Should I keep Hartford or Bridgeport?

[Susquatch]

Well, it's decision time. As many here will know, I was originally looking to buy a bigger more rigid mill to replace my old mill/drill. As luck would have it, I ended up buying two - both at a great price. Rather than just flip one, I decided to repair both for the purpose of making them work well enough to be able to decide which one of the two I wanted to keep and which one I would sell. Neither one worked as received. Several months have transpired and I've now repaired the essentials on both mills and I have used them both to make a few parts. One is a Hartford 2HP 3ph step pulley clone, and the other is a Bridgeport 2HP 3ph VariSpeed. With some significant differences, either one will meet my needs. So which is the better choice?

For those who have not been following along, and wish to review the background, here are links to the two threads that detail each mill's basic problems and all the repairs I have made to date:

https://canadianhobbymetalworkers.com/threads/new-to-me-hartford-mill.3490/

https://canadianhobbymetalworkers.com/threads/new-to-me-bridgeport-mill.3491/

Here are the highlights:

Hartford Step Pulley Mill
.. New 2HP VFD rated 3ph motor
.. Teco L510 VFD - 10 to 120Hz
.... Can go to zero but why?
.. All new belts
.. 9x42 Bed in good condition
.... A few peck marks
.. Backlash on x & y axis
.... Under 10 thou after adjusting
.. Gibbs - all excellent
.. Only 3 speeds on pulley
.... 1 sacrificed to fit motor shaft
.... VFD easily compensates
.. Auto down feed not working
.. Motor & drive smooth & quiet
.... Some minor clatter at startup
.. Additional Work Required
.... Repair auto down feed
.. Future Parts availability
....Most parts same as Bridgeport
.... Some parts are hard to find
.... A few are not available at all
.. Storage compartment in base
.. Extremely smooth quiet machine
.. Very good appearance
.. Overall Condition "Very Good"


Bridgeport VariSpeed Mill
.. Rewound 2HP VFD 3ph motor
.... Not VFD Rated
.. Teco L510 VFD - 30 - 75Hz
.... Might go slower with a fan
.. 9x42 Bed in fair condition
.... Lots of peck marks
.... But no high spots
.. Backlash on x & y axis
.... 80 - 90 thou after adjusting
.... No adjustment left
.. Gibbs - worn out
.... No adjustment left
.. Vari Spd belt noisy
.... Probably needs replacing
.. Auto down feed not working
.. Motor and drive a bit noisy
.... Minor noise at most spds
.... A few sweet spots
.. Additional Work Required
.... Repair auto down feed
.... Replace both leade screws
.... Replace all gibbs
.. Future Parts availability
.... All parts available @ H&W
.. No storage compartment in base
.. Appearance is rough
.... Machine has been well used
.... Needs rust removal
.... Needs a good cleaning
.... Needs a paint job
.. Overall Condition - Moderate
.... But still quite usable

Summary of Decision Factors
.. Hartford Pros
.... New VFD Rated Motor
........ Full speed 15 to 120Hz
.... Very Low Backlash
.... Very smooth, quiet, and solid
.... Great condition & appearance
.. Hartford Cons
.... Availability of parts
.... Not a genuine bridgeport
.... Loss of one pulley position
.... Not a varispeed

.. Bridgeport Pros
.... Genuine Bridgeport Mill
.... All parts are still available
.... Mill works as is but rough
.. Bridgeport Cons
.... Leade screws are worn out
.... Gibbs are worn out
.... Motor is not VFD Rated

Power down feed on both mills needs repair.

My thoughts:

I am old and God willing, at best I'll get 10 years use out of either mill. However, I believe either one will outlast me and do everything I need it to do with it over that time.

I really like the idea of owning a genuine Bridgeport. However, when I stand back and think about which girl I want to marry and which one I want to live with for the rest of my milling life, I realize how much I really love how smooth, quiet, solid, and good looking the Hartford mill is, and I don't like the idea of replacing the leade screws, split nuts, and gibbs on the Bridgeport. Yet, if I don't replace them, I will curse them every time I use the machine.

So, all things considered, I favour keeping the Hartford. But a wise man is never afraid to change his mind. Unless you guys change my mind, I plan to clean up the Bridgeport and then sell it - someone else can replace the leade screws, split nuts, and gibbs.

Anyone disagree? If so, please tell me why. And please don't hold back. You can't hurt my feelings.

