2 1/2” plate 3” hole

Upnorth4 · May 13, 2018

What is the best way to cut a 3” hole in 2 1/2” plate?
I’m in a pretty basic millwright shop, no CNC Mill or I would have just circular interpolated the hole with a indeaxble end mill and finished it with a boring head (this hole is for a bearing pocket)
Having only a big old knee mill ( odd controls and no quill) and no drills over 1 1/2” Im stumped.
Torch cutting a messy hole well undersized then trying to clean up with a boring head??

The material is mild steel,

Milland · May 13, 2018

Figure out a hole pattern with a 3/8" or so drill where you cut just inside your final diameter, such that you pop a slug out of the plate. Then finish with the boring head. Smaller drill gives you less to bore, but more holes to drill.

yardbird · May 13, 2018

I might try making crude trepanning tool that holds HSS toolbit. Drill a 1" pilot then carefully use the trepanning tool to cut the 3" hole leaving it undersize to finish with boring head feeding the knee up and down by hand.

Or if you have 1/2" variable speed hand drill you could make an adapter to fit the knee screw part of the mill then feed it up and down with the drill cutting with the boring head?

IDK just thinking out loud I guess?

That's a good idea from the guy ^^^ up there.

Brent

DMF_TomB · May 13, 2018

Upnorth4 said:
What is the best way to cut a 3” hole in 2 1/2” plate?
I’m in a pretty basic millwright shop, no CNC Mill or I would have just circular interpolated the hole with a indeaxble end mill and finished it with a boring head (this hole is for a bearing pocket)
Having only a big old knee mill ( odd controls and no quill) and no drills over 1 1/2” Im stumped.
Torch cutting a messy hole well undersized then trying to clean up with a boring head??

The material is mild steel,

.
your limitations are your own
.
use drill to 1.5" then use boring head .030 at a time til 2.990 then take finish cut..... like whats the problem ?

Hodge · May 13, 2018

Depending on tolerance, take a 2-3/4 to 3" diameter hole saw, deep depth. Buy good quality, keep coolant or oil in the cut, low rpm. Flip part of needed to get through. Bore to size with boring head or 4 jaw in lathe.

LKeithR · May 13, 2018

DMF_TomB said:
...use drill to 1.5" then use boring head .030 at a time til 2.990 then take finish cut..... like whats the problem ?

Yeah, I tend to agree. Just drill as big as you can and bore it out. A 3" hole really isn't that big. Unless you've got a real wimp of a machine you
should be able to take at least .100 thou DOC. In the time it would take to figure out some "neat" way to do it you'd be done. We've all been in
that situation--presented with a problem we spend (waste?) time trying to figure out an "elegant" solution when the low-tech tool is sitting in the
tool box the whole time,,, :eek:

A larger quantity would be a different story; then it's probably worth dickin' around a bit. If the quantity was large enough I'd probably look into
a large annular cutter--knock it out to within 1/16" and then finish bore...

yardbird · May 13, 2018

DMF_TomB said:
use drill to 1.5" then use boring head .030 at a time til 2.990 then take finish cut...

I agree also this is probably the simplest way to do this.

Brent

DMF_TomB · May 13, 2018

read a book about peace cor types working in Jungle somewhere no supplies. he wants to cut 1/2" steel plate and no torch or saw. he makes a hss blade cutter hand held like wood plane and he scores and scratches surface .001" deep. he adjust hand held cutter and takes .001 more deep cuts til he cuts 1/2" thick steel plate in half
.
sure he had to hand scratch score 500 cuts .001 at a time but he cut the steel plate in half

Upnorth4 · May 13, 2018

Thanks for the replies, great stuff.
I am a millwright with a couple years experience as a machinist, good mix of CNC and manual in those two years.
I suspect that it was the machining experience that landed this job. I have done a few little projects and fast repairs on the old Cardiff lathe and this beast of a mill. Embarrassingly I can’t recall the make and model, I’ll start a thread on it later.... It’s horizontal with a 90 degree head set up for vertical, feeds on all axis, but the feed is set as a percentage, I have used a stop watch and tape to set feeds when needed... it’s a very solid machine, and a massive X travel, 6’ I was told....
But there is only one DRO (on Y)working, not a huge deal as I set up the work on the table to make sure I have the DRO where I want it, with it on the Y it can be used to quickly centre key ways on long shafts....

I have learned that machining, once the foundations are learned, is all about being creative to find the best way to quickly get the job done within the precision needed. In this setting I am get a great understanding of what is needed so I get a chance to not waste time on precision that isn’t needed.

This forum is GREAT as I tended to be in a “one tool” mind set, with only a couple years experience I don’t have the “tools in the box” so to speak to see a set up that could save hours on a job.

gbent · May 13, 2018

How many? Any tooling budget?

DMF_TomB · May 13, 2018

Upnorth4 said:
Thanks for the replies, great stuff.
I am a millwright with a couple years experience as a machinist, good mix of CNC and manual in those two years.
I suspect that it was the machining experience that landed this job. I have done a few little projects and fast repairs on the old Cardiff lathe and this beast of a mill. Embarrassingly I can’t recall the make and model, I’ll start a thread on it later.... It’s horizontal with a 90 degree head set up for vertical, feeds on all axis, but the feed is set as a percentage, I have used a stop watch and tape to set feeds when needed... it’s a very solid machine, and a massive X travel, 6’ I was told....
But there is only one DRO (on Y)working, not a huge deal as I set up the work on the table to make sure I have the DRO where I want it, with it on the Y it can be used to quickly centre key ways on long shafts....

