Jet column clamp bolts

[FanMan]

Today I replaced the column clamp bolts on my Jet JMD-15 mill/drill. The threads on the original ones were bunged up to the point that they didn't turn easily, and the motor lock screw interfered with using a box wrench (I like the old flea market offset wrench I'm using, an don't feel like tying up a socket wrench). Anyway, the original bolts are a weird 1/2-12 (yes, that's not a typo) thread, and have 13/16 head, not the normal 3/4. Somewhere I saw a writeup on using 9/16 bolts (which do have a 13/16 head), but they had to turn down the center of the bolts to clear the column, and I wouldn't be able to use the 3/4" wrench.

Instead, I bought two 12-13 studs from McMaster-Carr, along with some oversize lock nuts (which are 13/16), and some long coupler nuts (which are 3/4, so I can still use the old wrench). The long coupler nuts put the wrench outside the motor lock screw so it's not in the way (you can see it just under the upper nut). I also added some hardened thick washers I had around (though McMaster has those, too).





For those who are interested, this is what I used:

	91025A740	Black-Oxide Steel Spacing Stud, 1/2"-13 Size, 8" L Overall, 2-1/2" & 3/4" Thread Lengths	2Each	2	0	2.33Each	4.66
	90977A195	Grade 5 Zinc-Plated Steel Coupling Nut, 1/2"-13 Thread Size, 1-3/4" Length, 3/4" Width	2Each	2	0	4.23Each	8.46
	94827A150	Cadmium-Plated Steel Expanding Heavy Hex Locknut, 1/2"-13 Thread Size, 13/16" Width, 1/2" Height, Packs of 5	1Pack	1	0	11.89Per Pack	11.89

 

[stupoty]

I had the same happen on ny rf25 recently, i had to use a nut splitter to get the nuts off.

i replaced mine with the very long hold down clamp bars from my clamping set (i never use the longest ones) just big enough and all the heads fitted in the holes quite well.

the clamp set was m12 size. I did double nut them on the fixed side to stop them coming undone.

stuart

 

[Canuck75]

Today I replaced the column clamp bolts on my Jet JMD-15 mill/drill. The threads on the original ones were bunged up to the point that they didn't turn easily, and the motor lock screw interfered with using a box wrench (I like the old flea market offset wrench I'm using, an don't feel like tying up a socket wrench). Anyway, the original bolts are a weird 1/2-12 (yes, that's not a typo) thread, and have 13/16 head, not the normal 3/4. Somewhere I saw a writeup on using 9/16 bolts (which do have a 13/16 head), but they had to turn down the center of the bolts to clear the column, and I wouldn't be able to use the 3/4" wrench.

Instead, I bought two 12-13 studs from McMaster-Carr, along with some oversize lock nuts (which are 13/16), and some long coupler nuts (which are 3/4, so I can still use the old wrench). The long coupler nuts put the wrench outside the motor lock screw so it's not in the way (you can see it just under the upper nut). I also added some hardened thick washers I had around (though McMaster has those, too).

View attachment 54734

View attachment 54735

For those who are interested, this is what I used:

	91025A740	Black-Oxide Steel Spacing Stud, 1/2"-13 Size, 8" L Overall, 2-1/2" & 3/4" Thread Lengths	2Each	2	0	2.33Each	4.66
	90977A195	Grade 5 Zinc-Plated Steel Coupling Nut, 1/2"-13 Thread Size, 1-3/4" Length, 3/4" Width	2Each	2	0	4.23Each	8.46
	94827A150	Cadmium-Plated Steel Expanding Heavy Hex Locknut, 1/2"-13 Thread Size, 13/16" Width, 1/2" Height, Packs of 5	1Pack	1	0	11.89Per Pack	11.89

Using the coupler nuts is a good idea. The original bolts on my King PDM30 were also in bad shape so I replaced them with grade 8 bolts. The casting didn't fit the bolt heads properly so I made custom washers with tabs that I bent around each hex flat and filed to the shape of the head. They now fit the casting nicely.



Thanks
Canuck75

 

[bronk]

I had similar problems. The original locking bolts were galled badly. I bought grade 8 bolts and nuts from Farm and Fleet. The holes had to be opened up slightly, and required washers and bit of shimmin as the surfaces were not square to the bolts. It was a HUGE improvement. Much easier to lock and no more creeping sideways under load. All for well under $20.