Cutting a perfect circle out of square steel

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little_sparky

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Hello all,

I was just wondering how I would go about cutting out some perfect circles from about 10-15mm thick cold rolled mild steel. I have a fair few basic tools, like all hand tools and grinders and a lathe but I don't have a mill or CNC machine.

The purpose for this is for a hub I am creating to put onto a custom made axle and wheels.

Here is a link to my thread about creating and strengthening the wheels/axle, and page 2 has a drawing of how I am thinking of doing the set-up, although I will post pics very soon,
http://www.hobby-machinist.com/showthread.php/31010-Beefing-up-an-axle-what-methods-could-i-use

Thanks, little_sparky
 
Here's an idea. you will probably get better ones from others.

1) rough it out with a hacksaw
2) drill a hole in the center
3) mount it on a mandrel (a large bolt perhaps)
4) chuck it in the lathe and true up the circle.
 
Depending on final dimensions ID / OD of the plate, I did a similar thing when making a wrench for my collet chuck. First I chucked the square stock ( 3/4" plate ) into the 4 jaw chuck and bored the ID with a boring bar, then reversed the jaws and grabbed it from the ID and prepared for the shower of chips that was to come proceding to cut the od.
 
I second herbet suggestion. As long as you can drill the center you can mount it on a mandrel. 10-15mm is fairly thick and you will have an interrupted cut at first. Make sure that the mandrel holds tight. You should layout the circle and remove as much material as you can with the grinder before turning on the lathe, the goal is to get it round not perfectly round. Remember you can always cut away but its very hard to put it back, get close but not too close. If the center hole has to be concentric I would drill the hole small for the mandrel, turn the work round then remount it on a chuck and bore the center hole. This will eliminate any movement of the work on the mandrel.

Caster
 
little_sparky said:
Hello all,

I was just wondering how I would go about cutting out some perfect circles from about 10-15mm thick cold rolled mild steel. I have a fair few basic tools, like all hand tools and grinders and a lathe but I don't have a mill or CNC machine.

The purpose for this is for a hub I am creating to put onto a custom made axle and wheels.

Here is a link to my thread about creating and strengthening the wheels/axle, and page 2 has a drawing of how I am thinking of doing the set-up, although I will post pics very soon,
http://www.hobby-machinist.com/showthread.php/31010-Beefing-up-an-axle-what-methods-could-i-use

Thanks, little_sparky
Click to expand...

Great question! I learned a lot from the replies.
 
Just a quick thought, if I put the piece in my 4 jaw chuck, (at this stage is it easier if its square or roughly cut?), how do I know that my piece is centred? or do I get it roughly in as a square piece, centre drill to give myself a starting point and then measure out from there with either a template or compass, after that roughly cut and then when I put it back into the lathe line up the centre drill with the hole and then drill out the centre from there, then put it on a mandrel (cant be a bolt as the mandrel will centre it?) and take off the rough cut until i'm satisfied?

thanks
little_sparky
 
Yes, in my idea, the center hole would be your starting point. Just make sure the hole is where there is enough metal around it to fit the final outside diameter.

If you can chuck the 150 mm in your lathe, then you can drill the center hole undersized, machine the outside diameter, and then chuck the outside diameter (without the mandrel). and then bore (or drill) out the final inside diameter. Just like Caster described.

I would think that 15mm thickness would be thick enough to chuck with out deforming the piece. Others might be better to comment on that.
 
Put dykem on it and use a rule to make an x from corner to corner. Center punch where the lines meet. Put in 4 jaw and use 2 dead centers. One in the tailstock and one pinched between the tailstock and with it's point in the center punch you made in the plate.
Put a dial inditator on the dead center and adjust the 4 jaw.

If you don't need it that close you can just eyeball it from the dead center in the tailstock. Just bring it up close not touching your plate and adjust 4 jaw till center punch mark lines up with dead center.
 
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