Moving a hole in a casting, by half a hole

I would like to convert my tailstock lock from a nasty split clamp to a normal locking system. I need to enlarge the clamp bolt hole and
centre the new hole on the edge of the existing one (approx).
The old hole will probably be entirely absorbed by the new one. The new hole will of course have to break into the bore of the tailstock spindle too. Could I bore the new hole with a slot drill, or maybe start with a slot drill and then use a D-bit ?
Is there any general guidance on moving holes as I also have a lathe bed and cast iron stand which are mismatched, with most bolt holes from 10% to 90% of a diameter out (threaded in the stand). I have been wondering the best way to get around that.
Any hints and tips ? Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hi Steve, This is what I would do. Machine a plug preferably out of cast iron to fit the full length into the existing hole and loctite it in position. Then you can make the new hole in the position you want leaving part of the plug in place. With any luck the change will not be seen. Regards An
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On or around Tue, 18 Mar 2008 02:22:59 -0700 (PDT), Cheshire Steve

How big is the hole?
Slot drill has some merit if the hole's a fair size.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You could try a small boring head.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 18 Mar, 13:41, Austin Shackles

The existing tailstock clamp bolt is 1/4", so I expect the new hole to have to be at least 1/2", maybe 5/8"- will measure up more accurately tomorrow.
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 18 Mar 2008 17:28:57 -0700 (PDT), Cheshire Steve

You may want bolts for alligning?
--
Richard

Email address is valid but remove burrs before sending!
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 19 Mar, 09:39, jontom snipped-for-privacy@hotmail.com wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 19 Mar, 10:34, jontom snipped-for-privacy@hotmail.com wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 19 Mar, 10:34, jontom snipped-for-privacy@hotmail.com wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I had to move a 12mm hole over by half its diameter in the cast banjo on my lathe. The cast was about 18mm thick. Slot drill made short work, no issues at all.
Was it the right way to do it - dunno.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.