Boring head

[John Conroy]

Any chance there is something hard in the casting that pushed the drill bit off center? A broken bolt for instance?

 

[ChazzC]

My process
Mill a flat
Spot drill with drill held very short in er collet
Drill with twist drill the same as the larger diameter or the spot drill
Drill up to final size
Start to bore for counter bore
Now I need to find what went wrong.
Gary

Good process, but if you're milling a flat anyway, why not just use a mill the size of the counterbore you want? Then spot, etc.

 

[Garyt]

OK I found the problem.
Some how the hole ended up off center.
I checked all the runouts and no real answer so I put a end mill that was as close to the finished hole size in the er and surprise surprise the pilot hole was off center. Now, can I save the casting? Maybe but it is my number 2 casting that I had planned to make mistakes on. So far so good one operation one mistake.

 

[Mcgyver]

lol, it can only get better.

One way to save it is to plug the hole and re-machine it. Bore it out oversized, and turn a close fitting plug of the same material, use cylindrical retaining compound to cement in place and file in the profile. If you want to get fancy, machine all the features you want in the plug before cementing in place.

 

[ChazzC]

OK I found the problem.
Some how the hole ended up off center.
I checked all the runouts and no real answer so I put a end mill that was as close to the finished hole size in the er and surprise surprise the pilot hole was off center. Now, can I save the casting? Maybe but it is my number 2 casting that I had planned to make mistakes on. So far so good one operation one mistake.

Finding the what is good, just need to figure out the why to prevent repeating. We all are constantly learning.

Now, to salvage the casting. I don't know what this particular SHCS will be doing, but assuming it is one of several attaching screws, I would do this:

​

Finish boring the counterbore (you're already setup and you have the offset through hole).​

​

Cautiously mill the through clearance hole in the correct location; the end mill will want to wander, but as it is Aluminum, if you go slow you should be OK.​

​

The clearance hole will be a mess, but the counterbore and other screws will locate the part properly in relation to what it is being attached to.​

​

Mods: we have to get the photos issues fixed: as @YYCHM noted, you can view the attachments, open in a new tab/window and also can't download them.

 

[Garyt]

As i said this is number 2 casting designated to be the recipient of (hopefully) all my screwups. Then i can do number one perfectly.
Thanks for all the help and attention
Gary