JET JTM-4VS-1 Knee Mill ~ Z-Axis Knee Powerfeed

A couple of weeks ago I started the process of mounting the JET Milling Machine's Z-Axis Powerfeed's Limit Switch Bracket.




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There isn't a lot of space between the One Shot Lubrication plumbing and the upper Z-Axis lock. I positioned the Bracket and used a transfer punch to locate the center of the upper mounting hole.




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I used a center drill to give the #4 drill bit a chance to start in the correct position. I used a small machinist square to ensure I was drilling the hole perpendicular to the side of the Mill. The blue tape was wrapped around the drill bit to give me a reference for the depth of the hole.

The #4 bit was the correct bit for a 1/4"-20 tapped hole with a 60% thread depth.




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I used a 1/4-20 Taper Tap; followed by a Plug Tap and then a Bottoming Tap to prepare the hole to receive the upper machine bolt.



Continued in the nest post...

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Continued...


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The hole was finished. This is only the second time I've tapped a hole for a bolt. I have to admit I was a bit concerned about doing this on my JET Mill. Time to see if I did it right.


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I screwed a 1/4"-20 machine bolt into the hole... Looks like it worked!



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I mounted the bracket using this upper hole to allow me to locate the center of the bottom hole.




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Once again, a transfer punch was used to locate the center of the hole.



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The bottom hole was prepared as the upper was. I was pleased to find that everything lined up and the base of the Bracket assembly was mounted to the Mill.


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Continued...



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The first part of the Bracket assembly was mounted to the Mill. As the pictures show, there wasn't a lot of clearance between the plumbing & the locking bolt.

This was all I had time for on that day a couple of weeks ago. I finally returned to the remainder of the installation a couple of days ago.
 
on June 12th I had enough time available to continue working on the JET Milling Machine's Z-Axis Powerfeed Limit Switch installation.



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The Limit Switch Stops live in two pieces of aluminum channel.




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The aluminum channel is held together with a bracket and 4 screws, washers & nuts.



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With the aluminum channel assembled, I now combined the components of the Limit Switch Bracket. I then held the aluminum channel in various positions on the side of the Milling Machine's pedestal until I felt comfortable that I'd found a satisfactory operating location.




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Using the upper standoff bracket as a guide, I used a transfer punch to locate the center of the aluminum channel's upper fastener.



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Using a #22 drill bit, I drilled and tapped the hole for a #10-24 screw.




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I tested it with a screw and all seemed to be well.


Continued in the next post...
 
Continued...



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I mounted the aluminum channel to the Milling Machine using the top screw hole.



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I used the transfer punch again to locate the bottom hole. I drilled and tapped the bottom hole as I had done the upper.





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I mounted the aluminum channel by screwing the remaining fastener into bottom hole. I then located the stops at the upper and lower range of the Z-Axis.



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This pretty well completes the Z-Axis Powerfeed installation. All that remains is to drill a 5mm hole through the Z-Axis Powerfeed shaft (white arrow points to the location) and drive in a pin.

...I have to get some metric drill bits.


Scott
 
Great photos. Should be very helpful for someone else in the future.
 
About a week ago I was working on the JET Mill's Z-Axis Powerfeed. At that time I had completed the installation of the Limit Switch Bracket.
The two tasks that remained were the drilling of a 5mm hole into the shaft of the Powerfeed followed by inserting a spring pin into the hole.

I procured a set of metric drill bits earlier this week. Today I thought I had time to finish this project.




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The 5mm hole needs to be drilled where the white arrow is pointing.




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I was concerned about my ability to drill a hole freehand through the coupler. I thought it would be better to do this on the JET Mill and then use a hand drill to finish the job on the shaft. I was playing around with how to set this up when I heard a small voice whispering in my ear...

"Is it possible", the voice said, "that drilling through the coupler without it being on a shaft will gall the internal threads?"

This did seem like a reasonable concern and I could fix it (I thought) by inserting a bolt into the coupler during the drilling process.

Without thinking about it too much, I grabbed the coupler and went back to the house basement where my hardware cabinets are. I had some 3/4" bolts and some 1" bolts. The coupler fell somewhere in between. The largest metric bolt I had was 14mm - much to small.

Off to the local Hardware Store. The Hardware Store had 7/8"-9 bolts and that barely started to thread onto the coupler and then stopped. The largest metric bolt they had was 16mm. I was leaning towards this being a metric thread at this point and I was guessing at a size of 22mm.

A Tractor Supply store was close by and they tend to carry larger hardware but I didn't know if they were going to have metric in larger sizes. They had 20mm but no 22mm bolts.




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I returned home and did what I should have done before I went on that wild goose chase. I measured the shaft's threads.

I got a surprise.

The metric thread gauges didn't really match. 2.0 pitch was close but didn't quite match.

SAE 12 matched exactly! I measured across the shaft's threads with a calipers and came up with .853"

7/8"-12?
22mm with not quite 2.0?

Two questions:

What thread am I dealing with here?

Do I need to be concerned about damaging the threads if I drill through the coupler without something threaded through the coupler?


Scott
 
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