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

    I need to cut a 2.75" diameter hole through a slab of 1/2 thick cold rolled steel. I'd like to have an accuracy of a couple of thousands on the final ID.

    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.

    My initial thought is to chuck the 3.25" x 4" plate in the 4 jaw chuck and drill a 1" hole with a Chinese drill I have, then start opening up the hole with a lathe bit, maybe finishing off with a boring bar. That seems like it will take forever.

    Any ideas on how to get near the final ID a little quicker with what I have? I doubt that a hole saw will cut through this thickness, at least not a hole saw on my budget.

    Thanks for your ideas.

  2. #2
    Super Star Member murphy1244's Avatar
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    You need to drill a couple thousands under then ream the hole to size. Why so tight tolarance?
    Murph ------------

  3. #3
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    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.
    "We, the Unwilling, Led by the Unknowing, set off to accomplish the impossible...the difficult...we do immediatly....the impossible just takes a little longer"

  4. #4
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    Quote Originally Posted by murphy1244 View Post
    .......... Why so tight tolerance?
    I'm making a hub adapter for a trailer and I want to keep the spindle perpendicular as well as have the plate to spindle a tight fit.

  5. #5
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    Quote Originally Posted by N8ghz View Post
    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.
    Interesting idea. So, you are saying remove the piece from the lathe chuck, then reinstall it trying to keep the same center?

    A holesaw under the size, can work too, just use plenty of coolant/lube & go slow enough to not burn it up.
    Do you think a bimetal saw would last through a 1/2" thick piece of steel even with lots of oil?

  6. #6
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    Quote Originally Posted by Travelover View Post
    Interesting idea. So, you are saying remove the piece from the lathe chuck, then reinstall it trying to keep the same center?

    Do you think a bimetal saw would last through a 1/2" thick piece of steel even with lots of oil?
    At slow speed, it should...

  7. #7
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    I have used the multi-hole thing many times. It is time consuming too, but not as bad as hogging from 1" to 2.75".

    I recently made an adapter for a hydraulic motor 2-bolt to a C-face gearbox with 1/4" plate. I used a 3" holesaw to get near where I wanted and did the rest on my 10" lathe.
    "We, the Unwilling, Led by the Unknowing, set off to accomplish the impossible...the difficult...we do immediatly....the impossible just takes a little longer"

  8. #8
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    Quote Originally Posted by Travelover View Post
    I'm making a hub adapter for a trailer and I want to keep the spindle perpendicular as well as have the plate to spindle a tight fit.
    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.

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

    Chuck the targeted plate in your 3jaw 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.

  9. #9
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    You can use a good hole saw to do the hole. problem is you need a drill press that has a speed that goes down to about 250 rpm. I used one when making the car dolly. Slow speed and lots of messy oil.

  10. #10
    Veteran Member Hooked_on_HP's Avatar
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    Default Re: How to Cut a Precise 2.75" hole in 1/2" Mild Steel Plate

    Quote Originally Posted by Travelover View Post
    Interesting idea. So, you are saying remove the piece from the lathe chuck, then reinstall it trying to keep the same center?

    Do you think a bimetal saw would last through a 1/2" thick piece of steel even with lots of oil?
    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

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