Can't Raise the Knee

[kcoffield]

Well now I've done it. I have a project that will stretch the under quill capacity of my mill and was lowering the knee to see what was possible and apparently ran it off the lifting mechanism. Now the lift crank just free wheels and the knee is stuck at/near the bottom. Didn’t even occur to me it would even be possible. Thought I’d ask for some help on this one so I don’t dork it up.

I assume it’s just a jack screw that has somehow disengaged at limit but the drawings in the manuals are so busy I can’t tell. I tried to lift the knee with a jack thinking I’d get enough movement to reengage the screw but even at the point of the machine base lifting, no luck. I might be applying the lifting force too far out on the knee to get movement in the ways. My next move will be to grab my manual fork lift, move the Y Axis on the mill to the rear, and either attach the forks to the surface or under the table clear of the screw and scale.

What am I up against here? Any advice appreciated.

As far as the model, not entirely sure, but we discussed it in this thread and it was suggested it could be a 745 head on 555.

https://www.hobby-machinist.com/threads/what-have-i-got.89454/

Best,
Kelly

 

[Cadillac]

It looks similar to the Bridgeport design. If so their is the screw in the knee driven through two gears to a shaft connecting to the handcrank . The center riser bolted to the base has the nut Which is stationary.
You should have access to all this by moving the saddle furthest away from the column. Slide the center telescoping metal shield forward. Best to see what’s going on before you start lifting. My guess is the screw has gone all the way through the nut to a recessed portion Of the shaft. Idk

 

[T. J.]

Try pushing in (axially) on the crank shaft while turning it. If a locking collar on the shaft has come loose, it can let the bevel gears become disengaged. Mine has done that.

 

[woodchucker]

do you have a bottle jack, put it under the knee near the ways.

I don't know what may have happened, but I suspect that you lost thread engagement and are missing a collar that might exist that prevents that.
maybe you entered a reduced area of the shaft.

again, just guessing. but I agree with your assertion that your lifting too far away from the ways.

good luck, don't panic, take it slow if it's not working don't force it.

edit, maybe you've spun the screw out of the gear. it may have pulled itself out as it lowered.

 

[T. J.]

After looking at my 645, I really don’t think there’s enough relief at the top of the screw to lose thread engagement. One other possibility though is that the set screw in the bevel gear has backed off, allowing it to spin on the screw shaft.

 

[kcoffield]

Thanks for the replies fellas. Think I'm just going to have to do enough disassembly to get a look at the bevel gear. If you look at the one picture I posted, it actually looks like there could be more travel available. I've never had the table this low and it may be the first time in a very long time it's seen any force in that downward and maybe the ways tighten up and instead of the weight of the table working for you in downward movement, it's actually loading the bevel gears and one came loose. It feels possible based upon the crank movement, and also how it behaved before stopping. It would also explain why it doesn't budge under external lifting force.....if the screw is still engaged I think I'll stop that until I can confirm the bevel gears and screw are actually engaged.

TJ, how did you get that picture of the bevel gear? Is the back of the knee opened enough to get a camera back there?

Best,
Kelly

 

[T. J.]

TJ, how did you get that picture of the bevel gear? Is the back of the knee opened enough to get a camera back there?

I stuck my phone in from the bottom of the knee, between the column and the screw riser. You may not have enough room to do that with your knee so close to the base.

There are a couple ways you may be able to get a look in there:
1) Through the sliding cover under the saddle. You'll have to move the saddle to its extent of travel to access it (I don't remember which way).
2) Remove the crank collar and the graduated dial from the knee crank shaft. You might be able to look through the hole and see what's going on.

 

[Cadillac]

Whenever I know I’m gonna lower the knee low I give it a extra pump on the oiler. I missed the knee was binding in your original post. You might want to try and loosen the gib or even take it out. Probably just loosen to keep everything aligned.

 

[kcoffield]

The set screw on the external dog drive collar came loose. Now I'd really like to be able to tell you all I noticed the shaft wasn't spinning even though the handle was before I slid the covers back and saw the bevel gear wasn't spinning but..............I'm a constant source of embarrassment to myself. Sure felt like it fell off a thread. It does bottom positively at the end of travel without disengaging.

On the bright side, I now have freshly cleaned and lubed bevel gears, saddle lead screw, and ways.

Thanks fellas. Back to regularly scheduled programming.

Best,
Kelly

 

[woodchucker]

The set screw on the external dog drive collar came loose. Now I'd really like to be able to tell you all I noticed the shaft wasn't spinning even though the handle was before I slid the covers back and saw the bevel gear wasn't spinning but..............I'm a constant source of embarrassment to myself. Sure felt like it fell off a thread. It does bottom positively at the end of travel without disengaging.

On the bright side, I now have freshly cleaned and lubed bevel gears, saddle lead screw, and ways.

Thanks fellas. Back to regularly scheduled programming.

Best,
Kelly

I'm surprised that's not a pin... or keyed. My little clausing is keyed...