the tapped holes go up through? And are the holes approximately centered in it? The smallest bolt whose tap drill would probably clean up the 20 and 26 TPI threads would be 5/16"-24 UNF or M8-1.0.

    Are the rest of the threaded fasteners on the machine all either UNC or UNF?

    One solution if the web is too thin for the size of tap drill that would clean up the holes would be to step over about 1/2 inch and drill entirely new holes.
     

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