 

[Mcgyver]

Spindle tapers the same?

you know if all that is badly worn on the bport, so are the bearing surfaces. Replacing that stuff without re scraping it will be expensive and might not accomplish much. otoh imo a VFD is poor speed control - they deliver constant toque but you want is constant HP. Overall I'd go with the one in better condition, but its imo sub optimal to lose the low speeds and high torque on a varispeed drive.

Put the bport head on Hartford?

What does a VFD rated motor mean? Marketing or is it a real difference. Guess I wasn't paying attention I've never had a problem putting a VFD on any old 3P motor

 

[John Conroy]

I think Mcgyver has a great idea. Putting the Bport head on the Hartford would save all the work of getting the sliding surfaces back in shape of the Bport chassis and you would have a varispeed head. Of course you would loose the re-sale value of the Bport if that is a concern for you. If it were me I'd keep the Harford and fix the few thing that it needs and then sell the Bport as it should bring good money.

 

[John Conroy]

This is a drawing of the power down feed if you haven't seen one before. There is a slip clutch under the round cover on the left side of the head that's not shown here.

 

[Susquatch]

Spindle tapers the same?

Yes, they are both R8. The taper on the Bridgeport is worn a bit though. It had no key when I got it and the previous owner probably undertightened it so it spun a few times.

A VFD is poor speed control - they deliver constant torque but you want constant HP. Overall I'd go with the one in better condition, but its imo sub optimal to lose the low speeds and high torque on a varispeed drive.

I guess I don't really understand this point. I have heard this before and didn't understand it then either. Perhaps you can help me "get it".

Torque is a rotational force independant of time or distance. Work is force x distance. Hp is the rate at which work is done (work done per unit time). So for any given load and rpm shouldn't either rating hold the same numbers?

But in any event, unless I am mistaken, my VFD doesn't control force or HP. It controls rpm. As long as it holds rpm, as the load increases, it will increase both torque and hp until its limit is reached.

Put the bport head on Hartford?

Hmmmmmm, I have thought about swapping tables, but I never thought of that one! I will have to give this some more thought.....

What does a VFD rated motor mean? Marketing or is it a real difference. Guess I wasn't paying attention I've never had a problem putting a VFD on any old 3P motor

Nor did I. While I think your tongue is in cheek a bit, my VFD worked just fine on both Motors too. However, my understanding of the difference goes like this.

Standard Motors are designed to run at a fixed speed. They have internal cooling systems that can handle the heat generated at the rated power level at the rated speed. But at lower speeds, the fan doesn't work as effectively and supplemental cooling is required. Similarly, standard Motors have bearings that can handle the standard speed. If you turn the motor too fast, the bearings can fry. The general rule of thumb that I found was to keep non-vfd rated motor speed within 50% of the rated speed.

On the other hand, VFD rated Motors can run at much lower speeds without overheating and have bearings that can handle the higher speeds too. My VFD rated motor is 1800 RPM at 60 hz. But it is rated to handle anything from 0 rpm to 3600rpm.

 

[Susquatch]

I think Mcgyver has a great idea. Putting the Bport head on the Hartford would save all the work of getting the sliding surfaces back in shape of the Bport chassis and you would have a varispeed head. Of course you would loose the re-sale value of the Bport if that is a concern for you. If it were me I'd keep the Harford and fix the few thing that it needs and then sell the Bport as it should bring good money.

I'm going to give the idea of swapping heads some more thought. More on that later.

But I agree that doing that will create two clones instead of one and it will probably affect selling price significantly.

 

[Susquatch]

This is a drawing of the power down feed if you haven't seen one before. There is a slip clutch under the round cover on the left side of the head that's not shown here.

View attachment 17542

There are a few pictures in this graphic missing.

I repaired the center gear system on that graphic on my Bridgeport already. That part works fine on the Hartford.

In both cases, I think the clutch system got sticky and didn't release. I expect I will find a broken or stripped worm gear or bevel gear.

In any case, I don't plan to fix that till this winter some time. Or maybe later.

 

[whydontu]

If it was me I’d keep the Hartford. Having Bridgeport on the side of a machine is irrelevant if it doesn’t work. If the intent is to make chips, it sounds like the Hartford will be able to make chips with much less hassle.

 

[6.5 Fan]

I'm in the Hartford camp. Bridgeport is just a name and it looks to require a lot more work.

 

[Tom O]

Hartford camp also.

 

[YYCHM]

Hmmm..... I wonder how you can add a survey to this thread? @Janger can you shed some light?

In any event I vote keep the Hartford, ditch the Bridgeport.

