Lathe worm gear repair

[Jayham]

I bought a parts kits Logan 1825. I've been assessing the individual assemblies and their parts, freeing up seized shafts etc. determining missing components.

I have identified several issues,
. So far nothing out of my ability or capability to repair/remake. With one exception.

This worm gear which runs off the lead screw keyway. It powers the power and cross feeds. The internal male key is mostly broken away and unlikely to survive much longer. I believe it was made of cast iron. Something that would be unlikely to increase wear in the lead screw.

A replacement can be purchased but a nearly $700 after conversion, shipping, taxes and tariffs. Taking on repair makes more sense.

The lead screw keyway is 0.125"
The internal male key is 0.080"( was likely slightly larger)

Ideally I would like to overbore the gear and bush it with a bearing and key. But not sure how to tackle this since the key is internal, male and needs to remain stationary and enough clearance to allow for carriage movement.

The "best" idea I have so far is too bore and bush, then use 4 set screws to become a "key". But the forces required they would need to be steel and I'm concerned about lead screw wear.

I'm all ears for ideas. Anyways equipment available is a lathe, mill and shaper.

Here's a few pictures of what I'm dealing with.

 

[PeterT]

I'm not quite clear. The existing key is full span within worm part 57? And the bushings 55 have set screws that engage OD of 57?

If this is the case & If I understand your idea - using set screws to act as (replace) the key is not a good approach IMO. All the torque applied to the small cross section area of screw(s) will more than likely mangle the keyway slot & then you have a new, more expensive problem. Keyway broaching is a PITA for most home shops, but it really is the optimal configuration.

Are Logan parts really that expensive? Holy crap.

 

[Jayham]

The existing key should run the full length, but only about 1" remains.

The set screws (#56) hold the end bushings in place in the main housing of the apron.

My "idea" like a said not a good one. Is to drill four new set screws in either end of the worm gear.

Broaching I didn't think would be possible due to the worm gear having the key internally.

 

[Susquatch]

Broaching I didn't think would be possible due to the worm gear having the key internally.

Where abouts are you. Maybe I could do it for you. First let's scope out the ideal fix. Most likely I can do that, but let's see what we need first.

 

[Susquatch]

Broaching I didn't think would be possible due to the worm gear having the key internally.

The ideal fix

Make or buy a new full length key.

Broach the full length of the inside of the worm gear to the same size as the key.

If the old key slot in the worm gear is mangled, then broach a new Keyway prolly at 180 degrees to the old one.

Correct?

 

[Jayham]

The ideal fix

Make or buy a new full length key.

Broach the full length of the inside of the worm gear to the same size as the key.

If the old key slot in the worm gear is mangled, then broach a new Keyway prolly at 180 degrees to the old one.

Correct?

The exist key was cast in place. Making a new key is the easy part (in my mind) permanently securing the key in place is the hold up. Plus using a wearing friendly material.

I thought I typed that in my first post but I must have edited that out.

I'm in Drumheller, but make my way into Calgary every few weeks.

 

[RobinHood]

If your are re-making the worm out of steel, you could weld the key into a shallow key way inside the bore. Use your shaper to make the key way in the worm. That is how Standard Modern does it on their 9” Utilate.

The key just needs to be axially constrained when the carriage moves along the shaft. The rotational torque is transmitted by the key from the key way in the shaft to the key way in the worm bore. A couple of retaining screws through the worm extension into the key may be all that is required (or a couple of tacks).

Are you planning on attending the 2025 Calgary Area Meet-up & BBQ on the 12th of July (held in Chestermere)? If yes, bring the part(s) and we can use the groups collective knowledge to come up with a suitable solution.

 

[Susquatch]

Are you planning on attending the 2025 Calgary Area Meet-up & BBQ on the 12th of July (held in Chestermere)? If yes, bring the part(s) and we can use the groups collective knowledge to come up with a suitable solution.

Now I am REALLY JEALOUS. What an awesome thing to do at a meetup!

I'm in Drumheller, but make my way into Calgary every few weeks.

I'm in Ontarible. So that isn't gunna work. But I love @RobinHood 's suggestion. Sounds like he is already familiar with your problem too.

 

[Johnwa]

The Southbend 9A uses a similar worm. The key is constrained from moving endwise by a small pin (maybe 1/16”) through the worm and into the key.

 

[Jayham]

The exist key was cast in place. Making a new key is the easy part (in my mind) permanently securing the key in place is the hold up. Plus using a wearing friendly material.

I thought I typed that in my first post but I must have edited that out.

I'm in Drumheller, but make my way into Calgary every few weeks.

The Southbend 9A uses a similar worm. The key is constrained from moving endwise by a small pin (maybe 1/16”) through the worm and into the key.

I like that idea. If it doesn't work then could still proceed with a broaching repair.

 

[Jayham]

Adding a broached area probably would be best. And then proceeded with rollpins. Now that I've given it some More thought.

I'll have to look at the dates for the meet up.

 

[Tom O]

Sounds like we’re going to need a video Sir.