How to stretch holes in a steel frame?

I ran into a glitch in rehabing an old park bench.  The wooden slats were rotted out, so I'm saving the wrought iron end frames and fitting them with new poplar slats.  I included a mid-project picture below of one of the end frames.

I don't know if you can notice from the picture, the holes in the frame for mounting the slats were not in a straight line, but rather haphazardly.  So each board needs to be custom-drilled to match the mounting holes in the frames.

Problem is, I originally measured the distance between the bolts on one of the old slats and used that measurement to drill ALL the new (expensive) hardwood boards.  I had made the careless assumption that the holes in the frames would be in a straight line. Never assume good workmanship!

After drilling the slats, I applied about 5 coats of clear urethane spar varnish.  The new slats look supreme, and I don't want to zorkk them up by drilling a second hole in each board to match the stupid end frames.  So the only way out of the quagmire I can see is to drill the frame to match the boards. 


Problem is, most of the new holes in the frames would intersect the old holes, and I know that drilling an intersecting hole is problematic, especially in 3/16" steel.  So I need advice on how to stretch holes in steel into an oval shape.  I'm thinking some sort of router bit, or a grinding bit that I could use with a hand drill.

Suggestions?  Thanks.

Picture of How to stretch holes in a steel frame?
lesizz (author) 1 year ago
I replaced one of the 2-1/2" slats at the top with a 1-1/2" slat. That offset the mounting holes for all the slats except for the top and bottom ones by 1". Then I just drilled new holes.

Even with that method, it's not perfect, as I didn't get all the holes drilled perfectly in the cast iron frame and still ended up doing some filing with the rat-tail.

I will post a picture when I have all the boards mounted.

Thanks for all the suggestions. Any of those would have worked, I just got lazy and did it the easiest way I could figure. It's not easy doing this kind of project on a condo balcony.
ANDY!1 year ago
Would cutting out the strip of metal with all the holes with a grinder and replacing it with a new bar of steel with the holes drilled out in the right places work?

Perhaps using a welder to patch in the old holes and re-drilling new ones might work too, I believe people who repair floorpans use that technique with MIG welders...
lesizz (author) 1 year ago
Thanks for the replies everyone. It seems all these solutions are doable, and I'll have to think some before embarking on one solution.

The chopping off the ends solution isn't as easy as it might be, as I live in a condo and I use the condo wood shop as opposed to just walking into my garage. So I'd have to take the boards to the shop and put them to the radial saw. Then mount the boards on one frame and mark the other end, then back to the wood shop and put them under the drill press to make new holes. Re-varnish the ends and holes and finally assemble the whole works. So maybe I'll do that. It's not like this has to be done in any hurry.

rickharris mentioned a round file. Now, if I could mount a round file in a power tool that has action similar to a portable jig saw, that might be another solution.
Aww come on by the time you have messed about you could have done it by hand!

If your somehow reliant on power tools though you can get rotoary files you can put in a drill that will do the same thing.

You may be able to find a tapered broach that is designed to make holes bigger.

or even a tapered drill or a stepped drill
lesizz (author)  rickharris1 year ago
Well, maybe so. I'll give the rat-tail file a try. If the bursitis in my elbow kicks in, I'll order the rotary file. Looks like a good gizmo to have anyway.
An hour, tops, to cut them with a file.....
Those holes look like they might be big enough for a round carbide grit hack saw blade to fit through.

You could put the blade through the hole ,then attach the blade to a hack saw. Hold the hacksaw with two hands, (one,hand at each end of the saw) as you elongate the hole.
Rinse and repeat for each  hole.

Something like this:

Hack saw blades come in 10 inch and 12 inch lengths, so be sure to get
the correct size for your hacksaw.
Round, bastard-cut file. Yes really, that's what it's called!
lesizz (author)  steveastrouk1 year ago
I'm familiar with that term, meaning a file with a medium cut, somewhere between rough and fine.

Or a file with questionable parentage.
I suggest cutting off the ends of the slats and drilling the right holes in them. The loss of an inch or 2 on the boards will hardly be noticed.
That's the way I'd do it too.
That's a really good solution..
You could use drumal grinding tips in a drill.
or do as rickharris said.
rickharris1 year ago
To make the holes elongated attack the with a round file and a bit of time and elbow grease.

Easier to cut ends off slats!