 

[Tom Kitta]

I would not worry too much about VFD rated motor or not - usually that just means better insulation. Older motors are over build and one can say most are also VFD rated for that reason. Bearings in both motors are almost always the same & for most smaller motors they have no issues running even at 5000 rpm or more. I would think the issue would more be of balancing. Main issue is heat.

Since VFD rated motors do not have any extra cooling their fans also move at a slow speed of non "VFD rated" motor.

Also a lot of things are rated at full load or even at service factor - not an issue for most pp as most pp do not run their mill close to full load continuously.

In short do not worry about it - just make sure you do not smell insulation burning in your motor and you are fine. Whatever it is VFD rated or not.

As for replacing lead screws - you can just go for rolled ball screws - very cheap from China. Main problem would be adding adapters to the setup but the benefit would be sub 0.001 backlash. Then again - it is a project.

*The main question is, do you want to fix the BP? If yes, you can keep her, if not then you can sell her.*

Have you considered keeping both? Or is it space / $ issue?

 

[kevin.decelles]

Adopt me, keep both, leave me the BP in your will.

I too would keep the one in best shape. Kind of like having a 64 1/2 Mustang, and some other muscle car isn't as sexy but puts down more HP....... some would keep the Mustang because it is iconic...... others would take the muscle.....

Either way you've got better machines than I -- good posts/pictures/journey! Thanks for posting!

 

[Susquatch]

*The main question is, do you want to fix the BP? If yes, you can keep her, if not then you can sell her.*

I am done fixing Mills for a while. I want to move on to making and fixing other things So I'll take your vote as one to keep the Hartford and sell the Bridgeport.

Have you considered keeping both? Or is it space / $ issue?

I have lots of space. But I got myself into a hot tub with a crazy lady. When this all started, I gave my bride my savings so she could buy an industrial sewing machine. That put a mill on hold for a while. Then along came this great deal on a Hartford and she agreed to dip into our regular spending (no steak for a year) to take advantage of the opportunity. Then along came a deal on a Bridgeport and I borrowed the money on our power line because it was an investment that would get paid back - no matter which one I ended up keeping.

So ya, I can make room for it. I'll just move my tractors around a bit. My shop is 40x80 (actually 40x60 because I have a room built into it). But I don't really want to sleep out there. I like my bed and the warm lady I share it with. So no matter how much I'd like to keep both, one of those mills has to go regardless of whether or not I have room.

 

[Susquatch]

Adopt me, keep both, leave me the BP in your will.

I too would keep the one in best shape. Kind of like having a 64 1/2 Mustang, and some other muscle car isn't as sexy but puts down more HP....... some would keep the Mustang because it is iconic...... others would take the muscle.....

Either way you've got better machines than I -- good posts/pictures/journey! Thanks for posting!

I have 4 kids and 9 grandkids and a possible great grandchild on the way already. So...... much as I might like you, I have this feeling you would cost more than all of them put together. Not happening! Sorry Kevin.

 

[Brent H]

@Susquatch: from all the work you have done to the machines, you appear to have poured more time and effort into getting the Hartford running to your satisfaction: it needs less to give you back more at this point.
You have the perfect motor for the Hartford and thus the pulley system is irrelevant- speed control is yours to command.
For the Bridgeport- new gibs are about $325 USD plus shipping, new x and y axis screws about $350 USD and new nuts for those are about $70 USD. Then you have any wear issues to also look into and the power feed. You are in another $1500 CDN and your time. Plus you say the quill has a worn collet holder - probably needs new bearings all around etc etc.
I think your decision was made when you made your first chips on the Hartford.

 

[Susquatch]

from all the work you have done to the machines, you appear to have poured more time and effort into getting the Hartford running to your satisfaction: it needs less to give you back more at this point.

I think they are pretty even in terms of research, work, and passion. Lots of little stuff required doing on the BP. But I did have to buy a motor for the Hartford and even though it was a great deal it was not free.

For the Bridgeport- new gibs are about $325 USD plus shipping, new x and y axis screws about $350 USD and new nuts for those are about $70 USD. Then you have any wear issues to also look into and the power feed. You are in another $1500 CDN and your time. Plus you say the quill has a worn collet holder - probably needs new bearings all around etc etc.

Wow...... That's way more than I figured. I think that's a show stopper.

I think your decision was made when you made your first chips on the Hartford.

You have great insight. When that cutter hit first steel, a bull alaskan moose couldn't have licked the smile off my face...... I couldn't believe my eyes or my ears......

