I absolutely hated hank cranking the knee on my Bridgeport mill. Might be old age or the fact that I work for a living to afford some conveniences, so I bought a Z-axis power feed unit from All Industrial Tool supply as a belated birthday present to myself. Don’t mind birthdays so much when stuff like this shows up on the porch!
The unit is made in China by Asong and is available ffrom many outlets. All Industrial Tool had it for $350 including shipping for price comparisons. There’s a photo of the parts in the kit spread out for view. Set all of the parts out and skimmed through the manual before getting started.
Frankly, the manual reminded me of a Jim Gaffigan shtick about Hot Pockets; the instructions should say “take out of package and insert directly into the toilet”. I’m not a total idiot here, but the instructions are about as bad as I’ve seen. Nothing mentioned about drilling holes through shafts for spring pins, light on the procedure to shim the drive gear for proper mesh with the motor pinion, light info on shimming the micrometer dial, etc.
I pretty much figured out how it would go together, but hit YouTube for some confirmation. Found this helpful link from Old Ironworker who installed a similar unit on his mill:
First step is to pull the crank, gear shaft clutch insert (Bridgeport’s name – castle nut on the elevating shaft), and micrometer dial from the mill. I fractured the castle nut when pulling it . . . It’s not reused and replacements are available for $35, but not a good start to the project.
The kit comes with an adapter ring that mounts to the bearing cover on the knee and provides a couple of tapped holes for mounting the power unit. Well, the holes on the adapter ring weren’t even close to lining up with my knee bearing cover. So, are you supposed to transfer punch the holes on the adapter to the knee bearing cover and drill/tap? Consulted the instructions to no avail.
I chose a different path and made a new adapter instead of drilling/tapping the bearing cover. Started by chucking up a 4” round and planned on turning down to 3 3/8”, drill/bore and part. However, there would be a lot sticking out of the chuck and a work peel out of the chuck was a risk, so I went the CNC mill route.
Used a piece of ½” thick HRS plate to make the adapter. Boy, that CNC is really nice! Programmed in a routine to clear out the center hole (G76 code; set the hole diameter, cutter diameter and let the mill do all of the work), set locations for the knee bearing cover and cut the OD.
Bolted the adapter over top the knee bearing cover and set the power unit in place. The knee lock was close to hitting the back of the motor so the unit was rotated 30 deg. Set the provided adapter on top of mine, spun it 30 deg. and transfer punched the mounting holes for the power unit to my shop-made adapter. Drilled and tapped the power unit mounting holes.
Ran the extension shaft on the elevating shaft (it screws onto the micrometer lock threads) and set the motor in place. So what keeps the extension shaft from spinning on the elevating shaft? There’s a mention of a spring pin in step 6 of the instructions, goes through the clutch nut on the end. But in my case the clutch nut would end up on the extension shaft beyond the end of the stock elevating crank, so the extension shaft would spin right off the elevating crank. Obviously, 2 spring pins are needed, one for attaching the extension shaft to the stock elevating shaft and a second one to attach the clutch nut to the extension shaft. Drilled spring pin holes through each of the details on the mill for hand drilling through the shafts when the parts were on the mill.
The brass drive gear was shimmed for proper engagement using Old Ironworker’s suggestion. Set the gear in place and measured the back side relative to the end of the shaft. Then started adding shim until the gear started to push away from the motor pinion. Then hand drilled the spring pin hole through the extension shaft and elevating shaft. Installed the shim, key and brass gear.
Next step was to drop on the micrometer dial and clamp nut. Shims are provided to space the micrometer dial away from the feed motor housing for some clearance, otherwise the dial would drag on the power feed unit when locked in place.
Clutch nut was screwed on next. I took it up to just light contact with the brass drive gear, then hand drilled the second spring pin hole.
I’m not familiar with variations in Series 1 Bridgeport knees, but apparently there are some differences through the years on the bearing cover on the knee. I could see from Old Ironworker’s video that his sets just sub-flush to the knee. Mine sets proud of the knee by about 3/8”. Also, the stock adapter was about 3/8” thick while mine was ½”. End result was the extension shaft was about ¼” short for my crank to fully set on the extension shaft. It’d work OK, but the compression spring that keeps the crank out of clutch nut engagement was really tight. So much so that the crank tended to spin with the power feed. So, another modification.
Made a ¾” long extension from 5/8” stock with a through hole for a longer M6 bolt to tie the crank/compression spring to the extension shaft. I Loctited the screw to the shaft, otherwise it unscrewed itself. Jury is still out if I’ll leave the crank on the knee, kind of nice to not bang your knee (pun intended) on the crank.
Second to the last step was to install the travel limit switch. A mounting block is screwed to the knee which gives mounting holes for the switch. The stops are set into a rail which is screwed to the column. No issues here, ran the table down to the bottom of travel and set the rail position. Took the table up about ½” and set the switch stop there. The power feed will kick out about ½” from the bottom of travel, but I can still manually crank it to the full range as the stop is spring loaded. Figured this was the prudent approach for the stop.
OK, last step was to run the table up and down and try to wipe the big sh*t-eatin' grin off my face!
Bruce
