Best tool ok to enlarge stainless hole

[C08]

I have 4 9mm holes through stainless box section 100x100 mm and 4 exit holes on the other side. The 304 is 4.8 mm thick. The holes do not quite match up with the fitting to bolt to the box section. These holes are only clearance for 8 mm bolts. What I should have done is just put 10mm or 11 mm drills through but that is very heavy going with a handheld drill and 4 of the holes are on the underside of the box section so drilling upwards and extra hard.

Anyway I tried to just move the 9 mm drill around in the hole and that was mildly successful in creating a little ovaliy perhaps to 10mm but still a not enough. The consequence of the ovality is that a bigger drill is not an option now.

What tool or drill attachment is best for this. I have tried Dremel points grinding stones without any success. I thought perhaps a chainsaw sharpening attachment would do. Any better ideas?

 

[colind3782]

Step drill bit?

 

[garvellachs]

I have 4 9mm holes through stainless box section 100x100 mm and 4 exit holes on the other side. The 304 is 4.8 mm thick. The holes do not quite match up with the fitting to bolt to the box section. These holes are only clearance for 8 mm bolts. What I should have done is just put 10mm or 11 mm drills through but that is very heavy going with a handheld drill and 4 of the holes are on the underside of the box section so drilling upwards and extra hard.

Anyway I tried to just move the 9 mm drill around in the hole and that was mildly successful in creating a little ovaliy perhaps to 10mm but still a not enough. The consequence of the ovality is that a bigger drill is not an option now.

What tool or drill attachment is best for this. I have tried Dremel points grinding stones without any success. I thought perhaps a chainsaw sharpening attachment would do. Any better ideas?

I would use a round file - but make sure it is a good one, not a weak-willed cheap one.

 

[Yellow Ballad]

Step drill bit?

+1

 

[thegasmannick]

+1 step the best way to get a neat hole

 

[neil_s]

If I understand your problem - you don't need to enlarge the holes all round, just 'move' them along a bit. I'd go with the round file.

 

[rogerthebodger]

If I understand your problem - you don't need to enlarge the holes all round, just 'move' them along a bit. I'd go with the round file.

That's how I would also do it especially when the stainless is 4.8 mm thick.

Step drills are generally only for thin sheet metal.

 

[vyv_cox]

Contrary to expectations and some forum advice, hacksawing and filing stainless steel is no more arduous than the same in mild steel. I have hacksawed my prop shaft several times, not difficult. So I would most certainly file the holes larger in the preferred direction. Nice new file preferred.

 

[Heckler]

Contrary to expectations and some forum advice, hacksawing and filing stainless steel is no more arduous than the same in mild steel. I have hacksawed my prop shaft several times, not difficult. So I would most certainly file the holes larger in the preferred direction. Nice new file preferred.

Nail on head, ive never understood the reluctwnce to use hand tools on SS

 

[Norman_E]

A decent quality round file will do the job as others have said. I recently needed to move and slightly enlarge a hole in some 4mm stainless and the only file in my boat toolbox small enough was a very fine toothed chainsaw sharpening file, which did the job surprisingly easily. Steady strokes with some pressure using as much of the length of the file as possible are the way to go.

 

[Daverw]

You’re unlikely to work harden with a file so with a good sharp file will not be that difficult

 

[lw395]

A file will do it fine. If you want to use a power tool, then a carbide burr is effective.
A 'rotary' file in a power drill might be good, if you can find one of good quality.