PM 45M keyway question

MecGen

MecGen

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Hello people

I have a 45M mill that I stripped down to clean out and replace seals and bearings. One thing that struck me is how loose the keyways are. These keys are made as a guide to let the gear slide up and down, not to lock down the gear to shaft so I would expect a looser then normal fit, but this is too loose.

I measured them and came up with an average 4.83 mm on one side and 4.65 mm on the other side which makes me think its a 3/16 key although I would expect it to be metric. I don't think its a 5 mm key ? That would never fit. McMaster Carr only has rounded keyways no longer then 2 inch so I have to buy key stock and cut/grind to fit. Google machinists seem to think (makes sense to me) that it's best to get a key that is a little softer then the gear or shaft, that way if it wears out in the future, the key will bear the brunt of the wear and not the shaft/gear.

So, there are a couple of key material choices as well as different hardness. I don't have a set of Rockwell files to cheack the hardness of the gear and to pay 100$ for a set just to buy 10$ worth of key stock does not make sense for a hobbiest. Basically my easy choices are between 1045 steel d50 hardness or (leaning towards this) 1095 spring steel d90 hardness. Spring steel only comes in standard size, 1045 has an oversized option.

So I am open to suggestions and would like to hear your thoughts, in the meantime I will reach out to PM to se if they have stock or recommendations, but I suspect he is on holidays till next week.

Happy New Years
 

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qualitymachinetools said:
If you were not having any problems, I would recommend leaving whats in there and not modifying it. If anything is broken of course replace it, but if it was working OK, use what was in there. Any keys in there should be Metric.
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Gotcha, I just bought the mill, it was sold (supposedly) because of the oil leaks. I never had the chance to use it. I appreciate your opinion but it's hard for me to knowingly leave a bad part in it.
Cheers
 
Don't over-think this. Given the size of the existing key and its looseness, 5mm sounds like the right size. The large end dimension is too big to have been 3/16, and they would probably have a harder time finding 3/16 in China than we would have finding 5mm. Just make one out of some CRS, the key should be the sacrificial part in the train.
 
MrWhoopee said:
Don't over-think this. Given the size of the existing key and its looseness, 5mm sounds like the right size. The large end dimension is too big to have been 3/16, and they would probably have a harder time finding 3/16 in China than we would have finding 5mm. Just make one out of some CRS, the key should be the sacrificial part in the train.
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I will be ordering both 5mm and 3/16, living in Canada the shiping will cost me 2X the price of the key stock, so might as well get both.
Thanks for responding.
 
Order some key stock from KBC Tools in Toronto to save on shipping.Item #: 1-958-04015
 
☆☆☆UPDATE☆☆☆
I received the 5mm key way. It needed to be filed down on the shaft side, which is strange as I ordered an undersized key, but it fit perfectly in the gear. I have a feeling these mills are just sloppy from the manufacturer.

It works, now to complete the rebuild.

Thanks everyone!
 
MecGen said:
☆☆☆UPDATE☆☆☆
I received the 5mm key way. It needed to be filed down on the shaft side, which is strange as I ordered an undersized key, but it fit perfectly in the gear. I have a feeling these mills are just sloppy from the manufacturer.

It works, now to complete the rebuild.

Thanks everyone!
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You made the right choice in replacing these loose keys especially in this application. I’ve seen a few who have replaced the loose keys and bearings in the RF45 mills and that made it drastic difference in the noise of the machine especially when using large cutters. It should also help to drastically improve surface finish..
 
@MecGen I didn't get to the thread in time... For a small mill like the RF 45, you should go with very soft keyways. I'm glad you got it fit well, and it works!
 
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