Colchester chipmaster lathe adjustment

  1. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Hi
    BS
    So its where the backplate fits into the recess in the back of chuck that gives it the precision, I think I've got it - maybe.:D

    Cheers
    Andy
     
  2. brightspark

    brightspark Member

    Messages:
    30,698
    Location:
    yarm stockton on tees
    yes maybee your 3 jaw chuck could possibly be ok and its just the backplate that needs replacing and chuck re mounted . if u want to see how acurate the chuck is mount it in a 4 jaw chuck on your lathe clock it up with a dti on the outer edge till acurate. put a bit of ground bar or silver steel in the 3 jaw and clock that up with the dti and see what run out u get if its marginal the chuck will be ok , if its a mile out bin it and buy new, it should only be a few thou out if it isnt worn
     
  3. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    That sounds like a plan BS :D

    I'll take the crappy backplate off and dust off the 4 jaw and see if how it goes.

    Cheers
    Andy
     
  4. Geoffm Member

    Chippie is a good lathe (at least when new-ish). Mine has seen plenty of life - replacing the Kobb variator with a VFD was a big improvement, as the variator was so loud before it died (although it took 10 years).
    My father in law had trouble with his 1970s Taiwanese lathe with a worn crossslide screw. - the standard one was mild steel and worn out. I got some 414. hardened and precision ground threaded rod (it was reverse thread) from MSC in the US - it was pretty cheap as I recall - about $NZ100 (UKP50ish) landed 10 years ago. He replaced the original threaded bit on the cross slide screw with a new piece, adjusted the nut and it was a big improvement. Not perfect but much better, and certainly cheaper than Colchester parts.
    Geoff
     
  5. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Cheers Geoff
    I'll look at the cross slide next after sorting the chucks out, along with the lathe I got a full set of screwcutting gears 5 chucks (some knackered), 2 faceplates and assorted tooling for less than £400 delivered. I've swapped the motor and added a VFD for about another 400 quid so £800 in all. If I have to spend another 400 on a decent chuck and some other fettling then I think it will be worth it. see here for my VFD conversion

    Here's the original test docs that came with the lathe in 1959, somehow I don't think i will get back to this kind of precision!

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    Cheers
    Andy
     
  6. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Well I gave it a go today.

    First I checked out my collet chuck, I don't have a ground bar so had to do with some 7/8" bright steel bar so cannot take these figures too seriously, however gives and indication.


    it clocked about 3 thou on the edge of the chuck and about the same on the bar near the chuck and about 8 thou 4" out from the chuck. Could be the bar. The chippie is all curves so difficult to find somewhere big and flat to put the DTI
    [​IMG]

    The dismantled the bodged backplate on the 3 jaw.
    [​IMG]
    [​IMG]
    Look like they have tried to fit a 125mm backplate to a 160mm chuck
    [​IMG]

    I mounted the chuck the best I could in the 4 jaw, got about 5 thou at the edge
    [​IMG]
    [​IMG]

    On the same bar near the chuck I got about 5 thou and at 4" about 14 thou

    Its definitely much better than the Bernerd 3 jaw which is 20 thou near the chuck and 50+ at 4"

    Cheers
    Andy
     
  7. Pete.

    Pete. Member

    Messages:
    9,479
    Location:
    Kent, UK

    There's some of your problem right there. Remove those pins and scrape that face clean with a stanley blade. Camlock chucks register against that face and on the small taper - they both have to be spotless.
     
  8. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,536
    Location:
    East Yorkshire
    You need to put the mag base on the bed, otherwise you are also measuring the saddle
     
  9. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Cheers Dave

    I couldn't get the cheapo mag base to stick to the bed as it only covered about half the width of the base, next time I'll clamp it some way, its all curves so not easy.. I had an hour window before I had to look after the kids so took the easy route but I see what you mean. However the spring on the DTI is not very strong so probably a reasonable indication.

    I'll scrape all the chucks and the mount on the lathe as Pete suggests and give it another go,


    Andy
     
  10. hareng Member

    Messages:
    1,497
    Location:
    Wolverhampton
  11. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,536
    Location:
    East Yorkshire
  12. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Bought an 160mm D1-3 backplate from RDG tools and a length of 22mm ground silver steel bar, should have time over Eater to get the chuck etc. sorted. Then on to the tailstock and crossslide.

    Cheers
    Andy
     
  13. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Time for an update, first I thought I would have a third attempt at fixing the annoying gearbox oil dribble. The fist time round I changed the O-ring on the lever that controls threads or feeds. This had gone crispy and leaking. This sits in it own housing to the left of the gearbox.

    The shaft is 12.65mm diameter and the diameter at the recess where the O-ring sits is 9.47mm. It is supposed to be an AS568/BS1806 dash 012 size which is 9.25 internal diameter and 1.78mm section. This seemed to fit, not much interference though, the next common size dash 110 at 9.19 ID and 2.62mm section just wouldn't allow the shaft to fit back in - far too big.

