Reaming out holes in thick steel?

[mikefamig]

An adjustable reamer and a lot of patience?

 

[tlharris]

I want to enlarge four 13/16" holes in 1/2" thick steel to accept 7/8" pins. This on a piece of equipment so I have to use a hand drill. I happened to have a 15/16" black oxide bit, not too surprisingly that doesn't work at all. In 10 minutes I only penetrated about 1/8" in one hole. So I need to decide between buying an $80 construction reamer (high speed steel, manufacturer says it is OK for stainless) or pick up a 29/32" cobalt drill for under $50. I'm guessing the reamer would work better even though it is softer. Is that correct?

The difference between a reamer and a drill is the difference in the cutting edge length.

When you try to enlarge an existing hole with a drill, you're only cutting on the very tip of a sharply-angled and brittle cutting edge. This is why it will want to grab, and is prone to fracture.
In contrast, the long taper on a reamer means that there's much more cutting edge engaged, meaning it's way less likely to catch, and each cutting edge is only trying to take a very light cut. In addition to being easier, more dependable and safer, you'll end up with hole that's much more accurate/round.

 

[MF1045]

You mentioned the reamer was ok for stainless. Is it stainless your working on?

 

[eddieirvine]

I am not there or know how you attempted to drill the 7/8 hole, I am going to say you ran the bit way to fast and work hardened your hole. When you try to enlarge a hole it is hard to do with a hand drill but as in your case no choice. when i say slow i mean really slow and it can be done. one other thing you can try is they make a step drill most are titanium coated and are a good choice for many jobs, just get a big enough one of course to drill out your 7/8 hole, and again really really slow. I worked as a machinist for 38 years retired but still work on my own things. I have seen more people run a bit way to fast, anything over 5/16 you need to slow down and the bigger you go the slower you want to run your bit speed. Trust me on this i have seen it many times. Get the step bit may hardware stores or home improvement have them. One thing also on the step bits you are taking material out from the inside of the hole you are trying to enlarge, so on the one i am sure you work hardened this will help you get it drilled out. Use cutting oil if you have some or regular oil will work. Let me know how this works for you, Eddie

 

[Crank Shaft]

So why not just leave them 13/16. You won’t be gaining any extra strength by boring them to 7/8.

Although technically not correct, Rob has a good point. The extra strength gained may not be worth the effort.
If you leave the holes at their existing size of 13/16" and use 13/16" pins you give up very little strength.

If we assume a conservative value of 60,000 PSI as the shear strength of the pin, then each 13/16" pin will fail at a shearing load of 31,109 pounds. Now if you go to all the work of enlarging the holes and using 7/8" pins, the failure shear load increases to 36,079 pounds.

Is it worth it to gain an extra ~5,000 pounds?

However, one has to consider that if the 13/16" holes were cut with oxy or plasma, it would be far better to have the pin resting in a true, round, machined hole. If it were me, I would ream it to 7/8"

 

[Stever00]

I want to enlarge four 13/16" holes in 1/2" thick steel to accept 7/8" pins. This on a piece of equipment so I have to use a hand drill. I happened to have a 15/16" black oxide bit, not too surprisingly that doesn't work at all. In 10 minutes I only penetrated about 1/8" in one hole. So I need to decide between buying an $80 construction reamer (high speed steel, manufacturer says it is OK for stainless) or pick up a 29/32" cobalt drill for under $50. I'm guessing the reamer would work better even though it is softer. Is that correct?

Drilled hole should be .857 to ream .875 . Thats only .018 to ream. If you drill a hole that big running drill fast it will burn drill up. Run slow and use cutting oil. It will ruin reamer if you leave a lot. Look at drill chart.

I want to enlarge four 13/16" holes in 1/2" thick steel to accept 7/8" pins. This on a piece of equipment so I have to use a hand drill. I happened to have a 15/16" black oxide bit, not too surprisingly that doesn't work at all. In 10 minutes I only penetrated about 1/8" in one hole. So I need to decide between buying an $80 construction reamer (high speed steel, manufacturer says it is OK for stainless) or pick up a 29/32" cobalt drill for under $50. I'm guessing the reamer would work better even though it is softer. Is that correct?

 

[Stampeder]

Make sure this is mild steel not hardened. If hardened drills won't work you will need to use a plasma cutter or torch. Don't ask me how I know.....Lessoned learned at the expense of several drill bits.
Good luck.

 

[lpakiz]

Here’s a “Hole Saw” job I helped my buddy with. He cut out an old solid axle out of this clam trailer and wanted to replace it with a 5” round semi trailer rear axle.
To get the holes aligned, we roughly torch cut them out, but not bigger than 5”. Then we stretched a string thru the 6 layers, but first installed 6 pieces of 1\8 by 1 flat, 6-7” long, predrilled with the pilot drill, onto the string. We moved the flats around until they were perfectly centered on the string, then tacked each of them on lightly with a welder. This provided a hole for the pilot on our 5” hole saw.
The trick is slow drill and generous application of heavy thread cutting oil, along with a long cheater pipe on the drill.
Worked like a charm, very little adjusting with a die grinder and carbide burr.

 

[oldtimer 66]

Where are all of the machinist at. A core drill is the thing to use, 3 flute preferable.

 

[Sberry]

He should something easy, something he can do and do with the tools he has cept for a bit.