for better students

[daver59]

I have 2 cnc mlls in my classroom-kids have made all kind of differnt signs
i want to challange some of my better students with some mechanical projects- leaning towards may from some molds or mechanical parts
both machines are 5 inches in z direction and 22 by 24 in yx
any help or places where i could find parts that they could reverse eng would be great

thanks dave

[tobyaxis]

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[scadvice]

Dave,
As a former teacher of adult CNC machine and programming classes (NTMA) I can tell you what I saw as lacking in those students and some of the teachers. First and foremost, there needs to be a better understanding of the math and preparatory codes. (i.e. program starts, tool changes, and ending the program.)
It would help if I knew the abilities (2.5 axis or full 3 axis) of your machines but I would suggest helical thread milling single and multipoint cutting as one challenge
Another would be to create a tall thin walled pocket or pockets inside a shaped part. It can be as simple as box on the outside or get real interesting with a few curves added in. The first milling operation will require milling the outside features and profile to size, then making fixture to support the outside form while milling the inside features to say a .040 wall. Make the depth of the pocket at least thirty to one on the wall thickness or it will not be enough of a challenge. Add a blow hole to the bottom of the fixture to help pop the part out. Fabricate a thin aluminum top plate screwed to the fixture and machine through it as you do the first part or, make it beforehand, as part of that fixture project. This top plate’s pocket is the same size as the inside pocket and is to hold the part in the pocket. An alternative is, if you have a vacuum pump, drill smaller and more holes in the bottom of the fixture and you will not need the top piece. It certainly will add to the learning experience. The first part or two will have chatter marks , so the next challenge to this project is to figure out how get rid of those marks.
Other notes for you the teacher:
It would be best to start this project using a .250 or larger end mill.
Extended length end mill will be needed. Back grind a regular end mill for side clearance. Buying extended length end mills will work but generally are all too long and chatter a whole lot.
Also grinding the side cut length of the end mill down to equal to or less than the diameter will minimize chatter. Another thing to do and a learning experience, is to test the hand ground end mill on a scrap of material.
Don’t start out roughing with the extended finishing mill.
Try this, step out, 3 to 5 thou., as you go deeper with a standard end mill and reach its side cut maximum length.
(hint: you will get an idea of speeds and feeds when testing the ground end mill, that you can apply to the programs)
(hint: high chip loads and slower feeds on finishing)
(hint: design the part so that the program radii are always be bigger than the end mill’s, forcing them to program the corners and not a sharp turn. This minimizes chatter. Make them keep the wall thickness always at .040.)
(hint: Use aluminum 6061- t6 for best chance of getting good results on all the task)
A simple mold for plastic injection… if you can get it tested later, check with a local mold shop, maybe you can get them to give a little talk on making one.
Steve

[daver59]

the projects i am looking for are for grade 10-11-12
the students can draw/design ok in mastercam
the machines are true 3axis and last project was a coke bottle- classic type
turned out not to bad- had to project log- from logur ru
onto the surface of model of actual bottle
thanks dave

[Hennessy]

have you thought about http://www.skillsusa.org/ or something similar? I would think that you would have something like V.I.C.A. in Canada. A little competition is all ways a good thing especially if you wan to push your students.

Hennessy