Page 4 of 9 FirstFirst ... 23456 ... LastLast
  1. Quote Originally Posted by CNCUK View Post
    Ok thanks for teaching me somthing today!, i see the bronze bushings are not really an option then.
    Well they are always an option, but need to consider all aspects... see my reply to Robin for another major reason why not...

  2. #32
    Quote Originally Posted by irving2008 View Post
    It would need to be turned down from a solid 1.75" round and bored out to 1.25" approximately 3/16" offcentre. But then the castings would need to be line bored to ensure they are concentric and parallel with the bed
    It seems very odd that they would have bored the headstock off centre. If the tail stock does not offset, have you checked for signs of jiggery pokery? It may have a history which can be undone, making the replacement bush easier, but you'd probably want a shoulder to take the end thrust.

  3. Robin,

    If you look at the picture below you can see how much of an offset it is... the bearing itself is quite thick and is side spilt. The main reason it is thicker on the split side is because the spindle is keyed to retain the bullgear and when you extract the spindle the key has to pass through the bearing. To give a strong positive drive they wanted to use a fairly substantial key and that meant they needed the bearing to be thick enough to allow a slot for the key to pass through (you can see the slot to the left in the pic, just above the split in the bearing, out of focus tho). But to have that thickness all round would have made it difficult to pinch down without straining the casting, so they offset it in the casting. Thats easy to do with a poured bearing and meant the casting didnt need to be too accurate. I suspect they had a jig that clamped to the bed with a long mandrel with a built-in key and this allowed them to pour both bearings at once and in alignment..


  4. #34
    Why doesn't the metal around that offset bush look like cast iron?

    Is this the back end or is there paint on the thrust bearing face?

    Why is there paint inside the bearing?
    Last edited by Robin Hewitt; 09-06-2008 at 08:48 PM.

  5. Quote Originally Posted by Robin Hewitt View Post
    Why doesn't the metal around that offset bush look like cast iron?

    Is this the back end or is there paint on the thrust bearing face?

    Why is there paint inside the bearing?
    I don't know, but it is definately cast iron. This is the thrust bearing face and as to the paint... an overzealous repaint job sometime in the past. Obviously the bearing was shot already and I reckon paint got in through the oiler hole and spread around... who knows maybe it made it run smoother for some unsuspecting buyer... I do know that the guy who owned it before me had it 6y and never used it and it was already painted when he got it - this isnt a standard colour BTW, as standard they were painted hi-gloss black like this one:



    It going to be stripped right back and repainted black with gold or red detailing (just cos I fancy it)

  6. #36
    Is it possible this is a fixit bushing inside the original bushing? Suggest you remove the paint :D

  7. Quote Originally Posted by Robin Hewitt View Post
    Is it possible this is a fixit bushing inside the original bushing? Suggest you remove the paint :D
    Nope...here's a pic with the white metal bearing removed... and all nicely cleaned up. You can clearly see the anchor which stops the bearing turning in the casting.


  8. #38
    Okay :D If they never machined it it has to be cast :D

    You can't preheat the cast iron mould because you don want to detemper the spindle. You can't upend it and pour from the front because you can't remove the spindle to clean it up afterwards.

    Suggestions :D

    Get a lot more heat in the metal before you pour, howsabout barbeque charcoal.

    A deep well around the sprue so you can pour faster.

    A damp leather pad on a wood backing that you can put over the well. This is an old goldsmith's trick, steam forces the metal in.

    Consider cuttle fish bone to seal the mould and make the well. It is very easy to cut, lets the air out and doesn't burn.

  9. Quote Originally Posted by Robin Hewitt View Post
    ... You can't preheat the cast iron mould because you don want to detemper the spindle. You can't upend it and pour from the front because you can't remove the spindle to clean it up afterwards...
    I wouldnt have thought it would have been hot enough to detemper the spindle... Its been suggested it needs to be at 150degC or so, the bearing metal melts at 380degC-ish, neither of which are hot enough to detemper a steel spindle, agreed?

  10. Kip, while I've seen references elsewhere to line boring I don't have the facilities to do that. And I'm sure the old-timers didnt go to that lengths. Also I don't see how you'd ensure the mandrel was aligned correctly with the tailstock if its just a short length of plaster.

    Anyway I've found a local company in Watford that'll regrind the shaft by 4thou to bring it parallel and they quoted me 35 so hopefully I'll get that done this week and try again next weekend. I got some 2mm sheet ally and cut with my hole-saws two 2" washers with 1.25" centres and then took a 6mm hole in the top of each to act as air vents. This should be less likely to blow out. I'll seal the edges with fire-cement and clamp them across the bearing with a couple of small G-clamps.

    In the meantime I've swapped out the 1.1hp 1-phase Atlas motor I had for a 1.5hp AEI (c1965) 3-phase with a Jaguar VXS-75 VFD courtesy of eBay (75 the pair, bargain). I've also cleaned up and rewired the 0.5hp motor that came with the 3.5" Gamages lathe. This motor is proudly labelled 'The British Thompson-Houston Motor Co Ltd' and is very British in its heavy cast iron casing and gloss black finish. BTH became AEI in 1959 (and then were taken over by GEC in '67) but this motor dates from the late 40s or maybe early 50's and runs beautifully and silently.

Page 4 of 9 FirstFirst ... 23456 ... LastLast

Similar Threads

  1. CNC style lathe home brew Lathe for drilling and cutting.
    By Bodge in forum Lathes, Lathe Rebuilding & Conversions
    Replies: 9
    Last Post: 18-04-2012, 10:45 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •