To Convert old Bridgeport to CNC or not ?

[KEJR]

Hello,

This is kind of an odd post, but I thought I'd as you guys. I bought a slightly worn Bridgeport on the cheap a couple years ago ($500). It does adequate work but I have not gone to the trouble of taking out the 0.040" of backlash (I think I can get it within 0.005" since it appears evenly worn...) and tightening the gibs up. I haven't even invested in a DRO yet until I figure out what I'm going to do with it.

As for some background, I am a home hobby user, but I value high precision and may some day make some prototype parts for a home business (Hence precision over speed...). I value CNC because you can make parts with more interesting profiles, and as a time saver in some cases. I also enjoy manual machining, so I would leave the handles on any machine I convert.

I also have done some poking around and noticed alot of guys are getting really usable machines out of those Rong Fu 45 clones and Weiss "BF20/BF25/BF30" style machines which are sure alot easier to convert to CNC than my 2000lb bridgeport due to the weight of the tables, size of the motors/ballscrews, etc. Obviously these can't take as huge a cut as a bridgeport, but without flood coolant and all of that you really don't want to take huge cuts anyway!

I didn't know if you guys had any opinions with regard to converting a sloppy bridgeport or if I should get my money back on the bridgeport and take my chances with the Chinese tooling to save space and be easier to move if I ever have to.

As a third option, I was looking at maybe getting the high end Smithy machine (Granite) and converting that to a 2 Axis CNC. the biggest thing here is I am having trouble getting over the lack of Dovetails on the Z axis Up/Down. I don't want to pick up zero every time I lift the head do go from Drill to mill. The attraction here is that I could CNC one machine and have a small CNC lathe and mill. For hobby and prototype work the light duty milling might be OK.

I've toyed around with evaluating the bridgeport a little more and just doing a 2 axis conversion with the existing ACME screws. I might be able to live with 0.005" or more backlash with backlash compensation turned on, but climb milling might be a bit scary. With this approach I can upgrade to ballscrews any time if I design around the stock leadscrews and use a ballscrew converstion kit.

Any ideas? I know thats quite a post, but I'm hoping to learn from the collective wisdom here!

THanks,
~Ken

[scmw]

Ken,

CNC is a wonderful way to do precision machining especially with 2D profiling as you mentioned. I would seriously consider 3 axis as that Z can be very useful with CNC. Again, it all depends upon the type of work you are doing.

The first question that I would ask is what materials are you planning to work with? Steel, aluminum, plastics, etc?

The second question would be what is your budget? Do you want to go the stepper route or servo route? Steppers can be less expensive. Servoes can add precision to your set up especially when backing up and restarting from a specific line of g code.

Third question is how much time do you have to dedicate to this kind of a project? It might be cheaper in the long run to keep your BP as is and look for a used mill that has already been converted. It's a buyers market and with the potential of the economy taking another dip, more deals may be forthcoming.

In May we decided that we needed a more rigid mill to handle some of our projects. We looked at various milling centers and mills. We decided to get a Bridgeport that had already been converted and was in working condition. I got lucky in finding a pair of Series II's in Southern IL for not too much.

You might also look at Tormach's and Novakon's. I believe that they're turnkey out of the crate. But you will be purchasing a Chinese sourced product there.

The benefit of purchasing something that has already been converted is the saving of time and knowing that it was done right from the get go. It can be a bit hair-raising for some folks to add CNC to an existing manual mill. It's certainly do-able but know that there are challenges.

You're also going to need to look at software. You'll need CAD, CAM, and a controller. CAD apps continually desire more powerful computers. I have one computer set up with Rhino and Alibre plus CAM. The computers on my mills just handle Mach 3 so they're pretty basic with the exception of touch screens. Bob Warfield has a good treatise on his website that covers CNC. Here's the link: http://www.cnccookbook.com

I drop in there from time to time as it's a great resource.

Hopefully I haven't confused you too much.

Good luck and let us know which way you go with it.

[KEJR]

Thanks for the reply.

I already have 3 stepper motors that I bought online that should work with the bridgeport. I'd be going the Mach or EMC route. I was tallying up the cost of upgrading to ballscrews and the amount of time going into the project and I'll still be left with a tired mill that is CNC in the end. I'm kind of afraid that I'll get the conversion done to find that the variable speed head needs rebuilding or something.

I agree with you on the third axis. I was just thinking of designing the electronics around 3 axes and doing the initial mechanicals around a 2 axis setup just to get going.

A this stage of the game I'd be happy to use one of the free DXF to 2d profile CAM programs out there. I could upgrade to more sophisticated 3D software when I need it.

I don't really have the time for this project, but I also don't have the cash to buy a CNC machine already done up. The space of the bridgeport and thought of moving the equipment is a big consideration which is why I'm entertaining buying a bench mill (Dovetail column) machine for $1000 and just offloading the bridgeport for cost (I should be able to get the $500 I spent back if not a bit more). I guess I just have to decide what to do!

Thanks,
~Ken

[macona]

Dont do it. A conversion of a non-cnc machine to cnc is a waste of time and money.

[gnm109]

I have to agree with Mr. Macona on that. The problem is the cost of the equipment in relation to the cost of the machine.

One item that would be necessary would be a set of ballscrew lead screws for X and Y. The expense of those, exclusive of labor, is prohibitive and might even exceed the cost of the used Bridgeport.

If I ever go to CNC, I will get a purpose-built machine all set up with motors, ballsscrews and software. JMO.

[Paul Alciatore]

I am not going to jump into the CNC built vs. converted manual machine thing as I have no experience with the former.

What I will say is you should address the slop in the machine before making any decisions as to what to do with it.

[mc_n_g]

THe market has come down on Bports. Find a older Boss 4-6 and gut it. Change out the motors to something modern. The ball screws should be in good condition in your Bport. For a hobby machine you should be able to hold good tolerances with it. The old Boss machines were heavy, rugged and could take good cuts.

[sansbury]

I would not do it, personally. If I needed a Bridgeport-sized cnc mill on the cheap, I'd look for a Boss with a dead control and run it with EMC. Machines like that can got very cheap, less even than a manual version. Besides the ballscrews you can get servos and all your home and limit switches and spindle control all wired up for you.

The RF-45 mills seem pretty capable, too. But after converting a few benchtop manual machines I am kind of sick of it. If tormach can get their ATC into production at a decent price then I know what my next machine will be.

[macona]

If their ATC uses their Tormach Tooling System I would avoid it at all costs. The retention of tools sucks.

[spope14]

One question:
1. What is your work envelop you envision?

With .040 backlash, you will need to invest in ball screws or spring loaded antibacklash acmes. Lots of cost there.

This said, you may want to check with Southwest industries and their "prototracks" or Rice industries for their either Mitutoyo or Mitsubishi equivelant. May go from 12K to 18K though, but if your work envelope is about bridgeport size and the ways and gibs are in good shape on the machine, may be a good investment.

New CNC for the same size envelope as a bridgeport includes buying the iron and such....but also the rigging cost, which could be 1500 to 3500. Almost comparable, it may be worth looking at less of an envelope with a Tormach (still have shipping on top of the base cost, about 700 to 1200 when I looked), but it is new.