Understanding Bridgeport Model Differences?
I have searched and read but haven't had much luck finding answers to my questions.
I am interested in purchasing a Bridgeport vertical knee mill, but I don't understand enough about the various models to be able to make an educated buying decision. When it does come time to look at a machine and to make the decision, I will have knowledgeable friends with me who can look the machine over. But in the mean time, I would like to be able to do the legwork myself and to track down the correct machine before involving my friends. Thus I need to understand the differences between the models.
I am hoping some of you gurus will answer some questions and offer some advice.
1) I have seen references to series I and series II models. What is the difference?
2) I have also seen references to the "J" head. What different types of heads are there and which head do you recommend? I have been told to stay away from the variable models and to go with a model with pulley adjustments because they are more reliable.
3) I assume more horsepower is better. Are the 1 1/2 horsepower models sufficient for everything a guy might want to do with the machine?
4) Is there a range of years to stay away from those models?
5) What questions should I ask the seller?
I know that I want a DRO and a table with power feed and power lift. Anything else you suggest?
How does a CNC bridgeport compare to a CNC milling center? As a computer programmer, I can see the value of CNC so as to be able to duplicate parts. Other than an automated tool changer with the milling center, are there other huge differences between the two?
I'll answer the easy ones.
1) The series 1 is about 2000# and the series 2 is about 5000#.
Series 1 is enough for just about anyone starting out.
2) I don't but the "stay away from the variable speed" argument.
Don't worry about the head model as much as the condition of the
iron. Both can work very well.
3) 1-1/2 or 2 is fine for most. The series 2 came in 4 hp unless it was a BOSS or "special" model.
4) I would stay away from the round ram and the "M" head.
Try to get one from the 1960's or newer. I can't recall when they
stopped making the round ram and the M head.
Just my opinion. Others may disagree.
5) The condition of these is very hard to evaluate unless you
are experienced with one, and you take the one you are looking
at for a test drive.
Last edited by Polaraligned; 02-04-2008 at 09:06 PM.
Some short differences I have figured out:
1.All BP tables are 9 inches wide and various lengths,
2. The X axis travel varies between table lengths and if it has a "Bridgeport" brand, X axis drive or other drives. I believe mills installed with the Bridgeport drive, has a lead screw and travel that is 3" shorter; table length the same.
3.All J heads (series 1) are the same casting. Just different drive housings mounted on top. Belt drive and Vari-speed. I like my vari-disk drive and really really really hated the belt drive system that the Enco drill/mill uses.(I have no longer) Vary hard to change speeds. Most recommend to use the step pulley model with a VFD drive. Vari-drive is just a little noisier. Don't know much about the Series II, 2 HP models.
4.Vary good location for information is here.
From this page go to all of these for more specific info. (Or click on the links and go direct)
Milling & Drilling Heads Cherrying & Slotting Heads Head Attachments Head Adaptors
Round-ram Model Accessories Measuring Equipment Quick-set Tooling
Collets & Adaptors At Work Right-angle Drives Horizontal Miller
Serial Numbers Hydraulic Copying, NC and other Special Machines
For manuals go here:
Tough Tool, when a VFD is used with a step pulley machine, what method do you use for accurate rpm settings ? Is it a math calc. with the hertz setting on the VFD ??? or a pre made chart ? Thanks, Mark
As for the Kneemill to VMC comparison, a CNC knee mill such as a BP is fine for the home shop. If you are doing production you want a VMC. Big difference is in speed, performance and maybe a bit of accuracy. But you can make fine, high quality parts with a nice CNC kneemill.
Originally Posted by ATV
You can convert any BP to CNC for about $1000 using Mach 3 as the controller. If you want a CNC machine right off the bat I would try to find some Series 2 BOSS machine that is in good condition. They are excellent machines and as close as a knee mill comes to a VMC. They use box ways and the table never overhanges the saddle. Very solid machines. I only paid $500 for my series 2 BOSS and it has just 4000 hours on it. The ways are in very good condition.
Thanks for the reply and the links! Excellent reading on those pages. It answered a lot of my questions.
Originally Posted by ToughTool
Originally Posted by Polaraligned
Where did you find your Boss machine for $500? I've been watching ebay and craigslist and they all seem to run quite a bit higher in price. I have a hunch a local auction might be the best opportunity for a "buy" on a bridgeport.
How does one tell if the ways are in good shape or not?
I've read about people having the top of the knee and the table ground and/or scraped. I assume "ground" is a machining operation, but do you happen to know what it means to "scrape" a knee or table? Is that something that requires special tools?
Response to Mark's question - When using a VFD on a step pulley machine, you would determine the actual spindle speed by dividing the nominal speed by the Hz displayed on the VFD. In other words, if the belt position on the step pulleys would normally have yielded 720 RPM's and the HZ indication on the VFD is 30 instead of 60, then you would actually be turning the spindle at around 360 RPM's.
I say "around" because there are minor issues like belt slippage that really will not make much of a difference. Also VFD's can normally be setup to turn the drive motor at higher than normal Hz rate. So for instance, if you set the max Hz rate in the VFD to 120, the spindle could be turned 1440 RPM's with the belt positions at 720.
Running a machines motor at very low RPM's loses HP and the cooling fan on the motor is not running as much air through the motor, so prolonged use can cause overheating. Over speeding the motor can also cause problems, so I don't do it.
Only 1/2 horsepower, not very popular B&S taper on most heads,
Originally Posted by SteveM
collet size limited to 1/2", quill travel only 3-1/2".
Sure it can do some real work but with so many J and 2J heads out there, why not shoot for a better head?
Last edited by Polaraligned; 02-05-2008 at 03:21 PM.
Guy on this list, Mr Bridgeport, contacted me after I posted
Originally Posted by ATV
how my series 1 ways were worn out. He had listed this Series 2 machine in the classified here several times and had no takers. Their loss, my gain. For $500 I was not letting that puppy go elsewhere...
As for telling if the ways are OK, probably the most popular method is just to look at the "flaking" on the ways. The more it disappears, the more worn the ways are. Having rebuilt 3 BP's I now know that there is a LOT more than just the "flaking" to look at.
Sometimes the gibs are worn worse than the ways. Sometimes the leadscrews/ballscrews are worn to the point that the machine could not ever operate properly even with perfect ways. Sometimes only several of the way surfaces need to be scraped to achieve good performance, etc... You could write a book on this.
If you need to rescrape the ways, it is going to cost about $3000.
This would include refitting the gibs.
As for the scraping vs grinding, scraping is done by hand with a manual or power scraper. Takes a lot of talent and experience.
Thanks for answering Marks question for me, about the motor RPM of VFD's. Here is another solution, and one I am considering, to verify my Vari-speed 2J is reporting the correct speed. Hate to advertise for this place , but here is a listing for new ones at "buy them now" prices; that seem reasonable. Put a little reflective tape on the spindle and point the laser. Cool, . As usual, flat-rate shipping a rip-off. Joe
Originally Posted by Polaraligned
The reason I'm considering one is that they run about 1/2 the price of a J. It may depend on how much money I have at the time.
Originally Posted by ATV
Everyone go to the tooling for sale section and buy all of my stuff so I can get a "J".
"As usual, flat-rate shipping a rip-off"
Since it's coming from Hong Kong shipping may be cheap.
Thanks to Dave and Tough Tool !!
Strobe disk for a lathe. Just put it on a disk mounted to an arbor with the image pasted on the arbor side, so it's up when it's in the mill. (in fact, mount one on both sides of the disk and you can use it on both the mill and the lathe).
Then your flourescent lights become the strobe light.