80mm hole to 90mm in 1/4" steel

[TractorGuy]

Do the holes need to be a precision press fit or will you weld them in?

Won't be cheap but you might try calling this company for a solution. Maybe their #94 style reamer with a straight arbor.
Straight, Tapered, & Shell Reamers & Parts | Tool Fabrication

 

[rScotty]

Is there a way to bolt or clamp metal behind the hole? If so, it could be drilled pilot size first (1/4") for a hole saw.

Very clever. I'll remember that one. And also the trick about mounting two hole saws one inside the other. That would work with a wooden plug around the pilot drill too.
rScotty
old dog; new tricks

 

[GLyford]

If you use a predrilled backer to pilot the hole saw, then you can also swap out the pilot bit for a chunk of 1/4" rod. Won't enlarge your pilot hole, less likely to break, and if it does it's not as spendy as a drill bit...

 

[herm0016]

i have used 3/4 plywood. drill the center, clamp to part, use hole saw. the Milwaukee hole saws are pretty good. you want a pretty coarse tooth. Think of it as a band saw blade wrapped in a circle. you don't want the blade to remind you of a hacksaw blade. lots of little teeth load up fast and get over heated fast because they cant clear the gullet of chips and the cutting pressure per tooth is very low. The rule for a bandsaw is having at least 4 teeth and not more than about 10 in the part at one time.

 

[BHD]

One could make a "template" and use the torch or plasma cutter in the template, (I guess it depends on how exact you need the hole),
Maybe letting us in on the use of these hole would help,

 

[M5farms]

One could make a "template" and use the torch or plasma cutter in the template, (I guess it depends on how exact you need the hole),
Maybe letting us in on the use of these hole would help,

I have also used a torch to rough it out then use a used grinder wheel to shape it .

 

[mike48130]

One could make a "template" and use the torch or plasma cutter in the template, (I guess it depends on how exact you need the hole),
Maybe letting us in on the use of these hole would help,

Plasma cutter with a wood template. You will get a decent clean hole, then a little grinding. Of if you can get your hands on one, a magnetic drill press. Very handy, wish I had one.

 

[BillyJoe JimBob]

This is what I have used with great success in the past and will work for your exact situation.
It's called the "OOPS Arbor" by Starrett although I'm sure this type of arbor is available from other manufacturers.



The hole-saw arbor can accommodate 2 cutters being used at the same time. One cutter, inside, for the original hole size and one cutter, outside, for the newer, larger size hole. Finding your "exact" hole sizes for the cutters may be a fun journey... ;-)
3 things:
1. Buy the best quality hole-saw cutters you can afford - "inexpensive" hole-saws do not hold last! "Quality is long remembered after the price is forgotten."
2. Use a good quality "tapping / cutting oil" and lots of it.
3. Stop the cut when about 1/2 or 2/3 of the way and remove the inner, smaller cutter and only then continue with the new, bigger hole. This will allow for the continuation of the larger hole cutting without trapping the small section between the 2 cutters. 1/2 to 2/3 the way through the new cut will allow for the cut to be finished after the inner cutter is removed. Easy Peasy!

 

[RUSTBUCKET BRONCO]

now that's a good idea

 

[hawkeye08]

This is what I have used with great success in the past and will work for your exact situation.
It's called the "OOPS Arbor" by Starrett although I'm sure this type of arbor is available from other manufacturers.

View attachment 607110

The hole-saw arbor can accommodate 2 cutters being used at the same time. One cutter, inside, for the original hole size and one cutter, outside, for the newer, larger size hole. Finding your "exact" hole sizes for the cutters may be a fun journey... ;-)
3 things:
1. Buy the best quality hole-saw cutters you can afford - "inexpensive" hole-saws do not hold last! "Quality is long remembered after the price is forgotten."
2. Use a good quality "tapping / cutting oil" and lots of it.
3. Stop the cut when about 1/2 or 2/3 of the way and remove the inner, smaller cutter and only then continue with the new, bigger hole. This will allow for the continuation of the larger hole cutting without trapping the small section between the 2 cutters. 1/2 to 2/3 the way through the new cut will allow for the cut to be finished after the inner cutter is removed. Easy Peasy!

Excellent idea! thanks for sharing