Drilling cast iron?

[PedroOhare]

So when I drilled the holes to mount my Kreg Bandsaw fence to my 14” Delta clone. I thought the fence rode in the slots on the mounting bar not above it. That means my fence rides too high. Looking at the Kreg Bandsaw fence manual, it says to drill two ‘overlapping’ holes and us a file to enlarge those into a slot. Yeah, I should have read the manual before I drilled the holes. However, that may save my bacon as I was planning on moving the holes over and just shifting the fence. I have been hesitant to do that, since the holes are now centered on some ‘flats’ that are obviously meant to be mounting points.

My question is, is it reasonable to be able to drill a second ‘overlapping’ hole? I have always thought that drilling overlapping holes will lead to run out and bit wandering which could really mess up the whole thing. I guess I could take the table off and bring it to my drill press and clamp it securely, but I am hesitant to do that. The other choice is to take a round file the appropriate size and just elongate the hole with that. Sounds like a lot of filing to me.

Any recommendations?

Thanks

Edited to add that now that I remember, I actually drilled and tapped the original holes to use bolts hold directly to the table rather than through bolts and nuts as Kreg instructs. So I will have to redrill the first hole anyway. Does that make it easier or harder?



Pedro

[fredhargis]

You can drill overlapping holes if you use a "bullet point" bit (think "brad point" but for metal). Of course there has be enough overlap. When you say you need to re drill the original holes, are you making them larger?

[daddo]

You can clamp the work down firmly on the drill press, lower the bit right where you want it, then raise the bit and clamp a 3/16" thick scrap piece of flat metal on top of that and then proceed to drill it out. The upper scrap metal will help guide the bit if you don't drill too slowly- use a sharp bit.
You can (and should) first drill a 1/8" pilot hole to make the whole experience more pleasurable.

Use a good bit! An unevenly sharpened bit will wander and chatter- then you'll blame me for it. lol

[rlnguy]

In my experience, drilling a "half hole" in metal is pretty "iffy".
Cast iron files pretty easily.
I'd either file it-chain saw files, work well, and come in different diameters, or I would use a 1/8"carbide burr, in a Dremel type tool.
Of course, you have to nibble at it, (kinda like using a pocket knife), lest the bit grab, and rattle in the existing hole.

[Tony Z]

I would get a drill guide bushing, insert into a piece of wood per instructions, clamp well over where the second hole is desired and then drill.

[castguy2003]

I would get a drill guide bushing, insert into a piece of wood per instructions, clamp well over where the second hole is desired and then drill.

Ditto to Tony, 
Fifty years in the metalworking trades.

[BloomingtonMike]

Id try a bottom cutting endmill. A drill bit will want to wander.

[mike4244]

So when I drilled the holes to mount my Kreg Bandsaw fence to my 14” Delta clone. I thought the fence rode in the slots on the mounting bar not above it. That means my fence rides too high. Looking at the Kreg Bandsaw fence manual, it says to drill two ‘overlapping’ holes and us a file to enlarge those into a slot. Yeah, I should have read the manual before I drilled the holes. However, that may save my bacon as I was planning on moving the holes over and just shifting the fence. I have been hesitant to do that, since the holes are now centered on some ‘flats’ that are obviously meant to be mounting points.

My question is, is it reasonable to be able to drill a second ‘overlapping’ hole? I have always thought that drilling overlapping holes will lead to run out and bit wandering which could really mess up the whole thing. I guess I could take the table off and bring it to my drill press and clamp it securely, but I am hesitant to do that. The other choice is to take a round file the appropriate size and just elongate the hole with that. Sounds like a lot of filing to me.

Any recommendations?

Thanks

Edited to add that now that I remember, I actually drilled and tapped the original holes to use bolts hold directly to the table rather than through bolts and nuts as Kreg instructs. So I will have to redrill the first hole anyway. Does that make it easier or harder?



Pedro

First drill thru the threaded holes to the size recommended. Then drill next to the first hole lapping it buy about 1/3. This will leave you a point that is easily filed. A Dremel tool may come in handy to clean up the slot instead of filing. Cast iron drills and files easily.
mike

[Wizard of Oz]

I'm with Mike, use an endmill in a drill press. Or contact me, and I could have it done on a bridgeport for ya. I'm down in Janesville, Wi.

Oz