Anyone know the weight of the knee?

[vecair]

Anyone got any idea what the weight of the knee including tables might be? I am guessing 500 lbs but someone might know better. Thanks if you do.

 

[MyLilMule]

Never weight it, but it's heavy. Why is the weight important to know?

 

[vecair]

I am going to add two gas struts to mine to help when cranking up the knee and also to take the load off the gears. I need to supply the approximate weight to the strut company so they can supply the correct one (or two in this case.)

 

[MyLilMule]

Interesting solution. I'd be curious to see the results. How are you going to mount them?

There's no load on the gears. There are two bevel gears in the knee, one to the crank, the other to the feed nut. All of the load is on the feed nut and screw. Why not a power feed or even one of those drill adapters?

 

[mksj]

Some weights posted by another person for a Bridgeport j head mill with a larger table (assume it is 48"), so with the table, saddle and knee probably closer to 650-750lbs. But one needs to factor in the table size/knee type. They tend to run around 2200-2500 lbs overall weight. My knee mill has a 42" table and is 2400lbs. I use an Align drive on the Z axis, a power drive my be a reasonable alternative.
Head - 91 kg 200lb
Ram - 99 kg 218lb
Ram adapter 41 kg 90lb
Turret - 97 kg 214lb
Column - 325 kg 715lb
Knee - 117 kg 258lb
Saddle - 65 kg 145lb
Table - 166 kg 365lb

 

[vecair]

Interesting solution. I'd be curious to see the results. How are you going to mount them?

There's no load on the gears. There are two bevel gears in the knee, one to the crank, the other to the feed nut. All of the load is on the feed nut and screw. Why not a power feed or even one of those drill adapters?

Might want to rethink that MLM. If the feed nut is having to lift 500 lbs then the bevel gears are seeing a force to turn that nut, if I reduce the table weight by say 250 lbs the bevel gears are going to see less force to turn the nut. The bevel gears wear as they turn the feed nut, the harder it is to turn the nut the more wear they will see. By adding gas struts it will reduce the amount of force required to turn the handle which in turn reduces the force on the bevel gears.

 

[vecair]

Interesting solution. I'd be curious to see the results. How are you going to mount them?

There's no load on the gears. There are two bevel gears in the knee, one to the crank, the other to the feed nut. All of the load is on the feed nut and screw. Why not a power feed or even one of those drill adapters?

Well the truth is I have an ExCello 602 mill but finding the knee weight is pretty much impossible. I do know the ExCello mill weights considerably more than a BP but it gives me some idea. Cranking up the ExCello knee is considerably harder than on a BP. So much so that the Servo Company recommends their 200 series knee power feed for the Ex and the 140 series for the BP. The gear on a drill will not work, I tried it. Plus nobody makes the ExCello drive cog, its has a different number of teeth vs the BP, can't even find a used handle. See this vid for the gas strut idea in action. It works and its cheap compared to the Servo 200 at $1300.00.

 

[vecair]

Some weights posted by another person for a Bridgeport j head mill with a larger table (assume it is 48"), so with the table, saddle and knee probably closer to 650-750lbs. But one needs to factor in the table size/knee type. They tend to run around 2200-2500 lbs overall weight. My knee mill has a 42" table and is 2400lbs. I use an Align drive on the Z axis, a power drive my be a reasonable alternative.
Head - 91 kg 200lb
Ram - 99 kg 218lb
Ram adapter 41 kg 90lb
Turret - 97 kg 214lb
Column - 325 kg 715lb
Knee - 117 kg 258lb
Saddle - 65 kg 145lb
Table - 166 kg 365lb

Thanks for your help, this gives me the ball park. As I mentioned in another post I have an ExCello 602 which weights even more, so I would say 800-850 for my knee and it has a factory power feed on the X table. Weight of the Ex runs between 3100 and 3500 lbs depending on the table and accessories.

 

[MyLilMule]

Might want to rethink that MLM. If the feed nut is having to lift 500 lbs then the bevel gears are seeing a force to turn that nut, if I reduce the table weight by say 250 lbs the bevel gears are going to see less force to turn the nut. The bevel gears wear as they turn the feed nut, the harder it is to turn the nut the more wear they will see. By adding gas struts it will reduce the amount of force required to turn the handle which in turn reduces the force on the bevel gears.

I'm not going to rethink it, because I stand by my opinion. The only thing I might have clarified is to say there isn't sufficient force. Especially when you're talking about reducing wear on maybe $200 in parts if you had to buy them new, that might wear out once every 50 years or more. My Bridgeport is from 1976 and when I disassembled the knee, the bevel gears were in perfect shape. Could they have been replaced prior? Possible, but judging from the conversation I had with its original owner at the time of purchase, I don't believe that to be the case.

FWIW, I am still interested in seeing the solution to this as I find it interesting just the same.

 

[7milesup]

I would think that some math could determine the weight of the knee. You will need the gear ratio of the Z-axis, along with the force required to turn the handle and the length of the handle to determine the moment arm. I don't really have time to come up with the formula for you, but it is a very solve-able problem.