Bridgeport 2J head variable speed to direct drive???

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hwboivin3

Bridgeport 2J head variable speed to direct drive???

Post by hwboivin3 »

I've been curious if anyone has converted a variable speed bridgeport head to direct drive or to just regular pulleys or timing belts.

I have replaced the belt and bushing on my mill twice in 3 years. At first it's really quiet, but soon becomes louder and louder.

I'm thinking that I could just do 2 timing pulleys and a VFD.

Any thoughts?


thanks
spro
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Re: Bridgeport 2J head variable speed to direct drive???

Post by spro »

I haven't done it but have read about it. Many are doing or did what you consider. Some just want to get another head while figuring it out. I think the issue is gravity and no getting past that. That system works well enough, laterally but I'm out of here.
SteveM
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Re: Bridgeport 2J head variable speed to direct drive???

Post by SteveM »

First I would investigate why they are making noise.

I can't imagine all of them do that, or we would have heard more about it.

When you say bushings, what bushings are they? Is the belt tension too tight and the tension puts too much side pressure on the bushings (like too much tension on your car's belts wears out the water pump or alternator bushing)?

Steve
Patio
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Re: Bridgeport 2J head variable speed to direct drive???

Post by Patio »

I have a step pulley head with a VFD drive on my clone. The problem I see with the direct drive and a VFD is when you want slow speed torque. You may be able to make that happen, but I don't know enough to tell you how. I keep my machine in set on the middle pulley, but will change it if I need either slow torque, or high speed. It is the same with my lathe that has a VFD. I will run in low gear if I need slow speed torque.
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BadDog
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Re: Bridgeport 2J head variable speed to direct drive???

Post by BadDog »

You can sort of do it with VFD. First, you need an upgraded "sensorless vector" (or better) VFD to provide better range without degradation of power. If that's not enough, you have to go with a larger motor so that even degraded at the limits it still has the required power. I once considered getting rid of the Reeves drive in my Rockwell 11" lathe. It was a 1 HP motor, and I wanted to stretch the upper RPM a bit above the stock 1500 max. By my calculations at the time I needed a 5 HP motor just to break even on the low end while extending the top to around 1800 rpm, and that was keeping the back gear mechanical advantage! So using a VFD for adjustments within a reasonably narrow range is practical, but you still need mechanical options if you don't want to sacrifice, particularly at the low end.
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hwboivin3

Re: Bridgeport 2J head variable speed to direct drive???

Post by hwboivin3 »

SteveM wrote:First I would investigate why they are making noise.

I can't imagine all of them do that, or we would have heard more about it.

When you say bushings, what bushings are they? Is the belt tension too tight and the tension puts too much side pressure on the bushings (like too much tension on your car's belts wears out the water pump or alternator bushing)?

Steve
The most common problem with these heads are caused by a thin plastic bushing that is in between the top cone pulley and the spindle.
The bushing protects both pieces so only the bushing wears. Over time, the wear causes the pulley to get a little out of balance....which makes the bushing worse.....and so on. I've replaced a lot of bushings over the years.......after putting the new ones in, the mill is really quiet. When it gets to the point where they need replaced, it sounds like a jackhammer.

The root cause, in my opinion is the belt placement on the cones. The belts wear unevenly.....which wears the bushing.

but I'm no expert......that's just what I think is happening.
hwboivin3

Re: Bridgeport 2J head variable speed to direct drive???

Post by hwboivin3 »

After thinking about it more.......I don't like going direct drive. I think I would just rather replace the variable cone pulleys with timing belt pulleys.......then just use the VFD to control the speed.

I typically use a range of 700-3000 rpm. I don't need a lot of torque as it's a cnc Boss and I run light cuts for long cycles.

3/32" - 3/4" E.M.s at .002 - .010 depth of cuts

So I figure if I figure things out so I can set the pulleys to run around 3000 rpm, then use the vfd to adjust down.
hwboivin3

Re: Bridgeport 2J head variable speed to direct drive???

Post by hwboivin3 »

I'm also wondering if I can just take the whole top assembly off and replace it with a regular step pulley assembly from a J head.

I have a couple J heads collecting dust that I could use
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ctwo
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Re: Bridgeport 2J head variable speed to direct drive???

Post by ctwo »

I think the BP 4-pole motors will do fine from 30 Hz up to 120 Hz. A direct 1:1 pulley then gives you a range of 900 to 3600, and you'd have back gear for low end torque. This seems to be relatively common... You may be able to work a ratio more suited to your application.

How many hours do you get out of the rebuild? Do you replace all 4 bushings? If they wear out premature, maybe you need to look at reworking the pulleys.
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hwboivin3

Re: Bridgeport 2J head variable speed to direct drive???

Post by hwboivin3 »

I've only replaced the thin bushing on the moving cone pulley.

So far, this one has lasted a year. It's louder than it was, but I think it'll last another year.
hwboivin3

Re: Bridgeport 2J head variable speed to direct drive???

Post by hwboivin3 »

I bought a 2j cnc Bridgeport for $400.....guess what? It's missing the variable speed top assembly.

So, I'll be tinkering with putting a step pulley assembly on it.

:D
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ctwo
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Re: Bridgeport 2J head variable speed to direct drive???

Post by ctwo »

Can never have too many machines.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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