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  1. #1
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    Default Bernerd Model 34 4 Jaw Chuck - Face plate bolts?

    All,
    Went to mount my Bernerd 34 4 Jaw to a new backplate today so I could finally get it spinning on the Hercus 260.

    The chuck has some cross-head screws that bolt to the faceplate from the front of the chuck (I think its currently its mounted on a backplate for a 9" Hercus). I unscrewed them and looked at the thread - its not metric and I don't have a an imperial tap with the same thread.

    The bolts (more accurately screws) look specific to the chuck as they are an excellent fit to the face of the chuck when installed.

    Does anyone know what thread they will be so I can get the appropriate tap? They have a tad smaller diameter than M10 with a finer thread. Could they be a 3/8 UNF?

    thx
    Jon

  2. #2
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    Default

    If they are smaller by about .5mm they may be 3/8.

    If they are they could be UNF or even BSF.

    Check them with a thread gage.

    Are the bolts/screws at present Cap screw,not sure what you mean by cross head.

    If they are set screws it might be better to change them to cap screws,unless they are fitted screws.

  3. #3
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    Default

    Ok, a few photos to paint a thousand words

    The screw heads are a very close fit into the face of the chuck.

    I had thought about replacing them with M10 cap screws, but I suspect the cap screw head would end up proud of the chuck face - does this matter?

    A quick search suggests that an M10 cap screw head diameter is 10.0mm, so less that the 14.31mm of my existing screws - does this matter with regards holding the chuck snug and in place / controlling accuracy over time?

    The M10 shank will fit through the chuck, so thats good

    Certainly the easiest thing would be to replace with M10 cap screws. I don't have an imperial thread gauge or correct tap so that would be a bind. With the M10 cap screw, Id simply need to buy four.

    Thoughts and advice please.

    Thx
    J
    Attached Images Attached Images

  4. #4
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    Probably just use 1 3/4" x 3/8" UNF cap screws.

    Head size is just under what you measured.

    Length is measured from under the head,they may be around .030" longer than what you have now.

    If that plate shown in the photo is off a 9" will you have enough clearance on the PCD to suit the 260 back plate.

  5. #5
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    Default

    Quote Originally Posted by pipeclay View Post
    Probably just use 1 3/4" x 3/8" UNF cap screws.

    Head size is just under what you measured.

    Length is measured from under the head,they may be around .030" longer than what you have now.

    If that plate shown in the photo is off a 9" will you have enough clearance on the PCD to suit the 260 back plate.
    Funny you should mention about the PCD clearance, that was my first concern yesterday. I took the current backplate off and offered it upto my new 260 backplate to check - It will be a close call thats for sure and certainly isn't ideal. The Engineer in me says the bolts should have the largest PCD possible, but I guess it will either work, or i'll need to make an adapter plate that will pick up on the current holes and then bolt through from what would be the back of the 260 plate to the adapter plate.

    A bit more close looking required I think!

  6. #6
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    Apr 2009
    Location
    Boronia Australia
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    Default Screw details

    Hi
    Just looked at the pictures of the screws you have for that Burnerd chuck and they look very much like 3/8" Whitworth cheese head screws, very popular in the 50s for mounting chucks etc. Back then socket head screws were slightly rare and expensive and also tradition played a large part.

    To check what you have, change your vernier to inch mode and set the jaws to one inch try and place one point at the crest of one thread and count the number of crests to the next point if it is 16 then it is 3/8" Whitworth. If by chance it is something else you can still use the counting method and check against a thread chart (plenty on the net.) The main problem with cheese head screws, they are hard to tighten and you realy need an impact screwdriver.

    If you have to tap new holes in the backplate you can use what you like (personaly I try to keep metric away from imperial machines) However if your backplate is cast iron I strongly suggest using a course thread, UNC will interchange with most Whitworth form threads. Fine threads will crumble the iron unless there is plenty of penetration.

    I hope this helps you in your quest.
    Cheers
    Ray

  7. #7
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    Default Bernerd Model 34 4 Jaw Chuck - Face plate bolts?

    Thanks Ray,
    Great tip re thread pitch counting. I guess now you've mentioned it, it's kinda obvious but I would never have thought to do it!

    The general consensus I'm getting is that the close fitting 'cheese head' against the chuck isn't needed and therefore anything that fits would be fair game.

    That said I do like the look of those original screws. They suit the chuck and look like a 'proper job'.

    Ray,
    Assuming its 3/8 Whitworth, would this tap into Cast OK or are you suggesting I should use another thread, if so what?

    (Ps. You can probably tell I'm a LONG way from being an expert in this kind of stuff!)


    Thx
    Jon

  8. #8
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    Default thread

    Just checked a chuck of the same vintage, you will find they measure 3/8"X 20tpi with a 9/16" head. This makes them 3/8" bsf.

  9. #9
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    Thanks Mal,
    I have just checked mine. 20tpi, 9/16 head.

    Having confirmed its a 3/8 bsf thread, will this tap OK into the cast iron backing plate and what size hole should I drill? Will 5/16 be too small?

    Next thing, PCD... The PCD on the chuck is approx 70mm... Picture below shows approx 70mm on the back of the faceplate. If I drill through from the face rather than the back, it should be OK.