I have learned that machining, once the foundations are learned, is all about being creative to find the best way to quickly get the job done within the precision needed. In this setting I am get a great understanding of what is needed so I get a chance to not waste time on precision that isn’t needed.

This forum is GREAT as I tended to be in a “one tool” mind set, with only a couple years experience I don’t have the “tools in the box” so to speak to see a set up that could save hours on a job.

.
if need ideals on a temporary DRO, i made adapters to clamp a 6" range one on just about anything. rubber bands are cheap

Illinoyance · May 13, 2018

Use an APT Multi-Tool.
APT E Series Taper Shank Multi-Tool Drilling Set

Open the hole in steps feeding with the knee. If final diameter has to be to a close tolerance, finish with a boring head.

Leg17 · May 13, 2018

OP says nothing about tolerance.
He apparently doesn't have a boring head available or he would not have asked the question.
He could drill as large as possible and invest in a cheap fly cutter.
Manually 'adjust' the tool bit with each pass until the hole is big enough.

Rob F. · May 13, 2018

Since you have no quill and raising and lowering knee to drill small holes all the way around would get tiring. Can you scribe a 2 7/8" circle where it needs to be, drill hole large enough to get a cutter through and carefully go around the circle (stay inside the line of course). This should give you a rough opening to run the boring head without the workout of knee up down.

azmachining · May 13, 2018

UpNorth said he has a boring head, but no quil. I would say hole saw it close or trepan it then use boring head. He implies he has a torch, if he has a circle burner that would be a good way to go, even if he doesnt have a circle burner he's only looking to rough it out. If your not wanting to spend the money or time on additional tooling and worth a crap with a torch and want to use what's on hand i would torch it and finish with the boring head. Real simple, I would also grind out the slag before machining it.

snowman · May 13, 2018

Annular cutter

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Matt_Maguire · May 13, 2018

One shot attempt, 2 1/2” thick mild steel plate with a big ugly horizontal knee mill & vertical head (feeding the knee) I’m gonna burn the hole to 2 or 2&1/2” & bore to size myself. The recipe…

Lay out the finished hole OD from center (center punch center & scribe circle). Then center punch the scribed circle 4 places (either chord off the X-Y locations or use the lines you used to layout the hole center). Then burn the hole.

Pick up the (layout) hole with a wiggler (or bend a paper clip & spin that) using the aforementioned punch marks (or the original scribed circle if you’re luckier than me at still finding it). Then mount the boring head and use this generic machining recipe (assuming a high speed steel boring tool).

Spindle speed is 100ish RPMs (stay there), feed for roughing is 1 inch per minute (.010” IPR) at whatever depth of cut the machine is happy with. Rough to -.060” & change to 1/2” per minute feed (.005” IPR) & play happy learning to finish bore with a really high horsepower mill that’s just loafing (and you’re learning to see what it & you can do).

If you have carbide tooling for the boring head the above speeds & feed should be no less than 3X the recipe & can go to more than 5X the recipe YMWV.

BTW, knee milling with old mills can be kind of exciting, be prepared to go a bit oversize (with an ID mic) before the fit suits you (sometimes the holes are a little less than straight).

Good luck,
Matt

gbent · May 13, 2018

I've got a big old knee mill, and to do just one piece as described, I'd lay out the hole, drill 1 1/2, and manually interpolate close to size with a 1 1/2" corncob rougher. Then I'd finish bore for size.

Upnorth4 · May 13, 2018

How well do torched holes clean up with a boring head? Unfortunately we don’t have good insert (indexable) bars for the head, just the cheap ones with brazed chunks of carbide.....

As for tooling budget available I would say that in the future if I can sell them on tooling that is multi purpose and can get them up and running quickly I have a good chance at getting it ordered.

The only experience I have with boring heads is getting an already close and clean hole to a bearing fit size, cutting at max .030”

The final fix to get this equipment up and running was to carbon arc gouge a similar flange off another spare and weld it in place of the damaged one.
I am pretty sure that I will be asked to make a new flange for that spare....

What I am likely to do here is:
- cut the flange out of the plate stock
-locate the bearing hole and set it up the mill with a fixture I can easily return it to
-remove the flange and drill a 3/4” ( big enough to start torching the hole)
-torch it out, depending on how that goes I’ll get as close as I can to reduce the amount to take out with the boring head
-return it to the fixture and see if the torch hardend the edges beyond what the cheap bars can handle, this is where inserts would be great,

azmachining · May 13, 2018

Depends on how well you are with a torch, if your really good with a torch you wouldn't even need to grind it other then the bottom, if your going to machine afterwards. I do recommend you grind it, but it will cut just fine, and hey it might be cheap, but at least you have carbide. We have a bunch of brazed carbide cutters that work great, they're also good quality stuff, don't know what you have.

Or you could do what gbent said and that's manually interpolate a corncob rougher or whatever end mill you have, it's only mild steel and one part at that. Then use your boring head.

2 1/2” plate 3” hole

Plastic

Diamond

Titanium

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Stainless

Stainless

Titanium

Diamond

Plastic

Diamond

Diamond

Attachments

Stainless

Cast Iron

Diamond

Cast Iron

Diamond

Stainless

Diamond

Plastic

Cast Iron

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