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APEowner
APEowner GRM+ Memberand SuperDork
7/15/21 8:58 a.m.
PMRacing said:
Tom Suddard said:

Another papercut: Just ordered a generic imported power feed. 
 

I think I have a good plan to get the mill running, but I'm going to hook up the VFD and make sure it actually runs before I order any more parts. 

That's got more torque than a Miata!  

You're not helping me ignore my desire for a mill in my garage...I have other priorities...like, um, like, give me a second to come up with one.

That's lbs-inches not lbs-ft.

zordak
zordak Reader
7/15/21 9:03 a.m.

You are going to need a dial indicator to tram the head in(make it perpendicular to the table), also to line the vise up to make square cuts.

PMRacing
PMRacing GRM+ Memberand UltraDork
7/15/21 9:06 a.m.
APEowner said:
PMRacing said:
Tom Suddard said:

Another papercut: Just ordered a generic imported power feed. 
 

I think I have a good plan to get the mill running, but I'm going to hook up the VFD and make sure it actually runs before I order any more parts. 

That's got more torque than a Miata!  

You're not helping me ignore my desire for a mill in my garage...I have other priorities...like, um, like, give me a second to come up with one.

That's lbs-inches not lbs-ft.

And your point is...?  LOL

ShawnG
ShawnG UltimaDork
7/15/21 10:39 a.m.

In reply to PMRacing :

More torque than a 13B

WonkoTheSane
WonkoTheSane GRM+ Memberand SuperDork
7/15/21 10:52 a.m.

Very cool, Tom.  Good call on going directly to the power feed.  It's that much better that I wouldn't recommend anyone really drive one without nowadays. 

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/15/21 10:57 a.m.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/15/21 12:47 p.m.

So I'm at my desk enjoying a cup of coffee, but instead of dreaming about dry sumps like usual I'm plotting this evening's VFD installation.

Am I correct in assuming that the VFD wants a direct connection to the motor, bypassing the standard switch on the side of the head?

Am I an idiot if I then hook that switch to the VFD's low-voltage control inputs to maintain the factory forward/reverse/off switch?

Is there any reason to put the speed dial within easy reach? With a variable speed head, it seems like I should set the speed to OEM for a three-phase power connection and vary the speed with the head, not with the VFD.

Should I drill and tap the machine and mount the VFD on it, or should I screw the magic box to the wall to keep it further from chips and coolant?

Thoughts?

 

Brotus7
Brotus7 Dork
7/15/21 1:18 p.m.

VFD hooks up to the motor itself. I think you'll receive an error if you hook it up to the switch - it ramps power up and down, it won't like the hard start stop of the switch.

You can wire up an external power switch to control the VFD, that's what I did. I reused the original BP switch as an external switch. What's nice is that this is completely optional, so you can power it up and then do it.  I like that the original switch is robust, the VFD controls are kinda wimpy.

I use the speed control on the VFD all the time, but I don't have the variable speed head that you do.  Mines mounted within hand reach, but in a clean spot. I wouldn't mount it on the machine unless it's shielded.

SkinnyG (Forum Supporter)
SkinnyG (Forum Supporter) UberDork
7/15/21 3:08 p.m.

My VFDs connect to remote switches.  You could probably reuse the original mill switches, but they would only be wired to the VFD.

I used an electronics "project box" for my mill, and a small electrical box for my lathe.  I used a fwd/rev switch, an e-stop, and a "jog" button which I have found IMMENSELY useful.  A potentiometer is on these boxes too, so I can easily change the speeds, even mid-cut.

Mill's VFD

Lathe's VFD

 

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/15/21 8:04 p.m.

It's aliiiiiiiiive!!!!

After a few minutes of tinkering, I had the VFD wired up for a bench test. Before I got too carried away ordering parts, I figured I should see if this Bridgeport actually ran like the seller said it would.

Don't touch the live terminals, kids:

With everything wired up, I flipped the breaker and turned on the VFD... SUCCESS! Not only does this mill spin, it runs smoothly across the variable head's speed range in both high and low. Phew...I'd be pretty disappointed if this thing turned out to be a paperweight.

With the mill running, I disconnected everything and sat down to order some parts. More on that later, but this VFD needs a proper enclosure and it's low-voltage controls hooked up before I can really call it installed. I also need to replace the mill's electrical cable: it's wired with three-wire cable, which means there's no equipment ground. Yikes! 

APEowner
APEowner GRM+ Memberand SuperDork
7/15/21 11:00 p.m.

Hot diggity dog!  Now the fun starts.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/16/21 8:28 a.m.

The fun sure did start...

TIME TO SPEND EVEN MORE MONEYcrying

Now that I knew the mill would run, it was time to sort out that missing right-side handle on the X axis. I emailed Industrial Control & Automation, Inc. a few photos and basically said "please please please help me!"

Shockingly, a nice person named Wayne replied almost instantly, and told me what he thought:

"It looks like your machine might originally have had a Bridgeport 6F powerfeed unit that has been removed; that is why your leadscrew does not extend past the end of the table."

"That's not so bad," I thought. Heck, I wanted a powerfeed anyway, and I don't mind rebuilding an old used Bridgeport model if it would get this thing running. Let's fire up the old eBay and figure out what a 6F powerfeed goes for.

Oh, wait, they don't exist. I mean, they probably exist, but all I could find was parts. And what I did find made it clear that I was probably looking at a $500-$1000 purchase if I ever found a 6F in the wild. Damn. ICAI does sell just the coupling and extension shaft that the 6F is built around for about $300, but Wayne said that wouldn't really work for me unless I planned to install a 6F.