    260 Backplate.jpg

    Thx
    Jon

  10. #10
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    Default

    Tapping drill size for 3/8"BSF is P or 8.2mm.

    What thickness will the finished back plate be (not including the threaded boss).

  11. #11
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    Default Bernerd Model 34 4 Jaw Chuck - Face plate bolts?

    Quote Originally Posted by pipeclay View Post
    Tapping drill size for 3/8"BSF is P or 8.2mm.

    What thickness will the finished back plate be (not including the threaded boss).
    Thanks Pipeclay.

    Would 8.5mm be too big, or would it just mean marginally less thread contact but still be ok?

    With regards thickness of backplate. Currently I'd guess its about 12mm thick, maybe 15mm at the absolute most? I will need to reduce this by 2 or 3 mm to accommodate the interface with the recess in the chuck.

    The backing plate for my 3 jaw is probably only 6mm thick (on the outside) and that hasn't fallen off yet, so I guess I could take 5mm out of the new 4 jaw backplate if required. Does this relate to of it will tap ok or not?




    Thx
    Jon

  12. #12
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    Default

    If anything it might be better to drill at 8mm and hope the drill runs out a little rather than going 8.5mm or bigger if the drill does runout.

    I would try and keep the backplate as thick as you can if possible.

    If you drill the holes right through you may just cut into the threaded bore slightly,this shouldnt give you any great concerns as it will only be slight.

    The other choice would be to drill as deep as possible without breaking through and then flatten the bottom and then tap to suit.

  13. #13
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    Default

    End of another day... Thought Id give an update.

    The cast iron backplate that I have was WAY out of alignment with the centre of the thread. Im talking 2.5mm - 3mm of runout! Is this normal with these things in their raw state?

    I got the front face and length (??) running true and then set about machining the the lip in the centre to fit the chuck.

    I quickly got a nice fit and then set about thinking how to mark out the PCD and bolt centres, knowing they all had to be spot on.

    In the absence of any callipers and no way of precisely measuring the PCD I decided to turn up a bit of mild steel rod with a point on the end that was a precise fit in the bolt holes of the chuck that I could use as a centre punch.

    I did this and marked the holes. The first was a success, the other three got progressively bigger as the point collapsed - no where near good enough to use as a pilot hole marker

    Remembering something Id read about hardening and annealing (??) I recut the point and then got the MAP gas to it. Got it bright red and quenched in water, re-heated to a dull cherry red and quenched again. Im not sure if this is the right process, but it worked. I re-punched the hoes and each was much better than the first and the point remained intact on the punch. Success.

    Then, using a new 5.0mm Cobalt Drill in the pillar drill (again turning slow) I drilled the pilot, expanding with an 8.0mm cobalt.

    I started the 3/8 BSF Intermediate (Goliath) tap by hand in the pillar drill, then once started finished off with a tap wrench.


    Must admit I was somewhat surprised when all 4 holes lined up and threads started perfectly. It probably took me longer than it should have done, but Im very happy with myself!


    Tomorrow I need to set about removing the 2-3mm runout on the back face of the backing plate as it causes a horrible vibration at some speeds. The problem I have is that I can't get my tool post behind it and when I put the plate on backwards the face Ive just trued up is out by the same 2-3mm!!!


    (I think) My solution is this:
    Mount a short 30mm Diameter Mild Steel Bar in the 4 jaw (why - because I have some and it wont bend under load). Turn and face it.

    Remove the 4 jaw, leaving the 30mm stock in the jaws. Mount the 3 jaw to the lathe and insert the end of the 30mm bar in the 3 jaw.

    Face the back face of the 4 jaw mounting plate.

    I realise this is not VERY accurate, but I should be able to get it within 0.1mm - 0.2mm and eliminate the vibration.

    What do people think - Is this a wise thing to do? I can't think of anything better.

    Thanks
    Jon

  14. #14
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    That doesnt sound normal for the backplate.

    When you mounted the backplate to it sit square against the register on your spindle,did it go all the way home so as to not be able to see any clearance/daylight between the faces.

    When the spindle register is machined along with the thread the back face of the backing plate is machined at the same time.

    There should not be any real visible runout on this face,the chuck mounting face of the back plate could have runout.

    Where did you purchase this back plate from.

  15. #15
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    Quote Originally Posted by pipeclay View Post
    That doesnt sound normal for the backplate.

    When you mounted the backplate to it sit square against the register on your spindle,did it go all the way home so as to not be able to see any clearance/daylight between the faces.

    When the spindle register is machined along with the thread the back face of the backing plate is machined at the same time.

    There should not be any real visible runout on this face,the chuck mounting face of the back plate could have runout.

    Where did you purchase this back plate from.
    Thanks pipeclay,
    I thought the runout seemed excessive and wasn't at all what I expected.

    The 4 jaw chuck and backing plate both came with the lathe, in two parts, not machine and fitted. I think, putting 2 and 2 together from conversations with the seller that the chuck came from Mal, but I have no idea if the backing plate did or not. Perhaps it was a home made one? Certainly the thread isn't half as good a fit as the plate on the 3 jaw, its got some slop in it when threading onto the spindle, but once its home its rock solid.

    I'll take a few photos tomorrow and see if it looks familiar to anyone.

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