Milling curved groove

I want to mill a groove with a 3" radius at one end in a 1" steel plate, (see diagram).

Any suggestions on how to get the curve?

Ideal job for a horizontal mill

Roy

Edited By roy entwistle on 27/12/2017 21:18:32

A flycutter with a piece of HSS toolbit set up at 3" radius would do the job.

If you use a flycutter to put the curve in as Hopper suggests its much kinder on the machine to rough out first to a series of steps on the curve with an ordinary end mill. Need to think carefully about tool tip shape grind and clearances if you need the curve to be exactly the same width as the slot with a sharp corner at the end. Much, much easier if you can allow a thou or two clearance on the side.

Horizontal mill is the right way.

Clive.

In the absence of a horizontal mill I would set the plate up on its side on my vertical mill table, with the slot-to-be horizontal. I would then use a slot saw of 6 inch diameter to cut the edges of the slot, ending each cut at the curve. How wide a saw would depend on the power and rigidity of the mill, and the type of steel, but it wouldn't be a hobby-sized machine. Then perhaps a third parallel cut (or two) along the middle of the slot. Then I would find a wider blade of the same diameter and use it to remove the remaining sections.

What I would avoid is any attempt to use a saw like this to cut only on one side of an existing slot. The blade would flex and try to follow the original slot, and quite likely jam if you were not paying 110% attention and had quick reactions.

In the absence of a saw big enough the fly-cutter idea would be an alternative, perhaps using the same sort of technique with a relatively thin cutter, and with the end of the cutter ground square (ie not angled) so it would not deflect itself up or down. After all, what would this be but a single tooth saw-blade?

The most difficult bit to get really neat, I suspect, is going to be the radius. A saw will make a clean job, but how it will cope when clearing the residual flanges depends on a lot of factors, including the sharpness of the blade (which might not be wonderful by then). It might be worth a try to leave the slot a few thou short, and finish the job by traversing the saw across the curved section several times, taking the most minute cuts each time and with plenty of lubricant.

I will certainly be keen to read alternative methods submitted by experts.

Regards, Tim

Lathe can always be used as a horizontal mill by packing the work up on the cross slide and having a suitable cutter on an arbor with tailstock support

If you apply the maths correctly it is fairly simple to work out the coordinates to get the shape with an end mill or slot drill. More maths though a bit more complicated and a ball nose cutter smooths things up. Can you get away with leaving a radius in the corner? Some of the latter/better DROs have a function to do things like stepping a radius with a ball end cutter.

Mount a three inch horizontal type cutter vertically on an arbour and clamp the work to an angle plate.

David, the OP is looking for a 3" radius so a 6" diameter cutter is required. Things could get a bit scary on a small machine. I would still do the maths to pick it out and a final flycut pass if required.

Depending what the final use is another alternative may be to mill a normal groove and then let in a curved piece, as Chris says easy enough to work out some co-ordinated and as it is easy to get a can soon be blended with a file.

Edited By JasonB on 29/12/2017 07:04:31

You sound as if you've been on the sauce again Jason! Or is it the spell checker?

Use a tee slot cutter. Mount the work on a rotary table (axis parallel to spindle but offset) so that the outer radius of the cutter is at the required 3" from the centre of rotation. Then you can get a "perfect" slot shape rather than approximate / filed slot.

Murray

Ouch! Must try reading harder