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

[KWentling]

I do this stuff for a living, but our smallest lathe is an 18" and I could do this in no time. Not knowing what you have for tooling makes it kind of hard to make a recommendation, but a bimetal hole saw to rough out the hole would probably be the quickest. Like was said, slow and lots of cutting oil, and you will need to clear it of the chips frequently to keep from ripping the teeth off. Then finish the hole to size with the boring bar. To hit an accurate size for the finish (provided your lathe is capable of that), I take three equal cuts. Say, rough out to .030" undersize, and then touch off and take a .010 cut. Mic the hole and then take the rest in two equal cuts. The last cut might be slightly more or less, but the idea is to have the same tool pressure or deflection. Another possibility, if you have a face grooving tool, (probably not) is trepanning the hole close to size. It could certainly be done by using facing cuts to open the hole up big enough to get the boring bar into the hole and then taking cuts to get to size, but if you are using high speed steel tooling (as opposed to carbide) and limited to light cuts due to lack of power and rigidity of a really small lathe, the hole saw would be the way to go.

Kim

 

[Travelover]

I am trying to visualize your hub adapter. Is this adapter just to keep the wheel centered on the hub, or are you going to install lugs to bolt this adapter to your current hub and also bolt the wheel to your new hub? If the latter, the half inch plate isnt going to be thick enough.

See Sketchup drawing at bottom. A purchased spindle (second picture) slides in to this hub adapter and is welded.

Not knowing what tooling you have for your lathe I will make a suggestion.

Chuck the targeted plate in your 3jaw chuck.

I assume you mean 4 jaw chuck.....

Make sure it is sitting flat in the chuck jaws so you dont cut a eccentric circle.I use a spring loaded dial caliper with a magnetic base for this, just check the plate on all four side amd make sure the reaidns are the same all the way around. If you have a drill chuck to use with your tail stock, take a bitmetal hole saw smaller than the desired spindle dia and chuck it in your tailstock. Using your lathe slowest speed slowly feed the hole saw into your material. Once you have cut thru your plate, remove the hole saw and attach your boring bar to your steady rest and slowly open the hole to the desired dia. Once desired hole size is reached,you can use a cutting bit in your steady rest to mark your bolt circle for the lug bolts. Just open the cutting bit up to the desired bolt hole dia and lightly score the plate with the cutting bit. This will ensure your bolt circle is centered with your spindle dia. You didnt say how many lugs your hub has but you can use a drawing compass, the little thing you used in school with a needle on one side and a pencil on the other, and a tape measure to accurately mark the location on your new bolt circle. Each lug will be evenly spaced if measured correctly. Once lug pattern is marked, centerpunch with sharp punch and then drill to desired size. Notice, no chucking and rechucking the piece in your lathe.

I like this suggestion. My biggest worry is that the bimetal saw will die before I get two holes in two plates. Flange bolts are symmetric but not evenly spaced, but I think I can lay them out with enough accuracy, as the flange is centered on the pilot of the OD of the pipe.

 

[Travelover]

Milwaukee has some new bimetal hole saws that are called ICE. They are cryogenically treated and are tough. I just used a 3" to cut some holes in 1/2 plate and after 4 holes it still looked new. I use atf for cutting fluid. The holes ended up .100 large. I had the plate clamped on the drill press table.
Bill

Thanks, I'll check them out.

 

[Travelover]

I do this stuff for a living, but our smallest lathe is an 18" and I could do this in no time. Not knowing what you have for tooling makes it kind of hard to make a recommendation, but a bimetal hole saw to rough out the hole would probably be the quickest. Like was said, slow and lots of cutting oil, and you will need to clear it of the chips frequently to keep from ripping the teeth off. Then finish the hole to size with the boring bar. To hit an accurate size for the finish (provided your lathe is capable of that), I take three equal cuts. Say, rough out to .030" undersize, and then touch off and take a .010 cut. Mic the hole and then take the rest in two equal cuts. The last cut might be slightly more or less, but the idea is to have the same tool pressure or deflection. Another possibility, if you have a face grooving tool, (probably not) is trepanning the hole close to size. It could certainly be done by using facing cuts to open the hole up big enough to get the boring bar into the hole and then taking cuts to get to size, but if you are using high speed steel tooling (as opposed to carbide) and limited to light cuts due to lack of power and rigidity of a really small lathe, the hole saw would be the way to go.

Kim

Thanks, Kim. I have Chinese carbide cutting tools, but I don't think I'm up to the face grooving technique.

Looking at my design above, what kind of tolerance is reasonable between the trailer spindle that slides into the center and the hub?

 

[scott_vt]

You could do what you mention, and cut the remainder on the lathe. It would take awhile though. Another way would be to chuck it up & scribe your desired diameter with a toolbit, then remove the piece (loosening just 2 jaws) and go to your drill press and drill a bunch of holes around (but slightly inside of) the diameter. Then cut the stock between those holes apart with a sabre-saw. Then go back to the lathe and finish the diameter. Use a bit big enough for your jigsaw blade to fit into. Mark the piece so it goes back in the lathe the same way it came out of the chuck, then indicate the scribed circle and finish it.

A holesaw under the size, can work too, just use plenty of coolant/lube & go slow enough to not burn it up.

Good Afternoon Travelover,
N8ghz has it right, your easiest bet is on the undersize holesaw, then rechuck your plate, and finish bore your plate. Remember to have the plate relatively cool to your touch before taking your finish cut. If the plate is hot, when it cools, your hole may be a bit undersize...

Cold rolled steel plate machines quite easy, and shouldnt pose much of a problem with a well lubricated hole saw.

I spent 35 years in the machining field, and on a larger lathe or miller, you could do that size hole in a matter of minutes... so it didnt present much of a problem...

With todays CNC equipment, they zip through steel plate in seconds...

BTW KWeitling, has made some good suggestions, with the size hole you are boring, if you have it you could use a good sized boring bar also, not much tol delection that way...

 

[KWentling]

Thanks, Kim. I have Chinese carbide cutting tools, but I don't think I'm up to the face grooving technique.

Looking at my design above, what kind of tolerance is reasonable between the trailer spindle that slides into the center and the hub?

I assume you are welding the spindle to the back side of the plate. Seeing how the plate is only 1/2" thick, I would keep it a close fit. It could even be up to a couple tight and you could heat the plate to install it. Your .002 clearance would be fine.

Kim

 

[Travelover]

I assume you are welding the spindle to the back side of the plate. Seeing how the plate is only 1/2" thick, I would keep it a close fit. It could even be up to a couple tight and you could heat the plate to install it. Your .002 clearance would be fine.

Kim

Thanks.

How about the clearance between the 1.75" spindle itself and the 1.75" hole in the center of the adapter. I have 2" overlap there. Looser OK?

 

[scott_vt]

Travelover,
If you had some transfer punches, you could lay your spindle flange over your steel plate, align the bores clamp them and then priick punch each of your bolt holes...

Sorry, I think I misunderstood what you were saying.....

 

[Travelover]

Travelover,
If you had some transfer punches, you could lay your spindle flange over your steel plate, align the bores clamp them and then priick punch each of your bolt holes...

Good idea, I may pick up a cheap set.

 

[tcartwri]

Can you not just redrill the existing hub for the new stud pattern.....