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Thread: Bridgeport CNC Conversion Advice
07-06-2006, 12:35 PM #1
we have a Bridgeport Series II Special milling machine in our powerplant machine shop. It sees light use and can hold tenths. We do certain light production runs of replacement parts for some of the plant equipment. This work requires using a large Troyke rotary table to do circular milling for certain parts with about a 25" radius. This same job requires multiple setups.
We do some other jobs that are a little less complex, but still require multiple setups and some fixturing.
As a result, we are considering converting this Bridgeport Series II mill to a combination manual/CNC machine tool. It presently has the 2 HP varaible speed head, and Accurite 2 axis DRO on it. This mill is our only milling machine and we do not have the shop space to put in a dedicated CNC machine. As a powerplant maintainence shop, we would also have a hard time justifying the expenditure for a dedicated CNC machine. We get a good deal of use out of the Bridgeport as a manual mill for one-off kinds of jobs. However, the profile and circular milling jobs along with the light production work have me considering the CNC conversion.
Has anyone got any opinions or 'druthers as to what they would recommend ? Our local Bridgeport dealer offers a retrofit that includes ball screws and Accurite CNC. Another firm is offering a conversion built by Centroid. Anyone have experience with either of these retrofits ?
I would appreciate any information based on experience, or suggestions or recommendations which anyone may have to offer.
07-06-2006, 12:39 PM #2
I have used both on a Taiwan built mill. The Accurite is the better of the two. Expecially for simple parts. It does not have all the extras that the centroid has but was quicker to learn, use, and operate. Plus it never broke down, the centroid did,
07-06-2006, 12:59 PM #3
07-06-2006, 01:39 PM #4
I think it definitely would be a good move to do the CNC retrofit, but the toughest call will be whether you go 2 axis or 3 axis. If you go for three with the typical retrofit of the machines quill, you will lose some of the manual flexibility of the quill feed.
For machinists used to doing quick one off jobs on a manual machine, especially things like tapping this will be the biggest negative. One way around this is to put the 3rd axis control on the knee instead of the quill, but I don't know if the retrofits you are looking at offer that.
I have a 3 axis CNC BP clone and a manual BP clone in our prototyping shop. You can control any axis on the CNC with an "MPG", basically a calibrated control knob. It allows you to manually position and cut with an axis, but you don't get any "feel" back through the lead screws. However, I use this capability often to do quick manual jobs with the CNC machine. The manual machine rarely gets used now, but I would use it for a "one off" tapping job or for some quick and dirty jobs.
If it was me I would go ahead and do a 3 axis retrofit and live with the loss of the manual quill feed, but if you are getting any resistance from "old school" machinists there this will give them more to squawk about. If you use the machine for tapping and you go 3 axis, it will take some additional setup and training to do tapping on the machine. This would be a good thing to ask the retrofit vendors about.
Even for simple parts, (brackets for lots of holes for example) having the 3 axis machine makes it much faster and less error prone to make the part as the drilling is fully automated.
07-06-2006, 01:45 PM #5
They've got all the conversion hardware and they also have a quill drive that allows, so they claim, the quill to be detached from the drive so it is just as sensitive for manual use as standard.
07-06-2006, 03:10 PM #6
I really like the Accurite...it even adjusts for skew...no need to indicate for alignment! SWI has some really neat features as well like Traking...you crank the handle and the servos power thru the program, really neat. They both have some feature neither has, but SWI is weird to deal with at least in our area. You never know who to buy from. Their tech dept left a bad taste. Accurite on the other hand was very helpful on the phone and all hands seemed to be on the same page. For a mill, I lean towards Accurite. Plus they have great scales to go with the conversion package.
07-07-2006, 02:00 AM #7
If I was going to do a retrofit on a Series II Special for the uses you mentioned, I'd go with either a 2 axis setup or put the Z on the knee if I was going with a 3 axis. In either case, I'd leave the spindle as is. The S II Spl already has the air counterbalanced knee, which takes care of the common problem when trying to do the knee on a Series I, namely the weight of the knee. The mass of the knee would slow the max rapids somewhat as compared to a spindle Z, but for your use that's probably a non-issue. For a multi-purpose machine, having a BP head that still functions just as it was intended to is too handy a thing to give up IMO.