3-5/8" holes in 18" 300# blind flange 2

[jcmech]

I am trying to develop a method for boring 3-5/8" holes in carbon steel blind flanges, 18" 300# is the thickest flange that we could possibly fit on our machine. I am thinking about using a two stage method by which we would bore a 1" hole, then change bits and finish up with the 3-5/8" hole.
However it will cost a couple of bucks to buy these additional bits. It would be helpful if there is anyone out there who has done something similar. Any ideas?

 

[unclesyd]

If you hole requirements will allow it you might want to use an annular cutter, otherwise your approach is fine. Depending on the HP of you machine you may have to look at a different sizes of drill bits.

http://www.hougen.com/cutters/hd_industrial/hdindustrial_cutters.html

 

[tripleZ]

Spade blades by chance? Kennametal makes them, as does an outfit out of Ohio. 3-5/8" should be in the vicinity of Kennametal's 7D8 variant. Blades are T15 tool steel, 65-67 HRC, and can be coated (TiN, TiAlN, TiCN, etc). The tool holder is usually what sets you back a pretty penny, but after that initial investment it's just blades. Changeover times are pretty quick (2 flathead screws) and positional tolerance is repeatable.

If you want to cut the part twice, I believe the 7D5 variants and 7D8 variants use the same holder.

Wear might be an issue, so I guess it all depends on how many holes you have to drill. The blades aren't cheap, but they're cheaper than buying drills. If you're looking for a large volume of spade blade bits, contact the Kennametal office in Rockford, IL. They grind the spade blades there, and also will do some custom variations if you need them.

 

[jcmech]

unclesyd,

Thanks for the link....
What do you mean by 'if your hole requirements allow it'?
Does an annular cutter give poor tolerance?
Tolerance is not really an issue, as we are welding 3" pipe into these holes.

 

[unclesyd]

That is what the annular cutters were originally made for.
The holes in fact are pretty good.

Reason for asking: I assumed that what you were going to do but I thought I would ask as I have seen call out for such holes that would require reaming to the achieve the dimensions on the print even though they would be doing the same as you.