Enlarging a Large Hole

[lukedwag]

Alright boys I need some ideas...

I need to make the center hole on this backing plate approx. 1/4" larger in diameter. I have looked all over for replacement of my original and no one knows why my Hayes 12x2 brakes have a backing plate hole size of a Hayes 3-1/2x12.

I have torches, welder, grinders, .... all see to be a lot of work or kinda crude. At this point i am leaning to clamping the old and new ones together and just burning the 1/8 off each side with the torch.... anyone got another idea?

 

[uniballer]

they make reamer that big?

 

[jhelrey]

Clamp it to wood. Drill a hole in the wood in the center. Grab a metal hole saw the size you need and go to town.

 

[ehaines]

Get a hole saw of the correct size, drill a hole with it in a piece of 3/4" plywood or mdf and then clamp that to the backing plate centered up on the existing hole. The plywood will hold the hole saw in the correct position without the pilot bit.

 

[CAOS]

Trace your circle, carbide burr on a die grinder would be the cleanest way in my opinion. Take less time then a hole saw too.

 

[Zeke]

You can use the old one as a guide as well. But, a hole saw that big might cost you the price of a backing plate. I don't think I'd go at it with a torch, though. You have a die grinder? With some patience and using the old plates as a guide, you can grind out an 1/8" pretty quickly.

Something I thought of to finish the job accurately is to mount a router bearing on the same size grinding stone shaft. The bearings are 1/4" ID. They make collars that increase the dia of a router guide bearing all the way out to 1 1/4 inches. You could possibly get that bearing to follow the circumference of the larger hole and grind the new hole to perfection. You could place a plywood stop to keep the bearing on the edge of the old hole.

Sorry, I don't draw diagrams, scan and post. But if you have an idea of what I'm saying, you can do this.

As I said, patience.

 

[cyamaha2007]

die grinder and a bur of your choice.

 

[fredybender]

It doesn't spin, nor move, nor care much. Carbide ream it out. It'll take very litle time....

Do you know how much a carbide reamer that size is?
And a reamer is only supposd to take 0.030", even at that size...

I would go with the carbide burr idea, with a guide for making a clean diameter.

 

[retrobuilder]

Just take it to a machine shop with small rotary table. machine to size. Is the bolt hole pattern acceptable for bolt head clearance. If machining is out of question check on hardened hole saw and oil or die grinder patiently with water cooling flushed on the steel. Only 1/8 per side- not that bad with right tools.

 

[Beytill]

Die grinder!

 

[welder4956]

I had to do something similar recently and put a hole saw bit the size of the original hole inside the larger bit. The smaller one projects out the end of the larger one enough to center it over the hole.

 

[tenlug]

Hey Welder that's a good idea. Im going to file it away. Thanks. Steve

 

[junk]

I had to do something similar recently and put a hole saw bit the size of the original hole inside the larger bit. The smaller one projects out the end of the larger one enough to center it over the hole.

This is what I would suggest.

 

[MBfreak]

Scribe the part with the right OD.
Clamp it up and file it with a half round file. Will take all of 20 minutes, you can get it very close to perfect and also spare some time at the gym.

Hand filing is great, start and you will see that you improve your skills and accuracy very fast.

I am lucky enough to live in an area of Sweden where many small machine shops are being closed and their excellent tools end up at markets. So buying absolutely top grade hand files in any size is no prob.
Have tried some new ones from various " hardware" shops. Steel like bubble gum and sharp as a roll of tissue. COO not even mentioned but they are marked the old reliable names. Progress.

Ola

 

[ephotrod]

Go to a salvage yard and buy the correct backing plate off a vehicle that's the same as yours. Or use a burr and die grinder.
Josh

 

[383 240z]

I'd clamp it to my mill, indicate it, and run my boring head thru it. Other than that scribe it, rough it in with a die grinder and a carbide, finish with a half-round. Keith

 

[Deadhead]

when you make your center hole bigger are you going to have enough material left between the bolt hole pattern and enlarged hole to even use the piece

 

[lilscorpion]

Trace your circle, carbide burr on a die grinder would be the cleanest way in my opinion. Take less time then a hole saw too.

This is how I'd do it if I didn't have a mill. It's a backing plate so it doesn't have to be press fit because it's located by the four bolts. Since it doesn't have to keep anything out, there's really no risk if the hole isn't perfect. If you mark where you need it to be, you could use a carbide bur (as suggested by CAOS) and then, when you're close, to back with a flapper wheel and true it up. http://www.amazon.com/dp/B003N9BT3W/?tag=atomicindus08-20

The flapper wheels can be gotten in a variety of grits so you could really tune the hole to look nearly perfect. It could be done completely with a bur - just depends how much of a perfectionist you are. I did like the hole saw within a hole saw idea though. That's a really neat idea. I imagine you could do the same thing with a piece of tubing as a guide if you had the right size tubing laying around (or a lathe to make a sleeve). Good luck.

 

[50cal]

Large rat tail file

 

[Kevin54]

You don't need a carbide burr because the backing plate is only sheetmetal. Use a drum sander, a Dremel, a burr on a drill, a burr on a die grinder, or even the rattail file.

 

[tcianci]

Look into an "oops" arbor for a hole saw. It will allow you to use a hole saw that is the same diameter as the existing hole as a "pilot" while running the correct size saw through the backing plate to create the new hole. Or create a "puck" the same size as the existing hole out of plywood or MDF, slip it over the pilot drill of a hole saw of the desired size and just walk right through it.

 

[lilscorpion]

No kidding, never heard of it before...oops arbor doesn't cost much and would take seconds with a drill press. We have a winner -

http://www.amazon.com/dp/B000WA7A56/?tag=atomicindus08-20