How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

[SandburRanch]

The good news is that I have a 6" lathe with 3 and 4 jaw chucks. The bad news is that I rarely use it and consider myself a rookie.



Thanks for your ideas.

The only way to advance from rookie level is to do it. Practice on a scrap piece.

If I had a lathe and a 4 jaw that's the only tool I'd consider rather than screwing around with multiple set ups that compound the chance of error.

Just do it to it.

There are several books for the beginner that will aid immensely in learning basic lathe processes. And maybe just as important it will teach you the language so you wont seem to be such a rookie when discussing the procedures.

Google "machine tool practices" and other titles for a long list of books and then look in your local library to determine if you would like to buy one of those for a handy reference in your shop.

I've found it quite satisfying to make projects on a metal lathe.

 

[charlz]

Just a few weeks ago I used those Milwaukee Ice hole saws to cut 1/4 steel. Went right through it, bit looked like new after four 2.5" holes, I was impressed.

I would do what has already been suggested; drill it under and bore it all right on the lathe. Assuming your lathe goes slow enough. I used 260rpm with oil when I drilled mine, the lowest option available to me and it worked fine.

 

[Travelover]

Just a few weeks ago I used those Milwaukee Ice hole saws to cut 1/4 steel. Went right through it, bit looked like new after four 2.5" holes, I was impressed.

I would do what has already been suggested; drill it under and bore it all right on the lathe. Assuming your lathe goes slow enough. I used 260rpm with oil when I drilled mine, the lowest option available to me and it worked fine.

My lowest speed is 55 rpm on my lathe, with back gear engaged. That ought to be slow enough.

 

[Travelover]

Seems to me like you're overthinking it a bit. I doubt that trailer axle manufacturers hold such tight tolerances when building axles. They also usually use 1/4" plate for the brake mounting flange. Even if you were to achieve your tolerance goals, as soon as you put the welder to it, the plate will more than likely distort out of your tolerances. If you absolutely must have mounting flange perfectly true, cut your hole, weld your plate on and then chuck the spindle assembly in the lathe and face the plate to true it up.

You are probably right. As I mentioned, the part I took off was also used on a Camaro front hub and was a very nicely machined, forged part. I wanted to error on the side of making it too good, lest I regret not taking more time in fabricating it.

Re the plate thickness, I'm combining the mounting flange for the whole spindle with the brake backing plate attachment to compress the packaging so the wheel will still fit inside my wheel well (it is a fiberglass camper).

 

[Travelover]

The only way to advance from rookie level is to do it. Practice on a scrap piece.

If I had a lathe and a 4 jaw that's the only tool I'd consider rather than screwing around with multiple set ups that compound the chance of error.

Just do it to it.

There are several books for the beginner that will aid immensely in learning basic lathe processes. And maybe just as important it will teach you the language so you wont seem to be such a rookie when discussing the procedures.

Google "machine tool practices" and other titles for a long list of books and then look in your local library to determine if you would like to buy one of those for a handy reference in your shop.

I've found it quite satisfying to make projects on a metal lathe.

Thanks for the encouragement. I actually got this lathe in the early 1980's and used it a lot, including making a working model steam engine. In the intervening 30 years I've regressed to a rookie.

 

[Travelover]

Follow up:

I bought a 2 5/8" bimetal hole saw (Morse, USA made) and it worked beautifully. I ran the lathe at 55 rpm and poured on the oil and backed it off often to clean out the chips. After two 1/2" thick cuts, the saw is still sharp. I used a boring bar to bring the ID to the required 2.75".

The worst part was on the second piece. I snapped off a 1/16" drill that I was using to drill a pilot for the center. Dumb of me to use a small Chinese drill through a 1/2" plate. I could not get that broken drill out, so I hogged through it with a carbide masonry drill. That made the pilot hole for the hole saw a little sloppy, but once the hole saw had started the cut, it piloted off the rim of the saw anyway. Cleaned up the ID on the lathe, so no harm done.

I really appreciate all the helpful advice and even offers to machine it for me. :thumbsup::thumbsup::thumbsup:

 

[N8ghz]

Great...half the fun is makin' it yourself.

 

[sunshine coaster]

I like that you have succeeded, but if it were me I would just have bought a replacement axle and move on to the next project....

 

[Travelover]

I like that you have succeeded, but if it were me I would just have bought a replacement axle and move on to the next project....

That's the difference between a guy like me that is retired and someone like you that values your time. :laughing:

 

[sunshine coaster]

That's the difference between a guy like me that is retired and someone like you that values your time. :laughing:

Thats a humbling reply, I have been there where you are but in my youth, growing up on a farm where in our case) there was no money for buying what we could build, I got money for now but if I live I will be back where I will do what you are doing, thanks for the great thread...

A buddy of mine has a jig to fit backing plates to oddball axles, it works great, I will take a pic of it next time I am there....