Bridgeport accuracy questions

[christian79]

Hello,

I am an electrical engineer by profession so please excuse my ignorance on this topic. I have always been interested in metal work but have never had the time or money to try it as a hobby. I have been contemplating building my own mill after reading www.5bears.com 's CNC page. BTW that was a great write up. However, I have noticed that to build a machine capable of turning metal harder than soft aluminum requires a large investment >$2500. I have also noticed that while the experience would be great you need to have access to a shop to build your own mill. Since I have no access to a shop I considered buying a mini mill to create my own cnc mill. This seemed a little redundant and foolish after I realized that minis ranged from $600 to $1400 while full size Bridgeports were <$3000 some <$1500.
1) What exactly should I look for in a machine?
2) Are some years better than others?
3) Are they accurate?
4) And if they are truly as good as they look then why can they be had so cheap. Some even have automated controls and tools for less than $2k

Here is an example of what I mean.

http://cgi.ebay.com/SV2-BRIDGEPORT-M...QQcmdZViewItem

This all seems too good to be true so please let me know where I am going wrong.

My needs are:

1) Mill plastic, aluminum and mild steal
2) Single phase hook up ( My garage/work shop)
3) Reasonable accuracy ( I do not know what that is yet I just know that I do not want to later regret spending $?k when the machine is sloppy.

Finally why do people make there own if these can be had so cheap? Is it simply a matter of having access to the pre-fabed machines and wanting to do it your own way? I can certainly understand that.

Also I have not specific plans for this tool aside from always wanting to do it and having extra time as my wife is in school and I have nothing else to do. ;-)

Thanks again guys

Christian79
(Alex)

[mactec54]

Hi christian79

Now thats a brute it is so cheap because it will be about 5,000 /7,000lbs & looks like 460v 3phase But this most likley can be changed to 230v you would be able to move some metal with that machine if the ( slide ways are in good condition ) if you have the room for a machine like this buy it the toy machines are not so good at moving metal like the bigger Bridgeport type machines can

The accuracy is also alot better on the bigger iron machines This also depends on how good the slide ways & screws are in the older machines

[Hoop]

I doubt the Bridgeport in the link was let go for $1800. Older Bridgeports will hold their value. They are plenty accurate to do what you want. However, these days, CNC machines can be had pretty reasonable and have customer support and a warranty.

The 5 bears link is very interesting.

[christian79]

I called the seller and there was nothing wrong with it and it did go fir $1800. So I will have to keep my eyes open.

I know that a hobbyist does not "need" something that big...... But the incremental cost from $1000 to $3000 to go from a Mini to a Bridgeport seems like a no brainer.

[Hoop]

That was a steal. Since the CNC crowd are phasing out manual mills, it has become affordable to get a nice older Bridgeport. I have a J Head I just purchased that was shipped to the fellow I bought it from. It was shipped in 1983. It is in great condition.

I would spend more time programming a CNC mill for the operations I do than it would take to just go ahead and get to work on my Manual mill. So the old J Head fits my needs perfect.

[NC Cams]

I have an Extrak Bridgeprot which is a DOS based CNC factory B/P fitted mill. THey go for various prices depending on how and where you find them, THis is a 2.5D mill but there are some 3D versions out there.

Mine originally had backlash and other issues which we eventually "tuned" out of them via bearing replacments, ball screw tune ups/preloading as well as a lot of tuning and adjusting of the gibbs. WHen we started you cou'd not mill a circle that was round nor one without flats at 12,3, 6 and 9 o'clock.

WHen we finished with ALL the tuning, we could mill a circle that was ROUND to withing a tenth or two and had NO perceptable flats anymore - we could find them with our ultra precise cam measuring machine but not visibly nor with a micrometer.

Do a "extrak" search on the zone for details. Granted this may be a bit/too much but it goes to show you what can be done with a lowly bridgeport if you take the time ans spend some money