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View Full Version : X-axis power feed on knee?



noah katz
10-28-2007, 02:56 AM
Is there any reason an X-axis power feed can't be used on the knee of a Bridgeport if I don't intend to use the limit switch?

Torque isn't an issue, as I'm going to add a gas strut to support most of the knee weight.

Also, because the reduced torque requirement, I'll be replacing the big crank handle with the same type as the X and Y.

Thanks

J.Ramsey
10-28-2007, 07:58 AM
No, but why not just buy a Z axis power feed? Forget the gas strut.

Dawai
10-28-2007, 08:40 AM
Are you hoping to increase spindle travel?

Some guys used a electric drill on the knee.

OKAY, a motorcycle cable operated linear digital slide works okay? if you want repeatable setups. I gotta put mine back on.

JRouche
10-28-2007, 12:34 PM
Hmmm, I'll also have to ask why a X-axis drive when there are knee specific drives. You get to keep the manual crank and you dont need any crazy struts. Oh, unless you already have the X drive and money is a concern, and when isn't it.. Then yeah, you make due with whatcha got. JRouche

Here is my knee drive. Works great and my knee is fairly heavy for a bridgeport..
http://img.photobucket.com/albums/v366/Jrouche/HSM/Zdrive.jpg

platypus2020
10-28-2007, 01:43 PM
I have a Jet JVM-836 and all of the drive motors (x,y & z) are all the same units, the only difference is the mounting hardware and brackets, they are different for each unit.

Jack

noah katz
10-28-2007, 05:52 PM
"No, but why not just buy a Z axis power feed?"

1) The Z-axis drives are $40 more

2) I'm concerned with short motor life from cranking all that weight up

3) I was concerned that it would be too hard to crank up manually for precise adjustment after I put on the smaller crank handle.

4) I already have the struts, which would address both of the above

On further consideration

1) Not that big of a deal

2) is a worry but not apparently a reality

3) I just tried it cranking while pushing closer to the rotation axis, and it will be fine for smaller adjustments

4) I'll think of something else to do with them, maybe even what I bought them for

So Z-axis unit it is, thanks.

"Are you hoping to increase spindle travel?"

If you mean get the greater travel of the knee over the spindle, no, the main issue is the tedium of cranking the knee up and down for different cutters and setups.

But another good reason is the increased stiffness and lower chatter on interrupted cuts when boring with the spindle locked.

IOWOLF
10-28-2007, 05:55 PM
There is supposed to be a difference, there is no pot.switch on the knee motor and they are always 150 ft # + units.

BadDog
10-28-2007, 05:58 PM
I'm one of those who uses a drill motor. Bought a NOS replacement dog clutch collar for $10. Used a piece of scrap HRS to make a 1/2" drill adapter, took about 30 minutes of "piddling around". I generally prefer to use the Bridgeport long leg handle for easy/precise control when milling, but the drill is OH SO WELCOME when going from a 1/2 carbide rougher in a collet to a 1/2 drill chuck and jobber drill (or as yesterday, followed by a LONG countersink, must have been about 10" of knee travel to fit the chuck and then countersink).

lane
10-28-2007, 06:25 PM
All the power feeds are the same motor. The price difference is in the extra stuff get to mount it . Use a 150 inch pound on all axis . They sell some 130 and 140 pound and I have seen the work . but the 150 is the better choice.. When servo started out they made 90 pound units for BP. went to something higher then 130 then 140 1nd I thank have something over 150 now . The Chinese just copied them and have seen 130 ,140 and 150 units for sale lately. would go with a 150 for the knee you get some extra stuff to extend the handle same on the y axis . But the motor box and mount system is the same .You will just have to figure out and build the extra parts to make it work.

Bill Pace
10-28-2007, 06:33 PM
I have the chinese versions of PF's on all three axes, and this is my findings on the 'Z'


"1) The Z-axis drives are $40 more"

That $40 is well worth it to get the necessary (VERY Necessary) parts to adapt the drive motor to the 'Z' shaft.

"2) I'm concerned with short motor life from cranking all that weight up"

Through a series of events that are too lengthy to go through here, (I dont wanna talk about! OK!!) I ended up with a 135lb unit on the 'Z' axis instead of the recommended 150lb and it is performing very well ... mind you, its in my home shop and not put to any great loads.

"3) I was concerned that it would be too hard to crank up manually for precise adjustment after I put on the smaller crank handle."

Mine isn't necessarily 'hard' to crank, but it is a bit of a pain to engage the spring loaded clutch teeth to start the crank ---- but, the beauty of the variable speed is its ability to just really creep/move the table easily in .001 moves. I dont know the last time I bothered with using the hand crank.

Have to really love those PF's .....AND my VFD!!! ......Oh, AND the DRO!!.... in fact, I just LOVE my Bridgeport clone, after having a mill-drill....

noah katz
10-28-2007, 11:03 PM
"would go with a 150 for the knee you get some extra stuff to extend the handle same on the y axis ."

"That $40 is well worth it to get the necessary (VERY Necessary) parts to adapt the drive motor to the 'Z' shaft."

Ah, words of wisdom, I'll definitely go with the Z-axis unit, thanks.