Tooling question

[mike102668]

Hello guys, I am new to this whole thing and I would like to get a few books on the subject. My primary concern is how to clamp work pieces to the mill table without obstructing the cutting bit. I have a small robotic head that is around 2" x 2" x 2.5" after cutting each face, it gets harder and harder to clamp. I know it can be done becuse a friend of mine cut my design, but I have no idea how he did it. I emailed him but he has not responded in a long time and I don't know if his email is active anymore or not.

Are there any books that cover how to machine round objects?

[Geof]

What kind of features are on this piece, plain holes, threaded holesanything like that? Sometimes you have to create a way to fixture a part. Possibly some holes can be tapped in a location that is not too important. These are then used for fixturing and in the end product simply plugged.

If you are making parts to soemone else's design you may be limited to using features that are present in the design.

If you are the designer then get creative right at the beginning and figure what features you can include that will facilitated fixturing. For a one-off it is not too important but if you are developing something that you hope will result in some volume figure out ways to make your manufacturing easier; easier normally means less cost which means more left over for you at the end of the day.

A picture could be useful for making suggestions.

[mike102668]

Thanks for your reply. I will provide photos of the design as well as the final product.

The guy that machined my design, I never met in person, we met in another forum and he offered to machine my design because he wanted a challenging project. He did an awesome job.

I want to have few more made, each with different configurations.

I will have to wait to get home from work today before I can post the photos, but in the mean time, I do have some screenshots and a photo posted of a different design I made that you can look at on my personal website: www.geocities.com/botwire

if the above link does not work, try changing the forward slash to a back slash. My PDA phone does not have a backslash character available.

[mike102668]

one more thing, whats a good first cnc mill to use for hobby projects?

[Geof]

I grabbed one of your pictures and made a minor addition that may not even be necessary.

The sequence I would use is to do the bottom first with the speaker mounting recess, the interior, the four tapped holes and my addition the dowel pin hole. In addition to the dowel hole it will be necessary to keep a tight tolerance on the speaker recess because these are used in positioning for subsequent operations.

Ideally the next operation would be to use a 4th axis, or an indexer, with the part mounted from the bottom; then everything could be finished in one fixturing. With a bit of luck that is; it would be necessary to do the top by coming in from the four sides.

If you do not have a 4th or indexer then you simulate it by making a fixture with a spigot that fits the speaker recess, a dowel pin for the dowel hole and holes for the screws. You are the indexer and simply remount the part for each side. The reason for keeping a tight tolerance on the recess and for adding the dowel pin is just to maintain precision in repositioning the part on the fixture. With a 4th axis where the part is attached only once it is not necessary to worry aboutmaking provision for precise re-alignment. Which is why I say at the top that the dowel hole may not be necessary.

This part is not really a challenge for fixturing but certainly the programming is not trivial.

Having a free form shape which is what it appears you have, means that probably a longish machining time will be necessary to get a good surface finish. this is not important if you are only machining prototypes and pre-production proof of concept units. If you are planning on going into volume production by machining out of solid this could be a killer.

Laboriously machining complex curves into a mold for injection molding parts is fine because it is done once and then hundreds of thousands of parts come out of the mold. But you need to have a demand for enough volume to justify the mold cost. If your expected volumes are too low for molding or you want to maintain a fully machine appearance, which can definitely enhance a product, then you need to look at ways to ehance the efficiency of machining. One way to do this is look at you shape and see if it can be generated by a turning operation on a lathe followed by milling operations. Generating spheres or oblate/prolate spheriods on a lathe is quick and you can get a very good surface finish. Then machining what are essentially facets on these in a mill is equally fast and it is possible to get very good finishes. Following up with a satinizing bead blast process before anodizing could make your part look very classy as well as being acceptably quick to make.

[mike102668]

geof,

I appreciate your help.

I have thought of selling some of these designs and I like the idea of using a lathe to machine the crown of the part. For starters, I plan to just experiment trying different things and gaining experiance using a mill/lathe.

what are your thoughts on a Syil X2? and what about Bob Cad?

[Geof]

Originally Posted by mike102668 .....what are your thoughts on a Syil X2? and what about Bob Cad?

No opinion on either of these. My machines are all production equipment and I do not use any CAD/CAM.

Perhaps you should find out what equipment and software the guy who did the part for you used. Obviously it is up to the job.

[mike102668]

Geof, I apreciate all your help.

Here are some photos of the design that Thomas sent me when he was cutting it:







And some photos after I recieved it in the mail:







The skull fully assembled: