CNC Bed vs. CNC Knee Mills

The idea of a CNC shop at a university is for training and not to show a profit.

The machine has been paid for or is heavily subsidised by state and therefore will give an unfair advantage over setups who must buy and maintain their own machines. The students must remember that they may also have to compete against the university one day. Would they consider it fair then?

We sometimes do prototyping of only 1 part but we Analise the single run and optimize the toolpath and speeds to obtain the fastest throughput whenever necessary.

My feeling is that a university shop should stick to prototyping but must learn as much as possible from that for training in design, scheduling, optimization etc.

While I do agree with you, i was actually employed at a CNC shop based in a university environment (UMaine Advanced Manufacturing Center), where the shop had several purposes. 1) To support businesses in Maine by performing 1-offs, prototyping, and short-run parts for custom/specialty applications 2) To give students in the engineering technology programs a solid hands-on real-world exposure to industrial environments, and to make sure they knew what it was like to be "the guy on the floor" that would have to deal with the designs that they handed down in the future.

The AMC was started with grants/and contributions from individuals, yes.. but past that, it had to be a self-sustaining entity, but working within the University environment (aka, had to keep itself alive, but could not compete with any Maine Business). The shop also had to purchase, retrofit (we did many CNC retrofits that were then sold to "local" businesses ), and maintain all of their equipment. We couldn't have been the ONLY such shop anywhere, and we did not compete with any businesses (in reality, we could not due to the cost of properly training students that were not familiar with processes & machinery).. but sometimes, there were many such short-run projects that came through, in which businesses within the state either did not have the time, the manpower, or the capability to do.

To answer the OP, we heavily utilized bridgeport series 1 and 2 mills (running on Mach 3 cnc control software... in-house retrofits), as well as a Mori-Seiki (sp?) SH-50, and now a Friar enclosed machine. The BP style machines were GREAT for the smaller-run projects, while the Mori & Friar were invaluable in the high-tolerance, larger-quantity (50ish units) projects.

For yet other projects, requiring large-sized components, we had a Cincinnati horizontal mill weighing in at approx 40k pounds, standing approx 20' tall... and a matsuura 1000 and 1500..

I think you need to ask yourself, "what kind of projects are we going to be taking on?" think of size, quantity, tolerances, etc. This will help you determine just what it is your shop should be looking into. If you would like more information about the UMaine AMC and just what kind of projects THEY have had to deal with (trust me, they have been a complete gamut of things), or how they have made their decisions for machinery, give me a shout, I would be glad to put you in touch with them!

A bed mill or "C" frame mill is definetly better for rigidity, z axis travel, precision and tool changer options.

Depending on the level of precision required, the economy of a knee mill might be an option.

I also work in a University prototype machine shop supporting research in the College of engineering, College of vet med, physical plant and a few other smaller areas. We also support undergrad labs i.e. making material testing specimens. This shop is a STAFF ONLY shop. CNC knee mills were selected for their larger workholding area. These mills have about 25000 hours on them, still able to work to + - 0.0002". These are 4-axis machines with high speed spindles. We also have a bed type machining center. It is not used nearly as much as our knee machines due to the smaller work holding area.

The Mechanical Engineering area has Bed type machines for teaching and student groups such as formula SAE race car, Robotics, etc.