The Home Machinist!

Hi all,
I disassembled my carriage last fall to tune up during winter. My son helped with dis-assembly, and pulled the lead screw out, when he did, the beveled gear on the end of the lead screw (the one inside the forward/reverse unit) fell off. I didn't really think anything of it at the time, just picked it up and dropped into the degreaser with some other parts. When I went to re-assemble last weekend, I see there is a thru hole in the gear, but no evidence a pin or anything was ever in the hole(s) to ride in the keyway on the lead screw? So for the million dollar question....what holds that gear on the lead screw. I cannot find any diagrams of the assembly that show a pin, my parts list from Clausing shows the assembly, but no pins (does show the Woodruff key for the connecting shaft on the far left) and the gear does not have a key slot. ?????

Thanks in advance for the help...I am very puzzled.

John

The gear has the key moulded in ,common problem worn/striped out. You need a new gear.

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www.chaski.com

Thanks for the reply John, but I believe you are referring to the power crossfeed miter gear, which indeed does have the key cast into the gear. The gear on the end of the lead screw does not have an integral key. I've attached a picture, the leadscrew would be coming out of the gear on the right and heading down toward the tailstock. I know there must have been something in one of the holes as it had no grease caked in it, the other hole was nearly invisible until the grease was removed. A free floating pin was my first thought since it fell out so easily, but if that is the case, what the devil keeps it in when mounted on the lead screw?

Edit: Note in the picture, the gearbox is upside down, however the right/left orientation is correct.

Neither of my Atlas lathes have that reversing gearbox. Therefore I can't say for sure but I think that gear would have the integral key. The Atlas gears are die-cast and including the key would be simple and cheap. I do know that the first time i came across the crossfeed gear key stripped, I went thru the same thinking you are doing. The bore showed little or no sign of ever having a key in it. If there is a keyway in the shaft end and no additional part shown in the parts list, that seems the only logical answer. I think the hole in the gear is for oil.

There are lots of Atlas parts available but several owners have used various methods to repair the stripped crossfeed gears by installing a new key.

Edit: After looking at the photo again, I think the leadscrew is driven by the sliding dog rather than by the gear, so the above would not apply. Is the housing broken or is that the way it is made?

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Don Young

I believe you are right on the drive mechanics of the screw, and the unit is open on the bottom (top in the photo) which is why the gear just fell out when the lead screw was extracted. I have looked inside that gear with my old eyes, and with magnification and cannot see where any shearing took place, the metal is even and smooth, and the patina over the entire inside surface is the same.

Plus, if the gear was keyed on the shaft, oil holes would be unnecessary since you wouldn't need to oil a fixed gear on the shaft? You are totally correct in the diagrams not showing a key (or pin) implying there isn't one, but what would fix that gear on the shaft when you transfer drive from the forward to reverse bevel gear?

The holes are not threaded, and as I said previously, one hole was completely packed with old grease, while the other was clear of it, again implying something was in that hole. But if it was a pin, what kept it in the hole during shaft rotation since the bottom of the gearbox is open?

I've been trying to puzzle it out, could it have been a "T" shaped affair, a square key with a pin that floated in the hole? If that is the case, why the devil wouldn't something that odd be on the parts list?

Gaaaaaaaa!!!!!! This is driving me nuts! (wife always tells me "that's a pretty short drive")

Maybe I should put in a call to Clausing and see if they can shed some light on this one....just been putting that off since I hate being on hold for 30 minutes, which seems to be the norm every time I call them.

Thank you all again,
John

The lead screw should be keyed to the dog between the 2 bevel gears.

When the dog is slid to the left, the input shaft turns the left gear, the left gear turns the dog, the dog turns the lead screw.

When the dog is slid to the right, the input shaft turns the left gear, the left gear turns the center gear, the center gear turns the right gear, the right gear turns the dog, the dog turns the lead screw in the reverse direction.

The right gear does not use a pin through the hole. I don't know what the intent of that hole is but it could be for oil since the right gear is allowed to rotate on the shaft when the dog is engaged in the left gear.

Charlie W.

Isn't there also a middle position where the dog drives nothing?
At least it was so on my old flatbed.

With the housing cutaway, it is not clear to me how the shaft and right gear are held radially in the housing. It seems probable that the shaft extends all the way thru and is supported by the left gear and shaft. The housing keeps the gear from sliding lengthwise along the shaft and the shaft is kept in position lengthwise by the bearing on the right hand end of the shaft. As Charlie mentioned, the right gear can not be fixed or keyed to the shaft. The shaft can be keyed only by a sliding keyway to a key in the center shifting dog. When the dog is shifted to the left to engage the shaft to the left gear, the shaft and right gear rotate in opposite directions. Oil or grease is therefore needed between the shaft and gear.

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Don Young