The Home Machinist!

I have to make a small rectangular cube to use as a jig and the top has a large radius as shown in the picture. The cube is about 1-1/2"x2" and about 1" high. the radius would be about 10" or maybe even larger. What would be the best way for me using a manual mill to accomplish this task. I looked at one that we had a machine shop make and it looked like they made small step cuts. If this is the way to go is there a online formula I could use to tell me the coordinates I would need to know to get the proper radius.

An extension plate on a rotab, with the use of a die sink end mill will work perfectly well. The larger the rotab, the better. Do not attempt a climb cut.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

The ROUNDER program on my webpage was written for just this sort of problem.

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Regards, Marv

Home Shop Freeware
http://www.myvirtualnetwork.com/mklotz

Thanks guys, mklotz I attempted to use your software but I get a error saying it wont run on my 64bit computer. Too bad because I was looking forward to trying it out.

Harold_V I thought about using my rotary table so maybe that is what I will try. I am not sure what the die sink end mill is for. If I clamp the part on its end with the face to have the radius facing outboard wouldn't I just use a regular endmill or am I going about this wrong. I never heard of a die sink end mill and when I google it I see what looks like a tapered end mill, is that right.

Die sink end mills are simply long-fluted end mills. I have known them only as die sinks----but you might try looking for end mills with long flutes. Don't buy anything longer than your requirements---they can be testy to run when they're long. They often require slower spindle speeds, to avoid chatter.

A standard end mill may serve your needs if you have one that's close to the proper length. Simply relieve the shank slightly (you can do that by hand if necessary), so it doesn't make contact with the surface being machined. You'd have to take more than one pass, so you'd cover the cut top to bottom. That's the reason for suggesting a die sink (a term that is now appearing to be either improper, or outdated).

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

Use DosBox,

http://www.dosbox.com/

to run legacy software on 64 bit systems. It's free and works well. You'll probably need it for other, older software as well.

_________________
Regards, Marv

Home Shop Freeware
http://www.myvirtualnetwork.com/mklotz

Ok I fully understand now Harold. Thank you. Im going to order a couple right now. mklotz I am going right now to get dosbox.

Harold, I assume I would want to use a larger type endmill to reduce any flex. Is that right. If so would a 3/4 be good or should I use something smaller. The material will be steel.

How many pieces, and what's the material?

If it's aluminum and 1 or 2 pieces, send me the material, and pay the shipping back to you and I'll just do it for you.

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You can buy good parts, or you can buy cheap parts, but you can't buy good cheap parts.

Rule of thumb dictates you should always use the largest end mill you can when running long end mills. As you alluded, it's to limit flexing, and chatter in particular. A 3/4" would be a good choice, however, even if you might consider a larger diameter. Consider cost, and make your decision accordingly. If your choice is longer than the cut, use the upper portion of the end mill instead of the end. Again, for rigidity.

I would normally suggest you take a climb milling cut for finish, but with an extended rotab, that's a recipe for disaster, for the mechanical advantage the end mill has over the extended table is too great to permit smooth feeding. Even with a spring cut, you risk the end mill picking up the part. Be careful!

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

well from your posting it sounds like the actual radius is not important, just that it is smooth,,
well one idea that is crazy but might work with some carefull set up and use. set up a large fly cutter, tilt the head over a bit , then come in under on the backside of the cutter on its high side. could only feed in to around the center point. would have to play with the cutter geometry a bit and light cuts. but you may get what you need? I have sean it done to get a "female" radius on parts, just use the upswing side to get the "hump" you need. would not be a true radius but more of an eclipse. just throwing it out there.

Mid Day MachiningThank you for the offer, that is very kind but I want to be able to do it myself so in the future if a similar circumstance arises I will know that I can do it.

Harold Again thanks, I already have a couple 3/4 endmills with about the right flute length so I will use them. I wasn't sure if the bigger the endmill the more cutting force it would apply and try to pick the part up.


gcarsenRadius is important but until I get the example part I am not sure what the accual radius is. I am just guessing based on what I saw. I never thought of doing what you suggested but my luck things would go wrong in a hurry. I do have a rotary table so that will be my first try.

If you can tolerate a spherical rather than cylindrical surface, Tom Lipton's book "Metalworking Sink or Swim" has an interesting article on pages 149 to 154. It's hard to explain (he takes 6 pages), but basically you put a single point tool in a boring head and angle the mill head. You then mount the part on a rotary table underneath the angled boring head and turn the part. The cutter describes a circle as the boring head turns. This circle lays on a spherical surface, and rotating the part moves the cutter circle around the part until the spherical surface is complete. It will do both concave and convex surfaces depending on the setup.

One example in the book puts a 13" radius on the surface of a 5" circular part, using a swept diameter on the single point tool of 2.550 inches, and the head angle at 11.31 degrees.

The example for a hemisphere on the end of a 2" round bar uses a 45 degree quill angle and a 1.414 swept diameter of the single point tool.

The Swept Diameter is given by the formula SD= D sin (angle) and the quill angle is perpendicular to the chord of the spherical segment you want to make.

ISBN is for the book is 978-0-8311-3362-7