UPDATE – CUTTING A SHAPE IN STEEL PLATE

[martyn nutlandParticipant @martynnutland79495]

Here it is chaps! With renewed thanks for comments, ideas and offers of help. (The small peripheral holes are to attach the dust cover.) Two photos attached.

Olypmian Martyn

 

[Speedy Builder5Participant @speedybuilder5]

And how did you do it so others could use the same process. Thickness of metal would be useful too.

[martyn nutlandParticipant @martynnutland79495]

Hello Speedy

I started with a piece of square mild steel plate 300mm x 300mm x 3mm from  RC Machines in Luxembourg. The thickness is not critical but should be  3 to 4 mm.

The diameter of the original back plates was 144mm. Again, this is not critical in itself to within a millimetre or so, but once you have set the diameter your other calculations are dependent on it.

I created the blank back plate with an angle grinder (rough shape), belt sander (bit nearer round), lathe to finish. This certainly is not the most efficient or elegant way to cut it, but I had to use the tools I had to hand! The set up on the lathe requires the blank to be held on a mandrel which obviously requires a hole in the centre and this hole becomes very important later.

I now had a blank back plate 144mm in diameter. I then cut a cardboard template from the lozenge shape on the converted axle tube fitting it over the journal for the inner hub bearing. Now, by transferring the template to the back plate blank you see that the curved top and bottom sides of the lozenge lie on an imaginary circle whose radius from the centre of the blank is 50mm (diameter 100mm leaving a ‘border’ around the back plate 20mm wide to eventually accommodate the hole for the brake operating camshaft and the fixed pivot for the heels of the brake shoes)

I now created a cardboard template 144mm in diameter containing a circle 100mm in diameter.

But we know from the converted tube the straight sides of the lozenge are 80 mm apart thus two vertical lines drawn 40mm out from the centre of the concentric circles will intersect the inner one (100mm diameter) at the extremities of the curved  top and bottom of the lozenge.

I then cut out the template, cut out the lozenge shaped hole, and stuck it to the back plate blank with double side sticky tape!

 

OPERATIONALLY I wanted to make this on a milling machine by holding the blank in a three jaw chuck on a rotary table and cutting the curves with an end mill by turning the rotary table through the requisite number of degrees. Then cutting the straight sides by simply moving the mill table along its Y axis.

The difficulty is holding the work sufficiently securely to make the cuts. I tried expanding mandrels which proved useless (and expensive) so I made a mandrel to fit the hole used all those hours ago when the blank was in the lathe. It was secured with spacers and a Loctite(d) nut. This worked.

I set things up by centring the mill spindle over the blank when it was held in the chuck. I then set the table on the Y axis over by 50mm until the end mill (6mm four flutes) I intended to use just touched the curve of the template. I then wound the rotary table from corner to corner of the curve (where it met the straight sides) and noted the number of degrees of rotation

I cut both curves with the 6mm end mill at 0.25 mm deep passes cutting in both directions. I cut the straight sides with a 6mm slot drill. It was much quicker but probably too heavy for the mandrel and next time, I’ll be more patient and do the sides with the end mill as well.

The rotary table I have (a three slot Vertex) tends to kick about under the cutting force and to overcome this I found it helped to hold the table locks partially on. Seemed to work.

 

Hope this is what you wanted and is of help. Sure there are much better ways!

 

Best  Martyn

[Howard LewisParticipant @howardlewis46836]

Glad that you got if done.

Hopefully only two, just for the rear axle!

Howard

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