Correcting pilot error

This topic has 11 replies, 9 voices, and was last updated 16 May 2011 at 18:19 by David Haynes.

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15 May 2011 at 08:59 #68501
David Haynes
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@davidhaynes53962
Hi folks,

Although I thought the centre pop was correct, I now find that the 1/8″ pilot hole does not quite lie on the intersection it should do. Final hole will be only a little bigger at 1/4″ dia. It will then be bushed and reamed. Not a lot of room for correction but any suggestions would be welcomed.

Thanks, Dave
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15 May 2011 at 08:59 #5515
David Haynes
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@davidhaynes53962
Correcting a pilot hole not correctly located
15 May 2011 at 09:19 #68502
Dusty
Participant
@dusty
David

If you have a milling machine or acess to one, then you could try setting it up with the hole in the correct relative position and use a 4mm slot drill to pull the hole into the correct position. This will not work with a drilling machine as it is not rigid enough and you need to be able to feed slowly, feed to fast and the slot drill will want to follow the original hole. This works best if the slot drill is new, an old blunt one is doomed to fail. By using a 4mm slot drill you have two more chances at correcting it with 5mm and 6mm slot drills. The other alternative is to set up in the 4jaw and bore it or use a slot drill in the tailstock.
15 May 2011 at 09:26 #68503
Les Jones 1
Participant
@lesjones1
Hi Dave,

The fact that you are marking out and centre popping makes me assume that you do not have a milling machine. If you did I would suggest using a slot drill. Assuming that you only have a drill press I suggest drilling a 1/4″hole in a piece of steel (Silver steel and harden it if possible.) and clamp this to the original piece of metal so that this will guide the drill to the correct position. More information would help other people to make suggestions. For example what equipment you have, the material you are drilling. the depth of the hole (And is it a blind hole.)

Les.
15 May 2011 at 09:41 #68504
ady
Participant
@ady
If you put the slot drill into a chunky 4jaw on a lathe and bolt the workpiece to the saddle, tighten the saddle gibs right up when you are happy with the drilling position then feed in nice and easy with the leadscrew. I usually peck drill.

A Slot drill is definitely the way to go.
15 May 2011 at 10:31 #68505
JasonB
Moderator
@jasonb
Posted by David Haynes on 15/05/2011 08:59:15:

Hi folks,

Although I thought the centre pop was correct, Thanks, Dave

You should really dot punch first and inspect the mark to make sure it is correct before centre punching, if its not right then a light dot punch mark can be adjusted by tilting the punch and hitting again.

If you can’t straighten it with a slotdrill then drill it to suit your bush but drill and ream the bush once it is pressed or stuck in position. In effect an eccentric bush

Jason
15 May 2011 at 13:36 #68515
mgj
Participant
@mgj
Would it be possible to weld (mig ideally) fill, or silver solder fill and just start again.

You haven’t specified what the object is, but if its feasible, adding metal for a fresh start is often a better solution than trying to take it out.

Sometimes, if strength is an issure, then a rough old screw thread carved in there will give a mechanical lock too- for SS or even loctite.(bush). Weld of course it will all be melted anyway.
15 May 2011 at 13:37 #68516
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
Loctite a pin of the same material into the hole , file flat , re mark out and re drill . Chose a drill size which is a little larger than previous pilot drill so that it effectively drills out the pin and leaves a new pilot hole in clean metal .
15 May 2011 at 18:34 #68536
David Haynes
Participant
@davidhaynes53962
Thanks for all these respnses. The fault is in a 1/8″ thick flange on a gunmetal motion plate. I have a drill press and lathe, 3 and 4 jaw and vertical slide (for which I now recognise the limitations for milling!)

Thanks

Dave
15 May 2011 at 18:42 #68538
Nicholas Farr
Participant
@nicholasfarr14254
Hi David, in which case I’d go for Micheal’s idea with the Loctite and pin, and then heed Jason’s advice about the dot punch.

Regards Nick.
15 May 2011 at 19:24 #68543
John Baguley
Participant
@johnbaguley78655
Why not simply draw the pilot hole over to the required side with a round needle file, then redrill with a slighty larger drill. Check again and repeat the process as necessary until you are happy. That’s the usual method quoted for correcting an off centre hole.

John
16 May 2011 at 18:19 #68626
David Haynes
Participant
@davidhaynes53962
Thanks all, I opted for drifting the hole and following up with slightly increasing diameter drills. The job is now spot on and no fussing about adhesive, filing or remarking.

Thanks again

Dave
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