Re: Moving a hole in a casting, by half a hole

On 19 Mar, 10:34, jontom_...@xxxxxxxxxxx wrote:
On 19 Mar, 09:44, Cheshire Steve <oldnoc...@xxxxxxxxxxxxxx> wrote:





On 19 Mar, 09:39, jontom_...@xxxxxxxxxxx wrote:

On 19 Mar, 00:28, Cheshire Steve <oldnoc...@xxxxxxxxxxxxxx> wrote:

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.

Steve

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.

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.

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.

Enjoy the lathe, the later Cromwell particularly is a nice lathe.

Regards

Keith

Thanks Keith,

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.

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.

Thanks for all your input guys - think I have the answer.

Steve- Hide quoted text -

- Show quoted text -

Steve

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 -

- Show quoted text -

Steve

One thing I forgot to mention is that (when in dire need) I have used
slot drills in a normal hand drills (variable speed is best) to move
holes. Drill a fairly thick bar with the appropriate size hole for the
slot drill and clamp into position over the new hole position. Use
this as a guide for the slot drill to machine out the new hole. A
warning though the guides don't last for many holes and be prepared
for a chipped slot drill. Do not try to use without the guide but you
won't need to ask how I know that one :-))

Keith
.

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