View Full Version : NEW MEMBER: Goal - Enable 3-Axis CNC Bed Mill to Perform 5-Axis Milling

21-01-2012, 07:20 PM
I have a 10-horsepower 7,000-pound 9.5-foot-wide 8-foot-tall 7-foot deep "Rigid Head" (no tilting for greater rigidity, and no quill within the head, just as are as most VMCs) CNC 3-axis bed mill with 20-position CAT-40 automatic tool changer. Addressable CNC working space limits are X=43.5 inches, Y= 19.5 inches, Z = 23.5 inches. This same machine is sold as a Vertical Milling Center with a different model number just by adding a full enclosure to confine chip and coolant spray and provide operator protection. It could have been purchased with the optional 10-inch CNC-driven rotary table 4th axis, but the manufacturing company from whom I bought it did not buy that option. So its CNC movements are currently limited to 3-axes, even though its software was written to address 4 axes. I could simply hunt for one of those optional 4th axis servo-driven vertical/horizontal-mountable 10" rotary tables with controller card to convert it to a factory-configuration 4-axis system. Original software sold with this machine can address 4 or 3 axes.

But having seen what 5-axis CNC control makes possible, I want to make an attachable/detachable additional 2-axis head attachment. Such a system has been marketed since 1996 by Tri Tech. Just search "Tri Tech 5 axis" to learn about that highly-desirable attachment. But according to my on-line research, they show $42,000 (currently 27,600 pounds) as their "on-sale price," and that's not including the required 2 Servo driver systems. To give you an ideal of their pricing, they were demanding an estimated $3500 ~ 2250-pounds extra for the required 2 servo motors and cables. Dealing with pricing like that is not in my budget. I'm not saying that Tri Tech's 5414 attachment is not fairly priced nor highly desirable. I'm just saying that I can't afford to buy one new or used. It seems odd to me that their 150-pound weight attachment is priced almost as high as a new mill like mine without tooling or tool holders.

So I want to make my own head-mountable 4th & 5th axis attachment for my 3-axis milling machine. I do not want to simply copy their evolved version of their 1996 design configuration. I think its mass is low enough, but its vertical projection of about 12 inches seems unnecessarily long.

Since this is my first post here, I'll mention that I also have a 2250-pound 2-horsepower BridgePort style mill with optional variable-speed drive (not fixed 8 or 16 speed step belt drive) X & Y axis digital read outs, and power X-axis feed. In other words, its a fully configured common manual BridgePort mill. I'm also building for CNC fun and family sharing entertainment a small CNC machine. I may post some photos of it as that work progresses.

I know this is rather atypical, but this group includes such a diversity of talents and experience that I decided to join your mainly UK but actually international group. Take a look at the Tri Tech configuration, consider the high precision and rigidity that will be required to be appropriate to become a compatible fit to a machine like mine, and let's discuss design paths and suitable existing components that could be purchased used or as salvage, machined and adapted for this project.

Also, I'll be eager to learn about what software packages can create 5-axis tool paths and send those instructions to CNC drivers. I want to use the existing spindle power drive to drive through the attachment's two additional axes.

Lots of "mind candy" for you innovative souls. Show the restraint not to instantly post back. Think about it for a few hours first. Your better-considered responses will enable a better discussion.
Thanks for your consideration,

22-01-2012, 10:09 PM

I will let those with more experience in the physical components deal with those issues. My question is what is the budget for the CAM side of things? I know of a software that is capable of doing 5 axis work and while not as expensive as say MasterCAM or Gibb's it is not cheap for the multi-axi set up either. Good luck and best wishes.


25-01-2012, 07:46 PM
Thanks for your reply. I found it interesting that you'd mention Gibbs software because a machine-specific version named Gibbs SFP Express Programming Software was factory installed on this machine. Here's how that appeared in their promotional images on the machine's control panel.
But that SPC version is limited to 3 or 4 axes.

I will want software that's workable though I understand that to buy one of the claimants to being able to generate the absolutely most efficient tool paths and speed variations along that path, very high cost products are required. I'll be most interested in lower-tier priced 5-axis software. What product brands would you suggest examining to find which best fits that general description?

I've been looking at large "slewing bearings" through which the driveshaft and adjustable-angle gear set's power can pass. I imagine the first slewing bearing attached to the head, enclosing the original spindle, with a worm drive to enable controlled-position rotation and power transfer. The first adjustable-angle bevel gear set would be as high as possible under the CAT 40 tool holder, limited by its required ability to rotate from +90 degrees through 0 degrees to -90 degrees. That pivoting section would be enclosed by a second slewing bearing positioned by a second servo or stepper motor and a second identical adjustable pivot angle gear set. If both adjustable-angle bevel gear sets are set to 90 degrees, vertical height loss caused by using this attachment would be at its minimum value. I think and hope that length can be significantly shorter than Tri Tech's product.

Some really clever slewing bearing race and cage configurations exist. I especially like one I've seen illustrated which alternates rollers positioned on axes about 90 degrees apart, forming two concentric and interleaved roller sets which load against roughly 90-degree separated thrusting race faces. I'll try to find an address where that configuration can be viewed and edit this note by adding that link.

Before anyone points out the obvious fact that my automatic tool changer won't be able to work with this attachment, I already know that. 99% of my use for this machine will probably still be 3-axis work. I'm also aware that every linkage and force extension reduces accuracy. So being able to maintain 0.0005-inch accuracy will disappear by adding two worm-driven slewing bearings and their housing's additional length. So far as I know, 5-axis machines are always less rigid and so less accurate than otherwise-comparable 3-axis machines. That accuracy loss is just another cost of swimming in those waters.