Machining 70 degree angle

[Hanz]

It's getting time for me to re-machine my steady rest base 'V' to the correct dimension, and I am having a mental block- how do I machine a 70 degree included angle, preferably without buying a cutter for one time use, assuming they even sell one?

I would like to do this in one setup on my Bridgeport, although the only thing I can come up is whittling away each side of the angle with a small endmill, maybe 3/16.

[Matt_Isserstedt]

I hate to say this Hanz, but I was going to do it with the shaper. I was going to try to skew the toolslide over to 35 degrees and then take light cuts to get the V with the keyway at the bottom. I got a little confirmation of this in the Audel's Toolmaker Handbook which showed a 90 deg V-block with keyway being made as a planer exercise. (Nice excuse to get a shaper or better, a planer, right? [img]/ubb/images/graemlins/smirk.gif"%20alt="[/img])

This is the best way I thought of short of having special rotary cutters made.

Seems like the Bpt could do it. I think if you were very careful and setup the centerline correctly, you could do both sides with 1 setup, just flip the part 180 degrees.

[Hanz]

I was thinking, nice excuse to get a cutter grinder. [img]/ubb/images/graemlins/smirk.gif"%20alt="[/img]

I have watched the 5914 auctions, hardly any with a steady rest. Strange, where'd they all go? I wonder if it was a not-included accessory on a new machine? Then you see loads of Southbend rests. Why were so many of these separated from their machines?

[philinmt]

It would be a lot better to do the job on a shaper or slotter, but if I had to do it on a mill I would use a rot. table and the lagest endmill that woud cut the face of the vee and then file the corner out by hand. You probly dont have enuff room to stand the stady resy up to cut it with the end of the endmill, if you do you would save a lot of filing...Phil in Mt

[JeffinWI]

Hanz, how were you thinking of setting up the steady rest on the mill? Split line of the steady rest down on the table, with the base up towards the spindle?? You could tip the head to 35º, using an indicator to accurately set the angle. Then "slab" or "endmill" one side of the "V", whichever you prefer. Turn part 180º, repeat.

[jpfalt]

The last time I did something like this I used a 60 degree large dovetail cutter I made ub by nickel silver brazing a triangular cabide insert into a steel shank. On the Bridgeport, I'd stand the steady rest up on end and dial in the flat base surface and then cut the angles by rolling the head of the mill to the left or right as needed to get the angles right.

[Hanz]

Yes, setting it up is not the problem, it's cutting a 70 degree angle with a 90 degree cutter-it won't work! (Unless as I was thinking, a very small dia endmill which would leave about a 1/4" clearance shape at the top of the 'V', or as suggested, making or buying a 60 degree cutter and swinging it 10 degrees more.)

[Jim_King]

If setup is no problem,I dont understand why you cant tip the head and fly cut it.Should work fine.

[JeffinWI]

oooops, my bad, Hanz. Ya, you'de have to use a small, maybe 1/4" end mill (assuming there is some kind of relief at the bottom of the "V". I like Jim King's idea better though...flycut it.

[Hanz]

Bingo! I knew there should be a way to do it with the tooling that I have. Thank you.

[Harold_V]

Hanz,
I couldn't help but note that you have had recommendations to cut your angle by tilting the head on your mill, and to cut both sides of the angle by rotating the part. Each of those will work, but the setup is a bit more demanding than you may realize. When you tilt the head on your mill, keep in mind that if the ram is not dialed in with the saddle, you will generate a compound angle and the cut will not be true. Just like in fly cutting a flat surface, if your cutter isn't cutting equally on
each side, leaving a cross hatch finish, the head is not set properly. The cut you generate will not be flat, it will be concave, and will not be the angle that you assume it to be, though it will be close.

Indexing the steady rest to cut the second side is likely to be a miserable failure, even using a rotary table. The degree of precision that is called for in a cut of this nature generally doesn't allow for moving the item being machined unless you have perfectly parallel faces and a square end, from which you can locate your part reliably. Give serious consideration to the fact that if your cuts are not dead parallel your steady will bear in one place only, not on the entire machined surface as it should.

The idea of making your cuts on a shaper or planer are the best, that or a form tool so the cuts can be made in one setup, thus guaranteeing that the cuts will be parallel to one another in both planes. Beyond that, I'd suggest that you set the rest such that you can make the cuts on both sides of the angle without moving the part, just change the angle of the head instead. You might fight a little hitting the exact angle you desire, but at least your cuts will be in proper relation to one another, the most important thing to consider aside from hitting the right size.

Harold

[Matt_Isserstedt]

Hanz, just wanted you to know I did test out my theory of cutting the 70 degree included recess with a shaper. I roughed out a groove from a scrap piece of CRS.

I had to grind a tool correctly for slotting (based on my newest favorite Audel's handbook) which improved the ease of cutting the middle, plunge cut.

Then tilted the toolhead 35 degrees each way, went up to the scribed line.

My test part was a scrap piece and I cut slightly too wide, but I can tell the surfaces are parallel. Tomorrow with a little smaller toolbit (1/4 or 5/16 instead of the 3/8" I used) I'll give it another shot. I also need to make a "finishing" toolbit as my roughed surface was, well, a little rough, and I only used 1 bit....

I've been kicking around using a thin 1/8 or 1/16" thick hardened piece of A2 steel on both inner angled surfaces, just trying to convince myself that flathead screws can be set slightly below the surface. I'm thinking TINY screws, #6-32 I think. That way it'll never lose tolerance....but not that it's gonna get that much wear....oh well, I seem to like overkill most of the time. [img]/ubb/images/graemlins/crazy.gif"%20alt="[/img]