CUTTING A SHAPE IN STEEL PLATE

[martyn nutlandParticipant @martynnutland79495]

I wonder if our experts could help me on the best ways to tackle this. I do have a plan, but I’m wondering if it’s realistic.

Background: I want to cut a lozenge shaped hole in a steel disc. I have two vintage Austin Seven axle tubes. Many of you will be familiar with the set up. The axle is in three parts (four if we’re pedantic). The central case for the differential, two side tubes for the axle shafts, and a torque tube at the front. The problem is, someone has cut the brake back plates off my tubes(!) and left a lozenge shaped end on which they intended to fit  some sort of hydraulic brake arrangement or; perhaps, the very late Austin Seven Girling mechanical set up. (Photo one)  I don’t want any of this, but I don’t want to discard the tubes either; rather to return them to their original vintage form. Photo two)

Thus, I need a new back plate (144mm diameter) with a big hole in the middle to weld onto what’s left at the tube end.

The complication with the hole, as you can see, is it needs a radius top and bottom to fit onto the tube and I’m not sure if my thinking on this is sound.

I thought –  establish the radius of an imaginery full circle (51.5mm actually)
whose circumference at its outer extremity would be about15mm inside the circumference of the back plate.(15mm is the distance from the radius on the hole to the  edge of the back plate. This is not a critical distance but it needs to accommodate a hole for the brake actuating cam shaft and the fixed pivot for the brake shoes). Given we know the lengths of the straight sides of the hole (12 cm) and the distance they are apart (width of the hole)  scribed vertical lines should touch the cicumferance of the imaginary circle,at a point that would create the correct radius on the hole. Is that correct?

But how do you make the hole?. I thought to secure the back plate on a rotary table, and with an end mill/slot drill in my  milling machine, off-set the spindle to the radius of the aforesaid imaginary circle  measured from the centre of the
back plate. Turning the table through the requisite number of degrees against the mill should then cut the radius shouldn’t it? The cutter could then clear the waste by moving down both sides on the mill’s Y axis? But if this is viable – what would be the correct/best type of  mill?

 

Many thanks in advance and for your patience.    Martyn

 

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[Martin KyteParticipant @martinkyte99762]

Draw it in CAD and send it off to the water jet or laser cutters?

regards Martin

[JasonBModerator @jasonb]

What thickness are we looking at?

If you want to do it yourself it may be better to stitch drill just inside the edge of the hole and knock the waste out. You are then just left with your rotary table setup to clean the edges up.

3-Flute milling cutter should do the job. And a lot less stick out that that cutter in your first image.

 

[DC31kParticipant @dc31k]

As it is necessary to break out the hot glue gun in order to secure this, make it in three parts. Your axle is made from multiple parts, so a few extra won’t matter.

Make a large washer with concentric ID and OD circular holes.

Make a circular piece that fits inside the ID hole of the piece above, with clearance for a glue joint.

Two straight cuts with a hacksaw on above piece and throw away the part that falls out. Decide for yourself if these cuts are best made before or after welding.

Grinder and paint to tidy up.

[noel shelleyParticipant @noelshelley55608]

Plasma or oxy fuel cutting ? Mark it out and cut it. clean up and prepare the edges, then weld in ! I’m near Kings Lynn,bring the materials and I’ll cut it for you ? Noel.

[martyn nutlandParticipant @martynnutland79495]

Thank you very much, everyone, that’s very helpful. Thanks especially to Noel. Unfortunately (or fortunately!) I’m in northern France, so King’s Lynn’s a bit of a hike. Nonetheless, many thanks for the generous offer.

Martyn

[Speedy Builder5Participant @speedybuilder5]

It sounds a big ask, but have you tried an ordinary jigsaw! Use some cutting oil and a new quality metal cutting blade, slow blade speed and plenty of pressure. I have cut 3/8″ plate like this. Once the blade is blunt – replace it.

Mark your plate out, support it on top of some closed cell insulation so that the blade doesn’t hit the table below. Drill a clearance hole for the blade and be surprised.

Bob

[martyn nutlandParticipant @martynnutland79495]

Bob

Sounds a brilliant approach. Only surprise would be if I was sufficiently skilled to wield the jig saw. Brilliany nontheless.

M

 

[Howard LewisParticipant @howardlewis46836]

If all else fails, Drill a hole, and then proceed with an Abrafile, finishing to size and shape with one or more files.

The ability to offer up, should make accuracy greater.

Howard

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