    Anyway the sodding thing leaked again but this time was coming from the o-ring on the main gearox drive shaft, this was crispy too. So dismantled again, you have to take the housing apart to get to the circlip to get to the drive shaft o-ring.

    Back to together, seemed OK. This was becasue it takes a while for oil to seep back into the housing. Yes it was leaking again from the lever, probably never stopped and was masked by the bigger leak.

    So I took it apart again, looked at the next size up O ring across all the various standards and none seemed to be that little bit bigger than dash 012 but smaller than dash 110 imperial O-rings.

    Polymax to the rescue, they do non-standard O-rings on line. I had to buy 20 but I am sick of taking it apart so bought some nitrile (NBR) 9mm ID 2.0mm section rings and this seems to fit so much better, in theory only 0.19mm OD bigger depending on manufacturing tolerences, and stretch when on the shaft but if they work then its worth it.

    The housing is half way up on the right, just behind/below the aluminium pulley, you can see the the lever with the white ball sticking out.

    [​IMG]

    The o-ring I used this time is in the centre with dash 012 on the right and 110 on the left.
    [​IMG]

    Here's the shaft in the housing, just need to put the roll pin back in and I can reassemble. Fingers crossed.
    [​IMG]

    Also been looking at the lathe's precision again. I've used the bed to mount the mag base this time. Its tricky but just reaches.
    [​IMG]

    Checked the chuck mount and the collet chuck first, they seemed fine
    [​IMG]

    However the bit of 22mm ground steel bar seems worse than my standard round bar close to the collet chuck and at 100mm. Going to investigate why first, its a short length cut on a guillotine so maybe bent. I don't have a surface plate so I'll find something else to check it with.

    Cheers
    Andy
     
  14. ronan

    ronan Forum Supporter

    Messages:
    9,996
    dublin
    Rdg and the other model maker engineers suppliers do lathe test bars, they aren't too expensive, around £40 i think.
     
  15. MattF

    MattF Member

    Messages:
    10,432
    Location:
    South Yorkshire, England
    An old printer is another good source for a test bar. The round rod which the printhead runs on is precision ground and has to be within a tight tolerance on the amount of run out allowed, for obvious reasons, so makes a good and cheap solution.
     
  16. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Cheers guys, I do have an old A3 inkjet that has seen better days. I have some fine sawn yorkstone slabs, about 3" thick - I wonder if they'll be flat enough to test the bit of ground silver steel I have? - I'll give it a go, nothing ventured etc.
     
  17. scott0031 Member

    Messages:
    1,054
    England Kent
    A bit of silver steel is as good as any, centreless ground and ample for the job.

    By the way, ensure you still seat things properly even though its a collet. Do up until the bar is a slide fit then nip up until it partially grips rotate and slide in and out a small amount this helps make everything seat properly. Its still not uncommon at all to need clock the bar and give it a gentle tap about. This will need to be done really to test accurately. Collets are not fool proof.



    Kind regards,


    Scott
     
  18. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Thanks Scott, I took it apart, cleaned the collet and tried it several times and it was repeatable, the bright bar seems better than the ground steel bar.

    I think the mystery is resolved. It's a 7/8" collet, and the two bars, brights steel and ground silver steel are the metric equivelent i.e. 22mm. 7/8" converts to about 22.225mm, the bright steel bar is almost spot on this however the ground silver steel has been ground to almost exactly 22mm. So my hypothesis is the collet is gripping the bright bar truer, whilst the collet is not gripping the silver steel parallel.

    I bought a 4 jaw D1-3 125mm self centreing chuck from RDG last week and I get about 3 thou variation on the silver steel bar at 100mm so I think that's good enough for a 50 year old lathe?

    I only have a few moments per evening at the moment as I'm getting hitched next Saturday and we are having the reception at the farm so we have loads to organise. I'll do something more scientific when the nuptuals are over. I have checked headstock alignment yet.

    I got the feed/thread selector housing back on last night, will fill her up with oil today as soon as I locate the modified funnel I use. (the lathe not the fiance!)

    Regards
    Andy
     
  19. brewdexta

    brewdexta Forum Supporter

    Messages:
    3,941
    Yorkshire
    Its only been 18 months, finally got back to this problem and your right Pete, its where the cross-slid screw is anchored, I had a quick butchers last night. Not sure when I will get chance to take it apart and try and find where I can shim it.

    Here's the diagram and parts list, this time from the manual that came with the lathe this time so same model/version ;)

    cross slide anchorage.jpg

    cross slide anchorage parts list.jpg

    Cheers
    Andy
     
  20. Fintray

    Fintray Forum Supporter

    Messages:
    781
    Location:
    Aberdeenshire (UK)
    "I'll do something more scientific when the nuptuals are over."

    That must have been some session.................:clapping:
     
    brewdexta likes this.
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