Drilling 1inch hole in 1.5 inch thick A36

Saw a recommendation for using an annular cutter for large holes in steel.

 
I would use a 1" diameter 2" long annular cutter, they work quite well and you can drill the hole in one pass. You need to run them at low speed (typically around 150-200 RPM for this diameter, but varies by material), use cutting oil, use continuous pressure when feeding, do not peck at the material. You want nice even strings of chips. I use a modified 3/4" end mill holder to hold the annular cutters, I drilled/ tapped two 90 degree holes for the cutter securing screws. The end mill holders are hardened, so my drill bit wasn't too happy.

287755
 
:grin: No , we all don't have 50 hp at the spindle , but what we try to give is advise .
I gave excellent advice, If the machine or process that one is using can not support sufficient feeds you will simply be rubbing the tool on the work.

This always ends in tears.

Slow down the spindle speed to the point that the tool will cut with the feed that you are able to apply, this may take a good deal of time however.

Patience is a virtue, stopping the operation many times to either change or sharpen tools is slow at best.

Good Luck
 
Final result for those still watching.

I couldn’t get enough power for 1 inch...got up to about 7/8th. Took to local machine shop and he knocked out for me no charge. The rest I could get on my lathe and they drilled easy enough.
 
developing an ear/ eye for these things is a good idea. You're after a nice spiral chip. If you get alot of shuddering and small flakey chips, slow down the spindle speed and/ or increase the feed (probably both to begin with). If you can't slow down the spindle, increase the drilling pressure. If you still can't get a nice spiral chip, you're SOL on that machine. One thing I would caution about, and this is from someone with light duty machines, is step drilling in too small steps - 1/8" step at a time is the minimum I would use or you'll be busting the tips of the corners of the drill and maybe getting the drill chattering as it doesn't have enough material to "bite" into. Holesawing is an option, but I doubt you'd be able to go slowly enough if your minimum is 300rpm. Likewise with annular cutters, which are even less tolerant of flexy machines in my experience. I drilled a 1" hole 2 1/2" deep into some stainless (400 series?) over Christmas and that took a looong time on my 6x26 mill, step drilling up from 1/2" to 1", though I can't remember the steps I used. Lots of cutting oil, 60-100rpm speed, need to touch up one of the S&D drills.

I do find it funny reading the advise of those with industrial machines. Drilling a 1 5/16" hole in one go on a Warner Swasey turret lathe (4-5000lb? 10hp+?) is VERY different to drilling a 1" hole on a light home shop machine. I'd love to drill a 1 5/16" hole in steel on my Atlas 618 in one go, but it just ain't gonna happen.
 
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