WM280 – Gearbox Clicks After Replacing Leadscrew Shearpin

[SillyOldDufferModerator @sillyoldduffer]

[SillyOldDufferModerator @sillyoldduffer]

A few weeks back I crashed my saddle into the chuck whilst thread cutting under power. I thought no damage had been done until today, when the cutter suddenly misaligned during a part cut thread. I found the shear pin had broken, leaving enough stuck metal to act as a kind of erratic dog clutch.

To get the jammed pin out I had to remove the lead-screw by taking off the bearing block so I could get at the pin on my bench.

Reassembly was straightforward except that, under power, the gearbox has developed a recurring click. It feels as if the thread/neutral/ self-act selector lever is not moving quite as far between positions as it did before. Although it all works I'm worried that something inside the gearbox is a little too close for comfort.

There's a roller bearing in the lead-screw bearing block that's secured by two 'C' nuts. (Photo below.)

I just did them up hand tight. I'm wondering if they should be tighter to pull the lead-screw/ gearbox shaft and create more clearance in the gearbox. I've mislaid the manual and don't want to accidentally over tighten the ball race if that's not the problem. Can anyone advise please?

Thanks,

Dave

[JasonBModerator @jasonb]

I did have a tight changewheel on the gearbox input about a year ago and using the copper hammer to ease it on or off shifted the leadscrew sideways and made it hard to engage the ABC lever. Is it possible you tapped something sideways while removing or refitting the leadscrew? I had to take the front off the headstock gearbox to sort it out.

Also check the two similar nuts against the headstock on the feed shaft o make sure they have not become tight.

I don't think either set of nuts need to be particularly tight against anything to me they just take up end float on the feedshaft and screw

Edited By JasonB on 05/06/2017 18:59:59

Edited By JasonB on 05/06/2017 19:01:39

[John Stevenson 1Participant @johnstevenson1]

Typical design and should have a 3 part thrust bearing, plate, ball thrust and then a second plate, either side the bearing block.

Just double check you have the order right and in the correct sequence of balls and grooves

[Mick B1Participant @mickb1]

Are you sure it's in the gearbox and not the wormwheel on the chasing dial skipping threads on the leadscrew?

I have that condition on my WM250V, dating from when I had to remove the leadscrew to clear a dropped-out crosslide shearpin that jammed the gearbox and broke the leadscrew shearpin. Since any screwcutting I do is mostly imperial pitches on a metric machine, I have to leave the halfnut engaged all the time when doing this, so it's not necessary to solve it at present. But I wonder whether it originates from a slight bend put into the leadscrew by the event?

[SillyOldDufferModerator @sillyoldduffer]

Good news, it's fixed. Bad news, I'm not completely sure why!

1. Mick's suggestion, chasing dial / bent lead-screw checked first. Not the problem, I thought it unlikely I'd bent the lead-screw but you never know : it wouldn't be that hard to do.

2. John's suggestion, that the 3-part bearing was assembled incorrectly. John has obviously got my measure! Although I had the parts in the right order, I hadn't noticed that one of the 'washers' is grooved on one side to fit the ball race. Unfortunately, reassembling the right way round didn't fix the clicking. (Or did it? Read on.)

3. Jason's question, 'Is it possible you tapped something sideways while removing or refitting the leadscrew?'. I think the answer to that is yes. The pin didn't sheer cleanly; instead it jammed leaving the lead-screw rather firmly attached to the gearbox sleeve. I had to use moderate force to get it out and it's possible that something moved in the process.

So I tried gently moving the headstock gearbox shaft right with a pry-bar: no obvious movement and the clicking continued. Second, I slackened off the lead-screw nuts and tapped it towards the gearbox with a small rubber mallet. I re-tightened the retaining collar an extra 1/8th turn. Bingo, no clicking!

So I either I moved the gear-box shaft slightly whilst removing the lead-screw OR the problem was the bearing plate being the wrong way round and I'd not tightened it up enough. Or perhaps both.

Jason also suggested 'check the two similar nuts against the headstock on the feed shaft to make sure they have not become tight.' I haven't done so yet, but that's next. I'm wondering if clean gearbox selections depend on tweaking both right and left nuts to adjust the innards of the gear-box. (How I wish the manual would turn up so I could look at the exploded parts diagram. I distinctly remember deciding to put it in a safe place…)

Fingers crossed, all is well now. If not I'll be back!

Once again, many, many thanks

Dave

[JasonBModerator @jasonb]

Dave, better than the parts diagram for the gearbox are photos. If you join this yahoo group then look through the photos there are several of the gearbox and slector forks

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