Bridgeport Power Knee Question

talvare · Sep 8, 2012

I'd like to know if any folks here have some great ideas for a power knee drive for a Series 1 BP mill that's a little easier on the bank account than the Servo drives.
Thanks,
Ted

JohnEvans · Sep 9, 2012

I'll probably be raked over the coals for this but I'm running 2 of the import ones on my BPs. One I bought from Rutland several years ago and was about $325 or so ,the other from ebay and was a lot cheaper like $250 or less as I recall. I will qualify this as I'm a home shop guy and don't put a lot of miles on them but so far they work just fine. For limited use a cordless drill can be put to use. I use mine for drilling as BPs power quill feed really is to light for such use.

talvare · Sep 9, 2012

JohnEvans said:
I'll probably be raked over the coals for this but I'm running 2 of the import ones on my BPs. One I bought from Rutland several years ago and was about $325 or so ,the other from ebay and was a lot cheaper like $250 or less as I recall. I will qualify this as I'm a home shop guy and don't put a lot of miles on them but so far they work just fine. For limited use a cordless drill can be put to use. I use mine for drilling as BPs power quill feed really is to light for such use.

John,
Thanks for your input. I am also a home hobby machinist so it becomes difficult to justify spending something like $1K for a genuine Servo knee drive. I haven't been able to find anyone who has actually used the import copies, so was curious about their reliability. In the little research that I've done, it seems that the major difference is the material the gears are made of, ie; plastics vs bronze or steel. I have also seen where people are using the cordless drill as you stated, but really would like to install something more permanent. It's good to hear that your import servos are providing good service. I may end up going that direction.
Regards,
Ted

kpotter · Sep 9, 2012

I have installed several and they work fine. In a shop seeing daily use with heavy table loads they will die, in a home shop they should be fine. The biggest thing to remember is to take the knee lock off before engaging the power feed, they hate that it breaks the plastic gears in them. The plastic gears are a good idea because you will forget and you will break them but they are easy to replace. I wish I had power feed on the knee of my tree mill it is killing me.

aerodark · Sep 9, 2012

Make or procure one of these for a drill motor:

http://www.practicalmachinist.com/v...geport-mill-knee-z-axis-crank-adapter-214134/

I put a hex on the shank of mine:

http://s411.photobucket.com/albums/pp196/aerodark/?action=view&current=Shoptour002.jpg

JRIowa · Sep 10, 2012

Gee, I didn't realize, it's been over 7 years since I posted this.
http://www.practicalmachinist.com/vb/bridgeport-hardinge-mills-lathes/poor-mans-power-knee-116302/
The drawing that is posted is close to what I posted way back then.
JR

talvare · Sep 10, 2012

Thanks Gentlemen for all of the input. The adapters for using the cordless drills are definitely the most cost effective and I may end up doing that. But before doing that I may make an attempt to adapt a small right angle gear head motor. If the torque calculations work out then I'll see if I can design a method to adapt it. If it works out, I'll post pictures. If not, I'll just fade into the sunset :-).
Thanks again.
Ted

talvare · Jan 25, 2013

Well, I finally decided to go ahead and fabricate a home brewed knee drive for my mill. I used a Bodine gearmotor that I bought on eBay, fabricated a mounting bracket and machined a torque limiter/clutch assembly. Finished installing it today and it seems to work well. My arms already love it

Some pics attached.
Ted

the man machine · Jan 25, 2013

Everyone is desperate for a Bridgeport knee-cranking solution, at 10 turns to go one inch who wouldn't be? And I'm one of those BP owners who refuses to mill with the quill down unless I absolutely have to, I'll never let some lazy slop who lowers the quill to mill instead of cranking the knee up anywhere near my beloved t-ram.

Anyhow, you might try contacting an authorized Servo Service Center. There's a chance someone put a table feed in for service an never claimed it back. I used a salvaged type 140 on my knee, it was never made to handle it but I cheated with counterbalancing. Fully rebuilt Servo feeds were averaging between $200-$300 years ago depending on the type and what was needed, that price could certainly be higher right now, you never know, a Service Center could be happy to recover on some "dead" benchwork and give you a great deal.

Nightshift · Jan 26, 2013

the man machine said:
Everyone is desperate for a Bridgeport knee-cranking solution, at 10 turns to go one inch who wouldn't be? And I'm one of those BP owners who refuses to mill with the quill down unless I absolutely have to, I'll never let some lazy slop who lowers the quill to mill instead of cranking the knee up anywhere near my beloved t-ram.

Anyhow, you might try contacting an authorized Servo Service Center. There's a chance someone put a table feed in for service an never claimed it back. I used a salvaged type 140 on my knee, it was never made to handle it but I cheated with counterbalancing. Fully rebuilt Servo feeds were averaging between $200-$300 years ago depending on the type and what was needed, that price could certainly be higher right now, you never know, a Service Center could be happy to recover on some "dead" benchwork and give you a great deal.

