Drilling in thick steel- Table saw side

[Jack01]

I am installing sliding table for Delta Table saw, unfortunately  the holes on sliding table to not aline with table saw holes

So I need to drill two 5/16 holes in 1/4 thick steel

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What is the best to drill it - also it need to be straight, do I need a jig

[Hank Knight]

Your saw table is cast iron which is very easy to drill with a standard twist drill bit. Take your time and use the slow speed on your drill. You don't even need any cutting oil or lubricant. It taps easy too with a hand tap. Again, no lubricant needed. I've done this several times and never used a jig. Be careful to line the bit up square and have at it.

[fredhargis]

What Hank said: it's easy to drill cast iron. I would get a quality drill bit, nothing from Harbor Freight.

[Robert Adams]

Yup just cast iron any drill but will do even ones from from the dollar store. It's more like drilling hard graphite than anything else as it has lots of carbon in it that will lubricate the bit and tap as it cuts. I have even drilled cast iron with wood type drill bits, the ones that look like a regular drill bit but the flutes stick out from the shank.

[AgGEM]

Your saw table is cast iron which is very easy to drill with a standard twist drill bit. Take your time and use the slow speed on your drill. You don't even need any cutting oil or lubricant. It taps easy too with a hand tap. Again, no lubricant needed. I've done this several times and never used a jig. Be careful to line the bit up square and have at it.

I THINK the OP wants to drill the slider, not the saw.
1/4 steel is not thick.
Center punch and drill.
I would use a smaller pilot bit to ensure the 5/16 finish bit does not wander.
But, that is not necessary. Just nice.
Ag

[Steve N]

I wasn't sure. I know cast is easily drilled. I also know once drilled if close to other holes it makes the area weaker, and breakage can occur. If it were mine to do I would definitely drill the 1/4" steel slider. Using a set to dimple the steel so you don't get wonder, best on a drill press, but can be done on a slow turning hand drill. As with the cast using a good bit always increases the odds of a clean, trouble free hole. I oil a drilling, some on 1/4" may not. Go for it........

[JGrout]

I think the two sharpie boxes in the pic  are where the attachment mounts. 

I know I would be drilling the cast over the slider although I would align one of the existing holes and drill just one new hole. 

Joe

[ez-duzit]

The proper way to drill a precisely located hole, in heavy steel, is to first center punch, then use a center drill, followed by a sharp finish drill.

https://www.midwayusa.com/product/459312...peed-steel

[regdor1999]

The proper way to drill a precisely located hole, in heavy steel, is to first center punch, then use a center drill, followed by a sharp finish drill.
https://www.midwayusa.com/product/459312...peed-steel

Oh man, thank you for posting that! I have quite a handful of those from an machinist estate sale lot and couldn't figure out what they were. At least I think that's them... There are a lot of little end mills, too, so I'll have to look closer. And drill bits. It seems like the guy had more drill bits and small taps than a small hardware store.

[ez-duzit]

99--you're welcome.

The center drill is short and stubby, so it won't/can't flex (or worse--break off in the hole) and mis-locate the pilot hole.