Thread: MC900 lathe knockout bar

Originally Posted by Fuzzie

The lathe I have didn't come with a knockout bar. Is there anything special about their shape? By the look of the (almost) hand drawn exploded parts diagrams I can find online it looks like there may be a reduced diameter section at the end.

Can somebody post the dimensions of a bar please? Also if there are any necessary design details. I've been thinking of maybe just cutting the tip off a long handle flat blade screwdriver and using that.

That will work fine. I made a more substantial one, rather than use the one that came with it, by taking an old long tent peg and putting a handle on it.

Peter.

Thanks Peter. I managed to knock the drive spur out of the head stock with a rod that fitted down the hole, but the tail stock is causing me grief. I'm beginning to think this lathe is a waste of time.

I have now found the tail stock adjuster is frozen. I took the hand wheel off and pushed the rod through but all I managed to do was pop the point out of the live centre. The live center mt quill is frozen in the tail quill and the tail quill is frozen in the tailstock, although the spindle lead screw does actually move in and out of the quill.

On closer inspection of the tail quill it appears it has been inserted in the tailstock incorrectly. The slot the locking handle is supposed to lock into is at the 6 o'clock position. I figured with the lock out and the hand wheel off, the quill should be moveable but I cannot get it to budge. In addition to the rust I suspect the slot edges have dug into the casing. I wasn't keen on hitting too hard on the lead screw spindle as I guess brute force there will break the threads. I tried twisting the quill by grabbing it with a stillson wrench, but it just burred the shaft.

I'm contemplating screwing the lead screw all the way in hoping it bottoms out on something useful that I can tap against with a bigger hammer, unless somebody has a better idea. (p.s. the leadscrew will be fully inside the tailstock when fully screwed in and I probably won't be able to unscrew it again later. I think there must also be a circlip on it somewhere to stop the hand wheel screwing out.)

Originally Posted by Fuzzie

I took the hand wheel off and pushed the rod through but all I managed to do was pop the point out of the live centre. The live center mt quill is frozen in the tail quill

Try knocking it out by placing the knockout bar against the edge of the live centre rather than the centre that you did. Slight taps with a hammer against your knock out bar should free it up. Lots of WD 40 won't go astray either.

With mine I don't use a knockout bar just wind the handle and it should come out, but it isn't rusty.

Peter.

Having the slot at 6 o'clock indicates that someone re-assembled it wrong at one time. Should be at 9 o'clock to mate with the locking handle. The slot doesn't extend full length, and partially removed lock handle normally hits the end of the slot to prevent release. The lock handle may now be hitting the retaining washer, so remove the lock handle completely. The washer is merely a snug fit, though, and may be rusted in place.

I just removed the handwheel for taking these pics, which may be informative.

Try lube as suggested, and try a more substantial drift punch only slightly smaller than the quill - about 9/16" (14mm).

Cheers,
Joe

Hi Fuzzie,
I made my own from a piece of 1/2in. Round Bar. Drilled a 3/8in. hole up the centre, found a bit of Brass Rod, used my Pin Jaws to hold & Turned down the end, just a whisker over size.
I heated the Steel Bar just a bit & dropped the Brass in.
Brass on Steel is better Than Steel on Steel.
Has been an excellent Knockout Bar, over the last 20 yrs.
I also Turned a large Wooden Knob for the other end.
As Sturdee said, maybe the Live Tail Stock Centre should just wind out.
Most of them do these days.
A bit of heat on the quill ? from a Hot Air Gun, may also do the trick.

Thanks Joe, That helps me visualize what's actually in there.

I don't seem to have enough play through the depth of the hole to catch the edge of the live centre. I suspect the hold diameter through the quill is the same as through the live centre. Getting the centre out of the quill can wait until the quill is out of the headstock.

Since the retractable screw section of the adjuster seems to have full play, the washer can't be rusted in. It doesn't look like the washer is retained in the tail stock casting, so if I screw the adjuster in as far as it goes, either the washer will bottom out on the end of the quill or possibly the thread will bottom out inside the quill. That looks like the most solid configuration to try and knock it out as a unit.

I'm dissappointed the pipe wrench failed to break the bond on the quill, that makes it sound like the rusting is bad. Setting up a diesel bath to drop it in sounds a bit easier said than done. Would diesel dissolve a plastic bucket? I'm not sure the petrol station would be too happy about me fronting up to the bowser with an empty bucket to buy a litre.

I'll try flooding wd40 down the slot and through the screw adjuster for a couple of days and maybe try the heat gun. Then try to knock the assemblage out again from the hand wheel end.

I think most gasoline (petrol) jugs are HDPE, as are most plastic buckets, so there shouldn't be any chemical drama.

With the lock handle completely removed, the quill is normally free to rotate, so my first assumption above isn't entirely true. Removing the quill facilitates cleaning wood dust from the linear scale, which I didn't realize until yesterday.

Back to your original question, the knockout bar is about 7mm diameter x 263mm to the shoulder of the knob.

As near as I can tell, the threaded shaft of the tailstock pushes against the base of the live center when wound all the way back. I can barely feel a slight ridge at the junction when nudged with the knockout bar, so that's another place to poke it.

Cheers,
Joe

It looks like the WD40 worked it's way around the quill. I wound the adjuster all the way in and a few taps of the hammer loosened the live centre insert. I then tried hitting directly on the quill end rather than the threaded insert and moved it a bit backwards towards the handle end, then swapped around and started hammering on the threaded insert end and it slowly came out of the tail stock casting.

I'll have to clean up the burring from the pipe wrench, but it should be straightforward from here.

Thanks all for your help.

Peter.