Wayne gave me two possible courses of action:

First, I could buy and install a Servo brand powerfeed. These mount just like the 6F, meaning I had the appropriate leadscrew to install one. Great idea, right? Well... by the time I bought the unit and the installation kit, I'd be spending nearly $1000. Oop.

Second, I could buy and install a new full-length leadscrew, then install my choice of import powerfeed. At $285, this option wasn't cheap, either, but so far nothing in this game has been and I think I've just become numb to it.

Wayne added some more costs onto the tab for me:

"If replacing the screw it's a good time to replace the leadscrew nut as well. You could use either the 1pc nut or the 2pc nut. You will still need the table end bracket, bearing, dial holder, dial, dial locknut, handle and hex jam nut if not installing a power feed. If installing a power feed the table bracket, bearing, and dial holder would be included in the power feed installation kit. "

Fantastic... of course, there is one more course of action: I have a lathe, so theoretically I could just make the shaft extension to combine my weird leadscrew with an import powerfeed and handle. I ran this idea by Steve Eckerich (my machining expert) and he shot that down pretty quickly: "Why introduce more slop on day one of your time with the machine, and try to make something with a bunch of keyways when your mill isn't working yet?" Steve told me to buy the new leadscrew and call it a day. "Plus, then you'll have a completely new X axis, which is awesome!"

So, I just spent more than $400 with ICAI, and another $80 on some used handles and dials from eBay. "Buy a used mill," they said, "it will be fun!"

I do need to give a shoutout to ICAI for being super helpful and pointing me in the right direction. I'm probably the worst customer ever: No big company to charge things to and no giant room full of machines to keep running, but they still gave me way more help than I expected.

Kendall_Jones
Kendall_Jones HalfDork
7/16/21 8:58 a.m.

One of the things I love about DROs is that they see & show the slop in the mill so you can adjust it on the fly.  In my world I use vibration fixtures that use a 2 x 2 or 4 x 4 grid patterned thru-hole setup.  I used to have a mill with no DRO and you could only use the dials on the handles and only cut one way (lots of slop) - over shoot your next hole?  you'd have to go back to the 1st hole and rezero the handle.

With a DRO, all the slop is shown - you can push the table back and forth and see it on the DRO.  Made it so much easier to make a good part / bracket / etc and have it all line up.

Old mills will have some slop - some you can adjust out / tighten up and some will be there forever.  I've never had to add a DRO to a mill but I'd love to see the process (I would think its a bit of a PITA) - they look pretty cheap on ebay :)

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/16/21 9:01 a.m.

Oh don't worry, I'll waste some money on a DRO before too long. But I want to see this thing make chips before I order one of those.

Brotus7
Brotus7 Dork
7/16/21 9:30 a.m.

That really stinks that you have to spend so much to piece if back together and that pickings are so slim down there.

ShawnG
ShawnG UltimaDork
7/16/21 9:32 a.m.

My mill has a 6F powerfeed.

It sucks, I'm in there adjusting microswitches at least twice a year.

The offshore one you bought will be better I'm sure.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/16/21 9:45 a.m.

In reply to Brotus7 :

Yeah, it is what it is. I'll still be money ahead compared to other mills I found for sale (which might have also needed new leadscrews; who knows). And Challenge math says this won't be as expensive as it seems, since in theory the screw that's currently in the machine is worth something to somebody trying to add a 6F powerfeed. There are used screws listed on eBay:

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/16/21 10:16 a.m.
Brotus7 said:

That really stinks that you have to spend so much to piece if back together and that pickings are so slim down there.

The question is - should this be expected when you buy a well-used Bridgeport? I suspect it is. They're heavily used, complex pieces of industrial equipment that require high levels of precision and have undergone considerable technological change during their lifespan, and when you buy one at the lower end of the market you can expect to have to do some work on it. I've always had the impression that buying any Bridgeport is just the first step. It's like buying an older race car, it's going to take some work to bring it back up to speed.

ShawnG
ShawnG UltimaDork
7/16/21 10:29 a.m.

They were all nice machines about two owners ago.

kellym
kellym New Reader
7/16/21 10:43 a.m.

For the DRO check out DRO Pros  - I've been really happy with mine 

If you need a tram, send me a message I'd be happy to loan you mine for shipping costs 

K

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/16/21 11:06 a.m.

In reply to Keith Tanner :

This exactly. If I go to look at a used car, I know exactly what to look for and can estimate repairs accordingly. How'd I learn how to do that? Simple: Decades of experience working on them.

I don't have those decades when it comes to machine tools, but shopping at the bottom of the market meant everything would need some form of repair. Without many other choices, I was content to roll the dice when shopping, and figured no matter what it would still be a good learning exercise. The other way to do this is to buy from a rebuilder, but you pay for that expertise and reconditioning. I'd rather learn how to do it myself.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
7/16/21 11:08 a.m.
kellym said:

If you need a tram, send me a message I'd be happy to loan you mine for shipping costs 

K

 

 

In all seriousness, I really appreciate the offer but I have a friend locally who's offered to come over and show me the basics of tramming the head. I should probably just buy the tool, since I'll need to be able to do it in the future, too. Thanks though!

Datsun310Guy
Datsun310Guy MegaDork
7/16/21 12:04 p.m.

If you had the right lathe and a way to harden the steel you can cut your own threads and make the lead screw you need.  

ShawnG
ShawnG UltimaDork
7/16/21 3:14 p.m.

You can tram the head with a dial indicator and a rod mounted in a collet. 

It's a skill you need to have in the box and it's all that hard really.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/16/21 3:20 p.m.

Someone please explain "tram the head" for those of us who prefer to learn from our friends instead of google :)

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