Power Cross Feed Repair/ Miter Gear Replacement

[bhusted]

Now that I've got the traverse gearbox working well, I think I should tackle the power cross feed. Like many of these lathes, the key cast into the miter gear is entirely gone. I was planning to broach a new keyway and pin a new key in there and be on my way. On closer inspection, the Zamak gears are crumbling so I don't think this repair would last long. I'm not sure what causes this, but I'd like to replace it with a steel gear.

From the measurements I've taken of the original, it appears to be a 12DP 18T miter gear. I'm not sure how to measure the pressure angle, but all of the commercial ones I've found are 20 deg, so I'm hoping that's a match. Has anyone used a gear from Boston or otherwise and adapted it to this purpose? I know there are steel versions available on eBay and elsewhere, but I'd like to do this myself for less $$$.

This one from Boston Gear is only $26.50 and seems to meet all of the necessary criteria. I would bore the center out to 3/4" to clear the leadscrew and then make a counterbore on the back to accept a sleeve pressed in for the shank where the keyway is. The pair could be silver soldered together or pinned if a sufficient press isn't achieved. Thoughts?

 

[benmychree]

The gear in your picture is obviously a 14 1/2 degree pressure angle, it would not mesh with a 20 degree gear.

 

[pdentrem]

I posted the Boston gear part numbers for this gear awhile back. I will have to look for it.
Pierre

 

[bhusted]

The gear in your picture is obviously a 14 1/2 degree pressure angle, it would not mesh with a 20 degree gear.

How can you tell so definitively? I've been trying to compare measurements from the model to the original to determine if it is a match. All of the descriptions for how to measure the PA I've found are based on spur gears and I have not found any that deal with miter or bevel gears.

I posted the Boston gear part numbers for this gear awhile back. I will have to look for it.
Pierre

That would be excellent. I was not able to find anything in their catalog that was a 14.5 degree PA.

 

[benmychree]

A view of the large end of the teeth would be more definitive, the large end of the gear is equivalent to a spur gear of the same pitch, if you had a set of gear gages, you could compare pressure angles; if a picture of the big end were posted, I could tell pressure angle for certain, the difference is obvious.

 

[bhusted]

Here's are images of the gear profiles from the back side.

20 deg PA CAD model:

Original Gear:

Here are the two laid over the top of each other:

The tooth form sure looks the same to me. I also measured the distances at the root of each tooth.

# of Teeth	1	2	3	4
Original Gear	.170	.405	.635	.831
20 deg PA	.147	.379	.599	.802

 

[benmychree]

Yes, it does appear to be 20 degree P.A. What is the condition of the mating gear?

 

[pdentrem]

Here you go, not Boston Gear! It is a Browning YSM12B18X5/8




Pierre

 

[pdentrem]

This gear can be used for both locations with some machining and addition of a pressed on regular spur gear to drive the crossfeed screw gear. The Zamak metal has issues over time. The Zinc pest it is known as.
Pierre

 

[bhusted]

This gear can be used for both locatiuons with some machining and addition of a pressed on regular spur gear to drive the crossfeed screw gear. The Zamak metal has issues over time. The Zinc pest it is known as.
Pierre

Thanks for the info. I ordered the Boston version from Amazon and hopefully I can get it fixed up. The mating gear is in worse condition, but I was able to source one of the steel versions for $35, and I didn't think I would be able to price out another miter gear and the spur for less.