I really like your counterbalanced knee solution! I think I will add that to mine while I wait for a power Z solution as this will make the cranking much easier I would suspect. I totally agree with you about running the knee up to avoid milling with the quill fully extended. Thanks for the simple solution. Cheers, Bill

the man machine · Jan 26, 2013

Nightshift said:
I really like your counterbalanced knee solution! I think I will add that to mine while I wait for a power Z solution as this will make the cranking much easier I would suspect. I totally agree with you about running the knee up to avoid milling with the quill fully extended. Thanks for the simple solution. Cheers, Bill

Thanks, are the pics showing enough detail? Any questions about it? Btw, I've switched from the handwheel shown in the pic to a regular table crank handle from Y axis, the movement is butter-soft both up and down, I love it. I'll get a couple more pics up here soon, sorry to hijack. m-m.

Nightshift · Jan 27, 2013

the man machine said:
Thanks, are the pics showing enough detail? Any questions about it? Btw, I've switched from the handwheel shown in the pic to a regular table crank handle from Y axis, the movement is butter-soft both up and down, I love it. I'll get a couple more pics up here soon, sorry to hijack. m-m.

No I think I can see how you did it ... run the cable around 2 pulleys mounted at the top of the base casting front and back. Then thread the cable thru the ram dovetail hole there and attach a weight to the rear side of the base. What are u using for a weight? I've got a 12" handwheel I use most of the time on my knee. I made an adapter to match the cogs and it slides on just like the original crank handle. I find it's easier to crank with the hand wheel than the standard handle, and I'm sure it will be much easier cranking once I add a counter-weight to the knee. I may not need to go the final step and power the knee! Cheers, Bill

adama · Jan 27, 2013

I too am curious at to what your using as a weight. Is it enough to fully balance the weight of the knee, or just balance a decent chunk of the Knee Weight?

As to 10 cranks a inch, its not too bad. You want to try my jones and shipman 540 surface grinder. That thing is 50 cranks a inch. That truly takes a good few minutes of handle spinning to go 6"!! Advantage is at that ratio its kinda irrelivent what it weighs, it could be damn near pushing the grinder down through the floor and it would still be easy going.

the man machine · Jan 27, 2013

Counterweights, brackets, ect.

(1st pic) the counterweights themselves are just two treepanned slugs of scrap steel. Believe it or not, they are attached to each other with a piece of 3/8"-16 all thread.
They are not nearly to fully counterbalance the full weight of the knee and everything on it but knocks off a good (I'm guessing ) 1/3 or so, very noticable. There's more that can be done, I just haven't done it. Think of bags of lead shot draped over each side, crazy stuff, anything, a bar with bodybuilding weights, or those flat, rectangular RV plastic waterjugs filled with concrete with cast-in eyebolts, that's an ideal shape. Melt the lead out of scavenged batteries, go nuts....

Lead is a great choice because of it's compact weight density and easily castable nature.

the man machine · Jan 28, 2013

more insanity:

Spare Y-axis crank used on the knee, it's that easy to move.

Word of warning: Keep your wrist the heck out of the way before running full speed down or up, you have to reach up, over, & around to avoid getting "whackety-whacked"....

Also note my knee lock lever is replaced by stainless and a teardrop-shaped ball knob.
The man-machine Bridgeport: "Where luxury is the standard" Bwa-ha-ha

gjrepesh · Jan 29, 2013

I made an adapter that used a drill for activation. It was better than hand cranking for awhile but over time I said this is a PITA. I bought a Z-axis power feed from Harbor Freight, I believe. Its been on 6 or 7 years and still works like new. To me, Z-axis power feed is right up there with a DRO. Once you have it, it would be hard to go back. I'm also a home shop machinist.

Nightshift · Jan 29, 2013

gjrepesh said:
I made an adapter that used a drill for activation. It was better than hand cranking for awhile but over time I said this is a PITA. I bought a Z-axis power feed from Harbor Freight, I believe. Its been on 6 or 7 years and still works like new. To me, Z-axis power feed is right up there with a DRO. Once you have it, it would be hard to go back. I'm also a home shop machinist.

I've never seen a z-axis power feed at Harbor Freight. Are you sure it was from there? Bill

the man machine · Jan 30, 2013

Yeah I've never seen Harbor Freight carry anything so Bridgeport-specific besides the red box of parallels for $35... Which aren't bad btw, just take the razor-edge off on your ScotchBrite wheel.

Nightshift · Jan 30, 2013

the man machine said:
...(snip)... besides the red box of parallels for $35... Which aren't bad btw, just take the razor-edge off on your ScotchBrite wheel.

LMAO @ man machine

the man machine · Feb 1, 2013

Looking around at work I didn't see any other BPs with the knee button thingy like mine has. Must be one of those quirky deals like the two knee gib locks on the side, it's a mystery why some do and others don't.

Eh-boy if your's doesn't have the magic button for your cable counterbalance life just got suckier. As you can see there's zero room for a traditional cable thimble and cable "clips" (clamps). Brazing a cable loop does seem a little insane but that's a long length of braze with inter-strand penetration, who's worried? Not me.

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