Knockout bar

[Marco Silva]

Hello,

I'm renovating an old lathe, and i need to drill the spindle so i can eject the drive center.

What's the average diameter for a knockout bar?

[John Keeton]

Just make your own knockout bar from rod stock and drill your hole accordingly.

[Marco Silva]

That's the plan, but i don't know how large it needs to be. I dont want to overshoot it and get a weaker spindle, it's 1/4 inch ok?

[Sid Matheny]

A 1/4" rod should be fine but I would drill the hole to 5/16 in case you get some swelling on the end of the rod.

[Clint Bach]

If you want to use a vacuum chuck concider making it to fit a lamp rod. 3/8 inch or 10 mm.

[Steve Peterson]

The knockout bar that came with my lathe is 1/4" steel BY about 14" long. The last inch has a brass tip to help prevent any damage to the item being knocked out.

Steve

[Marco Silva]

Thanks guys, now i have a pretty good idea what to aim for. I would love to have a vacuum chuck, but this spindle is drilled across for the "spindle lock".

Maybe i could thread it and put some plugs on it but the spindle is hardened.

WP_20170328_17_27_07_Pro.jpg

[Brice Rogers]

Do you have to drill the entire length of the spindle or just the chuck end? If it is the entire length, give some thought on how you are going to keep the drill centered. Google "gun drill".

Also, I noted that you said that the spindle is hardened. Hopefully the center won't be as hard as the outside.

[Marco Silva]

I need to drill the entire lenght of the spindle less the morse taper #3....probably over 10 inches, i'm going to try to find a suitable drill and going to do it on the drill press it's easy because it has center mark on both sides. If i cant find a drill at decent price locally i will send it to a machine shop.

[John K Jordan]

Thanks guys, now i have a pretty good idea what to aim for. I would love to have a vacuum chuck, but this spindle is drilled across for the "spindle lock".
Maybe i could thread it and put some plugs on it but the spindle is hardened.

The knockout bar I use is 5/16" as is a drawbar I use. If the spindle is hardened you might not be able to drill through it without annealing. But that could risk warping.

JKJ

[Brice Rogers]

To check hardness (if you haven't already), do a "file test" on some some areas along the spindle that aren't critical areas like bearing surfaces. If it just "skitters" off the spindle without leaving scratches, it is HARD (at least on the outside). In some cases, when a manufacturer hardens steel, the outside is hard but the inside isn't "as hard". If you are lucky, perhaps the center is soft enough or only the spindle threads are hardened.

If you need to drill the spindle in the hardened condition, you'll need to use a carbide tipped (gun) drill. Maybe Cobalt HSS could work. Regular high speed steel drills will have a tough time. They won't cut much before they dull.

BTW, on my Grizzly G0766, the spindle is about a foot long and the mfr. drilled it from each end rather than attempting to drill it all from one side. The through hole is supposed to be 10 mm (0.394) but the bores don't line up perfectly. But most of their spindles will allow a 3/8" rod to go through. Drill on a drill press over about 10" is an ambitious challenge.

Marco, keep us posted on your progress.

[Wes Ramsey]

Thought I might suggest a different option - rather than drilling for a knockout bar, would you be able to pry the attachment out? I do this on my tailstock, which isn't drilled through. I have a thin, stamped, flat wrench - probably came with a tool, but no idea which one - and it just fits over a MT2 shaft. I can slide it over the shaft and pull it back toward the tailstock and it pops right out. I can't imagine there's enough force applied to bend anything. Don't know if it will work for your application, but figured I would throw it out there.

[Marco Silva]

Thought I might suggest a different option - rather than drilling for a knockout bar, would you be able to pry the attachment out? I do this on my tailstock, which isn't drilled through. I have a thin, stamped, flat wrench - probably came with a tool, but no idea which one - and it just fits over a MT2 shaft. I can slide it over the shaft and pull it back toward the tailstock and it pops right out. I can't imagine there's enough force applied to bend anything. Don't know if it will work for your application, but figured I would throw it out there.

My tailstock isn't drilled also, but is a self ejecting MT3. On the spindle the manufacturer made the drive center threaded so you would tighten the nut to get it out
I would like to keep it simple and drilling the spindle should be ok ...it's 2 inches on the thickest part.

drive.jpg

[Leo Van Der Loo]

My tailstock isn't drilled also, but is a self ejecting MT3. On the spindle the manufacturer made the drive center threaded so you would tighten the nut to get it out
I would like to keep it simple and drilling the spindle should be ok ...it's 2 inches on the thickest part.

drive.jpg

That’s a heavy spindle Marco, I would go for a 7/16” hole or at least a 13/32” hole through the spindle, so you could use a ⅜” bar.

My Delta midi lathe even has a ⅜” bar to drive the mt pieces out, you do want some weight to remove these pieces, on my large lathe I use a thick-walled ½” brass pipe filled with lead to remove the MT5 pieces, that weight really helps.

If your lathe is operational you could drill it with a jacobs chuck in the tailstock holding the drill bit, there are tungsten carbide tipped drills that are used in the aircraft industry, I have bought some used ones and they drill through some pretty hard material.

ebay probably has some, and they do come in long lenghts.