Cut large holes in steel

[JimEb]

I have two pieces of 1" thick, 6" round 1045 steel in which one will have 3.75" hole in the center, the other a 4.25" hole. My basement workshop isn't that well equipped, so here's what I'm debating.

1) Run it in the lathe. Drill the center out with the biggest drill I own (.75) and then hog out with a boring bar to size. However, that's a lot of good material to turn into chips. Would prefer to salvage that block of steel.
2) I have a 6" rotary table. Could drill holes in the part and bolt it directly to the rotab. Will be a lot of hand cranking.
3) I can get 3.5" & 4" bimetal hole saws cheaply enough at the hardware store. Hog out the center with that and clean up the bore to size on the lathe. If I only get one cut out of that hole saw, so be it. Problem is my mill's slowest speed is 250 RPM, my lathe can do 100rpm but isn't very powerful. Never heard of anyone running a hole saw like this on a lathe and that's a lot of material for a hole saw.
4) Drill a hole big enough for a jig saw blade. Cut the circle with a jig saw with a metal cutting blade. Would probably take forever.

Any ideas?

[tornitore45]

I would consider 1) or 2) but not the others.
Start with your approach 2) but use a drill like 11/32 spaced to leave a tin web finish with a 5/16 end mill, one pass or take the chicken approach and go two passes.
Whatever you do not achieve complete separation with the end mill, either plunge only 0.99" or skip drilling 4 holes to leave metal webs that can be removed with a saw.
Drilling go a lot faster than milling and uses a cheaper tool.

In the old days of middle school shop, no rotary table just center punching, drilling and sawing. On thinner plates we cut the webs with a chisel.

[SteveR]

I see on Mcmaster that each of those extra pieces you are trying to save is about $15 each. Maybe another $10 for shipping? And then the project you are saving them for will require just a size just a wee bit bigger....
I would just drill and bore. Seems like your time is worth more than what you will save. If not, have you considered WEDM or water jet?

SteveR

[earlgo]

I have used a hole saw on 5/8 plate, the saw being around 2" diameter. One has to 'peck-saw' the hole because there is no room for chips. Then the part should be reversed and 'peck-sawed' from the other side. Takes a long time and a lot of cutting oil. You should check to be sure the saw you choose is deep enough to go half way through the material.

For a 4" hole you might consider finding someone with a cutting torch to get rid of most of the scrap. BUT it will cause 'some' warping and may not be worth while.

Drilling a ring of holes and then using the jig saw may be a combination that might work, too. A sawzall would work too if the holes were big enough.

--earlgo

[warmstrong1955]

I just cut some 2-1/4" holes thru 3/4" A36 with a Morse hole-saw. They had a bi-metal set on sale at Enco a while back.

I used cutting oil.
I used the RPM on a Starrett chart I downloaded. (150 RPM)

Important part:
A couple guys here, Russ (BadDog) & Spro (Thank-you guys) said to drill holes along the inside circumference, to give the chips somewhere to go.
I drilled (2) 3/16" diameter holes 180 degrees apart. No peck-drilling & chip blowing required. I just plunged straight down with a squirt of cutting oil now & then.
Those holes for the chips to fall out make an amazing difference. And, after cutting 4 holes, the hole saw looks as sharp as it did new.

Bill

[Hopefuldave]

Could always trepan[1] the holes in the lathe? If so, i's worth supporting the slug in the middle with the tailstock (and a spacer between the "core" and the chuck face) so it doesn't flop around and jam when you break through

Dave H. (the other one)

[1] The tool looks like a parting tool with a curved cross-section below the blade that slips inside the slot as you cut - http://www.homemadetools.net/forum/lath ... ning-33447

[steamin10]

IMHO, I would lathe this thing all the way. I run wheels on a SB lathe, and boring tires and such is much the same.

Drill a start hole as large as you are comfortable with, even if you go like 3/8 and then 3/4. Its ok, you just need clearance for chips and tool

I use a sharp 2 flute mill of larger size, in a boring bar holder, or 4 side tool post, packed out to center the flute, and then it is just repeat plunge cuts, to hog ( relative word for small lathes) the bulk of the material. With my small lathe in back gear I can take about 1/8 on the cross slide and hand feed the carriage by ear. My machine talks to my deaf ears, and I know where I am at.

A chalk or paint mark for target diameter, will let you know when you are close for final dimension. With a slight clearance angle on the cutter, a fair finish can be had, and fine cuts at higher speed, or changing to a real boring bar, will get to the finish needed.

More than one way to make a hole without making mouse holes. (I hate chain drilling! It is too much like Primitive Pete for me, to beat on things with a hammer for fine work. Blah.)

I wont trepan a deep hole, but is ideal for sheet stuff. Sawing brass to save the 'waste' material, I will zip saw about 6-8 angled slots in a hole saw, for chip clearance. Medium to heavy pressure will keep the saw from hardening the brass, and enough oil will float the chips, until the slots are reached. This is a good way to use a saw with broken teeth too. A drill press works best, as a saw dressed like this, will be aggressive and snatchy with a hand drill. Keep the speed down and have patience. Haste is waste.

Just some things that work for me.

[tornitore45]

Would prefer to salvage that block of steel.

Regardless of various opinions on the economic of saving the slug the OP expressed the desire to save the slug.
Solutions creating 6.7 Lbs of chips aren't really helping the OP.

[Magicniner]

Would prefer to salvage that block of steel.

Regardless of various opinions on the economic of saving the slug the OP expressed the desire to save the slug.
Solutions creating 6.7 Lbs of chips aren't really helping the OP.

In that case stitch drill and chisel out would involve the least expense, save the plug and offer a learning and growing experience,
HTH,
Nick

[liveaboard]

I did it several times with a cutting torch; the hole was pretty rough and it took a long time to machine it smooth.
Hole saws start to be troublesome when bigger than 2 or 3" [in my opinion].
1" is a thick chunk of plate.
One day, when I'm rich, I'll have a plasma arc cutter...

[warmstrong1955]

I did it several times with a cutting torch; the hole was pretty rough and it took a long time to machine it smooth.
Hole saws start to be troublesome when bigger than 2 or 3" [in my opinion].
1" is a thick chunk of plate.
One day, when I'm rich, I'll have a plasma arc cutter...

Yeah.....I get some stuff like that from a local fab shop to machine for 'em. (3" A36)
Some pieces even come with a warning.......

Ka-thump-ka-thump-ka-thump.......


Bill

[liveaboard]

Yes, all that thumping and bouncing makes me feel guilty about the terrible deed I'm doing to my poor old lathe.
As the machine complains, I often think about posting the question here myself; Now that we've explore the options for large hole cutting, here's another question.

How do you make discs?
I often need a steel disk for something of other.
Torch cut? what a mess.
Hole saw? Arggg, how aggravating.
Cut an octagon with saw + grinder...
Slice a piece of bar [my saw doesn't like heavy stock].

Any other ideas?