 

[Mcgyver]

I guess I don't really understand this point. I have heard this before and didn't understand it then either. Perhaps you can help me "get it".
.

real simple, power = torque x angular velocity. Power, HP, is a direct function of torque and speed. Because of cutting speeds, we have to run big cutters more slowly, right? So if speed (RPM) is reduced, torque has to increase to equal the same power.

Think if you put a VFD on a 1800 rpm motor. slow it to 180. You can (depending motor size) probably stop it by hand - you need torque to go up as speed goes down to maintain the same HP.

Another example is conveyors. It takes about the same torque at an speed so VFD's work well for speed control. So if the 1800 rpm motor runs it a 40 feet minute, and you slow it down to 900 via the VFD, torque is the same, but you're gonna a pile of say stone off the conveyor half the size. Torque stayed the same, speed cut in half, the power got halved (half work was done in a given period of time)

VFD's might claim to offer constant torque, but none offer constant HP. When guys say it works just fine for them, what they're saying at whatever lower speed they're running, they only need a small fraction of the full speed HP. Thats fine, but its still a big built in compromise imo

On the other hand, VFD rated Motors can run at much lower speeds without overheating and have bearings that can handle the higher speeds too. My VFD rated motor is 1800 RPM at 60 hz. But it is rated to handle anything from 0 rpm to 3600rpm.

that makes sense, powered fans vs the blades on the rotor.

 

[Susquatch]

real simple, power = torque x angular velocity. Power, HP, is a direct function of torque and speed. Because of cutting speeds, we have to run big cutters more slowly, right? So if speed (RPM) is reduced, torque has to increase to equal the same power.

Right on. Torque is force, rpm is speed distance. A totally linear relationship.

Yup, torque has to go up to equal same hp at lower rpm. Linear math.

Think if you put a VFD on a 1800 rpm motor. slow it to 180. You can (depending motor size) probably stop it by hand - you need torque to go up as speed goes down to maintain the same HP.

I think braking by hand confuses the issue. I doubt very much that I could stop my spindle by hand. It isn't a matter of hp. It's pure torque. My hand is a big strong one. But I cannot generate the torque required to stop the spindle.

Here is a graph of the relationship. You can see the linear nature of the two factors in the two straight lines. The torque stays constant below rated rpm and hp stays constant above. One gets traded for the other because the third variable (rpm) changes. (I believe the slight uptick in the torque above rated rpm is the result of lower losses in the motor.)

Another example is conveyors. It takes about the same torque at an speed so VFD's work well for speed control. So if the 1800 rpm motor runs it a 40 feet minute, and you slow it down to 900 via the VFD, torque is the same, but you're gonna a pile of say stone off the conveyor half the size. Torque stayed the same, speed cut in half, the power got halved (half work was done in a given period of time)

I don't know anything about conveyors but I accept what you say.

VFD's might claim to offer constant torque, but none offer constant HP. When guys say it works just fine for them, what they're saying at whatever lower speed they're running, they only need a small fraction of the full speed HP. Thats fine, but its still a big built in compromise imo

I have never seen any VFD claim anything other than as shown above in the graph. Constant torque below rated rpm and constant hp above. Its a linear relationship. As rpm changes, one has to give to maintain the other.

I think that you are probably correct about what people say. But since hp is a measure of the rate at which work is being done. Lower rpm almost always means less work so no surprise there.

I also think that most of the stuff I have read make the assumption that a 2hp motor always produces 2hp when its running at its rated rpm. But I don't agree. It only produces that much when it is working at its peak capacity. If it has no load, I just sits there spinning at virtually zero hp because it isn't doing any work. Maybe that's what you were getting at in your conveyor example.

I'm not really sure, but I think perhaps we may be talking in circles here - saying the same thing from different perspectives. Perhaps you think HP is more important than torque and I feel they are both important because they are so closely related. Or perhaps you are above the curve and I'm below it..... LOL!!

 

[Brent H]

Lads:

For some clarity: torque being the force and horsepower being the rate at which that force is done. The difference is torque is doing the work, while horsepower is how fast that work is being done.
Depending on the load being applied an electric motor only needs to develop enough Hp to overcome the applied load(resistive force) or counter torque. So if no load is applied to the electric motor only the Hp to keep it rotating will be developed and very little torque. A 2 Hp motor can develop up to 2 Hp at the rated RPM but may run at rated RPM at much lower Hp.