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Posted by on March 19, 2008, 7:09 am
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On 19 Mar, 10:34, jontom_...@hotmail.com wrote:
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> > On 19 Mar, 09:39, jontom_...@hotmail.com wrote:
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> > > > The holes in the lathe bed are bigger, and its a heavy lathe even
> > > > though only 3.5 inch, a Cromwell, not easy to get under the pillar
> > > > drill (until some B returns my engine hoist, and even then it will be
> > > > a challenge!). Maybe I can do with less bolting and use dowels for
> > > > location. While I have it I can guarantee the entire thing won't be
> > > > lifted by a sling around the bed, it can be lifted via the stand.
> > > > There can't be many forces on a lathe that try and bodily lift it from
> > > > the stand.
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> > > Steve
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> > > You haven't said if you are using a Cromwell stand but from memory I
> > > think the Cromwell was an underdrive design and therefore the bed to
> > > stand fixing is critical to drive belt tension and alignment. Without
> > > being bolted it will move about when running and the starting torque
> > > will tend to twist the lathe bed, while it may not move far it will
> > > certainly increase/decrease the belt tension.
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> > > When faced with mounting plate miss-match we would look to introduce
> > > an adaptor plate possibly 25-30mm thick between the two faces. If the
> > > drive belt goes through this mounting face then two strips front and
> > > back will do. This of course depends on getting access from inside the
> > > stand to attach the adaptor plate to the stand from below and will
> > > need the stand holes to be through holes. It would of course need a
> > > longer belt and increase the lathe height a little. My memory has
> > > failed me here as I have a very faint recollection that the Cromwell
> > > stand was a very heavy cast iron one with no/difficult internal access
> > > and if so then I would agree that An's suggested method of full depth
> > > plugging, loctite, re-drill and tap to match the lathe bed would be
> > > the best solution.
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> > > We would also have looked to see if we could move the lathe bed
> > > forward or back slightly (bolt diameter plus a little bit) to find
> > > virgin metal and refix to new holes but this could well be limited in
> > > your case by the drive belt path.
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> > > Enjoy the lathe, the later Cromwell particularly is a nice lathe.
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> > > Regards
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> > > Keith
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> > Thanks Keith,
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> > Yes its the Cromwell stand, which is a massive casting with precision
> > ground landing pads for the bed at each end. The underside is
> > accessible from inside the cabinet. The lathe would have to move too
> > far to put virgin metal under the bolt holes, it wouldn't look right
> > and would affect the drive belt alignment passing through the slots in
> > the bed to the motor underneath. So I am faced with moving threaded
> > holes in the stand by varying amounts, say from 20% to 90% of a
> > diameter.
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> > I am quite surprised that a loctitited-in blank will stay in place
> > when drilling a new overlapping hole. I would have thought there is a
> > risk of rotation. As they are through holes, I could plug the holes
> > with studding and use a nut underneath as a further resistance to
> > rotation. In fact I think that sounds the best way out - I expect I
> > can pick up a few feet of BSW studding easy enough.
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> > Thanks for all your input guys - think I have the answer.
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> > Steve- Hide quoted text -
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> > - Show quoted text -
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> Steve
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> It depends on the thickness of the stand really and I agree that if it
> is thin there will be a chance of rotation particularly if you are
> going to tap the holes as per the original. Plugs work best in blind
> or at least long holes although the further the hole has to be moved
> the better the plug will work. I have also used countersunk headed
> screws as plugs from the top so that when you re-drill - the remaining
> part of the countersunk head stops any posibility of rotation.
> Obviously you would need to countersink the stand before fitting. If
> you have easy access from below I might enlarge the closest ones (20%)
> in both stand and bed to provide the positive alignment (dowel) and
> then just redrill the others using a large load spreading washer and
> nut below. Whatever method you use, always use loctite to fit the
> plugs and nine times out of ten they will not move if you take care
> drilling.You will still need to plug when drilling to avoid broken
> drills. I'm not sure how you will use a nut below with the studding as
> your new holes will have to go through the nut as well?? A certain way
> to break drills/taps particularly as the typical nuts that come with
> studding are very loose fitting. As has been said if you can get the
> stand under a radial drill/mill head then a slot drill will work very
> well to move the holes, failing that plug the holes and re-drill with
> a normal drill. One thing to watch out for is that you end up with
> your lathe attached to plugs which themselves are held to the stand
> with very little metal so make sure your plugs are thinner than the
> stand. Much better to use the plugs to fill the hole and attach the
> lathe with bolts, nuts and large load spreading washers below. If you
> have the kit then you could always braze or silver solder your plugs
> into position if you don't trust loctite.
>
> Regards
>
> Keith- Hide quoted text -
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> - Show quoted text -
For those on Google I've removed my using a slot drill post because if
you don't have experience of the forces involved then using a slot
drill in a hand drill could easily end up with a broken wrist. Sorry I
will think harder next time.
Keith
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