# Power Cross Feed Repair/ Miter Gear Replacement



## bhusted (Jul 1, 2020)

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?


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## benmychree (Jul 1, 2020)

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


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## pdentrem (Jul 1, 2020)

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


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## bhusted (Jul 1, 2020)

benmychree said:


> 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.



pdentrem said:


> 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.


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## benmychree (Jul 1, 2020)

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.


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## bhusted (Jul 1, 2020)

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 Teeth1234Original Gear.170.405.635.83120 deg PA.147.379.599.802


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## benmychree (Jul 1, 2020)

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


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## pdentrem (Jul 1, 2020)

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





Pierre


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## pdentrem (Jul 1, 2020)

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


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## bhusted (Jul 1, 2020)

pdentrem said:


> 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.


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## chippermat (Jul 2, 2020)

pdentrem said:


> Zamak metal has issues over time. The Zinc pest it is known as.
> Pierre


Does this inevitably and unavoidably happen to all Zamak?  I mean is my Atlas lathe going to crumble to bits eventually?


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## Buffalo21 (Jul 2, 2020)

The atlas gears I’m looking for are the two bevel gears for the table feed on my Altas MFC,


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## francist (Jul 2, 2020)

chippermat said:


> Does this inevitably and unavoidably happen to all Zamak?


I have only ever seen this particular delamination or fracturing happen to gears. I have three Atlas machines of varying vintage and there is no apparent rhyme nor reason to the deterioration other than the parts themselves, but in some cases it can be quite dramatic.




I’ve also seen what has been described as zinc pest exhibit quite different appearance so I always wonder if it’s the same thing or whether there are separate things going on with each. Just my observations though, I’m no expert on the topic.

-frank


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## bhusted (Jul 2, 2020)

francist said:


> I have only ever seen this particular delamination or fracturing happen to gears. I have three Atlas machines of varying vintage and there is no apparent rhyme nor reason to the deterioration other than the parts themselves, but in some cases it can be quite dramatic.
> -frank



This has been my observation as well.  Some of the parts on this machine have been perfectly fine, but others just crumble.  One of the back gears flew apart into 4 pieces.  Besides some gears, the pull knob for the power cross feed and the knob for changing feed directions have both fallen apart.


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## francist (Jul 2, 2020)

Oh that’s interesting. Like I said, I’ve only ever seen it on gears but your experience with seeing it on knobs is quite illuminating.

-frank


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## pdentrem (Jul 2, 2020)

Totally random, but very likely, depending on the impurities that are in the alloy. The older or cheaper, the more likely this will occur.


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## chippermat (Jul 2, 2020)

Thanks for those responses.

Good job with the gear, bhusted, looks tricky to me.


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## bhusted (Jul 3, 2020)

The replacement gear from Boston Gear arrived today and I can breathe a sigh of relief that it is a match with the original gears.  For anyone looking to do this, the Boston PN is L102Y.  L127Y would also work, but has a 1/2" bore instead of 5/8".  If you're just looking for the specifications to buy from Browning, Leif, Martin or others, you need 12 diametral pitch, 18 teeth, and a 20 degree pressure angle.  Any of these will require some machining to make fit, but isn't that the purpose of having a machine like this?  I'll document the rest of the project here as I get to it.


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## bhusted (Jul 8, 2020)

I'm still waiting on some material to be delivered for the keyed shaft portion of the miter gear.  The pull knob to engage the cross feed was broken when I got it, so I took the opportunity to make a new knob for it and for the feed direction selector.


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## bhusted (Jul 10, 2020)

Does anyone know how far the key is meant to extend into the slot on the leadscrew?  I know it's a 1/8" key, but I dropped a square key in the slot just to check and the whole thing fits in the slot with nothing to engage the miter gear.  Obviously I don't want it dragging on the bottom of the keyway, but deep enough to fully engage the screw.  I plan to cut a keyway partway into the replacement gear and secure the key with silver solder.


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## wa5cab (Jul 10, 2020)

Are you saying that the keyway in the gear is 1/8" wide and 1/8" deep?  If that is the case and if the keyway in the lead screw is 1/8" wide by 1/16" deep, then the mating key will need to be 1/8" x 3/16".


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## yendor (Jul 10, 2020)

I think he means the other way around.
He dropped a 1/8 x 1/8 keyway into the Lead Screw Slot and it went to the bottom with nothing showing.


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## bhusted (Jul 10, 2020)

yendor said:


> I think he means the other way around.
> He dropped a 1/8 x 1/8 keyway into the Lead Screw Slot and it went to the bottom with nothing showing.



This is what I meant, but I made a stupid mistake.  I was looking at the leadscrew for the Logan lathe I'm restoring which was on the bench next to the Craftsman one.  The depth on the keyway on the Craftsman leadscrew is 0.07, so making the keyway in the gear 1/16" deep will work nicely with the 1/8" square key moving just above the bottom.  All is well.

I got the first part of the machining finished today for the replacement gear.  The steel part of the shaft on the old gear measures 0.997, so I made a counterbore of 0.995 on the new gear.  Holding it backwards was achieved by making a ring with a internal bore that was a slip fit with the OD of the Boston gear and then splitting it.  Then I could indicate the ID of the gear to get it on center.







I finished the back side of the gear to length by turning a quick mandrel to the 5/8 ID of the bore and tapping a 1/4-20 hole for a cap screw to secure it.  









Next step is to turn the new part that will become the shaft.  I plan to do the inside bore once the two have been fit together.  Then broach a keyway and get it soldered in.


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## wa5cab (Jul 11, 2020)

Looks like you are making good progress.


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## bhusted (Jul 15, 2020)

It's getting closer.  I turned the shaft portion so that it was a press-fit with the counterbore created in the gear.  I kept going back and forth on if I should press it or silver solder and ultimately decided to press it.  





Once the two were pressed together, the center bore could be enlarged to accommodate the 3/4" leadscrew.  I went .005 over so that it would slide over.  The final machining op was to cut the keyway with a series of cuts from a boring bar.






Here's where it stands now.  The key is a good fit in the slot and the whole thing fits over the leadscrew nicely.  I only wish I had been able to center the cut on one of the teeth...









Hopefully tomorrow I can solder the key in place and try it out!


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## bhusted (Jul 15, 2020)

It works!  I got the key soldered in and cleaned up.  The apron is reassembled and installed.


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